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Re: [dmarc-ietf] ARC-Seal is meaningless security theatre

Bron Gondwana <brong@fastmailteam.com> Thu, 17 August 2017 00:21 UTC

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From: Bron Gondwana <brong@fastmailteam.com>
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Date: Thu, 17 Aug 2017 10:21:43 +1000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/dmarc/mlISzqVkCbR3Ec12nJtHE-5scyc>
Subject: Re: [dmarc-ietf] ARC-Seal is meaningless security theatre
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On Thu, 17 Aug 2017, at 03:46, Hector Santos wrote:
> On 8/13/2017 10:28 AM, Kurt Andersen (b) wrote:
>> On Sat, Aug 12, 2017 at 4:51 PM, Hector Santos wrote:
>> 
>>   If we even have a DMARC ARC Policy concept, than that may be
>>   enough to begin pursuing the high cost of experimentation and
>>   development here.
>> 
>> 
>> Beyond the protocol and usage specs, what are you looking for?
>> 
> 
> A practical purpose for supporting (implementing) this work.   It
> appears ARC wants the network to stamp mail "blindly" as the mail
> travels from point to point.  I am trying to grasp how it helps
> resolve the main issue with "unauthorized" indirect 3rd party
> signatures, in particular when dealing with strong, exclusive DKIM
> signature policy models such as DMARC p=reject.

We spent a while thinking about this (Neil and myself from FastMail) at
IETF99 after learning how ARC works, and came to the conclusion that ARC
as specified can't help with DMARC p=reject.
The only way you could even hope (as a mailing list) to avoid rewriting
the sender is for every site that currently has DMARC p=reject to change
that to a new policy which explicitly means "only reject if no ARC
chain" - otherwise you can't stop rewriting sender until you know that
every receiver on your list is ARC-aware.
Bron.

--
  Bron Gondwana, CEO, FastMail Pty Ltd
  brong@fastmailteam.com

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