PKIX Working Group R. Housley (SPYRUS)
Internet Draft W. Ford (Nortel)
D. Solo (BBN)
expires in six months February 1996
Internet Public Key Infrastructure
Part I: X.509 Certificate and CRL Profile
<draft-ietf-pkix-ipki-part1-01.txt>
Status of this Memo
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Abstract
This is the second draft of the Internet Public Key Infrastructure
X.509 Certificate and CRL Profile. This document was sections 1
through 5 and section 11 of draft-ietf-pkix-ipki-00.txt. That
original document has been divided into four parts; it was simply too
big. This is the first part. Many changes are the result of
discussion at the Dallas IETF in December 1995 and discussion on the
ietf-pkix@tandem.com mail list. The intent of this document is to
generate further productive discussion and build concensus.
1 Executive Summary
<< Write this last. >>
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2 Requirements and Assumptions
Goal is to develop a profile and associated management structure to
facilitate the adoption/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, electronic payment systems, IPSEC, as well as others.
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, as
opposed to syntax.
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
application developers can obtain necessary information without
regard to the issuer of a particular certificate or certificate
revocation list (CRL).
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 be more appropriate method 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
availablity. In addition, the profile allows for the presence of
firewall or other filtered communication.
2.2 Acceptability Criteria
The goal of the Internet Public Key Infrstructure (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.
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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, and the key manager for IPSEC within a router. This
profile recognizes the limitations of the platforms these users
employ and the sophistication/attentiveness of the users themselves.
This manifests itself in minimal user configuration responsibility
(e.g., root keys, rules), explicit platform usage constraints within
the certificate, certification path constraints which shield the user
from many malicious actions, and applications which sensibly automate
validation functions.
2.4 Administrator Expectations
As with users, the Internet PKI profile is structured to support the
individuals who generally operate Certification Authorities (CAs).
Providing administrators with unbounded choices increases the chances
that a subtle CA administrator mistake will result in broad
compromise. Also, unbounded choices greatly complicates the software
that must 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 PKIX specifications.
+---+
| C | +------------+
| e | <-------------------->| End entity |
| r | Operational +------------+
| t | transactions ^
| | and management | Management
| / | transactions | transactions
| | |
| C | PKI users v
| R | -------+-------+--------+------
| L | PKI management ^ ^
| | entities | |
| | v |
| R | +------+ |
| e | <-------------- | RA | <-----+ |
| p | certificate | | | |
| o | publish +------+ | |
| s | | |
| i | v v
| t | +------------+
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| o | <--------------------------| CA |
| r | certificate publish +------------+
| y | CRL publish ^
| | |
+---+ | Management
| transactions
v
+------+
| CA |
+------+
Figure 1 - PKI Entities
The components in this model are:
end entity: user of PKI certificates and/or end user system that
the PKI certifies;
CA: certification authority;
RA: registration authority, i.e., an optional system to
which a CA delegates certain manaagement functions;
repository: a system or collection of distributed systems that
store certificates and CRLs and serves as a means of
distributing these certificates and CRLs to end entities.
3.1 X.509 Version 3 Certificate
Application of public key technology requires the user of a public
key to be confident that the public key belongs to 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 subject identities. The binding is
achieved by having a trusted certification authority (CA) digitally
sign each certificate. 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
untrusted communications and server systems, and can be cached in
unsecured storage in certificate-using systems.
The standard known as 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. 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. These two fields are used to
support directory access control.
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The Internet Privacy Enhanced Mail (PEM) proposals, published in
1993, include specifications for a public key infrastructure based on
X.509 v1 certificates [RFC 1422]. The experience gained in attempts
to deploy RFC 1422 made it clear that the v1 and v2 certificate
formats are deficient in several respects. Most importantly, more
fields were needed to carry information which PEM design and
implementation experience has proven necessary. In response to these
new requirements, ISO/IEC 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 August 1995,
standardization of the basic v3 format was completed [ISO TC].
ISO/IEC and ANSI X9 have also developed a set of standard extensions
for use in the v3 extensions field [ISO DAM, ANSI 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 and ANSI 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,
then it might need an additional certificate to obtain that public
key. In general, a chain of multiple certificates 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 (often one) 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:
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(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 must
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 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.
The RFC 1422 CA hierarchical model has been found to have several
deficiencies, including:
(a) The pure top-down hierarchy, with all ertification paths
starting from the root, is too restrictive for many purposes. For
some applications, verification of certification paths should start
with a public key of a CA in a user's own domain, rather than
mandating that verification commence at the top of a hierarchy. In
many environments, the local domain is often the most trusted. Also,
initialization and key-pair-update operations can be more effectively
conducted between an end entity and a local management system.
(b) The name subordination rule introduces undesirable constraints
upon the X.500 naming system an organization may use.
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(c) Use of the PCA concept requires knowledge of individual PCAs to
be built into certificate chain verification logic. In the
particular case of Internet mail, this is not a major problem -- the
PCA name can always be displayed to the human user who can make a
decision as to what trust to imply from a particular chain. However,
in many commercial applications, such as electronic commerce or EDI,
operator intervention to make policy decisions is impractical. The
process needs to be automated to a much higher degree. In fact, the
full process of certificate chain processing needs to be
implementable in trusted software.
Because of the above shortcomings, it is proposed that more flexible
CA structures than the RFC 1422 hierarchy be supported by the PKIX
specifications. In fact, the main reason for the structural
restrictions imposed by RFC 1422 was the restricted certificate
format provided with X.509 v1. 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.
