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Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
RFC 5280

Document type: RFC - Proposed Standard (May 2008; Errata)
Updated by RFC 6818
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 5280 (Proposed Standard)
Responsible AD: Sam Hartman
Send notices to: pkix-chairs@tools.ietf.org, tim.polk@nist.gov, housley@vigilsec.com

Network Working Group                                          D. Cooper
Request for Comments: 5280                                          NIST
Obsoletes: 3280, 4325, 4630                                 S. Santesson
Category: Standards Track                                      Microsoft
                                                              S. Farrell
                                                  Trinity College Dublin
                                                               S. Boeyen
                                                                 Entrust
                                                              R. Housley
                                                          Vigil Security
                                                                 W. Polk
                                                                    NIST
                                                                May 2008

         Internet X.509 Public Key Infrastructure Certificate
             and Certificate Revocation List (CRL) Profile

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This memo profiles the X.509 v3 certificate and X.509 v2 certificate
   revocation list (CRL) for use in the Internet.  An overview of this
   approach and model is provided as an introduction.  The X.509 v3
   certificate format is described in detail, with additional
   information regarding the format and semantics of Internet name
   forms.  Standard certificate extensions are described and two
   Internet-specific extensions are defined.  A set of required
   certificate extensions is specified.  The X.509 v2 CRL format is
   described in detail along with standard and Internet-specific
   extensions.  An algorithm for X.509 certification path validation is
   described.  An ASN.1 module and examples are provided in the
   appendices.

Cooper, et al.              Standards Track                     [Page 1]
RFC 5280            PKIX Certificate and CRL Profile            May 2008

Table of Contents

   1. Introduction ....................................................4
   2. Requirements and Assumptions ....................................6
      2.1. Communication and Topology .................................7
      2.2. Acceptability Criteria .....................................7
      2.3. User Expectations ..........................................7
      2.4. Administrator Expectations .................................8
   3. Overview of Approach ............................................8
      3.1. X.509 Version 3 Certificate ................................9
      3.2. Certification Paths and Trust .............................10
      3.3. Revocation ................................................13
      3.4. Operational Protocols .....................................14
      3.5. Management Protocols ......................................14
   4. Certificate and Certificate Extensions Profile .................16
      4.1. Basic Certificate Fields ..................................16
           4.1.1. Certificate Fields .................................17
                  4.1.1.1. tbsCertificate ............................18
                  4.1.1.2. signatureAlgorithm ........................18
                  4.1.1.3. signatureValue ............................18
           4.1.2. TBSCertificate .....................................18
                  4.1.2.1. Version ...................................19
                  4.1.2.2. Serial Number .............................19
                  4.1.2.3. Signature .................................19
                  4.1.2.4. Issuer ....................................20
                  4.1.2.5. Validity ..................................22
                           4.1.2.5.1. UTCTime ........................23
                           4.1.2.5.2. GeneralizedTime ................23
                  4.1.2.6. Subject ...................................23
                  4.1.2.7. Subject Public Key Info ...................25
                  4.1.2.8. Unique Identifiers ........................25
                  4.1.2.9. Extensions ................................26
      4.2. Certificate Extensions ....................................26
           4.2.1. Standard Extensions ................................27
                  4.2.1.1. Authority Key Identifier ..................27
                  4.2.1.2. Subject Key Identifier ....................28
                  4.2.1.3. Key Usage .................................29
                  4.2.1.4. Certificate Policies ......................32
                  4.2.1.5. Policy Mappings ...........................35
                  4.2.1.6. Subject Alternative Name ..................35
                  4.2.1.7. Issuer Alternative Name ...................38
                  4.2.1.8. Subject Directory Attributes ..............39
                  4.2.1.9. Basic Constraints .........................39
                  4.2.1.10. Name Constraints .........................40
                  4.2.1.11. Policy Constraints .......................43
                  4.2.1.12. Extended Key Usage .......................44
                  4.2.1.13. CRL Distribution Points ..................45
                  4.2.1.14. Inhibit anyPolicy ........................48

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

                  4.2.1.15. Freshest CRL (a.k.a. Delta CRL
                            Distribution Point) ......................48
           4.2.2. Private Internet Extensions ........................49
                  4.2.2.1. Authority Information Access ..............49
                  4.2.2.2. Subject Information Access ................51
   5. CRL and CRL Extensions Profile .................................54
      5.1. CRL Fields ................................................55
           5.1.1. CertificateList Fields .............................56
                  5.1.1.1. tbsCertList ...............................56
                  5.1.1.2. signatureAlgorithm ........................57
                  5.1.1.3. signatureValue ............................57
           5.1.2. Certificate List "To Be Signed" ....................58
                  5.1.2.1. Version ...................................58
                  5.1.2.2. Signature .................................58
                  5.1.2.3. Issuer Name ...............................58
                  5.1.2.4. This Update ...............................58
                  5.1.2.5. Next Update ...............................59
                  5.1.2.6. Revoked Certificates ......................59
                  5.1.2.7. Extensions ................................60
      5.2. CRL Extensions ............................................60
           5.2.1. Authority Key Identifier ...........................60
           5.2.2. Issuer Alternative Name ............................60
           5.2.3. CRL Number .........................................61
           5.2.4. Delta CRL Indicator ................................62
           5.2.5. Issuing Distribution Point .........................65
           5.2.6. Freshest CRL (a.k.a. Delta CRL Distribution
                  Point) .............................................67
           5.2.7. Authority Information Access .......................67
      5.3. CRL Entry Extensions ......................................69
           5.3.1. Reason Code ........................................69
           5.3.2. Invalidity Date ....................................70
           5.3.3. Certificate Issuer .................................70
   6. Certification Path Validation ..................................71
      6.1. Basic Path Validation .....................................72
           6.1.1. Inputs .............................................75
           6.1.2. Initialization .....................................77
           6.1.3. Basic Certificate Processing .......................80
           6.1.4. Preparation for Certificate i+1 ....................84
           6.1.5. Wrap-Up Procedure ..................................87
           6.1.6. Outputs ............................................89
      6.2. Using the Path Validation Algorithm .......................89
      6.3. CRL Validation ............................................90
           6.3.1. Revocation Inputs ..................................91
           6.3.2. Initialization and Revocation State Variables ......91
           6.3.3. CRL Processing .....................................92
   7. Processing Rules for Internationalized Names ...................95
      7.1. Internationalized Names in Distinguished Names ............96
      7.2. Internationalized Domain Names in GeneralName .............97

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      7.3. Internationalized Domain Names in Distinguished Names .....98
      7.4. Internationalized Resource Identifiers ....................98
      7.5. Internationalized Electronic Mail Addresses ..............100
   8. Security Considerations .......................................100
   9. IANA Considerations ...........................................105
   10. Acknowledgments ..............................................105
   11. References ...................................................105
      11.1. Normative References ....................................105
      11.2. Informative References ..................................107
   Appendix A.  Pseudo-ASN.1 Structures and OIDs ....................110
      A.1. Explicitly Tagged Module, 1988 Syntax ....................110
      A.2. Implicitly Tagged Module, 1988 Syntax ....................125
   Appendix B. ASN.1 Notes ..........................................133
   Appendix C. Examples .............................................136
      C.1. RSA Self-Signed Certificate ..............................137
      C.2. End Entity Certificate Using RSA .........................140
      C.3. End Entity Certificate Using DSA .........................143
      C.4. Certificate Revocation List ..............................147

1.  Introduction

   This specification is one part of a family of standards for the X.509
   Public Key Infrastructure (PKI) for the Internet.

   This specification profiles the format and semantics of certificates
   and certificate revocation lists (CRLs) for the Internet PKI.
   Procedures are described for processing of certification paths in the
   Internet environment.  Finally, ASN.1 modules are provided in the
   appendices for all data structures defined or referenced.

   Section 2 describes Internet PKI requirements and the assumptions
   that affect the scope of this document.  Section 3 presents an
   architectural model and describes its relationship to previous IETF
   and ISO/IEC/ITU-T standards.  In particular, this document's
   relationship with the IETF PEM specifications and the ISO/IEC/ITU-T
   X.509 documents is described.

   Section 4 profiles the X.509 version 3 certificate, and Section 5
   profiles the X.509 version 2 CRL.  The profiles include the
   identification of ISO/IEC/ITU-T and ANSI extensions that may be
   useful in the Internet PKI.  The profiles are presented in the 1988
   Abstract Syntax Notation One (ASN.1) rather than the 1997 ASN.1
   syntax used in the most recent ISO/IEC/ITU-T standards.

   Section 6 includes certification path validation procedures.  These
   procedures are based upon the ISO/IEC/ITU-T definition.
   Implementations are REQUIRED to derive the same results but are not
   required to use the specified procedures.

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   Procedures for identification and encoding of public key materials
   and digital signatures are defined in [RFC3279], [RFC4055], and
   [RFC4491].  Implementations of this specification are not required to
   use any particular cryptographic algorithms.  However, conforming
   implementations that use the algorithms identified in [RFC3279],
   [RFC4055], and [RFC4491] MUST identify and encode the public key
   materials and digital signatures as described in those
   specifications.

   Finally, three appendices are provided to aid implementers.  Appendix
   A contains all ASN.1 structures defined or referenced within this
   specification.  As above, the material is presented in the 1988
   ASN.1.  Appendix B contains notes on less familiar features of the
   ASN.1 notation used within this specification.  Appendix C contains
   examples of conforming certificates and a conforming CRL.

   This specification obsoletes [RFC3280].  Differences from RFC 3280
   are summarized below:

      * Enhanced support for internationalized names is specified in
        Section 7, with rules for encoding and comparing
        Internationalized Domain Names, Internationalized Resource
        Identifiers (IRIs), and distinguished names.  These rules are
        aligned with comparison rules established in current RFCs,
        including [RFC3490], [RFC3987], and [RFC4518].

      * Sections 4.1.2.4 and 4.1.2.6 incorporate the conditions for
        continued use of legacy text encoding schemes that were
        specified in [RFC4630].  Where in use by an established PKI,
        transition to UTF8String could cause denial of service based on
        name chaining failures or incorrect processing of name
        constraints.

      * Section 4.2.1.4 in RFC 3280, which specified the
        privateKeyUsagePeriod certificate extension but deprecated its
        use, was removed.  Use of this ISO standard extension is neither
        deprecated nor recommended for use in the Internet PKI.

      * Section 4.2.1.5 recommends marking the policy mappings extension
        as critical.  RFC 3280 required that the policy mappings
        extension be marked as non-critical.

      * Section 4.2.1.11 requires marking the policy constraints
        extension as critical.  RFC 3280 permitted the policy
        constraints extension to be marked as critical or non-critical.

      * The Authority Information Access (AIA) CRL extension, as
        specified in [RFC4325], was added as Section 5.2.7.

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

      * Sections 5.2 and 5.3 clarify the rules for handling unrecognized
        CRL extensions and CRL entry extensions, respectively.

      * Section 5.3.2 in RFC 3280, which specified the
        holdInstructionCode CRL entry extension, was removed.

      * The path validation algorithm specified in Section 6 no longer
        tracks the criticality of the certificate policies extensions in
        a chain of certificates.  In RFC 3280, this information was
        returned to a relying party.

      * The Security Considerations section addresses the risk of
        circular dependencies arising from the use of https or similar
        schemes in the CRL distribution points, authority information
        access, or subject information access extensions.

      * The Security Considerations section addresses risks associated
        with name ambiguity.

      * The Security Considerations section references RFC 4210 for
        procedures to signal changes in CA operations.

   The ASN.1 modules in Appendix A are unchanged from RFC 3280, except
   that ub-emailaddress-length was changed from 128 to 255 in order to
   align with PKCS #9 [RFC2985].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Requirements and Assumptions

   The goal of this specification is to develop a profile to facilitate
   the use of X.509 certificates within Internet applications for those
   communities wishing to make use of X.509 technology.  Such
   applications may include WWW, electronic mail, user authentication,
   and IPsec.  In order to relieve some of the obstacles to using X.509
   certificates, this document defines a profile to promote the
   development of certificate management systems, development of
   application tools, and interoperability determined by policy.

   Some communities will need to supplement, or possibly replace, this
   profile in order to meet the requirements of specialized application
   domains or environments with additional authorization, assurance, or
   operational requirements.  However, for basic applications, common
   representations of frequently used attributes are defined so that

Cooper, et al.              Standards Track                     [Page 6]
RFC 5280            PKIX Certificate and CRL Profile            May 2008

   application developers can obtain necessary information without
   regard to the issuer of a particular certificate or certificate
   revocation list (CRL).

   A certificate user should review the certificate policy generated by
   the certification authority (CA) before relying on the authentication
   or non-repudiation services associated with the public key in a
   particular certificate.  To this end, this standard does not
   prescribe legally binding rules or duties.

   As supplemental authorization and attribute management tools emerge,
   such as attribute certificates, it may be appropriate to limit the
   authenticated attributes that are included in a certificate.  These
   other management tools may provide more appropriate methods of
   conveying many authenticated attributes.

2.1.  Communication and Topology

   The users of certificates will operate in a wide range of
   environments with respect to their communication topology, especially
   users of secure electronic mail.  This profile supports users without
   high bandwidth, real-time IP connectivity, or high connection
   availability.  In addition, the profile allows for the presence of
   firewall or other filtered communication.

   This profile does not assume the deployment of an X.500 directory
   system [X.500] or a Lightweight Directory Access Protocol (LDAP)
   directory system [RFC4510].  The profile does not prohibit the use of
   an X.500 directory or an LDAP directory; however, any means of
   distributing certificates and certificate revocation lists (CRLs) may
   be used.

2.2.  Acceptability Criteria

   The goal of the Internet Public Key Infrastructure (PKI) is to meet
   the needs of deterministic, automated identification, authentication,
   access control, and authorization functions.  Support for these
   services determines the attributes contained in the certificate as
   well as the ancillary control information in the certificate such as
   policy data and certification path constraints.

2.3.  User Expectations

   Users of the Internet PKI are people and processes who use client
   software and are the subjects named in certificates.  These uses
   include readers and writers of electronic mail, the clients for WWW
   browsers, WWW servers, and the key manager for IPsec within a router.
   This profile recognizes the limitations of the platforms these users

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   employ and the limitations in sophistication and attentiveness of the
   users themselves.  This manifests itself in minimal user
   configuration responsibility (e.g., trusted CA keys, rules), explicit
   platform usage constraints within the certificate, certification path
   constraints that shield the user from many malicious actions, and
   applications that sensibly automate validation functions.

2.4.  Administrator Expectations

   As with user expectations, the Internet PKI profile is structured to
   support the individuals who generally operate CAs.  Providing
   administrators with unbounded choices increases the chances that a
   subtle CA administrator mistake will result in broad compromise.
   Also, unbounded choices greatly complicate the software that process
   and validate the certificates created by the CA.

3.  Overview of Approach

   Following is a simplified view of the architectural model assumed by
   the Public-Key Infrastructure using X.509 (PKIX) specifications.

   The components in this model are:

   end entity: user of PKI certificates and/or end user system that is
               the subject of a certificate;

   CA:         certification authority;

   RA:         registration authority, i.e., an optional system to which
               a CA delegates certain management functions;

   CRL issuer: a system that generates and signs CRLs; and

   repository: a system or collection of distributed systems that stores
               certificates and CRLs and serves as a means of
               distributing these certificates and CRLs to end entities.

   CAs are responsible for indicating the revocation status of the
   certificates that they issue.  Revocation status information may be
   provided using the Online Certificate Status Protocol (OCSP)
   [RFC2560], certificate revocation lists (CRLs), or some other
   mechanism.  In general, when revocation status information is
   provided using CRLs, the CA is also the CRL issuer.  However, a CA
   may delegate the responsibility for issuing CRLs to a different
   entity.

   Note that an Attribute Authority (AA) might also choose to delegate
   the publication of CRLs to a CRL issuer.

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

   +---+
   | C |                       +------------+
   | e | <-------------------->| End entity |
   | r |       Operational     +------------+
   | t |       transactions          ^
   | i |      and management         |  Management
   | f |       transactions          |  transactions        PKI
   | i |                             |                     users
   | c |                             v
   | a | =======================  +--+------------+  ==============
   | t |                          ^               ^
   | e |                          |               |         PKI
   |   |                          v               |      management
   | & |                       +------+           |       entities
   |   | <---------------------|  RA  |<----+     |
   | C |  Publish certificate  +------+     |     |
   | R |                                    |     |
   | L |                                    |     |
   |   |                                    v     v
   | R |                                +------------+
   | e | <------------------------------|     CA     |
   | p |   Publish certificate          +------------+
   | o |   Publish CRL                     ^      ^
   | s |                                   |      |  Management
   | i |                +------------+     |      |  transactions
   | t | <--------------| CRL Issuer |<----+      |
   | o |   Publish CRL  +------------+            v
   | r |                                      +------+
   | y |                                      |  CA  |
   +---+                                      +------+

                      Figure 1. PKI Entities

3.1.  X.509 Version 3 Certificate

   Users of a public key require confidence that the associated private
   key is owned by the correct remote subject (person or system) with
   which an encryption or digital signature mechanism will be used.
   This confidence is obtained through the use of public key
   certificates, which are data structures that bind public key values
   to subjects.  The binding is asserted by having a trusted CA
   digitally sign each certificate.  The CA may base this assertion upon
   technical means (a.k.a., proof of possession through a challenge-
   response protocol), presentation of the private key, or on an
   assertion by the subject.  A certificate has a limited valid
   lifetime, which is indicated in its signed contents.  Because a
   certificate's signature and timeliness can be independently checked
   by a certificate-using client, certificates can be distributed via

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   untrusted communications and server systems, and can be cached in
   unsecured storage in certificate-using systems.

   ITU-T X.509 (formerly CCITT X.509) or ISO/IEC 9594-8, which was first
   published in 1988 as part of the X.500 directory recommendations,
   defines a standard certificate format [X.509].  The certificate
   format in the 1988 standard is called the version 1 (v1) format.
   When X.500 was revised in 1993, two more fields were added, resulting
   in the version 2 (v2) format.

   The Internet Privacy Enhanced Mail (PEM) RFCs, published in 1993,
   include specifications for a public key infrastructure based on X.509
   v1 certificates [RFC1422].  The experience gained in attempts to
   deploy RFC 1422 made it clear that the v1 and v2 certificate formats
   were deficient in several respects.  Most importantly, more fields
   were needed to carry information that PEM design and implementation
   experience had proven necessary.  In response to these new
   requirements, the ISO/IEC, ITU-T, and ANSI X9 developed the X.509
   version 3 (v3) certificate format.  The v3 format extends the v2
   format by adding provision for additional extension fields.
   Particular extension field types may be specified in standards or may
   be defined and registered by any organization or community.  In June
   1996, standardization of the basic v3 format was completed [X.509].

   ISO/IEC, ITU-T, and ANSI X9 have also developed standard extensions
   for use in the v3 extensions field [X.509][X9.55].  These extensions
   can convey such data as additional subject identification
   information, key attribute information, policy information, and
   certification path constraints.

   However, the ISO/IEC, ITU-T, and ANSI X9 standard extensions are very
   broad in their applicability.  In order to develop interoperable
   implementations of X.509 v3 systems for Internet use, it is necessary
   to specify a profile for use of the X.509 v3 extensions tailored for
   the Internet.  It is one goal of this document to specify a profile
   for Internet WWW, electronic mail, and IPsec applications.
   Environments with additional requirements may build on this profile
   or may replace it.

3.2.  Certification Paths and Trust

   A user of a security service requiring knowledge of a public key
   generally needs to obtain and validate a certificate containing the
   required public key.  If the public key user does not already hold an
   assured copy of the public key of the CA that signed the certificate,
   the CA's name, and related information (such as the validity period
   or name constraints), then it might need an additional certificate to
   obtain that public key.  In general, a chain of multiple certificates

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   may be needed, comprising a certificate of the public key owner (the
   end entity) signed by one CA, and zero or more additional
   certificates of CAs signed by other CAs.  Such chains, called
   certification paths, are required because a public key user is only
   initialized with a limited number of assured CA public keys.

   There are different ways in which CAs might be configured in order
   for public key users to be able to find certification paths.  For
   PEM, RFC 1422 defined a rigid hierarchical structure of CAs.  There
   are three types of PEM certification authority:

      (a)  Internet Policy Registration Authority (IPRA):  This
           authority, operated under the auspices of the Internet
           Society, acts as the root of the PEM certification hierarchy
           at level 1.  It issues certificates only for the next level
           of authorities, PCAs.  All certification paths start with the
           IPRA.

      (b)  Policy Certification Authorities (PCAs):  PCAs are at level 2
           of the hierarchy, each PCA being certified by the IPRA.  A
           PCA shall establish and publish a statement of its policy
           with respect to certifying users or subordinate certification
           authorities.  Distinct PCAs aim to satisfy different user
           needs.  For example, one PCA (an organizational PCA) might
           support the general electronic mail needs of commercial
           organizations, and another PCA (a high-assurance PCA) might
           have a more stringent policy designed for satisfying legally
           binding digital signature requirements.

      (c)  Certification Authorities (CAs):  CAs are at level 3 of the
           hierarchy and can also be at lower levels.  Those at level 3
           are certified by PCAs.  CAs represent, for example,
           particular organizations, particular organizational units
           (e.g., departments, groups, sections), or particular
           geographical areas.

   RFC 1422 furthermore has a name subordination rule, which requires
   that a CA can only issue certificates for entities whose names are
   subordinate (in the X.500 naming tree) to the name of the CA itself.
   The trust associated with a PEM certification path is implied by the
   PCA name.  The name subordination rule ensures that CAs below the PCA
   are sensibly constrained as to the set of subordinate entities they
   can certify (e.g., a CA for an organization can only certify entities
   in that organization's name tree).  Certificate user systems are able
   to mechanically check that the name subordination rule has been
   followed.

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   RFC 1422 uses the X.509 v1 certificate format.  The limitations of
   X.509 v1 required imposition of several structural restrictions to
   clearly associate policy information or restrict the utility of
   certificates.  These restrictions included:

      (a)  a pure top-down hierarchy, with all certification paths
           starting from IPRA;

      (b)  a naming subordination rule restricting the names of a CA's
           subjects; and

      (c)  use of the PCA concept, which requires knowledge of
           individual PCAs to be built into certificate chain
           verification logic.  Knowledge of individual PCAs was
           required to determine if a chain could be accepted.

   With X.509 v3, most of the requirements addressed by RFC 1422 can be
   addressed using certificate extensions, without a need to restrict
   the CA structures used.  In particular, the certificate extensions
   relating to certificate policies obviate the need for PCAs and the
   constraint extensions obviate the need for the name subordination
   rule.  As a result, this document supports a more flexible
   architecture, including:

      (a)  Certification paths start with a public key of a CA in a
           user's own domain, or with the public key of the top of a
           hierarchy.  Starting with the public key of a CA in a user's
           own domain has certain advantages.  In some environments, the
           local domain is the most trusted.

      (b)  Name constraints may be imposed through explicit inclusion of
           a name constraints extension in a certificate, but are not
           required.

      (c)  Policy extensions and policy mappings replace the PCA
           concept, which permits a greater degree of automation.  The
           application can determine if the certification path is
           acceptable based on the contents of the certificates instead
           of a priori knowledge of PCAs.  This permits automation of
           certification path processing.

   X.509 v3 also includes an extension that identifies the subject of a
   certificate as being either a CA or an end entity, reducing the
   reliance on out-of-band information demanded in PEM.

   This specification covers two classes of certificates: CA
   certificates and end entity certificates.  CA certificates may be
   further divided into three classes: cross-certificates, self-issued

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   certificates, and self-signed certificates.  Cross-certificates are
   CA certificates in which the issuer and subject are different
   entities.  Cross-certificates describe a trust relationship between
   the two CAs.  Self-issued certificates are CA certificates in which
   the issuer and subject are the same entity.  Self-issued certificates
   are generated to support changes in policy or operations.  Self-
   signed certificates are self-issued certificates where the digital
   signature may be verified by the public key bound into the
   certificate.  Self-signed certificates are used to convey a public
   key for use to begin certification paths.  End entity certificates
   are issued to subjects that are not authorized to issue certificates.

3.3.  Revocation

   When a certificate is issued, it is expected to be in use for its
   entire validity period.  However, various circumstances may cause a
   certificate to become invalid prior to the expiration of the validity
   period.  Such circumstances include change of name, change of
   association between subject and CA (e.g., an employee terminates
   employment with an organization), and compromise or suspected
   compromise of the corresponding private key.  Under such
   circumstances, the CA needs to revoke the certificate.

   X.509 defines one method of certificate revocation.  This method
   involves each CA periodically issuing a signed data structure called
   a certificate revocation list (CRL).  A CRL is a time-stamped list
   identifying revoked certificates that is signed by a CA or CRL issuer
   and made freely available in a public repository.  Each revoked
   certificate is identified in a CRL by its certificate serial number.
   When a certificate-using system uses a certificate (e.g., for
   verifying a remote user's digital signature), that system not only
   checks the certificate signature and validity but also acquires a
   suitably recent CRL and checks that the certificate serial number is
   not on that CRL.  The meaning of "suitably recent" may vary with
   local policy, but it usually means the most recently issued CRL.  A
   new CRL is issued on a regular periodic basis (e.g., hourly, daily,
   or weekly).  An entry is added to the CRL as part of the next update
   following notification of revocation.  An entry MUST NOT be removed
   from the CRL until it appears on one regularly scheduled CRL issued
   beyond the revoked certificate's validity period.

   An advantage of this revocation method is that CRLs may be
   distributed by exactly the same means as certificates themselves,
   namely, via untrusted servers and untrusted communications.

   One limitation of the CRL revocation method, using untrusted
   communications and servers, is that the time granularity of
   revocation is limited to the CRL issue period.  For example, if a

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   revocation is reported now, that revocation will not be reliably
   notified to certificate-using systems until all currently issued CRLs
   are scheduled to be updated -- this may be up to one hour, one day,
   or one week depending on the frequency that CRLs are issued.

   As with the X.509 v3 certificate format, in order to facilitate
   interoperable implementations from multiple vendors, the X.509 v2 CRL
   format needs to be profiled for Internet use.  It is one goal of this
   document to specify that profile.  However, this profile does not
   require the issuance of CRLs.  Message formats and protocols
   supporting on-line revocation notification are defined in other PKIX
   specifications.  On-line methods of revocation notification may be
   applicable in some environments as an alternative to the X.509 CRL.
   On-line revocation checking may significantly reduce the latency
   between a revocation report and the distribution of the information
   to relying parties.  Once the CA accepts a revocation report as
   authentic and valid, any query to the on-line service will correctly
   reflect the certificate validation impacts of the revocation.
   However, these methods impose new security requirements: the
   certificate validator needs to trust the on-line validation service
   while the repository does not need to be trusted.

3.4.  Operational Protocols

   Operational protocols are required to deliver certificates and CRLs
   (or status information) to certificate-using client systems.
   Provisions are needed for a variety of different means of certificate
   and CRL delivery, including distribution procedures based on LDAP,
   HTTP, FTP, and X.500.  Operational protocols supporting these
   functions are defined in other PKIX specifications.  These
   specifications may include definitions of message formats and
   procedures for supporting all of the above operational environments,
   including definitions of or references to appropriate MIME content
   types.

3.5.  Management Protocols

   Management protocols are required to support on-line interactions
   between PKI user and management entities.  For example, a management
   protocol might be used between a CA and a client system with which a
   key pair is associated, or between two CAs that cross-certify each
   other.  The set of functions that potentially need to be supported by
   management protocols include:

      (a)  registration:  This is the process whereby a user first makes
           itself known to a CA (directly, or through an RA), prior to
           that CA issuing a certificate or certificates for that user.

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      (b)  initialization:  Before a client system can operate securely,
           it is necessary to install key materials that have the
           appropriate relationship with keys stored elsewhere in the
           infrastructure.  For example, the client needs to be securely
           initialized with the public key and other assured information
           of the trusted CA(s), to be used in validating certificate
           paths.

           Furthermore, a client typically needs to be initialized with
           its own key pair(s).

      (c)  certification:  This is the process in which a CA issues a
           certificate for a user's public key, and returns that
           certificate to the user's client system and/or posts that
           certificate in a repository.

      (d)  key pair recovery:  As an option, user client key materials
           (e.g., a user's private key used for encryption purposes) may
           be backed up by a CA or a key backup system.  If a user needs
           to recover these backed-up key materials (e.g., as a result
           of a forgotten password or a lost key chain file), an on-line
           protocol exchange may be needed to support such recovery.

      (e)  key pair update:  All key pairs need to be updated regularly,
           i.e., replaced with a new key pair, and new certificates
           issued.

      (f)  revocation request:  An authorized person advises a CA of an
           abnormal situation requiring certificate revocation.

      (g)  cross-certification:  Two CAs exchange information used in
           establishing a cross-certificate.  A cross-certificate is a
           certificate issued by one CA to another CA that contains a CA
           signature key used for issuing certificates.

   Note that on-line protocols are not the only way of implementing the
   above functions.  For all functions, there are off-line methods of
   achieving the same result, and this specification does not mandate
   use of on-line protocols.  For example, when hardware tokens are
   used, many of the functions may be achieved as part of the physical
   token delivery.  Furthermore, some of the above functions may be
   combined into one protocol exchange.  In particular, two or more of
   the registration, initialization, and certification functions can be
   combined into one protocol exchange.

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   The PKIX series of specifications defines a set of standard message
   formats supporting the above functions.  The protocols for conveying
   these messages in different environments (e.g., email, file transfer,
   and WWW) are described in those specifications.

4.  Certificate and Certificate Extensions Profile

   This section presents a profile for public key certificates that will
   foster interoperability and a reusable PKI.  This section is based
   upon the X.509 v3 certificate format and the standard certificate
   extensions defined in [X.509].  The ISO/IEC and ITU-T documents use
   the 1997 version of ASN.1; while this document uses the 1988 ASN.1
   syntax, the encoded certificate and standard extensions are
   equivalent.  This section also defines private extensions required to
   support a PKI for the Internet community.

   Certificates may be used in a wide range of applications and
   environments covering a broad spectrum of interoperability goals and
   a broader spectrum of operational and assurance requirements.  The
   goal of this document is to establish a common baseline for generic
   applications requiring broad interoperability and limited special
   purpose requirements.  In particular, the emphasis will be on
   supporting the use of X.509 v3 certificates for informal Internet
   electronic mail, IPsec, and WWW applications.

4.1.  Basic Certificate Fields

   The X.509 v3 certificate basic syntax is as follows.  For signature
   calculation, the data that is to be signed is encoded using the ASN.1
   distinguished encoding rules (DER) [X.690].  ASN.1 DER encoding is a
   tag, length, value encoding system for each element.

   Certificate  ::=  SEQUENCE  {
        tbsCertificate       TBSCertificate,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

   TBSCertificate  ::=  SEQUENCE  {
        version         [0]  EXPLICIT Version DEFAULT v1,
        serialNumber         CertificateSerialNumber,
        signature            AlgorithmIdentifier,
        issuer               Name,
        validity             Validity,
        subject              Name,
        subjectPublicKeyInfo SubjectPublicKeyInfo,
        issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                             -- If present, version MUST be v2 or v3

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        subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                             -- If present, version MUST be v2 or v3
        extensions      [3]  EXPLICIT Extensions OPTIONAL
                             -- If present, version MUST be v3
        }

   Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }

   CertificateSerialNumber  ::=  INTEGER

   Validity ::= SEQUENCE {
        notBefore      Time,
        notAfter       Time }

   Time ::= CHOICE {
        utcTime        UTCTime,
        generalTime    GeneralizedTime }

   UniqueIdentifier  ::=  BIT STRING

   SubjectPublicKeyInfo  ::=  SEQUENCE  {
        algorithm            AlgorithmIdentifier,
        subjectPublicKey     BIT STRING  }

   Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

   Extension  ::=  SEQUENCE  {
        extnID      OBJECT IDENTIFIER,
        critical    BOOLEAN DEFAULT FALSE,
        extnValue   OCTET STRING
                    -- contains the DER encoding of an ASN.1 value
                    -- corresponding to the extension type identified
                    -- by extnID
        }

   The following items describe the X.509 v3 certificate for use in the
   Internet.

4.1.1.  Certificate Fields

   The Certificate is a SEQUENCE of three required fields.  The fields
   are described in detail in the following subsections.

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4.1.1.1.  tbsCertificate

   The field contains the names of the subject and issuer, a public key
   associated with the subject, a validity period, and other associated
   information.  The fields are described in detail in Section 4.1.2;
   the tbsCertificate usually includes extensions, which are described
   in Section 4.2.

4.1.1.2.  signatureAlgorithm

   The signatureAlgorithm field contains the identifier for the
   cryptographic algorithm used by the CA to sign this certificate.
   [RFC3279], [RFC4055], and [RFC4491] list supported signature
   algorithms, but other signature algorithms MAY also be supported.

   An algorithm identifier is defined by the following ASN.1 structure:

   AlgorithmIdentifier  ::=  SEQUENCE  {
        algorithm               OBJECT IDENTIFIER,
        parameters              ANY DEFINED BY algorithm OPTIONAL  }

   The algorithm identifier is used to identify a cryptographic
   algorithm.  The OBJECT IDENTIFIER component identifies the algorithm
   (such as DSA with SHA-1).  The contents of the optional parameters
   field will vary according to the algorithm identified.

