On Rerouting And Scalar Anonymity In Anonymous Communication Systems

With the rapid progress of information technologies, computer networks have been widely used in communications among individuals, parties and governments. Concerns on security of network and privacy of communication have been grown. Anonymity needed by many applications on Internet, such as Anonymous email, Web browsing, E-Voting, E-Banking, E-Commerce, and E-Auctions, could not meet by encryption alone. In this dissertation, we mainly address related techniques in anonymity communications based on current settings. We study the problems of partially connected network traffic camouflage, rerouting path selection in anonymity systems and scalar anonymity.Firstly, we survey the current technologies of anonymity communications; summarize the state-of-the-art of anonymity protocols and anonymity systems; generalize the properties of attacks in anonymity systems; and compare the abilities of anonymity systems defending typical attacks.Secondly, we propose a model to solve the problem of traffic camouflage of partially connected networks; discuss the process of camouflage and analyze its cost; design an algorithm for traffic camouflage and analyze its complexity and efficiency. It is shown that the algorithm could camouflage the traffic of partially connected networks at a lower cost.Next, we focus on the effects of fixed-rerouting paths and variable-rerouting paths upon the anonymity degree in anonymity system. It is recognized that senders sending packets by either fixed-reroutingpaths or variable-rerouting paths are vulnerable to certain attacks, thus degrading their anonymity. The dynamic fixed-rerouting path scheme is proposed to resist efficiently the attacks which aim at both fixed-rerouting paths and variable-rerouting paths; thus it improves the sender anonymity. Theoretical analyses and simulation results show that anonymity system based on the scheme will provide better anonymity if the size of the system and the length of the rerouting path meet certain conditions.Finally, we propose scalar anonymity techniques aiming at providing trade-off between anonymity and cost. First, we discuss scalar anonymity, which is achieved with layered encryption and multi-hop routing, based on Crowds system. By providing different users or different applications with different forwarding probability levels, a forwarding load level will be assigned accordingly, thus the tradeoff between anonymity and cost is achieved. Then, we also propose a scalar anonymity system model based on DC-Nets by partitioning the whole anonymity system into many groups, where the round protocol of intra-group adopts improved secure multi-party addition protocol. We analyze the efficiency, security, and anonymity of the system. The results of theoretical analyses and simulations show the efficiency and the performance of scalar anonymity systems.Our research on related techniques in anonymity communications will not only complement the basic theories but also guide to set up better anonymity systems.