Modified relay selection and circuit selection for faster Tor

Abstract

Users of the Tor anonymity system suffer from less-than-ideal performance, in part because circuit building and selection processes are not tuned for speed. In this study, the authors 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, the authors 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, they propose a new path selection algorithm that includes broad geographic location information together with bandwidth to reduce delays. In shadow simulations, 20% faster median TTFB and 11% faster median total download times over congestion-aware routing for accessing web page-sized objects were found. The proposed 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. The authors explore this trade-off and find settings of the proposed system that offers good performance, modestly better security against a generic adversary, and only slightly more vulnerability to a targeted adversary.