Securing Tor Tunnels under the Selective-DoS Attack

Low-latency anonymous networks like Tor are subject to selective denial-of-service (DoS) attacks. Selective-DoS attacks lowers anonymity as it forces paths to be rebuilt multiple times to ensure delivery which increases the opportunity for more attack. In this paper we present a detection algorithm which filters out compromised tunnels from a set of Tor tunnels to ensure better anonymity. Our detection algorithm uses two levels of probing to filter out potential compromised tunnels. We perform probabilistic analysis and extensive simulation to show the robustness of our detection algorithm. We also analyze the cost of our algorithm and show a tradeoff between efficiency and computation overhead. Real world experiments reveal that our detection algorithm provides good defence against selective DoS attack.