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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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].

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.

      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.

   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