Abstract
Anonymous communication aims to hide the relationship between communicating parties on the Internet. It is the technical basis for achieving privacy and overcoming censorship. Presently there are only a few systems that are of practical relevance for providing anonymity. One of the most widespread and well researched is Tor which is based on onion routing. Usage of Tor, however, often leads to long delays which are not tolerated by end-users. This, in return, discourages many of them from using the system and lowers the protection for the remaining ones. In this paper we analyze the bottlenecks in the Tor network and propose new methods of path selection that better utilize available capacities in the heterogeneous network and allow performance-improved onion routing. Our methods are based on the combination of remotely measured current load of the nodes and an estimation of their maximum capacity. We evaluate the proposed methods in a Tor network running in PlanetLab where we tried as far as possible to recreate real-world conditions. Finally, we present a practical approach to empirically analyze the strength of anonymity that different methods of path selection provide in comparison to each other. We show the risk of the currently used method for path selection in Tor and provide a countermeasure to protect against this risk by effectively detecting nodes that lie about their capacity.