BitBlender: Light-weight anonymity for Bittorrent

We present BitBlender, an efficient protocol that provides an anonymity layer for BitTorrent traffic. BitBlender works by creating an ad-hoc multi-hop network consisting of special peers called "relay peers" that proxy requests and replies on behalf of other peers. To understand the effect of introducing relay peers into the BitTorrent system architecture, we provide an analysis of the expected path lengths as the ratio of relay peers to normal peers varies. A prototype is implemented and experiments are conducted on Planetlab to quantify the performance overhead associated with the protocol. We also propose protocol extensions to add confidentiality and access control mechanisms, countermeasures against traffic analysis attacks, and selective caching policies that simultaneously increase both anonymity and performance. We finally discuss the potential legal obstacles to deploying an anonymous file sharing protocol. This work is among the first to propose a privacy enhancing system that is designed specifically for a particular class of peer-to-peer traffic.