[OTR-dev] Thinking about mpOTR and secure multiparty chat protocols in general

[Michael Rogers]

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On 21/02/13 18:30, George Kadianakis wrote:
> * Is the shutdown phase of OTR the only place where transcript 
> soundness is guaranteed? By 'transcript soundness', I mean the 
> guarantee that all participants see the exact same transcript.
> What happens, if an 3vil server drops packets in the middle of the 
> conversation? Do participants learn this only in the end of the 
> conversation?

A related threat: can a chat participant send different messages to
different participants, without this being detected until the
transcripts are compared? For example:

Alice -> Everyone: Let's make plans for Friday
Bob -> Alice: Who wants to get ice cream?
Bob -> Carol: Who want to shoot the president?
Alice -> Everyone: Ooh, me me me!

If an attacker forces the transcript comparison to fail (e.g. by
knocking the server offline before the comparison is complete), how
should the client communicate the failure to the user? I'm not sure
whether someone who's just taken part in a long multi-way conversation
will be able to make much use of a warning that says "What you just
saw may not be what everyone else saw."

Cheers,
Michael

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