[OTR-dev] Fwd: Ensuring transcript soundness in a multiparty chat setting

[Мария Коростелёва]

---------- Forwarded message ----------
From: Мария Коростелёва <maria at korosteleva.com>
Date: 2013/11/28
Subject: Re: [OTR-dev] Ensuring transcript soundness in a multiparty chat
setting
To: Trevor Perrin <trevp at trevp.net>


2013/11/28 Trevor Perrin <trevp at trevp.net>

> On Thu, Nov 28, 2013 at 8:29 AM, Мария Коростелёва
> <maria at 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.
>

This approach reminds me more about OldBlue, than the algorithms described
in papers [0] and [1], that were mentioned in the first letter. What's the
difference?

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

They sure will :)

>
>
> Trevor
>

[0]: http://www-users.cs.umn.edu/~hopper/gotr.pdf
[1]: http://matt.singlethink.net/projects/mpotr/oldblue-draft.pdf

Maria
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