Enhanced Security Services (ESS) Update: Adding CertID Algorithm Agility
RFC 5035

Network Working Group                                          J. Schaad
Request for Comments: 5035                       Soaring Hawk Consulting
Updates: 2634                                                August 2007
Category: Standards Track

                Enhanced Security Services (ESS) Update:
                    Adding CertID Algorithm Agility

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

   In the original Enhanced Security Services for S/MIME document (RFC
   2634), a structure for cryptographically linking the certificate to
   be used in validation with the signature was introduced; this
   structure was hardwired to use SHA-1.  This document allows for the
   structure to have algorithm agility and defines a new attribute for
   this purpose.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  Notation . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.2.  Updates to RFC 2634  . . . . . . . . . . . . . . . . . . .  2
   2.  Replace Section 5.4 'Signing Certificate Attribute
       Definitions' . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Insert New Section 5.4.1 'Signing Certificate Attribute
       Definition Version 2'  . . . . . . . . . . . . . . . . . . . .  4
   4.  Insert New Section 5.4.1.1 'Certificate Identification
       Version 2' . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Insert New Section 5.4.2 'Signing Certificate Attribute
       Definition Version 1'  . . . . . . . . . . . . . . . . . . . .  7
   6.  Insert New Section 5.4.2.1 'Certificate Identification
       Version 1' . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   In the original Enhanced Security Services (ESS) for S/MIME document
   [ESS], a structure for cryptographically linking the certificate to
   be used in validation with the signature was defined.  This
   structure, called ESSCertID, identifies a certificate by its hash.
   The structure is hardwired to use a SHA-1 hash value.  The recent
   attacks on SHA-1 require that we define a new attribute that allows
   for the use of different algorithms.  This document performs that
   task.

   This document defines the structure ESSCertIDv2 along with a new
   attribute SigningCertificateV2, which uses the updated structure.
   This document allows for the structure to have algorithm agility by
   including an algorithm identifier and defines a new signed attribute
   to use the new structure.

   This document specifies the continued use of ESSCertID to ensure
   compatibility when SHA-1 is used for certificate disambiguation.

1.1.  Notation

   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].

1.2.  Updates to RFC 2634

   This document updates Section 5.4 of RFC 2634.  Once the updates are
   applied, the revised section will have the following structure:

   5.4  Signing Certificate Attribute Definitions

   5.4.1  Signing Certificate Attribute Definition Version 2

   5.4.1.1  Certificate Identification Version 2

   5.4.2  Signing Certificate Attribute Definition Version 1

   5.4.2.1  Certificate Identification Version 1

   In addition, the ASN.1 module in Appendix A is replaced.

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2.  Replace Section 5.4 'Signing Certificate Attribute Definitions'

   5.4 Signing Certificate Attribute Definitions

   The signing certificate attribute is designed to prevent simple
   substitution and re-issue attacks, and to allow for a restricted set
   of certificates to be used in verifying a signature.

   Two different attributes exist for this due to a flaw in the original
   design.  The only substantial difference between the two attributes
   is that SigningCertificateV2 allows for hash algorithm agility, while
   SigningCertificate forces the use of the SHA-1 hash algorithm.  With
   the recent advances in the ability to create hash collisions for
   SHA-1, it is wise to move forward sooner rather than later.

   When the SHA-1 hash function is used, the SigningCertificate
   attribute MUST be used.  The SigningCertificateV2 attribute MUST be
   used if any algorithm other than SHA-1 is used and SHOULD NOT be used
   for SHA-1.  Applications SHOULD recognize both attributes as long as
   they consider SHA-1 able to distinguish between two different
   certificates, (i.e., the possibility of a collision is sufficiently
   low).  If both attributes exist in a single message, they are
   independently evaluated.

   Four cases exist that need to be taken into account when using this
   attribute for correct processing:

   1.  Signature validates and the hashes match: This is the success
       case.

   2.  Signature validates and the hashes do not match: In this case,
       the certificate contained the correct public key, but the
       certificate containing the public key is not the one that the
       signer intended to be used.  In this case the application should
       attempt a search for a different certificate with the same public
       key and for which the hashes match.  If no such certificate can
       be found, this is a failure case.