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 might 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 which is signed by a CA 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 CA
issues a new CRL on a regular periodic basis (e.g., hourly, daily, or
weekly). Entries are added to CRLs as revocations occur, and an
entry may be removed when the certificate expiration date is reached.
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An advantage of this revocation method is that CRLs may be
distributed by exactly the same means as certificates themselves,
namely, via untrusted communications and server systems.
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
revocation is reported now, that revocation will not be reliably
notified to certificate-using systems until the next periodic CRL is
issued -- this may be up to one hour, one day, or one week depending
on the frequency that the CA issues CRLs.
Another potential problem with CRLs is the risk of a CRL growing to
an entirely unacceptable size. In the 1988 and 1993 versions of
X.509, the CRL for the end-user certificates needed to cover the
entire population of end-users for one CA. It is desirable to allow
such populations to be in the range of thousands, tens of thousands,
or possibly even hundreds of thousands of users. The end-user CRL is
therefore at risk of growing to such sizes, which present major
communication and storage overhead problems. With the version 2 CRL
format, introduced along with the v3 certificate format, it becomes
possible to arbitrarily divide the population of certificates for one
CA into a number of partitions, each partition being associated with
one CRL distribution point (e.g., directory entry or URL) from which
CRLs are distributed. Therefore, the maximum CRL size can be
controlled by a CA. Separate CRL distribution points can also exist
for different revocation reasons. For example, routine revocations
(e.g., name change) may be placed on a different CRL to revocations
resulting from suspected key compromises, and policy may specify that
the latter CRL be updated and issued more frequently than the former.
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 such profiles.
Furthermore, it is recognized that on-line methods of revocation
notification may be applicable in some environments as an alternative
to the X.509 CRL. On-line revocation checking eliminates the latency
between a revocation report and CRL the next issue. Once the
revocation is reported, any query to the on- line service will
correctly reflect the certificate validation impacts of the
revocation. Therefore, this document will also consider standard
approaches to on-line revocation notification.
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3.4 Operational Protocols
Operational protocols are required to deliver certificates and CRLs
to certificate using client systems. Provision is needed for a
variety of different means of certificate and CRL delivery, including
request/delivery procedures based on E-mail, http, X.500, and
WHOIS++. These specifications include definitions of, and/or
references to, 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 Public Key Infrastructure (PKI) components. For example,
management protocol might be used between a CA and a client system
with which a key pair is associated, or between two CAs which cross-
certify each other. The set of functions which 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, prior to that CA issuing a certificate or
certificates for that user.
(b) initialization: Before a client system can operate securely it
is necessary to install in it necessary key materials which have the
appropriate relationship with keys stored elsewhere in the
infrastructure. For example, the client needs to be securely
initialized with the public key of a CA, 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 public
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 associated with a CA. 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
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abnormal situation requiring certificate revocation.
(g) cross-certification: Two CAs exchange the information necessary
to establish cross-certificates between those CAs.
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 through 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.
Part 3 of 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 (on-line, e-mail,
and WWW) are also specified.
4 Certificate and Certificate Extensions Profile
As described above, the goal of this section is to create a profile
for X.509 v3 certificates that will foster interoperability and a
reusable public key infrastructure. To achieve this goal, some
assumptions need to be made about the nature of information to be
included along with guidelines for how extensibility will be
employed.
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 section 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. This section defines a
baseline set of information, common locations within a certificate
for this information, and common representations for this
information. Environments with additional requirements may build on
this profile or may replace it.
4.1 Basic Certificate Fields
The X.509 v3 certificate Basic syntax follows. For signature
calculation, the certificate is ASN.1 DER encoded [reference X.509?].
ASN.1 DER encoding is a tag, length, value encoding system for each
element.
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Certificate ::= SIGNED { 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 UTCTime,
notAfter UTCTime }
UniqueIdentifier ::= BIT STRING
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }
The following items describe a proposed use of the X.509 v3
certificate for the Internet.
4.1.1 Version
This field describes the version of the encoded certificate. When
extensions are used, as expected in this profile, use X.509 version 3
(value is 2). If no extensions are present, but a UniqueIdentifier
is present, use version 2 (value is 1). If only basic fields are
present, use version 1 (the value is absent).
Implementations should be prepared to accept any version certificate.
In particular, at a minimum, implementations should recognize version
3 certificates; determine whether any critical extensions are
present; and accept certificates without critical extensions even if
they don't recognize any extensions. A certificate with an
unrecognized critical extension must always be rejected.
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Generation of version 2 certificates is not expected by CAs using
this profile.
4.1.2 Serial number
The serial number is an integer assigned by the CA to each
certificate. It must be unique for each certificate issued by a CA
(i.e., the issuer name and serial number identify a unique
certificate).
<< Do we want to define a maximum value for the serial number? >>
4.1.3 Signature
This field contains the algorithm identifier for the algorithm used
to sign the certificate. Section 7.2 of this profile lists the
supported signature algorithms.
4.1.4 Issuer Name
The issuer name (combined with the IssuerUniqueID, if present)
provides a globally unique identifier of the authority signing the
certificate. Reliance on the IssuerUniqueID is strongly discouraged.
The syntax of the issuer name is an X.500 distinguished name. A name
in the certificate may provide semantic information, may provide a
reference to an external information store or service, provides a
unique identifier, may provide authorization information, or may
provide a basis for managing the CA relationships and certificate
paths (other purposes are also possible). This strawman suggests
that the issuer (and subject) name fields must provide a globally
unique identifier. In addition, they should contain semantic
information identifying the issuer/subject (e.g. a full name,
organization name, etc.). Access information will be provided in a
separate extension (when other than via X.500 directory) and internet
specific identities (electronic mail address, DNS name, and URLs)
will be carried in alternative name extensions.
