Research On Trust Mechanism Of Gnutella-based P2P File-sharing System

Nowadays, with the rapid development of Internet, the centralized file-sharing system becomes more and more incompetent with user's increasing need in sharing information and resource. Hence, P2P-based file-sharing system has been widely used. However, because of the absence of central control, large amount of fake files and viruses spread over the p2p network, bringing about threat to the security of system, reducing the quality of service. Therefore, the problem of security in P2P file-sharing systems comes to be prominent. Introducing trust management to P2P systems aims at solving those security problems. It is a promising research field in term of great practical significance.This thesis firstly makes an investigation over the popular file-sharing system, for instance, Napster, Gnutella, Kazaa, and analyzes several trust mechanisms in P2P which have been under academic discussion recently. After fully studying the existing trust mechanisms, it finally chooses Gnutella, a purely distributed file-sharing protocol, as the basic file-sharing protocol and the RCert protocol as the basic trust management protocol in further research. It then labors on Gnutella and RCert protocol, and finds out some deficiencies. Gnutella, though applying TTL, unique descriptor ID and not sending the descriptor which had been processed to avoid network congestion, may cause network congestion to some extent owing to its simple flooding search technique, which needs to be improved farther. RCert protocol adopts simple trust rating algorithm which can not ensure the global character. And the trust certificate updating scheme can not support subsequent downloading.By solving these deficiencies, the paper proposes an enhanced trust mechanism GRTMP. GRTMP introduces trust mechanism into the search process of Gnutella. Moreover, this mechanism can decrease the amount of the query messages and avoid network congestion in the process of source search. And, it can efficiently avoid the selection of nodes providing fake documents and viruses. GRTMP also improves the global trust rating algorithm to ensure the global character of trust rating. In addition, GRTMP reconstructs the trust certificate updating scheme of RCert, the updating scheme of which can support subsequent downloading.PeerSim emulator is used to simulate the Gnutella Protocol, RCert and GRTMP. In the simulation, several experiments were performed to see the performance of GRTMP and to compare it with Gnutella and RCert. The results of the experiment shows that GRTMP can decrease the amount of descriptors, lower the malicious activity and enhance the downloading success rate.