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rfc:rfc4853

Network Working Group R. Housley Request for Comments: 4853 Vigil Security Updates: 3852 April 2007 Category: Standards Track

                 Cryptographic Message Syntax (CMS)
                   Multiple Signer Clarification

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 This document updates the Cryptographic Message Syntax (CMS), which
 is published in RFC 3852.  This document clarifies the proper
 handling of the SignedData protected content type when more than one
 digital signature is present.

Housley Standards Track [Page 1] RFC 4853 CMS Multiple Signer Clarification April 2007

1. Introduction

 This document updates the Cryptographic Message Syntax [CMS].  The
 CMS SignedData protected content type allows multiple digital
 signatures, but the specification is unclear about the appropriate
 processing by a recipient of such a signed content.  This document
 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 digital signatures from that signer are valid.
 This property is especially important in two cases.  First, when the
 recipients do not all implement the same digital signature algorithm,
 a signer can sign the content with several different digital
 signature algorithms so that each of the recipients can find an
 acceptable signature.  For example, if some recipients support RSA
 and some recipients support ECDSA, then the signer can generate two
 signatures, one with RSA and one with ECDSA, so that each recipient
 will be able to validate one of the signatures.  Second, when a
 community is transitioning one-way hash functions or digital
 signature algorithms, a signer can sign the content with the older
 and the newer signature algorithms so that each recipient can find an
 acceptable signature, regardless of their state in the transition.
 For example, consider a transition from RSA with SHA-1 to RSA with
 SHA-256.  The signer can generate two signatures, one with SHA-1 and
 one with SHA-256, so that each recipient will be able to validate at
 least one of the RSA signatures.

2. 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 [STDWORDS].

3. Update to RFC 3852, Section 5: Signed-data Content Type

 RFC 3852, section 5, the next to the last paragraph says:

Housley Standards Track [Page 2] RFC 4853 CMS Multiple Signer Clarification April 2007

 This block of text is replaced with:

4. Update to RFC 3852, Section 5.1: SignedData Type

 RFC 3852, section 5.1, the next to the last paragraph says:
 This block of text is replaced with:

Housley Standards Track [Page 3] RFC 4853 CMS Multiple Signer Clarification April 2007

6. Security Considerations

 The replacement text will reduce the likelihood of interoperability
 errors during the transition from MD5 and SHA-1 to stronger one-way
 hash functions, or to better signature algorithms.

7. Normative References

 [CMS]       Housley, R., "Cryptographic Message Syntax (CMS)", RFC
             3852, July 2004.
 [STDWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

Author's Address

 Russell Housley
 Vigil Security, LLC
 918 Spring Knoll Drive
 Herndon, VA 20170
 USA
 EMail: housley@vigilsec.com

Housley Standards Track [Page 4] RFC 4853 CMS Multiple Signer Clarification April 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Housley Standards Track [Page 5]

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