   This field MUST contain the same algorithm identifier as the
   signature field in the sequence tbsCertificate (Section 4.1.2.3).

4.1.1.3.  signatureValue

   The signatureValue field contains a digital signature computed upon
   the ASN.1 DER encoded tbsCertificate.  The ASN.1 DER encoded
   tbsCertificate is used as the input to the signature function.  This
   signature value is encoded as a BIT STRING and included in the
   signature field.  The details of this process are specified for each
   of the algorithms listed in [RFC3279], [RFC4055], and [RFC4491].

   By generating this signature, a CA certifies the validity of the
   information in the tbsCertificate field.  In particular, the CA
   certifies the binding between the public key material and the subject
   of the certificate.

4.1.2.  TBSCertificate

   The sequence TBSCertificate contains information associated with the
   subject of the certificate and the CA that issued it.  Every
   TBSCertificate contains the names of the subject and issuer, a public

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   key associated with the subject, a validity period, a version number,
   and a serial number; some MAY contain optional unique identifier
   fields.  The remainder of this section describes the syntax and
   semantics of these fields.  A TBSCertificate usually includes
   extensions.  Extensions for the Internet PKI are described in Section
   4.2.

4.1.2.1.  Version

   This field describes the version of the encoded certificate.  When
   extensions are used, as expected in this profile, version MUST be 3
   (value is 2).  If no extensions are present, but a UniqueIdentifier
   is present, the version SHOULD be 2 (value is 1); however, the
   version MAY be 3.  If only basic fields are present, the version
   SHOULD be 1 (the value is omitted from the certificate as the default
   value); however, the version MAY be 2 or 3.

   Implementations SHOULD be prepared to accept any version certificate.
   At a minimum, conforming implementations MUST recognize version 3
   certificates.

   Generation of version 2 certificates is not expected by
   implementations based on this profile.

4.1.2.2.  Serial Number

   The serial number MUST be a positive integer assigned by the CA to
   each certificate.  It MUST be unique for each certificate issued by a
   given CA (i.e., the issuer name and serial number identify a unique
   certificate).  CAs MUST force the serialNumber to be a non-negative
   integer.

   Given the uniqueness requirements above, serial numbers can be
   expected to contain long integers.  Certificate users MUST be able to
   handle serialNumber values up to 20 octets.  Conforming CAs MUST NOT
   use serialNumber values longer than 20 octets.

   Note: Non-conforming CAs may issue certificates with serial numbers
   that are negative or zero.  Certificate users SHOULD be prepared to
   gracefully handle such certificates.

4.1.2.3.  Signature

   This field contains the algorithm identifier for the algorithm used
   by the CA to sign the certificate.

   This field MUST contain the same algorithm identifier as the
   signatureAlgorithm field in the sequence Certificate (Section

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   4.1.1.2).  The contents of the optional parameters field will vary
   according to the algorithm identified.  [RFC3279], [RFC4055], and
   [RFC4491] list supported signature algorithms, but other signature
   algorithms MAY also be supported.

4.1.2.4.  Issuer

   The issuer field identifies the entity that has signed and issued the
   certificate.  The issuer field MUST contain a non-empty distinguished
   name (DN).  The issuer field is defined as the X.501 type Name
   [X.501].  Name is defined by the following ASN.1 structures:

   Name ::= CHOICE { -- only one possibility for now --
     rdnSequence  RDNSequence }

   RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

   RelativeDistinguishedName ::=
     SET SIZE (1..MAX) OF AttributeTypeAndValue

   AttributeTypeAndValue ::= SEQUENCE {
     type     AttributeType,
     value    AttributeValue }

   AttributeType ::= OBJECT IDENTIFIER

   AttributeValue ::= ANY -- DEFINED BY AttributeType

   DirectoryString ::= CHOICE {
         teletexString           TeletexString (SIZE (1..MAX)),
         printableString         PrintableString (SIZE (1..MAX)),
         universalString         UniversalString (SIZE (1..MAX)),
         utf8String              UTF8String (SIZE (1..MAX)),
         bmpString               BMPString (SIZE (1..MAX)) }

   The Name describes a hierarchical name composed of attributes, such
   as country name, and corresponding values, such as US.  The type of
   the component AttributeValue is determined by the AttributeType; in
   general it will be a DirectoryString.

   The DirectoryString type is defined as a choice of PrintableString,
   TeletexString, BMPString, UTF8String, and UniversalString.  CAs
   conforming to this profile MUST use either the PrintableString or
   UTF8String encoding of DirectoryString, with two exceptions.  When
   CAs have previously issued certificates with issuer fields with
   attributes encoded using TeletexString, BMPString, or
   UniversalString, then the CA MAY continue to use these encodings of
   the DirectoryString to preserve backward compatibility.  Also, new

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   CAs that are added to a domain where existing CAs issue certificates
   with issuer fields with attributes encoded using TeletexString,
   BMPString, or UniversalString MAY encode attributes that they share
   with the existing CAs using the same encodings as the existing CAs
   use.

   As noted above, distinguished names are composed of attributes.  This
   specification does not restrict the set of attribute types that may
   appear in names.  However, conforming implementations MUST be
   prepared to receive certificates with issuer names containing the set
   of attribute types defined below.  This specification RECOMMENDS
   support for additional attribute types.

   Standard sets of attributes have been defined in the X.500 series of
   specifications [X.520].  Implementations of this specification MUST
   be prepared to receive the following standard attribute types in
   issuer and subject (Section 4.1.2.6) names:

      * country,
      * organization,
      * organizational unit,
      * distinguished name qualifier,
      * state or province name,
      * common name (e.g., "Susan Housley"), and
      * serial number.

   In addition, implementations of this specification SHOULD be prepared
   to receive the following standard attribute types in issuer and
   subject names:

      * locality,
      * title,
      * surname,
      * given name,
      * initials,
      * pseudonym, and
      * generation qualifier (e.g., "Jr.", "3rd", or "IV").

   The syntax and associated object identifiers (OIDs) for these
   attribute types are provided in the ASN.1 modules in Appendix A.

   In addition, implementations of this specification MUST be prepared
   to receive the domainComponent attribute, as defined in [RFC4519].
   The Domain Name System (DNS) provides a hierarchical resource
   labeling system.  This attribute provides a convenient mechanism for
   organizations that wish to use DNs that parallel their DNS names.
   This is not a replacement for the dNSName component of the
   alternative name extensions.  Implementations are not required to

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   convert such names into DNS names.  The syntax and associated OID for
   this attribute type are provided in the ASN.1 modules in Appendix A.
   Rules for encoding internationalized domain names for use with the
   domainComponent attribute type are specified in Section 7.3.

   Certificate users MUST be prepared to process the issuer
   distinguished name and subject distinguished name (Section 4.1.2.6)
   fields to perform name chaining for certification path validation
   (Section 6).  Name chaining is performed by matching the issuer
   distinguished name in one certificate with the subject name in a CA
   certificate.  Rules for comparing distinguished names are specified
   in Section 7.1.  If the names in the issuer and subject field in a
   certificate match according to the rules specified in Section 7.1,
   then the certificate is self-issued.

4.1.2.5.  Validity

   The certificate validity period is the time interval during which the
   CA warrants that it will maintain information about the status of the
   certificate.  The field is represented as a SEQUENCE of two dates:
   the date on which the certificate validity period begins (notBefore)
   and the date on which the certificate validity period ends
   (notAfter).  Both notBefore and notAfter may be encoded as UTCTime or
   GeneralizedTime.

   CAs conforming to this profile MUST always encode certificate
   validity dates through the year 2049 as UTCTime; certificate validity
   dates in 2050 or later MUST be encoded as GeneralizedTime.
   Conforming applications MUST be able to process validity dates that
   are encoded in either UTCTime or GeneralizedTime.

   The validity period for a certificate is the period of time from
   notBefore through notAfter, inclusive.

   In some situations, devices are given certificates for which no good
   expiration date can be assigned.  For example, a device could be
   issued a certificate that binds its model and serial number to its
   public key; such a certificate is intended to be used for the entire
   lifetime of the device.

   To indicate that a certificate has no well-defined expiration date,
   the notAfter SHOULD be assigned the GeneralizedTime value of
   99991231235959Z.

   When the issuer will not be able to maintain status information until
   the notAfter date (including when the notAfter date is
   99991231235959Z), the issuer MUST ensure that no valid certification
   path exists for the certificate after maintenance of status

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   information is terminated.  This may be accomplished by expiration or
   revocation of all CA certificates containing the public key used to
   verify the signature on the certificate and discontinuing use of the
   public key used to verify the signature on the certificate as a trust
   anchor.

4.1.2.5.1.  UTCTime

   The universal time type, UTCTime, is a standard ASN.1 type intended
   for representation of dates and time.  UTCTime specifies the year
   through the two low-order digits and time is specified to the
   precision of one minute or one second.  UTCTime includes either Z
   (for Zulu, or Greenwich Mean Time) or a time differential.

   For the purposes of this profile, UTCTime values MUST be expressed in
   Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are
   YYMMDDHHMMSSZ), even where the number of seconds is zero.  Conforming
   systems MUST interpret the year field (YY) as follows:

      Where YY is greater than or equal to 50, the year SHALL be
      interpreted as 19YY; and

      Where YY is less than 50, the year SHALL be interpreted as 20YY.

4.1.2.5.2.  GeneralizedTime

   The generalized time type, GeneralizedTime, is a standard ASN.1 type
   for variable precision representation of time.  Optionally, the
   GeneralizedTime field can include a representation of the time
   differential between local and Greenwich Mean Time.

   For the purposes of this profile, GeneralizedTime values MUST be
   expressed in Greenwich Mean Time (Zulu) and MUST include seconds
   (i.e., times are YYYYMMDDHHMMSSZ), even where the number of seconds
   is zero.  GeneralizedTime values MUST NOT include fractional seconds.

4.1.2.6.  Subject

   The subject field identifies the entity associated with the public
   key stored in the subject public key field.  The subject name MAY be
   carried in the subject field and/or the subjectAltName extension.  If
   the subject is a CA (e.g., the basic constraints extension, as
   discussed in Section 4.2.1.9, is present and the value of cA is
   TRUE), then the subject field MUST be populated with a non-empty
   distinguished name matching the contents of the issuer field (Section
   4.1.2.4) in all certificates issued by the subject CA.  If the
   subject is a CRL issuer (e.g., the key usage extension, as discussed
   in Section 4.2.1.3, is present and the value of cRLSign is TRUE),

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   then the subject field MUST be populated with a non-empty
   distinguished name matching the contents of the issuer field (Section
   5.1.2.3) in all CRLs issued by the subject CRL issuer.  If subject
   naming information is present only in the subjectAltName extension
   (e.g., a key bound only to an email address or URI), then the subject
   name MUST be an empty sequence and the subjectAltName extension MUST
   be critical.

   Where it is non-empty, the subject field MUST contain an X.500
   distinguished name (DN).  The DN MUST be unique for each subject
   entity certified by the one CA as defined by the issuer field.  A CA
   MAY issue more than one certificate with the same DN to the same
   subject entity.

   The subject field is defined as the X.501 type Name.  Implementation
   requirements for this field are those defined for the issuer field
   (Section 4.1.2.4).  Implementations of this specification MUST be
   prepared to receive subject names containing the attribute types
   required for the issuer field.  Implementations of this specification
   SHOULD be prepared to receive subject names containing the
   recommended attribute types for the issuer field.  The syntax and
   associated object identifiers (OIDs) for these attribute types are
   provided in the ASN.1 modules in Appendix A.  Implementations of this
   specification MAY use the comparison rules in Section 7.1 to process
   unfamiliar attribute types (i.e., for name chaining) whose attribute
   values use one of the encoding options from DirectoryString.  Binary
   comparison should be used when unfamiliar attribute types include
   attribute values with encoding options other than those found in
   DirectoryString.  This allows implementations to process certificates
   with unfamiliar attributes in the subject name.

   When encoding attribute values of type DirectoryString, conforming
   CAs MUST use PrintableString or UTF8String encoding, with the
   following exceptions:

      (a)  When the subject of the certificate is a CA, the subject
           field MUST be encoded in the same way as it is encoded in the
           issuer field (Section 4.1.2.4) in all certificates issued by
           the subject CA.  Thus, if the subject CA encodes attributes
           in the issuer fields of certificates that it issues using the
           TeletexString, BMPString, or UniversalString encodings, then
           the subject field of certificates issued to that CA MUST use
           the same encoding.

      (b)  When the subject of the certificate is a CRL issuer, the
           subject field MUST be encoded in the same way as it is
           encoded in the issuer field (Section 5.1.2.3) in all CRLs
           issued by the subject CRL issuer.

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      (c)  TeletexString, BMPString, and UniversalString are included
           for backward compatibility, and SHOULD NOT be used for
           certificates for new subjects.  However, these types MAY be
           used in certificates where the name was previously
           established, including cases in which a new certificate is
           being issued to an existing subject or a certificate is being
           issued to a new subject where the attributes being encoded
           have been previously established in certificates issued to
           other subjects.  Certificate users SHOULD be prepared to
           receive certificates with these types.

   Legacy implementations exist where an electronic mail address is
   embedded in the subject distinguished name as an emailAddress
   attribute [RFC2985].  The attribute value for emailAddress is of type
   IA5String to permit inclusion of the character '@', which is not part
   of the PrintableString character set.  emailAddress attribute values
   are not case-sensitive (e.g., "subscriber@example.com" is the same as
   "SUBSCRIBER@EXAMPLE.COM").

   Conforming implementations generating new certificates with
   electronic mail addresses MUST use the rfc822Name in the subject
   alternative name extension (Section 4.2.1.6) to describe such
   identities.  Simultaneous inclusion of the emailAddress attribute in
   the subject distinguished name to support legacy implementations is
   deprecated but permitted.

4.1.2.7.  Subject Public Key Info

   This field is used to carry the public key and identify the algorithm
   with which the key is used (e.g., RSA, DSA, or Diffie-Hellman).  The
   algorithm is identified using the AlgorithmIdentifier structure
   specified in Section 4.1.1.2.  The object identifiers for the
   supported algorithms and the methods for encoding the public key
   materials (public key and parameters) are specified in [RFC3279],
   [RFC4055], and [RFC4491].

4.1.2.8.  Unique Identifiers

   These fields MUST only appear if the version is 2 or 3 (Section
   4.1.2.1).  These fields MUST NOT appear if the version is 1.  The
   subject and issuer unique identifiers are present in the certificate
   to handle the possibility of reuse of subject and/or issuer names
   over time.  This profile RECOMMENDS that names not be reused for
   different entities and that Internet certificates not make use of
   unique identifiers.  CAs conforming to this profile MUST NOT generate
   certificates with unique identifiers.  Applications conforming to

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   this profile SHOULD be capable of parsing certificates that include
   unique identifiers, but there are no processing requirements
   associated with the unique identifiers.

4.1.2.9.  Extensions

   This field MUST only appear if the version is 3 (Section 4.1.2.1).
   If present, this field is a SEQUENCE of one or more certificate
   extensions.  The format and content of certificate extensions in the
   Internet PKI are defined in Section 4.2.

4.2.  Certificate Extensions

   The extensions defined for X.509 v3 certificates provide methods for
   associating additional attributes with users or public keys and for
   managing relationships between CAs.  The X.509 v3 certificate format
   also allows communities to define private extensions to carry
   information unique to those communities.  Each extension in a
   certificate is designated as either critical or non-critical.  A
   certificate-using system MUST reject the certificate if it encounters
   a critical extension it does not recognize or a critical extension
   that contains information that it cannot process.  A non-critical
   extension MAY be ignored if it is not recognized, but MUST be
   processed if it is recognized.  The following sections present
   recommended extensions used within Internet certificates and standard
   locations for information.  Communities may elect to use additional
   extensions; however, caution ought to be exercised in adopting any
   critical extensions in certificates that might prevent use in a
   general context.

   Each extension includes an OID and an ASN.1 structure.  When an
   extension appears in a certificate, the OID appears as the field
   extnID and the corresponding ASN.1 DER encoded structure is the value
   of the octet string extnValue.  A certificate MUST NOT include more
   than one instance of a particular extension.  For example, a
   certificate may contain only one authority key identifier extension
   (Section 4.2.1.1).  An extension includes the boolean critical, with
   a default value of FALSE.  The text for each extension specifies the
   acceptable values for the critical field for CAs conforming to this
   profile.

   Conforming CAs MUST support key identifiers (Sections 4.2.1.1 and
   4.2.1.2), basic constraints (Section 4.2.1.9), key usage (Section
   4.2.1.3), and certificate policies (Section 4.2.1.4) extensions.  If
   the CA issues certificates with an empty sequence for the subject
   field, the CA MUST support the subject alternative name extension
   (Section 4.2.1.6).  Support for the remaining extensions is OPTIONAL.
   Conforming CAs MAY support extensions that are not identified within

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   this specification; certificate issuers are cautioned that marking
   such extensions as critical may inhibit interoperability.

   At a minimum, applications conforming to this profile MUST recognize
   the following extensions: key usage (Section 4.2.1.3), certificate
   policies (Section 4.2.1.4), subject alternative name (Section
   4.2.1.6), basic constraints (Section 4.2.1.9), name constraints
   (Section 4.2.1.10), policy constraints (Section 4.2.1.11), extended
   key usage (Section 4.2.1.12), and inhibit anyPolicy (Section
   4.2.1.14).

   In addition, applications conforming to this profile SHOULD recognize
   the authority and subject key identifier (Sections 4.2.1.1 and
   4.2.1.2) and policy mappings (Section 4.2.1.5) extensions.

4.2.1.  Standard Extensions

   This section identifies standard certificate extensions defined in
   [X.509] for use in the Internet PKI.  Each extension is associated
   with an OID defined in [X.509].  These OIDs are members of the id-ce
   arc, which is defined by the following:

   id-ce   OBJECT IDENTIFIER ::=  { joint-iso-ccitt(2) ds(5) 29 }

4.2.1.1.  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the public key corresponding to the private key used to
   sign a certificate.  This extension is used where an issuer has
   multiple signing keys (either due to multiple concurrent key pairs or
   due to changeover).  The identification MAY be based on either the
   key identifier (the subject key identifier in the issuer's
   certificate) or the issuer name and serial number.

   The keyIdentifier field of the authorityKeyIdentifier extension MUST
   be included in all certificates generated by conforming CAs to
   facilitate certification path construction.  There is one exception;
   where a CA distributes its public key in the form of a "self-signed"
   certificate, the authority key identifier MAY be omitted.  The
   signature on a self-signed certificate is generated with the private
   key associated with the certificate's subject public key.  (This
   proves that the issuer possesses both the public and private keys.)
   In this case, the subject and authority key identifiers would be
   identical, but only the subject key identifier is needed for
   certification path building.

   The value of the keyIdentifier field SHOULD be derived from the
   public key used to verify the certificate's signature or a method

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   that generates unique values.  Two common methods for generating key
   identifiers from the public key are described in Section 4.2.1.2.
   Where a key identifier has not been previously established, this
   specification RECOMMENDS use of one of these methods for generating
   keyIdentifiers or use of a similar method that uses a different hash
   algorithm.  Where a key identifier has been previously established,
   the CA SHOULD use the previously established identifier.

   This profile RECOMMENDS support for the key identifier method by all
   certificate users.

   Conforming CAs MUST mark this extension as non-critical.

   id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 35 }

   AuthorityKeyIdentifier ::= SEQUENCE {
      keyIdentifier             [0] KeyIdentifier           OPTIONAL,
      authorityCertIssuer       [1] GeneralNames            OPTIONAL,
      authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL  }

   KeyIdentifier ::= OCTET STRING

4.2.1.2.  Subject Key Identifier

   The subject key identifier extension provides a means of identifying
   certificates that contain a particular public key.

   To facilitate certification path construction, this extension MUST
   appear in all conforming CA certificates, that is, all certificates
   including the basic constraints extension (Section 4.2.1.9) where the
   value of cA is TRUE.  In conforming CA certificates, the value of the
   subject key identifier MUST be the value placed in the key identifier
   field of the authority key identifier extension (Section 4.2.1.1) of
   certificates issued by the subject of this certificate.  Applications
   are not required to verify that key identifiers match when performing
   certification path validation.

   For CA certificates, subject key identifiers SHOULD be derived from
   the public key or a method that generates unique values.  Two common
   methods for generating key identifiers from the public key are:

      (1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the
           value of the BIT STRING subjectPublicKey (excluding the tag,
           length, and number of unused bits).

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      (2) The keyIdentifier is composed of a four-bit type field with
           the value 0100 followed by the least significant 60 bits of
           the SHA-1 hash of the value of the BIT STRING
           subjectPublicKey (excluding the tag, length, and number of
           unused bits).

   Other methods of generating unique numbers are also acceptable.

   For end entity certificates, the subject key identifier extension
   provides a means for identifying certificates containing the
   particular public key used in an application.  Where an end entity
   has obtained multiple certificates, especially from multiple CAs, the
   subject key identifier provides a means to quickly identify the set
   of certificates containing a particular public key.  To assist
   applications in identifying the appropriate end entity certificate,
   this extension SHOULD be included in all end entity certificates.

   For end entity certificates, subject key identifiers SHOULD be
   derived from the public key.  Two common methods for generating key
   identifiers from the public key are identified above.

   Where a key identifier has not been previously established, this
   specification RECOMMENDS use of one of these methods for generating
   keyIdentifiers or use of a similar method that uses a different hash
   algorithm.  Where a key identifier has been previously established,
   the CA SHOULD use the previously established identifier.

   Conforming CAs MUST mark this extension as non-critical.

   id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }

   SubjectKeyIdentifier ::= KeyIdentifier

4.2.1.3.  Key Usage

   The key usage extension defines the purpose (e.g., encipherment,
   signature, certificate signing) of the key contained in the
   certificate.  The usage restriction might be employed when a key that
   could be used for more than one operation is to be restricted.  For
   example, when an RSA key should be used only to verify signatures on
   objects other than public key certificates and CRLs, the
   digitalSignature and/or nonRepudiation bits would be asserted.
   Likewise, when an RSA key should be used only for key management, the
   keyEncipherment bit would be asserted.

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   Conforming CAs MUST include this extension in certificates that
   contain public keys that are used to validate digital signatures on
   other public key certificates or CRLs.  When present, conforming CAs
   SHOULD mark this extension as critical.

      id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

      KeyUsage ::= BIT STRING {
           digitalSignature        (0),
           nonRepudiation          (1), -- recent editions of X.509 have
                                -- renamed this bit to contentCommitment
           keyEncipherment         (2),
           dataEncipherment        (3),
           keyAgreement            (4),
           keyCertSign             (5),
           cRLSign                 (6),
           encipherOnly            (7),
           decipherOnly            (8) }

   Bits in the KeyUsage type are used as follows:

      The digitalSignature bit is asserted when the subject public key
      is used for verifying digital signatures, other than signatures on
      certificates (bit 5) and CRLs (bit 6), such as those used in an
      entity authentication service, a data origin authentication
      service, and/or an integrity service.

      The nonRepudiation bit is asserted when the subject public key is
      used to verify digital signatures, other than signatures on
      certificates (bit 5) and CRLs (bit 6), used to provide a non-
      repudiation service that protects against the signing entity
      falsely denying some action.  In the case of later conflict, a
      reliable third party may determine the authenticity of the signed
      data.  (Note that recent editions of X.509 have renamed the
      nonRepudiation bit to contentCommitment.)

      The keyEncipherment bit is asserted when the subject public key is
      used for enciphering private or secret keys, i.e., for key
      transport.  For example, this bit shall be set when an RSA public
      key is to be used for encrypting a symmetric content-decryption
      key or an asymmetric private key.

      The dataEncipherment bit is asserted when the subject public key
      is used for directly enciphering raw user data without the use of
      an intermediate symmetric cipher.  Note that the use of this bit
      is extremely uncommon; almost all applications use key transport
      or key agreement to establish a symmetric key.

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      The keyAgreement bit is asserted when the subject public key is
      used for key agreement.  For example, when a Diffie-Hellman key is
      to be used for key management, then this bit is set.

      The keyCertSign bit is asserted when the subject public key is
      used for verifying signatures on public key certificates.  If the
      keyCertSign bit is asserted, then the cA bit in the basic
      constraints extension (Section 4.2.1.9) MUST also be asserted.

      The cRLSign bit is asserted when the subject public key is used
      for verifying signatures on certificate revocation lists (e.g.,
      CRLs, delta CRLs, or ARLs).

      The meaning of the encipherOnly bit is undefined in the absence of
      the keyAgreement bit.  When the encipherOnly bit is asserted and
      the keyAgreement bit is also set, the subject public key may be
      used only for enciphering data while performing key agreement.

      The meaning of the decipherOnly bit is undefined in the absence of
      the keyAgreement bit.  When the decipherOnly bit is asserted and
      the keyAgreement bit is also set, the subject public key may be
      used only for deciphering data while performing key agreement.

   If the keyUsage extension is present, then the subject public key
   MUST NOT be used to verify signatures on certificates or CRLs unless
   the corresponding keyCertSign or cRLSign bit is set.  If the subject
   public key is only to be used for verifying signatures on
   certificates and/or CRLs, then the digitalSignature and
   nonRepudiation bits SHOULD NOT be set.  However, the digitalSignature
   and/or nonRepudiation bits MAY be set in addition to the keyCertSign
   and/or cRLSign bits if the subject public key is to be used to verify
   signatures on certificates and/or CRLs as well as other objects.

   Combining the nonRepudiation bit in the keyUsage certificate
   extension with other keyUsage bits may have security implications
   depending on the context in which the certificate is to be used.
   Further distinctions between the digitalSignature and nonRepudiation
   bits may be provided in specific certificate policies.

   This profile does not restrict the combinations of bits that may be
   set in an instantiation of the keyUsage extension.  However,
   appropriate values for keyUsage extensions for particular algorithms
   are specified in [RFC3279], [RFC4055], and [RFC4491].  When the
   keyUsage extension appears in a certificate, at least one of the bits
   MUST be set to 1.

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4.2.1.4.  Certificate Policies

   The certificate policies extension contains a sequence of one or more
   policy information terms, each of which consists of an object
   identifier (OID) and optional qualifiers.  Optional qualifiers, which
   MAY be present, are not expected to change the definition of the
   policy.  A certificate policy OID MUST NOT appear more than once in a
   certificate policies extension.

   In an end entity certificate, these policy information terms indicate
   the policy under which the certificate has been issued and the
   purposes for which the certificate may be used.  In a CA certificate,
   these policy information terms limit the set of policies for
   certification paths that include this certificate.  When a CA does
   not wish to limit the set of policies for certification paths that
   include this certificate, it MAY assert the special policy anyPolicy,
   with a value of { 2 5 29 32 0 }.

   Applications with specific policy requirements are expected to have a
   list of those policies that they will accept and to compare the
   policy OIDs in the certificate to that list.  If this extension is
   critical, the path validation software MUST be able to interpret this
   extension (including the optional qualifier), or MUST reject the
   certificate.

   To promote interoperability, this profile RECOMMENDS that policy
   information terms consist of only an OID.  Where an OID alone is
   insufficient, this profile strongly recommends that the use of
   qualifiers be limited to those identified in this section.  When
   qualifiers are used with the special policy anyPolicy, they MUST be
   limited to the qualifiers identified in this section.  Only those
   qualifiers returned as a result of path validation are considered.

   This specification defines two policy qualifier types for use by
   certificate policy writers and certificate issuers.  The qualifier
   types are the CPS Pointer and User Notice qualifiers.

   The CPS Pointer qualifier contains a pointer to a Certification
   Practice Statement (CPS) published by the CA.  The pointer is in the
   form of a URI.  Processing requirements for this qualifier are a
   local matter.  No action is mandated by this specification regardless
   of the criticality value asserted for the extension.

   User notice is intended for display to a relying party when a
   certificate is used.  Only user notices returned as a result of path
   validation are intended for display to the user.  If a notice is

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   duplicated, only one copy need be displayed.  To prevent such
   duplication, this qualifier SHOULD only be present in end entity
   certificates and CA certificates issued to other organizations.

   The user notice has two optional fields: the noticeRef field and the
   explicitText field.  Conforming CAs SHOULD NOT use the noticeRef
   option.

      The noticeRef field, if used, names an organization and
      identifies, by number, a particular textual statement prepared by
      that organization.  For example, it might identify the
      organization "CertsRUs" and notice number 1.  In a typical
      implementation, the application software will have a notice file
      containing the current set of notices for CertsRUs; the
      application will extract the notice text from the file and display
      it.  Messages MAY be multilingual, allowing the software to select
      the particular language message for its own environment.

      An explicitText field includes the textual statement directly in
      the certificate.  The explicitText field is a string with a
      maximum size of 200 characters.  Conforming CAs SHOULD use the
      UTF8String encoding for explicitText, but MAY use IA5String.
      Conforming CAs MUST NOT encode explicitText as VisibleString or
      BMPString.  The explicitText string SHOULD NOT include any control
      characters (e.g., U+0000 to U+001F and U+007F to U+009F).  When
      the UTF8String encoding is used, all character sequences SHOULD be
      normalized according to Unicode normalization form C (NFC) [NFC].

   If both the noticeRef and explicitText options are included in the
   one qualifier and if the application software can locate the notice
   text indicated by the noticeRef option, then that text SHOULD be
   displayed; otherwise, the explicitText string SHOULD be displayed.

   Note: While the explicitText has a maximum size of 200 characters,
   some non-conforming CAs exceed this limit.  Therefore, certificate
   users SHOULD gracefully handle explicitText with more than 200
   characters.

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   id-ce-certificatePolicies OBJECT IDENTIFIER ::=  { id-ce 32 }

   anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificatePolicies 0 }

   certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

   PolicyInformation ::= SEQUENCE {
        policyIdentifier   CertPolicyId,
        policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                                PolicyQualifierInfo OPTIONAL }

   CertPolicyId ::= OBJECT IDENTIFIER

   PolicyQualifierInfo ::= SEQUENCE {
        policyQualifierId  PolicyQualifierId,
        qualifier          ANY DEFINED BY policyQualifierId }

   -- policyQualifierIds for Internet policy qualifiers

   id-qt          OBJECT IDENTIFIER ::=  { id-pkix 2 }
   id-qt-cps      OBJECT IDENTIFIER ::=  { id-qt 1 }
   id-qt-unotice  OBJECT IDENTIFIER ::=  { id-qt 2 }

   PolicyQualifierId ::= OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

   Qualifier ::= CHOICE {
        cPSuri           CPSuri,
        userNotice       UserNotice }

   CPSuri ::= IA5String

   UserNotice ::= SEQUENCE {
        noticeRef        NoticeReference OPTIONAL,
        explicitText     DisplayText OPTIONAL }

   NoticeReference ::= SEQUENCE {
        organization     DisplayText,
        noticeNumbers    SEQUENCE OF INTEGER }

   DisplayText ::= CHOICE {
        ia5String        IA5String      (SIZE (1..200)),
        visibleString    VisibleString  (SIZE (1..200)),
        bmpString        BMPString      (SIZE (1..200)),
        utf8String       UTF8String     (SIZE (1..200)) }

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4.2.1.5.  Policy Mappings

   This extension is used in CA certificates.  It lists one or more
   pairs of OIDs; each pair includes an issuerDomainPolicy and a
   subjectDomainPolicy.  The pairing indicates the issuing CA considers
   its issuerDomainPolicy equivalent to the subject CA's
   subjectDomainPolicy.

   The issuing CA's users might accept an issuerDomainPolicy for certain
   applications.  The policy mapping defines the list of policies
   associated with the subject CA that may be accepted as comparable to
   the issuerDomainPolicy.

   Each issuerDomainPolicy named in the policy mappings extension SHOULD
   also be asserted in a certificate policies extension in the same
   certificate.  Policies MUST NOT be mapped either to or from the
   special value anyPolicy (Section 4.2.1.4).

   In general, certificate policies that appear in the
   issuerDomainPolicy field of the policy mappings extension are not
   considered acceptable policies for inclusion in subsequent
   certificates in the certification path.  In some circumstances, a CA
   may wish to map from one policy (p1) to another (p2), but still wants
   the issuerDomainPolicy (p1) to be considered acceptable for inclusion
   in subsequent certificates.  This may occur, for example, if the CA
   is in the process of transitioning from the use of policy p1 to the
   use of policy p2 and has valid certificates that were issued under
   each of the policies.  A CA may indicate this by including two policy
   mappings in the CA certificates that it issues.  Each policy mapping
   would have an issuerDomainPolicy of p1; one policy mapping would have
   a subjectDomainPolicy of p1 and the other would have a
   subjectDomainPolicy of p2.

