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Versions: 00 01 02 03 RFC 4325

PKIX Working Group                              S. Santesson (Microsoft)
INTERNET-DRAFT                               R. Housley (Vigil Security)
Expires February 2006
Updates RFC 3280                                             August 2005

                Internet X.509 Public Key Infrastructure
               Authority Information Access CRL Extension

Status of this Memo

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   This document updates RFC 3280 by defining the Authority Information
   Access Certificate Revocation Lists (CRL) extension.  RFC 3280
   defines the Authority Information Access certificate extension using
   the same syntax.  The CRL extension provides a means of discovering
   and retrieving CRL issuer certificates.

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005

Table of Contents

   1  Introduction ................................................    2
   1.1 Terminology ................................................    3
   2  Authority Information Access Extension in CRL ...............    4
   3  Security Considerations .....................................    5
   4  IANA Considerations .........................................    6
   5  References ..................................................    6
   Authors' Addresses .............................................    7
   Disclaimer .....................................................    8
   IPR Notice .....................................................    8
   Copyright Statement ............................................    8

1.  Introduction

   RFC 3280 [PKIX1] specifies the validation of certification paths.
   One aspect involves the determination that a certificate has not been
   revoked, and one revocation checking mechanism is the Certificate
   Revocation List (CRL).  CRL validation is also specified in RFC 3280,
   which involves the constructions of a valid certification path for
   the CRL issuer.  Building a CRL issuer certification path from the
   signer of the CRL to a trust anchor is straightforward when the
   certificate of the CRL issuer is present in the certification path
   associated with the target certificate, but it can be complex in
   other situations.

   There are several legitimate scenarios where the certificate of the
   CRL issuer is not present, or easily discovered, from the target
   certification path.  This can be the case when indirect CRLs are
   used, when the certification Authority (CA) that issued the target
   certificate changes its certificate signing key, or when the CA
   employs separate keys for certificate signing and CRL signing.

   Methods of finding the certificate of the CRL issuer are currently
   available, such as though an accessible directory location or through
   use of the Subject Information Access extension in intermediary CA

   Directory lookup requires existence and access to a directory that
   has been populated with all of the necessary certificates.  The
   Subject Information Access extension, which supports building the CRL
   issuer certification path top-down (in the direction from the trust
   anchor to the CRL issuer), requires that some certificates in the CRL
   issuer certification path includes an appropriate Subject Information
   Access extension.

   RFC 3280 [PKIX1] provides for bottom-up discovery of certification
   paths through the Authority Information Access extension, where the

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005

   id-ad-caIssuers access method may specify one or more accessLocation
   fields that reference CA certificates associated with the certificate
   containing this extension.

   This document enables the use of the Authority Information Access
   extension in CRLs, enabling a CRL checking application to use the
   access method (id-ad-caIssuers) to locate certificates that may be
   useful in the construction of a valid CRL issuer certification path
   to an appropriate trust anchor.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC 2119].

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005

2.  Authority Information Access CRL Extension

   This section defines the use of the Authority Information Access
   extension in a CRL.  The syntax and semantics defined in RFC 3280
   [PKIX1] for the certificate extensions are also used for the CRL

   This CRL extension MUST NOT be marked critical.

   This extension MUST be identified by the extension object identifier
   (OID) defined in RFC 3280 (, and the
   AuthorityInfoAccessSyntax MUST be used to form the extension value.
   For convenience, the ASN.1 [X.680] definition of the Authority
   Information Access extension is repeated below.

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

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

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

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

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

   When present in a CRL, this extension MUST include at least one
   AccessDescription specifying id-ad-caIssuers as the accessMethod.
   Access method types other than id-ad-caIssuers MUST NOT be included.
   At least one instance of AccessDescription SHOULD specify an
   accessLocation that is an HTTP [HTTP/1.1] or LDAP [LDAP] URI.

   Where the information is available via HTTP or FTP, accessLocation
   MUST be a uniformResourceIdentifier and the URI MUST point to a
   certificate containing file.  The certificate file MUST contain
   either a single DER [X.690] encoded certificate (indicated by the
   .cer file extension) or a collection of certificates (indicated by
   the .p7c file extension):

      .cer   A single DER encoded certificate as specified in
             RFC 2585 [PKIX-CERT].