   3.  Signature fails validation and the hashes match: In this case, it
       can be assumed that the signature has been modified in some
       fashion.  This is a failure case.

   4.  Signature fails validation and the hashes do not match: In this
       case, it can be either that the signature has been modified, or
       that the wrong certificate has been used.  Applications should
       attempt a search for a different certificate that matches the
       hash value in the attribute and use the new certificate to retry
       the signature validation.

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3.  Insert New Section 5.4.1 'Signing Certificate Attribute Definition
    Version 2'

   5.4.1 Signing Certificate Attribute Definition Version 2

   The signing certificate attribute is designed to prevent the simple
   substitution and re-issue attacks, and to allow for a restricted set
   of certificates to be used in verifying a signature.

   SigningCertificateV2 is identified by the OID:

       id-aa-signingCertificateV2 OBJECT IDENTIFIER ::= { iso(1)
           member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
           smime(16) id-aa(2) 47 }

   The attribute has the ASN.1 definition:

       SigningCertificateV2 ::=  SEQUENCE {
           certs        SEQUENCE OF ESSCertIDv2,
           policies     SEQUENCE OF PolicyInformation OPTIONAL
       }

   certs
      contains the list of certificates that are to be used in
      validating the message.  The first certificate identified in the
      sequence of certificate identifiers MUST be the certificate used
      to verify the signature.  The encoding of the ESSCertIDv2 for this
      certificate SHOULD include the issuerSerial field.  If other
      constraints ensure that issuerAndSerialNumber will be present in
      the SignerInfo, the issuerSerial field MAY be omitted.  The
      certificate identified is used during the signature verification
      process.  If the hash of the certificate does not match the
      certificate used to verify the signature, the signature MUST be
      considered invalid.

      If more than one certificate is present, subsequent certificates
      limit the set of certificates that are used during validation.
      Certificates can be either attribute certificates (limiting
      authorizations) or public key certificates (limiting path
      validation).  The issuerSerial field (in the ESSCertIDv2
      structure) SHOULD be present for these certificates, unless the
      client who is validating the signature is expected to have easy
      access to all the certificates required for validation.  If only
      the signing certificate is present in the sequence, there are no
      restrictions on the set of certificates used in validating the
      signature.

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   policies
      contains a sequence of policy information terms that identify
      those certificate policies that the signer asserts apply to the
      certificate, and under which the certificate should be relied
      upon.  This value suggests a policy value to be used in the
      relying party's certification path validation.  The definition of
      PolicyInformation can be found in [RFC3280].

   If present, the SigningCertificateV2 attribute MUST be a signed
   attribute; it MUST NOT be an unsigned attribute.  CMS defines
   SignedAttributes as a SET OF Attribute.  A SignerInfo MUST NOT
   include multiple instances of the SigningCertificateV2 attribute.
   CMS defines the ASN.1 syntax for the signed attributes to include
   attrValues SET OF AttributeValue.  A SigningCertificateV2 attribute
   MUST include only a single instance of AttributeValue.  There MUST
   NOT be zero or multiple instances of AttributeValue present in the
   attrValues SET OF AttributeValue.

4.  Insert New Section 5.4.1.1 'Certificate Identification Version 2'

   Insert the following text as a new section.

   5.4.1.1 Certificate Identification Version 2

   The best way to identify certificates is an often-discussed issue.
   The ESSCertIDv2 structure supplies two different fields that are used
   for this purpose.

   The hash of the entire certificate allows for a verifier to check
   that the certificate used in the verification process was the same
   certificate the signer intended.  Hashes are convenient in that they
   are frequently used by certificate stores as a method of indexing and
   retrieving certificates as well.  The use of the hash is required by
   this structure since the detection of substituted certificates is
   based on the fact they would map to different hash values.

