On the Effectiveness of Continuous-Time Mixes under Flow-Correlation Based Anonymity Attacks

In flow-based mix networks, so-called flow correlation attacks have been proposed earlier and have been shown empirically to seriously degrade mix-based anonymous communication systems. In this paper, we theoretically analyze the effectiveness of a mix network under flow correlation attacks. Our formulae clearly show how a mix network will ultimately fail when an adversary has access to sufficiently long flow samples, independently of the type of flows (TCP or UDP). We illustrate the analysis methodology by modeling a continuous-time mix, which randomly delays each incoming packet. Our queuing-model-based analysis captures the essence of flow correlation attacks and can provide useful guidelines for designers who develop and deploy anonymity systems