Analysing censorship incidents targeting popular circumvention tools such as Tor can be a tedious task. Access to censoring networks is typically difficult to obtainand remote analysis is not always possible. Analysis is however feasible if users behind the censoring networks are given the opportunity to help. In this paper, we propose a lightweight censorship analyser for Tor which is meant to be run by volunteering users. The analyser automatically gathers relevant data and the final report is sent back to the Tor developers. Our design builds on existing software and should be easy to bundle and deploy.

Internet censorship in China is not just limited to the web: the Great Firewall of China prevents thousands of potential Tor users from accessing the network. In this paper, we investigate how the blocking mechanism is implemented, we conjecture how China's Tor blocking infrastructure is designed and we propose circumvention techniques. Our work bolsters the understanding of China's censorship capabilities and thus paves the way towards more effective circumvention techniques.

Deep packet inspection technology became a cornerstone of Internet censorship by facilitating cheap and effective filtering of what censors consider undesired information. Moreover, filtering is not limited to simple pattern matching but makes use of sophisticated techniques such as active probing and protocol classification to block access to popular circumvention tools such as Tor.

In this paper, we propose ScrambleSuit; a thin protocol layer above TCP whose purpose is to obfuscate the transported application data. By using morphing techniques and a secret exchanged out-of-band, we show that ScrambleSuit can defend against active probing and other fingerprinting techniques such as protocol classification and regular expressions.

We finally demonstrate that our prototype exhibits little overhead and enables effective and lightweight obfuscation for application layer protocols.