   This extension MAY be supported by CAs and/or applications.
   Conforming CAs SHOULD mark this extension as critical.

   id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }

   PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
        issuerDomainPolicy      CertPolicyId,
        subjectDomainPolicy     CertPolicyId }

4.2.1.6.  Subject Alternative Name

   The subject alternative name extension allows identities to be bound
   to the subject of the certificate.  These identities may be included
   in addition to or in place of the identity in the subject field of
   the certificate.  Defined options include an Internet electronic mail

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   address, a DNS name, an IP address, and a Uniform Resource Identifier
   (URI).  Other options exist, including completely local definitions.
   Multiple name forms, and multiple instances of each name form, MAY be
   included.  Whenever such identities are to be bound into a
   certificate, the subject alternative name (or issuer alternative
   name) extension MUST be used; however, a DNS name MAY also be
   represented in the subject field using the domainComponent attribute
   as described in Section 4.1.2.4.  Note that where such names are
   represented in the subject field implementations are not required to
   convert them into DNS names.

   Because the subject alternative name is considered to be definitively
   bound to the public key, all parts of the subject alternative name
   MUST be verified by the CA.

   Further, if the only subject identity included in the certificate is
   an alternative name form (e.g., an electronic mail address), then the
   subject distinguished name MUST be empty (an empty sequence), and the
   subjectAltName extension MUST be present.  If the subject field
   contains an empty sequence, then the issuing CA MUST include a
   subjectAltName extension that is marked as critical.  When including
   the subjectAltName extension in a certificate that has a non-empty
   subject distinguished name, conforming CAs SHOULD mark the
   subjectAltName extension as non-critical.

   When the subjectAltName extension contains an Internet mail address,
   the address MUST be stored in the rfc822Name.  The format of an
   rfc822Name is a "Mailbox" as defined in Section 4.1.2 of [RFC2821].
   A Mailbox has the form "Local-part@Domain".  Note that a Mailbox has
   no phrase (such as a common name) before it, has no comment (text
   surrounded in parentheses) after it, and is not surrounded by "<" and
   ">".  Rules for encoding Internet mail addresses that include
   internationalized domain names are specified in Section 7.5.

   When the subjectAltName extension contains an iPAddress, the address
   MUST be stored in the octet string in "network byte order", as
   specified in [RFC791].  The least significant bit (LSB) of each octet
   is the LSB of the corresponding byte in the network address.  For IP
   version 4, as specified in [RFC791], the octet string MUST contain
   exactly four octets.  For IP version 6, as specified in
   [RFC2460], the octet string MUST contain exactly sixteen octets.

   When the subjectAltName extension contains a domain name system
   label, the domain name MUST be stored in the dNSName (an IA5String).
   The name MUST be in the "preferred name syntax", as specified by
   Section 3.5 of [RFC1034] and as modified by Section 2.1 of
   [RFC1123].  Note that while uppercase and lowercase letters are
   allowed in domain names, no significance is attached to the case.  In

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   addition, while the string " " is a legal domain name, subjectAltName
   extensions with a dNSName of " " MUST NOT be used.  Finally, the use
   of the DNS representation for Internet mail addresses
   (subscriber.example.com instead of subscriber@example.com) MUST NOT
   be used; such identities are to be encoded as rfc822Name.  Rules for
   encoding internationalized domain names are specified in Section 7.2.

   When the subjectAltName extension contains a URI, the name MUST be
   stored in the uniformResourceIdentifier (an IA5String).  The name
   MUST NOT be a relative URI, and it MUST follow the URI syntax and
   encoding rules specified in [RFC3986].  The name MUST include both a
   scheme (e.g., "http" or "ftp") and a scheme-specific-part.  URIs that
   include an authority ([RFC3986], Section 3.2) MUST include a fully
   qualified domain name or IP address as the host.  Rules for encoding
   Internationalized Resource Identifiers (IRIs) are specified in
   Section 7.4.

   As specified in [RFC3986], the scheme name is not case-sensitive
   (e.g., "http" is equivalent to "HTTP").  The host part, if present,
   is also not case-sensitive, but other components of the scheme-
   specific-part may be case-sensitive.  Rules for comparing URIs are
   specified in Section 7.4.

   When the subjectAltName extension contains a DN in the directoryName,
   the encoding rules are the same as those specified for the issuer
   field in Section 4.1.2.4.  The DN MUST be unique for each subject
   entity certified by the one CA as defined by the issuer field.  A CA
   MAY issue more than one certificate with the same DN to the same
   subject entity.

   The subjectAltName MAY carry additional name types through the use of
   the otherName field.  The format and semantics of the name are
   indicated through the OBJECT IDENTIFIER in the type-id field.  The
   name itself is conveyed as value field in otherName.  For example,
   Kerberos [RFC4120] format names can be encoded into the otherName,
   using a Kerberos 5 principal name OID and a SEQUENCE of the Realm and
   the PrincipalName.

   Subject alternative names MAY be constrained in the same manner as
   subject distinguished names using the name constraints extension as
   described in Section 4.2.1.10.

   If the subjectAltName extension is present, the sequence MUST contain
   at least one entry.  Unlike the subject field, conforming CAs MUST
   NOT issue certificates with subjectAltNames containing empty
   GeneralName fields.  For example, an rfc822Name is represented as an
   IA5String.  While an empty string is a valid IA5String, such an
   rfc822Name is not permitted by this profile.  The behavior of clients

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   that encounter such a certificate when processing a certification
   path is not defined by this profile.

   Finally, the semantics of subject alternative names that include
   wildcard characters (e.g., as a placeholder for a set of names) are
   not addressed by this specification.  Applications with specific
   requirements MAY use such names, but they must define the semantics.

   id-ce-subjectAltName OBJECT IDENTIFIER ::=  { id-ce 17 }

   SubjectAltName ::= GeneralNames

   GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

   GeneralName ::= CHOICE {
        otherName                       [0]     OtherName,
        rfc822Name                      [1]     IA5String,
        dNSName                         [2]     IA5String,
        x400Address                     [3]     ORAddress,
        directoryName                   [4]     Name,
        ediPartyName                    [5]     EDIPartyName,
        uniformResourceIdentifier       [6]     IA5String,
        iPAddress                       [7]     OCTET STRING,
        registeredID                    [8]     OBJECT IDENTIFIER }

   OtherName ::= SEQUENCE {
        type-id    OBJECT IDENTIFIER,
        value      [0] EXPLICIT ANY DEFINED BY type-id }

   EDIPartyName ::= SEQUENCE {
        nameAssigner            [0]     DirectoryString OPTIONAL,
        partyName               [1]     DirectoryString }

4.2.1.7.  Issuer Alternative Name

   As with Section 4.2.1.6, this extension is used to associate Internet
   style identities with the certificate issuer.  Issuer alternative
   name MUST be encoded as in 4.2.1.6.  Issuer alternative names are not
   processed as part of the certification path validation algorithm in
   Section 6.  (That is, issuer alternative names are not used in name
   chaining and name constraints are not enforced.)

   Where present, conforming CAs SHOULD mark this extension as non-
   critical.

   id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }

   IssuerAltName ::= GeneralNames

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4.2.1.8.  Subject Directory Attributes

   The subject directory attributes extension is used to convey
   identification attributes (e.g., nationality) of the subject.  The
   extension is defined as a sequence of one or more attributes.
   Conforming CAs MUST mark this extension as non-critical.

   id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }

   SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

4.2.1.9.  Basic Constraints

   The basic constraints extension identifies whether the subject of the
   certificate is a CA and the maximum depth of valid certification
   paths that include this certificate.

   The cA boolean indicates whether the certified public key may be used
   to verify certificate signatures.  If the cA boolean is not asserted,
   then the keyCertSign bit in the key usage extension MUST NOT be
   asserted.  If the basic constraints extension is not present in a
   version 3 certificate, or the extension is present but the cA boolean
   is not asserted, then the certified public key MUST NOT be used to
   verify certificate signatures.

   The pathLenConstraint field is meaningful only if the cA boolean is
   asserted and the key usage extension, if present, asserts the
   keyCertSign bit (Section 4.2.1.3).  In this case, it gives the
   maximum number of non-self-issued intermediate certificates that may
   follow this certificate in a valid certification path.  (Note: The
   last certificate in the certification path is not an intermediate
   certificate, and is not included in this limit.  Usually, the last
   certificate is an end entity certificate, but it can be a CA
   certificate.)  A pathLenConstraint of zero indicates that no non-
   self-issued intermediate CA certificates may follow in a valid
   certification path.  Where it appears, the pathLenConstraint field
   MUST be greater than or equal to zero.  Where pathLenConstraint does
   not appear, no limit is imposed.

   Conforming CAs MUST include this extension in all CA certificates
   that contain public keys used to validate digital signatures on
   certificates and MUST mark the extension as critical in such
   certificates.  This extension MAY appear as a critical or non-
   critical extension in CA certificates that contain public keys used
   exclusively for purposes other than validating digital signatures on
   certificates.  Such CA certificates include ones that contain public
   keys used exclusively for validating digital signatures on CRLs and
   ones that contain key management public keys used with certificate

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   enrollment protocols.  This extension MAY appear as a critical or
   non-critical extension in end entity certificates.

   CAs MUST NOT include the pathLenConstraint field unless the cA
   boolean is asserted and the key usage extension asserts the
   keyCertSign bit.

   id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }

   BasicConstraints ::= SEQUENCE {
        cA                      BOOLEAN DEFAULT FALSE,
        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

4.2.1.10.  Name Constraints

   The name constraints extension, which MUST be used only in a CA
   certificate, indicates a name space within which all subject names in
   subsequent certificates in a certification path MUST be located.
   Restrictions apply to the subject distinguished name and apply to
   subject alternative names.  Restrictions apply only when the
   specified name form is present.  If no name of the type is in the
   certificate, the certificate is acceptable.

   Name constraints are not applied to self-issued certificates (unless
   the certificate is the final certificate in the path).  (This could
   prevent CAs that use name constraints from employing self-issued
   certificates to implement key rollover.)

   Restrictions are defined in terms of permitted or excluded name
   subtrees.  Any name matching a restriction in the excludedSubtrees
   field is invalid regardless of information appearing in the
   permittedSubtrees.  Conforming CAs MUST mark this extension as
   critical and SHOULD NOT impose name constraints on the x400Address,
   ediPartyName, or registeredID name forms.  Conforming CAs MUST NOT
   issue certificates where name constraints is an empty sequence.  That
   is, either the permittedSubtrees field or the excludedSubtrees MUST
   be present.

   Applications conforming to this profile MUST be able to process name
   constraints that are imposed on the directoryName name form and
   SHOULD be able to process name constraints that are imposed on the
   rfc822Name, uniformResourceIdentifier, dNSName, and iPAddress name
   forms.  If a name constraints extension that is marked as critical
   imposes constraints on a particular name form, and an instance of
   that name form appears in the subject field or subjectAltName
   extension of a subsequent certificate, then the application MUST
   either process the constraint or reject the certificate.

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   Within this profile, the minimum and maximum fields are not used with
   any name forms, thus, the minimum MUST be zero, and maximum MUST be
   absent.  However, if an application encounters a critical name
   constraints extension that specifies other values for minimum or
   maximum for a name form that appears in a subsequent certificate, the
   application MUST either process these fields or reject the
   certificate.

   For URIs, the constraint applies to the host part of the name.  The
   constraint MUST be specified as a fully qualified domain name and MAY
   specify a host or a domain.  Examples would be "host.example.com" and
   ".example.com".  When the constraint begins with a period, it MAY be
   expanded with one or more labels.  That is, the constraint
   ".example.com" is satisfied by both host.example.com and
   my.host.example.com.  However, the constraint ".example.com" is not
   satisfied by "example.com".  When the constraint does not begin with
   a period, it specifies a host.  If a constraint is applied to the
   uniformResourceIdentifier name form and a subsequent certificate
   includes a subjectAltName extension with a uniformResourceIdentifier
   that does not include an authority component with a host name
   specified as a fully qualified domain name (e.g., if the URI either
   does not include an authority component or includes an authority
   component in which the host name is specified as an IP address), then
   the application MUST reject the certificate.

   A name constraint for Internet mail addresses MAY specify a
   particular mailbox, all addresses at a particular host, or all
   mailboxes in a domain.  To indicate a particular mailbox, the
   constraint is the complete mail address.  For example,
   "root@example.com" indicates the root mailbox on the host
   "example.com".  To indicate all Internet mail addresses on a
   particular host, the constraint is specified as the host name.  For
   example, the constraint "example.com" is satisfied by any mail
   address at the host "example.com".  To specify any address within a
   domain, the constraint is specified with a leading period (as with
   URIs).  For example, ".example.com" indicates all the Internet mail
   addresses in the domain "example.com", but not Internet mail
   addresses on the host "example.com".

   DNS name restrictions are expressed as host.example.com.  Any DNS
   name that can be constructed by simply adding zero or more labels to
   the left-hand side of the name satisfies the name constraint.  For
   example, www.host.example.com would satisfy the constraint but
   host1.example.com would not.

   Legacy implementations exist where an electronic mail address is
   embedded in the subject distinguished name in an attribute of type
   emailAddress (Section 4.1.2.6).  When constraints are imposed on the

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   rfc822Name name form, but the certificate does not include a subject
   alternative name, the rfc822Name constraint MUST be applied to the
   attribute of type emailAddress in the subject distinguished name.
   The ASN.1 syntax for emailAddress and the corresponding OID are
   supplied in Appendix A.

   Restrictions of the form directoryName MUST be applied to the subject
   field in the certificate (when the certificate includes a non-empty
   subject field) and to any names of type directoryName in the
   subjectAltName extension.  Restrictions of the form x400Address MUST
   be applied to any names of type x400Address in the subjectAltName
   extension.

   When applying restrictions of the form directoryName, an
   implementation MUST compare DN attributes.  At a minimum,
   implementations MUST perform the DN comparison rules specified in
   Section 7.1.  CAs issuing certificates with a restriction of the form
   directoryName SHOULD NOT rely on implementation of the full ISO DN
   name comparison algorithm.  This implies name restrictions MUST be
   stated identically to the encoding used in the subject field or
   subjectAltName extension.

   The syntax of iPAddress MUST be as described in Section 4.2.1.6 with
   the following additions specifically for name constraints.  For IPv4
   addresses, the iPAddress field of GeneralName MUST contain eight (8)
   octets, encoded in the style of RFC 4632 (CIDR) to represent an
   address range [RFC4632].  For IPv6 addresses, the iPAddress field
   MUST contain 32 octets similarly encoded.  For example, a name
   constraint for "class C" subnet 192.0.2.0 is represented as the
   octets C0 00 02 00 FF FF FF 00, representing the CIDR notation
   192.0.2.0/24 (mask 255.255.255.0).

   Additional rules for encoding and processing name constraints are
   specified in Section 7.

   The syntax and semantics for name constraints for otherName,
   ediPartyName, and registeredID are not defined by this specification,
   however, syntax and semantics for name constraints for other name
   forms may be specified in other documents.

      id-ce-nameConstraints OBJECT IDENTIFIER ::=  { id-ce 30 }

      NameConstraints ::= SEQUENCE {
           permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
           excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

      GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

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      GeneralSubtree ::= SEQUENCE {
           base                    GeneralName,
           minimum         [0]     BaseDistance DEFAULT 0,
           maximum         [1]     BaseDistance OPTIONAL }

      BaseDistance ::= INTEGER (0..MAX)

4.2.1.11.  Policy Constraints

   The policy constraints extension can be used in certificates issued
   to CAs.  The policy constraints extension constrains path validation
   in two ways.  It can be used to prohibit policy mapping or require
   that each certificate in a path contain an acceptable policy
   identifier.

   If the inhibitPolicyMapping field is present, the value indicates the
   number of additional certificates that may appear in the path before
   policy mapping is no longer permitted.  For example, a value of one
   indicates that policy mapping may be processed in certificates issued
   by the subject of this certificate, but not in additional
   certificates in the path.

   If the requireExplicitPolicy field is present, the value of
   requireExplicitPolicy indicates the number of additional certificates
   that may appear in the path before an explicit policy is required for
   the entire path.  When an explicit policy is required, it is
   necessary for all certificates in the path to contain an acceptable
   policy identifier in the certificate policies extension.  An
   acceptable policy identifier is the identifier of a policy required
   by the user of the certification path or the identifier of a policy
   that has been declared equivalent through policy mapping.

   Conforming applications MUST be able to process the
   requireExplicitPolicy field and SHOULD be able to process the
   inhibitPolicyMapping field.  Applications that support the
   inhibitPolicyMapping field MUST also implement support for the
   policyMappings extension.  If the policyConstraints extension is
   marked as critical and the inhibitPolicyMapping field is present,
   applications that do not implement support for the
   inhibitPolicyMapping field MUST reject the certificate.

   Conforming CAs MUST NOT issue certificates where policy constraints
   is an empty sequence.  That is, either the inhibitPolicyMapping field
   or the requireExplicitPolicy field MUST be present.  The behavior of
   clients that encounter an empty policy constraints field is not
   addressed in this profile.

   Conforming CAs MUST mark this extension as critical.

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   id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }

   PolicyConstraints ::= SEQUENCE {
        requireExplicitPolicy           [0] SkipCerts OPTIONAL,
        inhibitPolicyMapping            [1] SkipCerts OPTIONAL }

   SkipCerts ::= INTEGER (0..MAX)

4.2.1.12.  Extended Key Usage

   This extension indicates one or more purposes for which the certified
   public key may be used, in addition to or in place of the basic
   purposes indicated in the key usage extension.  In general, this
   extension will appear only in end entity certificates.  This
   extension is defined as follows:

   id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }

   ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

   KeyPurposeId ::= OBJECT IDENTIFIER

   Key purposes may be defined by any organization with a need.  Object
   identifiers used to identify key purposes MUST be assigned in
   accordance with IANA or ITU-T Recommendation X.660 [X.660].

   This extension MAY, at the option of the certificate issuer, be
   either critical or non-critical.

   If the extension is present, then the certificate MUST only be used
   for one of the purposes indicated.  If multiple purposes are
   indicated the application need not recognize all purposes indicated,
   as long as the intended purpose is present.  Certificate using
   applications MAY require that the extended key usage extension be
   present and that a particular purpose be indicated in order for the
   certificate to be acceptable to that application.

   If a CA includes extended key usages to satisfy such applications,
   but does not wish to restrict usages of the key, the CA can include
   the special KeyPurposeId anyExtendedKeyUsage in addition to the
   particular key purposes required by the applications.  Conforming CAs
   SHOULD NOT mark this extension as critical if the anyExtendedKeyUsage
   KeyPurposeId is present.  Applications that require the presence of a
   particular purpose MAY reject certificates that include the
   anyExtendedKeyUsage OID but not the particular OID expected for the
   application.

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   If a certificate contains both a key usage extension and an extended
   key usage extension, then both extensions MUST be processed
   independently and the certificate MUST only be used for a purpose
   consistent with both extensions.  If there is no purpose consistent
   with both extensions, then the certificate MUST NOT be used for any
   purpose.

   The following key usage purposes are defined:

   anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

   id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }

   id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
   -- TLS WWW server authentication
   -- Key usage bits that may be consistent: digitalSignature,
   -- keyEncipherment or keyAgreement

   id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
   -- TLS WWW client authentication
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or keyAgreement

   id-kp-codeSigning             OBJECT IDENTIFIER ::= { id-kp 3 }
   -- Signing of downloadable executable code
   -- Key usage bits that may be consistent: digitalSignature

   id-kp-emailProtection         OBJECT IDENTIFIER ::= { id-kp 4 }
   -- Email protection
   -- Key usage bits that may be consistent: digitalSignature,
   -- nonRepudiation, and/or (keyEncipherment or keyAgreement)

   id-kp-timeStamping            OBJECT IDENTIFIER ::= { id-kp 8 }
   -- Binding the hash of an object to a time
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or nonRepudiation

   id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }
   -- Signing OCSP responses
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or nonRepudiation

4.2.1.13.  CRL Distribution Points

   The CRL distribution points extension identifies how CRL information
   is obtained.  The extension SHOULD be non-critical, but this profile
   RECOMMENDS support for this extension by CAs and applications.
   Further discussion of CRL management is contained in Section 5.

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   The cRLDistributionPoints extension is a SEQUENCE of
   DistributionPoint.  A DistributionPoint consists of three fields,
   each of which is optional: distributionPoint, reasons, and cRLIssuer.
   While each of these fields is optional, a DistributionPoint MUST NOT
   consist of only the reasons field; either distributionPoint or
   cRLIssuer MUST be present.  If the certificate issuer is not the CRL
   issuer, then the cRLIssuer field MUST be present and contain the Name
   of the CRL issuer.  If the certificate issuer is also the CRL issuer,
   then conforming CAs MUST omit the cRLIssuer field and MUST include
   the distributionPoint field.

   When the distributionPoint field is present, it contains either a
   SEQUENCE of general names or a single value, nameRelativeToCRLIssuer.
   If the DistributionPointName contains multiple values, each name
   describes a different mechanism to obtain the same CRL.  For example,
   the same CRL could be available for retrieval through both LDAP and
   HTTP.

   If the distributionPoint field contains a directoryName, the entry
   for that directoryName contains the current CRL for the associated
   reasons and the CRL is issued by the associated cRLIssuer.  The CRL
   may be stored in either the certificateRevocationList or
   authorityRevocationList attribute.  The CRL is to be obtained by the
   application from whatever directory server is locally configured.
   The protocol the application uses to access the directory (e.g., DAP
   or LDAP) is a local matter.

   If the DistributionPointName contains a general name of type URI, the
   following semantics MUST be assumed: the URI is a pointer to the
   current CRL for the associated reasons and will be issued by the
   associated cRLIssuer.  When the HTTP or FTP URI scheme is used, the
   URI MUST point to a single DER encoded CRL as specified in
   [RFC2585].  HTTP server implementations accessed via the URI SHOULD
   specify the media type application/pkix-crl in the content-type
   header field of the response.  When the LDAP URI scheme [RFC4516] is
   used, the URI MUST include a <dn> field containing the distinguished
   name of the entry holding the CRL, MUST include a single <attrdesc>
   that contains an appropriate attribute description for the attribute
   that holds the CRL [RFC4523], and SHOULD include a <host>
   (e.g., <ldap://ldap.example.com/cn=example%20CA,dc=example,dc=com?
   certificateRevocationList;binary>).  Omitting the <host> (e.g.,
   <ldap:///cn=CA,dc=example,dc=com?authorityRevocationList;binary>) has
   the effect of relying on whatever a priori knowledge the client might
   have to contact an appropriate server.  When present,
   DistributionPointName SHOULD include at least one LDAP or HTTP URI.

   If the DistributionPointName contains the single value
   nameRelativeToCRLIssuer, the value provides a distinguished name

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   fragment.  The fragment is appended to the X.500 distinguished name
   of the CRL issuer to obtain the distribution point name.  If the
   cRLIssuer field in the DistributionPoint is present, then the name
   fragment is appended to the distinguished name that it contains;
   otherwise, the name fragment is appended to the certificate issuer
   distinguished name.  Conforming CAs SHOULD NOT use
   nameRelativeToCRLIssuer to specify distribution point names.  The
   DistributionPointName MUST NOT use the nameRelativeToCRLIssuer
   alternative when cRLIssuer contains more than one distinguished name.

   If the DistributionPoint omits the reasons field, the CRL MUST
   include revocation information for all reasons.  This profile
   RECOMMENDS against segmenting CRLs by reason code.  When a conforming
   CA includes a cRLDistributionPoints extension in a certificate, it
   MUST include at least one DistributionPoint that points to a CRL that
   covers the certificate for all reasons.

   The cRLIssuer identifies the entity that signs and issues the CRL.
   If present, the cRLIssuer MUST only contain the distinguished name
   (DN) from the issuer field of the CRL to which the DistributionPoint
   is pointing.  The encoding of the name in the cRLIssuer field MUST be
   exactly the same as the encoding in issuer field of the CRL.  If the
   cRLIssuer field is included and the DN in that field does not
   correspond to an X.500 or LDAP directory entry where CRL is located,
   then conforming CAs MUST include the distributionPoint field.

   id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::=  { id-ce 31 }

   CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

   DistributionPoint ::= SEQUENCE {
        distributionPoint       [0]     DistributionPointName OPTIONAL,
        reasons                 [1]     ReasonFlags OPTIONAL,
        cRLIssuer               [2]     GeneralNames OPTIONAL }

   DistributionPointName ::= CHOICE {
        fullName                [0]     GeneralNames,
        nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

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   ReasonFlags ::= BIT STRING {
        unused                  (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6),
        privilegeWithdrawn      (7),
        aACompromise            (8) }

4.2.1.14.  Inhibit anyPolicy

   The inhibit anyPolicy extension can be used in certificates issued to
   CAs.  The inhibit anyPolicy extension indicates that the special
   anyPolicy OID, with the value { 2 5 29 32 0 }, is not considered an
   explicit match for other certificate policies except when it appears
   in an intermediate self-issued CA certificate.  The value indicates
   the number of additional non-self-issued certificates that may appear
   in the path before anyPolicy is no longer permitted.  For example, a
   value of one indicates that anyPolicy may be processed in
   certificates issued by the subject of this certificate, but not in
   additional certificates in the path.

   Conforming CAs MUST mark this extension as critical.

   id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }

   InhibitAnyPolicy ::= SkipCerts

   SkipCerts ::= INTEGER (0..MAX)

4.2.1.15.  Freshest CRL (a.k.a. Delta CRL Distribution Point)

   The freshest CRL extension identifies how delta CRL information is
   obtained.  The extension MUST be marked as non-critical by conforming
   CAs.  Further discussion of CRL management is contained in Section 5.

   The same syntax is used for this extension and the
   cRLDistributionPoints extension, and is described in Section
   4.2.1.13.  The same conventions apply to both extensions.

   id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

   FreshestCRL ::= CRLDistributionPoints

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4.2.2.  Private Internet Extensions

   This section defines two extensions for use in the Internet Public
   Key Infrastructure.  These extensions may be used to direct
   applications to on-line information about the issuer or the subject.
   Each extension contains a sequence of access methods and access
   locations.  The access method is an object identifier that indicates
   the type of information that is available.  The access location is a
   GeneralName that implicitly specifies the location and format of the
   information and the method for obtaining the information.

   Object identifiers are defined for the private extensions.  The
   object identifiers associated with the private extensions are defined
   under the arc id-pe within the arc id-pkix.  Any future extensions
   defined for the Internet PKI are also expected to be defined under
   the arc id-pe.

      id-pkix  OBJECT IDENTIFIER  ::=
               { iso(1) identified-organization(3) dod(6) internet(1)
                       security(5) mechanisms(5) pkix(7) }

      id-pe  OBJECT IDENTIFIER  ::=  { id-pkix 1 }

4.2.2.1.  Authority Information Access

   The authority information access extension indicates how to access
   information and services for the issuer of the certificate in which
   the extension appears.  Information and services may include on-line
   validation services and CA policy data.  (The location of CRLs is not
   specified in this extension; that information is provided by the
   cRLDistributionPoints extension.)  This extension may be included in
   end entity or CA certificates.  Conforming CAs MUST mark this
   extension as non-critical.

   id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

   AuthorityInfoAccessSyntax  ::=
           SEQUENCE SIZE (1..MAX) OF AccessDescription

   AccessDescription  ::=  SEQUENCE {
           accessMethod          OBJECT IDENTIFIER,
           accessLocation        GeneralName  }

   id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

   id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 }

   id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }

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   Each entry in the sequence AuthorityInfoAccessSyntax describes the
   format and location of additional information provided by the issuer
   of the certificate in which this extension appears.  The type and
   format of the information are specified by the accessMethod field;
   the accessLocation field specifies the location of the information.
   The retrieval mechanism may be implied by the accessMethod or
   specified by accessLocation.

   This profile defines two accessMethod OIDs: id-ad-caIssuers and
   id-ad-ocsp.

   In a public key certificate, the id-ad-caIssuers OID is used when the
   additional information lists certificates that were issued to the CA
   that issued the certificate containing this extension.  The
   referenced CA issuers description is intended to aid certificate
   users in the selection of a certification path that terminates at a
   point trusted by the certificate user.

   When id-ad-caIssuers appears as accessMethod, the accessLocation
   field describes the referenced description server and the access
   protocol to obtain the referenced description.  The accessLocation
   field is defined as a GeneralName, which can take several forms.

   When the accessLocation is a directoryName, the information is to be
   obtained by the application from whatever directory server is locally
   configured.  The entry for the directoryName contains CA certificates
   in the crossCertificatePair and/or cACertificate attributes as
   specified in [RFC4523].  The protocol that application uses to access
   the directory (e.g., DAP or LDAP) is a local matter.

   Where the information is available via LDAP, the accessLocation
   SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
   include a <dn> field containing the distinguished name of the entry
   holding the certificates, MUST include an <attributes> field that
   lists appropriate attribute descriptions for the attributes that hold
   the DER encoded certificates or cross-certificate pairs [RFC4523],
   and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
   dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).
   Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
   cACertificate;binary>) has the effect of relying on whatever a priori
   knowledge the client might have to contact an appropriate server.

   Where the information is available via HTTP or FTP, accessLocation
   MUST be a uniformResourceIdentifier and the URI MUST point to either
   a single DER encoded certificate as specified in [RFC2585] or a
   collection of certificates in a BER or DER encoded "certs-only" CMS
   message as specified in [RFC2797].

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   Conforming applications that support HTTP or FTP for accessing
   certificates MUST be able to accept individual DER encoded
   certificates and SHOULD be able to accept "certs-only" CMS messages.

   HTTP server implementations accessed via the URI SHOULD specify the
   media type application/pkix-cert [RFC2585] in the content-type header
   field of the response for a single DER encoded certificate and SHOULD
   specify the media type application/pkcs7-mime [RFC2797] in the
   content-type header field of the response for "certs-only" CMS
   messages.  For FTP, the name of a file that contains a single DER
   encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
   name of a file that contains a "certs-only" CMS message SHOULD have a
   suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
   or file extension as a hint to the content, but should not depend
   solely on the presence of the correct media type or file extension in
   the server response.

   The semantics of other id-ad-caIssuers accessLocation name forms are
   not defined.

   An authorityInfoAccess extension may include multiple instances of
   the id-ad-caIssuers accessMethod.  The different instances may
   specify different methods for accessing the same information or may
   point to different information.  When the id-ad-caIssuers
   accessMethod is used, at least one instance SHOULD specify an
   accessLocation that is an HTTP [RFC2616] or LDAP [RFC4516] URI.

   The id-ad-ocsp OID is used when revocation information for the
   certificate containing this extension is available using the Online
   Certificate Status Protocol (OCSP) [RFC2560].

   When id-ad-ocsp appears as accessMethod, the accessLocation field is
   the location of the OCSP responder, using the conventions defined in
   [RFC2560].

   Additional access descriptors may be defined in other PKIX
   specifications.

4.2.2.2.  Subject Information Access

   The subject information access extension indicates how to access
   information and services for the subject of the certificate in which
   the extension appears.  When the subject is a CA, information and
   services may include certificate validation services and CA policy
   data.  When the subject is an end entity, the information describes
   the type of services offered and how to access them.  In this case,
   the contents of this extension are defined in the protocol

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   specifications for the supported services.  This extension may be
   included in end entity or CA certificates.  Conforming CAs MUST mark
   this extension as non-critical.

   id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

   SubjectInfoAccessSyntax  ::=
           SEQUENCE SIZE (1..MAX) OF AccessDescription

   AccessDescription  ::=  SEQUENCE {
           accessMethod          OBJECT IDENTIFIER,
           accessLocation        GeneralName  }

   Each entry in the sequence SubjectInfoAccessSyntax describes the
   format and location of additional information provided by the subject
   of the certificate in which this extension appears.  The type and
   format of the information are specified by the accessMethod field;
   the accessLocation field specifies the location of the information.
   The retrieval mechanism may be implied by the accessMethod or
   specified by accessLocation.

   This profile defines one access method to be used when the subject is
   a CA and one access method to be used when the subject is an end
   entity.  Additional access methods may be defined in the future in
   the protocol specifications for other services.

   The id-ad-caRepository OID is used when the subject is a CA that
   publishes certificates it issues in a repository.  The accessLocation
   field is defined as a GeneralName, which can take several forms.

   When the accessLocation is a directoryName, the information is to be
   obtained by the application from whatever directory server is locally
   configured.  When the extension is used to point to CA certificates,
   the entry for the directoryName contains CA certificates in the
   crossCertificatePair and/or cACertificate attributes as specified in
   [RFC4523].  The protocol the application uses to access the directory
   (e.g., DAP or LDAP) is a local matter.

   Where the information is available via LDAP, the accessLocation
   SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
   include a <dn> field containing the distinguished name of the entry
   holding the certificates, MUST include an <attributes> field that
   lists appropriate attribute descriptions for the attributes that hold
   the DER encoded certificates or cross-certificate pairs [RFC4523],
   and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
   dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).

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   Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
   cACertificate;binary>) has the effect of relying on whatever a priori
   knowledge the client might have to contact an appropriate server.

   Where the information is available via HTTP or FTP, accessLocation
   MUST be a uniformResourceIdentifier and the URI MUST point to either
   a single DER encoded certificate as specified in [RFC2585] or a
   collection of certificates in a BER or DER encoded "certs-only" CMS
   message as specified in [RFC2797].

   Conforming applications that support HTTP or FTP for accessing
   certificates MUST be able to accept individual DER encoded
   certificates and SHOULD be able to accept "certs-only" CMS messages.

