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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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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