[Mailman-Developers] dkim-signature headers

[Stephen J. Turnbull]

Michael Thomas writes:

 > Let's be clear that I'm advocating a dialog here,

In some sense, there's very little room for dialog, unless it involves
substantial amendments to DKIM.  This is inherent in the design: the
whole message is signed.  Preserve it nearly verbatim or break the
signature.

This need not be a problem, however, as long as users can be taught
not to panic because one signature doesn't verify.  See below.

 > I'm hoping that we can  come up with some finesse.

It's not obvious to me that a finesse is necessary or desirable.  IMO,
the right answer is for mailing lists to sign the posts that pass
through them, and to publish a BCP that extols the manifold advantages
to lazy admins<wink> of vetting a bunch of mailing lists and then
trusting the signatures of the trustworthy ones.

The transition period may be painful, but so is spam.

 > In any case, if you have some ideas about what list friendly
 > wording is, I'd be happy to hear it.

After reading dkim-base-8, things are a lot clearer.  Specifically,
the updated Section 4 makes it clear that there's no reason why a
mailing list is a second-class citizen:

   Of course, a message might also have multiple signatures because it
   passed through multiple signers.  A common case is expected to be
   that of a signed message that passes through a mailing list that also
   signs all messages.  Assuming both of those signatures verify, a
   recipient might choose to accept the message if either of those
   signatures were known to come from trusted sources.

While I could wish for a stronger endorsement, I realize that is about
as strong an endorsement as you'll find in an informative section in a
standards-track RFC.  I guess in the BCP I'd like to see that language
(at least) repeated with encouragement to implementers to (eg) have
verifiers look for a mailing list signature if RFC 2369 headers are
present.  The heuristic being the one I've been hammering on: if your
users are subscribed to a mailing list, they evidently trust it to a
greater or lesser degree.  And of course users and ISPs should be
encouraged to use MUAs and servers that employ verifiers with those
features.

By the way: *WARNING* Most of the links from the DKIM site point to
version dkim-base-7b, while the current version is dkim-base-8.  The
latter has a much more satisfactory Section 4 (on multiple
signatures).  Most recent version (currently v8) is here:

https://datatracker.ietf.org/public/idindex.cgi?command=id_detail&id=14210