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TSS Seminar: Tariq Ehsan Elahi: "Censorship Resistance on the Internet: Strategies and techniques for free and open communication"

Event Type
Information Trust Institute
4405 Siebel Center
Jan 31, 2013   4:00 pm  
Tariq Ehsan Elahi, University of Waterloo
Originating Calendar
Information Trust Institute


Censorship resistance, also known as censorship circumvention, is a response to the pervasive Internet censorship that exists today and continues to expand and adapt in step with technological advances; it is an active area of research interest. Either reactionary or preemptive, the aim is to mitigate the power of the censor. While there may be a plurality of motives, the basic goal is the same: free and open communication on the Internet.

The focus of this talk is on technological solutions for censorship resistance, and we provide a systematization, as a taxonomy, of current censorship resistance knowledge. Our taxonomy, CORDON, provides an understanding of the general strategies, techniques, and assumptions at play in previous work.

We categorize the strategies into the following six types to form the CORDON taxonomy: Collateral damage, where the damage caused by censorship would outweigh its benefits; Outside scope of influence, where the censor is powerless to act due to it having no control over entities or traffic; Rate limiting, where the censor's monitoring abilities are curtailed; Decoupled communication, where bidirectional communications are asynchronous and asymmetric to take advantage of weaknesses in the censor's defenses or hide the fact that the communications are related; Overwhelm, where the censor is deluged with large amounts of network traffic, paths, and vectors to increase the cost and difficulty of effective censorship; and No target, where the censor is unable to accurately detect and identify the people, infrastructure, and network traffic to target. For each strategy, we identify the common supporting techniques used or proposed by resistance systems.

We will also discuss the fundamental problems facing censorship resistance today and possible research directions that may address them.


Tariq Ehsan Elahi is a member of the Cryptography, Security and Privacy group at the University of Waterloo. Currently a Ph.D. candidate, he is most interested in technological solutions for Internet privacy and censorship resistance. He is also interested in game-theoretic models applicable to censorship resistance that provide insight on how to design more robust systems. He gets excited about the prospects of public-sourced networks that avoid central control and observation. To that end, he is a member of the Waterloo Satellite group and designs cubesats with censorship resistance capabilities. He is also a research contributor to the Tor project investigating how design choices impact client security.


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