Multiple Signatures in Cryptographic Message Syntax (CMS)
RFC 5752
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RFC - Proposed Standard
(January 2010; Errata)
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2015-10-14
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RFC 5752 (Proposed Standard)
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Tim Polk
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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
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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
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