Strong Anonymity is not Enough: Introducing Fault Tolerance to Planet-Scale Anonymous Communication Systems

Abstract

Current Anonymous Communication Systems (ACS) lack fault tolerance and thus risk becoming unavailable when failures occur, forcing users offline or to less private messengers. In this work, we evaluate end-to-end message transmission latencies and resource demands of state-of-the-art mixnet Vuvuzela and CPIR system Pung under different network failure scenarios on an ACS test bed across four continents. We compare Vuvuzela and Pung to proof-of-concept mixnet FTMix that we equip with simple fault tolerance measures. Our analysis shows that FTMix maintains the smallest divergence of end-to-end latencies under failures from their respective baseline among all three ACS, while also achieving a balanced resource consumption trade-off. Thus, we consider fault tolerance effective in ensuring service availability and a crucial design principle for future ACS proposals.