   HTTP server implementations accessed via the URI SHOULD specify the
   media type application/pkix-cert [RFC2585] in the content-type header
   field of the response for a single DER encoded certificate and SHOULD
   specify the media type application/pkcs7-mime [RFC2797] in the
   content-type header field of the response for "certs-only" CMS
   messages.  For FTP, the name of a file that contains a single DER
   encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
   name of a file that contains a "certs-only" CMS message SHOULD have a
   suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
   or file extension as a hint to the content, but should not depend
   solely on the presence of the correct media type or file extension in
   the server response.

   The semantics of other id-ad-caRepository accessLocation name forms
   are not defined.

   A subjectInfoAccess extension may include multiple instances of the
   id-ad-caRepository accessMethod.  The different instances may specify
   different methods for accessing the same information or may point to
   different information.  When the id-ad-caRepository accessMethod is
   used, at least one instance SHOULD specify an accessLocation that is
   an HTTP [RFC2616] or LDAP [RFC4516] URI.

   The id-ad-timeStamping OID is used when the subject offers
   timestamping services using the Time Stamp Protocol defined in
   [RFC3161].  Where the timestamping services are available via HTTP or
   FTP, accessLocation MUST be a uniformResourceIdentifier.  Where the
   timestamping services are available via electronic mail,
   accessLocation MUST be an rfc822Name.  Where timestamping services
   are available using TCP/IP, the dNSName or iPAddress name forms may
   be used.  The semantics of other name forms of accessLocation (when
   accessMethod is id-ad-timeStamping) are not defined by this
   specification.

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   Additional access descriptors may be defined in other PKIX
   specifications.

   id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

   id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

   id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }

5.  CRL and CRL Extensions Profile

   As discussed above, one goal of this X.509 v2 CRL profile is to
   foster the creation of an interoperable and reusable Internet PKI.
   To achieve this goal, guidelines for the use of extensions are
   specified, and some assumptions are made about the nature of
   information included in the CRL.

   CRLs may be used in a wide range of applications and environments
   covering a broad spectrum of interoperability goals and an even
   broader spectrum of operational and assurance requirements.  This
   profile establishes a common baseline for generic applications
   requiring broad interoperability.  The profile defines a set of
   information that can be expected in every CRL.  Also, the profile
   defines common locations within the CRL for frequently used
   attributes as well as common representations for these attributes.

   CRL issuers issue CRLs.  The CRL issuer is either the CA or an entity
   that has been authorized by the CA to issue CRLs.  CAs publish CRLs
   to provide status information about the certificates they issued.
   However, a CA may delegate this responsibility to another trusted
   authority.

   Each CRL has a particular scope.  The CRL scope is the set of
   certificates that could appear on a given CRL.  For example, the
   scope could be "all certificates issued by CA X", "all CA
   certificates issued by CA X", "all certificates issued by CA X that
   have been revoked for reasons of key compromise and CA compromise",
   or a set of certificates based on arbitrary local information, such
   as "all certificates issued to the NIST employees located in
   Boulder".

   A complete CRL lists all unexpired certificates, within its scope,
   that have been revoked for one of the revocation reasons covered by
   the CRL scope.  A full and complete CRL lists all unexpired
   certificates issued by a CA that have been revoked for any reason.
   (Note that since CAs and CRL issuers are identified by name, the
   scope of a CRL is not affected by the key used to sign the CRL or the
   key(s) used to sign certificates.)

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   If the scope of the CRL includes one or more certificates issued by
   an entity other than the CRL issuer, then it is an indirect CRL.  The
   scope of an indirect CRL may be limited to certificates issued by a
   single CA or may include certificates issued by multiple CAs.  If the
   issuer of the indirect CRL is a CA, then the scope of the indirect
   CRL MAY also include certificates issued by the issuer of the CRL.

   The CRL issuer MAY also generate delta CRLs.  A delta CRL only lists
   those certificates, within its scope, whose revocation status has
   changed since the issuance of a referenced complete CRL.  The
   referenced complete CRL is referred to as a base CRL.  The scope of a
   delta CRL MUST be the same as the base CRL that it references.

   This profile defines one private Internet CRL extension but does not
   define any private CRL entry extensions.

   Environments with additional or special purpose requirements may
   build on this profile or may replace it.

   Conforming CAs are not required to issue CRLs if other revocation or
   certificate status mechanisms are provided.  When CRLs are issued,
   the CRLs MUST be version 2 CRLs, include the date by which the next
   CRL will be issued in the nextUpdate field (Section 5.1.2.5), include
   the CRL number extension (Section 5.2.3), and include the authority
   key identifier extension (Section 5.2.1).  Conforming applications
   that support CRLs are REQUIRED to process both version 1 and version
   2 complete CRLs that provide revocation information for all
   certificates issued by one CA.  Conforming applications are not
   required to support processing of delta CRLs, indirect CRLs, or CRLs
   with a scope other than all certificates issued by one CA.

5.1.  CRL Fields

   The X.509 v2 CRL syntax is as follows.  For signature calculation,
   the data that is to be signed is ASN.1 DER encoded.  ASN.1 DER
   encoding is a tag, length, value encoding system for each element.

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   CertificateList  ::=  SEQUENCE  {
        tbsCertList          TBSCertList,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

   TBSCertList  ::=  SEQUENCE  {
        version                 Version OPTIONAL,
                                     -- if present, MUST be v2
        signature               AlgorithmIdentifier,
        issuer                  Name,
        thisUpdate              Time,
        nextUpdate              Time OPTIONAL,
        revokedCertificates     SEQUENCE OF SEQUENCE  {
             userCertificate         CertificateSerialNumber,
             revocationDate          Time,
             crlEntryExtensions      Extensions OPTIONAL
                                      -- if present, version MUST be v2
                                  }  OPTIONAL,
        crlExtensions           [0]  EXPLICIT Extensions OPTIONAL
                                      -- if present, version MUST be v2
                                  }

   -- Version, Time, CertificateSerialNumber, and Extensions
   -- are all defined in the ASN.1 in Section 4.1

   -- AlgorithmIdentifier is defined in Section 4.1.1.2

   The following items describe the use of the X.509 v2 CRL in the
   Internet PKI.

5.1.1.  CertificateList Fields

   The CertificateList is a SEQUENCE of three required fields.  The
   fields are described in detail in the following subsections.

5.1.1.1.  tbsCertList

   The first field in the sequence is the tbsCertList.  This field is
   itself a sequence containing the name of the issuer, issue date,
   issue date of the next list, the optional list of revoked
   certificates, and optional CRL extensions.  When there are no revoked
   certificates, the revoked certificates list is absent.  When one or
   more certificates are revoked, each entry on the revoked certificate
   list is defined by a sequence of user certificate serial number,
   revocation date, and optional CRL entry extensions.

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5.1.1.2.  signatureAlgorithm

   The signatureAlgorithm field contains the algorithm identifier for
   the algorithm used by the CRL issuer to sign the CertificateList.
   The field is of type AlgorithmIdentifier, which is defined in Section
   4.1.1.2.  [RFC3279], [RFC4055], and [RFC4491] list supported
   algorithms for this specification, but other signature algorithms MAY
   also be supported.

   This field MUST contain the same algorithm identifier as the
   signature field in the sequence tbsCertList (Section 5.1.2.2).

5.1.1.3.  signatureValue

   The signatureValue field contains a digital signature computed upon
   the ASN.1 DER encoded tbsCertList.  The ASN.1 DER encoded tbsCertList
   is used as the input to the signature function.  This signature value
   is encoded as a BIT STRING and included in the CRL signatureValue
   field.  The details of this process are specified for each of the
   supported algorithms in [RFC3279], [RFC4055], and [RFC4491].

   CAs that are also CRL issuers MAY use one private key to digitally
   sign certificates and CRLs, or MAY use separate private keys to
   digitally sign certificates and CRLs.  When separate private keys are
   employed, each of the public keys associated with these private keys
   is placed in a separate certificate, one with the keyCertSign bit set
   in the key usage extension, and one with the cRLSign bit set in the
   key usage extension (Section 4.2.1.3).  When separate private keys
   are employed, certificates issued by the CA contain one authority key
   identifier, and the corresponding CRLs contain a different authority
   key identifier.  The use of separate CA certificates for validation
   of certificate signatures and CRL signatures can offer improved
   security characteristics; however, it imposes a burden on
   applications, and it might limit interoperability.  Many applications
   construct a certification path, and then validate the certification
   path (Section 6).  CRL checking in turn requires a separate
   certification path to be constructed and validated for the CA's CRL
   signature validation certificate.  Applications that perform CRL
   checking MUST support certification path validation when certificates
   and CRLs are digitally signed with the same CA private key.  These
   applications SHOULD support certification path validation when
   certificates and CRLs are digitally signed with different CA private
   keys.

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5.1.2.  Certificate List "To Be Signed"

   The certificate list to be signed, or TBSCertList, is a sequence of
   required and optional fields.  The required fields identify the CRL
   issuer, the algorithm used to sign the CRL, and the date and time the
   CRL was issued.

   Optional fields include the date and time by which the CRL issuer
   will issue the next CRL, lists of revoked certificates, and CRL
   extensions.  The revoked certificate list is optional to support the
   case where a CA has not revoked any unexpired certificates that it
   has issued.  This profile requires conforming CRL issuers to include
   the nextUpdate field and the CRL number and authority key identifier
   CRL extensions in all CRLs issued.

5.1.2.1.  Version

   This optional field describes the version of the encoded CRL.  When
   extensions are used, as required by this profile, this field MUST be
   present and MUST specify version 2 (the integer value is 1).

5.1.2.2.  Signature

   This field contains the algorithm identifier for the algorithm used
   to sign the CRL.  [RFC3279], [RFC4055], and [RFC4491] list OIDs for
   the most popular signature algorithms used in the Internet PKI.

   This field MUST contain the same algorithm identifier as the
   signatureAlgorithm field in the sequence CertificateList (Section
   5.1.1.2).

5.1.2.3.  Issuer Name

   The issuer name identifies the entity that has signed and issued the
   CRL.  The issuer identity is carried in the issuer field.
   Alternative name forms may also appear in the issuerAltName extension
   (Section 5.2.2).  The issuer field MUST contain a non-empty X.500
   distinguished name (DN).  The issuer field is defined as the X.501
   type Name, and MUST follow the encoding rules for the issuer name
   field in the certificate (Section 4.1.2.4).

5.1.2.4.  This Update

   This field indicates the issue date of this CRL.  thisUpdate may be
   encoded as UTCTime or GeneralizedTime.

   CRL issuers conforming to this profile MUST encode thisUpdate as
   UTCTime for dates through the year 2049.  CRL issuers conforming to

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   this profile MUST encode thisUpdate as GeneralizedTime for dates in
   the year 2050 or later.  Conforming applications MUST be able to
   process dates that are encoded in either UTCTime or GeneralizedTime.

   Where encoded as UTCTime, thisUpdate MUST be specified and
   interpreted as defined in Section 4.1.2.5.1.  Where encoded as
   GeneralizedTime, thisUpdate MUST be specified and interpreted as
   defined in Section 4.1.2.5.2.

5.1.2.5.  Next Update

   This field indicates the date by which the next CRL will be issued.
   The next CRL could be issued before the indicated date, but it will
   not be issued any later than the indicated date.  CRL issuers SHOULD
   issue CRLs with a nextUpdate time equal to or later than all previous
   CRLs.  nextUpdate may be encoded as UTCTime or GeneralizedTime.

   Conforming CRL issuers MUST include the nextUpdate field in all CRLs.
   Note that the ASN.1 syntax of TBSCertList describes this field as
   OPTIONAL, which is consistent with the ASN.1 structure defined in
   [X.509].  The behavior of clients processing CRLs that omit
   nextUpdate is not specified by this profile.

   CRL issuers conforming to this profile MUST encode nextUpdate as
   UTCTime for dates through the year 2049.  CRL issuers conforming to
   this profile MUST encode nextUpdate as GeneralizedTime for dates in
   the year 2050 or later.  Conforming applications MUST be able to
   process dates that are encoded in either UTCTime or GeneralizedTime.

   Where encoded as UTCTime, nextUpdate MUST be specified and
   interpreted as defined in Section 4.1.2.5.1.  Where encoded as
   GeneralizedTime, nextUpdate MUST be specified and interpreted as
   defined in Section 4.1.2.5.2.

5.1.2.6.  Revoked Certificates

   When there are no revoked certificates, the revoked certificates list
   MUST be absent.  Otherwise, revoked certificates are listed by their
   serial numbers.  Certificates revoked by the CA are uniquely
   identified by the certificate serial number.  The date on which the
   revocation occurred is specified.  The time for revocationDate MUST
   be expressed as described in Section 5.1.2.4.  Additional information
   may be supplied in CRL entry extensions; CRL entry extensions are
   discussed in Section 5.3.

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5.1.2.7.  Extensions

   This field may only appear if the version is 2 (Section 5.1.2.1).  If
   present, this field is a sequence of one or more CRL extensions.  CRL
   extensions are discussed in Section 5.2.

5.2.  CRL Extensions

   The extensions defined by ANSI X9, ISO/IEC, and ITU-T for X.509 v2
   CRLs [X.509] [X9.55] provide methods for associating additional
   attributes with CRLs.  The X.509 v2 CRL format also allows
   communities to define private extensions to carry information unique
   to those communities.  Each extension in a CRL may be designated as
   critical or non-critical.  If a CRL contains a critical extension
   that the application cannot process, then the application MUST NOT
   use that CRL to determine the status of certificates.  However,
   applications may ignore unrecognized non-critical extensions.  The
   following subsections present those extensions used within Internet
   CRLs.  Communities may elect to include extensions in CRLs that are
   not defined in this specification.  However, caution should be
   exercised in adopting any critical extensions in CRLs that might be
   used in a general context.

   Conforming CRL issuers are REQUIRED to include the authority key
   identifier (Section 5.2.1) and the CRL number (Section 5.2.3)
   extensions in all CRLs issued.

5.2.1.  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the public key corresponding to the private key used to
   sign a CRL.  The identification can be based on either the key
   identifier (the subject key identifier in the CRL signer's
   certificate) or the issuer name and serial number.  This extension is
   especially useful where an issuer has more than one signing key,
   either due to multiple concurrent key pairs or due to changeover.

   Conforming CRL issuers MUST use the key identifier method, and MUST
   include this extension in all CRLs issued.

   The syntax for this CRL extension is defined in Section 4.2.1.1.

5.2.2.  Issuer Alternative Name

   The issuer alternative name extension allows additional identities to
   be associated with the issuer of the CRL.  Defined options include an
   electronic mail address (rfc822Name), a DNS name, an IP address, and
   a URI.  Multiple instances of a name form and multiple name forms may

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   be included.  Whenever such identities are used, the issuer
   alternative name extension MUST be used; however, a DNS name MAY be
   represented in the issuer field using the domainComponent attribute
   as described in Section 4.1.2.4.

   Conforming CRL issuers SHOULD mark the issuerAltName extension as
   non-critical.

   The OID and syntax for this CRL extension are defined in Section
   4.2.1.7.

5.2.3.  CRL Number

   The CRL number is a non-critical CRL extension that conveys a
   monotonically increasing sequence number for a given CRL scope and
   CRL issuer.  This extension allows users to easily determine when a
   particular CRL supersedes another CRL.  CRL numbers also support the
   identification of complementary complete CRLs and delta CRLs.  CRL
   issuers conforming to this profile MUST include this extension in all
   CRLs and MUST mark this extension as non-critical.

   If a CRL issuer generates delta CRLs in addition to complete CRLs for
   a given scope, the complete CRLs and delta CRLs MUST share one
   numbering sequence.  If a delta CRL and a complete CRL that cover the
   same scope are issued at the same time, they MUST have the same CRL
   number and provide the same revocation information.  That is, the
   combination of the delta CRL and an acceptable complete CRL MUST
   provide the same revocation information as the simultaneously issued
   complete CRL.

   If a CRL issuer generates two CRLs (two complete CRLs, two delta
   CRLs, or a complete CRL and a delta CRL) for the same scope at
   different times, the two CRLs MUST NOT have the same CRL number.
   That is, if the this update field (Section 5.1.2.4) in the two CRLs
   are not identical, the CRL numbers MUST be different.

   Given the requirements above, CRL numbers can be expected to contain
   long integers.  CRL verifiers MUST be able to handle CRLNumber values
   up to 20 octets.  Conforming CRL issuers MUST NOT use CRLNumber
   values longer than 20 octets.

   id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

   CRLNumber ::= INTEGER (0..MAX)

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5.2.4.  Delta CRL Indicator

   The delta CRL indicator is a critical CRL extension that identifies a
   CRL as being a delta CRL.  Delta CRLs contain updates to revocation
   information previously distributed, rather than all the information
   that would appear in a complete CRL.  The use of delta CRLs can
   significantly reduce network load and processing time in some
   environments.  Delta CRLs are generally smaller than the CRLs they
   update, so applications that obtain delta CRLs consume less network
   bandwidth than applications that obtain the corresponding complete
   CRLs.  Applications that store revocation information in a format
   other than the CRL structure can add new revocation information to
   the local database without reprocessing information.

   The delta CRL indicator extension contains the single value of type
   BaseCRLNumber.  The CRL number identifies the CRL, complete for a
   given scope, that was used as the starting point in the generation of
   this delta CRL.  A conforming CRL issuer MUST publish the referenced
   base CRL as a complete CRL.  The delta CRL contains all updates to
   the revocation status for that same scope.  The combination of a
   delta CRL plus the referenced base CRL is equivalent to a complete
   CRL, for the applicable scope, at the time of publication of the
   delta CRL.

   When a conforming CRL issuer generates a delta CRL, the delta CRL
   MUST include a critical delta CRL indicator extension.

   When a delta CRL is issued, it MUST cover the same set of reasons and
   the same set of certificates that were covered by the base CRL it
   references.  That is, the scope of the delta CRL MUST be the same as
   the scope of the complete CRL referenced as the base.  The referenced
   base CRL and the delta CRL MUST omit the issuing distribution point
   extension or contain identical issuing distribution point extensions.
   Further, the CRL issuer MUST use the same private key to sign the
   delta CRL and any complete CRL that it can be used to update.

   An application that supports delta CRLs can construct a CRL that is
   complete for a given scope by combining a delta CRL for that scope
   with either an issued CRL that is complete for that scope or a
   locally constructed CRL that is complete for that scope.

   When a delta CRL is combined with a complete CRL or a locally
   constructed CRL, the resulting locally constructed CRL has the CRL
   number specified in the CRL number extension found in the delta CRL
   used in its construction.  In addition, the resulting locally
   constructed CRL has the thisUpdate and nextUpdate times specified in

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   the corresponding fields of the delta CRL used in its construction.
   In addition, the locally constructed CRL inherits the issuing
   distribution point from the delta CRL.

   A complete CRL and a delta CRL MAY be combined if the following four
   conditions are satisfied:

      (a)  The complete CRL and delta CRL have the same issuer.

      (b)  The complete CRL and delta CRL have the same scope.  The two
           CRLs have the same scope if either of the following
           conditions are met:

         (1)  The issuingDistributionPoint extension is omitted from
              both the complete CRL and the delta CRL.

         (2)  The issuingDistributionPoint extension is present in both
              the complete CRL and the delta CRL, and the values for
              each of the fields in the extensions are the same in both
              CRLs.

      (c)  The CRL number of the complete CRL is equal to or greater
           than the BaseCRLNumber specified in the delta CRL.  That is,
           the complete CRL contains (at a minimum) all the revocation
           information held by the referenced base CRL.

      (d)  The CRL number of the complete CRL is less than the CRL
           number of the delta CRL.  That is, the delta CRL follows the
           complete CRL in the numbering sequence.

   CRL issuers MUST ensure that the combination of a delta CRL and any
   appropriate complete CRL accurately reflects the current revocation
   status.  The CRL issuer MUST include an entry in the delta CRL for
   each certificate within the scope of the delta CRL whose status has
   changed since the generation of the referenced base CRL:

      (a)  If the certificate is revoked for a reason included in the
           scope of the CRL, list the certificate as revoked.

      (b)  If the certificate is valid and was listed on the referenced
           base CRL or any subsequent CRL with reason code
           certificateHold, and the reason code certificateHold is
           included in the scope of the CRL, list the certificate with
           the reason code removeFromCRL.

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      (c)  If the certificate is revoked for a reason outside the scope
           of the CRL, but the certificate was listed on the referenced
           base CRL or any subsequent CRL with a reason code included in
           the scope of this CRL, list the certificate as revoked but
           omit the reason code.

      (d)  If the certificate is revoked for a reason outside the scope
           of the CRL and the certificate was neither listed on the
           referenced base CRL nor any subsequent CRL with a reason code
           included in the scope of this CRL, do not list the
           certificate on this CRL.

   The status of a certificate is considered to have changed if it is
   revoked (for any revocation reason, including certificateHold), if it
   is released from hold, or if its revocation reason changes.

   It is appropriate to list a certificate with reason code
   removeFromCRL on a delta CRL even if the certificate was not on hold
   in the referenced base CRL.  If the certificate was placed on hold in
   any CRL issued after the base but before this delta CRL and then
   released from hold, it MUST be listed on the delta CRL with
   revocation reason removeFromCRL.

   A CRL issuer MAY optionally list a certificate on a delta CRL with
   reason code removeFromCRL if the notAfter time specified in the
   certificate precedes the thisUpdate time specified in the delta CRL
   and the certificate was listed on the referenced base CRL or in any
   CRL issued after the base but before this delta CRL.

   If a certificate revocation notice first appears on a delta CRL, then
   it is possible for the certificate validity period to expire before
   the next complete CRL for the same scope is issued.  In this case,
   the revocation notice MUST be included in all subsequent delta CRLs
   until the revocation notice is included on at least one explicitly
   issued complete CRL for this scope.

   An application that supports delta CRLs MUST be able to construct a
   current complete CRL by combining a previously issued complete CRL
   and the most current delta CRL.  An application that supports delta
   CRLs MAY also be able to construct a current complete CRL by
   combining a previously locally constructed complete CRL and the
   current delta CRL.  A delta CRL is considered to be the current one
   if the current time is between the times contained in the thisUpdate
   and nextUpdate fields.  Under some circumstances, the CRL issuer may
   publish one or more delta CRLs before the time indicated by the
   nextUpdate field.  If more than one current delta CRL for a given
   scope is encountered, the application SHOULD consider the one with
   the latest value in thisUpdate to be the most current one.

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   id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

   BaseCRLNumber ::= CRLNumber

5.2.5.  Issuing Distribution Point

   The issuing distribution point is a critical CRL extension that
   identifies the CRL distribution point and scope for a particular CRL,
   and it indicates whether the CRL covers revocation for end entity
   certificates only, CA certificates only, attribute certificates only,
   or a limited set of reason codes.  Although the extension is
   critical, conforming implementations are not required to support this
   extension.  However, implementations that do not support this
   extension MUST either treat the status of any certificate not listed
   on this CRL as unknown or locate another CRL that does not contain
   any unrecognized critical extensions.

   The CRL is signed using the CRL issuer's private key.  CRL
   distribution points do not have their own key pairs.  If the CRL is
   stored in the X.500 directory, it is stored in the directory entry
   corresponding to the CRL distribution point, which may be different
   from the directory entry of the CRL issuer.

   The reason codes associated with a distribution point MUST be
   specified in onlySomeReasons.  If onlySomeReasons does not appear,
   the distribution point MUST contain revocations for all reason codes.
   CAs may use CRL distribution points to partition the CRL on the basis
   of compromise and routine revocation.  In this case, the revocations
   with reason code keyCompromise (1), cACompromise (2), and
   aACompromise (8) appear in one distribution point, and the
   revocations with other reason codes appear in another distribution
   point.

   If a CRL includes an issuingDistributionPoint extension with
   onlySomeReasons present, then every certificate in the scope of the
   CRL that is revoked MUST be assigned a revocation reason other than
   unspecified.  The assigned revocation reason is used to determine on
   which CRL(s) to list the revoked certificate, however, there is no
   requirement to include the reasonCode CRL entry extension in the
   corresponding CRL entry.

   The syntax and semantics for the distributionPoint field are the same
   as for the distributionPoint field in the cRLDistributionPoints
   extension (Section 4.2.1.13).  If the distributionPoint field is
   present, then it MUST include at least one of names from the
   corresponding distributionPoint field of the cRLDistributionPoints

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   extension of every certificate that is within the scope of this CRL.
   The identical encoding MUST be used in the distributionPoint fields
   of the certificate and the CRL.

   If the distributionPoint field is absent, the CRL MUST contain
   entries for all revoked unexpired certificates issued by the CRL
   issuer, if any, within the scope of the CRL.

   If the scope of the CRL only includes certificates issued by the CRL
   issuer, then the indirectCRL boolean MUST be set to FALSE.
   Otherwise, if the scope of the CRL includes certificates issued by
   one or more authorities other than the CRL issuer, the indirectCRL
   boolean MUST be set to TRUE.  The authority responsible for each
   entry is indicated by the certificate issuer CRL entry extension
   (Section 5.3.3).

   If the scope of the CRL only includes end entity public key
   certificates, then onlyContainsUserCerts MUST be set to TRUE.  If the
   scope of the CRL only includes CA certificates, then
   onlyContainsCACerts MUST be set to TRUE.  If either
   onlyContainsUserCerts or onlyContainsCACerts is set to TRUE, then the
   scope of the CRL MUST NOT include any version 1 or version 2
   certificates.  Conforming CRLs issuers MUST set the
   onlyContainsAttributeCerts boolean to FALSE.

   Conforming CRLs issuers MUST NOT issue CRLs where the DER encoding of
   the issuing distribution point extension is an empty sequence.  That
   is, if onlyContainsUserCerts, onlyContainsCACerts, indirectCRL, and
   onlyContainsAttributeCerts are all FALSE, then either the
   distributionPoint field or the onlySomeReasons field MUST be present.

   id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

   IssuingDistributionPoint ::= SEQUENCE {
        distributionPoint          [0] DistributionPointName OPTIONAL,
        onlyContainsUserCerts      [1] BOOLEAN DEFAULT FALSE,
        onlyContainsCACerts        [2] BOOLEAN DEFAULT FALSE,
        onlySomeReasons            [3] ReasonFlags OPTIONAL,
        indirectCRL                [4] BOOLEAN DEFAULT FALSE,
        onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

        -- at most one of onlyContainsUserCerts, onlyContainsCACerts,
        -- and onlyContainsAttributeCerts may be set to TRUE.

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5.2.6.  Freshest CRL (a.k.a. Delta CRL Distribution Point)

   The freshest CRL extension identifies how delta CRL information for
   this complete CRL is obtained.  Conforming CRL issuers MUST mark this
   extension as non-critical.  This extension MUST NOT appear in delta
   CRLs.

   The same syntax is used for this extension as the
   cRLDistributionPoints certificate extension, and is described in
   Section 4.2.1.13.  However, only the distribution point field is
   meaningful in this context.  The reasons and cRLIssuer fields MUST be
   omitted from this CRL extension.

   Each distribution point name provides the location at which a delta
   CRL for this complete CRL can be found.  The scope of these delta
   CRLs MUST be the same as the scope of this complete CRL.  The
   contents of this CRL extension are only used to locate delta CRLs;
   the contents are not used to validate the CRL or the referenced delta
   CRLs.  The encoding conventions defined for distribution points in
   Section 4.2.1.13 apply to this extension.

   id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

   FreshestCRL ::= CRLDistributionPoints

5.2.7.  Authority Information Access

   This section defines the use of the Authority Information Access
   extension in a CRL.  The syntax and semantics defined in Section
   4.2.2.1 for the certificate extension are also used for the CRL
   extension.

   This CRL extension MUST be marked as non-critical.

   When present in a CRL, this extension MUST include at least one
   AccessDescription specifying id-ad-caIssuers as the accessMethod.
   The id-ad-caIssuers OID is used when the information available lists
   certificates that can be used to verify the signature on the CRL
   (i.e., certificates that have a subject name that matches the issuer
   name on the CRL and that have a subject public key that corresponds
   to the private key used to sign the CRL).  Access method types other
   than id-ad-caIssuers MUST NOT be included.  At least one instance of
   AccessDescription SHOULD specify an accessLocation that is an HTTP
   [RFC2616] or LDAP [RFC4516] URI.

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   Where the information is available via HTTP or FTP, accessLocation
   MUST be a uniformResourceIdentifier and the URI MUST point to either
   a single DER encoded certificate as specified in [RFC2585] or a
   collection of certificates in a BER or DER encoded "certs-only" CMS
   message as specified in [RFC2797].

   Conforming applications that support HTTP or FTP for accessing
   certificates MUST be able to accept individual DER encoded
   certificates and SHOULD be able to accept "certs-only" CMS messages.

   HTTP server implementations accessed via the URI SHOULD specify the
   media type application/pkix-cert [RFC2585] in the content-type header
   field of the response for a single DER encoded certificate and SHOULD
   specify the media type application/pkcs7-mime [RFC2797] in the
   content-type header field of the response for "certs-only" CMS
   messages.  For FTP, the name of a file that contains a single DER
   encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
   name of a file that contains a "certs-only" CMS message SHOULD have a
   suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
   or file extension as a hint to the content, but should not depend
   solely on the presence of the correct media type or file extension in
   the server response.

   When the accessLocation is a directoryName, the information is to be
   obtained by the application from whatever directory server is locally
   configured.  When one CA public key is used to validate signatures on
   certificates and CRLs, the desired CA certificate is stored in the
   crossCertificatePair and/or cACertificate attributes as specified in
   [RFC4523].  When different public keys are used to validate
   signatures on certificates and CRLs, the desired certificate is
   stored in the userCertificate attribute as specified in [RFC4523].
   Thus, implementations that support the directoryName form of
   accessLocation MUST be prepared to find the needed certificate in any
   of these three attributes.  The protocol that an application uses to
   access the directory (e.g., DAP or LDAP) is a local matter.

   Where the information is available via LDAP, the accessLocation
   SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
   include a <dn> field containing the distinguished name of the entry
   holding the certificates, MUST include an <attributes> field that
   lists appropriate attribute descriptions for the attributes that hold
   the DER encoded certificates or cross-certificate pairs [RFC4523],
   and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
   dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).
   Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
   cACertificate;binary>) has the effect of relying on whatever a priori
   knowledge the client might have to contact an appropriate server.

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5.3.  CRL Entry Extensions

   The CRL entry extensions defined by ISO/IEC, ITU-T, and ANSI X9 for
   X.509 v2 CRLs provide methods for associating additional attributes
   with CRL entries [X.509] [X9.55].  The X.509 v2 CRL format also
   allows communities to define private CRL entry extensions to carry
   information unique to those communities.  Each extension in a CRL
   entry may be designated as critical or non-critical.  If a CRL
   contains a critical CRL entry extension that the application cannot
   process, then the application MUST NOT use that CRL to determine the
   status of any certificates.  However, applications may ignore
   unrecognized non-critical CRL entry extensions.

   The following subsections present recommended extensions used within
   Internet CRL entries and standard locations for information.
   Communities may elect to use additional CRL entry extensions;
   however, caution should be exercised in adopting any critical CRL
   entry extensions in CRLs that might be used in a general context.

   Support for the CRL entry extensions defined in this specification is
   optional for conforming CRL issuers and applications.  However, CRL
   issuers SHOULD include reason codes (Section 5.3.1) and invalidity
   dates (Section 5.3.2) whenever this information is available.

5.3.1.  Reason Code

   The reasonCode is a non-critical CRL entry extension that identifies
   the reason for the certificate revocation.  CRL issuers are strongly
   encouraged to include meaningful reason codes in CRL entries;
   however, the reason code CRL entry extension SHOULD be absent instead
   of using the unspecified (0) reasonCode value.

   The removeFromCRL (8) reasonCode value may only appear in delta CRLs
   and indicates that a certificate is to be removed from a CRL because
   either the certificate expired or was removed from hold.  All other
   reason codes may appear in any CRL and indicate that the specified
   certificate should be considered revoked.

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   id-ce-cRLReasons OBJECT IDENTIFIER ::= { id-ce 21 }

   -- reasonCode ::= { CRLReason }

   CRLReason ::= ENUMERATED {
        unspecified             (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6),
             -- value 7 is not used
        removeFromCRL           (8),
        privilegeWithdrawn      (9),
        aACompromise           (10) }

5.3.2.  Invalidity Date

   The invalidity date is a non-critical CRL entry extension that
   provides the date on which it is known or suspected that the private
   key was compromised or that the certificate otherwise became invalid.
   This date may be earlier than the revocation date in the CRL entry,
   which is the date at which the CA processed the revocation.  When a
   revocation is first posted by a CRL issuer in a CRL, the invalidity
   date may precede the date of issue of earlier CRLs, but the
   revocation date SHOULD NOT precede the date of issue of earlier CRLs.
   Whenever this information is available, CRL issuers are strongly
   encouraged to share it with CRL users.

