Performance or Anonymity? Source-Driven Tor Relay Selection for Performance Enhancement

Tor implements Mixnet to route communications through multiple relay nodes for anonymous routing. The artificial relay additions, while providing anonymity and making the communications difficult to trace, introduce additional communication latency. We advance the current Tor’s source-driven circuit path selection to improve the networking performance. While Tor builds circuits using the Consensus Directory, we design and build new directories (building on the existing Consensus Directory to increase the relay-node selectivity) and the routing algorithm (using the directories). In contrast to the previous research works which had similar goals to enhance the path selection algorithms for low latency performance, we take a systems approach to build on the existing Tor network (introducing new directories and algorithms but using the rest of the existing Tor mechanism for the circuit construction) and implement and experiment on the real-world Tor network to empirically validate our scheme design and the theoretical analyses. Our scheme controls the tradeoff between anonymity vs. performance so that the source node can control the degree of circuit selectivity or even opt to use the current Tor (Vanilla Tor). To inform the source user’s selection, we study how reducing the relay pool impacts anonymity (quantified and measured in entropy). Our prototype experiment results show significant improvements in latency performance. For example, our scheme controlling the immediate relay latency to be less than 30 milliseconds yields the latency cost to become one-third and the throughput to increase by more than 1.4x compared to the current Vanilla Tor performance.