[Ietf-dkim] Adding an aim= tag to DKIM Signature Tag Specifications

Alessandro Vesely <vesely@tana.it> Mon, 11 May 2020 17:22 UTC

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To: ietf-dkim@ietf.org
From: Alessandro Vesely <vesely@tana.it>
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Date: Mon, 11 May 2020 19:21:55 +0200
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Subject: [Ietf-dkim] Adding an aim= tag to DKIM Signature Tag Specifications
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Hi all,

consider the famous incipit:

   DomainKeys Identified Mail (DKIM) permits a person, role, or
   organization to claim some responsibility for a message by
   associating a domain name [RFC1034] with the message [RFC5322], which
   they are authorized to use.

The question is, what responsibility is being claimed?  Some sites allow
authenticated users to use any From:, but are able to find out who the actual
author was, if needed.  Other sites only sign if the From: matches the actual
user, or at least its domain part.  Still others just sign everything.

Discussions about what kind of assurance would a signature imply are rather
frequent.  At least, specifying an aim= tag should shred some light on the
various possibilities.

Tagging keys with aim= would allow senders to choose an appropriate selector
under different circumstances.  Some mail sites use different sending IP
addresses to meet a similar purpose.  Others use different domain names, opaque
chunks of base64 data, or X-Google-DKIM-Signatures.  An aim= would serve a
similar purpose in a more open manner, introducing yet another means to discern
among different mail flows.