Multiple Signatures in Cryptographic Message Syntax (CMS)
RFC 5752
Internet Engineering Task Force (IETF) S. Turner
Request for Comments: 5752 IECA
Category: Standards Track J. Schaad
ISSN: 2070-1721 Soaring Hawk
January 2010
Multiple Signatures in Cryptographic Message Syntax (CMS)
Abstract
Cryptographic Message Syntax (CMS) SignedData includes the SignerInfo
structure to convey per-signer information. SignedData supports
multiple signers and multiple signature algorithms per signer with
multiple SignerInfo structures. If a signer attaches more than one
SignerInfo, there are concerns that an attacker could perform a
downgrade attack by removing the SignerInfo(s) with the 'strong'
algorithm(s). This document defines the multiple-signatures
attribute, its generation rules, and its processing rules to allow
signers to convey multiple SignerInfo objects while protecting
against downgrade attacks. Additionally, this attribute may assist
during periods of algorithm migration.
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 in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5752.
Copyright Notice
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Turner & Schaad Standards Track [Page 1]
RFC 5752 Multiple Signatures in S/MIME January 2010
include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
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Table of Contents
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................3
2. Rationale .......................................................3
2.1. Attribute Design Requirements ..............................4
3. Multiple Signature Indication ...................................5
4. Message Generation and Processing ...............................6
4.1. SignedData Type ............................................6
4.2. EncapsulatedContentInfo Type ...............................7
4.3. SignerInfo Type ............................................7
4.4. Message Digest Calculation Process .........................7
4.4.1. multiple-signatures Signed Attribute Generation .....7
4.4.2. Message Digest Calculation Process ..................7
4.5. Signature Generation Process ...............................8
4.6. Signature Verification Process .............................8
5. Signature Evaluation Processing .................................8
5.1. Evaluation of a SignerInfo Object ..........................9
5.2. Evaluation of a SignerInfo Set .............................9
5.3. Evaluation of a SignedData Set ............................10
6. Security Considerations ........................................11
7. References .....................................................11
7.1. Normative References ......................................11
7.2. Informative References ....................................12
Appendix A. ASN.1 Module...........................................13
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