<< Further discussion of naming guidelines for internet use is
needed. >>
4.1.5 Validity
This field indicates the dates on which the certificate becomes valid
(notBefore) and on which the certificate ceases to be valid
(notAfter).
The UTCTime (Coordinated Universal Time) values included in this
field shall be expressed in Greenwich Mean Time (Zulu) and include
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granularity to the minute, even though finer granularity can be
expressed in the UTCTime format. That is, UTCTime should be
expressed as YYMMDDHHMMZ.
Implementors are warned that no DER is defined for UTCTime, thus
transformation between local time representations and the DER
transfer syntax must be performed carefully when computing the hash
value for a certificate signature. For example, a UTCTime value
which includes explict, zero values for seconds will not produce the
same hash value as one in which the seconds are omitted. UTCTime
expresses the value of a year modulo 100, with no indication of
century, hence comparisons involving dates in different centuries
must be performed with care.
4.1.6 Subject Name
The purpose of the subject name (combined with the SubjectUniqueID,
if present) is to provide a unique identifier of the subject of the
certificate. Reliance on the IssuerUniqueID is discouraged. The
syntax of the subject name is an X.500 distinguished name. The
discussion in section 4.1.4 on issuer names applies to subject names
as well.
<< How do we bind a public key to an Internet e-mail address? One
alternative is to make Subject Name as a unique identifier. Or, it
could be legal to have a null Subject Name. Either way the
SubjectAltName contains the e-mail address. >>
4.1.7 Subject Public Key Info
This field is used to carry the public key and identify the algorithm
with which the key is used.
4.1.8 Unique Identifiers
The subject and issuer unique identifier are present in the
certificate to handle the possibility of reuse of subject and/or
issuer names over time. This profile strongly recommends that names
not be reused, thus certificates conforming to this profile do not
make use of unique identifiers.
4.2 Certificate Extensions
The extensions already defined by ANSI X9 and ISO for X.509 v3
certificates provide methods for associating additional attributes
with users or public keys and for managing the certification
hierarchy. The X.509 v3 certificate format also allows communities to
define private extensions to carry information unique to those
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communities. Each extension in a certificate may be designated as
critical or non-critical. A certificate using system (an application
validating a certificate) must reject the certificate if it
encounters a critical extension it does not recognize. A non-
critical extension may be ignored if it is not recognized. The
following presents recommended extensions used within Internet
certificates and standard locations for information. Communities may
elect to use additional extensions; however, caution should be
exercised in adopting any critical extensions in certificates which
might be used in a general context.
<< Need to add table of OIDs for all extensions from X.509 and X9.55.
Say which are allowed in this profile, and which are prohibited in
this profile. >>
4.2.1 Subject Alternative Name
The altNames extension allows additional identities to be bound to
the subject of the certificate. Defined options include an rfc822
name (electronic mail address), a DNS name, and a URL. Each of these
are IA5 strings. Multiple instances may be included. Whenever such
identities are to be bound in a certificate, the subject alternative
name (or issuer alternative name) field shall be used. A form of
such an identifier may also be present in the subject distinguished
name; however, the altName field is the preferred location for
finding such information.
The following definition is an enhanced version of the X9.55
definition of GeneralName. This definition is anticipated to be used
in the X.509 Amendment.
rfc822Name, dNSName, url, and ipAddress are name forms expected to be
used with this profile. Such names are subject to the basic
constraint extension for issuers which may restrict the names a given
CA can certify (see section on Basic Constraint extension).
The use of otherName should not be used in conjunction with this
profile.
AltNames ::= SEQUENCE OF GeneralName
GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] IA5String,
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url [6] IA5String,
ipAddress [7] OCTET STRING }
4.2.2 Issuer Alternative Name
As with 4.2.1, this extension is used to bind Internet style
identities to the issuer name.
4.2.3 Certificate Policies
The certificatePolicies extension contains one or more object
identifiers (OIDs). Each OID indicates the policy under which the
certificate has been issued. This profile expects that a simple OID
will be present in each PolicyElementInfo. The qualifier within the
PolicyElementInfo should be absent.
Implementations processing certificate policy fields are expected to
have lists of those policies which they will accept. The
implementations compare the policy identifier(s) in the certificate
to that list. This field provides information to be used at the
discretion of a relying party. In contrast, the policy identifier(s)
in the keyUsageRestriction is a mandate by the issuer that a
certificate be used only in particular environments.
CertificatePolicies ::= SEQUENCE OF PolicyInformation
PolicyInformation ::= SEQUENCE OF PolicyElementInfo
PolicyElementInfo ::= SEQUENCE {
policyElementId OBJECT IDENTIFIER,
qualifier ANY DEFINED BY policyElementId OPTIONAL }
4.2.4 Key Attributes
The keyAttributes extension contains information about the key itself
including a unique key identifier, a key usage period (lifetime of
the private key as opposed to the lifetime of the certificate), and
an intended key usage. The Internet certificate should use the
keyAttributes extension and contain a key identifier and private key
validity to aid in system management. The key usage field in this
extension is intended to be advisory (as contrasted with the key
usage restriction extension which imposes mandatory restrictions).
The key usage field in this extension should be used to differentiate
certificates containing public keys for validating CA certificate
signatures, for validating CA CRL signatures, and validating
signatures on on-line transactions. However, the nonrepudiation and
dataEncipherment values should not be used. Where a reference to a
public key identifier is needed (as with an Authority Key ID) and is
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not included in an attribute in the associated certificate, an SHA-1
hash of the public key shall be used.
