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List:       otr-dev
Subject:    Re: [OTR-dev] Ensuring transcript soundness in a multiparty chat setting
From:       Trevor Perrin <trevp () trevp ! net>
Date:       2013-11-28 17:23:05
Message-ID: CAGZ8ZG2yJQKhoKc+YvV_USb-m852UpUZT8VceT1H-+mwvi4z6g () mail ! gmail ! com
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On Thu, Nov 28, 2013 at 8:29 AM, Мария Коростелёва
<maria@korosteleva.com> wrote:
> Hi everyone,
>
> I have a question considering the topic of this converstion.
>
> If we have a situation like this:
>
>>> At some point t_0, it so happens that A and B each send a message (m_a
>>> and m_b) to all other participants at approximately the same time [0].
>>> At t_0, the internal transcript state of A, B and C is the same.
>>>
>>> When C receives m_a, the consensus check matches and C updates her
>>> internal transcript state to include m_a.
>>> Now, when C receives m_b, the consensus check won't match since the
>>> internal transcript state of C includes m_a, while the consensus check
>>> of m_b doesn't (B was not aware of m_a when m_b was sent and hence it
>>> was not included in its consensus check).
>>>
>> That's OK.  m_b's consensus check doesn't have to include every
>> message in C's transcript, it just has to be consistent with C's
>> transcript.  Which it is!
>
> how exactly C checks the consistency of m_b's consensus check?

Every message will state what its "predecessors" are.

So when C receives m_b, C will know that m_a is not a predecessor of
m_b.  Thus C will not include m_a when checking m_b's consensus hash.

Agreed this isn't explained well.  Maybe a wiki with an algorithm
description would help?


Trevor
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