   The issuer/serial number pair is the method of identification of
   certificates used in [RFC3280].  That document imposes a restriction
   for certificates that the issuer distinguished name must be present.
   The issuer/serial number pair would therefore normally be sufficient
   to identify the correct signing certificate.  (This assumes the same
   issuer name is not reused from the set of trust anchors.)  The
   issuer/serial number pair can be stored in the sid field of the
   SignerInfo object.  However, the sid field is not covered by the
   signature.  In the cases where the issuer/serial number pair is not
   used in the sid or the issuer/serial number pair needs to be signed,
   it SHOULD be placed in the issuerSerial field of the ESSCertIDv2
   structure.

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   Attribute certificates and additional public key certificates
   containing information do not have an issuer/serial number pair
   represented anywhere in a SignerInfo object.  When an attribute
   certificate or an additional public key certificate is not included
   in the SignedData object, it becomes much more difficult to get the
   correct set of certificates based only on a hash of the certificate.
   For this reason, these certificates SHOULD be identified by the
   IssuerSerial object.

   This document defines a certificate identifier as:

        ESSCertIDv2 ::=  SEQUENCE {
            hashAlgorithm           AlgorithmIdentifier
                   DEFAULT {algorithm id-sha256},
            certHash                 Hash,
            issuerSerial             IssuerSerial OPTIONAL
        }

        Hash ::= OCTET STRING

        IssuerSerial ::= SEQUENCE {
            issuer                   GeneralNames,
            serialNumber             CertificateSerialNumber
       }

   The fields of ESSCertIDv2 are defined as follows:

   hashAlgorithm
      contains the identifier of the algorithm used in computing
      certHash.

   certHash
      is computed over the entire DER-encoded certificate (including the
      signature) using the SHA-1 algorithm.

   issuerSerial
      holds the identification of the certificate.  The issuerSerial
      would normally be present unless the value can be inferred from
      other information (e.g., the sid field of the SignerInfo object).

   The fields of IssuerSerial are defined as follows:

   issuer
      contains the issuer name of the certificate.  For non-attribute
      certificates, the issuer MUST contain only the issuer name from
      the certificate encoded in the directoryName choice of
      GeneralNames.  For attribute certificates, the issuer MUST contain
      the issuer name field from the attribute certificate.

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   serialNumber
      holds the serial number that uniquely identifies the certificate
      for the issuer.

5.  Insert New Section 5.4.2 'Signing Certificate Attribute Definition
    Version 1'

   (Note: This section does not present new material.  This section
   contains the original contents of Section 5.4 in [ESS], which are
   retained with minor changes in this specification to achieve
   backwards compatibility.)

   Insert the following text as a new section.

   5.4.2 Signing Certificate Attribute Definition Version 1

   The signing certificate attribute is designed to prevent the simple
   substitution and re-issue attacks, and to allow for a restricted set
   of certificates to be used in verifying a signature.

   The definition of SigningCertificate is

       SigningCertificate ::=  SEQUENCE {
           certs        SEQUENCE OF ESSCertID,
           policies     SEQUENCE OF PolicyInformation OPTIONAL
       }

       id-aa-signingCertificate OBJECT IDENTIFIER ::= { iso(1)
           member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
           smime(16) id-aa(2) 12 }

   The first certificate identified in the sequence of certificate
   identifiers MUST be the certificate used to verify the signature.
   The encoding of the ESSCertID for this certificate SHOULD include the
   issuerSerial field.  If other constraints ensure that
   issuerAndSerialNumber will be present in the SignerInfo, the
   issuerSerial field MAY be omitted.  The certificate identified is
   used during the signature verification process.  If the hash of the
   certificate does not match the certificate used to verify the
   signature, the signature MUST be considered invalid.

