How to cheat BitTorrent and why nobody does
David A. Hales, Simon Patarin · 2005
The BitTorrent peer-to-peer file-sharing system attempts to build robustness to free-riding by implementing a tit-for-tat-like strategy within its protocol. It is often believed that this strategy alone is responsible for the the high-levels of cooperation found within the BitTorrent system. However, we highlight some of the weaknesses of the approach and indicate where it would be easy to cheat and free-ride. Given that cheating of this kind currently appears rare, this motivates the question: why is the system not dominated by free-riders? We advance a hypothesis which argues that BitTorrent may resist free-riders in a way that has not been previously fully comprehended. Ironically, this process relies on what is commonly believed to be a weakness of BitTorrent - the lack of meta-data search. One consequence of this is to partition the BitTorrent network into numerous isolated swarms - often with several independent swarms for an identical file - which is one of the necessary conditions for a kind of evolutionary group selective process, a process that has been recently identified in similar simulated systems.