The GeneralizedTime values included in this field shall be expressed
in Greenwich Mean Time (Zulu) and include granularity to the minute,
even though finer granularity can be expressed in the GeneralizedTime
format. That is, GeneralizedTime should be expressed as
YYYYMMDDHHMMZ.
Implementors are warned that no DER is defined for GeneralizedTime,
thus transformation between local time representations and the DER
transfer syntax must be performed carefully when computing the hash
value for a certificate signature. For example, a GeneralizedTime
value which includes explict, zero values for seconds will not
produce the same hash value as one in which the seconds are omitted.
GeneralizedTime expresses the using four digits. Remember that
UTCTime represents the value of a year modulo 100, with no indication
of century.
KeyAttributes ::= SEQUENCE {
keyIdentifier KeyIdentifier OPTIONAL,
intendedKeyUsage KeyUsage OPTIONAL,
privateKeyUsagePeriod PrivateKeyValidity OPTIONAL }
KeyIdentifier ::= OCTET STRING
PrivateKeyValidity ::= SEQUENCE {
notBefore [0] GeneralizedTime OPTIONAL,
notAfter [1] GeneralizedTime OPTIONAL }
KeyUsage ::= BIT STRING {
digitalSignature (0),
nonRepudiation (1),
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),
offLineCRLSign (6) }
4.2.5 Key Usage Restriction
The keyUsageRestriction extension defines mandatory restrictions on
the use of the key contained in the certificate based on policy
and/or usage (e.g., signature, encryption). This field should be
used whenever the use of the key is to be restricted based on either
usage or policy (see discussion in policies). The usage restriction
would be employed when a multipurpose key is to be restricted (e.g.,
when an RSA key should be used only for signing or only for key
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encipherment).
The policy restriction in this field provides a mandate by the issuer
that a certificate be used only in selected environments (for
example, that a certificate be used only for a given type of
financial transaction). In contrast, the policy identifier in the
certificatePolicies extension is information which may be used at the
discretion of a relying party.
keyUsageRestriction ::= SEQUENCE {
certPolicySet SEQUENCE OF CertPolicyId OPTIONAL,
restrictedKeyUsage KeyUsage OPTIONAL }
4.2.6 Basic Constraints
The basicConstraints extension identifies whether the subject of the
certificate is a CA or an end user. In addition, this field can
limit the authority of a subject CA in terms of the certificates it
can issue. Discussion of certification path restriction is covered
elsewhere in this draft. The subject type field should be present in
all Internet certificates.
basicConstraints ::= SEQUENCE {
subjectType SubjectType,
pathLenConstraint INTEGER OPTIONAL,
permittedSubtrees [0] SEQUENCE OF GeneralName OPTIONAL,
excludedSubtrees [1] SEQUENCE OF GeneralName OPTIONAL }
SubjectType ::= BIT STRING {
cA (0),
endEntity (1) }
4.2.7 CRL Distribution Points
The cRLDistributionPoints extension identifies the CRL distribution
point or points to which a certificate user should refer to acertain
if the certificate has been revoked. This extenstion provides a
mechanism to divide the CRL inot manageable pieces if the CA has a
large constituency. Further discussion of CRL management is
contained in section 5.
4.2.8 Authority Key Identifier
The authority key identifier extension provides a means of
identifying the particular public key used to sign a certificate.
The identification can be based on either the key identifier (from
the key Attributes extension) or on the issuer name and serial
number. The key identifier method is recommended in this profile.
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This extension would be used where an issuer has multiple signing
keys (either due to multiple concurrent key pairs or due to
changeover). In general, this extension should be included in
certificates. If the issuer name/serial number approach is used, both
the certIssuer and certSerialNumber fields must be present.
authorityKeyId ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
certIssuer [1] Name OPTIONAL,
certSerialNumber [2] CertificateSerialNumber OPTIONAL }
4.2.9 Subject Directory Attributes
The DAM provides an extension for subject directory attributes. This
extension may hold any information about the subject where that
information has a defined X.500 Directory attribute. This extension
is not recommended as an essential part of this profile but may be
used in local environments. This extension is always non-critical.
subjectDirectoryAttributes ::= SEQUENCE OF Attribute
4.2.10 Information Access
The informationAccess field is proposed as a private extension to
tell how information about a subject or CA (or ancillary CA services)
may be accessed. For example, this field might provide a pointer to
information about a user (e.g., a URL) or might tell how to access CA
information such as certificate status or on-line validation
services.
In many cases, the accuracy of this information is not certified by
the CA.
<< Can IssuerAltNames and SubjectAltNames be used instead of some of
this information? If not, then add a paragraph describing each of
the optional components? >>
informationAccess ::= SEQUENCE {
certRetrieval GeneralName OPTIONAL,
certValidation GeneralName OPTIONAL,
caInfo GeneralName OPTIONAL,
userInfo GeneralName OPTIONAL }
Url ::= IA5String
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4.2.11 Other extensions
The X.509 DAM defines additional extensions; however, this
specification does not include them in the profile.
<< policyMappings? We could say this optional. It is non-critical,
so not problematical. >>
<< nameConstraints. We should add a paragraph that strictly forbids
use of this extensions. >>
<< policyConstraints? We should encourage support of this extension.
Since it is critical, we should include it in our profile so that all
implementations are prepared to process it. It will be needed for
interoperability in the future. >>
4.3 Examples
<< Certificate samples including descriptive text and ASN.1 encoded
blobs will be inserted. >>
5 CRL and CRL Extensions Profile
As described 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. Emphasis is placed on support for
X.509 v2 CRLs. The profile defines a baseline set of information
that can be expected in every CRL. Also, the profile defines common
locations within the CRL for frequently used attributes, and common
representations for these attributes.