   If more than one certificate is present in the sequence of
   ESSCertIDs, the certificates after the first one limit the set of
   certificates that are used during validation.  Certificates can be
   either attribute certificates (limiting authorizations) or public key
   certificates (limiting path validation).  The issuerSerial field (in
   the ESSCertID structure) SHOULD be present for these certificates,
   unless the client who is validating the signature is expected to have

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   easy access to all the certificates required for validation.  If only
   the signing certificate is present in the sequence, there are no
   restrictions on the set of certificates used in validating the
   signature.

   The sequence of policy information terms identifies those certificate
   policies that the signer asserts apply to the certificate, and under
   which the certificate should be relied upon.  This value suggests a
   policy value to be used in the relying party's certification path
   validation.

   If present, the SigningCertificate attribute MUST be a signed
   attribute; it MUST NOT be an unsigned attribute.  Cryptographic
   Message Syntax (CMS) defines SignedAttributes as a SET OF Attribute.
   A SignerInfo MUST NOT include multiple instances of the
   SigningCertificate attribute.  CMS defines the ASN.1 syntax for the
   signed attributes to include attrValues SET OF AttributeValue.  A
   SigningCertificate attribute MUST include only a single instance of
   AttributeValue.  There MUST NOT be zero or multiple instances of
   AttributeValue present in the attrValues SET OF AttributeValue.

6.  Insert New Section 5.4.2.1 'Certificate Identification Version 1'

   (Note: This section does not present new material.  This section
   contains the original contents of Section 5.4 in [ESS], which are
   retained with minor changes in this specification to achieve
   backwards compatibility.)

   Delete old Section 5.4.1

   Insert the following as new text

   5.4.2.1 Certificate Identification Version 1

   Certificates are uniquely identified using the information in the
   ESSCertID structure.  Discussion can be found in Section 5.4.1.1.

   This document defines a certificate identifier as:

       ESSCertID ::=  SEQUENCE {
            certHash                 Hash,
            issuerSerial             IssuerSerial OPTIONAL
       }

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   The fields of ESSCertID are defined as follows:

   certHash
      is computed over the entire DER-encoded certificate (including the
      signature).

   issuerSerial
      holds the identification of the certificate.  This field would
      normally be present unless the value can be inferred from other
      information (e.g., the sid field of the SignerInfo object).

   The fields of IssuerSerial are discussed in Section 5.4.1.1

7.  Security Considerations

   This document is designed to address the security issue of a
   substituted certificate used by the validator.  If a different
   certificate is used by the validator than the signer, the validator
   may not get the correct result.  An example of this would be that the
   original certificate was revoked and a new certificate with the same
   public key was issued for a different individual.  Since the issuer/
   serial number field is not protected, the attacker could replace this
   and point to the new certificate and validation would be successful.

   The attributes defined in this document are to be placed in locations
   that are protected by the signature.  This attribute does not provide
   any additional security if placed in an unsigned or un-authenticated
   location.

   The attributes defined in this document permit a signer to select a
   hash algorithm to identify a certificate.  A poorly selected hash
   algorithm may provide inadequate protection against certificate
   substitution or result in denial of service for this protection.  By
   employing the attributes defined in this specification with the same
   hash algorithm used for message signing, the sender can ensure that
   these attributes provide commensurate security.

   Since recipients must support the hash algorithm to verify the
   signature, selecting the same hash algorithm also increases the
   likelihood that the hash algorithm is supported in the context of
   certificate identification.  Note that an unsupported hash algorithm
   for certificate identification does not preclude validating the
   message but does deny the message recipient protection against
   certificate substitution.

   To ensure that legacy implementations are provided protection against
   certificate substitution, clients are permitted to include both
   ESScertID and ESScertIDv2 in the same message.  Since these

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   attributes are generated and evaluated independently, the contents
   could conceivably be in conflict.  Specifically, where a signer has
   multiple certificates containing the same public key, the two
   attributes could specify different signing certificates.  The result
   of signature processing may vary depending on which certificate is
   used to validate the signature.

   Recipients that attempt to evaluate both attributes may choose to
   reject such a message.

8.  Normative References

   [ESS]      Hoffman, P., "Enhanced Security Services for S/MIME",
              RFC 2634, June 1999.

