Subject: [dmarc-ietf] invalid ARC chains

From: Gene Shuman <[email-masked]>
Date: Mon, 30 Jan 2017 10:24:51 -0800

Extricating this discussion from the one about key sizes.  We left off
at discussing whether we should implement something like a cv=invalid
for arc chains that are no longer well defined.

Brandon, I think you had the last response, and suggested that
receivers just refuse to continue to process invalid chains?  This
seems plausible, and might be simpler.  I have no strong opinions one
way or the other, although I think I slightly prefer the cv=invalid
state, as it strictly defines what receivers are to do with invalid
chains.

Regardless, I still stand by the fact that section 5.2.1 needs to go &
that we should probably explicitly codify what constitutes an invalid
arc chain.

Regards,
=Gene

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From: Kurt Andersen <[email-masked]>
Date: Mon, 30 Jan 2017 14:59:00 -0800

> that we should probably explicitly codify what constitutes an invalid

I don't think that 5.2.1 needs to be deleted, just significantly refactored
(which I plan to do next weekend).

I think that having a participating receiver mark an chain as "broken
beyond repair" (aka = invalid) is a beneficial terminal state beyond which
no other mediators should perform any further ARC machinations. It's
certainly possible that a malicious mediator could essentially break every
ARC chain that it sees, but that's no different than what can happen today
and also is a situation that we are not trying to solve.

--Kurt