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Internet Engineering Task Force (IETF)                      S. SantessonRequest for Comments: 5816                                  3xA SecurityUpdates:3161                                                    N. PopeCategory: Standards Track                                         ThalesISSN: 2070-1721                                               March 2010ESSCertIDv2 Update forRFC 3161Abstract   This document updatesRFC 3161.  It allows the use of ESSCertIDv2, as   defined inRFC 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5816.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of thisSantesson & Pope             Standards Track                    [Page 1]

RFC 5816             ESSCertIDv2 Update forRFC 3161          March 2010   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1. Introduction ....................................................21.1. Terminology ................................................22. Updates toRFC 3161 .............................................32.1. Changes toSection 2.4.1, Request Format ...................32.2. Changes toSection 2.4.2, Response Format ..................32.2.1. Signature of Time-Stamp Token .......................32.2.2. Verifying the Time-Stamp Token ......................43. Security Considerations .........................................44. References ......................................................54.1. Normative References .......................................54.2. Informative References .....................................51.  Introduction   The time-stamping protocol defined inRFC 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 fromRFC 2634   [ESS].RFC 5035 [ESSV2] updated ESSCertID with ESSCertIDv2 to allow   the use of any hash algorithm.   The changes toRFC 3161 [RFC3161] defined in this document allow   ESSCertIDv2 to be used to include an identifier of the signing   certificate as defined inRFC 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 inRFC 2119 [RFC2119].Santesson & Pope             Standards Track                    [Page 2]

RFC 5816             ESSCertIDv2 Update forRFC 3161          March 20102.  Updates toRFC 31612.1.  Changes toSection 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 toSection 2.4.2, Response Format2.2.1.  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 forRFC 3161          March 2010      Note: As mentioned inRFC 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 withRFC 5035, both            ESSCertID and ESSCertIDv2 MAY be present.  Systems MAY            ignore ESSCertIDv2 ifRFC 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] andSection 3 of [ESSV2]).3.  Security Considerations   This document incorporates the security considerations ofRFC 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 forRFC 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.  References4.1.  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.comSantesson & Pope             Standards Track                    [Page 5]