[MLS] Virtual Interim minutes

Nick Sullivan <nick@cloudflare.com> Wed, 29 January 2020 21:39 UTC

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From: Nick Sullivan <nick@cloudflare.com>
Date: Wed, 29 Jan 2020 13:38:34 -0800
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Subject: [MLS] Virtual Interim minutes
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Draft minutes from the productive first virtual interim posted below. If
you find an issue, submit a PR to Github:

Nick & Sean

Joel Alwen, Richard Barnes, Raphael Robert, Britta Hale, Brendan McMillion,
Nick Sullivan

#247 - Welcome confirmation and key derivation
* Fixes bugs RLB found in the last draft while implementing
* OK to merge after rebase / conflict resolution

#246 - Bugfixes in ClientInitKey, Commit, and Welcome
* Derives the Welcome encryption key instead of generating fresh
* ... under the general theory about not requiring freshness when not
* OK to merge after rebase / conflict resolution

#283 - Use the same ratchet for Handshake and Application keys
* There's no point to FS for Proposals because clients have to cache the
plaintext anyway
* Given that, the "flat derivation" approach should be fine
* We should have separate keys per sender to it easier to avoid nonce
* RLB and RR to decide whether we should derive nonces on a hash ratchet or
just use a counter

#287 - Switch to signing strategy using one signature per leaf.
* There was agreement among those on the call to proceed with this strategy
* ... given the deniability concerns and unclear benefit of the alternative
* If further considerations come to light from analysis, we can revisit