A Simulation of Circuit Creation in Tor

This thesis presents an accurate simulation of the circuit creation behavior of the anonymity network Tor. Systems of all types are subject to attacks, which must often be tested in simulation; many simulations do not accurately model the behavior of the target network, making it difficult to discern which attacks are of greatest concern. We simulate the circuit creation behavior of Tor using hidden Markov models trained to the observed behavior of the real network. We first observe the behavior of the network by probing individual routers; we then cluster those observations into a few smaller observation sets, and train a hidden Markov model from each cluster. We show by a probabilistic evaluation that our model accurately simulates the behavior of Tor.