Counter Attack against Free-Riders: Filling a Security Hole in Bittorrent Protocol

eer-to-Peer(P2P) networks are powerful distributed solutions which do not rely on external servers and gather required resources from their users. Therefor fairness is an important feature for designers of these networks. To have a fair network we always want to prevent free-riding. One of the most important file-sharing protocols in P2P is Bittorrent. What separates Bittorrent from other P2P protocols is 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. But unfortunately 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 and rules, we can easily achieve free-riding. In this paper by taking a simple yet efficient approach and without changing original protocol we make free-riding a much harder process. This will be achieved by changing the role of Tracker from an indexing server to a much more intelligent entity which makes free-riding a much harder process.