   The GeneralizedTime values included in this field MUST be expressed
   in Greenwich Mean Time (Zulu), and MUST be specified and interpreted
   as defined in Section 4.1.2.5.2.

   id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

   InvalidityDate ::=  GeneralizedTime

5.3.3.  Certificate Issuer

   This CRL entry extension identifies the certificate issuer associated
   with an entry in an indirect CRL, that is, a CRL that has the
   indirectCRL indicator set in its issuing distribution point
   extension.  When present, the certificate issuer CRL entry extension
   includes one or more names from the issuer field and/or issuer
   alternative name extension of the certificate that corresponds to the
   CRL entry.  If this extension is not present on the first entry in an
   indirect CRL, the certificate issuer defaults to the CRL issuer.  On

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   subsequent entries in an indirect CRL, if this extension is not
   present, the certificate issuer for the entry is the same as that for
   the preceding entry.  This field is defined as follows:

   id-ce-certificateIssuer   OBJECT IDENTIFIER ::= { id-ce 29 }

   CertificateIssuer ::=     GeneralNames

   Conforming CRL issuers MUST include in this extension the
   distinguished name (DN) from the issuer field of the certificate that
   corresponds to this CRL entry.  The encoding of the DN MUST be
   identical to the encoding used in the certificate.

   CRL issuers MUST mark this extension as critical since an
   implementation that ignored this extension could not correctly
   attribute CRL entries to certificates.  This specification RECOMMENDS
   that implementations recognize this extension.

6.  Certification Path Validation

   Certification path validation procedures for the Internet PKI are
   based on the algorithm supplied in [X.509].  Certification path
   processing verifies the binding between the subject distinguished
   name and/or subject alternative name and subject public key.  The
   binding is limited by constraints that are specified in the
   certificates that comprise the path and inputs that are specified by
   the relying party.  The basic constraints and policy constraints
   extensions allow the certification path processing logic to automate
   the decision making process.

   This section describes an algorithm for validating certification
   paths.  Conforming implementations of this specification are not
   required to implement this algorithm, but MUST provide functionality
   equivalent to the external behavior resulting from this procedure.
   Any algorithm may be used by a particular implementation so long as
   it derives the correct result.

   In Section 6.1, the text describes basic path validation.  Valid
   paths begin with certificates issued by a trust anchor.  The
   algorithm requires the public key of the CA, the CA's name, and any
   constraints upon the set of paths that may be validated using this
   key.

   The selection of a trust anchor is a matter of policy: it could be
   the top CA in a hierarchical PKI, the CA that issued the verifier's
   own certificate(s), or any other CA in a network PKI.  The path

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   validation procedure is the same regardless of the choice of trust
   anchor.  In addition, different applications may rely on different
   trust anchors, or may accept paths that begin with any of a set of
   trust anchors.

   Section 6.2 describes methods for using the path validation algorithm
   in specific implementations.

   Section 6.3 describes the steps necessary to determine if a
   certificate is revoked when CRLs are the revocation mechanism used by
   the certificate issuer.

6.1.  Basic Path Validation

   This text describes an algorithm for X.509 path processing.  A
   conforming implementation MUST include an X.509 path processing
   procedure that is functionally equivalent to the external behavior of
   this algorithm.  However, support for some of the certificate
   extensions processed in this algorithm are OPTIONAL for compliant
   implementations.  Clients that do not support these extensions MAY
   omit the corresponding steps in the path validation algorithm.

   For example, clients are not required to support the policy mappings
   extension.  Clients that do not support this extension MAY omit the
   path validation steps where policy mappings are processed.  Note that
   clients MUST reject the certificate if it contains an unsupported
   critical extension.

   While the certificate and CRL profiles specified in Sections 4 and 5
   of this document specify values for certificate and CRL fields and
   extensions that are considered to be appropriate for the Internet
   PKI, the algorithm presented in this section is not limited to
   accepting certificates and CRLs that conform to these profiles.
   Therefore, the algorithm only includes checks to verify that the
   certification path is valid according to X.509 and does not include
   checks to verify that the certificates and CRLs conform to this
   profile.  While the algorithm could be extended to include checks for
   conformance to the profiles in Sections 4 and 5, this profile
   RECOMMENDS against including such checks.

   The algorithm presented in this section validates the certificate
   with respect to the current date and time.  A conforming
   implementation MAY also support validation with respect to some point
   in the past.  Note that mechanisms are not available for validating a
   certificate with respect to a time outside the certificate validity
   period.

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   The trust anchor is an input to the algorithm.  There is no
   requirement that the same trust anchor be used to validate all
   certification paths.  Different trust anchors MAY be used to validate
   different paths, as discussed further in Section 6.2.

   The primary goal of path validation is to verify the binding between
   a subject distinguished name or a subject alternative name and
   subject public key, as represented in the target certificate, based
   on the public key of the trust anchor.  In most cases, the target
   certificate will be an end entity certificate, but the target
   certificate may be a CA certificate as long as the subject public key
   is to be used for a purpose other than verifying the signature on a
   public key certificate.  Verifying the binding between the name and
   subject public key requires obtaining a sequence of certificates that
   support that binding.  The procedure performed to obtain this
   sequence of certificates is outside the scope of this specification.

   To meet this goal, the path validation process verifies, among other
   things, that a prospective certification path (a sequence of n
   certificates) satisfies the following conditions:

      (a)  for all x in {1, ..., n-1}, the subject of certificate x is
           the issuer of certificate x+1;

      (b)  certificate 1 is issued by the trust anchor;

      (c)  certificate n is the certificate to be validated (i.e., the
           target certificate); and

      (d)  for all x in {1, ..., n}, the certificate was valid at the
           time in question.

   A certificate MUST NOT appear more than once in a prospective
   certification path.

   When the trust anchor is provided in the form of a self-signed
   certificate, this self-signed certificate is not included as part of
   the prospective certification path.  Information about trust anchors
   is provided as inputs to the certification path validation algorithm
   (Section 6.1.1).

   A particular certification path may not, however, be appropriate for
   all applications.  Therefore, an application MAY augment this
   algorithm to further limit the set of valid paths.  The path
   validation process also determines the set of certificate policies
   that are valid for this path, based on the certificate policies
   extension, policy mappings extension, policy constraints extension,
   and inhibit anyPolicy extension.  To achieve this, the path

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   validation algorithm constructs a valid policy tree.  If the set of
   certificate policies that are valid for this path is not empty, then
   the result will be a valid policy tree of depth n, otherwise the
   result will be a null valid policy tree.

   A certificate is self-issued if the same DN appears in the subject
   and issuer fields (the two DNs are the same if they match according
   to the rules specified in Section 7.1).  In general, the issuer and
   subject of the certificates that make up a path are different for
   each certificate.  However, a CA may issue a certificate to itself to
   support key rollover or changes in certificate policies.  These
   self-issued certificates are not counted when evaluating path length
   or name constraints.

   This section presents the algorithm in four basic steps: (1)
   initialization, (2) basic certificate processing, (3) preparation for
   the next certificate, and (4) wrap-up.  Steps (1) and (4) are
   performed exactly once.  Step (2) is performed for all certificates
   in the path.  Step (3) is performed for all certificates in the path
   except the final certificate.  Figure 2 provides a high-level
   flowchart of this algorithm.

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                           +-------+
                           | START |
                           +-------+
                               |
                               V
                       +----------------+
                       | Initialization |
                       +----------------+
                               |
                               +<--------------------+
                               |                     |
                               V                     |
                       +----------------+            |
                       |  Process Cert  |            |
                       +----------------+            |
                               |                     |
                               V                     |
                       +================+            |
                       |  IF Last Cert  |            |
                       |    in Path     |            |
                       +================+            |
                         |            |              |
                    THEN |            | ELSE         |
                         V            V              |
              +----------------+ +----------------+  |
              |    Wrap up     | |  Prepare for   |  |
              +----------------+ |   Next Cert    |  |
                      |          +----------------+  |
                      V               |              |
                  +-------+           +--------------+
                  | STOP  |
                  +-------+

         Figure 2.  Certification Path Processing Flowchart

6.1.1.  Inputs

   This algorithm assumes that the following nine inputs are provided to
   the path processing logic:

      (a)  a prospective certification path of length n.

      (b)  the current date/time.

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      (c)  user-initial-policy-set:  A set of certificate policy
           identifiers naming the policies that are acceptable to the
           certificate user.  The user-initial-policy-set contains the
           special value any-policy if the user is not concerned about
           certificate policy.

      (d)  trust anchor information, describing a CA that serves as a
           trust anchor for the certification path.  The trust anchor
           information includes:

         (1)  the trusted issuer name,

         (2)  the trusted public key algorithm,

         (3)  the trusted public key, and

         (4)  optionally, the trusted public key parameters associated
              with the public key.

      The trust anchor information may be provided to the path
      processing procedure in the form of a self-signed certificate.
      When the trust anchor information is provided in the form of a
      certificate, the name in the subject field is used as the trusted
      issuer name and the contents of the subjectPublicKeyInfo field is
      used as the source of the trusted public key algorithm and the
      trusted public key.  The trust anchor information is trusted
      because it was delivered to the path processing procedure by some
      trustworthy out-of-band procedure.  If the trusted public key
      algorithm requires parameters, then the parameters are provided
      along with the trusted public key.

      (e)  initial-policy-mapping-inhibit, which indicates if policy
           mapping is allowed in the certification path.

      (f)  initial-explicit-policy, which indicates if the path must be
           valid for at least one of the certificate policies in the
           user-initial-policy-set.

      (g)  initial-any-policy-inhibit, which indicates whether the
           anyPolicy OID should be processed if it is included in a
           certificate.

      (h)  initial-permitted-subtrees, which indicates for each name
           type (e.g., X.500 distinguished names, email addresses, or IP
           addresses) a set of subtrees within which all subject names
           in every certificate in the certification path MUST fall.
           The initial-permitted-subtrees input includes a set for each
           name type.  For each name type, the set may consist of a

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           single subtree that includes all names of that name type or
           one or more subtrees that each specifies a subset of the
           names of that name type, or the set may be empty.  If the set
           for a name type is empty, then the certification path will be
           considered invalid if any certificate in the certification
           path includes a name of that name type.

      (i)  initial-excluded-subtrees, which indicates for each name type
           (e.g., X.500 distinguished names, email addresses, or IP
           addresses) a set of subtrees within which no subject name in
           any certificate in the certification path may fall.  The
           initial-excluded-subtrees input includes a set for each name
           type.  For each name type, the set may be empty or may
           consist of one or more subtrees that each specifies a subset
           of the names of that name type.  If the set for a name type
           is empty, then no names of that name type are excluded.

   Conforming implementations are not required to support the setting of
   all of these inputs.  For example, a conforming implementation may be
   designed to validate all certification paths using a value of FALSE
   for initial-any-policy-inhibit.

6.1.2.  Initialization

   This initialization phase establishes eleven state variables based
   upon the nine inputs:

      (a)  valid_policy_tree:  A tree of certificate policies with their
           optional qualifiers; each of the leaves of the tree
           represents a valid policy at this stage in the certification
           path validation.  If valid policies exist at this stage in
           the certification path validation, the depth of the tree is
           equal to the number of certificates in the chain that have
           been processed.  If valid policies do not exist at this stage
           in the certification path validation, the tree is set to
           NULL.  Once the tree is set to NULL, policy processing
           ceases.

           Each node in the valid_policy_tree includes three data
           objects: the valid policy, a set of associated policy
           qualifiers, and a set of one or more expected policy values.
           If the node is at depth x, the components of the node have
           the following semantics:

         (1)  The valid_policy is a single policy OID representing a
              valid policy for the path of length x.

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         (2)  The qualifier_set is a set of policy qualifiers associated
              with the valid policy in certificate x.

         (3)  The expected_policy_set contains one or more policy OIDs
              that would satisfy this policy in the certificate x+1.

      The initial value of the valid_policy_tree is a single node with
      valid_policy anyPolicy, an empty qualifier_set, and an
      expected_policy_set with the single value anyPolicy.  This node is
      considered to be at depth zero.

      Figure 3 is a graphic representation of the initial state of the
      valid_policy_tree.  Additional figures will use this format to
      describe changes in the valid_policy_tree during path processing.

              +----------------+
              |   anyPolicy    |   <---- valid_policy
              +----------------+
              |       {}       |   <---- qualifier_set
              +----------------+
              |  {anyPolicy}   |   <---- expected_policy_set
              +----------------+

      Figure 3.  Initial Value of the valid_policy_tree State Variable

      (b)  permitted_subtrees:  a set of root names for each name type
           (e.g., X.500 distinguished names, email addresses, or IP
           addresses) defining a set of subtrees within which all
           subject names in subsequent certificates in the certification
           path MUST fall.  This variable includes a set for each name
           type, and the initial value is initial-permitted-subtrees.

      (c)  excluded_subtrees:  a set of root names for each name type
           (e.g., X.500 distinguished names, email addresses, or IP
           addresses) defining a set of subtrees within which no subject
           name in subsequent certificates in the certification path may
           fall.  This variable includes a set for each name type, and
           the initial value is initial-excluded-subtrees.

      (d)  explicit_policy:  an integer that indicates if a non-NULL
           valid_policy_tree is required.  The integer indicates the
           number of non-self-issued certificates to be processed before
           this requirement is imposed.  Once set, this variable may be
           decreased, but may not be increased.  That is, if a
           certificate in the path requires a non-NULL
           valid_policy_tree, a later certificate cannot remove this
           requirement.  If initial-explicit-policy is set, then the
           initial value is 0, otherwise the initial value is n+1.

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      (e)  inhibit_anyPolicy:  an integer that indicates whether the
           anyPolicy policy identifier is considered a match.  The
           integer indicates the number of non-self-issued certificates
           to be processed before the anyPolicy OID, if asserted in a
           certificate other than an intermediate self-issued
           certificate, is ignored.  Once set, this variable may be
           decreased, but may not be increased.  That is, if a
           certificate in the path inhibits processing of anyPolicy, a
           later certificate cannot permit it.  If initial-any-policy-
           inhibit is set, then the initial value is 0, otherwise the
           initial value is n+1.

      (f)  policy_mapping:  an integer that indicates if policy mapping
           is permitted.  The integer indicates the number of non-self-
           issued certificates to be processed before policy mapping is
           inhibited.  Once set, this variable may be decreased, but may
           not be increased.  That is, if a certificate in the path
           specifies that policy mapping is not permitted, it cannot be
           overridden by a later certificate.  If initial-policy-
           mapping-inhibit is set, then the initial value is 0,
           otherwise the initial value is n+1.

      (g)  working_public_key_algorithm:  the digital signature
           algorithm used to verify the signature of a certificate.  The
           working_public_key_algorithm is initialized from the trusted
           public key algorithm provided in the trust anchor
           information.

      (h)  working_public_key:  the public key used to verify the
           signature of a certificate.  The working_public_key is
           initialized from the trusted public key provided in the trust
           anchor information.

      (i)  working_public_key_parameters:  parameters associated with
           the current public key that may be required to verify a
           signature (depending upon the algorithm).  The
           working_public_key_parameters variable is initialized from
           the trusted public key parameters provided in the trust
           anchor information.

      (j)  working_issuer_name:  the issuer distinguished name expected
           in the next certificate in the chain.  The
           working_issuer_name is initialized to the trusted issuer name
           provided in the trust anchor information.

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      (k)  max_path_length:  this integer is initialized to n, is
           decremented for each non-self-issued certificate in the path,
           and may be reduced to the value in the path length constraint
           field within the basic constraints extension of a CA
           certificate.

   Upon completion of the initialization steps, perform the basic
   certificate processing steps specified in 6.1.3.

6.1.3.  Basic Certificate Processing

   The basic path processing actions to be performed for certificate i
   (for all i in [1..n]) are listed below.

      (a)  Verify the basic certificate information.  The certificate
           MUST satisfy each of the following:

         (1)  The signature on the certificate can be verified using
              working_public_key_algorithm, the working_public_key, and
              the working_public_key_parameters.

         (2)  The certificate validity period includes the current time.

         (3)  At the current time, the certificate is not revoked.  This
              may be determined by obtaining the appropriate CRL
              (Section 6.3), by status information, or by out-of-band
              mechanisms.

         (4)  The certificate issuer name is the working_issuer_name.

      (b)  If certificate i is self-issued and it is not the final
           certificate in the path, skip this step for certificate i.
           Otherwise, verify that the subject name is within one of the
           permitted_subtrees for X.500 distinguished names, and verify
           that each of the alternative names in the subjectAltName
           extension (critical or non-critical) is within one of the
           permitted_subtrees for that name type.

      (c)  If certificate i is self-issued and it is not the final
           certificate in the path, skip this step for certificate i.
           Otherwise, verify that the subject name is not within any of
           the excluded_subtrees for X.500 distinguished names, and
           verify that each of the alternative names in the
           subjectAltName extension (critical or non-critical) is not
           within any of the excluded_subtrees for that name type.

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      (d)  If the certificate policies extension is present in the
           certificate and the valid_policy_tree is not NULL, process
           the policy information by performing the following steps in
           order:

         (1)  For each policy P not equal to anyPolicy in the
              certificate policies extension, let P-OID denote the OID
              for policy P and P-Q denote the qualifier set for policy
              P.  Perform the following steps in order:

            (i)   For each node of depth i-1 in the valid_policy_tree
                  where P-OID is in the expected_policy_set, create a
                  child node as follows: set the valid_policy to P-OID,
                  set the qualifier_set to P-Q, and set the
                  expected_policy_set to
                  {P-OID}.

                  For example, consider a valid_policy_tree with a node
                  of depth i-1 where the expected_policy_set is {Gold,
                  White}.  Assume the certificate policies Gold and
                  Silver appear in the certificate policies extension of
                  certificate i.  The Gold policy is matched, but the
                  Silver policy is not.  This rule will generate a child
                  node of depth i for the Gold policy.  The result is
                  shown as Figure 4.

                             +-----------------+
                             |       Red       |
                             +-----------------+
                             |       {}        |
                             +-----------------+   node of depth i-1
                             |  {Gold, White}  |
                             +-----------------+
                                      |
                                      |
                                      |
                                      V
                             +-----------------+
                             |      Gold       |
                             +-----------------+
                             |       {}        |
                             +-----------------+   node of depth i
                             |     {Gold}      |
                             +-----------------+

                    Figure 4.  Processing an Exact Match

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            (ii)  If there was no match in step (i) and the
                  valid_policy_tree includes a node of depth i-1 with
                  the valid_policy anyPolicy, generate a child node with
                  the following values: set the valid_policy to P-OID,
                  set the qualifier_set to P-Q, and set the
                  expected_policy_set to  {P-OID}.

                  For example, consider a valid_policy_tree with a node
                  of depth i-1 where the valid_policy is anyPolicy.
                  Assume the certificate policies Gold and Silver appear
                  in the certificate policies extension of certificate
                  i.  The Gold policy does not have a qualifier, but the
                  Silver policy has the qualifier Q-Silver.  If Gold and
                  Silver were not matched in (i) above, this rule will
                  generate two child nodes of depth i, one for each
                  policy.  The result is shown as Figure 5.

                                   +-----------------+
                                   |    anyPolicy    |
                                   +-----------------+
                                   |       {}        |
                                   +-----------------+ node of depth i-1
                                   |   {anyPolicy}   |
                                   +-----------------+
                                      /           \
                                     /             \
                                    /               \
                                   /                 \
                     +-----------------+          +-----------------+
                     |      Gold       |          |     Silver      |
                     +-----------------+          +-----------------+
                     |       {}        |          |   {Q-Silver}    |
                     +-----------------+ nodes of +-----------------+
                     |     {Gold}      | depth i  |    {Silver}     |
                     +-----------------+          +-----------------+

                  Figure 5.  Processing Unmatched Policies when a
                  Leaf Node Specifies anyPolicy

         (2)  If the certificate policies extension includes the policy
              anyPolicy with the qualifier set AP-Q and either (a)
              inhibit_anyPolicy is greater than 0 or (b) i<n and the
              certificate is self-issued, then:

              For each node in the valid_policy_tree of depth i-1, for
              each value in the expected_policy_set (including
              anyPolicy) that does not appear in a child node, create a
              child node with the following values: set the valid_policy

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              to the value from the expected_policy_set in the parent
              node, set the qualifier_set to AP-Q, and set the
              expected_policy_set to the value in the valid_policy from
              this node.

              For example, consider a valid_policy_tree with a node of
              depth i-1 where the expected_policy_set is {Gold, Silver}.
              Assume anyPolicy appears in the certificate policies
              extension of certificate i with no policy qualifiers, but
              Gold and Silver do not appear.  This rule will generate
              two child nodes of depth i, one for each policy.  The
              result is shown below as Figure 6.

                               +-----------------+
                               |      Red        |
                               +-----------------+
                               |       {}        |
                               +-----------------+ node of depth i-1
                               |  {Gold, Silver} |
                               +-----------------+
                                  /           \
                                 /             \
                                /               \
                               /                 \
                 +-----------------+          +-----------------+
                 |      Gold       |          |     Silver      |
                 +-----------------+          +-----------------+
                 |       {}        |          |       {}        |
                 +-----------------+ nodes of +-----------------+
                 |     {Gold}      | depth i  |    {Silver}     |
                 +-----------------+          +-----------------+

              Figure 6.  Processing Unmatched Policies When the
              Certificate Policies Extension Specifies anyPolicy

         (3)  If there is a node in the valid_policy_tree of depth i-1
              or less without any child nodes, delete that node.  Repeat
              this step until there are no nodes of depth i-1 or less
              without children.

              For example, consider the valid_policy_tree shown in
              Figure 7 below.  The two nodes at depth i-1 that are
              marked with an 'X' have no children, and they are deleted.
              Applying this rule to the resulting tree will cause the
              node at depth i-2 that is marked with a 'Y' to be deleted.
              In the resulting tree, there are no nodes of depth i-1 or
              less without children, and this step is complete.

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      (e)  If the certificate policies extension is not present, set the
           valid_policy_tree to NULL.

      (f)  Verify that either explicit_policy is greater than 0 or the
           valid_policy_tree is not equal to NULL;

   If any of steps (a), (b), (c), or (f) fails, the procedure
   terminates, returning a failure indication and an appropriate reason.

   If i is not equal to n, continue by performing the preparatory steps
   listed in Section 6.1.4.  If i is equal to n, perform the wrap-up
   steps listed in Section 6.1.5.

                                 +-----------+
                                 |           | node of depth i-3
                                 +-----------+
                                 /     |     \
                                /      |      \
                               /       |       \
                   +-----------+ +-----------+ +-----------+
                   |           | |           | |     Y     | nodes of
                   +-----------+ +-----------+ +-----------+ depth i-2
                   /   \               |             |
                  /     \              |             |
                 /       \             |             |
      +-----------+ +-----------+ +-----------+ +-----------+ nodes of
      |           | |     X     | |           | |    X      |  depth
      +-----------+ +-----------+ +-----------+ +-----------+   i-1
            |                      /    |    \
            |                     /     |     \
            |                    /      |      \
      +-----------+ +-----------+ +-----------+ +-----------+ nodes of
      |           | |           | |           | |           |  depth
      +-----------+ +-----------+ +-----------+ +-----------+   i

             Figure 7.  Pruning the valid_policy_tree

6.1.4.  Preparation for Certificate i+1

      To prepare for processing of certificate i+1, perform the
      following steps for certificate i:

      (a)  If a policy mappings extension is present, verify that the
           special value anyPolicy does not appear as an
           issuerDomainPolicy or a subjectDomainPolicy.

      (b)  If a policy mappings extension is present, then for each
           issuerDomainPolicy ID-P in the policy mappings extension:

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         (1)  If the policy_mapping variable is greater than 0, for each
              node in the valid_policy_tree of depth i where ID-P is the
              valid_policy, set expected_policy_set to the set of
              subjectDomainPolicy values that are specified as
              equivalent to ID-P by the policy mappings extension.

              If no node of depth i in the valid_policy_tree has a
              valid_policy of ID-P but there is a node of depth i with a
              valid_policy of anyPolicy, then generate a child node of
              the node of depth i-1 that has a valid_policy of anyPolicy
              as follows:

            (i)    set the valid_policy to ID-P;

            (ii)   set the qualifier_set to the qualifier set of the
                   policy anyPolicy in the certificate policies
                   extension of certificate i; and

            (iii)  set the expected_policy_set to the set of
                   subjectDomainPolicy values that are specified as
                   equivalent to ID-P by the policy mappings extension.

         (2)  If the policy_mapping variable is equal to 0:

            (i)    delete each node of depth i in the valid_policy_tree
                   where ID-P is the valid_policy.

            (ii)   If there is a node in the valid_policy_tree of depth
                   i-1 or less without any child nodes, delete that
                   node.  Repeat this step until there are no nodes of
                   depth i-1 or less without children.

      (c)  Assign the certificate subject name to working_issuer_name.

      (d)  Assign the certificate subjectPublicKey to
           working_public_key.

      (e)  If the subjectPublicKeyInfo field of the certificate contains
           an algorithm field with non-null parameters, assign the
           parameters to the working_public_key_parameters variable.

           If the subjectPublicKeyInfo field of the certificate contains
           an algorithm field with null parameters or parameters are
           omitted, compare the certificate subjectPublicKey algorithm
           to the working_public_key_algorithm.  If the certificate
           subjectPublicKey algorithm and the
           working_public_key_algorithm are different, set the
           working_public_key_parameters to null.

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      (f)  Assign the certificate subjectPublicKey algorithm to the
           working_public_key_algorithm variable.

      (g)  If a name constraints extension is included in the
           certificate, modify the permitted_subtrees and
           excluded_subtrees state variables as follows:

         (1)  If permittedSubtrees is present in the certificate, set
              the permitted_subtrees state variable to the intersection
              of its previous value and the value indicated in the
              extension field.  If permittedSubtrees does not include a
              particular name type, the permitted_subtrees state
              variable is unchanged for that name type.  For example,
              the intersection of example.com and foo.example.com is
              foo.example.com.  And the intersection of example.com and
              example.net is the empty set.

         (2)  If excludedSubtrees is present in the certificate, set the
              excluded_subtrees state variable to the union of its
              previous value and the value indicated in the extension
              field.  If excludedSubtrees does not include a particular
              name type, the excluded_subtrees state variable is
              unchanged for that name type.  For example, the union of
              the name spaces example.com and foo.example.com is
              example.com.  And the union of example.com and example.net
              is both name spaces.

      (h)  If certificate i is not self-issued:

         (1)  If explicit_policy is not 0, decrement explicit_policy by
              1.

         (2)  If policy_mapping is not 0, decrement policy_mapping by 1.

         (3)  If inhibit_anyPolicy is not 0, decrement inhibit_anyPolicy
              by 1.

      (i)  If a policy constraints extension is included in the
           certificate, modify the explicit_policy and policy_mapping
           state variables as follows:

         (1)  If requireExplicitPolicy is present and is less than
              explicit_policy, set explicit_policy to the value of
              requireExplicitPolicy.

         (2)  If inhibitPolicyMapping is present and is less than
              policy_mapping, set policy_mapping to the value of
              inhibitPolicyMapping.

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      (j)  If the inhibitAnyPolicy extension is included in the
           certificate and is less than inhibit_anyPolicy, set
           inhibit_anyPolicy to the value of inhibitAnyPolicy.

      (k)  If certificate i is a version 3 certificate, verify that the
           basicConstraints extension is present and that cA is set to
           TRUE.  (If certificate i is a version 1 or version 2
           certificate, then the application MUST either verify that
           certificate i is a CA certificate through out-of-band means
           or reject the certificate.  Conforming implementations may
           choose to reject all version 1 and version 2 intermediate
           certificates.)

      (l)  If the certificate was not self-issued, verify that
           max_path_length is greater than zero and decrement
           max_path_length by 1.

      (m)  If pathLenConstraint is present in the certificate and is
           less than max_path_length, set max_path_length to the value
           of pathLenConstraint.

      (n)  If a key usage extension is present, verify that the
           keyCertSign bit is set.

      (o)  Recognize and process any other critical extension present in
           the certificate.  Process any other recognized non-critical
           extension present in the certificate that is relevant to path
           processing.

   If check (a), (k), (l), (n), or (o) fails, the procedure terminates,
   returning a failure indication and an appropriate reason.

   If (a), (k), (l), (n), and (o) have completed successfully, increment
   i and perform the basic certificate processing specified in Section
   6.1.3.

6.1.5.  Wrap-Up Procedure

   To complete the processing of the target certificate, perform the
   following steps for certificate n:

      (a)  If explicit_policy is not 0, decrement explicit_policy by 1.

      (b)  If a policy constraints extension is included in the
           certificate and requireExplicitPolicy is present and has a
           value of 0, set the explicit_policy state variable to 0.

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      (c)  Assign the certificate subjectPublicKey to
           working_public_key.

      (d)  If the subjectPublicKeyInfo field of the certificate contains
           an algorithm field with non-null parameters, assign the
           parameters to the working_public_key_parameters variable.

           If the subjectPublicKeyInfo field of the certificate contains
           an algorithm field with null parameters or parameters are
           omitted, compare the certificate subjectPublicKey algorithm
           to the working_public_key_algorithm.  If the certificate
           subjectPublicKey algorithm and the
           working_public_key_algorithm are different, set the
           working_public_key_parameters to null.

      (e)  Assign the certificate subjectPublicKey algorithm to the
           working_public_key_algorithm variable.

      (f)  Recognize and process any other critical extension present in
           the certificate n.  Process any other recognized non-critical
           extension present in certificate n that is relevant to path
           processing.

      (g)  Calculate the intersection of the valid_policy_tree and the
           user-initial-policy-set, as follows:

         (i)    If the valid_policy_tree is NULL, the intersection is
                NULL.

         (ii)   If the valid_policy_tree is not NULL and the user-
                initial-policy-set is any-policy, the intersection is
                the entire valid_policy_tree.

         (iii)  If the valid_policy_tree is not NULL and the user-
                initial-policy-set is not any-policy, calculate the
                intersection of the valid_policy_tree and the user-
                initial-policy-set as follows:

             1.  Determine the set of policy nodes whose parent nodes
                 have a valid_policy of anyPolicy.  This is the
                 valid_policy_node_set.

             2.  If the valid_policy of any node in the
                 valid_policy_node_set is not in the user-initial-
                 policy-set and is not anyPolicy, delete this node and
                 all its children.

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             3.  If the valid_policy_tree includes a node of depth n
                 with the valid_policy anyPolicy and the user-initial-
                 policy-set is not any-policy, perform the following
                 steps:

               a.  Set P-Q to the qualifier_set in the node of depth n
                   with valid_policy anyPolicy.

               b.  For each P-OID in the user-initial-policy-set that is
                   not the valid_policy of a node in the
                   valid_policy_node_set, create a child node whose
                   parent is the node of depth n-1 with the valid_policy
                   anyPolicy.  Set the values in the child node as
                   follows: set the valid_policy to P-OID, set the
                   qualifier_set to P-Q, and set the expected_policy_set
                   to {P-OID}.

               c.  Delete the node of depth n with the valid_policy
                   anyPolicy.

             4.  If there is a node in the valid_policy_tree of depth
                 n-1 or less without any child nodes, delete that node.
                 Repeat this step until there are no nodes of depth n-1
                 or less without children.

   If either (1) the value of explicit_policy variable is greater than
   zero or (2) the valid_policy_tree is not NULL, then path processing
   has succeeded.

6.1.6.  Outputs

   If path processing succeeds, the procedure terminates, returning a
   success indication together with final value of the
   valid_policy_tree, the working_public_key, the
   working_public_key_algorithm, and the working_public_key_parameters.

6.2.  Using the Path Validation Algorithm

   The path validation algorithm describes the process of validating a
   single certification path.  While each certification path begins with
   a specific trust anchor, there is no requirement that all
   certification paths validated by a particular system share a single
   trust anchor.  The selection of one or more trusted CAs is a local
   decision.  A system may provide any one of its trusted CAs as the
   trust anchor for a particular path.  The inputs to the path
   validation algorithm may be different for each path.  The inputs used
   to process a path may reflect application-specific requirements or
   limitations in the trust accorded a particular trust anchor.  For

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   example, a trusted CA may only be trusted for a particular
   certificate policy.  This restriction can be expressed through the
   inputs to the path validation procedure.

   An implementation MAY augment the algorithm presented in Section 6.1
   to further limit the set of valid certification paths that begin with
   a particular trust anchor.  For example, an implementation MAY modify
   the algorithm to apply a path length constraint to a specific trust
   anchor during the initialization phase, or the application MAY
   require the presence of a particular alternative name form in the
   target certificate, or the application MAY impose requirements on
   application-specific extensions.  Thus, the path validation algorithm
   presented in Section 6.1 defines the minimum conditions for a path to
   be considered valid.

   Where a CA distributes self-signed certificates to specify trust
   anchor information, certificate extensions can be used to specify
   recommended inputs to path validation.  For example, a policy
   constraints extension could be included in the self-signed
   certificate to indicate that paths beginning with this trust anchor
   should be trusted only for the specified policies.  Similarly, a name
   constraints extension could be included to indicate that paths
   beginning with this trust anchor should be trusted only for the
   specified name spaces.  The path validation algorithm presented in
   Section 6.1 does not assume that trust anchor information is provided
   in self-signed certificates and does not specify processing rules for
   additional information included in such certificates.
   Implementations that use self-signed certificates to specify trust
   anchor information are free to process or ignore such information.

