An analysis of forwarding mechanism in crowds

The mechanism of forwarding request plays the most important role in crowds anonymous communication protocol. On one hand, it hides the identity of the request initiator against the responder; the participants in protocol, and eavesdroppers. On the other hand, it causes additional latency on communication and payload on participants in the protocol. In this paper, we investigated the influence of the forwarding mechanism with respect to the performance and the security in crowds. Different from the previous approaches, our analysis focuses on the length of forwarding paths, and is independent of the underlying length control strategy. In the study of system performance, we consider the participant payload in crowds and prove that the expected participant payload is equal to the expected length of forwarding paths. Applying this result to the currently used length control strategy in crowds, we derive that the expected participant payload in crowds is 1/(1-f) + 1, where P_f is the forwarding probability in crowds. This improves Reiter and Rubin´s original result and demonstrates that the participant payload in crowds is entirely independent of the size of crowds protocol.