SoK on Performance Bounds in Anonymous Communication

Communicating anonymously comes at a cost - and large communities have been in a constant tug-of-war between the development of faster protocols, and the improvement of security analyses. Thereby more intricate privacy goals emerged and more detailed bounds on the minimum overhead necessary to achieve them were proven. The entanglement of requirements, scenarios, and protocols complicates analysis, and the published results are hardly comparable, due to deviating, yet specific choices of assumptions and goals (some explicit, most implicit). In this paper, we systematize the field by harmonizing the models, comparing the proven performance bounds, and contextualizing these theoretical results in a broad set of proposed and implemented systems. By identifying inaccuracies, we demonstrate that the attacks, on which the results are based, indeed break much weaker privacy goals than postulated, and tighten the bounds along the way. We further show the equivalence of two seemingly alternative bounds. Finally, we argue how several assumptions and requirements of the papers likely are of limited applicability in reality and suggest relaxations for future work.