6.3.  CRL Validation

   This section describes the steps necessary to determine if a
   certificate is revoked when CRLs are the revocation mechanism used by
   the certificate issuer.  Conforming implementations that support CRLs
   are not required to implement this algorithm, but they MUST be
   functionally equivalent to the external behavior resulting from this
   procedure when processing CRLs that are issued in conformance with
   this profile.  Any algorithm may be used by a particular
   implementation so long as it derives the correct result.

   This algorithm assumes that all of the needed CRLs are available in a
   local cache.  Further, if the next update time of a CRL has passed,
   the algorithm assumes a mechanism to fetch a current CRL and place it
   in the local CRL cache.

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   This algorithm defines a set of inputs, a set of state variables, and
   processing steps that are performed for each certificate in the path.
   The algorithm output is the revocation status of the certificate.

6.3.1.  Revocation Inputs

   To support revocation processing, the algorithm requires two inputs:

      (a)  certificate:  The algorithm requires the certificate serial
           number and issuer name to determine whether a certificate is
           on a particular CRL.  The basicConstraints extension is used
           to determine whether the supplied certificate is associated
           with a CA or an end entity.  If present, the algorithm uses
           the cRLDistributionPoints and freshestCRL extensions to
           determine revocation status.

      (b)  use-deltas:  This boolean input determines whether delta CRLs
           are applied to CRLs.

6.3.2.  Initialization and Revocation State Variables

   To support CRL processing, the algorithm requires the following state
   variables:

      (a)  reasons_mask:  This variable contains the set of revocation
           reasons supported by the CRLs and delta CRLs processed so
           far.  The legal members of the set are the possible
           revocation reason values minus unspecified: keyCompromise,
           cACompromise, affiliationChanged, superseded,
           cessationOfOperation, certificateHold, privilegeWithdrawn,
           and aACompromise.  The special value all-reasons is used to
           denote the set of all legal members.  This variable is
           initialized to the empty set.

      (b)  cert_status:  This variable contains the status of the
           certificate.  This variable may be assigned one of the
           following values: unspecified, keyCompromise, cACompromise,
           affiliationChanged, superseded, cessationOfOperation,
           certificateHold, removeFromCRL, privilegeWithdrawn,
           aACompromise, the special value UNREVOKED, or the special
           value UNDETERMINED.  This variable is initialized to the
           special value UNREVOKED.

      (c)  interim_reasons_mask:  This contains the set of revocation
           reasons supported by the CRL or delta CRL currently being
           processed.

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   Note: In some environments, it is not necessary to check all reason
   codes.  For example, some environments are only concerned with
   cACompromise and keyCompromise for CA certificates.  This algorithm
   checks all reason codes.  Additional processing and state variables
   may be necessary to limit the checking to a subset of the reason
   codes.

6.3.3.  CRL Processing

   This algorithm begins by assuming that the certificate is not
   revoked.  The algorithm checks one or more CRLs until either the
   certificate status is determined to be revoked or sufficient CRLs
   have been checked to cover all reason codes.

   For each distribution point (DP) in the certificate's CRL
   distribution points extension, for each corresponding CRL in the
   local CRL cache, while ((reasons_mask is not all-reasons) and
   (cert_status is UNREVOKED)) perform the following:

      (a)  Update the local CRL cache by obtaining a complete CRL, a
           delta CRL, or both, as required:

         (1)  If the current time is after the value of the CRL next
              update field, then do one of the following:

            (i)   If use-deltas is set and either the certificate or the
                  CRL contains the freshest CRL extension, obtain a
                  delta CRL with a next update value that is after the
                  current time and can be used to update the locally
                  cached CRL as specified in Section 5.2.4.

            (ii)  Update the local CRL cache with a current complete
                  CRL, verify that the current time is before the next
                  update value in the new CRL, and continue processing
                  with the new CRL.  If use-deltas is set and either the
                  certificate or the CRL contains the freshest CRL
                  extension, then obtain the current delta CRL that can
                  be used to update the new locally cached complete CRL
                  as specified in Section 5.2.4.

         (2)  If the current time is before the value of the next update
              field, use-deltas is set, and either the certificate or
              the CRL contains the freshest CRL extension, then obtain
              the current delta CRL that can be used to update the
              locally cached complete CRL as specified in Section 5.2.4.

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      (b)  Verify the issuer and scope of the complete CRL as follows:

         (1)  If the DP includes cRLIssuer, then verify that the issuer
              field in the complete CRL matches cRLIssuer in the DP and
              that the complete CRL contains an issuing distribution
              point extension with the indirectCRL boolean asserted.
              Otherwise, verify that the CRL issuer matches the
              certificate issuer.

         (2)  If the complete CRL includes an issuing distribution point
              (IDP) CRL extension, check the following:

            (i)   If the distribution point name is present in the IDP
                  CRL extension and the distribution field is present in
                  the DP, then verify that one of the names in the IDP
                  matches one of the names in the DP.  If the
                  distribution point name is present in the IDP CRL
                  extension and the distribution field is omitted from
                  the DP, then verify that one of the names in the IDP
                  matches one of the names in the cRLIssuer field of the
                  DP.

            (ii)  If the onlyContainsUserCerts boolean is asserted in
                  the IDP CRL extension, verify that the certificate
                  does not include the basic constraints extension with
                  the cA boolean asserted.

            (iii) If the onlyContainsCACerts boolean is asserted in the
                  IDP CRL extension, verify that the certificate
                  includes the basic constraints extension with the cA
                  boolean asserted.

            (iv)  Verify that the onlyContainsAttributeCerts boolean is
                  not asserted.

      (c)  If use-deltas is set, verify the issuer and scope of the
           delta CRL as follows:

         (1)  Verify that the delta CRL issuer matches the complete CRL
              issuer.

         (2)  If the complete CRL includes an issuing distribution point
              (IDP) CRL extension, verify that the delta CRL contains a
              matching IDP CRL extension.  If the complete CRL omits an
              IDP CRL extension, verify that the delta CRL also omits an
              IDP CRL extension.

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         (3)  Verify that the delta CRL authority key identifier
              extension matches the complete CRL authority key
              identifier extension.

      (d)  Compute the interim_reasons_mask for this CRL as follows:

         (1)  If the issuing distribution point (IDP) CRL extension is
              present and includes onlySomeReasons and the DP includes
              reasons, then set interim_reasons_mask to the intersection
              of reasons in the DP and onlySomeReasons in the IDP CRL
              extension.

         (2)  If the IDP CRL extension includes onlySomeReasons but the
              DP omits reasons, then set interim_reasons_mask to the
              value of onlySomeReasons in the IDP CRL extension.

         (3)  If the IDP CRL extension is not present or omits
              onlySomeReasons but the DP includes reasons, then set
              interim_reasons_mask to the value of DP reasons.

         (4)  If the IDP CRL extension is not present or omits
              onlySomeReasons and the DP omits reasons, then set
              interim_reasons_mask to the special value all-reasons.

      (e)  Verify that interim_reasons_mask includes one or more reasons
           that are not included in the reasons_mask.

      (f)  Obtain and validate the certification path for the issuer of
           the complete CRL.  The trust anchor for the certification
           path MUST be the same as the trust anchor used to validate
           the target certificate.  If a key usage extension is present
           in the CRL issuer's certificate, verify that the cRLSign bit
           is set.

      (g)  Validate the signature on the complete CRL using the public
           key validated in step (f).

      (h)  If use-deltas is set, then validate the signature on the
           delta CRL using the public key validated in step (f).

      (i)  If use-deltas is set, then search for the certificate on the
           delta CRL.  If an entry is found that matches the certificate
           issuer and serial number as described in Section 5.3.3, then
           set the cert_status variable to the indicated reason as
           follows:

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         (1)  If the reason code CRL entry extension is present, set the
              cert_status variable to the value of the reason code CRL
              entry extension.

         (2)  If the reason code CRL entry extension is not present, set
              the cert_status variable to the value unspecified.

      (j)  If (cert_status is UNREVOKED), then search for the
           certificate on the complete CRL.  If an entry is found that
           matches the certificate issuer and serial number as described
           in Section 5.3.3, then set the cert_status variable to the
           indicated reason as described in step (i).

      (k)  If (cert_status is removeFromCRL), then set cert_status to
           UNREVOKED.

      (l)  Set the reasons_mask state variable to the union of its
           previous value and the value of the interim_reasons_mask
           state variable.

   If ((reasons_mask is all-reasons) OR (cert_status is not UNREVOKED)),
   then the revocation status has been determined, so return
   cert_status.

   If the revocation status has not been determined, repeat the process
   above with any available CRLs not specified in a distribution point
   but issued by the certificate issuer.  For the processing of such a
   CRL, assume a DP with both the reasons and the cRLIssuer fields
   omitted and a distribution point name of the certificate issuer.
   That is, the sequence of names in fullName is generated from the
   certificate issuer field as well as the certificate issuerAltName
   extension.  After processing such CRLs, if the revocation status has
   still not been determined, then return the cert_status UNDETERMINED.

7.  Processing Rules for Internationalized Names

   Internationalized names may be encountered in numerous certificate
   and CRL fields and extensions, including distinguished names,
   internationalized domain names, electronic mail addresses, and
   Internationalized Resource Identifiers (IRIs).  Storage, comparison,
   and presentation of such names require special care.  Some characters
   may be encoded in multiple ways.  The same names could be represented
   in multiple encodings (e.g., ASCII or UTF8).  This section
   establishes conformance requirements for storage or comparison of
   each of these name forms.  Informative guidance on presentation is
   provided for some of these name forms.

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7.1.  Internationalized Names in Distinguished Names

   Representation of internationalized names in distinguished names is
   covered in Sections 4.1.2.4, Issuer Name, and 4.1.2.6, Subject Name.
   Standard naming attributes, such as common name, employ the
   DirectoryString type, which supports internationalized names through
   a variety of language encodings.  Conforming implementations MUST
   support UTF8String and PrintableString.  RFC 3280 required only
   binary comparison of attribute values encoded in UTF8String, however,
   this specification requires a more comprehensive handling of
   comparison.  Implementations may encounter certificates and CRLs with
   names encoded using TeletexString, BMPString, or UniversalString, but
   support for these is OPTIONAL.

   Conforming implementations MUST use the LDAP StringPrep profile
   (including insignificant space handling), as specified in [RFC4518],
   as the basis for comparison of distinguished name attributes encoded
   in either PrintableString or UTF8String.  Conforming implementations
   MUST support name comparisons using caseIgnoreMatch.  Support for
   attribute types that use other equality matching rules is optional.

   Before comparing names using the caseIgnoreMatch matching rule,
   conforming implementations MUST perform the six-step string
   preparation algorithm described in [RFC4518] for each attribute of
   type DirectoryString, with the following clarifications:

      *  In step 2, Map, the mapping shall include case folding as
         specified in Appendix B.2 of [RFC3454].

      *  In step 6, Insignificant Character Removal, perform white space
         compression as specified in Section 2.6.1, Insignificant Space
         Handling, of [RFC4518].

   When performing the string preparation algorithm, attributes MUST be
   treated as stored values.

   Comparisons of domainComponent attributes MUST be performed as
   specified in Section 7.3.

   Two naming attributes match if the attribute types are the same and
   the values of the attributes are an exact match after processing with
   the string preparation algorithm.  Two relative distinguished names
   RDN1 and RDN2 match if they have the same number of naming attributes
   and for each naming attribute in RDN1 there is a matching naming
   attribute in RDN2.  Two distinguished names DN1 and DN2 match if they
   have the same number of RDNs, for each RDN in DN1 there is a matching
   RDN in DN2, and the matching RDNs appear in the same order in both
   DNs.  A distinguished name DN1 is within the subtree defined by the

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   distinguished name DN2 if DN1 contains at least as many RDNs as DN2,
   and DN1 and DN2 are a match when trailing RDNs in DN1 are ignored.

7.2.  Internationalized Domain Names in GeneralName

   Internationalized Domain Names (IDNs) may be included in certificates
   and CRLs in the subjectAltName and issuerAltName extensions, name
   constraints extension, authority information access extension,
   subject information access extension, CRL distribution points
   extension, and issuing distribution point extension.  Each of these
   extensions uses the GeneralName type; one choice in GeneralName is
   the dNSName field, which is defined as type IA5String.

   IA5String is limited to the set of ASCII characters.  To accommodate
   internationalized domain names in the current structure, conforming
   implementations MUST convert internationalized domain names to the
   ASCII Compatible Encoding (ACE) format as specified in Section 4 of
   RFC 3490 before storage in the dNSName field.  Specifically,
   conforming implementations MUST perform the conversion operation
   specified in Section 4 of RFC 3490, with the following
   clarifications:

      *  in step 1, the domain name SHALL be considered a "stored
         string".  That is, the AllowUnassigned flag SHALL NOT be set;

      *  in step 3, set the flag called "UseSTD3ASCIIRules";

      *  in step 4, process each label with the "ToASCII" operation; and

      *  in step 5, change all label separators to U+002E (full stop).

   When comparing DNS names for equality, conforming implementations
   MUST perform a case-insensitive exact match on the entire DNS name.
   When evaluating name constraints, conforming implementations MUST
   perform a case-insensitive exact match on a label-by-label basis.  As
   noted in Section 4.2.1.10, any DNS name that may be constructed by
   adding labels to the left-hand side of the domain name given as the
   constraint is considered to fall within the indicated subtree.

   Implementations should convert IDNs to Unicode before display.
   Specifically, conforming implementations should perform the
   conversion operation specified in Section 4 of RFC 3490, with the
   following clarifications:

      *  in step 1, the domain name SHALL be considered a "stored
         string".  That is, the AllowUnassigned flag SHALL NOT be set;

      *  in step 3, set the flag called "UseSTD3ASCIIRules";

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      *  in step 4, process each label with the "ToUnicode" operation;
         and

      *  skip step 5.

   Note:  Implementations MUST allow for increased space requirements
   for IDNs.  An IDN ACE label will begin with the four additional
   characters "xn--" and may require as many as five ASCII characters to
   specify a single international character.

7.3.  Internationalized Domain Names in Distinguished Names

   Domain Names may also be represented as distinguished names using
   domain components in the subject field, the issuer field, the
   subjectAltName extension, or the issuerAltName extension.  As with
   the dNSName in the GeneralName type, the value of this attribute is
   defined as an IA5String.  Each domainComponent attribute represents a
   single label.  To represent a label from an IDN in the distinguished
   name, the implementation MUST perform the "ToASCII" label conversion
   specified in Section 4.1 of RFC 3490.  The label SHALL be considered
   a "stored string".  That is, the AllowUnassigned flag SHALL NOT be
   set.

   Conforming implementations shall perform a case-insensitive exact
   match when comparing domainComponent attributes in distinguished
   names, as described in Section 7.2.

   Implementations should convert ACE labels to Unicode before display.
   Specifically, conforming implementations should perform the
   "ToUnicode" conversion operation specified, as described in Section
   7.2, on each ACE label before displaying the name.

7.4.  Internationalized Resource Identifiers

   Internationalized Resource Identifiers (IRIs) are the
   internationalized complement to the Uniform Resource Identifier
   (URI).  IRIs are sequences of characters from Unicode, while URIs are
   sequences of characters from the ASCII character set.  [RFC3987]
   defines a mapping from IRIs to URIs.  While IRIs are not encoded
   directly in any certificate fields or extensions, their mapped URIs
   may be included in certificates and CRLs.  URIs may appear in the
   subjectAltName and issuerAltName extensions, name constraints
   extension, authority information access extension, subject
   information access extension, issuing distribution point extension,
   and CRL distribution points extension.  Each of these extensions uses
   the GeneralName type; URIs are encoded in the
   uniformResourceIdentifier field in GeneralName, which is defined as
   type IA5String.

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   To accommodate IRIs in the current structure, conforming
   implementations MUST map IRIs to URIs as specified in Section 3.1 of
   [RFC3987], with the following clarifications:

      *  in step 1, generate a UCS character sequence from the original
         IRI format normalizing according to the NFC as specified in
         Variant b (normalization according to NFC);

      *  perform step 2 using the output from step 1.

   Implementations MUST NOT convert the ireg-name component before
   performing step 2.

   Before URIs may be compared, conforming implementations MUST perform
   a combination of the syntax-based and scheme-based normalization
   techniques described in [RFC3987].  Specifically, conforming
   implementations MUST prepare URIs for comparison as follows:

      *  Step 1: Where IRIs allow the usage of IDNs, those names MUST be
         converted to ASCII Compatible Encoding as specified in Section
         7.2 above.

      *  Step 2: The scheme and host are normalized to lowercase, as
         described in Section 5.3.2.1 of [RFC3987].

      *  Step 3: Perform percent-encoding normalization, as specified in
         Section 5.3.2.3 of [RFC3987].

      *  Step 4: Perform path segment normalization, as specified in
         Section 5.3.2.4 of [RFC3987].

      *  Step 5: If recognized, the implementation MUST perform scheme-
         based normalization as specified in Section 5.3.3 of [RFC3987].

   Conforming implementations MUST recognize and perform scheme-based
   normalization for the following schemes: ldap, http, https, and ftp.
   If the scheme is not recognized, step 5 is omitted.

   When comparing URIs for equivalence, conforming implementations shall
   perform a case-sensitive exact match.

   Implementations should convert URIs to Unicode before display.
   Specifically, conforming implementations should perform the
   conversion operation specified in Section 3.2 of [RFC3987].

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7.5.  Internationalized Electronic Mail Addresses

   Electronic Mail addresses may be included in certificates and CRLs in
   the subjectAltName and issuerAltName extensions, name constraints
   extension, authority information access extension, subject
   information access extension, issuing distribution point extension,
   or CRL distribution points extension.  Each of these extensions uses
   the GeneralName construct; GeneralName includes the rfc822Name
   choice, which is defined as type IA5String.  To accommodate email
   addresses with internationalized domain names using the current
   structure, conforming implementations MUST convert the addresses into
   an ASCII representation.

   Where the host-part (the Domain of the Mailbox) contains an
   internationalized name, the domain name MUST be converted from an IDN
   to the ASCII Compatible Encoding (ACE) format as specified in Section
   7.2.

   Two email addresses are considered to match if:

      1)  the local-part of each name is an exact match, AND

      2)  the host-part of each name matches using a case-insensitive
          ASCII comparison.

   Implementations should convert the host-part of internationalized
   email addresses specified in these extensions to Unicode before
   display.  Specifically, conforming implementations should perform the
   conversion of the host-part of the Mailbox as described in Section
   7.2.

8.  Security Considerations

   The majority of this specification is devoted to the format and
   content of certificates and CRLs.  Since certificates and CRLs are
   digitally signed, no additional integrity service is necessary.
   Neither certificates nor CRLs need be kept secret, and unrestricted
   and anonymous access to certificates and CRLs has no security
   implications.

   However, security factors outside the scope of this specification
   will affect the assurance provided to certificate users.  This
   section highlights critical issues to be considered by implementers,
   administrators, and users.

   The procedures performed by CAs and RAs to validate the binding of
   the subject's identity to their public key greatly affect the
   assurance that ought to be placed in the certificate.  Relying

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   parties might wish to review the CA's certification practice
   statement.  This is particularly important when issuing certificates
   to other CAs.

   The use of a single key pair for both signature and other purposes is
   strongly discouraged.  Use of separate key pairs for signature and
   key management provides several benefits to the users.  The
   ramifications associated with loss or disclosure of a signature key
   are different from loss or disclosure of a key management key.  Using
   separate key pairs permits a balanced and flexible response.
   Similarly, different validity periods or key lengths for each key
   pair may be appropriate in some application environments.
   Unfortunately, some legacy applications (e.g., Secure Sockets Layer
   (SSL)) use a single key pair for signature and key management.

   The protection afforded private keys is a critical security factor.
   On a small scale, failure of users to protect their private keys will
   permit an attacker to masquerade as them or decrypt their personal
   information.  On a larger scale, compromise of a CA's private signing
   key may have a catastrophic effect.  If an attacker obtains the
   private key unnoticed, the attacker may issue bogus certificates and
   CRLs.  Existence of bogus certificates and CRLs will undermine
   confidence in the system.  If such a compromise is detected, all
   certificates issued to the compromised CA MUST be revoked, preventing
   services between its users and users of other CAs.  Rebuilding after
   such a compromise will be problematic, so CAs are advised to
   implement a combination of strong technical measures (e.g., tamper-
   resistant cryptographic modules) and appropriate management
   procedures (e.g., separation of duties) to avoid such an incident.

   Loss of a CA's private signing key may also be problematic.  The CA
   would not be able to produce CRLs or perform normal key rollover.
   CAs SHOULD maintain secure backup for signing keys.  The security of
   the key backup procedures is a critical factor in avoiding key
   compromise.

   The availability and freshness of revocation information affects the
   degree of assurance that ought to be placed in a certificate.  While
   certificates expire naturally, events may occur during its natural
   lifetime that negate the binding between the subject and public key.
   If revocation information is untimely or unavailable, the assurance
   associated with the binding is clearly reduced.  Relying parties
   might not be able to process every critical extension that can appear
   in a CRL.  CAs SHOULD take extra care when making revocation
   information available only through CRLs that contain critical
   extensions, particularly if support for those extensions is not
   mandated by this profile.  For example, if revocation information is
   supplied using a combination of delta CRLs and full CRLs, and the

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   delta CRLs are issued more frequently than the full CRLs, then
   relying parties that cannot handle the critical extensions related to
   delta CRL processing will not be able to obtain the most recent
   revocation information.  Alternatively, if a full CRL is issued
   whenever a delta CRL is issued, then timely revocation information
   will be available to all relying parties.  Similarly, implementations
   of the certification path validation mechanism described in Section 6
   that omit revocation checking provide less assurance than those that
   support it.

   The certification path validation algorithm depends on the certain
   knowledge of the public keys (and other information) about one or
   more trusted CAs.  The decision to trust a CA is an important
   decision as it ultimately determines the trust afforded a
   certificate.  The authenticated distribution of trusted CA public
   keys (usually in the form of a "self-signed" certificate) is a
   security critical out-of-band process that is beyond the scope of
   this specification.

   In addition, where a key compromise or CA failure occurs for a
   trusted CA, the user will need to modify the information provided to
   the path validation routine.  Selection of too many trusted CAs makes
   the trusted CA information difficult to maintain.  On the other hand,
   selection of only one trusted CA could limit users to a closed
   community of users.

   The quality of implementations that process certificates also affects
   the degree of assurance provided.  The path validation algorithm
   described in Section 6 relies upon the integrity of the trusted CA
   information, and especially the integrity of the public keys
   associated with the trusted CAs.  By substituting public keys for
   which an attacker has the private key, an attacker could trick the
   user into accepting false certificates.

   The binding between a key and certificate subject cannot be stronger
   than the cryptographic module implementation and algorithms used to
   generate the signature.  Short key lengths or weak hash algorithms
   will limit the utility of a certificate.  CAs are encouraged to note
   advances in cryptology so they can employ strong cryptographic
   techniques.  In addition, CAs SHOULD decline to issue certificates to
   CAs or end entities that generate weak signatures.

   Inconsistent application of name comparison rules can result in
   acceptance of invalid X.509 certification paths or rejection of valid
   ones.  The X.500 series of specifications defines rules for comparing
   distinguished names that require comparison of strings without regard

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   to case, character set, multi-character white space substring, or
   leading and trailing white space.  This specification relaxes these
   requirements, requiring support for binary comparison at a minimum.

   CAs MUST encode the distinguished name in the subject field of a CA
   certificate identically to the distinguished name in the issuer field
   in certificates issued by that CA.  If CAs use different encodings,
   implementations might fail to recognize name chains for paths that
   include this certificate.  As a consequence, valid paths could be
   rejected.

   In addition, name constraints for distinguished names MUST be stated
   identically to the encoding used in the subject field or
   subjectAltName extension.  If not, then name constraints stated as
   excludedSubtrees will not match and invalid paths will be accepted
   and name constraints expressed as permittedSubtrees will not match
   and valid paths will be rejected.  To avoid acceptance of invalid
   paths, CAs SHOULD state name constraints for distinguished names as
   permittedSubtrees wherever possible.

   In general, using the nameConstraints extension to constrain one name
   form (e.g., DNS names) offers no protection against use of other name
   forms (e.g., electronic mail addresses).

   While X.509 mandates that names be unambiguous, there is a risk that
   two unrelated authorities will issue certificates and/or CRLs under
   the same issuer name.  As a means of reducing problems and security
   issues related to issuer name collisions, CA and CRL issuer names
   SHOULD be formed in a way that reduces the likelihood of name
   collisions.  Implementers should take into account the possible
   existence of multiple unrelated CAs and CRL issuers with the same
   name.  At a minimum, implementations validating CRLs MUST ensure that
   the certification path of a certificate and the CRL issuer
   certification path used to validate the certificate terminate at the
   same trust anchor.

   While the local-part of an electronic mail address is case sensitive
   [RFC2821], emailAddress attribute values are not case sensitive
   [RFC2985].  As a result, there is a risk that two different email
   addresses will be treated as the same address when the matching rule
   for the emailAddress attribute is used, if the email server exploits
   the case sensitivity of mailbox local-parts.  Implementers should not
   include an email address in the emailAddress attribute if the email
   server that hosts the email address treats the local-part of email
   addresses as case sensitive.

   Implementers should be aware of risks involved if the CRL
   distribution points or authority information access extensions of

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   corrupted certificates or CRLs contain links to malicious code.
   Implementers should always take the steps of validating the retrieved
   data to ensure that the data is properly formed.

   When certificates include a cRLDistributionPoints extension with an
   https URI or similar scheme, circular dependencies can be introduced.
   The relying party is forced to perform an additional path validation
   in order to obtain the CRL required to complete the initial path
   validation!  Circular conditions can also be created with an https
   URI (or similar scheme) in the authorityInfoAccess or
   subjectInfoAccess extensions.  At worst, this situation can create
   unresolvable dependencies.

   CAs SHOULD NOT include URIs that specify https, ldaps, or similar
   schemes in extensions.  CAs that include an https URI in one of these
   extensions MUST ensure that the server's certificate can be validated
   without using the information that is pointed to by the URI.  Relying
   parties that choose to validate the server's certificate when
   obtaining information pointed to by an https URI in the
   cRLDistributionPoints, authorityInfoAccess, or subjectInfoAccess
   extensions MUST be prepared for the possibility that this will result
   in unbounded recursion.

   Self-issued certificates provide CAs with one automated mechanism to
   indicate changes in the CA's operations.  In particular, self-issued
   certificates may be used to implement a graceful change-over from one
   non-compromised CA key pair to the next.  Detailed procedures for "CA
   key update" are specified in [RFC4210], where the CA protects its new
   public key using its previous private key and vice versa using two
   self-issued certificates.  Conforming client implementations will
   process the self-issued certificate and determine whether
   certificates issued under the new key may be trusted.  Self-issued
   certificates MAY be used to support other changes in CA operations,
   such as additions to the CA's policy set, using similar procedures.

   Some legacy implementations support names encoded in the ISO 8859-1
   character set (Latin1String) [ISO8859] but tag them as TeletexString.
   TeletexString encodes a larger character set than ISO 8859-1, but it
   encodes some characters differently.  The name comparison rules
   specified in Section 7.1 assume that TeletexStrings are encoded as
   described in the ASN.1 standard.  When comparing names encoded using
   the Latin1String character set, false positives and negatives are
   possible.

   When strings are mapped from internal representations to visual
   representations, sometimes two different strings will have the same
   or similar visual representations.  This can happen for many
   different reasons, including use of similar glyphs and use of

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   composed characters (such as e + ' equaling U+00E9, the Korean
   composed characters, and vowels above consonant clusters in certain
   languages).  As a result of this situation, people doing visual
   comparisons between two different names may think they are the same
   when in fact they are not.  Also, people may mistake one string for
   another.  Issuers of certificates and relying parties both need to be
   aware of this situation.

9.  IANA Considerations

   Extensions in certificates and CRLs are identified using object
   identifiers.  The objects are defined in an arc delegated by IANA to
   the PKIX Working Group.  No further action by IANA is necessary for
   this document or any anticipated updates.

10.  Acknowledgments

   Warwick Ford participated with the authors in some of the design team
   meetings that directed development of this document.  The design
   team's efforts were guided by contributions from Matt Crawford, Tom
   Gindin, Steve Hanna, Stephen Henson, Paul Hoffman, Takashi Ito, Denis
   Pinkas, and Wen-Cheng Wang.

11.  References

11.1.  Normative References

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791, September
              1981.

   [RFC1034]  Mockapetris, P., "Domain Names - Concepts and Facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts --
              Application and Support", STD 3, RFC 1123, October 1989.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2585]  Housley, R. and P. Hoffman, "Internet X.509 Public Key
              Infrastructure: Operational Protocols: FTP and HTTP", RFC
              2585, May 1999.

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   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2797]  Myers, M., Liu, X., Schaad, J., and J. Weinstein,
              "Certificate Management Messages over CMS", RFC 2797,
              April 2000.

   [RFC2821]  Klensin, J., Ed., "Simple Mail Transfer Protocol", RFC
              2821, April 2001.

   [RFC3454]  Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              December 2002.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, March 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4516]  Smith, M., Ed., and T. Howes, "Lightweight Directory
              Access Protocol (LDAP): Uniform Resource Locator", RFC
              4516, June 2006.

   [RFC4518]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Internationalized String Preparation", RFC 4518,
              June 2006.

   [RFC4523]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP) Schema Definitions for X.509 Certificates", RFC
              4523, June 2006.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

   [X.680]    ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002,
              Information technology - Abstract Syntax Notation One
              (ASN.1):  Specification of basic notation.

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   [X.690]    ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
              Information technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER).

11.2.  Informative References

   [ISO8859]  ISO/IEC 8859-1:1998.  Information technology -- 8-bit
              single-byte coded graphic character sets -- Part 1: Latin
              alphabet No. 1.

   [ISO10646] ISO/IEC 10646:2003.  Information technology -- Universal
              Multiple-Octet Coded Character Set (UCS).

   [NFC]      Davis, M. and M. Duerst, "Unicode Standard Annex #15:
              Unicode Normalization Forms", October 2006,
              <http://www.unicode.org/reports/tr15/>.

   [RFC1422]  Kent, S., "Privacy Enhancement for Internet Electronic
              Mail: Part II: Certificate-Based Key Management", RFC
              1422, February 1993.

   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, January 1998.

   [RFC2459]  Housley, R., Ford, W., Polk, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and CRL
              Profile", RFC 2459, January 1999.

   [RFC2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
              Adams, "X.509 Internet Public Key Infrastructure Online
              Certificate Status Protocol - OCSP", RFC 2560, June 1999.

   [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
              Classes and Attribute Types Version 2.0", RFC 2985,
              November 2000.

   [RFC3161]  Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
              "Internet X.509 Public Key Infrastructure Time-Stamp
              Protocol (TSP)", RFC 3161, August 2001.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

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   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210, September 2005.

   [RFC4325]  Santesson, S. and R. Housley, "Internet X.509 Public Key
              Infrastructure Authority Information Access Certificate
              Revocation List (CRL) Extension", RFC 4325, December 2005.

   [RFC4491]  Leontiev, S., Ed., and D. Shefanovski, Ed., "Using the
              GOST R 34.10-94, GOST R 34.10-2001, and GOST R 34.11-94
              Algorithms with the Internet X.509 Public Key
              Infrastructure Certificate and CRL Profile", RFC 4491, May
              2006.

   [RFC4510]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
              (LDAP): Technical Specification Road Map", RFC 4510, June
              2006.

   [RFC4512]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
              (LDAP): Directory Information Models", RFC 4512, June
              2006.

   [RFC4514]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
              (LDAP): String Representation of Distinguished Names", RFC
              4514, June 2006.

   [RFC4519]  Sciberras, A., Ed., "Lightweight Directory Access Protocol
              (LDAP): Schema for User Applications", RFC 4519, June
              2006.

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   [RFC4630]  Housley, R. and S. Santesson, "Update to DirectoryString
              Processing in the Internet X.509 Public Key Infrastructure
              Certificate and Certificate Revocation List (CRL)
              Profile", RFC 4630, August 2006.

   [X.500]    ITU-T Recommendation X.500 (2005) | ISO/IEC 9594-1:2005,
              Information technology - Open Systems Interconnection -
              The Directory: Overview of concepts, models and services.

   [X.501]    ITU-T Recommendation X.501 (2005) | ISO/IEC 9594-2:2005,
              Information technology - Open Systems Interconnection -
              The Directory: Models.

   [X.509]    ITU-T Recommendation X.509 (2005) | ISO/IEC 9594-8:2005,
              Information technology - Open Systems Interconnection -
              The Directory: Public-key and attribute certificate
              frameworks.

   [X.520]    ITU-T Recommendation X.520 (2005) | ISO/IEC 9594-6:2005,
              Information technology - Open Systems Interconnection -
              The Directory: Selected attribute types.

   [X.660]    ITU-T Recommendation X.660 (2004) | ISO/IEC 9834-1:2005,
              Information technology - Open Systems Interconnection -
              Procedures for the operation of OSI Registration
              Authorities: General procedures, and top arcs of the ASN.1
              Object Identifier tree.

