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S/MIME WG                                                     S. Turner
Internet Draft                                               IECA, Inc.
Intended Status: Standard Track                            May 20, 2007
Expires: November 20, 2007



          Using SHA2 Algorithms with Cryptographic Message Syntax
                       draft-ietf-smime-sha2-00.txt


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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes the conventions for using the message digest
   algorithms SHA-224, as defined in [RFC3874], and SHA-256, SHA-384,
   SHA-512, as defined in [SHA2], with the Cryptographic Message Syntax
   (CMS) [RFC3852].





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Conventions used in this document

   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 [RFC2119].

Table of Contents

   1. Introduction...................................................2
   2. SHA2 Message Digest Algorithms.................................2
      2.1. SHA-224...................................................3
      2.2. SHA-256...................................................4
      2.3. SHA-384...................................................4
      2.4. SHA-512...................................................4
   3. Security Considerations........................................4
   4. IANA Considerations............................................4
   5. References.....................................................5
      5.1. Normative References......................................5
      5.2. Informative References....................................5

1. Introduction

   This document specifies the algorithm identifiers and specifies
   parameters for the message digest algorithms SHA-224, SHA-256, SHA-
   384, and SHA-512 for use with the Cryptographic Message Syntax (CMS)
   [RFC3852].  The message digest algorithms are defined in [RFC3874]
   and [SHA2].  If an implementation chooses to support one of the
   algorithms discussed in this document, then the implementation MUST
   do so as described in this document.

   This document does not define new identifiers; they are taken from
   [RFC3874] and [RFC4055].  Additionally, the parameters follow the
   conventions specified therein.  Therefore, there is no ASN.1 module
   included in this document.

   Note that [RFC4231] specifies the conventions for use of for the
   message authentication code (MAC) algorithms: HMAC with SHA-224, HMAC
   with SHA-256, HMAC with SHA-384, and HMAC with SHA-512.

2. SHA2 Message Digest Algorithms

   Digest algorithm identifiers are located in the SignedData
   digestAlgorithms field, the SignerInfo digestAlgorithm field, the
   DigestedData digestAlgorithm field, and the AuthenticatedData
   digestAlgorithm field.




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   Digest values are located in the DigestedData digest field and the
   Message Digest authenticated attribute.  In addition, digest values
   are input to signature algorithms.

   In CMS, the digest algorithm identifiers use the AlgorithmIdentifier
   syntax, which is included here for convenience:

     AlgorithmIdentifier  ::=  SEQUENCE  {
       algorithm   OBJECT IDENTIFIER,
       parameters  ANY DEFINED BY algorithm OPTIONAL  }

   The algorithm field is discussed in Sections 2.1-2.4 for each message
   digest algorithm.

   The following addresses the parameters field:

   There are two possible encodings for the SHA AlgorithmIdentifier
   parameters field.  The two alternatives arise from the fact that when
   the 1988 syntax for AlgorithmIdentifier was translated into the 1997
   syntax, the OPTIONAL associated with the AlgorithmIdentifier
   parameters got lost.  Later the OPTIONAL was recovered via a defect
   report, but by then many people thought that algorithm parameters
   were mandatory.  Because of this history some implementations encode
   parameters as a NULL element and others omit them entirely.  The
   correct encoding is to omit the parameters field; however,
   implementations MUST also handle a SHA AlgorithmIdentifier parameters
   field which contains a NULL.

   The AlgorithmIdentifier parameters field is OPTIONAL.  If present,
   the parameters field MUST contain a NULL.  Implementations MUST
   accept SHA2 AlgorithmIdentifiers with absent parameters.
   Implementations MUST accept SHA2 AlgorithmIdentifiers with NULL
   parameters.  Implementations SHOULD generate SHA2
   AlgorithmIdentifiers with absent parameters.

2.1. SHA-224

   The SHA-224 message digest algorithm is defined in [RFC3874].  The
   algorithm identifier for SHA-224 is:

     id-sha224 OBJECT IDENTIFIER ::= {
        joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
        csor(3) nistalgorithm(4) hashalgs(2) 4 }

   The parameters are as specified in Section 2.




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2.2. SHA-256

   The SHA-256 message digest algorithm is defined in [SHA2].  The
   algorithm identifier for SHA-256 is:

    id-sha256 OBJECT IDENTIFIER ::= {
        joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
        csor(3) nistalgorithm(4) hashalgs(2) 1 }

   The parameters are as specified in Section 2.

2.3. SHA-384

   The SHA-384 message digest algorithm is defined in [SHA2].  The
   algorithm identifier for SHA-384 is:

     id-sha384 OBJECT IDENTIFIER ::= {
       joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
       csor(3) nistalgorithm(4) hashalgs(2) 2 }

   The parameters are as specified in Section 2.

2.4. SHA-512

   The SHA-256 message digest algorithm is defined in [SHA2].  The
   algorithm identifier for SHA-512 is:

     id-sha512 OBJECT IDENTIFIER ::= {
       joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
       csor(3) nistalgorithm(4) hashalgs(2) 3 }

   The parameters are as specified in Section 2.

3. Security Considerations

   No new security considerations are added to those already documented
   in [RFC3370], [RFC3874], and [RFC4055].

4. IANA Considerations

   None: All identifiers are already registered.  Please remove this
   section prior to publication as an RFC.







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5. References

5.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119. March 1997.

   [RFC3852] Housley, R., "The Cryptographic Message Syntax (CMS)", RFC
             3852. July 2004.

   [RFC3874] Housley, R., "A 224-bit One Way Hash Function: SHA-224",
             RFC 3874. September 2004.

   [RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional
             Algorithms and Identifiers for RSA Cryptography for use in
             the Internet Public Key Infrastructure Certificate and
             Certificate Revocation List (CRL) Profile", RFC 4055. June
             2005.

   [SHA2]    National Institute of Standards and Technology (NIST), FIPS
             Publication 180-2: Secure Hash Standard, 1 August 2002.

5.2. Informative References

   [RFC4231] Nystrom, A. "Identifiers and Test Vectors for HMAC-SHA-224,
             HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC4231.
             December 2005.

Author's Addresses

   Sean Turner
   IECA, Inc.

   Email: turners@ieca.com















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