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

Tom Ritter tom at ritter.vg
Sat Aug 24 19:46:27 UTC 2019

Do we have data on bridge uptime, length of operation, and bandwidth
capacity? (Or 2 of those 3?)  Would it make sense to pool at our
entire pool of bridges and contact operators about being default
bridges from that pool, as opposed to our current ad-hoc request

(Or do we do that already and I wasn't aware?)


On Sat, 24 Aug 2019 at 18:47, David Fifield <david at bamsoftware.com> wrote:
> Rob Jansen, Tavish Vidya, and Micah Sherr have a paper about
> bandwidth-based DoS against Tor. Section 5 is about default bridges.
> https://www.usenix.org/conference/usenixsecurity19/presentation/jansen
> https://www.usenix.org/system/files/sec19-jansen.pdf#page=6
> While elsewhere in the paper they discuss in-protocol attacks, in the
> context of bridges they limit themselves to attacks using third-party
> paid "stresser" DoS services, which you can rent for about $1/Gbps/hour
> (Section 3.1).
> 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.
> 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
> (Figure 1).
> They estimate that disabling the 12 default obfs4 bridges would require
> 30 stresser jobs, at a rate of $22/hour or $17K/month. If all users of
> default obfs4 bridges switched to BridgeDB bridges, the median bandwidth
> of BridgeDB bridges would slow down to under 100 KB/s (Figure 2). If
> even half of default obfs4 users switch to using meek, the cost to
> operate meek will at least double (Figure 3).
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