Research On The Statistical Hitting Set Attack And Countermeasure In Mix System

Anonymity systems can be used to protect the privacy of the communication correspondents. Anonymity degree is an important aspect to measure the performance of an anonymity system. To strengthen it, many attacks and countermeasures need to be studied. Mix system is the major channel for anonymous communication. Since no special way to conceal the traffic in and out of the system, from which, the attacker can reveal the relationship between sender and receiver. Statistical Hitting Set Attack (SHS-attack) is the very typical attack against Mix. Yet, three flaws are remaining: first, high rate of misjudgment exists; second, the attacker must know the number of victim's communication partners beforehand; third, it is only available for Threshold Mix, the research on the attacks and countermeasures in other types of Mix should be carried on. For these problems, this paper discusses anonymous communication system, together with the SHS-attack and countermeasures in Mix system.To begin with, the techniques of anonymous communication and the research status of Mix are described. We also present the regular attacks and countermeasures in anonymous communication system. Meanwhile, the major implementation mechanisms of statistical attack in Mix system have been analyzed.Secondly, based on Threshold Mix, we proposed a SHS-attack under the conditions that the number of victim's communication partners is determined both undetermined. It relies on the fact that, the total times of communications with respect to sender is no less than the number of observed recipient sets, thus it minimizes the hitting sets and improves the efficiency. Probability statistic is employed to condense these hitting sets so as to improve the hit ratio of this attack. We also proposed two strategies against SHS-attack, which are Padding and Random Routing. Theoretical analysis and simulations show that, our attack is more efficient than previous SHS-attack while all the recipients congregate in a small group and the above two countermeasures can effectively decrease the accuracy of this attack.Finally, while it can hardly determine the forwarding rounds in Stop-and-Go Mix (SG-Mix), the paper presents a SHS-attack using the number of data packets to statistic. We test the capacity of resisting SHS-attack in SG-Mix, which reveals a positive impact. Padding and Random Routing can prevent SHS-attack efficiently.