Research On P2P Anonymous Communication System

With the rapid spread of Internet, more and more people focus on the anonymity of user in E-Voting, E-Banking, and E-Commerce. Being the main tool to protect anonymity during communication, Anonymous Communication Systems as Mix-Net, Freedom, are challenged by the limit in scalability and anonymity. Peer-to-Peer Anonymous Communication Systems, taking the Peer-to-Peer infrastructure, are becoming the focus of many researches recently because of its advantage in scalability.This thesis investigated key issues in the anonymity and performance of P2P anonymous communication system. First, we analyzed the underlying rerouting mechanism in P2P anonymous communication system and proposed some improvements. Based on an analysis of impact of the max length of rerouting path with respect on the bounds of predecessor attack, a rerouting algorithm base on decreased forwarding probability, DFPR, is proposed for limiting the rerouting path in next-hop rerouting without decreasing the anonymity. To determine the collaborators in active reset predecessor attack, Active Detection based Rerouting algorithm, ADR, is proposed. And SSR, Secret Shared-based Rerouting algorithm, is also proposed for the sender and the last hop on the rerouting path to share secret key, which enable the sender establish a secure channel to the last hop, therefore end-to-end encrypt the transferring messages in the next hop rerouting, increase the complexity of predecessor attacks.Second, the scalability of P2P anonymous communication system was studied in a more rigid way. The payload of participate in system was derived in terms of the length of rerouting path and the number of participate, which demonstrated that payload of participate is independent of the number of participate. Thus, the system could scale well even the number of participate becomes large.Third, the impact of disclosure attack on P2P system was studied. A formal model of dynamic user behavior was presented firstly and the anonymity with respect to the disclosure attack was investigated. The theoretical and simulate resultdemonstrated that, disclosure attack could not be effective in practical P2P system because of the large number of users. Then, we proposed an extending version of the attack - Sum based Statistical Disclosure Attack, which keep effective even the number of users is very large. Therefore, it is an effective method to evaluate the P2P anonymous communication.In addition, we proposed Anonymity Abusing Control Strategy Based on Multi-hash Encoding, which mark the messages with multi-hash encoding method. Therefore, victim could reconstruct the attack path and figure out the attack source on being attacked by the malicious users in system. Meanwhile, legal user's identity is kept anonymous. The analysis result demonstrated that, false rate can be maintained low even in large-scale system.