[tor-dev] moved from [Tor-censorship-events] Improving the censorship event detector.

George Danezis georged at gmail.com
Thu Aug 20 21:31:41 UTC 2015

Hi all,

For all my sins I wrote parts of the algorithm that is at fault here.

I also echo, and confirm all the problems mentioned. One thing that
would greatly help tune such systems is a database of known censored
periods from different jurisdictions. The issue is that "anomalies"
occur all the time -- and tor is presumably only interested in
"intersting anomalies" that related to attacks.

Now I know more about this field, and happy to work with others to
improve the state of the detector if there is interest.


On Thu, Aug 20, 2015 at 7:36 PM, l.m <ter.one.leeboi at hush.com> wrote:
> Hi Joss,
> Thank you for the fine paper. I look forward to reading it. Karsten would be
> keen on it too (and maybe also your offer) if you haven't already forwarded
> it to them. My interest in fixing it is (mostly) recreational. I have some
> thoughts on how to proceed, but I'm not a representative of tor project.
> Regards
> --leeroy
> Hi,
> These are well identified issues. We've been working here on a way to
> improve the current filtering detection approach, and several of the
> points above are things that we're actively hoping to work into our
> approach. Differentiating 'filtering' from 'other events that affect Tor
> usage' is tricky, and will most likely have to rely on other
> measurements from outside Tor. We're currently looking at ways to
> construct models of 'normal' behaviour in a way that incorporates
> multiple sources of data.
> We have a paper up on arXiv that might be of interest. I'd be interested
> to be in touch with anyone who's actively working on this. (We have
> code, and would be very happy to work on getting it into production.)
> I've shared the paper with a few people directly, but not here on the
> list.
> arXiv link: http://arxiv.org/abs/1507.05819
> We were looking at any anomalies, not only pure Tor-based filtering
> events. For the broader analysis, significant shifts in Tor usage are
> very interesting. It's therefore useful to detect a range of unusual
> behaviours occurring around Tor, and have a set of criteria within that
> to allow differentiating 'hard' filtering events from softer anomalies
> occurring due to other factors.
> Joss
> --
> Dr. Joss Wright | Research Fellow
> Oxford Internet Institute, University of Oxford
> http://www.oii.ox.ac.uk/people/?id=176
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