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

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

   [RFC3852]  Housley, R., "Cryptographic Message Syntax (CMS)",
              RFC 3852, July 2004.

   [UTF8]     Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

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Appendix A.  ASN.1 Module

   Replace the ASN.1 module in RFC 2634 with this one.

ExtendedSecurityServices-2006
      { iso(1) member-body(2) us(840) rsadsi(113549)
        pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-ess-2006(30) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
-- Cryptographic Message Syntax (CMS) [RFC3852]
    ContentType, IssuerAndSerialNumber, SubjectKeyIdentifier
       FROM CryptographicMessageSyntax2004 { iso(1) member-body(2)
                us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
                modules(0) cms-2004(24)}
-- PKIX Certificate and CRL Profile, Section A.1 Explicity Tagged Module
--  1988 Syntax             [RFC3280]
    AlgorithmIdentifier, CertificateSerialNumber
       FROM PKIX1Explicit88 { iso(1) identified-organization(3) dod(6)
                internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
                id-pkix1-explicit(18) }

-- PKIX Certificate and CRL Profile, Sec A.2 Implicitly Tagged Module,
--  1988 Syntax             [RFC3280]
    PolicyInformation, GeneralNames
          FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
                internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
                id-pkix1-implicit(19)};

-- Extended Security Services
-- The construct "SEQUENCE SIZE (1..MAX) OF" appears in several ASN.1
-- constructs in this module.  A valid ASN.1 SEQUENCE can have zero or
-- more entries.  The SIZE (1..MAX) construct constrains the SEQUENCE to
-- have at least one entry.  MAX indicates the upper bound is
-- unspecified.  Implementations are free to choose an upper bound that
-- suits their environment.

-- UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING

-- The contents are formatted as described in [UTF8]

-- Section 2.7

ReceiptRequest ::= SEQUENCE {
  signedContentIdentifier ContentIdentifier,
  receiptsFrom ReceiptsFrom,
  receiptsTo SEQUENCE SIZE (1..ub-receiptsTo) OF GeneralNames
}

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ub-receiptsTo INTEGER ::= 16

id-aa-receiptRequest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 1}

ContentIdentifier ::= OCTET STRING

id-aa-contentIdentifier OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 7}

ReceiptsFrom ::= CHOICE {
 allOrFirstTier [0] AllOrFirstTier, -- formerly "allOrNone [0]AllOrNone"
 receiptList [1] SEQUENCE OF GeneralNames
}

AllOrFirstTier ::= INTEGER { -- Formerly AllOrNone
 allReceipts (0),
 firstTierRecipients (1)
}

-- Section 2.8

Receipt ::= SEQUENCE {
  version ESSVersion,
  contentType ContentType,
  signedContentIdentifier ContentIdentifier,
  originatorSignatureValue OCTET STRING
}

id-ct-receipt OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
   rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-ct(1) 1}

ESSVersion ::= INTEGER  { v1(1) }

-- Section 2.9

ContentHints ::= SEQUENCE {
  contentDescription UTF8String (SIZE (1..MAX)) OPTIONAL,
  contentType ContentType
}

id-aa-contentHint OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
    rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 4}

-- Section 2.10

MsgSigDigest ::= OCTET STRING

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id-aa-msgSigDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
   us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 5}

-- Section 2.11

ContentReference ::= SEQUENCE {
  contentType ContentType,
  signedContentIdentifier ContentIdentifier,
  originatorSignatureValue OCTET STRING
}

id-aa-contentReference   OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 10 }

-- Section 3.2

ESSSecurityLabel ::= SET {
  security-policy-identifier SecurityPolicyIdentifier,
  security-classification SecurityClassification OPTIONAL,
  privacy-mark ESSPrivacyMark OPTIONAL,
  security-categories SecurityCategories OPTIONAL
}

id-aa-securityLabel OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 2}
SecurityPolicyIdentifier ::= OBJECT IDENTIFIER

