PKIX Working Group S. Santesson (Microsoft) INTERNET-DRAFT R. Housley (Vigil Security) Expires July 2005 Updates RFC 3280 January 2005 Internet X.509 Public Key Infrastructure Authority Information Access CRL Extension Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668 Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract 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. Santesson & Housley [Page 1] INTERNET DRAFT Authority Information Access CRL Extension January 2005 Table of Contents 1 Introduction ................................................ 2 2 Authority Information Access Extension in CRL ............... 4 3 Security Considerations ..................................... 5 4 References .................................................. 5 Authors' Addresses ............................................. 6 Disclaimer ..................................................... 7 Copyright Statement ............................................ 7 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 One aspect involves the determination that a certificate has not been revoked, and one revocation checking mechanism is the Certificate Revocation List (CRL).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. There is however 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. Standardized methods of finding the certificate of the CRL issuer are currently available either though an accessible directory location or through use of the Subject Information Access extension in intermediary CA certificates. These methods are however not generally applicable, and they do not provide a generic solution to the problem. Directory lookup requires presence and access to a directory. The Subject Information Access extension supports building the CRL issuer certification path top-down (in the direction from the trust anchor to the CRL issuer), which can be complex and will fail if critical certificates in the CRL issuer certification path do not include an appropriate Subject Information Access extension. RFC 3280 [PKIX1] has provided for bottom-up discovery of certification paths through the Authority Information Access extension, where the id-ad-caIssuers access method may specify one or more accessLocation fields that contain references to CA certificates superior to the certificate containing this extension. Santesson & Housley [Page 2] INTERNET DRAFT Authority Information Access CRL Extension January 2005 This document provides a straightforward and generic solution to the CRL issuer certification path building problem by permitting use of the Authority Information Access extension in CRLs, enabling a CRL checking application to use the same access method (id-ad-caIssuers) to locate the certificate of the CRL issuer and, if necessary, complete the CRL issuer certification path building to an appropriate trust anchor. Santesson & Housley [Page 3] INTERNET DRAFT Authority Information Access CRL Extension January 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 extension. This CRL extension MUST NOT be marked critical. This extension MUST be identified by the extension object identifier (OID) defined in RFC 3280 (1.3.6.1.5.5.7.1.1), and the AuthotiyInfoAccessSyntax 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 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 acessMethod. Access method types other than id-ad-caIssuers MUST NOT be included. All present accessLocation values MUST use the uniformResourceIdentifier [URI] form, and the values MUST use either the ldap scheme [LDAP] or the http scheme [HTTP/1.1]. When ldap scheme is specified, the URI MUST point to an attribute containing one or more binary DER [X.660] encoded certificate. When the http scheme is specified, the URI MUST point to a certificate file. The certificate file MUST contain either a single DER encoded certificate (indicated by the .cer file extension) or contain a certification path (indicated by the .p7c file extension): .cer A single DER encoded certificate as specified in RFC 2585 [PKIX-CERT]. .p7c A MIME encoded application/pkcs7-mime "certs-only" file Santesson & Housley [Page 4] INTERNET DRAFT Authority Information Access CRL Extension January 2005 as specified in RFC 2797 [CMC]. 3 Security Considerations Implementers should take into account the possible existence of multiple unrelated CAs and CRL issuers with the same name. As means of reducing problems and security issues related to issuer name collisions, CA names SHOULD be formed in a way that reduce the likelihood of name collisions. Implementations validating CRLs MUST ensure that the certification path of the target certificate and the CRL issuer certification path used to validate the target certificate, terminate at the same trust anchor. 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 formed. 4 References Normative references: [RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. Santesson & Housley [Page 5] INTERNET DRAFT Authority Information Access CRL Extension January 2005 [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.660] ITU-T Recommendation X.660 Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER), 1997. Authors' Addresses Stefan Santesson Microsoft Tuborg Boulevard 12 2900 Hellerup Denmark EMail: stefans@microsoft.com Russell Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA EMail: housley@vigilsec.com Santesson & Housley [Page 6] INTERNET DRAFT Authority Information Access CRL Extension January 2005 Disclaimer This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2004). 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. Expires July 2005 Santesson & Housley [Page 7]