draft-ietf-smime-cms-mult-sign-03.txt   rfc4853.txt 
S/MIME Working Group R. Housley Network Working Group R. Housley
Updates: 3852 (once approved) Vigil Security Request for Comments: 4853 Vigil Security
Expires August 2007 February 2007
Category: Standards Track
Cryptographic Message Syntax (CMS) Cryptographic Message Syntax (CMS)
Multiple Signer Clarification Multiple Signer Clarification
<draft-ietf-smime-cms-mult-sign-03.txt>
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Abstract Abstract
This document updates the Cryptographic Message Syntax (CMS), which This document updates the Cryptographic Message Syntax (CMS), which
is published in RFC 3852. This document clarifies the proper is published in RFC 3852. This document clarifies the proper
handling of the SignedData protected content type when more than one handling of the SignedData protected content type when more than one
digital signature is present. digital signature is present.
1. Introduction 1. Introduction
This document updates the Cryptographic Message Syntax (CMS) [CMS]. This document updates the Cryptographic Message Syntax [CMS]. The
The CMS SignedData protected content type allows multiple digital CMS SignedData protected content type allows multiple digital
signatures, but the specification is unclear about the appropriate signatures, but the specification is unclear about the appropriate
processing by a recipient of such a signed content. This document processing by a recipient of such a signed content. This document
provides replacement text for a few paragraphs, making it clear that provides replacement text for a few paragraphs, making it clear that
the protected content is validly signed by a given signer, if any of the protected content is validly signed by a given signer, if any of
the digital signatures from that signer is valid. the digital signatures from that signer are valid.
This property is especially important in two cases. First, when the This property is especially important in two cases. First, when the
recipients do not all implement the same digital signature algorithm, recipients do not all implement the same digital signature algorithm,
a signer can sign the content with several different digital a signer can sign the content with several different digital
signature algorithms so that each of the recipients can find an signature algorithms so that each of the recipients can find an
acceptable signature. For example, if some recipients support RSA acceptable signature. For example, if some recipients support RSA
and some recipients support ECDSA, then the signer can generate two and some recipients support ECDSA, then the signer can generate two
signatures, one with RSA and one with ECDSA, so that each recipient signatures, one with RSA and one with ECDSA, so that each recipient
will be able to validate one of the signatures. Second, when a will be able to validate one of the signatures. Second, when a
community is transitioning one-way hash functions or digital community is transitioning one-way hash functions or digital
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| signerInfos is a collection of per-signer information. There MAY | signerInfos is a collection of per-signer information. There MAY
| be any number of elements in the collection, including zero. When | be any number of elements in the collection, including zero. When
| the collection represents more than one signature, the successful | the collection represents more than one signature, the successful
| validation of one of signature from a given signer ought to be | validation of one of signature from a given signer ought to be
| treated as a successful signature by that signer. However, | treated as a successful signature by that signer. However,
| there are some application environments where other rules are | there are some application environments where other rules are
| needed. The details of the SignerInfo type are discussed in | needed. The details of the SignerInfo type are discussed in
| section 5.3. Since each signer can employ a different digital | section 5.3. Since each signer can employ a different digital
| signature technique and future specifications could update the | signature technique, and future specifications could update the
| syntax, all implementations MUST gracefully handle unimplemented | syntax, all implementations MUST gracefully handle unimplemented
| versions of SignerInfo. Further, since all implementations will | versions of SignerInfo. Further, since all implementations will
| not support every possible signature algorithm, all | not support every possible signature algorithm, all
| implementations MUST gracefully handle unimplemented signature | implementations MUST gracefully handle unimplemented signature
| algorithms when they are encountered. | algorithms when they are encountered.
6. Security Considerations 6. Security Considerations
The replacement text will reduce the likelihood of interoperability The replacement text will reduce the likelihood of interoperability
errors during the transition from MD5 and SHA-1 to stronger one-way errors during the transition from MD5 and SHA-1 to stronger one-way
hash functions, or to better signature algorithms. hash functions, or to better signature algorithms.
7. Normative References 7. Normative References
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", [CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
RFC 3852, July 2004. 3852, July 2004.
[STDWORDS] S. Bradner, "Key words for use in RFCs to Indicate [STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
8. IANA Considerations Author's Address
None. Please remove this section prior to publication as an RFC.
Authors' Addresses
Russell Housley Russell Housley
Vigil Security, LLC Vigil Security, LLC
918 Spring Knoll Drive 918 Spring Knoll Drive
Herndon, VA 20170 Herndon, VA 20170
USA USA
EMail: housley(at)vigilsec.com EMail: housley@vigilsec.com
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