SecurityClassification ::= INTEGER {
  unmarked (0),
  unclassified (1),
  restricted (2),
  confidential (3),
  secret (4),
  top-secret (5)
}(0..ub-integer-options)

ub-integer-options INTEGER ::= 256

ESSPrivacyMark ::= CHOICE {
    pString      PrintableString (SIZE (1..ub-privacy-mark-length)),
    utf8String   UTF8String (SIZE (1..MAX))
}

ub-privacy-mark-length INTEGER ::= 128

SecurityCategories ::= SET SIZE (1..ub-security-categories) OF
        SecurityCategory

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ub-security-categories INTEGER ::= 64

SecurityCategory ::= SEQUENCE {
  type  [0] OBJECT IDENTIFIER,
  value [1] ANY DEFINED BY type
}

--Note: The aforementioned SecurityCategory syntax produces identical
--hex encodings as the following SecurityCategory syntax that is
--documented in the X.411 specification:
--
--SecurityCategory ::= SEQUENCE {

--     type  [0]  SECURITY-CATEGORY,
--     value [1]  ANY DEFINED BY type }
--
--SECURITY-CATEGORY MACRO ::=
--BEGIN
--TYPE NOTATION ::= type | empty
--VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER)
--END

-- Section 3.4

EquivalentLabels ::= SEQUENCE OF ESSSecurityLabel

id-aa-equivalentLabels OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 9}

-- Section 4.4

MLExpansionHistory ::= SEQUENCE
      SIZE (1..ub-ml-expansion-history) OF MLData

id-aa-mlExpandHistory OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 3 }

ub-ml-expansion-history INTEGER ::= 64  MLData ::= SEQUENCE {
  mailListIdentifier EntityIdentifier,
  expansionTime GeneralizedTime,
  mlReceiptPolicy MLReceiptPolicy OPTIONAL
}

EntityIdentifier ::= CHOICE {
  issuerAndSerialNumber IssuerAndSerialNumber,
  subjectKeyIdentifier SubjectKeyIdentifier
}

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MLReceiptPolicy ::= CHOICE {
  none [0] NULL,
  insteadOf [1] SEQUENCE SIZE (1..MAX) OF GeneralNames,
  inAdditionTo [2] SEQUENCE SIZE (1..MAX) OF GeneralNames
}

-- Section 5.4

SigningCertificate ::=  SEQUENCE {
    certs        SEQUENCE OF ESSCertID,
    policies     SEQUENCE OF PolicyInformation OPTIONAL
}

id-aa-signingCertificate OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 12 }

SigningCertificateV2 ::=  SEQUENCE {
    certs        SEQUENCE OF ESSCertIDv2,
    policies     SEQUENCE OF PolicyInformation OPTIONAL
}

id-aa-signingCertificateV2 OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
    smime(16) id-aa(2) 47 }

id-sha256  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
    country(16) us(840) organization(1) gov(101)
    csor(3) nistalgorithm(4) hashalgs(2) 1 }

ESSCertIDv2 ::= SEQUENCE {
     hashAlgorithm           AlgorithmIdentifier
            DEFAULT {algorithm id-sha256},
     certHash                Hash,
     issuerSerial            IssuerSerial OPTIONAL
}

ESSCertID ::=  SEQUENCE {
     certHash                 Hash,
     issuerSerial             IssuerSerial OPTIONAL
}

Hash ::= OCTET STRING  IssuerSerial ::= SEQUENCE {
     issuer                   GeneralNames,
     serialNumber             CertificateSerialNumber
}

END

Schaad                      Standards Track                    [Page 15]
RFC 5035                    ESSCertID Update                 August 2007

-- of ExtendedSecurityServices-2006

Author's Address

   Jim Schaad
   Soaring Hawk Consulting
   PO Box 675
   Gold Bar, WA  98251

   EMail: jimsch@exmsft.com

Schaad                      Standards Track                    [Page 16]
RFC 5035                    ESSCertID Update                 August 2007

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Schaad                      Standards Track                    [Page 17]