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Tor, an onion-routing anonymity network, can be attacked by Website Fingerprinting (WF), which de-anonymizes encrypted web browsing traffic by analyzing its unique sequence characteristics. Although many defenses have been proposed, few have been implemented and tested in the real world; most state-of-the-art defenses were only simulated. Simulations fail to capture the real performance of these defenses as they make simplifying assumptions about the protocol stack and network conditions. To allow WF defenses to be analyzed as real implementations, we create WFDefProxy, the first general platform for WF defense implementation on Tor as pluggable transports. We implement three state-of-the-art WF defenses: FRONT, Tamaraw, and RegulaTor. We evaluate each defense extensively by directly collecting defended datasets under WFDefProxy. Our results show that simulation can be inaccurate in many cases. Specifically, Tamaraw's time overhead was underestimated by 22% in one setting and overestimated by 24% in another. RegulaTor's time overhead was underestimated by 30-40%. We find that a major source of simulation inaccuracy is that they cannot incorporate how packets depend on each other. We also find that adverse network conditions (which are ignored in simulation), especially congestion, can affect the evaluated overhead of defenses. These results show that it is important to evaluate defenses as implementations instead of only simulations to avoid errors in evaluation. © 2005-2012 IEEE.

Website Fingerprinting (WF) attacks utilize size and timing information of encrypted network traffic to infer the user’s browsing activity, posing a great threat to privacy-enhancing technologies like Tor; nevertheless, Tor has not adopted any defense because existing defenses are not convincing enough to show their effectiveness. Some defenses have been overcome by newer attacks; other defenses are never implemented and tested in the real open-world scenario. In this paper, we propose Surakav, a tunable and practical defense that is effective against WF attacks with reasonable overhead. Surakav makes use of a Generative Adversarial Network (GAN) to generate realistic sending patterns and regulates buffered data according to the sampled patterns. We implement Surakav and evaluate it on the live Tor network. Experiments show that Surakav is able to reduce the attacker’s true positive rate by 57% with 55% data overhead and 16% time overhead, saving 42% data overhead compared to FRONT. In the heavyweight setting, Surakav outperforms the strongest known defense, Tamaraw, requiring 50% less overhead in data and time to lower the attacker’s true positive rate to only 8%. We also show that two existing defenses, Walkie-Talkie and TrafficSliver, can be fortified with our GAN-based trace generator.

Website Fingerprinting (WF) attacks threaten user privacy on anonymity networks such as Tor because they can be used by network surveillants to identify the web pages a user is visiting by extracting the size and timing information of the user’s encrypted network traffic; however, Tor is currently undefended against WF because existing defenses have not convincingly shown their effectiveness. Some defenses have been overcome by newer attacks; other defenses have never been implemented and tested in a real open-world scenario, as they had unsolved practical issues for deployment. In this thesis, we focused on designing and evaluating effective defenses that can be deployed in the real Tor network. We proposed three effective defenses that incurred different overhead levels, targeting users with different security preferences. To deploy and evaluate the effectiveness of the WF defenses, we built a general platform for WF defense implementation. We first proposed two zero-delay defenses, FRONT, and GLUE. FRONT and GLUE are two practical defenses specifically designed for achieving low overhead. We observed that WF attacks rely on the feature-rich trace front, so FRONT focuses on obfuscating the trace front with dummy packets. It also randomizes the number and distribution of dummy packets for trace-to-trace randomness to impede the attacker’s learning process. GLUE adds dummy packets between separate traces so that they appear to the attacker as a long consecutive trace, rendering the attacker unable to find their start or end points, let alone classify them. Our experiments show that with only 33% data overhead, FRONT reduces the F1-score of the best attack from 0.94 to 0.47. By comparison, the best-known lightweight defense, WTF-PAD, only reduces it to 0.70. With around 22% ― 44% data overhead, GLUE can lower the true positive rate and precision of the best WF attacks to less than 15%, approaching the performance of the best heavyweight defenses. FRONT is strong and

Website Fingerprinting (WF) attacks threaten user privacy on anonymity networks because they can be used by network surveillants to identify the webpage being visited by extracting features from network traffic. A number of defenses have been put forward to mitigate the threat of WF, but they are flawed: some have been defeated by stronger WF attacks, some are too expensive in overhead, while others are impractical to deploy. In this work, we propose two novel zero-delay lightweight defenses, FRONT and GLUE. We find that WF attacks rely on the feature-rich trace front, so FRONT focuses on obfuscating the trace front with dummy packets. It also randomizes the number and distribution of dummy packets for trace-to-trace randomness to impede the attacker’s learning process. GLUE adds dummy packets between separate traces so that they appear to the attacker as a long consecutive trace, rendering the attacker unable to find their start or end points, let alone classify them. Our experiments show that with 33% data overhead, FRONT outperforms the best known lightweight defense, WTF-PAD, which has a similar data overhead. With around 22%–44% data overhead, GLUE can lower the accuracy and precision of the best WF attacks to a degree comparable with the best heavyweight defenses. Both defenses have no latency overhead.