On Fri, Aug 23, 2013 at 03:45:31AM -0400, Roger Dingledine wrote:
On Fri, Aug 23, 2013 at 09:19:32AM +0200, Paul-Olivier Dehaye wrote:
The short summary of the weakness of Tor here:
- We would like the whole protocol to be mixing (to an observer, the
probability of exiting at any node C given entrance at node A is close to 1/N),
Right, you're using terminology and threat models from the mixnet literature. Tor doesn't aim to (and doesn't) defend against that.
You might find the explanation in https://blog.torproject.org/blog/one-cell-enough to be useful. The first trouble with mixing in the Tor environment is that "messages" from each user aren't the same size, and it's really expensive to make them the same size ("round up to the largest expected web browsing session").
Another key point: it's not about the paths inside the network -- it's about the connections from the users to the network, and from the network to the destinations.
That said, for the beginning of your related work, see http://freehaven.net/anonbib/#danezis:pet2003
And for a much later follow-up, see http://freehaven.net/anonbib/#topology-pet2010
You might also want to look at the following for a design that tries to address your issues. http://freehaven.net/anonbib/#active-pet2010 See also citations therein for partial solutions.
High-order bit: I think this is about state-of-the-art for this area, and it's my paper, but we still need a lot of basic research progress in this space before we would have anything worth putting into Tor. And, except for adding small amounts of noise (besides uniform cell sizes, but that should be a gauge of tolerable overhead for anything we do) to complicate trawling, I'm not very sanguine about the prospects of this ever making practical sense. You might also consult my "Why I'm not an Entropist" http://www.syverson.org/entropist-final.pdf
aloha, Paul