Environments with additional or special purpose requirements may
build on this profile or may replace it.
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 ::= SIGNED { SEQUENCE {
version Version OPTIONAL,
-- if present, must be v2
signature AlgorithmIdentifier,
issuer Name,
thisUpdate UTCTime,
nextUpdate UTCTime,
revokedCertificates SEQUENCE OF SEQUENCE {
userCertificate CertificateSerialNumber,
revocationDate UTCTime,
crlEntryExtensions Extensions OPTIONAL } OPTIONAL,
crlExtensions [0] Extensions OPTIONAL } }
Version ::= INTEGER { v1(0), v2(1), v3(2) }
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
CertificateSerialNumber ::= INTEGER
Extensions ::= SEQUENCE OF Extension
Extension ::= SEQUENCE {
extnId OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }
-- contains a DER encoding of a value
-- of the type registered for use with
-- the extnId object identifier value
The following items describe the proposed use of the X.509 v2 CRL for
in Internet PKI.
5.1.1 Version
This field describes the version of the encoded CRL. When extensions
are used, as expected in this profile, use version 2 (the integer
value is 1). If neither CRL extensions nor CRL entry extensions are
present, use version 1 (the integer value must be omitted).
5.1.2 Signature
This field contains the algorithm identifier for the algorithm used
to sign the CRL. Section 7.2 lists the signature algorithms used in
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the Internet PKI.
5.1.3 Issuer Name
The issuer name provides a globally unique identifier of the
certification authority signing the CRL. The syntax of the issuer
name is an X.500 distinguished name.
5.1.4 Last Update
This field indicates the issue date of this CRL.
The UTCTime (Coordinated Universal Time) value included in this field
shall be expressed in Greenwich Mean Time (Zulu) and include
granularity to the minute, even though finer granularity can be
expressed in the UTCTime format. That is, UTCTime should be
expressed as YYMMDDHHMMZ.
Implementors are warned that no DER is defined for UTCTime, thus
transformation between local time representations and the DER
transfer syntax must be performed carefully when computing the hash
value for a CRL signature. For example, a UTCTime value which
includes explict, zero values for seconds will not produce the same
hash value as one in which the seconds are omitted. UTCTime
expresses the value of a year modulo 100, with no indication of
century, hence comparisons involving dates in different centuries
must be performed with care.
5.1.5 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.
The same restrictions associated with UTCTime for Last Update apply
to Next Update.
5.1.6 Revoked Certificates
Revoked certificates are listed. The revoked certificates are named
by their serial numbers. Certificates are uniquely identified by the
combination of the issuer name and the user certificate serial
number. The date on which the revocation occured is specified. The
same restrictions associated with UTCTime for Last Update apply to
the revocation date. CRL entry extensions are discussed in section
5.3.
When a CA wishes to revoke a certificate that it issued to another
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CA, the revocation shall appear on the CRL. The revocation should
also appear on the ARL. The CA is revoking a certificate that it
issued.
5.2 CRL Extensions
The extensions already defined by ANSI X9 and ISO for X.509 v2 CRLs
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. A
CRL validation must fail if it encounters an critical extension which
it does not know how to process. However, an unrecognized non-
critical extension may be ignored. The following presents those
extensions used within Internet CRLs. Communities may elect to use
additional extensions; however, caution should be exercised in
adopting any critical extensions in CRLs which might be used in a
general context.
<< Need to add table of OIDs for all extensions from X.509 and X9.55.
Say which are allowed in this profile, and which are prohibited in
this profile. >>
5.2.1 Authority Key Identifier
The authorityKeyIdentifier is a non-critical CRL extension that
identifies the CA's key used to sign the CRL. This extension is
useful when a CA uses more than one key; it allows distinct keys
differentiated (e.g., as key updating occurs). The key may be
identified by an explicit key identifier, by identification of a
certificate for the key (giving certificate issuer and certificate
serial number), or both. If both are used then the CA issuer shall
ensure that all three fields are consistent.
AuthorityKeyId ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
certIssuer [1] Name OPTIONAL,
certSerialNumber [2] CertificateSerialNumber OPTIONAL }
-- certIssuer and certSerialNumber constitute a logical pair,
-- and if either is present both must be present. Either this
-- pair or the keyIdentifier field or all shall be present
KeyIdentifier ::= OCTET STRING
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5.2.2 Issuer Alternative Name
The issuerAltName is a non-critical CRL extension that provides
additional CA names. Multiple instances may be included. The syntax
for the issuerAltName is the same as described in section 4.2.1.
Whenever such alternative names are included in a CRL, the issuer
alternative name field shall be used. Implementations which
recognize this extension are not required to be able to process all
the alternative name formats. Unrecognized alternative name formats
may be ignored by an implementation.
The following definition is an enhanced version of the X9.55
definition of GeneralName. This definition is anticipated to be used
in the X.509 Amendment.
rfc822Name, dNSName, url, and ipAddress are name forms expected to be
used with this profile. Such names are subject to the basic
constraint extension for issuers which may restrict the names a given
CA can certify (see section on Basic Constraint extension).
The use of otherName should not be used in conjunction with this
profile.
AltNames ::= SEQUENCE OF GeneralName
GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] IA5String,
url [6] IA5String,
ipAddress [7] OCTET STRING }
5.2.3 CRL Number
The cRLNumber is a non-critical CRL extension which conveys a
monotonically increacing sequence number for each CRL issued by a
given CA through a specific CA X.500 Directory entry or CRL
distribution point. This extension allows users to easily determine
when a particular CRL superceeds another CRL. CAs conforming to this
profile shall include this CRL.
