Effective Anonymous Messaging: the Role of Altruism

TL;DR

This paper analyzes the Fuzzy Message Detection protocol for anonymous messaging, demonstrating that altruistic users are essential for its proper functioning and proposing a mechanism to optimize social welfare.

Contribution

It models FMD using empirical game theory, highlights the importance of altruism, and introduces a BC-based mechanism for social optimization.

Findings

Altruistic users are crucial for FMD's viability.

The system's equilibria depend on levels of altruism.

A BC-based mechanism can achieve social optimality.

Abstract

Anonymous messaging and payments have gained momentum recently due to their impact on individuals, society, and the digital landscape. Fuzzy Message Detection (FMD) is a privacy-preserving protocol where an untrusted server performs message anonymously filtering for its clients. To prevent the server from linking the sender and the receiver, the latter can set how much cover traffic they should download along with genuine messages. This could cause unwanted messages to appear on the user's end, thereby creating a need to balance one's bandwidth cost with the desired level of unlinkability. Previous work showed that FMD is not viable with selfish users. In this paper, we model and analyze FMD using the tools of empirical game theory and show that the system needs at least a few altruistic users to operate properly. Utilizing real-world communication datasets, we characterize the emerging equilibria, quantify the impact of different types and levels of altruism, and assess the efficiency of potential outcomes versus socially optimal allocations. Moreover, taking a mechanism design approach, we show how the betweenness centrality (BC) measure can be utilized to achieve the social optimum.