      .p7c   A "certs-only" CMS message as specified in RFC 2797 [CMC].

     Conforming applications that support HTTP or FTP for accessing
     certificates MUST be able to accept .cer files and SHOULD be able

Santesson & Housley                                             [Page 4]

INTERNET DRAFT Authority Information Access CRL Extension    August 2005

     to accept .p7c files.

     HTTP server implementations accessed via the URI SHOULD use the
     appropriate MIME content-type for the certificate containing file.
     Specifically, the HTTP server SHOULD use the content-type
     application/pkix-cert [PKIX-CERT] for a single DER encoded
     certificate and application/pkcs7-mime [CMC] for CMS certs-only
     (PKCS#7).  Consuming clients may use the MIME type and file
     extension as a hint to the file content, but should not depend
     solely on the presence of the correct MIME type or file extension
     in the server response.

     When the accessLocation is a directoryName, the information is to
     be obtained by the application from whatever directory server is
     locally configured.  When one CA public key is used to validate
     signatures on certificates and CRLs, the desired CA certificate is
     stored in the crossCertificatePair and/or cACertificate attributes
     as specified in [RFC 2587].  When different public keys are used to
     validate signatures on certificates and CRLs, the desired
     certificate is stored in the userCertificate attribute as specified
     in [RFC 2587]. Thus, implementations that support the directoryName
     form of accessLocation MUST be prepared to find the needed
     certificate in any of these three attributes.  The protocol that an
     application uses to access the directory (e.g., DAP or LDAP) is a
     local matter.

     Where the information is available via LDAP, the accessLocation
     SHOULD be a uniformResourceIdentifier.  The URI MUST specify a
     distingishedName and attribute(s) and MAY specify a host name
     (e.g., ldap://ldap.example.com/cn=example%20CA,dc=example,dc=com?
     cACertificate;binary,crossCertificatePair;binary).  Omitting the
     host name (e.g.,
     ldap:///cn=example%20CA,dc=example,dc=com?cACertificate;binary) has
     the effect of specifying the use of whatever LDAP server is locally
     configured.  The URI MUST list appropriate attribute descriptions
     for one or more attributes holding certificates or cross-
     certificate pairs.

3  Security Considerations

     Implementers should take into account the possible existence of
     multiple unrelated CAs and CRL issuers with the same name.

     Implementers should be aware of risks involved if the Authority
     Information Access extensions of corrupted CRLs contain links to
     malicious code.  Implementers should always take the steps of
     validating the retrieved data to ensure that the data is properly

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005

4  IANA Considerations

     This document has no actions for IANA.

5 References

     Normative references:

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

     [RFC 2587]  Boeyen, S., T. Howes, and P. Richard, "Internet X.509
                 Public Key Infrastructure: LDAPv2 Schema", June 1999.

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

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

     [URI]       Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
                 Resource Identifiers (URI): Generic Syntax", RFC 2396,
                 August 1998.

     [LDAP]      Wahl, M., Howes, T., and S. Kille, "Lightweight
                 Directory Access Protocol (v3)", RFC 2251,
                 December 1997.

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

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

     Informative references:

     [X.680]     ITU-T Recommendation X.680 (2002) | ISO/IEC
                 8824-1:2002), Information Technology - Abstract Syntax
                 Notation One, 2002.

     [X.690]     ITU-T Recommendation X.690 Information Technology -
                 ASN.1 encoding rules: Specification of Basic Encoding
                 Rules (BER), Canonical Encoding Rules (CER) and
                 Distinguished Encoding Rules (DER), 1997.

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005

Authors' Addresses

     Stefan Santesson
     Tuborg Boulevard 12
     2900 Hellerup

     EMail: stefans@microsoft.com

     Russell Housley
     Vigil Security, LLC
     918 Spring Knoll Drive
     Herndon, VA 20170

     EMail: housley@vigilsec.com

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INTERNET DRAFT Authority Information Access CRL Extension    August 2005


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Copyright Statement

     Copyright (C) The Internet Society (2005).

     This document is subject to the rights, licenses and restrictions
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Expires February 2006

Santesson & Housley                                             [Page 8]

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