Making Contribution-Aware Peer-Assisted Content Distribution Robust to Collusion Using Bandwidth Puzzles

Many peer-assisted content-distribution systems reward a peer based on the amount of datathat this peer serves to others. However, validating that a peer did so is, to our knowledge, anopen problem; e.g., a group of colluding attackers can earn rewards by claiming to have servedcontent to one another, when they have not. We propose a bandwidth puzzle mechanism tomake contribution-aware peer-assisted content distribution robust to such collusion. Ourconstruction both ties solving the puzzle to possession of content and, by issuing puzzlechallenges simultaneously to all parties claiming to have the same content, prevents onecontent-holder from solving many others’ puzzles. We bound (in the random oracle model)the adversaries’ ability to defeat our puzzle scheme. We also describe our integration ofbandwidth puzzles into a fully operational media streaming system, and demonstrate theattack resilience offered by bandwidth puzzles through simulations of both streaming andfile-sharing systems.