ARC (was - Re: DMARC and ietf.org)

Dave Crocker <dhc@dcrocker.net> Sat, 13 August 2016 15:23 UTC

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Subject: ARC (was - Re: DMARC and ietf.org)
To: John R Levine <johnl@taugh.com>, "Theodore Ts'o" <tytso@mit.edu>
References: <c87f5578-be42-5a4e-d979-f4166e2f2ef2@gmail.com> <20160813023957.5679.qmail@ary.lan> <CAPt1N1mO0xxfc3SghV1pcNUjOz9yKk-g=bgU+dWrgy2LWcwhBg@mail.gmail.com> <20160813150004.GM10626@thunk.org> <alpine.OSX.2.11.1608131101040.12562@ary.local>
From: Dave Crocker <dhc@dcrocker.net>
Organization: Brandenburg InternetWorking
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Date: Sat, 13 Aug 2016 08:22:52 -0700
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On 8/13/2016 8:10 AM, John R Levine wrote:
> More to the point, ARC lets lists keep working they way they're supposed
> to.

I participate in the informal group that created ARC.  I am hoping ARC 
will be helpful.

But we need to be cautious with our expectations.  First, it isn't 
operational yet, so we don't even know whether it will do what we want 
it to.  Worse, we don't know how much that will help.

That's not a claim that it won't work or won't be useful, but it is 
playing amidst some Internet-scale, multi-stage dynamics that can get 
complicated.

By way of example:  With DKIM, trust assessment is of the entity doing 
the signing, typically the originating service.  With ARC, that 
assessment still must be made, but it must be coupled with an assessment 
of the first ARC-signing entity.

Maybe that's not a big deal.  But I think that combinatorial trust 
assessments are new and therefore might be challenging.

And that's not counting the question of whether an ARC signature will 
survive better than a DKIM signature...  (The design is intended to have 
better survival, but again, it hasn't been tested in the field.)

In terms of the current discussion, the essential point is that we need 
to make decision based on the here and now, and ARC isn't part of it and 
won't be for some time yet.

d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net