   [X.683]    ITU-T Recommendation X.683 (2002) | ISO/IEC 8824-4:2002,
              Information technology - Abstract Syntax Notation One
              (ASN.1): Parameterization of ASN.1 specifications.

   [X9.55]    ANSI X9.55-1997, Public Key Cryptography for the Financial
              Services Industry: Extensions to Public Key Certificates
              and Certificate Revocation Lists, January 1997.

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Appendix A.  Pseudo-ASN.1 Structures and OIDs

   This appendix describes data objects used by conforming PKI
   components in an "ASN.1-like" syntax.  This syntax is a hybrid of the
   1988 and 1993 ASN.1 syntaxes.  The 1988 ASN.1 syntax is augmented
   with 1993 UNIVERSAL Types UniversalString, BMPString, and UTF8String.

   The ASN.1 syntax does not permit the inclusion of type statements in
   the ASN.1 module, and the 1993 ASN.1 standard does not permit use of
   the new UNIVERSAL types in modules using the 1988 syntax.  As a
   result, this module does not conform to either version of the ASN.1
   standard.

   This appendix may be converted into 1988 ASN.1 by replacing the
   definitions for the UNIVERSAL Types with the 1988 catch-all "ANY".

A.1.  Explicitly Tagged Module, 1988 Syntax

PKIX1Explicit88 { iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) }

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

-- IMPORTS NONE --

-- UNIVERSAL Types defined in 1993 and 1998 ASN.1
-- and required by this specification

UniversalString ::= [UNIVERSAL 28] IMPLICIT OCTET STRING
        -- UniversalString is defined in ASN.1:1993

BMPString ::= [UNIVERSAL 30] IMPLICIT OCTET STRING
      -- BMPString is the subtype of UniversalString and models
      -- the Basic Multilingual Plane of ISO/IEC 10646

UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
      -- The content of this type conforms to RFC 3629.

-- PKIX specific OIDs

id-pkix  OBJECT IDENTIFIER  ::=
         { iso(1) identified-organization(3) dod(6) internet(1)
                    security(5) mechanisms(5) pkix(7) }

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-- PKIX arcs

id-pe OBJECT IDENTIFIER ::= { id-pkix 1 }
        -- arc for private certificate extensions
id-qt OBJECT IDENTIFIER ::= { id-pkix 2 }
        -- arc for policy qualifier types
id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
        -- arc for extended key purpose OIDS
id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
        -- arc for access descriptors

-- policyQualifierIds for Internet policy qualifiers

id-qt-cps      OBJECT IDENTIFIER ::=  { id-qt 1 }
      -- OID for CPS qualifier
id-qt-unotice  OBJECT IDENTIFIER ::=  { id-qt 2 }
      -- OID for user notice qualifier

-- access descriptor definitions

id-ad-ocsp         OBJECT IDENTIFIER ::= { id-ad 1 }
id-ad-caIssuers    OBJECT IDENTIFIER ::= { id-ad 2 }
id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }
id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

-- attribute data types

Attribute               ::= SEQUENCE {
      type             AttributeType,
      values    SET OF AttributeValue }
            -- at least one value is required

AttributeType           ::= OBJECT IDENTIFIER

AttributeValue          ::= ANY -- DEFINED BY AttributeType

AttributeTypeAndValue   ::= SEQUENCE {
        type    AttributeType,
        value   AttributeValue }

-- suggested naming attributes: Definition of the following
--   information object set may be augmented to meet local
--   requirements.  Note that deleting members of the set may
--   prevent interoperability with conforming implementations.
-- presented in pairs: the AttributeType followed by the
--   type definition for the corresponding AttributeValue

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-- Arc for standard naming attributes

id-at OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 4 }

-- Naming attributes of type X520name

id-at-name                AttributeType ::= { id-at 41 }
id-at-surname             AttributeType ::= { id-at  4 }
id-at-givenName           AttributeType ::= { id-at 42 }
id-at-initials            AttributeType ::= { id-at 43 }
id-at-generationQualifier AttributeType ::= { id-at 44 }

-- Naming attributes of type X520Name:
--   X520name ::= DirectoryString (SIZE (1..ub-name))
--
-- Expanded to avoid parameterized type:
X520name ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-name)),
      printableString   PrintableString (SIZE (1..ub-name)),
      universalString   UniversalString (SIZE (1..ub-name)),
      utf8String        UTF8String      (SIZE (1..ub-name)),
      bmpString         BMPString       (SIZE (1..ub-name)) }

-- Naming attributes of type X520CommonName

id-at-commonName        AttributeType ::= { id-at 3 }

-- Naming attributes of type X520CommonName:
--   X520CommonName ::= DirectoryName (SIZE (1..ub-common-name))
--
-- Expanded to avoid parameterized type:
X520CommonName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-common-name)),
      printableString   PrintableString (SIZE (1..ub-common-name)),
      universalString   UniversalString (SIZE (1..ub-common-name)),
      utf8String        UTF8String      (SIZE (1..ub-common-name)),
      bmpString         BMPString       (SIZE (1..ub-common-name)) }

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-- Naming attributes of type X520LocalityName

id-at-localityName      AttributeType ::= { id-at 7 }

-- Naming attributes of type X520LocalityName:
--   X520LocalityName ::= DirectoryName (SIZE (1..ub-locality-name))
--
-- Expanded to avoid parameterized type:
X520LocalityName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-locality-name)),
      printableString   PrintableString (SIZE (1..ub-locality-name)),
      universalString   UniversalString (SIZE (1..ub-locality-name)),
      utf8String        UTF8String      (SIZE (1..ub-locality-name)),
      bmpString         BMPString       (SIZE (1..ub-locality-name)) }

-- Naming attributes of type X520StateOrProvinceName

id-at-stateOrProvinceName AttributeType ::= { id-at 8 }

-- Naming attributes of type X520StateOrProvinceName:
--   X520StateOrProvinceName ::= DirectoryName (SIZE (1..ub-state-name))
--
-- Expanded to avoid parameterized type:
X520StateOrProvinceName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-state-name)),
      printableString   PrintableString (SIZE (1..ub-state-name)),
      universalString   UniversalString (SIZE (1..ub-state-name)),
      utf8String        UTF8String      (SIZE (1..ub-state-name)),
      bmpString         BMPString       (SIZE (1..ub-state-name)) }

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-- Naming attributes of type X520OrganizationName

id-at-organizationName  AttributeType ::= { id-at 10 }

-- Naming attributes of type X520OrganizationName:
--   X520OrganizationName ::=
--          DirectoryName (SIZE (1..ub-organization-name))
--
-- Expanded to avoid parameterized type:
X520OrganizationName ::= CHOICE {
      teletexString     TeletexString
                          (SIZE (1..ub-organization-name)),
      printableString   PrintableString
                          (SIZE (1..ub-organization-name)),
      universalString   UniversalString
                          (SIZE (1..ub-organization-name)),
      utf8String        UTF8String
                          (SIZE (1..ub-organization-name)),
      bmpString         BMPString
                          (SIZE (1..ub-organization-name))  }

-- Naming attributes of type X520OrganizationalUnitName

id-at-organizationalUnitName AttributeType ::= { id-at 11 }

-- Naming attributes of type X520OrganizationalUnitName:
--   X520OrganizationalUnitName ::=
--          DirectoryName (SIZE (1..ub-organizational-unit-name))
--
-- Expanded to avoid parameterized type:
X520OrganizationalUnitName ::= CHOICE {
      teletexString     TeletexString
                          (SIZE (1..ub-organizational-unit-name)),
      printableString   PrintableString
                          (SIZE (1..ub-organizational-unit-name)),
      universalString   UniversalString
                          (SIZE (1..ub-organizational-unit-name)),
      utf8String        UTF8String
                          (SIZE (1..ub-organizational-unit-name)),
      bmpString         BMPString
                          (SIZE (1..ub-organizational-unit-name)) }

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-- Naming attributes of type X520Title

id-at-title             AttributeType ::= { id-at 12 }

-- Naming attributes of type X520Title:
--   X520Title ::= DirectoryName (SIZE (1..ub-title))
--
-- Expanded to avoid parameterized type:
X520Title ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-title)),
      printableString   PrintableString (SIZE (1..ub-title)),
      universalString   UniversalString (SIZE (1..ub-title)),
      utf8String        UTF8String      (SIZE (1..ub-title)),
      bmpString         BMPString       (SIZE (1..ub-title)) }

-- Naming attributes of type X520dnQualifier

id-at-dnQualifier       AttributeType ::= { id-at 46 }

X520dnQualifier ::=     PrintableString

-- Naming attributes of type X520countryName (digraph from IS 3166)

id-at-countryName       AttributeType ::= { id-at 6 }

X520countryName ::=     PrintableString (SIZE (2))

-- Naming attributes of type X520SerialNumber

id-at-serialNumber      AttributeType ::= { id-at 5 }

X520SerialNumber ::=    PrintableString (SIZE (1..ub-serial-number))

-- Naming attributes of type X520Pseudonym

id-at-pseudonym         AttributeType ::= { id-at 65 }

-- Naming attributes of type X520Pseudonym:
--   X520Pseudonym ::= DirectoryName (SIZE (1..ub-pseudonym))
--
-- Expanded to avoid parameterized type:
X520Pseudonym ::= CHOICE {
   teletexString     TeletexString   (SIZE (1..ub-pseudonym)),
   printableString   PrintableString (SIZE (1..ub-pseudonym)),
   universalString   UniversalString (SIZE (1..ub-pseudonym)),
   utf8String        UTF8String      (SIZE (1..ub-pseudonym)),
   bmpString         BMPString       (SIZE (1..ub-pseudonym)) }

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-- Naming attributes of type DomainComponent (from RFC 4519)

id-domainComponent   AttributeType ::= { 0 9 2342 19200300 100 1 25 }

DomainComponent ::=  IA5String

-- Legacy attributes

pkcs-9 OBJECT IDENTIFIER ::=
       { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 9 }

id-emailAddress      AttributeType ::= { pkcs-9 1 }

EmailAddress ::=     IA5String (SIZE (1..ub-emailaddress-length))

-- naming data types --

Name ::= CHOICE { -- only one possibility for now --
      rdnSequence  RDNSequence }

RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

DistinguishedName ::=   RDNSequence

RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue

-- Directory string type --

DirectoryString ::= CHOICE {
      teletexString       TeletexString   (SIZE (1..MAX)),
      printableString     PrintableString (SIZE (1..MAX)),
      universalString     UniversalString (SIZE (1..MAX)),
      utf8String          UTF8String      (SIZE (1..MAX)),
      bmpString           BMPString       (SIZE (1..MAX)) }

-- certificate and CRL specific structures begin here

Certificate  ::=  SEQUENCE  {
     tbsCertificate       TBSCertificate,
     signatureAlgorithm   AlgorithmIdentifier,
     signature            BIT STRING  }

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TBSCertificate  ::=  SEQUENCE  {
     version         [0]  Version DEFAULT v1,
     serialNumber         CertificateSerialNumber,
     signature            AlgorithmIdentifier,
     issuer               Name,
     validity             Validity,
     subject              Name,
     subjectPublicKeyInfo SubjectPublicKeyInfo,
     issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                          -- If present, version MUST be v2 or v3
     subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                          -- If present, version MUST be v2 or v3
     extensions      [3]  Extensions OPTIONAL
                          -- If present, version MUST be v3 --  }

Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }

CertificateSerialNumber  ::=  INTEGER

Validity ::= SEQUENCE {
     notBefore      Time,
     notAfter       Time  }

Time ::= CHOICE {
     utcTime        UTCTime,
     generalTime    GeneralizedTime }

UniqueIdentifier  ::=  BIT STRING

SubjectPublicKeyInfo  ::=  SEQUENCE  {
     algorithm            AlgorithmIdentifier,
     subjectPublicKey     BIT STRING  }

Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

Extension  ::=  SEQUENCE  {
     extnID      OBJECT IDENTIFIER,
     critical    BOOLEAN DEFAULT FALSE,
     extnValue   OCTET STRING
                 -- contains the DER encoding of an ASN.1 value
                 -- corresponding to the extension type identified
                 -- by extnID
     }

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-- CRL structures

CertificateList  ::=  SEQUENCE  {
     tbsCertList          TBSCertList,
     signatureAlgorithm   AlgorithmIdentifier,
     signature            BIT STRING  }

TBSCertList  ::=  SEQUENCE  {
     version                 Version OPTIONAL,
                                   -- if present, MUST be v2
     signature               AlgorithmIdentifier,
     issuer                  Name,
     thisUpdate              Time,
     nextUpdate              Time OPTIONAL,
     revokedCertificates     SEQUENCE OF SEQUENCE  {
          userCertificate         CertificateSerialNumber,
          revocationDate          Time,
          crlEntryExtensions      Extensions OPTIONAL
                                   -- if present, version MUST be v2
                               }  OPTIONAL,
     crlExtensions           [0] Extensions OPTIONAL }
                                   -- if present, version MUST be v2

-- Version, Time, CertificateSerialNumber, and Extensions were
-- defined earlier for use in the certificate structure

AlgorithmIdentifier  ::=  SEQUENCE  {
     algorithm               OBJECT IDENTIFIER,
     parameters              ANY DEFINED BY algorithm OPTIONAL  }
                                -- contains a value of the type
                                -- registered for use with the
                                -- algorithm object identifier value

-- X.400 address syntax starts here

ORAddress ::= SEQUENCE {
   built-in-standard-attributes BuiltInStandardAttributes,
   built-in-domain-defined-attributes
                   BuiltInDomainDefinedAttributes OPTIONAL,
   -- see also teletex-domain-defined-attributes
   extension-attributes ExtensionAttributes OPTIONAL }

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-- Built-in Standard Attributes

BuiltInStandardAttributes ::= SEQUENCE {
   country-name                  CountryName OPTIONAL,
   administration-domain-name    AdministrationDomainName OPTIONAL,
   network-address           [0] IMPLICIT NetworkAddress OPTIONAL,
     -- see also extended-network-address
   terminal-identifier       [1] IMPLICIT TerminalIdentifier OPTIONAL,
   private-domain-name       [2] PrivateDomainName OPTIONAL,
   organization-name         [3] IMPLICIT OrganizationName OPTIONAL,
     -- see also teletex-organization-name
   numeric-user-identifier   [4] IMPLICIT NumericUserIdentifier
                                 OPTIONAL,
   personal-name             [5] IMPLICIT PersonalName OPTIONAL,
     -- see also teletex-personal-name
   organizational-unit-names [6] IMPLICIT OrganizationalUnitNames
                                 OPTIONAL }
     -- see also teletex-organizational-unit-names

CountryName ::= [APPLICATION 1] CHOICE {
   x121-dcc-code         NumericString
                           (SIZE (ub-country-name-numeric-length)),
   iso-3166-alpha2-code  PrintableString
                           (SIZE (ub-country-name-alpha-length)) }

AdministrationDomainName ::= [APPLICATION 2] CHOICE {
   numeric   NumericString   (SIZE (0..ub-domain-name-length)),
   printable PrintableString (SIZE (0..ub-domain-name-length)) }

NetworkAddress ::= X121Address  -- see also extended-network-address

X121Address ::= NumericString (SIZE (1..ub-x121-address-length))

TerminalIdentifier ::= PrintableString (SIZE (1..ub-terminal-id-length))

PrivateDomainName ::= CHOICE {
   numeric   NumericString   (SIZE (1..ub-domain-name-length)),
   printable PrintableString (SIZE (1..ub-domain-name-length)) }

OrganizationName ::= PrintableString
                            (SIZE (1..ub-organization-name-length))
  -- see also teletex-organization-name

NumericUserIdentifier ::= NumericString
                            (SIZE (1..ub-numeric-user-id-length))

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PersonalName ::= SET {
   surname     [0] IMPLICIT PrintableString
                    (SIZE (1..ub-surname-length)),
   given-name  [1] IMPLICIT PrintableString
                    (SIZE (1..ub-given-name-length)) OPTIONAL,
   initials    [2] IMPLICIT PrintableString
                    (SIZE (1..ub-initials-length)) OPTIONAL,
   generation-qualifier [3] IMPLICIT PrintableString
                    (SIZE (1..ub-generation-qualifier-length))
                    OPTIONAL }
  -- see also teletex-personal-name

OrganizationalUnitNames ::= SEQUENCE SIZE (1..ub-organizational-units)
                             OF OrganizationalUnitName
  -- see also teletex-organizational-unit-names

OrganizationalUnitName ::= PrintableString (SIZE
                    (1..ub-organizational-unit-name-length))

-- Built-in Domain-defined Attributes

BuiltInDomainDefinedAttributes ::= SEQUENCE SIZE
                    (1..ub-domain-defined-attributes) OF
                    BuiltInDomainDefinedAttribute

BuiltInDomainDefinedAttribute ::= SEQUENCE {
   type PrintableString (SIZE
                   (1..ub-domain-defined-attribute-type-length)),
   value PrintableString (SIZE
                   (1..ub-domain-defined-attribute-value-length)) }

-- Extension Attributes

ExtensionAttributes ::= SET SIZE (1..ub-extension-attributes) OF
               ExtensionAttribute

ExtensionAttribute ::=  SEQUENCE {
   extension-attribute-type [0] IMPLICIT INTEGER
                   (0..ub-extension-attributes),
   extension-attribute-value [1]
                   ANY DEFINED BY extension-attribute-type }

-- Extension types and attribute values

common-name INTEGER ::= 1

CommonName ::= PrintableString (SIZE (1..ub-common-name-length))

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teletex-common-name INTEGER ::= 2

TeletexCommonName ::= TeletexString (SIZE (1..ub-common-name-length))

teletex-organization-name INTEGER ::= 3

TeletexOrganizationName ::=
                TeletexString (SIZE (1..ub-organization-name-length))

teletex-personal-name INTEGER ::= 4

TeletexPersonalName ::= SET {
   surname     [0] IMPLICIT TeletexString
                    (SIZE (1..ub-surname-length)),
   given-name  [1] IMPLICIT TeletexString
                    (SIZE (1..ub-given-name-length)) OPTIONAL,
   initials    [2] IMPLICIT TeletexString
                    (SIZE (1..ub-initials-length)) OPTIONAL,
   generation-qualifier [3] IMPLICIT TeletexString
                    (SIZE (1..ub-generation-qualifier-length))
                    OPTIONAL }

teletex-organizational-unit-names INTEGER ::= 5

TeletexOrganizationalUnitNames ::= SEQUENCE SIZE
      (1..ub-organizational-units) OF TeletexOrganizationalUnitName

TeletexOrganizationalUnitName ::= TeletexString
                  (SIZE (1..ub-organizational-unit-name-length))

pds-name INTEGER ::= 7

PDSName ::= PrintableString (SIZE (1..ub-pds-name-length))

physical-delivery-country-name INTEGER ::= 8

PhysicalDeliveryCountryName ::= CHOICE {
   x121-dcc-code NumericString (SIZE (ub-country-name-numeric-length)),
   iso-3166-alpha2-code PrintableString
                               (SIZE (ub-country-name-alpha-length)) }

postal-code INTEGER ::= 9

PostalCode ::= CHOICE {
   numeric-code   NumericString (SIZE (1..ub-postal-code-length)),
   printable-code PrintableString (SIZE (1..ub-postal-code-length)) }

physical-delivery-office-name INTEGER ::= 10

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PhysicalDeliveryOfficeName ::= PDSParameter

physical-delivery-office-number INTEGER ::= 11

PhysicalDeliveryOfficeNumber ::= PDSParameter

extension-OR-address-components INTEGER ::= 12

ExtensionORAddressComponents ::= PDSParameter

physical-delivery-personal-name INTEGER ::= 13

PhysicalDeliveryPersonalName ::= PDSParameter

physical-delivery-organization-name INTEGER ::= 14

PhysicalDeliveryOrganizationName ::= PDSParameter

extension-physical-delivery-address-components INTEGER ::= 15

ExtensionPhysicalDeliveryAddressComponents ::= PDSParameter

unformatted-postal-address INTEGER ::= 16

UnformattedPostalAddress ::= SET {
   printable-address SEQUENCE SIZE (1..ub-pds-physical-address-lines)
        OF PrintableString (SIZE (1..ub-pds-parameter-length)) OPTIONAL,
   teletex-string TeletexString
        (SIZE (1..ub-unformatted-address-length)) OPTIONAL }

street-address INTEGER ::= 17

StreetAddress ::= PDSParameter

post-office-box-address INTEGER ::= 18

PostOfficeBoxAddress ::= PDSParameter

poste-restante-address INTEGER ::= 19

PosteRestanteAddress ::= PDSParameter

unique-postal-name INTEGER ::= 20

UniquePostalName ::= PDSParameter

local-postal-attributes INTEGER ::= 21

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LocalPostalAttributes ::= PDSParameter

PDSParameter ::= SET {
   printable-string PrintableString
                (SIZE(1..ub-pds-parameter-length)) OPTIONAL,
   teletex-string TeletexString
                (SIZE(1..ub-pds-parameter-length)) OPTIONAL }

extended-network-address INTEGER ::= 22

ExtendedNetworkAddress ::= CHOICE {
   e163-4-address SEQUENCE {
      number      [0] IMPLICIT NumericString
                       (SIZE (1..ub-e163-4-number-length)),
      sub-address [1] IMPLICIT NumericString
                       (SIZE (1..ub-e163-4-sub-address-length))
                       OPTIONAL },
   psap-address   [0] IMPLICIT PresentationAddress }

PresentationAddress ::= SEQUENCE {
    pSelector     [0] EXPLICIT OCTET STRING OPTIONAL,
    sSelector     [1] EXPLICIT OCTET STRING OPTIONAL,
    tSelector     [2] EXPLICIT OCTET STRING OPTIONAL,
    nAddresses    [3] EXPLICIT SET SIZE (1..MAX) OF OCTET STRING }

terminal-type  INTEGER ::= 23

TerminalType ::= INTEGER {
   telex        (3),
   teletex      (4),
   g3-facsimile (5),
   g4-facsimile (6),
   ia5-terminal (7),
   videotex     (8) } (0..ub-integer-options)

-- Extension Domain-defined Attributes

teletex-domain-defined-attributes INTEGER ::= 6

TeletexDomainDefinedAttributes ::= SEQUENCE SIZE
   (1..ub-domain-defined-attributes) OF TeletexDomainDefinedAttribute

TeletexDomainDefinedAttribute ::= SEQUENCE {
        type TeletexString
               (SIZE (1..ub-domain-defined-attribute-type-length)),
        value TeletexString
               (SIZE (1..ub-domain-defined-attribute-value-length)) }

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--  specifications of Upper Bounds MUST be regarded as mandatory
--  from Annex B of ITU-T X.411 Reference Definition of MTS Parameter
--  Upper Bounds

-- Upper Bounds
ub-name INTEGER ::= 32768
ub-common-name INTEGER ::= 64
ub-locality-name INTEGER ::= 128
ub-state-name INTEGER ::= 128
ub-organization-name INTEGER ::= 64
ub-organizational-unit-name INTEGER ::= 64
ub-title INTEGER ::= 64
ub-serial-number INTEGER ::= 64
ub-match INTEGER ::= 128
ub-emailaddress-length INTEGER ::= 255
ub-common-name-length INTEGER ::= 64
ub-country-name-alpha-length INTEGER ::= 2
ub-country-name-numeric-length INTEGER ::= 3
ub-domain-defined-attributes INTEGER ::= 4
ub-domain-defined-attribute-type-length INTEGER ::= 8
ub-domain-defined-attribute-value-length INTEGER ::= 128
ub-domain-name-length INTEGER ::= 16
ub-extension-attributes INTEGER ::= 256
ub-e163-4-number-length INTEGER ::= 15
ub-e163-4-sub-address-length INTEGER ::= 40
ub-generation-qualifier-length INTEGER ::= 3
ub-given-name-length INTEGER ::= 16
ub-initials-length INTEGER ::= 5
ub-integer-options INTEGER ::= 256
ub-numeric-user-id-length INTEGER ::= 32
ub-organization-name-length INTEGER ::= 64
ub-organizational-unit-name-length INTEGER ::= 32
ub-organizational-units INTEGER ::= 4
ub-pds-name-length INTEGER ::= 16
ub-pds-parameter-length INTEGER ::= 30
ub-pds-physical-address-lines INTEGER ::= 6
ub-postal-code-length INTEGER ::= 16
ub-pseudonym INTEGER ::= 128
ub-surname-length INTEGER ::= 40
ub-terminal-id-length INTEGER ::= 24
ub-unformatted-address-length INTEGER ::= 180
ub-x121-address-length INTEGER ::= 16

-- Note - upper bounds on string types, such as TeletexString, are
-- measured in characters.  Excepting PrintableString or IA5String, a
-- significantly greater number of octets will be required to hold
-- such a value.  As a minimum, 16 octets, or twice the specified
-- upper bound, whichever is the larger, should be allowed for

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-- TeletexString.  For UTF8String or UniversalString at least four
-- times the upper bound should be allowed.

END

A.2.  Implicitly Tagged Module, 1988 Syntax

PKIX1Implicit88 { iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

IMPORTS
      id-pe, id-kp, id-qt-unotice, id-qt-cps,
      -- delete following line if "new" types are supported --
      BMPString, UTF8String,  -- end "new" types --
      ORAddress, Name, RelativeDistinguishedName,
      CertificateSerialNumber, Attribute, DirectoryString
      FROM PKIX1Explicit88 { iso(1) identified-organization(3)
            dod(6) internet(1) security(5) mechanisms(5) pkix(7)
            id-mod(0) id-pkix1-explicit(18) };

-- ISO arc for standard certificate and CRL extensions

id-ce OBJECT IDENTIFIER  ::=  {joint-iso-ccitt(2) ds(5) 29}

-- authority key identifier OID and syntax

id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 35 }

AuthorityKeyIdentifier ::= SEQUENCE {
    keyIdentifier             [0] KeyIdentifier            OPTIONAL,
    authorityCertIssuer       [1] GeneralNames             OPTIONAL,
    authorityCertSerialNumber [2] CertificateSerialNumber  OPTIONAL }
    -- authorityCertIssuer and authorityCertSerialNumber MUST both
    -- be present or both be absent

KeyIdentifier ::= OCTET STRING

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-- subject key identifier OID and syntax

id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }

SubjectKeyIdentifier ::= KeyIdentifier

-- key usage extension OID and syntax

id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

KeyUsage ::= BIT STRING {
     digitalSignature        (0),
     nonRepudiation          (1),  -- recent editions of X.509 have
                                -- renamed this bit to contentCommitment
     keyEncipherment         (2),
     dataEncipherment        (3),
     keyAgreement            (4),
     keyCertSign             (5),
     cRLSign                 (6),
     encipherOnly            (7),
     decipherOnly            (8) }

-- private key usage period extension OID and syntax

id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::=  { id-ce 16 }

PrivateKeyUsagePeriod ::= SEQUENCE {
     notBefore       [0]     GeneralizedTime OPTIONAL,
     notAfter        [1]     GeneralizedTime OPTIONAL }
     -- either notBefore or notAfter MUST be present

-- certificate policies extension OID and syntax

id-ce-certificatePolicies OBJECT IDENTIFIER ::=  { id-ce 32 }

anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificatePolicies 0 }

CertificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {
     policyIdentifier   CertPolicyId,
     policyQualifiers   SEQUENCE SIZE (1..MAX) OF
             PolicyQualifierInfo OPTIONAL }

CertPolicyId ::= OBJECT IDENTIFIER

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PolicyQualifierInfo ::= SEQUENCE {
     policyQualifierId  PolicyQualifierId,
     qualifier          ANY DEFINED BY policyQualifierId }

-- Implementations that recognize additional policy qualifiers MUST
-- augment the following definition for PolicyQualifierId

PolicyQualifierId ::= OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

-- CPS pointer qualifier

CPSuri ::= IA5String

-- user notice qualifier

UserNotice ::= SEQUENCE {
     noticeRef        NoticeReference OPTIONAL,
     explicitText     DisplayText OPTIONAL }

NoticeReference ::= SEQUENCE {
     organization     DisplayText,
     noticeNumbers    SEQUENCE OF INTEGER }

DisplayText ::= CHOICE {
     ia5String        IA5String      (SIZE (1..200)),
     visibleString    VisibleString  (SIZE (1..200)),
     bmpString        BMPString      (SIZE (1..200)),
     utf8String       UTF8String     (SIZE (1..200)) }

-- policy mapping extension OID and syntax

id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }

PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
     issuerDomainPolicy      CertPolicyId,
     subjectDomainPolicy     CertPolicyId }

-- subject alternative name extension OID and syntax

id-ce-subjectAltName OBJECT IDENTIFIER ::=  { id-ce 17 }

SubjectAltName ::= GeneralNames

GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

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GeneralName ::= CHOICE {
     otherName                 [0]  AnotherName,
     rfc822Name                [1]  IA5String,
     dNSName                   [2]  IA5String,
     x400Address               [3]  ORAddress,
     directoryName             [4]  Name,
     ediPartyName              [5]  EDIPartyName,
     uniformResourceIdentifier [6]  IA5String,
     iPAddress                 [7]  OCTET STRING,
     registeredID              [8]  OBJECT IDENTIFIER }

-- AnotherName replaces OTHER-NAME ::= TYPE-IDENTIFIER, as
-- TYPE-IDENTIFIER is not supported in the '88 ASN.1 syntax

AnotherName ::= SEQUENCE {
     type-id    OBJECT IDENTIFIER,
     value      [0] EXPLICIT ANY DEFINED BY type-id }

EDIPartyName ::= SEQUENCE {
     nameAssigner              [0]  DirectoryString OPTIONAL,
     partyName                 [1]  DirectoryString }

-- issuer alternative name extension OID and syntax

id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }

IssuerAltName ::= GeneralNames

id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }

SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

-- basic constraints extension OID and syntax

id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }

BasicConstraints ::= SEQUENCE {
     cA                      BOOLEAN DEFAULT FALSE,
     pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

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-- name constraints extension OID and syntax

id-ce-nameConstraints OBJECT IDENTIFIER ::=  { id-ce 30 }

NameConstraints ::= SEQUENCE {
     permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
     excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

GeneralSubtree ::= SEQUENCE {
     base                    GeneralName,
     minimum         [0]     BaseDistance DEFAULT 0,
     maximum         [1]     BaseDistance OPTIONAL }

BaseDistance ::= INTEGER (0..MAX)

-- policy constraints extension OID and syntax

id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }

PolicyConstraints ::= SEQUENCE {
     requireExplicitPolicy   [0]     SkipCerts OPTIONAL,
     inhibitPolicyMapping    [1]     SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

-- CRL distribution points extension OID and syntax

id-ce-cRLDistributionPoints     OBJECT IDENTIFIER  ::=  {id-ce 31}

CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

DistributionPoint ::= SEQUENCE {
     distributionPoint       [0]     DistributionPointName OPTIONAL,
     reasons                 [1]     ReasonFlags OPTIONAL,
     cRLIssuer               [2]     GeneralNames OPTIONAL }

DistributionPointName ::= CHOICE {
     fullName                [0]     GeneralNames,
     nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

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ReasonFlags ::= BIT STRING {
     unused                  (0),
     keyCompromise           (1),
     cACompromise            (2),
     affiliationChanged      (3),
     superseded              (4),
     cessationOfOperation    (5),
     certificateHold         (6),
     privilegeWithdrawn      (7),
     aACompromise            (8) }

-- extended key usage extension OID and syntax

id-ce-extKeyUsage OBJECT IDENTIFIER ::= {id-ce 37}

ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

KeyPurposeId ::= OBJECT IDENTIFIER

-- permit unspecified key uses

anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

-- extended key purpose OIDs

id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
id-kp-codeSigning            OBJECT IDENTIFIER ::= { id-kp 3 }
id-kp-emailProtection        OBJECT IDENTIFIER ::= { id-kp 4 }
id-kp-timeStamping           OBJECT IDENTIFIER ::= { id-kp 8 }
id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }

-- inhibit any policy OID and syntax

id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }

InhibitAnyPolicy ::= SkipCerts

-- freshest (delta)CRL extension OID and syntax

id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

FreshestCRL ::= CRLDistributionPoints

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-- authority info access

id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

AuthorityInfoAccessSyntax  ::=
        SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription  ::=  SEQUENCE {
        accessMethod          OBJECT IDENTIFIER,
        accessLocation        GeneralName  }

-- subject info access

id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

SubjectInfoAccessSyntax  ::=
        SEQUENCE SIZE (1..MAX) OF AccessDescription

-- CRL number extension OID and syntax

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

CRLNumber ::= INTEGER (0..MAX)

-- issuing distribution point extension OID and syntax

id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

IssuingDistributionPoint ::= SEQUENCE {
     distributionPoint          [0] DistributionPointName OPTIONAL,
     onlyContainsUserCerts      [1] BOOLEAN DEFAULT FALSE,
     onlyContainsCACerts        [2] BOOLEAN DEFAULT FALSE,
     onlySomeReasons            [3] ReasonFlags OPTIONAL,
     indirectCRL                [4] BOOLEAN DEFAULT FALSE,
     onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }
     -- at most one of onlyContainsUserCerts, onlyContainsCACerts,
     -- and onlyContainsAttributeCerts may be set to TRUE.

id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

BaseCRLNumber ::= CRLNumber

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-- reason code extension OID and syntax

id-ce-cRLReasons OBJECT IDENTIFIER ::= { id-ce 21 }

CRLReason ::= ENUMERATED {
     unspecified             (0),
     keyCompromise           (1),
     cACompromise            (2),
     affiliationChanged      (3),
     superseded              (4),
     cessationOfOperation    (5),
     certificateHold         (6),
     removeFromCRL           (8),
     privilegeWithdrawn      (9),
     aACompromise           (10) }

-- certificate issuer CRL entry extension OID and syntax

id-ce-certificateIssuer OBJECT IDENTIFIER ::= { id-ce 29 }

CertificateIssuer ::= GeneralNames

-- hold instruction extension OID and syntax

id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

HoldInstructionCode ::= OBJECT IDENTIFIER

-- ANSI x9 arc holdinstruction arc

holdInstruction OBJECT IDENTIFIER ::=
          {joint-iso-itu-t(2) member-body(2) us(840) x9cm(10040) 2}

-- ANSI X9 holdinstructions

id-holdinstruction-none OBJECT IDENTIFIER  ::=
                                      {holdInstruction 1} -- deprecated

id-holdinstruction-callissuer OBJECT IDENTIFIER ::= {holdInstruction 2}

id-holdinstruction-reject OBJECT IDENTIFIER ::= {holdInstruction 3}

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-- invalidity date CRL entry extension OID and syntax

id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

InvalidityDate ::=  GeneralizedTime

END

Appendix B.  ASN.1 Notes

   CAs MUST force the serialNumber to be a non-negative integer, that
   is, the sign bit in the DER encoding of the INTEGER value MUST be
   zero.  This can be done by adding a leading (leftmost) `00'H octet if
   necessary.  This removes a potential ambiguity in mapping between a
   string of octets and an integer value.

