[anti-censorship-team] Summary of Point Break (Jansen et al. USENIX Security '19) as it pertains to bridges

Philipp Winter phw at torproject.org
Mon Aug 26 17:01:17 UTC 2019


On Sat, Aug 24, 2019 at 12:46:52PM -0600, David Fifield wrote:
> They looked at the default bridges in Tor Browser 8.0.3 (October 2018).
> Only 12 of 25 default obfs4 bridges were working. (I think most of the
> non-working bridges have since been pruned, e.g. in #29378, #30264.) The
> median bandwidth of the 12 working bridges was 368 KB/s, with a large
> variance: minimum of 67 KB/s and maximum of 1190 KB/s.

Yes, we've been cleaning up our default bridges over the last few
months.  Here's an up-to-date list of our current default bridges:
<https://trac.torproject.org/projects/tor/wiki/doc/TorBrowser/DefaultBridges>

> Besides the default bridges, they requested 135 bridges from BridgeDB,
> and found that only 70% (95/135) of them worked. (This has also been at
> least partially addressed by #30441.) BridgeDB bridges are faster than
> default bridges, with a median bandwidth of closer to 600 KB/s
> (FigureĀ 1).

For context: many obfs4 bridges had an unreachable obfs4 port because
some operators were not aware that they had to expose both their OR
*and* their obfs4 port.  Our documentation wasn't sufficiently clear
about this.  We have since reached out to all affected operators.  Many
responded and fixed the issue.  We eventually had to blacklist the
bridges of the operators who did not respond.

Cheers,
Philipp


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