Subject: Concerning http://www.ietf.org/internet-drafts/draft-ietf-smime-cms-mult-sign-01.txt

From: "Dale Moberg" <[email-masked]>
Date: Thu, 20 Jul 2006 16:14:07 -0700

Readers of this list are likely to recognize that the CMS specification,
which underlies some SMIME RFCs, defines ASN.1 cryptographic data
layouts that are used in EDIINT application statements (AS1, AS2, ...)
 
A proposed revision is under discussion that may be of interest to this
group as it could impact underlying implementations eventually.
 
Cryptographic Message Syntax (CMS) Multiple Signer Clarification
<draft-ietf-smime-cms-mult-sign-01.txt>

Normally, multiple signers are not used in EDIINT messages, but they
could occur because CMS allows them.

The internet-draft says (and please read it for the exact language) that
when receiving CMS messages with multiple signatures, the default rule
(as I will call it) will be that the message is OK if one of the
signatures is OK. It also mentions that certain communities may wish to
have a different rule that replaces the default rule.

One justification for the default rule is that it will promote
interoperability for use cases in which an old and a new certificate are
both used, and the signers want to provide signatures using both the old
and the new certificate (which may have different strengths, use new
improved hashes, etc). That way, receivers who have not managed to
update their systems (even after using CEM!) may still validate the
signatures and continue operations. 

I have not seen much discussion about security threats or risks that
might arise from adhering to this rule.

Because changes to CMS options may impact security toolkits, it is worth
considering whether readers of this group have any questions for the
security group that is considering this change. Please send questions or
assessment of risks or threats to them.