Counter attack to free-riders: Filling a security hole in BitTorrent protocol

Peer-to-Peer (P2P) networks are powerful distributed solutions which do not rely on external servers and gather required resources from their users. Therefore, fairness is an important feature for designers of these networks. Prevention of free-riding is a key aspect for fairness. One of the most important file-sharing protocols in P2P is BitTorrent. This protocol is distinguished from other P2P systems for its unique way of uploading process and its novel approach to fairness. For the first time by implementing eminent game theory strategy, “tit-for-tat” for its protocol, BitTorrent made a breakthrough on fairness for P2P networks. However, it did not take long for researchers to find security holes in its approach. It was proven several times that by making specific clients which do not follow BitTorrent algorithms, it is possible to achieve free-riding. In this paper, by making fairness a universal problem we make free-riding a much harder process. This is achieved by changing the role of Tracker from an indexing server to a more intelligent entity which makes the proper decisions based on different situations.