Subject: [ietf-dkim] ISSUE: Verifiers MUST implement rsa-sha256

From: Alessandro Vesely <[email-masked]>
Date: Mon, 18 Apr 2011 18:22:28 +0200

Section 3.3 has the phrase

   Verifiers MUST implement rsa-sha256

Implementers will understand that they can go away with a verifier
that does not implement rsa-sha1.  Their verifier would then return
PERMFAIL for the sha1-signed newsletter in the following informative
note.  I suggest to clarify this as follows:

   INFORMATIVE NOTE: Although sha256 is strongly encouraged, some
   senders of low-security messages (such as routine newsletters) may
   prefer to use sha1 because of reduced CPU requirements to compute
   a sha1 hash.  MTAs whose verifiers don't implement rsa-sha1 will
   treat these messages as if they were not signed.  In general,
   sha256 should always be used whenever possible.

See also http://mipassoc.org/pipermail/ietf-dkim/2011q1/015464.html
(which was written at a time when verifiers were mandated to implement
both sha digests.)  This change is meant to prevent that kind of
misunderstandings.

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