Payload analysis of anonymous communication system with host-based rerouting mechanism

Host-based rerouting mechanism is a routing scheme that stores and forwards data in application layer. With this, users can communicate in a indirect way. Thus, identity information such as IP addresses can be effectively hidden against eavesdropper. In anonymous communication systems, such as mixes, onion routing, and crowds, this mechanism is adopted to provide anonymity. This mechanism, however, can result in extra overhead in performance such as communication delay and participant payload, which may affect the applications of anonymous communication systems. In this paper, we study quantitatively the participant payload induced by host-based rerouting mechanisms. A probability formula for calculating the participant payload is derived, which shows that the number of participants, the number of rerouting paths, and the probability distribution of the length of rerouting paths determine the participant payload. Applying this formula to the practical anonymous communication system, crowds, we get immediately the precise expected participant payload, which significantly improves Reiter and Rubin´s original analysis and demonstrates that the participant payload in crowds remains a constant and independent of the variation of the number of participants in crowds. Simulation results are presented to testify our theoretical analysis.