CRLNumber ::= INTEGER
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5.2.4 Issuing Distribution Point
The issuingDistributionPoint is a critical CRL extension that
identifiers the CRL distribution point for this particular CRL, and
it indicates whether the CRL covers revocation for end entity
certificates only, CA certificates only, or a limitied set of reason
codes. Support for CRL distribution points is strongly encouraged.
The use of certificateHold is strictly prohibited in this profile.
Only the following reason codes may be used in conjunction with this
profile. The use of keyCompromise (1) shall be used to indicate
compromise or suspected compromise. The use of affiliationChanged
(3), superseded (4), or cessationOfOperation (5)shall be used to
indicate routine compromise.
<< Does anyone see a use for (2)? >>
The CRL is signed by the CA's key. CRL Distribution Points do not
have their own key pairs. If the CRL is stored in the X.500
Directory, it is stored entry corresponding to the CRL distribution
point, which may be different that the directory entry of the CA.
CRL distribution points, if used, should be partitioned the CRL on
the basis of compromise and routine revocation. That is, the
revocations with reason code (1) shall appear in one distribution
point, and the revocations with reason codes (3), (4), and (5) shall
appear in another distribution point.
DistributionPoint ::= SEQUENCE {
distributionPoint DistributionPointName,
reasons ReasonFlags OPTIONAL }
DistributionPointName ::= CHOICE {
fullName [0] Name,
nameRelativeToCA [1] RelativeDistinguishedName,
generalName [2] GeneralName }
GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] IA5String,
uniformResourceLocator [6] IA5String }
OTHER-NAME ::= TYPE-IDENTIFIER
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ReasonFlags ::= BIT STRING {
unused (0),
keyCompromise (1),
caCompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6) }
5.2.5 Delta CRL Indicator
The deltaCRLIndicator is a critical CRL extension that identifies a
delta-CRL. The use of delta-CRLs can significantly improve
processing time for applications which store revocation information
in a format other than the CRLstructure. This allows changes to be
added to the local database while ignoring unchanged information that
is already in the local databse.
CAs are shall always issue a complete CRL when a delta-CRL is issued.
The value of BaseCRLNumber identifies the CRL number of the base CRL
that was used as the starting point in the generation of this delta-
CRL. The delta-CRL contains the changes between the base CRL and the
current CRL issued along with the delta-CRL. It is the decision of a
CA as to whether to provide delta-CRLs. Again, a delta-CRL shall not
be issued without a corresponding CRL. The value of CRLNumber for
both the delta-CRL and the corresponding CRL shall be identical.
A CRL user constructing a locally held CRL from delta-CRLs shall
consider the constructed CRL incomplete and unusable if the CRLNumber
of the received delta-CRL is more that one greater that the CRLnumber
of the delta-CRL last processed.
5.3 CRL Entry Extensions
The CRL entry extensions already defined by ANSI X9 and ISO for X.509
v2 CRLs provide methods for associating additional attributes with
CRL entries. 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. A CRL validation must fail if it
encounters an critical CRL entry extension which it does not know how
to process. However, an unrecognized non-critical CRL entry
extension may be ignored. The following presents 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 extensions in CRL entries which might be used in a general
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context.
<< Need to add table of OIDs for all extensions from X.509 and X9.55.
Say which are allowed in this profile, and which are prohibited in
this profile. >>
5.3.1 Reason Code
The reasonCode is a non-critical CRL entry extension that identifies
the reason for the certificate revocation. CAs are strongly
encouraged to include reason codes in CRL entries; however, some
reasonCode values are strictly prohibited. The reason code extension
permits certificates to placed on hold or suspended. The processing
associated with suspended certificates greatly complicates
certificate validation, therefore the use of reasonCode values
certificateHold (6), certHoldRelease (7), and removeFromCRL (8) shall
not be used. Also, the reasonCode CRL entry extension should be
absent instead of using the unspecified (0) reasonCode value.
<< Again, is there any reason to permit caCompromise (2)? >>
CRLReason ::= ENUMERATED {
unspecified (0),
keyCompromise (1),
caCompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
certHoldRelease (7),
removeFromCRL (8) }
5.3.2 Expiration Date
The expirationDate is a non-critical CRL entry extension that
indicates the expiration of a hold entry in a CRL. The use of this
extension is strictly prohibited by this profile.
5.3.3 Instruction Code
The instructionCode is a non-critical CRL entry extension that
provides a registered instruction identifier which indicates the
action to be taken after encountering a certificate that has been
placed on hold. The use of this extension is strictly prohibited by
this profile.
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5.3.4 Invalidity Date
The invalidityDate 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,
but it must be later than the issue date of the previously issued
CRL. Remember that the revocation date in the CRL entry specifies
the date that the CA revoked the certificate. Whenever this
information is available, CAs are strongly encouraged to share it
with CRL users.
The GeneralizedTime values included in this field shall be expressed
in Greenwich Mean Time (Zulu) and include granularity to the minute,
even though finer granularity can be expressed in the GeneralizedTime
format. That is, GeneralizedTime should be expressed as
YYYYMMDDHHMMZ.
Implementors are warned that no DER is defined for GeneralizedTime,
thus transformation between local time representations and the DER
transfer syntax must be performed carefully when computing the hash
value for a certificate signature. For example, a GeneralizedTime
value which includes explict, zero values for seconds will not
produce the same hash value as one in which the seconds are omitted.
