Tor: the second-generation onion router
SSYM'04 Proceedings of the 13th conference on USENIX Security Symposium - Volume 13
Chipping away at censorship firewalls with user-generated content
USENIX Security'10 Proceedings of the 19th USENIX conference on Security
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Oppressive regimes and even democratic governments restrict Internet access. Existing anti-censorship systems often require users to connect through proxies, but these systems are relatively easy for a censor to discover and block. We explore a possible next step in the censorship arms race: rather than relying on a single system or set of proxies to circumvent censorship firewalls, we use the vast deployment of sites that host user-generated content to breach these firewalls. We have developed Collage, which allows users to exchange messages through hidden channels in sites that host user-generated content. To send a message, a user embeds it into cover traffic and posts the content on some site, where receivers retrieve this content. Collage makes it difficult for a censor to monitor or block these messages by exploiting the sheer number of sites where users can exchange messages and the variety of ways that a message can be hidden. We have built a censorship-resistant news reader using Collage that can retrieve from behind a censorship firewall and show Collage's effectiveness with a live demonstration of its complete infrastructure.