IETF S. Farrell
Internet-Draft Trinity College Dublin
Intended status: Informational December 21, 2007
Expires: June 23, 2008
Other Certificates Extension
draft-farrell-pkix-other-certs-00
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Some applications using public key certificates can benefit from a
way to link together a set of certificates belonging to the same end
entity. This memo defines a certificate extension that supports such
linkage.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. A Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Other Certificates Extension . . . . . . . . . . . . . . . . . 4
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . . . 6
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1. Introduction
RFC 3280 [RFC3280] defines a profile for the use of public key
certificates for Internet applications. Some applications may
require a way to link together a set of certificates belonging to the
same end entity so this memo defines a new public key certificate
extension that supports such linkage.
Other than asserting that the set of certificates belong to the same
end entity, the semantics of the actual linkage of certifcates is not
defined here, that is a matter for application developers and the
operators of certification authorities (CAs). In particular we do
not define how a CA can validate that the same end entity is the
holder of the various private keys, nor how any application should
make use of this information. This memo simply defines the relevant
syntax.
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. A Use Case
Public key certificates expire, typically about a year after they are
created. Some applications might need to know that the same entity
is the subject of this certificate and a previously used certificate.
For example, if a web server certificate expires, it could be useful
for a web browser to know that the server currently presenting a
certificate in a TLS [RFC4346] handshake represents the same web
server that previously presented a certificate. This could be used
for example to allow the browser to automatically fill in form fields
for the server in question, even if the server certificate has been
replaced. While the same effect can be achieved based on the use of
the same issuer and subject fields in a certificate there could be
security issues involved in such comparisons, e.g. if the subject
name includes a DNS name and the ownership of that DNS domain has
changed.
The use of the new extension provides a way for the CA to signal to
the application that the same end entity is involved, regardless of
name changes. The new extension could also allow the web site
operator to more easily change CA when renewing its certificate.
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3. Other Certificates Extension
This section defines the syntax for the other certificates extension.
The new extension is simply a list of other issuer/serial number
pairs from the linked certificates. The IssuerAndSerialNumber
construct is taken from CMS [RFC3852].
When this extension is present the CA is asserting that the same end
entity is the subject of the relevant certificates. Mechanisms for
how this assertion is validated by the CA or used by consumers of the
certificate are out of scope of this memo.
This extension MUST NOT be marked critical.
id-ce-otherCerts OBJECT IDENTIFIER ::== { id-ce XXX }
OtherCertificates ::= SEQUENCE OF IssuerAndSerialNumber
4. Acknowledgements
The use case motivating this was contributed to the W3C web security
context (WSC) working group by Tyler Close. See
http://www.w3.org/2006/WSC/wiki/SafeWebFormEditor for details.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
TBD. Some warnings for CAs and applications needed.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3280] 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.
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[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
7.2. Informative References
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
Appendix A. ASN.1 Module
TBD
Author's Address
Stephen Farrell
Trinity College Dublin
Department of Computer Science
Trinity College
Dublin, 2
Ireand
Phone: +353-1-896-1761
Email: stephen.farrell@cs.tcd.ie
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