Re: [MLS] Functional Definition of End-to-End Secure Messaging

Alec Muffett <alec.muffett@gmail.com> Sat, 08 May 2021 21:10 UTC

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From: Alec Muffett <alec.muffett@gmail.com>
Date: Sat, 8 May 2021 22:09:50 +0100
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To: Raphael Robert <ietf@raphaelrobert.com>
Cc: Messaging Layer Security WG <mls@ietf.org>
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Subject: Re: [MLS] Functional Definition of End-to-End Secure Messaging
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On Sat, 8 May 2021 at 20:26, Alec Muffett <alec.muffett@gmail.com> wrote:

> We must also quote Section 4.1:
>
> > Participant: A participant is any entity - human, machine, software bot,
> conversation archiver, or other, that is bounded by the extent of that
> entity's [TrustedComputingBase].
>
> In the case of the WhatsApp resending "backdoor", each individual message
> is legitimately encrypted to key material associated with the participant.
> As we all opined at the time, this is a possibly unwise but legitimate
> implementational choice: https://technosociology.org/?page_id=1687
>
> To leverage this mechanism a malicious actor needs to steal your
> phone/SIM, or clone your phone, both of which are initial failures of the
> Trusted Compute Base (TCB, Section 4.1) and are outside the scope of this
> standard. [...deletia...].
>
> At some point all "security" comes down to "standing on a bunch of
> assumptions", and this standard uses the well-documented concept of a TCB
> to express that point.
>


Incidentally, there's a great pun / potential vulnerability name inherent
in this observation, viz: *"split ends attack"*.

Just wanted to call dibs. :-)

Have a great weekend!

    - alec

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