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

"Kurt Andersen (b)" <kboth@drkurt.com> Tue, 08 August 2017 13:36 UTC

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From: "Kurt Andersen (b)" <kboth@drkurt.com>
Date: Tue, 08 Aug 2017 06:36:02 -0700
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To: Bron Gondwana <brong@fastmailteam.com>
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Subject: Re: [dmarc-ietf] ARC-Seal is meaningless security theatre
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On Mon, Aug 7, 2017 at 9:10 PM, Bron Gondwana <brong@fastmailteam.com>
wrote:

> . . .  If you aren't willing to agree that the most recent liar can
> repurpose an existing chain, I'm happy to avoid making the forgery,
> otherwise I'll make up a forgery and send it to the list.
>
> But since you either trust every hop to do good checks, or you don't trust
> the entire message - then the ARC-Seal is literally adding nothing.  It
> adds no meaning, just extra work.  Hence my snakeoil claim.
>

Is your concern that the last hop (or any other) can essentially do a
wholesale replacement of the message contents and that there is no way to
distinguish that from a semantically meaningless footer tweak?

I'm not sure that I understand your assertion that you can forge an AS any
more than you could forge a DKIM signature.

--Kurt

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