Passive-Logging Attacks Against Anonymous Communications Systems

Abstract

Using analysis, simulation, and experimentation, we examine the threat against anonymous communications posed by passive-logging attacks. In previous work, we analyzed the success of such attacks under various assumptions. Here, we evaluate the effects of these assumptions more closely. First, we analyze the Onion Routing-based model used in prior work in which a fixed set of nodes remains in the system indefinitely. We show that for this model, by removing the assumption of uniformly random selection of nodes for placement in the path, initiators can greatly improve their anonymity. Second, we show by simulation that attack times are significantly lower in practice than bounds given by analytical results from prior work. Third, we analyze the effects of a dynamic membership model, in which nodes are allowed to join and leave the system; we show that all known defenses fail more quickly when the assumption of a static node set is relaxed. Fourth, intersection attacks against peer-to-peer systems are shown to be an additional danger, either on their own or in conjunction with the predecessor attack. Finally, we address the question of whether the regular communication patterns required by the attacks exist in real traffic. We collected and analyzed the Web requests of users to determine the extent to which basic patterns can be found. We show that, for our study, frequent and repeated communication to the same Web site is common.