Unblocking the Internet: Social networks foil censors NYU Technical Report TR2008-918

Many countries and administrative domains exploit control over their communication infrastructure to censor online content.This paper presentsthe design, implementationand evaluationofKaleidoscope, a peer-to-peer system of relays that enables users within a censored domain to access blocked content. The main challenge facing Kaleidoscope is to resist the censor's efforts to block the circumvention system itself. Kaleidoscope achieves blocking-resilience using restricted service discovery that allows each user to discover a small set of unblocked relays while only exposing a small fraction of relays to the censor. To restrict service discovery, Kaleidoscope leverages a trust network where links reflects real-world social relationships among users and uses a limited advertisement protocol based on random routes to disseminate relay addresses along the trust network; the number of nodes reached by a relay advertisement should ideally be inversely proportional to the maximum fraction of infiltration and is independent of the network size. To increase service availability in large networks with few exit relay nodes, Kaleidoscope forwards the actual data traffic across multiple relay hops without risking exposure of exit relays. Using detailed analysis and simulations, we show that Kaleidoscope provides > 90% service avail- ability even under substantial infiltration (close to 0.5% of edges) and when only 30% of the relay nodes are online. We have implemented and deployed our system on a small scale serving over 100,000 requests to 40 censored users (relatively small user base to realize Kaleidoscope's anti-blocking guaran- tees) spread across different countries and administrative domains over a 6-month period.