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Versions: 00 01 02 03 04 05 06 RFC 5035

Network Working Group                                          J. Schaad
Internet-Draft                                   Soaring Hawk Consulting
Intended status: Informational                         December 21, 2006
Expires: June 24, 2007


              ESS Update: Adding CertID Algorithm Agility
                    draft-ietf-smime-escertid-03.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on June 24, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).














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Abstract

   In the original Enhanced Security Services for S/MIME draft, 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 new attributes to deal with the
   updating.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Notation . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Replace Section 5.4 'Signing Certificate Attribute
       Definitions' . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Insert new section 5.4.1 'Signing Certificate Attribute
       Definition Version 2'  . . . . . . . . . . . . . . . . . . . .  5
   4.  Insert new section 5.4.1.1 'Certificate Identification
       Version 2' . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Insert new section 5.4.2 ' Signing Certificate Attribute
       Defintion Version 1  . . . . . . . . . . . . . . . . . . . . .  9
   6.  Renumber Section 5.4.1 Certificate Identification Version 1  . 11
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Appendix A.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 19
























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1.  Introduction

   In the original Enhanced Security Services (ESS) for S/MIME draft
   [ESS], a structure for cryptographically linking the certificate to
   be used in validation with the signature was defined.  This
   structure, called ESSCertID was hardwired to use a SHA-1 hash value.
   The recent attacks on SHA-1 require that we change define a new
   attribute which allows for the use of a different algorithm.  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 and
   defines new attributes to deal with the updating.

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].































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2.  Replace Section 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 authorization 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 deemed 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 sufficently
   low.)

   Four cases exist which 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, 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 which 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 authorization 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 authorization certificates that are used during
      signature validation.  Authorization certificates can be either
      attribute certificates or normal certificates.  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 authorization
      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 [PKIXCERT].

   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 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.



































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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 [PKIXCERT].  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 re-used 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.

   Attribute certificates and additional public key certificates
   containing authorization 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:










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

   Hash ::= OCTET STRING

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

   The fields of ESSCertIDv2 are defined as follows:

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

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

   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.

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















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5.  Insert new section 5.4.2 ' Signing Certificate Attribute Defintion
    Version 1

   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 authorization 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
   authorization certificates that are used during signature validation.
   Authorization certificates can be either attribute certificates or
   normal certificates.  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 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 authorization 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.




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   If present, the SigningCertificate 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 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.










































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6.  Renumber Section 5.4.1 Certificate Identification Version 1

   Change the number on this section from 5.4.1 to 5.4.2.1

   Change the title on this section to "Certificate Identification
   Version 1".













































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7.  Normative References

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

   [PKIXCERT]
              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.

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






































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Appendix A.  ASN.1 Module

   Replace the ASN.1 module 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)
    ContentType, IssuerAndSerialNumber, SubjectKeyIdentifier,
AlgorithmIdentifier
    FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840)
    rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1)}

-- PKIX Certificate and CRL Profile, Sec A.2 Implicitly Tagged Module,
--  1988 Syntax
    PolicyInformation, CertificateSerialNumber, 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 }

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}




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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

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,



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  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

ub-security-categories INTEGER ::= 64

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

--Note: The aforementioned SecurityCategory syntax produces identical
--hex encodings as the following SecurityCategory syntax that is



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--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 }

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 {



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    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 parameters NULL}
        certHash                Hash,
        issuerSerial            IssuerSerial OPTIONAL
}

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

Hash ::= OCTET STRING -- SHA1 hash of entire certificate

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

END -- of ExtendedSecurityServices-2006











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Author's Address

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

   Phone: (425) 785-1031
   Email: jimsch@exmsft.com










































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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
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   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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