GeneralizedTime expresses the using four digits. Remember that
UTCTime represents the value of a year modulo 100, with no indication
of century.
InvalidityDate ::= GeneralizedTime
5.4 Examples
<< CRL samples including descriptive text and ASN.1 encoded blobs
will be inserted. >>
6 Certificate Path Validation
Certification path processing verifies the binding between the
subject distinguished name and subject public key. The basic
constraints and policy constraints extensions facilitate automated,
self-contained implementation of certification path processing logic.
The following is an outline of a procedure for validating
certification paths. An implementation shall be functionally
equivalent to the external behaviour resulting from this procedure.
Any algorithm may be used by a particular implementation so long as
it derives the correct result.
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The inputs to the certification path processing procedure are:
(a) a set of certificates comprising a certification path;
(b) a CA name and trusted public key value (or an identifier of
such a key if the key is stored internally to the certification
path processing module) for use in verifying the first certificate
in the certification path;
(c) a set of initial-policy identifiers (each comprising a
sequence of policy element identifiers), which identifies one or
more certificate policies, any one of which would be acceptable
for the purposes of certification path processing; and
(d) the current date/time (if not available internally to the
certification path processing module).
The outputs of the procedure are:
(a) an indication of success or failure of certification path
validation;
(b) if validation failed, a reason for failure; and
(c) if validation was successful, a (possibly empty) set of
policy qualifiers obtained from CAs on the path.
The procedure makes use of the following set of state variables:
(a) acceptable policy set: A set of certificate policy identifiers
comprising the policy or policies recognized by the public key user
together with policies deemed equivalent through policy mapping;
(b) constrained subtrees: A set of root names defining a set of
subtrees within which all subject names in subsequent certificates in
the certification path shall fall; if no restriction is in force this
state variable takes the special value unbounded; and
(c) excluded subtrees: A set of root names defining a set of
subtrees within which no subject name in subsequent certificates in
the certification path may fall; if no restriction is in force this
state variable takes the special value empty.
The procedure involves an initialization step, followed by a series
of certificate-processing steps. The initialization step comprises:
(a) Initialize the constrained subtress to unbounded;
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(b) Initialize the excluded subtrees indicator to empty; and
(c) Initialize the acceptable policy set to the set of initial-
policy identifiers.
Each certificate is then processed in turn, starting with the
certificate signed using the trusted CA public key which was input to
this procedure. The last certificate is processed as an end-entity
certificate; all other certificates (if any) are processed as CA-
certificates.
The following checks are applied to all certificates:
(a) Check that the signature verifies, that dates are valid, that
the subject and issuer names chain correctly, and that the
certificate has not been revoked;
(b) If a key usage restriction extension is present in the
certificate and contains a certPolicySet component, check that at
least one member of the acceptable policy set appears in the
field;
(c) Check that the subject name is consistent with the
constrained subtrees state variables; and
(d) Check that the subject name is consistent with the excluded
subtrees state variables.
If any one of the above checks fails, the procedure terminates,
returning a failure indication and an appropriate reason. If none of
the above checks fail on the end-entity certificate, the procedure
terminates, returning a success indication together with the set of
all policy qualifier values encountered in the set of certificates.
For a CA-certificate, the following constraint recording actions are
then performed, in order to correctly set up the state variables for
the processing of the next certificate:
(a) If permittedSubtrees is present in the certificate, set the
constrained subtrees state variable to the intersection of its
previous value and the value indicated in the extension field.
(b) 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.
Note: It is possible to specify an extended version of the above
certification path processing procedure which results in default
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behaviour identical to the rules of Privacy Enhanced Mail [RFC 1422].
In this extended version, additional inputs to the procedure are a
list of one or more Policy Certification Authority (PCA) names and an
indicator of the position in the certification path where the PCA is
expected. At the nominated PCA position, the CA name is compared
against this list. If a recognized PCA name is found, then a
constraint of SubordinateToCA is implicitly assumed for the remainder
of the certification path and processing continues. If no valid PCA
name is found, and if the certification path cannot be validated on
the basis of identified policies, then the certification path is
considered invalid.
7 Algorithm Support
7.1 One-way Hash Functions
One-way hash functions are also called message digest algorithms.
SHA-1 is be the most popular one-way hash function used in the
Internet PKI. However, PEM uses MD2 for certificates [RFC1422,
RFC1423]. For this reason, MD2 may continue to be used in
certificates for many years.
7.1.1 MD2 One-way Hash Function
MD2 was also developed by Ron Rivest, but RSA Data Security has not
placed the MD2 algorithm in the public domain. Rather, RSA Data
Security has granted license to use MD2 for non-commerical Internet
Privacy-Enhanced Mail. For this reason, MD2 may continue to be used
with PEM certificates, but MD5 is preferred. MD2 is fully described
in RFC 1319.
<< Add a paragraph about the MD2 flaw that was recently discovered.
Urge MD2 replacement with SHA-1. >>
7.1.2 SHA-1 One-way Hash Function
SHA-1 was developed by the U.S. Government. SHA-1 is fully described
in FIPS 180-1.
SHA-1 is the one-way hash function of choice for use with both RSA
the DSA signature algorithms.
7.2 Signature Algorithms
RSA and DSA are the most popular signature algorithms used in the
Internet.
There is some ambiguity in 1988 X.509 document regarding the
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definition of the SIGNED macro regarding, the representation of a
signature in a certificate or a CRL. The interpretation selected for
the Internet requires that the data to be signed (e.g., the one-way
function output value) is first ASN.1 encoded as an OCTET STRING and
the result is encrypted (e.g., using RSA Encryption) to form the
signed quantity, which is then ASN.1 encoded as a BIT STRING.
