Tor is one of the more popular systems for anonymizing near-real-time communications on the Internet. [2007] proposed a denial-of-service-based attack on Tor (and related systems) that significantly increases the probability of compromising the anonymity provided. In this article, we analyze the effectiveness of the attack using both an analytic model and simulation. We also describe two algorithms for detecting such attacks, one deterministic and proved correct, the other probabilistic and verified in simulation.
Traditional mix-based systems are composed of a small set of static, well known, and highly reliable mixes. To resist traffic analysis attacks at a mix, cover traffic must be used, which results in significant bandwidth overhead. End-to-end traffic analysis attacks are even more difficult to counter because there are only a few entry-and exit-points in the system. Static mix networks also suffer from scalability problems and in several countries, institutions operating a mix could be targeted by legal attacks. In this paper, we introduce MorphMix, a system for peer-to-peer based anonymous Internet usage. Each MorphMix node is a mix and anyone can easily join the system. We believe that MorphMix overcomes or reduces several drawbacks of static mix networks. In particular, we argue that our approach offers good protection from traffic analysis attacks without employing cover traffic. But MorphMix also introduces new challenges. One is that an adversary can easily operate several malicious nodes in the system and try to break the anonymity of legitimate users by getting full control over their anonymous paths. To counter this attack, we have developed a collusion detection mechanism, which allows to identify compromised paths with high probability before they are being used.