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Re: [freehaven-dev] mix-acc: witnesses provide linkability in rare case
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Roger Dingledine wrote:
> Mix path P consists of mixes M_i.
>
> A --X-- M1 --X-- M2 --X-- M3 --X-- M4 ...
> \ / \ / \ / \ / .
> \ / \ / \ / \ / .
> \w/ \w/ \w/ \w/ .
>
> If
>
> * Each edge in the path P is broken, as X above
> * Every node M_i in P does reach some specific w
>
> Then that w can determine P.
I don't think that's correct. Remember that each mix is batching and
reordering the messages, so w will not be able to link incoming and
outgoing messages from each uncorrupted mix, any more than a passive
adversary would in a standard mix-net.
(Of course a standard mix-net is not completely proof against active
attacks - for example an adversary can force all but a small number of
messages in a batch to be dropped, and make up the batch size with
dummy messages - but adding witnesses doesn't make that problem
any worse, AFAICS.)
> Speaking of which, does our deadline notion itself increase linkability?
> I believe it does.
Why?
- --
David Hopwood <david.hopwood@zetnet.co.uk>
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