[lamps] Fw: New Version Notification for draft-ietf-lamps-cms-euf-cma-signeddata-03.txt

[Daniel Van Geest <[e-mail]>]

This version address Roman's AD review.

Falko also performed a Claude Fable 5.1 review of the document, which pointed out a key separation issue which is addressed in a new section.

If this document is followed and signedAttrs is mandated (either through using a non-id-data content type, or explicitly by a protocol which defines a use of CMS SignedData), but the signing key is used in another context (other protocol or content type where signedAttrs is not mandated), then the other context might be used as a signing oracle against the stronger context.  In particular, this issue arises if you update a protocol to require signedAttrs but an application has to continue to support signing with the older version with the same key for backwards compatibility reasons.  This is also an issue if you have multiple applications signing with the same key (e.g. desktop and mobile S/MIME client) and they are not updated at the same time. Mitigations for this are to use separate keys (not always possible) or apply the sender detection mitigations (difficult because this could apply to deployed code).

Significant changes:

  *
This document now updates RFC 5652.
  *
"new use" of CMS Signed data is defined in the Conventions and Definitions section.
  *
Give more details on the contents of the mimeData content type.
  *
Add explanations for SHOULDs.
  *
Add Key Separation section and security considerations.
  *
Change some SHOULDs to MUSTs when it is a new use of CMS SignedData.

Daniel

________________________________
From: [e-mail] <[e-mail]>
Sent: Monday, September 14, 2026 1:10 PM
To: Daniel Van Geest <[e-mail]>; Falko Strenzke <[e-mail]>
Subject: New Version Notification for draft-ietf-lamps-cms-euf-cma-signeddata-03.txt

A new version of Internet-Draft draft-ietf-lamps-cms-euf-cma-signeddata-03.txt
has been successfully submitted by Daniel Van Geest and posted to the
IETF repository.

Name:     draft-ietf-lamps-cms-euf-cma-signeddata
Revision: 03
Title:    Best Practices for Signed Attributes in CMS SignedData
Date:     2026-09-14
Group:    lamps
Pages:    19
URL:      https://www.ietf.org/archive/id/draft-ietf-lamps-cms-euf-cma-signeddata-03.txt
Status:   https://datatracker.ietf.org/doc/draft-ietf-lamps-cms-euf-cma-signeddata/
HTML:     https://www.ietf.org/archive/id/draft-ietf-lamps-cms-euf-cma-signeddata-03.html
HTMLized: https://datatracker.ietf.org/doc/html/draft-ietf-lamps-cms-euf-cma-signeddata
Diff:     https://author-tools.ietf.org/iddiff?url2=draft-ietf-lamps-cms-euf-cma-signeddata-03

Abstract:

   The Cryptographic Message Syntax (CMS) has different signature
   verification behaviour based on whether signed attributes are present
   or not.  This results in a potential existential forgery
   vulnerability in CMS and protocols which use CMS.  This document
   describes the vulnerability and lists mitigations and best practices
   to avoid it.  This document updates RFC 5652 by prohibiting the use
   of the id-data content type for new uses of the CMS SignedData type.



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