Affiliations: [a] Laboratory of Cryptography and Systems Security (CrySyS), Department of Telecommunications, Budapest University of Technology and Economics, Magyar tudósok krt 2, H-1117 Budapest, Hungary | [b] Laboratory of Computer Communications and Applications, School of Computer and Communication Sciences, Swiss Federal Institute of Technology – Lausanne (EPFL), EPFL-IC-LCA, CH-1015 Lausanne, Switzerland
Abstract: We propose a formal model of rational exchange and exchange protocols in general, which is based on game theory. In this model, an exchange protocol is represented as a set of strategies in a game that is played by the protocol parties and the network that they use to communicate with each other. Within this model, we give a formal definition for rational exchange and various other properties of exchange protocols, including fairness. In particular, rational exchange is defined in terms of a Nash equilibrium in the protocol game. We also study the relationship between rational and fair exchange, and prove that fairness implies rationality, but not vice versa. Finally, we illustrate the usage of our formal model for the analysis of existing rational exchange protocols by analyzing a protocol proposed by Syverson. We show that the protocol is rational only under the assumption that the network is reliable.
