Abstract. The Tor network is designed to provide users with low-latency anonymous communications. Tor clients build circuits with publicly listed relays to anonymously reach their destinations. However, since the relays are publicly listed, they can be easily blocked by censoring adversaries. Consequently, the Tor project envisioned the possibility of unlisted entry points to the Tor network, commonly known as bridges. We address the issue of preventing censors from detecting the bridges by observing the communications between them and nodes in their network. We propose a model in which the client obfuscates its messages to the bridge in a widely used protocol over the Internet. We investigate using Skype video calls as our target protocol and our goal is to make it difficult for the censoring adversary to distinguish between the obfuscated bridge connections and actual Skype calls using statistical comparisons. We have implemented our model as a proof-of-concept plauggable transport for Tor, which is available under an open-source licence. Using this implementation we observed the obfuscated bridge communications and compared it with those of Skype calls and presented the results.

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SRI International Abstract. While Internet access to certain sites is blocked in some parts of the world, these restrictions are often circumvented using proxies outside the censored region. Often these proxies are blocked as soon as they are discovered. In this paper we propose a browser-based proxy creation system that generates a large number of short-lived proxies. Clients using the system seamlessly hop from one proxy to the next as these browserbased proxies appear and disappear. We discuss a number of technical challenges that had to be overcome for this system to work and report on its performance and security. We show that browser-based short-lived proxies provide adequate bandwidth for video delivery and argue that blocking them can be challenging. 1