TightRope: Towards Optimal Load-balancing of Paths in Anonymous Networks.

We study the problem of load-balancing in path selection in anonymous networks such as Tor. We first find that the current Tor path selection strategy can create significant imbalances. We then develop a (locally) optimal algorithm for selecting paths and show, using flow-level simulation, that it results in much better balancing of load across the network. Our initial algorithm uses the complete state of the network, which is impractical in a distributed setting and can compromise users' privacy. We therefore develop a revised algorithm that relies on a periodic, differentially private summary of the network state to approximate the optimal assignment. Our simulations show that the revised algorithm significantly outpe forms the current strategy while maintaining provable privacy guarantees.