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

[Bron Gondwana <[e-mail]>]

On Sat, 19 Aug 2017, at 11:43, Murray S. Kucherawy wrote:
> On Thu, Aug 17, 2017 at 5:22 PM, Brandon Long
> <[e-mail]> wrote:>> We went down the path of including a diff of the message in the
>> headers, but you run up against more complicated changes that make
>> that challenging.  Ie, mailing lists which strip attachments.  If all
>> we cared about were subject munging and footers, there probably would
>> have been a practical solution there.> 
> I wrote a draft a while ago that would allow a DKIM-Signature to
> include an annotation indicating that the signing ADMD did one or more
> of a specific set of small but well-defined message changes (e.g., add
> a footer, add a Subject tag).  Knowing what those are, a verifier
> could undo them and attempt validation of earlier signatures in the
> handling chain.  Presumably if no other modifications were made, the
> original content is thus discoverable, and you could then produce a
> chain of custody of the actual content before you that makes sense.> 
> If that's worthy of consideration now I could certainly revivify it.

That seems really valuable to me.  Being able to track the provenance on
individual parts of the message payload is a much stronger way to
determine who is at fault when bad content is being injected than just
knowing some bits of the message handling chain.
Bron.

--
  Bron Gondwana, CEO, FastMail Pty Ltd
  [e-mail]