Fingerprinting Attack on the Tor Anonymity System

We present a novel way to implement a fingerprinting attack against Onion Routing anonymity systems such as Tor. Our attack is a realistic threat in the sense that it can be mounted by a single controller of entrance routers and furthermore require very few resources. The conventional fingerprinting attack based on incoming traffic does not work straightforwardly against Tor due to its multiplex and quantized nature of traffic. By contrast, our novel attack can degrade Tor's anonymity by a metric based on both incoming and outgoing packets. In addition, our method keeps the fingerprinting attack's advantage of being realistic in terms of the few required resources. Regarding evaluation, the effectiveness of our method is discussed in a comprehensive manner: experimentally and theoretically. In order to enhance further studies and show the significance of our idea, we also discuss methods for defending against our attack and other applications of our idea.