Pessimism of the Will, Optimism of the Intellect: Fair Protocols with Malicious but Rational Agents

TL;DR

This paper introduces a game-theoretic framework for analyzing fairness protocols with rational, potentially malicious agents, providing decision procedures to assess protocol immunity and existence based on game structure.

Contribution

It develops a novel game-based approach for fairness protocol analysis without predefined attacker models, using strong secure equilibria and complexity bounds.

Findings

Decision procedures for protocol immunity against coalitions

Complexity bounds for protocol existence based on graph structure

Framework applicable to finite and infinite games

Abstract

Fairness is a desirable and crucial property of many protocols that handle, for instance, exchanges of message. It states that if at least one agent engaging in the protocol is honest, then either the protocol will unfold correctly and fulfill its intended goal for all participants, or it will fail for everyone. In this work, we present a game-based framework for the study of fairness protocols, that does not define a priori an attacker model. It is based on the notion of strong secure equilibria, and leverages the conceptual and algorithmic toolbox of game theory. In the case of finite games, we provide decision procedures with tight complexity bounds for determining whether a protocol is immune to nefarious attacks from a coalition of participants, and whether such a protocol could exist based on the underlying graph structure and objectives.