Anonymity protocols are a privacy-enhancing technology for Internet-based communication. Two important characteristics of anonymity protocols are the strength of anonymity provided, and the overhead required for anonymous communication. In this paper, we focus on the latter characteristic, and develop simple performance models for two anonymous communication protocols: Practical Buses and Taxis. We show that the message latency of the Practical Buses protocol scales quadratically with the number of participants, while that of the Taxis protocol scales linearly with the number of participants. Both models are validated with experimental measurements from prototype implementations of the protocols. We show that the Taxis protocol provides more scalable anonymous communication, without compromising the strength of anonymity provided.
Andreas Hirt, Michael J. Jacobson Jr., Carey L. Wi