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Re: [dmarc-ietf] Reversing modifications from mailing lists

"Murray S. Kucherawy" <superuser@gmail.com> Tue, 30 November 2021 07:27 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Mon, 29 Nov 2021 23:27:34 -0800
Message-ID: <CAL0qLwa-bMyOKnQxJ0bzPAVAt41TQxTGU-qriiHZHswUMbgZxg@mail.gmail.com>
To: Wei Chuang <weihaw@google.com>
Cc: Alessandro Vesely <vesely@tana.it>, IETF DMARC WG <dmarc@ietf.org>
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Subject: Re: [dmarc-ietf] Reversing modifications from mailing lists
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On Thu, Nov 25, 2021 at 12:07 AM Wei Chuang <weihaw@google.com> wrote:

> Sorry I wasn't too clear here.  It's largely the same idea as the DKIM
> body length "l=" field above except for reformulated for the Subject header
> and its mailing list mutations.  The original sender would encode a length
> of the original subject say "s.l=<value>".  A receiver would only hash the
> right most "s.l=<value>" length string when validating a Subject hash from
> the original sender.  This assumes that mailing lists may prepend a string
> typically for identification.


Seems to me that means I could insert anything I want before the last N
octets of Subject -- say, a URI pointing you to an ad or other unsavory
content -- and the original signature will verify.

-MSK

>

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