multi-party support for axolotl ratchet?

[Sean Lynch]

On Wed, Jan 1, 2014 at 9:51 PM, coderman <coderman at gmail.com> wrote:

> per https://github.com/trevp/axolotl/wiki
>
> is there a straightforward way to make this multi-party capable, and
> what optimizations could be done to reduce keys/messages required?
>
> i have not looked at mpOTR in depth yet, to see what lessons might be
> applicable to axolotl...
>

Worst case, can't you just compute pairwise keys for each pair of
participants? It'll add (n-2)*keylen bytes to each of your messages, but
it's easy to understand and implement, and most multi-party conversations
don't end up with that many participants anyway.

I think the biggest problem with trying to do anything clever here is that
keeping everyone in sync while simultaneously preventing DoS by one
participant would be pretty difficult. You'd need something like Paxos to
ensure everybody got the messages in the same order, and you'd have to keep
around old keys and messages until everyone acknowledged them, otherwise
participants could easily get "lost."
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