Re: [MLS] Use Cases for avoiding Forward Secrecy

Dave Cridland <dave@cridland.net> Fri, 02 March 2018 20:27 UTC

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From: Dave Cridland <dave@cridland.net>
Date: Fri, 2 Mar 2018 20:27:02 +0000
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To: Nadim Kobeissi <nadim@symbolic.software>
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Subject: Re: [MLS] Use Cases for avoiding Forward Secrecy
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On 2 March 2018 at 18:14, Nadim Kobeissi <nadim@symbolic.software> wrote:
> A3. With regards to retention, I think EKR makes the best point in saying that these are use cases best addressed by features implemented by the client application itself. This rhymes with Dave Cridland's original mention that business users are those who most require this: business users are also those with the most tailored client applications, usually, providing ample room for archiving features that do not necessarily affect protocol security goals or expose MLS to a riskier threat model.

After various side-discussions, I'm comfortable that we can address
the demands of enterprise and government cases within MLS - as long as
we keep a half-eye on it.

> A4. With regards to compliance with, for example, MIKEY-SAKKE, it is worth thinking about whether the entire MLS effort remains as worthwhile were it boiled down to that common denominator. MIKEY-SAKKE (and company) are by design allergic to strong security guarantees. Phillip Hallam-Baker is correct to note that strong security guarantees are not our explicit goal here, but rather a tangential goal to securing MLS use cases to the fullest possible extent. That said, as noted by Jon Millican, any run-of-the-mill secure messaging application today, be it WhatsApp, Signal, iMessage, Facebook Messenger, Google Allo, Viber, Wire, or Threema shows an obvious preference for ephemerality and resistance to scenarios where the mobile phone, an increasingly disposable device, gets lost, stolen or traded away.

To be absolutely clear, I'm not a big fan of SAKKE and I think it's
entirely unsuitable for the consumer in any form. Consumers generally
benefit from FS, and SAKKE's mandatory escrow is just plain wrong in
that setting.

The properties that interest me within MIKEY-SAKKE are the possibility
of a secure archive with offline escrow, and I think we can do that
within MLS after discussion.

I actually think this is a fairly well-understood requirement, and as
such it'd be useful to document it somewhere in the charter.

Dave.