Multiple Identities in BitTorrent Networks

Peer-to-peer (P2P) file sharing systems have become ubiquitous and at present the BitTorrent (BT) based P2P systems are very popular and successful. It has been argued that this is mostly due to the Tit-For-Tat (TFT) strategy used in BT [1] that discourages free-ride behavior. However, Hale and Patarin [2] identify the weakness of TFT and hypothesize that it is possible to use multiple identities to cheat. To test this hypothesis we modify the official BT source code to allow the creation of multiple processes by one BT client. They use different identities to download the same file cooperatively. We experiment with several piece selection and sharing algorithms and show that BT is fairly robust to the exploitation of multiple identities except for one case. In most cases, the use of multiple identities does not provide siginificant speedup consistently. Interestingly, clients with multiple identities are still punished if they do not maintain a comparable upload rate with other normal clients. We attribute this to the robust way that the TitFor-Tat policy works. From our experiments we observe that the BT protocol is rather resilient to exploits using multiple identities and it encourages self-regulation among BT clients.