UC San Diego

Tor, the Onion Router, is a popular anonymity overlay network. Its goal is to provide anonymity at little cost to performance. However, Tor network performance is still fairly slow, due to the fact that the bandwidth it provides is limited by how much the volunteers running the Tor routers wish to give. There are a few studies that investigate changing the structure of the Tor network to improve performance. We go in a different direction and investigate different path selection strategies; specifically, that of varying the number of hops in a circuit, varying the performance flags in a circuit, and varying the geographic distance between routers in a circuit. We show how much improvement can be had by reducing the path length, which gives the user guidance on how to trade off anonymity for performance. Our throughput results are as follows: a two hop circuit had an average throughput of 9.6Kbps, and a three hop circuit had an average throughput of 6.7Kbps, and a four hop circuit had an average throughput of 5.2Kbps. We found that there was not much difference between having "stable", "fast", or s̀t̀able and fast" flags, but found that for preserving anonymity the latter was preferable. These were also reasonably fast, with average throughputs between 7.2Kbps and 7.4Kbps. We also found that some improvement could be had by keeping the distance between routers small, with distances between 200-600 miles and 3800-4200 miles providing throughput around 6.5Kbps, and distances greater than that dropping by about 2Kbps