NavigaTor: Finding Faster Paths to Anonymity

The Tor network is currently by far the most popular system for providing anonymity on the Internet. Even though both latency and throughput have been significantly improved in recent years, Tor users still experience variable delays on connecting to servers. Such delays have been shown to be especially harmful for browsing the web and prevent altogether the use of protocols where a certain quality of service is indispensable. In this paper we propose and evaluate methods to measure and improve performance in the Tor network. To estimate the quality of circuits for future traffic, we use active Round-Trip-Time (RTT) measurements and a-priori information of the distribution of RTT values. In this way, slow circuits can be discarded before having negative impact on user experience. Using NavigaTor, our high performance measurement software which includes a custom Tor path generator, we are the first to conduct large-scale performance measurements on the live Tor network, building millions of circuits within days, without stressing the anonymity network. As part of our study, we conduct several experiments from PlanetLab on the live Tor network to analyze the trade-off between the quality of protection and the quality of service. We compare our Circuit-RTT method to the current state-of-the-art method Circuit Build Time (CBT) and the more recently proposed congestion-aware scheme, finding that the congestion-aware scheme in its original design achieves only minor improvements on the current Tor network and that Circuit-RTT improves latency and throughput more effectively than CBT.