Modified Relay Selection and Circuit Selection for Faster Tor

Abstract: Users of the Tor anonymity system suffer from lessthan- ideal performance, in part because circuit building and selection processes are not tuned for speed. In this paper, we examine both the process of selecting among pre-built circuits and the process of selecting the path of relays for use in building new circuits to improve performance while maintaining anonymity. First, we show that having three pre-built circuits available allows the Tor client to identify fast circuits and improves median time to first byte (TTFB) by 15% over congestion-aware routing, the current state-of-the-art method. Second, we propose a new path selection algorithm that includes broad geographic location information together with bandwidth to reduce delays. In Shadow simulations, we find 20% faster median TTFB and 11% faster median total download times over congestion-aware routing for accessing webpage-sized objects. Our security evaluations show that this approach leads to better or equal security against a generic relay-level adversary compared to Tor, but increased vulnerability to targeted attacks. We explore this trade-off and find settings of our system that offer good performance, modestly better security against a generic adversary, and only slightly more vulnerability to a targeted adversary.