Re: [tor-bugs] #32657 [Circumvention/Snowflake]: Investigate Snowflake blocking in China

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#32657: Investigate Snowflake blocking in China
-------------------------------------+-----------------------------------
 Reporter:  cohosh                   |          Owner:  cohosh
     Type:  defect                   |         Status:  needs_information
 Priority:  High                     |      Milestone:
Component:  Circumvention/Snowflake  |        Version:
 Severity:  Normal                   |     Resolution:
 Keywords:  blocking, china          |  Actual Points:
Parent ID:                           |         Points:
 Reviewer:                           |        Sponsor:  Sponsor28
-------------------------------------+-----------------------------------
Changes (by cohosh):

 * status:  assigned => needs_information


Comment:

 Here are the results from some throughput tests I ran from the VPS in
 China on December 6th:

 To summarize the tests, I attempted to bootstrap a Tor connection using
 Snowflake as the pluggable transport 100 times. If the bootstrap was
 successful, I then proceeded to download a 1MB file using `torsocks`. I
 measured the bootstrap progress (i.e., how far the Tor connection
 bootstrap proceeded before the 90 second timeout), and also looked at
 packet captures of UDP traffic to determine where, if at all, the
 Snowflake WebRTC connection failed.

 [[Image(snowflake-tor-bootstrap-china-2019-12-06.png,50%)]]

 Surprisingly, almost all Snowflake connections succeeded this time around,
 with only 4 connections that failed to bootstrap to 100%.

 [[Image(snowflake-webrtc-stages-china-2019-12-06.png,80%)]]

 Looking at the snowflake connection data, only three connections to the
 snowflake provided by the snowflake-broker failed at the phase where the
 client tries to open a data channel to the snowflake.

 The throughput was also better than expected:

 [[Image(snowflake-throughput-china-2019-12-06.png,80%)]]

 The mean throughput was 110 KBps, with a standard deviation of 80 KBps.
 This isn't that much slower than the throughput of 190 KBps reported from
 a VPS in Canada in #32545:comment3. Some slowness is to be expected given
 the geographical distance of this probe site.

 This data contradicts the previous tests above where half of all
 snowflakes are failing. We used the same basic probe test to collect this
 data, which suggests that if censorship is happening, it is not consistent
 yet. I'm going to set up some recurring probes of this type to see if the
 reachability of snowflake changes over the next few days.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32657#comment:4>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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