Re: [MLS] AppAck

Brendan McMillion <brendan@cloudflare.com> Sun, 22 November 2020 22:07 UTC

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From: Brendan McMillion <brendan@cloudflare.com>
Date: Sun, 22 Nov 2020 14:07:11 -0800
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To: Richard Barnes <rlb@ipv.sx>
Cc: Messaging Layer Security WG <mls@ietf.org>
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Subject: Re: [MLS] AppAck
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Hey Richard

I wrote a lot about this in the discussion in #219 but to recap, I
generally don't think we should do this because:

1. We don't know how applications expect to lose messages, or what
properties on message delivery/order they want to ensure.
2. Applications can easily implement some algorithm for ensuring what they
want and keep that data in the AAD
3. If what we specify doesn't match exactly what applications want, they'll
have to do #2 anyway and we wasted our time.

If you had a construction that could bend to suit a large number of
application use-cases, I think that would be good to include in the
standard. But like you say in the PR, you're being fairly prescriptive in
terms of how you expect messages to be lost and what you want to guarantee.
Namely, a.) you expect infrequent loss, b.) clients only want to validate
receipt of messages at a Commit, and c.) you don't care about total message
ordering. I would say that probably won't cover even most use-cases.

On Sat, Nov 21, 2020 at 12:45 PM Richard Barnes <rlb@ipv.sx> wrote:

> Hey all,
>
> For one more "feature" before feature freeze, I've just posted a PR for an
> AppAck proposal.  This is joint work with Raphael and Benjamin, who had the
> idea of doing a proposal for this; I'm really just the scribe.
>
> https://github.com/mlswg/mls-protocol/pull/442
>
> This PR addresses issue #160, which dates all the way back to May 2019.
> You may recall that Benjamin raised it on the IETF call last week.  The
> idea is to enable the members of the group to detect when the DS drops
> application messages.
>
> Please take a look, and speak up with any comments.  I would like to merge
> this (or decide not to) in the next week or so, so that we can get draft-11
> out and begin feature freeze / analysis.
>
> Thanks,
> --Richard
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