With a speed of approximately 20 seconds per scanned router or under three minutes for scanning the whole network in a parallelized manner we are also able to observe dynamics in the topology.įigure 2: Connectivity of the 105 fastest Tor relays on March 14th, 2012, 13:59 GMT.īased on these data we have devised attacks that compromise the anonymity of users exhibiting one of the following two communication patterns over the Tor network: These can provide us with a topological map of the Tor network (see Figure 2 for an example). We have found techniques to scan the connectivity of Tor relays. Guard relays remain in this set for approximately one month.įigure 1: User contacts server through the Tor network. The concept of guard nodes was introduced to give users a chance to avoid falling prey to attackers controlling a fraction of the Tor network. Moreover, the first relay in the chain, the so-called “guard”, is picked from a small set of relays – usually consisting of only three elements – that is randomly chosen by the user’s Tor client on its first start. To make this mechanism more secure, the series of servers used for new connections is changed every ten minutes and connections between Tor relays multiplex sessions of multiple users. By routing connections through a variable chain of three “relays”, volunteer-operated Tor servers, the origin of the user establishing the “circuit” is cloaked.Īs a consequence, services that the user connects to do not see the real IP address of the user but rather the IP address of the last computer in the chain of relays. The Tor network is one of the most popular and widely used tools for enabling anonymous Internet communications. On the one hand, anonymity allows people to express their thoughts and ideas without fear of repression on the other hand it can be used to commit crimes in the digital domain with impunity. We have devised novel attacks against the Tor network that can compromise the anonymity of users accessing services that exhibit frequent and predictable communication patterns and users establishing long-lived connections.Īnonymity on the Internet is a double-edged sword. Tor is one of the most widely used tools for providing anonymity on the Internet. TorScan: Deanonymizing Connections Using Topology Leaksīy Alex Biryukov, Ivan Pustogarov and Ralf-Philipp Weinmann
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