Network Working Group S. Santesson
Request for Comments: 4325 Microsoft
Updates: 3280 R. Housley
Category: Standards Track Vigil Security
December 2005
Internet X.509 Public Key Infrastructure Authority Information
Access Certificate Revocation List (CRL) Extension
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.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document updates RFC 3280 by defining the Authority Information
Access Certificate Revocation List (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.
Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................3
2. Authority Information Access CRL Extension ......................3
3. Security Considerations .........................................5
4. References ......................................................5
4.1. Normative References .......................................5
4.2. Informative References .....................................6
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RFC 4325 Authority Information Access CRL Extension December 2005
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One aspect involves the determination that a certificate has not been
revoked, and one revocation checking mechanism is the Certificate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 through an accessible directory location or
through use of the Subject Information Access extension in
intermediary CA certificates.
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
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.
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RFC 4325 Authority Information Access CRL Extension December 2005
1.1. Terminology
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 RFC 2119 [RFC2119].
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
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
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 Lightweight Directory
Access Protocol [LDAP] Uniform Resource Identifier [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 Distinguished Encoding Rules (DER) [X.690] encoded
certificate (indicated by the .cer file extension) or a collection of
certificates (indicated by the .p7c file extension):
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RFC 4325 Authority Information Access CRL Extension December 2005
.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
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 [RFC2587]. 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 [RFC2587]. 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.
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RFC 4325 Authority Information Access CRL Extension December 2005
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
formed.
4. References
4.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2587] Boeyen, S., Howes, T., and P. Richard, "Internet X.509
Public Key Infrastructure: LDAPv2 Schema", RFC 2587, June
1999.
[PKIX1] Housley, R., Polk, W., Ford, W., 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 Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[LDAP] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[PKIX-CERT] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP", RFC
2585, May 1999.
[CMC] Myers, M., Liu, X., Schaad, J., and J. Weinstein,
"Certificate Management Messages over CMS", RFC 2797,
April 2000.
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RFC 4325 Authority Information Access CRL Extension December 2005
4.2. 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.
Authors' Addresses
Stefan Santesson
Microsoft
Tuborg Boulevard 12
2900 Hellerup
Denmark
EMail:
[email protected]
Russell Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail:
[email protected]
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RFC 4325 Authority Information Access CRL Extension December 2005
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Copyright (C) The Internet Society (2005).
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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