   As noted in Section 4.1.2.2, serial numbers can be expected to
   contain long integers.  Certificate users MUST be able to handle
   serialNumber values up to 20 octets in length.  Conforming CAs MUST
   NOT use serialNumber values longer than 20 octets.

   As noted in Section 5.2.3, CRL numbers can be expected to contain
   long integers.  CRL validators MUST be able to handle cRLNumber
   values up to 20 octets in length.  Conforming CRL issuers MUST NOT
   use cRLNumber values longer than 20 octets.

   The construct "SEQUENCE SIZE (1..MAX) OF" appears in several ASN.1
   constructs.  A valid ASN.1 sequence will have zero or more entries.
   The SIZE (1..MAX) construct constrains the sequence to have at least
   one entry.  MAX indicates that the upper bound is unspecified.
   Implementations are free to choose an upper bound that suits their
   environment.

   The character string type PrintableString supports a very basic Latin
   character set: the lowercase letters 'a' through 'z', uppercase
   letters 'A' through 'Z', the digits '0' through '9', eleven special
   characters ' = ( ) + , - . / : ? and space.

   Implementers should note that the at sign ('@') and underscore ('_')
   characters are not supported by the ASN.1 type PrintableString.
   These characters often appear in Internet addresses.  Such addresses
   MUST be encoded using an ASN.1 type that supports them.  They are
   usually encoded as IA5String in either the emailAddress attribute
   within a distinguished name or the rfc822Name field of GeneralName.
   Conforming implementations MUST NOT encode strings that include
   either the at sign or underscore character as PrintableString.

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   The character string type TeletexString is a superset of
   PrintableString.  TeletexString supports a fairly standard (ASCII-
   like) Latin character set: Latin characters with non-spacing accents
   and Japanese characters.

   Named bit lists are BIT STRINGs where the values have been assigned
   names.  This specification makes use of named bit lists in the
   definitions for the key usage, CRL distribution points, and freshest
   CRL certificate extensions, as well as the freshest CRL and issuing
   distribution point CRL extensions.  When DER encoding a named bit
   list, trailing zeros MUST be omitted.  That is, the encoded value
   ends with the last named bit that is set to one.

   The character string type UniversalString supports any of the
   characters allowed by [ISO10646].  ISO 10646 is the Universal
   multiple-octet coded Character Set (UCS).

   The character string type UTF8String was introduced in the 1997
   version of ASN.1, and UTF8String was added to the list of choices for
   DirectoryString in the 2001 version of [X.520].  UTF8String is a
   universal type and has been assigned tag number 12.  The content of
   UTF8String was defined by RFC 2044 and updated in RFC 2279, which was
   updated in [RFC3629].

   In anticipation of these changes, and in conformance with IETF Best
   Practices codified in [RFC2277], IETF Policy on Character Sets and
   Languages, this document includes UTF8String as a choice in
   DirectoryString and in the userNotice certificate policy qualifier.

   For many of the attribute types defined in [X.520], the
   AttributeValue uses the DirectoryString type.  Of the attributes
   specified in Appendix A, the name, surname, givenName, initials,
   generationQualifier, commonName, localityName, stateOrProvinceName,
   organizationName, organizationalUnitName, title, and pseudonym
   attributes all use the DirectoryString type.  X.520 uses a
   parameterized type definition [X.683] of DirectoryString to specify
   the syntax for each of these attributes.  The parameter is used to
   indicate the maximum string length allowed for the attribute.  In
   Appendix A, in order to avoid the use of parameterized type
   definitions, the DirectoryString type is written in its expanded form
   for the definition of each of these attribute types.  So, the ASN.1
   in Appendix A describes the syntax for each of these attributes as
   being a CHOICE of TeletexString, PrintableString, UniversalString,
   UTF8String, and BMPString, with the appropriate constraints on the
   string length applied to each of the types in the CHOICE, rather than
   using the ASN.1 type DirectoryString to describe the syntax.

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   Implementers should note that the DER encoding of the SET OF values
   requires ordering of the encodings of the values.  In particular,
   this issue arises with respect to distinguished names.

   Implementers should note that the DER encoding of SET or SEQUENCE
   components whose value is the DEFAULT omit the component from the
   encoded certificate or CRL.  For example, a BasicConstraints
   extension whose cA value is FALSE would omit the cA boolean from the
   encoded certificate.

   Object Identifiers (OIDs) are used throughout this specification to
   identify certificate policies, public key and signature algorithms,
   certificate extensions, etc.  There is no maximum size for OIDs.
   This specification mandates support for OIDs that have arc elements
   with values that are less than 2^28, that is, they MUST be between 0
   and 268,435,455, inclusive.  This allows each arc element to be
   represented within a single 32-bit word.  Implementations MUST also
   support OIDs where the length of the dotted decimal (see Section 1.4
   of [RFC4512]) string representation can be up to 100 bytes
   (inclusive).  Implementations MUST be able to handle OIDs with up to
   20 elements (inclusive).  CAs SHOULD NOT issue certificates that
   contain OIDs that exceed these requirements.  Likewise, CRL issuers
   SHOULD NOT issue CRLs that contain OIDs that exceed these
   requirements.

   The content-specific rules for encoding GeneralName field values in
   the nameConstraints extension differ from rules that apply in other
   extensions.  In all other certificate, CRL, and CRL entry extensions
   specified in this document the encoding rules conform to the rules
   for the underlying type.  For example, values in the
   uniformResourceIdentifier field must contain a valid URI as specified
   in [RFC3986].  The content-specific rules for encoding values in the
   nameConstraints extension are specified in Section 4.2.1.10, and
   these rules may not conform to the rules for the underlying type.
   For example, when the uniformResourceIdentifier field appears in a
   nameConstraints extension, it must hold a DNS name (e.g.,
   "host.example.com" or ".example.com") rather than a URI.

   Implementors are warned that the X.500 standards community has
   developed a series of extensibility rules.  These rules determine
   when an ASN.1 definition can be changed without assigning a new
   Object Identifier (OID).  For example, at least two extension
   definitions included in [RFC2459], the predecessor to this profile
   document, have different ASN.1 definitions in this specification, but
   the same OID is used.  If unknown elements appear within an
   extension, and the extension is not marked as critical, those unknown
   elements ought to be ignored, as follows:

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      (a)  ignore all unknown bit name assignments within a bit string;

      (b)  ignore all unknown named numbers in an ENUMERATED type or
           INTEGER type that is being used in the enumerated style,
           provided the number occurs as an optional element of a SET or
           SEQUENCE; and

      (c)  ignore all unknown elements in SETs, at the end of SEQUENCEs,
           or in CHOICEs where the CHOICE is itself an optional element
           of a SET or SEQUENCE.

   If an extension containing unexpected values is marked as critical,
   the implementation MUST reject the certificate or CRL containing the
   unrecognized extension.

Appendix C.  Examples

   This appendix contains four examples: three certificates and a CRL.
   The first two certificates and the CRL comprise a minimal
   certification path.

   Appendix C.1 contains an annotated hex dump of a "self-signed"
   certificate issued by a CA whose distinguished name is
   cn=Example CA,dc=example,dc=com.  The certificate contains an RSA
   public key, and is signed by the corresponding RSA private key.

   Appendix C.2 contains an annotated hex dump of an end entity
   certificate.  The end entity certificate contains an RSA public key,
   and is signed by the private key corresponding to the "self-signed"
   certificate in Appendix C.1.

   Appendix C.3 contains an annotated hex dump of an end entity
   certificate that contains a DSA public key with parameters, and is
   signed with DSA and SHA-1.  This certificate is not part of the
   minimal certification path.

   Appendix C.4 contains an annotated hex dump of a CRL.  The CRL is
   issued by the CA whose distinguished name is
   cn=Example CA,dc=example,dc=com and the list of revoked certificates
   includes the end entity certificate presented in Appendix C.2.

   The certificates were processed using Peter Gutmann's dumpasn1
   utility to generate the output.  The source for the dumpasn1 utility
   is available at <http://www.cs.auckland.ac.nz/~pgut001/dumpasn1.c>.
   The binaries for the certificates and CRLs are available at
   http://csrc.nist.gov/groups/ST/crypto_apps_infra/documents/pkixtools.

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   In places in this appendix where a distinguished name is specified
   using a string representation, the strings are formatted using the
   rules specified in [RFC4514].

C.1.  RSA Self-Signed Certificate

   This appendix contains an annotated hex dump of a 578 byte version 3
   certificate.  The certificate contains the following information:

   (a)  the serial number is 17;
   (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
   (c)  the issuer's distinguished name is
        cn=Example CA,dc=example,dc=com;
   (d)  the subject's distinguished name is
        cn=Example CA,dc=example,dc=com;
   (e)  the certificate was issued on April 30, 2004 and expired on
        April 30, 2005;
   (f)  the certificate contains a 1024-bit RSA public key;
   (g)  the certificate contains a subject key identifier extension
        generated using method (1) of Section 4.2.1.2; and
   (h)  the certificate is a CA certificate (as indicated through the
        basic constraints extension).

   0  574: SEQUENCE {
   4  423:   SEQUENCE {
   8    3:     [0] {
  10    1:       INTEGER 2
         :       }
  13    1:     INTEGER 17
  16   13:     SEQUENCE {
  18    9:       OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
  29    0:       NULL
         :       }
  31   67:     SEQUENCE {
  33   19:       SET {
  35   17:         SEQUENCE {
  37   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  49    3:           IA5String 'com'
         :           }
         :         }
  54   23:       SET {
  56   21:         SEQUENCE {
  58   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  70    7:           IA5String 'example'
         :           }

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         :         }
  79   19:       SET {
  81   17:         SEQUENCE {
  83    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
  88   10:           PrintableString 'Example CA'
         :           }
         :         }
         :       }
 100   30:     SEQUENCE {
 102   13:       UTCTime 30/04/2004 14:25:34 GMT
 117   13:       UTCTime 30/04/2005 14:25:34 GMT
         :       }
 132   67:     SEQUENCE {
 134   19:       SET {
 136   17:         SEQUENCE {
 138   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
 150    3:           IA5String 'com'
         :           }
         :         }
 155   23:       SET {
 157   21:         SEQUENCE {
 159   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
 171    7:           IA5String 'example'
         :           }
         :         }
 180   19:       SET {
 182   17:         SEQUENCE {
 184    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
 189   10:           PrintableString 'Example CA'
         :           }
         :         }
         :       }
 201  159:     SEQUENCE {
 204   13:       SEQUENCE {
 206    9:         OBJECT IDENTIFIER
         :           rsaEncryption (1 2 840 113549 1 1 1)
 217    0:         NULL
         :         }
 219  141:       BIT STRING, encapsulates {
 223  137:         SEQUENCE {
 226  129:           INTEGER
         :             00 C2 D7 97 6D 28 70 AA 5B CF 23 2E 80 70 39 EE
         :             DB 6F D5 2D D5 6A 4F 7A 34 2D F9 22 72 47 70 1D
         :             EF 80 E9 CA 30 8C 00 C4 9A 6E 5B 45 B4 6E A5 E6
         :             6C 94 0D FA 91 E9 40 FC 25 9D C7 B7 68 19 56 8F
         :             11 70 6A D7 F1 C9 11 4F 3A 7E 3F 99 8D 6E 76 A5

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         :             74 5F 5E A4 55 53 E5 C7 68 36 53 C7 1D 3B 12 A6
         :             85 FE BD 6E A1 CA DF 35 50 AC 08 D7 B9 B4 7E 5C
         :             FE E2 A3 2C D1 23 84 AA 98 C0 9B 66 18 9A 68 47
         :             E9
 358    3:           INTEGER 65537
         :           }
         :         }
         :       }
 363   66:     [3] {
 365   64:       SEQUENCE {
 367   29:         SEQUENCE {
 369    3:           OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
 374   22:           OCTET STRING, encapsulates {
 376   20:             OCTET STRING
         :               08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A 4A
         :               20 84 2C 32
         :             }
         :           }
 398   14:         SEQUENCE {
 400    3:           OBJECT IDENTIFIER keyUsage (2 5 29 15)
 405    1:           BOOLEAN TRUE
 408    4:           OCTET STRING, encapsulates {
 410    2:             BIT STRING 1 unused bits
         :               '0000011'B
         :             }
         :           }
 414   15:         SEQUENCE {
 416    3:           OBJECT IDENTIFIER basicConstraints (2 5 29 19)
 421    1:           BOOLEAN TRUE
 424    5:           OCTET STRING, encapsulates {
 426    3:             SEQUENCE {
 428    1:               BOOLEAN TRUE
         :               }
         :             }
         :           }
         :         }
         :       }
         :     }
 431   13:   SEQUENCE {
 433    9:     OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
 444    0:     NULL
         :     }
 446  129:   BIT STRING
         :     6C F8 02 74 A6 61 E2 64 04 A6 54 0C 6C 72 13 AD
         :     3C 47 FB F6 65 13 A9 85 90 33 EA 76 A3 26 D9 FC
         :     D1 0E 15 5F 28 B7 EF 93 BF 3C F3 E2 3E 7C B9 52
         :     FC 16 6E 29 AA E1 F4 7A 6F D5 7F EF B3 95 CA F3

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         :     66 88 83 4E A1 35 45 84 CB BC 9B B8 C8 AD C5 5E
         :     46 D9 0B 0E 8D 80 E1 33 2B DC BE 2B 92 7E 4A 43
         :     A9 6A EF 8A 63 61 B3 6E 47 38 BE E8 0D A3 67 5D
         :     F3 FA 91 81 3C 92 BB C5 5F 25 25 EB 7C E7 D8 A1
         :   }

C.2.  End Entity Certificate Using RSA

   This appendix contains an annotated hex dump of a 629-byte version 3
   certificate.  The certificate contains the following information:

   (a)  the serial number is 18;
   (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
   (c)  the issuer's distinguished name is
        cn=Example CA,dc=example,dc=com;
   (d)  the subject's distinguished name is
        cn=End Entity,dc=example,dc=com;
   (e)  the certificate was valid from September 15, 2004 through March
        15, 2005;
   (f)  the certificate contains a 1024-bit RSA public key;
   (g)  the certificate is an end entity certificate, as the basic
        constraints extension is not present;
   (h)  the certificate contains an authority key identifier extension
        matching the subject key identifier of the certificate in
        appendix C.1; and
   (i)  the certificate includes one alternative name -- an electronic
        mail address (rfc822Name) of "end.entity@example.com".

   0  625: SEQUENCE {
   4  474:   SEQUENCE {
   8    3:     [0] {
  10    1:       INTEGER 2
         :       }
  13    1:     INTEGER 18
  16   13:     SEQUENCE {
  18    9:       OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
  29    0:       NULL
         :       }
  31   67:     SEQUENCE {
  33   19:       SET {
  35   17:         SEQUENCE {
  37   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  49    3:           IA5String 'com'
         :           }
         :         }
  54   23:       SET {

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  56   21:         SEQUENCE {
  58   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  70    7:           IA5String 'example'
         :           }
         :         }
  79   19:       SET {
  81   17:         SEQUENCE {
  83    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
  88   10:           PrintableString 'Example CA'
         :           }
         :         }
         :       }
 100   30:     SEQUENCE {
 102   13:       UTCTime 15/09/2004 11:48:21 GMT
 117   13:       UTCTime 15/03/2005 11:48:21 GMT
         :       }
 132   67:     SEQUENCE {
 134   19:       SET {
 136   17:         SEQUENCE {
 138   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
 150    3:           IA5String 'com'
         :           }
         :         }
 155   23:       SET {
 157   21:         SEQUENCE {
 159   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
 171    7:           IA5String 'example'
         :           }
         :         }
 180   19:       SET {
 182   17:         SEQUENCE {
 184    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
 189   10:           PrintableString 'End Entity'
         :           }
         :         }
         :       }
 201  159:     SEQUENCE {
 204   13:       SEQUENCE {
 206    9:         OBJECT IDENTIFIER
         :           rsaEncryption (1 2 840 113549 1 1 1)
 217    0:         NULL
         :         }
 219  141:       BIT STRING, encapsulates {
 223  137:         SEQUENCE {
 226  129:           INTEGER

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         :             00 E1 6A E4 03 30 97 02 3C F4 10 F3 B5 1E 4D 7F
         :             14 7B F6 F5 D0 78 E9 A4 8A F0 A3 75 EC ED B6 56
         :             96 7F 88 99 85 9A F2 3E 68 77 87 EB 9E D1 9F C0
         :             B4 17 DC AB 89 23 A4 1D 7E 16 23 4C 4F A8 4D F5
         :             31 B8 7C AA E3 1A 49 09 F4 4B 26 DB 27 67 30 82
         :             12 01 4A E9 1A B6 C1 0C 53 8B 6C FC 2F 7A 43 EC
         :             33 36 7E 32 B2 7B D5 AA CF 01 14 C6 12 EC 13 F2
         :             2D 14 7A 8B 21 58 14 13 4C 46 A3 9A F2 16 95 FF
         :             23
 358    3:           INTEGER 65537
         :           }
         :         }
         :       }
 363  117:     [3] {
 365  115:       SEQUENCE {
 367   33:         SEQUENCE {
 369    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 374   26:           OCTET STRING, encapsulates {
 376   24:             SEQUENCE {
 378   22:               [1] 'end.entity@example.com'
         :               }
         :             }
         :           }
 402   29:         SEQUENCE {
 404    3:           OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
 409   22:           OCTET STRING, encapsulates {
 411   20:             OCTET STRING
         :               17 7B 92 30 FF 44 D6 66 E1 90 10 22 6C 16 4F C0
         :               8E 41 DD 6D
         :             }
         :           }
 433   31:         SEQUENCE {
 435    3:           OBJECT IDENTIFIER
         :             authorityKeyIdentifier (2 5 29 35)
 440   24:           OCTET STRING, encapsulates {
 442   22:             SEQUENCE {
 444   20:               [0]
         :                 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
         :                 4A 20 84 2C 32
         :               }
         :             }
         :           }
 466   14:         SEQUENCE {
 468    3:           OBJECT IDENTIFIER keyUsage (2 5 29 15)
 473    1:           BOOLEAN TRUE
 476    4:           OCTET STRING, encapsulates {
 478    2:             BIT STRING 6 unused bits
         :               '11'B

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         :             }
         :           }
         :         }
         :       }
         :     }
 482   13:   SEQUENCE {
 484    9:     OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
 495    0:     NULL
         :     }
 497  129:   BIT STRING
         :     00 20 28 34 5B 68 32 01 BB 0A 36 0E AD 71 C5 95
         :     1A E1 04 CF AE AD C7 62 14 A4 1B 36 31 C0 E2 0C
         :     3D D9 1E C0 00 DC 10 A0 BA 85 6F 41 CB 62 7A B7
         :     4C 63 81 26 5E D2 80 45 5E 33 E7 70 45 3B 39 3B
         :     26 4A 9C 3B F2 26 36 69 08 79 BB FB 96 43 77 4B
         :     61 8B A1 AB 91 64 E0 F3 37 61 3C 1A A3 A4 C9 8A
         :     B2 BF 73 D4 4D E4 58 E4 62 EA BC 20 74 92 86 0E
         :     CE 84 60 76 E9 73 BB C7 85 D3 91 45 EA 62 5D CD
         :   }

C.3.  End Entity Certificate Using DSA

   This appendix contains an annotated hex dump of a 914-byte version 3
   certificate.  The certificate contains the following information:

   (a)  the serial number is 256;

   (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;

   (c)  the issuer's distinguished name is cn=Example DSA
        CA,dc=example,dc=com;

   (d)  the subject's distinguished name is cn=DSA End
        Entity,dc=example,dc=com;

   (e)  the certificate was issued on May 2, 2004 and expired on May 2,
        2005;

   (f)  the certificate contains a 1024-bit DSA public key with
        parameters;

   (g)  the certificate is an end entity certificate (not a CA
        certificate);

   (h)  the certificate includes a subject alternative name of
        "<http://www.example.com/users/DSAendentity.html>" and an issuer
        alternative name of "<http://www.example.com>" -- both are URLs;

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   (i)  the certificate includes an authority key identifier extension
        and a certificate policies extension specifying the policy OID
        2.16.840.1.101.3.2.1.48.9; and

   (j)  the certificate includes a critical key usage extension
        specifying that the public key is intended for verification of
        digital signatures.

   0  910: SEQUENCE {
   4  846:   SEQUENCE {
   8    3:     [0] {
  10    1:       INTEGER 2
         :       }
  13    2:     INTEGER 256
  17    9:     SEQUENCE {
  19    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
         :       }
  28   71:     SEQUENCE {
  30   19:       SET {
  32   17:         SEQUENCE {
  34   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  46    3:           IA5String 'com'
         :           }
         :         }
  51   23:       SET {
  53   21:         SEQUENCE {
  55   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  67    7:           IA5String 'example'
         :           }
         :         }
  76   23:       SET {
  78   21:         SEQUENCE {
  80    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
  85   14:           PrintableString 'Example DSA CA'
         :           }
         :         }
         :       }
 101   30:     SEQUENCE {
 103   13:       UTCTime 02/05/2004 16:47:38 GMT
 118   13:       UTCTime 02/05/2005 16:47:38 GMT
         :       }
 133   71:     SEQUENCE {
 135   19:       SET {
 137   17:         SEQUENCE {
 139   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)

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 151    3:           IA5String 'com'
         :           }
         :         }
 156   23:       SET {
 158   21:         SEQUENCE {
 160   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
 172    7:           IA5String 'example'
         :           }
         :         }
 181   23:       SET {
 183   21:         SEQUENCE {
 185    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
 190   14:           PrintableString 'DSA End Entity'
         :           }
         :         }
         :       }
 206  439:     SEQUENCE {
 210  300:       SEQUENCE {
 214    7:         OBJECT IDENTIFIER dsa (1 2 840 10040 4 1)
 223  287:         SEQUENCE {
 227  129:           INTEGER
         :             00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC FB 95
         :             32 AC 01 12 33 B9 E0 1C AD 90 9B BC 48 54 9E F3
         :             94 77 3C 2C 71 35 55 E6 FE 4F 22 CB D5 D8 3E 89
         :             93 33 4D FC BD 4F 41 64 3E A2 98 70 EC 31 B4 50
         :             DE EB F1 98 28 0A C9 3E 44 B3 FD 22 97 96 83 D0
         :             18 A3 E3 BD 35 5B FF EE A3 21 72 6A 7B 96 DA B9
         :             3F 1E 5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
         :             FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48 63 FE
         :             43
 359   21:           INTEGER
         :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA 55 F7
         :             7D 57 74 81 E5
 382  129:           INTEGER
         :             00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91 C0 8E
         :             47 F1 0A C3 01 47 C2 44 42 36 A9 92 81 DE 57 C5
         :             E0 68 86 58 00 7B 1F F9 9B 77 A1 C5 10 A5 80 91
         :             78 51 51 3C F6 FC FC CC 46 C6 81 78 92 84 3D F4
         :             93 3D 0C 38 7E 1A 5B 99 4E AB 14 64 F6 0C 21 22
         :             4E 28 08 9C 92 B9 66 9F 40 E8 95 F6 D5 31 2A EF
         :             39 A2 62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
         :             F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE 1E 57
         :             18
         :           }
         :         }
 514  132:       BIT STRING, encapsulates {
 518  128:         INTEGER

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         :           30 B6 75 F7 7C 20 31 AE 38 BB 7E 0D 2B AB A0 9C
         :           4B DF 20 D5 24 13 3C CD 98 E5 5F 6C B7 C1 BA 4A
         :           BA A9 95 80 53 F0 0D 72 DC 33 37 F4 01 0B F5 04
         :           1F 9D 2E 1F 62 D8 84 3A 9B 25 09 5A 2D C8 46 8E
         :           2B D4 F5 0D 3B C7 2D C6 6C B9 98 C1 25 3A 44 4E
         :           8E CA 95 61 35 7C CE 15 31 5C 23 13 1E A2 05 D1
         :           7A 24 1C CB D3 72 09 90 FF 9B 9D 28 C0 A1 0A EC
         :           46 9F 0D B8 D0 DC D0 18 A6 2B 5E F9 8F B5 95 BE
         :         }
         :       }
 649  202:     [3] {
 652  199:       SEQUENCE {
 655   57:         SEQUENCE {
 657    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 662   50:           OCTET STRING, encapsulates {
 664   48:             SEQUENCE {
 666   46:               [6]
         :                 'http://www.example.com/users/DSAendentity.'
         :                 'html'
         :               }
         :             }
         :           }
 714   33:         SEQUENCE {
 716    3:           OBJECT IDENTIFIER issuerAltName (2 5 29 18)
 721   26:           OCTET STRING, encapsulates {
 723   24:             SEQUENCE {
 725   22:               [6] 'http://www.example.com'
         :               }
         :             }
         :           }
 749   29:         SEQUENCE {
 751    3:           OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
 756   22:           OCTET STRING, encapsulates {
 758   20:             OCTET STRING
         :               DD 25 66 96 43 AB 78 11 43 44 FE 95 16 F9 D9 B6
         :               B7 02 66 8D
         :             }
         :           }
 780   31:         SEQUENCE {
 782    3:           OBJECT IDENTIFIER
         :             authorityKeyIdentifier (2 5 29 35)
 787   24:           OCTET STRING, encapsulates {
 789   22:             SEQUENCE {
 791   20:               [0]
         :                 86 CA A5 22 81 62 EF AD 0A 89 BC AD 72 41 2C
         :                 29 49 F4 86 56
         :               }
         :             }

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         :           }
 813   23:         SEQUENCE {
 815    3:           OBJECT IDENTIFIER certificatePolicies (2 5 29 32)
 820   16:           OCTET STRING, encapsulates {
 822   14:             SEQUENCE {
 824   12:               SEQUENCE {
 826   10:                 OBJECT IDENTIFIER '2 16 840 1 101 3 2 1 48 9'
         :                 }
         :               }
         :             }
         :           }
 838   14:         SEQUENCE {
 840    3:           OBJECT IDENTIFIER keyUsage (2 5 29 15)
 845    1:           BOOLEAN TRUE
 848    4:           OCTET STRING, encapsulates {
 850    2:             BIT STRING 7 unused bits
         :               '1'B (bit 0)
         :             }
         :           }
         :         }
         :       }
         :     }
 854    9:   SEQUENCE {
 856    7:     OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
         :     }
 865   47:   BIT STRING, encapsulates {
 868   44:     SEQUENCE {
 870   20:       INTEGER
         :         65 57 07 34 DD DC CA CC 5E F4 02 F4 56 42 2C 5E
         :         E1 B3 3B 80
 892   20:       INTEGER
         :         60 F4 31 17 CA F4 CF FF EE F4 08 A7 D9 B2 61 BE
         :         B1 C3 DA BF
         :       }
         :     }
         :   }

C.4.  Certificate Revocation List

   This appendix contains an annotated hex dump of a version 2 CRL with
   two extensions (cRLNumber and authorityKeyIdentifier).  The CRL was
   issued by cn=Example CA,dc=example,dc=com on February 5, 2005; the
   next scheduled issuance was February 6, 2005.  The CRL includes one
   revoked certificate: serial number 18, which was revoked on November
   19, 2004 due to keyCompromise.  The CRL itself is number 12, and it
   was signed with RSA and SHA-1.

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

   0  352: SEQUENCE {
   4  202:   SEQUENCE {
   7    1:     INTEGER 1
  10   13:     SEQUENCE {
  12    9:       OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
  23    0:       NULL
         :       }
  25   67:     SEQUENCE {
  27   19:       SET {
  29   17:         SEQUENCE {
  31   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  43    3:           IA5String 'com'
         :           }
         :         }
  48   23:       SET {
  50   21:         SEQUENCE {
  52   10:           OBJECT IDENTIFIER
         :             domainComponent (0 9 2342 19200300 100 1 25)
  64    7:           IA5String 'example'
         :           }
         :         }
  73   19:       SET {
  75   17:         SEQUENCE {
  77    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
  82   10:           PrintableString 'Example CA'
         :           }
         :         }
         :       }
  94   13:     UTCTime 05/02/2005 12:00:00 GMT
 109   13:     UTCTime 06/02/2005 12:00:00 GMT
 124   34:     SEQUENCE {
 126   32:       SEQUENCE {
 128    1:         INTEGER 18
 131   13:         UTCTime 19/11/2004 15:57:03 GMT
 146   12:         SEQUENCE {
 148   10:           SEQUENCE {
 150    3:             OBJECT IDENTIFIER cRLReason (2 5 29 21)
 155    3:             OCTET STRING, encapsulates {
 157    1:               ENUMERATED 1
         :               }
         :             }
         :           }
         :         }
         :       }
 160   47:     [0] {
 162   45:       SEQUENCE {

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

 164   31:         SEQUENCE {
 166    3:           OBJECT IDENTIFIER
         :             authorityKeyIdentifier (2 5 29 35)
 171   24:           OCTET STRING, encapsulates {
 173   22:             SEQUENCE {
 175   20:               [0]
         :                 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
         :                 4A 20 84 2C 32
         :               }
         :             }
         :           }
 197   10:         SEQUENCE {
 199    3:           OBJECT IDENTIFIER cRLNumber (2 5 29 20)
 204    3:           OCTET STRING, encapsulates {
 206    1:             INTEGER 12
         :             }
         :           }
         :         }
         :       }
         :     }
 209   13:   SEQUENCE {
 211    9:     OBJECT IDENTIFIER
         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
 222    0:     NULL
         :     }
 224  129:   BIT STRING
         :     22 DC 18 7D F7 08 CE CC 75 D0 D0 6A 9B AD 10 F4
         :     76 23 B4 81 6E B5 6D BE 0E FB 15 14 6C C8 17 6D
         :     1F EE 90 17 A2 6F 60 E4 BD AA 8C 55 DE 8E 84 6F
         :     92 F8 9F 10 12 27 AF 4A D4 2F 85 E2 36 44 7D AA
         :     A3 4C 25 38 15 FF 00 FD 3E 7E EE 3D 26 12 EB D8
         :     E7 2B 62 E2 2B C3 46 80 EF 78 82 D1 15 C6 D0 9C
         :     72 6A CB CE 7A ED 67 99 8B 6E 70 81 7D 43 42 74
         :     C1 A6 AF C1 55 17 A2 33 4C D6 06 98 2B A4 FC 2E
         :   }

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Authors' Addresses

   David Cooper
   National Institute of Standards and Technology
   100 Bureau Drive, Mail Stop 8930
   Gaithersburg, MD 20899-8930
   USA
   EMail: david.cooper@nist.gov

   Stefan Santesson
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA
   EMail: stefans@microsoft.com

   Stephen Farrell
   Distributed Systems Group
   Computer Science Department
   Trinity College Dublin
   Ireland
   EMail: stephen.farrell@cs.tcd.ie

   Sharon Boeyen
   Entrust
   1000 Innovation Drive
   Ottawa, Ontario
   Canada K2K 3E7
   EMail: sharon.boeyen@entrust.com

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA
   EMail: housley@vigilsec.com

   Tim Polk
   National Institute of Standards and Technology
   100 Bureau Drive, Mail Stop 8930
   Gaithersburg, MD 20899-8930
   USA
   EMail: wpolk@nist.gov

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RFC 5280            PKIX Certificate and CRL Profile            May 2008

Full Copyright Statement

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