7.2.1 RSA Signature Algorithm
A patent statement regarding the RSA algorithm can be found at the
end of this profile.
The RSA algorithm is named for it's inventors: Rivest, Shamir, and
Adleman. The RSA signature algorithm is defined in PKCS #1. It
combines the either the MD2 or the SHA-1 one-way hash function with
the RSA asymmetric encryption algorithm. As defined in PKCS #1, the
ASN.1 object identifiers used to identify these signature algorithms
are:
md2WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 2 }
sha-1WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) oiw(14) secsig(3)
algorithm(2) 29 }
When either of these object identifiers is used within the ASN.1 type
AlgorithmIdentifier, the parameters component of that type shall be
absent or the ASN.1 type NULL.
7.2.2 DSA Signature Algorithm
A patent statement regarding the DSA can be found at the end of this
profile.
The Digital Signature Algorithm (DSA) is also called the Digital
Signature Standard (DSS). DSA was developed by the U.S. Government,
and DSA is used in conjunction with the the SHA-1 one-way hash
function. DSA is fully described in FIPS 186. The ASN.1 object
identifiers used to identify this signature algorithm is:
dsaWithSHA-1 OBJECT IDENTIFIER ::= {
joint-iso-ccitt(2) country(16) US(840) organization(1)
us-government(101) dod(2) infosec(1) algorithms(1) 2 }
When this object identifier is used with the ASN.1 type
AlgorithmIdentifier, the parameters component of that type is
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optional. If it is absent, the DSA parameters p, q, and g are
assumed to be known, otherwise the parameters are included using the
following ASN.1 structure:
Dss-Parms ::= SEQUENCE {
p OCTET STRING,
q OCTET STRING,
g OCTET STRING }
7.3 Subject Public Key Algorithms
<< Add a section that lists the public key algorithms that are
supported by this profile. Obviously, RSA, DSA, Diffie-Hellman, and
KEA will be included. Are there others? >>
<< Should a different algorithm identifier be assigned to RSA
signature keys and RSA key management keys? If so, there will be one
subsection for each within this section.>>
Patent Statements
The Internet PKI relies on the use of patented public key technology.
The Internet Standards Process as defined in RFC 1310 requires a
written statement from the Patent holder that a license will be made
available to applicants under reasonable terms and conditions prior
to approving a specification as a Proposed, Draft or Internet
Standard.
Patent statements for DSA, RSA, and Diffie-Hellman follow. These
statements have been supplied by the patent holders, not the authors
of this profile.
Digital Signature Algorithm (DSA)
The U.S. Government holds patent 5,231,668 on the Digital
Signature Algorithm (DSA), which has been incorporated into
Federal Information Processing Standard (FIPS) 186. The patent
was issued on July 27, 1993.
The National Institute of Standards and Technology (NIST) has a
long tradition of supplying U.S. Government-developed techniques
to committees and working groups for inclusion into standards on a
royalty-free basis. NIST has made the DSA patent available
royalty-free to users worldwide.
Regarding patent infringement, FIPS 186 summarizes our position;
the Department of Commerce is not aware of any patents that would
be infringed by the DSA. Questions regarding this matter may be
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directed to the Deputy Chief Counsel for NIST.
RSA Signature and Encryption
<< Now that PKP has dissolved, a revised patent statement for RSA
from RSADSI is needed. >>
Diffie-Hellman Key Agreement
<< Now that PKP has dissolved, a revised patent statement for
Diffie-Hellman from Cylink is needed. >>
Obsolete PKP Patent Statement
<< This statement is included here until a replacement from RSADSI
and Cylink can be obtained. >>
The Massachusetts Institute of Technology and the Board of
Trustees of the Leland Stanford Junior University have granted
Public Key Partners (PKP) exclusive sub-licensing rights to the
following patents issued in the United States, and all of their
corresponding foreign patents:
Cryptographic Apparatus and Method
("Diffie-Hellman")......................... No. 4,200,770
Public Key Cryptographic Apparatus
and Method ("Hellman-Merkle").............. No. 4,218,582
Cryptographic Communications System and
Method ("RSA")............................. No. 4,405,829
Exponential Cryptographic Apparatus
and Method ("Hellman-Pohlig").............. No. 4,424,414
These patents are stated by PKP to cover all known methods of
practicing the art of Public Key encryption, including the
variations collectively known as El Gamal.
Public Key Partners has provided written assurance to the Internet
Society that parties will be able to obtain, under reasonable,
nondiscriminatory terms, the right to use the technology covered
by these patents. This assurance is documented in RFC 1170 titled
"Public Key Standards and Licenses". A copy of the written
assurance dated April 20, 1990, may be obtained from the Internet
Assigned Number Authority (IANA).
The Internet Society, Internet Architecture Board, Internet
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Engineering Steering Group and the Corporation for National
Research Initiatives take no position on the validity or scope of
the patents and patent applications, nor on the appropriateness of
the terms of the assurance. The Internet Society and other groups
mentioned above have not made any determination as to any other
intellectual property rights which may apply to the practice of
this standard. Any further consideration of these matters is the
user's own responsibility.
Security Considerations
This entire memo is about security mechanisms.
Author Addresses:
Russell Housley
SPYRUS
PO Box 1198
Herndon, VA 22070
USA
housley@spyrus.com
Warwick Ford
Nortel Secure Networks
PO Box 3511, Station C
Ottawa, Ontario
Canada KY 4H7
wford@bnr.ca
David Solo
BBN
150 CambridgePark Drive
Cambridge, MA 02140
USA
solo@bbn.com
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