[messaging] Value of deniability

[Mike Hearn]

For anyone following along who also never heard of "the anakata case", this
is the trial of Per Gottfrid Svartholm Warg for hacking Danish government
databases:


http://torrentfreak.com/pirate-bay-founder-guilty-of-hacking-sentenced-to-two-years-in-prison-130620/

He was found guilty for two years. Part of the evidence was chat logs
showing him chatting with an accomplice. Presumably he tried to claim the
logs were forged:

*The Court said that it had found the prosecution’s case against Gottfrid
and his accomplice convincing, since among other things it ruled out the
possibility that a third party could have carried out the hacking from the
defendants’ computers.*

*The Court also noted that chat conversations between the defendants showed
that in addition to being the perpetrators of the hacking offenses, they
also acted in concert.*

*As a result, Gottfrid was found guilty of hacking, aggravated fraud and
attempted aggravated fraud, and sentenced to two years in prison. His
36-year-old accomplice was sentenced to probation.*


I think I agree with Eleanor that the costs of real deniability seem to
radically outweigh the benefits, as anything that doesn't involve a simple
on-screen editor for chat logs probably wouldn't be convincing, and that
seems like a lot of effort and UI complexity.

Moreover, I'm struggling to find a use case for this that doesn't involve
someone lying in court. If I'm in a two-party chat, and we have strong
privacy, then I'd probably prefer to have strong evidence (on my local
device only) that what was said, was said. It seems like it can only help
me because:

   - .... if I'm saying "hey dude, let's engage in conspiracy against the
   government!" and I'm talking to a double agent, that guy can probably
   convince me to do something that isn't deniable i.e. in the real world
   before closing the net. So it's hardly enough, to be a dissident.

   - .... if I'm an ordinary every day guy who is talking to someone, they
   accuse me of something and the text message evidence supports my case, I
   very much want it to be undeniable.

   - .... I don't want to ask every chat participant to activate some
   special signing mode before they chat to me. This would be interpreted as
   saying "I don't trust you". Of course people only usually want undeniable
   chat logs after it turns out their trust was misplaced. I'd much prefer to
   use a chat network where the social default was undeniability. You never
   know when you might turn out to be the poor guy in the newspaper article.

W.R.T being quoted out of context, that happens with private speech
conversations all the time and hardly anyone ever says "I didn't say that",
they say "I'm being quoted out of context, here's the full conversation".

Are there other use cases I've overlooked?
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