[messaging] Partial ordering, dynamic groups and event ordering

[Michael Rogers]

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On 12/03/14 20:42, Ximin Luo wrote:
> However, in the mpOTR (and general group chat) setting, we have 
> dynamic groups, with the condition that new members should not see 
> previous messages[3].

Hi Ximin,

Without casting any doubt on the value of pure research, I wonder if
it might be worth considering whether the above condition is really
needed.

Not all group conversations have the property that new members can't
see what happened before they joined - some mailing lists have private
archives that any subscriber can access, for example, and I think I've
heard that when you join a Facebook thread you can see the whole
conversation so far.

If it turns out that we can solve the problem of multi-party encrypted
chat by sacrificing the property that new members can't see what
happened before they joined, I personally think that's acceptable. As
long as users understand what the privacy properties are, they'll be fine.

I've recently been reading 'Distributed Systems for Fun and Profit',
and the way it tells the history of distributed systems research is
really interesting. According to this account there are decades of
impossibility results and really complex algorithms trying to make
distributed systems behave like single computers - and then about 15
years ago there's this second wave of research that asks, do we
actually need those guarantees, or do we just need something that
scales well enough and works reliably enough to run a business on top
of? The emphasis shifts from making failures theoretically impossible
to making them manageable - and there's an explosion of new ideas, and
lo the Amazons and the Googles doth flourish.

Anyway this is turning into a sermon, but here's the book - it's a
good read even if you already know all this stuff (I didn't):

http://book.mixu.net/distsys/

Cheers,
Michael
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