Abstract
Tor is one of the most popular anonymity networks. It has been reported that over 2 million unique users utilize the Tor network daily. The Tor network is run by over 6, 000 volunteer relays. Each Tor client telescopically builds a circuit by choosing three Tor relays and then uses that circuit to connect to a server. The Tor relay selection algorithm makes sure that no two relays with the same /16 IP address are chosen. Our objective is to determine the popularity of Tor relays when building circuits. With over 44 vantage points (machines running Tor clients) and over 145,000 circuits built, we found that some Tor relays are chosen more often than others. Although a completely balanced selection algorithm is not possible, analysis of our dataset shows that some Tor relays are over 3 times more likely to be chosen than others. An adversary could potentially eavesdrop or correlate more Tor traffic.
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Acknowledgments
We thank Mr. Ippei Okamura for his help with collecting the data, and Google for providing us Google Cloud credits to increase our number of vantage points.
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© 2019 ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering
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Chen, T., Cui, W., Chan-Tin, E. (2019). Measuring Tor Relay Popularity. In: Chen, S., Choo, KK., Fu, X., Lou, W., Mohaisen, A. (eds) Security and Privacy in Communication Networks. SecureComm 2019. Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, vol 304. Springer, Cham. https://doi.org/10.1007/978-3-030-37228-6_19
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