A traffic analysis of Link-Based Relay Selection? (PETS 2009)

7 August 2009

Micah Sherr presented at PETS a few days ago his work on “Scalable Link-Based Relay Selection for Anonymous Routing“. The key idea is that paths are generated by taking into account the network performance of each link to be used. The overhead of distributing performance information can be reduced by associating with each server a network coordinate, that allows to estimate the latency between pairs of nodes.

This is a pure path selection proposal, as quite a few have appeared in the past year to reduce latency, or increase node utilization in Tor. The question with all those proposals is: how much anonymity would these path selection strategies provide?

The methodology we present in  “The Bayesian Traffic Analysis of Mix Networks” provides a way of answering such questions, by carefully modelling the path selection strategy. Applying the same methodology to these path selection proposals would be of clear benefit, and an excellent project for anyone interested in understanding better how to apply inference based techniques to traffic analysis.

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2 Responses to “A traffic analysis of Link-Based Relay Selection? (PETS 2009)”

  1. Andrei said

    I think we should start by formalizing the threat model of Tor. Whatever it is. For instance, coming up with a threat model which shows why 3 nodes is optimal. That is pretty easy.

    Much as I hate to admit it, I think it *is* worth retrofitting a threat model onto this existing design.
    This might yield some intuition and progress (at least in this direction.

    A.

  2. Clive Robinson said

    @ Andrei,

    The answer to your first statment (threat model for TOR) is yes, but it’s not going to be easy and it will change a lot with time/experiance.

    Traffic analysis threat models are not that well known in the “open arena” and those from other areas tend either not to be too relevant or insufficiently specific.

    And with regard to retro fitting be carefull of what you wish for 😉

    Seriously though TOR is just one of a number of lower level systems it would perhaps be prudent to think up a framework into which various bits could be dropped thus (hopefully) maximising utility of effort.

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