Slipping Past the Cordon: A Systematization of Internet Censorship Resistance

The Internet censorship conflict is like a game of cat-and-mouse, in which the censor discovers and acts on distinguishers that set the usage of censorship resistance systems (CRSs) apart from other Internet usage, and the CRSs’ attempts to remove and mitigate these distinguishers. Our systematization is based on a simple and intuitive model of the distinguisher-leveraging censorship apparatus, but one that is grounded in the inherent limitations of the censor and the unavoidable error rates of the apparatus used. We are then able to categorize CRS techniques and designs in terms of their impact on distinguishers, and thereby evaluate a broad range of systems with respect to their security and applicability for certain use cases. We present a taxonomy of censorship circumvention strategies and techniques and an evaluation of the systems that utilize them. Our evaluation leads us to identify gaps in the literature, question the assumptions at play, and formulate a plan of action to develop effective CRSs.