TUC: Time-Sensitive and Modular Analysis of Anonymous Communication

Abstract

The anonymous communication protocol Tor constitutes the most widely deployed technology for providing anonymity for user communication over the Internet. Several frameworks have been proposed that show strong anonymity guarantees, none of these, however, are capable of modeling the class of traffic-related timing attacks against Tor, such as traffic correlation and website fingerprinting. In this work, we present TUC: the first framework that allows for establishing strong anonymity guarantees in the presence of time-sensitive adversaries that mount traffic-related timing attacks. TUC incorporates a comprehensive notion of time in an asynchronous communication model with sequential activation, while offering strong compositionality properties for security proofs. We apply TUC to evaluate a novel countermeasure for Tor against website fingerprinting attacks. Our analysis relies on a formalization of the onion routing protocol that underlies Tor and proves rigorous anonymity guarantees in the presence of traffic-related timing attacks.