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Description: http://events.ccc.de/congress/2011/Fahrplan/events/4800.en.html
Jacob Appelbaum, Roger Dingledine: How governments have tried to block Tor
Iran blocked Tor handshakes using Deep Packet Inspection (DPI) in January 2011 and September 2011. Bluecoat tested out a Tor handshake filter in Syria in June 2011. China has been harvesting and blocking IP addresses for both public Tor relays and private Tor bridges for years.

State of the arms race between repressive governments and anti - censorship/surveillance Tor technology (and why American companies are on the repressive governments' side)