Re: Aptness of DKIM for MLs

Hi Alessandro,
At 03:23 09-05-2014, Alessandro Vesely wrote:
>No, it doesn't.  It broke elandsys' signature, but check tana's
>signature on this message.  (I send this to ietf-822 only, to avoid
>any confusion.)

The verifier at my end validated the ietf.org signature instead of 
the tana.it signature.

>So it seems I could publish a strict DMARC policy right now, and cause
>minimal disruptions.  However, some verifiers (NetEase) consider
>tana's h= inadequate, see "objection" below.
>
> > Gratuitous changes to a mailing list message is a matter of
> > opinion.
>
>Well, not exactly.
>
>For corrections, section 6.4 of RFC 5321 is rather clear that
>submission servers MAY, while intermediate relays MUST NOT, apply
>certain changes.  So the range where opinions may vary is whether an
>MLM is to be considered akin to submission servers or relays.
>
>By /gratuitous/ changes, such as adding/removing double quote marks, I
>mean unnecessary embellishments that were already disputable before
>DKIM took root.

I thought that you mean subject tagging, etc.  If the objective is to 
ensure that an MLM does not make any change it is easier to say "MLM 
must not make any change as that will break X" instead of looking for 
a clause to justify whether any change is appropriate.

>Yes, much of this discussion was recited at the time of ADSP, for
>example http://mipassoc.org/pipermail/ietf-dkim/2010q3/013829.html
>
>The most relevant objection to weak signatures is why would domains so
>concerned about security as to publish a strong policy weaken their
>DKIM signatures?  A solution is to do so for ML messages only.

Yes, it would weaken the DKIM signature.

>To recap, assume a domain has a DB of (user, mailing list) pairs which
>defines ML traffic.  Messages to ML are then sent in separate SMTP
>transactions and weakly signed.  MLMs sign those messages in turn,
>using strong signatures.  Verifiers derive the validity of MLM domains
>by comparing d= against To: or Cc: mailboxes.
>
>Besides minor refinements, the major bar is to build that DB.  I
>proposed to do it manually for starting, and then find out how to
>automate its maintenance.

I'd say try it. :-)  You may have to convince the people writing the 
software to make changes.  That's usually the difficult part.

Regards,
S. Moonesamy 

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