[tor-dev] Estimating censorship lag by obfs4 blocking

[David Fifield]

According to a couple of blog comments on February 1, 2015, the default
obfs4 bridges are blocked by GFW.

https://blog.torproject.org/blog/tor-browser-45a3-released#comment-86416
https://blog.torproject.org/blog/tor-browser-45a3-released#comment-86907

The obfs4 bridges were introduced on November 17, 2014.
https://blog.torproject.org/blog/tor-browser-45-alpha-1-released
I have a message from Yawning Angel verifying that the obfs4 bridges
were reachable on December 2, 2014.

With this information, we can put rough bounds on how long it took the
GFW to react to a new circumvention system: between 2 and 10 weeks.

Does anyone know information that could tighten up the bounds, a date
between December 2 and February 1 when obfs4 bridges were known to be
either accessible or inaccessible?

David Fifield