Research On Reputation Mechanism In Peer-to-Peer File Sharing System

The rapid development of Intemet has brought new challenge to the traditional network model,resulting in the emergence of P2P system.It makes the transfer of Internet computing model,from client/server model to peer-to-peer.At present,P2P technology has been widely utilized in many fields,especially the P2P file sharing system,as the power source of the P2P technology development.However,due to the nature of dynamics and heterogeneity,there are many issues worthing to research in P2P file sharing system,such as the reliability of sharing files and the trustness between nodes.The reputation mechanism of P2P network predicts future behavior of users or resources by making qualitative or quantitative evaluation of them.It can encourage benign behavior and inhibit malicious behavior,to play an important role in system. Therefore,it is of a very important and practical significance to carry out the research on the reputation mechanism in P2P file sharing system,and design and implement the attack proof reputation system,to improve the availability of P2P network.After investigating related works deeply,this dissertation focuses on three main parts of P2P file sharing system respectively,the object reputation,the node reputation and the overlay topology.A complete reputation system on the P2P file sharing network is designed and implemented.The main structure of this dissertation is as follows:At first,we analyse the general operation flow of users and the impact of the user action on the document propagation,and establish object-based model of pollution proliferation.The model describes the process of document propagation and state transition diagram of node,and revealed the important role of reputation mechanism in file sharing system.Based on the propagation model above,we establish an object reputation based P2P file sharing anti-pollution system,instead of node reputation.We utilize the query message to trigger the dissemination and collection of votes,and measure the similarity between nodes by calculating the cosine between voting vectors,then weight the votes.Self-adaptive threshold is used to determine the credibility of documents. In order to achieve effective utilization of reputation information,we propose a trust propagation algorithm based on Kirchhoffs law,instead of the classic maximum flow based algorithm.The resistance reputation network is established based on the resistor network theory.It is more precise and more natural to reflect the relationship and transitivity of trust.We also optimize the time complexity of algorithm.Finally,we consider the interactivity between network topology and reputation system in the macroscopical view.Inspired by the natural immune principles,we employ the artificial immune algorithm based reputation system to achieve the neighbor selection,connection optimization,and topology construction.The spread of pollution is inhibited at the level of overlay network.The simulation experiment and practical system show that our reputation system can control the pollution prolification effectively at a low cost.And it can punish the free-riding behavior,and cope with various attack situations.