Internet Engineering Task Force (IETF) S. Santesson
Request for Comments: 5816 3xA Security
Updates: 3161 N. Pope
Category: Standards Track Thales
ISSN: 2070-1721 March 2010
ESSCertIDv2 Update for RFC 3161
Abstract
This document updates RFC 3161. It allows the use of ESSCertIDv2, as
defined in RFC 5035, to specify the hash of a signer certificate when
the hash is calculated with a function other than the Secure Hash
Algorithm (SHA-1).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5816.
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Santesson & Pope Standards Track [Page 1]RFC 5816 ESSCertIDv2 Update for RFC 3161 March 2010
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Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................2
2. Updates to RFC 3161 .............................................3
2.1. Changes to Section 2.4.1, Request Format ...................3
2.2. Changes to Section 2.4.2, Response Format ..................3
2.2.1. Signature of Time-Stamp Token .......................3
2.2.2. Verifying the Time-Stamp Token ......................4
3. Security Considerations .........................................4
4. References ......................................................5
4.1. Normative References .......................................5
4.2. Informative References .....................................5
1. Introduction
The time-stamping protocol defined in RFC 3161 [RFC3161] requires
that the Cryptographic Message Syntax (CMS) SignedData [RFC5652],
used to apply a digital signature on the time-stamp token, include a
signed attribute that identifies the signer's certificate.
This identifier only allows SHA-1 [SHA1] to be used as the hash
algorithm to generate the identifier value.
The mechanism used in [RFC3161] employed ESSCertID from RFC 2634
[ESS]. RFC 5035 [ESSV2] updated ESSCertID with ESSCertIDv2 to allow
the use of any hash algorithm.
The changes to RFC 3161 [RFC3161] defined in this document allow
ESSCertIDv2 to be used to include an identifier of the signing
certificate as defined in RFC 5035 [ESSV2].
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].
Santesson & Pope Standards Track [Page 2]RFC 5816 ESSCertIDv2 Update for RFC 3161 March 2010
2. Updates to RFC 3161
2.1. Changes to Section 2.4.1, Request Format
Last paragraph on Page 5.
Old:
If the certReq field is present and set to true, the TSA's public
key certificate that is referenced by the ESSCertID identifier
inside a SigningCertificate attribute in the response MUST be
provided by the TSA in the certificates field from the SignedData
structure in that response. That field may also contain other
certificates.
New:
If the certReq field is present and set to true, the TSA's public
key certificate that is referenced by the ESSCertID [ESS] field
inside a SigningCertificate attribute or by the ESSCertIDv2
[ESSV2] field inside a SigningCertificateV2 attribute in the
response MUST be provided by the TSA in the certificates field
from the SignedData structure in that response. That field may
also contain other certificates.
2.2. Changes to Section 2.4.2, Response Format
2.2.1. Signature of Time-Stamp Token
Fifth paragraph on Page 8, just before the definition of TSTInfo.
Old:
The time-stamp token MUST NOT contain any signatures other than
the signature of the TSA. The certificate identifier (ESSCertID)
of the TSA certificate MUST be included as a signerInfo attribute
inside a SigningCertificate attribute.
New:
The time-stamp token MUST NOT contain any signatures other than
the signature of the TSA. The certificate identifier (either
ESSCertID [ESS] or ESSCertIDv2 [ESSV2]) of the TSA certificate
MUST be included as a signerInfo attribute inside a
SigningCertificate attribute.
Santesson & Pope Standards Track [Page 3]RFC 5816 ESSCertIDv2 Update for RFC 3161 March 2010
Note: As mentioned in RFC 5035 [ESSV2], the SigningCertificateV2
attribute MUST be used if any algorithm other than SHA-1 is
used and SHOULD NOT be used for SHA-1.
Note: For backwards compatibility, in line with RFC 5035, both
ESSCertID and ESSCertIDv2 MAY be present. Systems MAY
ignore ESSCertIDv2 if RFC 5035 has not been implemented.
2.2.2. Verifying the Time-Stamp Token
Third paragraph on Page 11.
Old:
The purpose of the tsa field is to give a hint in identifying the
name of the TSA. If present, it MUST correspond to one of the
subject names included in the certificate that is to be used to
verify the token. However, the actual identification of the
entity that signed the response will always occur through the use
of the certificate identifier (ESSCertID Attribute) inside a
SigningCertificate attribute which is part of the signerInfo (See
Section 5 of [ESS]).
New:
The purpose of the tsa field is to give a hint in identifying the
name of the TSA. If present, it MUST correspond to one of the
subject names included in the certificate that is to be used to
verify the token. However, the actual identification of the
entity that signed the response will always occur through the use
of the certificate identifier (ESSCertID inside a
SigningCertificate attribute or ESSCertIDv2 inside a
SigningCertificateV2 attribute) that is part of the signerInfo
(see Section 5 of [ESS] and Section 3 of [ESSV2]).
3. Security Considerations
This document incorporates the security considerations of RFC 5035
[ESSV2] with further explanations in this section.
ESSCertID provides a means based on the SHA-1 hash algorithm for
identifying the certificate used to verify the signature on a time
stamp. The use of ESSCertIDv2 aims to enable implementers to comply
with policies that require phasing out all uses of the SHA-1
algorithm.
Santesson & Pope Standards Track [Page 4]RFC 5816 ESSCertIDv2 Update for RFC 3161 March 2010
The update provided by this document is motivated by reasons of
interoperability and migration to other hash algorithms rather than
mitigating new security issues.
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.
[ESS] Hoffman, P., Ed., "Enhanced Security Services for
S/MIME", RFC 2634, June 1999.
[ESSV2] Schaad, J., "Enhanced Security Services (ESS) Update:
Adding CertID Algorithm Agility", RFC 5035, August 2007.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, August 2001.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 5652, September 2009.
4.2. Informative References
[SHA1] Secure Hash Standard. FIPS Pub 180-1. National Institute
of Standards and Technology. 17 April 1995.
Authors' Addresses
Stefan Santesson
3xA Security AB
Sweden
EMail: sts@aaa-sec.com
Nick Pope
Thales Information Systems Security
Long Crendon, Aylesbury
United Kingdom
EMail: nick.pope@thales-esecurity.com
Santesson & Pope Standards Track [Page 5]
