MorphMix: Peer-to-Peer based Anonymous Internet Usage with Collusion Detection

Several MIX-based systems offering anonymity have been operational. They are usually based on a relatively small set of static, well known and highly reliable nodes with good performance and connectivity that offer the MIX functionality. Due to the small number of nodes in such a system, they must be made very resistant against traffic analysis attacks by exchanging lots of cover traffic, resulting in an unacceptable bandwidth overhead. End-to-end traffic analysis attacks are even more difficult to counter as there are only a few entryand exit-points in the system. Additionally, static MIX-networks suffer from scalability problems and in several countries, institutions operating a MIX could be targeted by legal attacks. In this technical report, we introduce MorphMix, a system for peer-to-peer based anonymous Internet usage. Each MorphMix node is a MIX in the system and anyone with access to a computer connected to the Internet with a public IP address can join the system. We believe that MorphMix overcomes or reduces several drawbacks of static MIX networks. On the other hand, MorphMix introduces new challenges. Particularly, an adversary can easily operate several malicious nodes in the system and try to break the anonymity of a legitimate user by getting full control over an anonymous path she is using. To counter this attack, we have developed a collusion detection mechanism, which allows to identify compromised paths with a very high probability before they are being used.