Statistical and combinatorial analysis of the TOR routing protocol: structural weaknesses identified in the TOR network

In this paper, we present the results of a deep TOR routing protocol analysis from a statistical and combinatorial point of view. We have modelled all possible routes of this famous anonymity network exhaustively while taking different parameters into account with the data provided by the TOR foundation only. We have then confronted our theoretical model with the reality on the ground. To do this, we have generated thousands of roads on the actual TOR network and compared the results obtained with those predicted by the theory. A last step of combinatorial analysis has enabled us to identify critical subsets of Onion routers (ORs) which 33%, 50%, 66% and 75% of the TOR traffic respectively depends on. We have also managed to extract most of the TOR relay bridges which are non public nodes managed by the TOR foundation. The same results as for the ORs have been observed.