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Distributed computing meets game theory

2011, ACM SIGACT News

Abstract

Traditionally fault tolerance and security have divided processes into "good guys" and "bad guys". Work on fault tolerance has focused on assuring that certain goals are met, as long as the number of "bad guys" is bounded (e.g., at most one third or one half of the total number of players). The viewpoint in game theory has been quite different. There are no good guys or bad guys, only rational players who will make moves in their own self interest. Making this precise requires assigning payoffs (or utilities) to outcomes. There are various solution concepts in game theorypredictions regarding the outcome of a game with rational players. They all essentially involve players making best responses to their beliefs, but differ in what players are assumed to know about what the other players are doing. Perhaps the best-known and most widely-used solution concept is Nash equilibrium (NE). A profile σ of strategies-that is, a collection of strategies consisting of one strategy σ i for each player i-is a Nash equilibrium if no player can improve his payoff by changing his strategy unilaterally, even assuming that he knows the strategies of all the other players. In the notation traditionally used in game theory, σ is a Nash equilibrium if, for all i and all strategies τ i for player i, u i (σ −i , τ i) ≤ u i (σ): player i does not gain any utility by switching to τ i if all the remaining players continue to play their component of σ. (See a standard game theory text, such as [20], for an introduction to solution concepts, and more examples and intuition.) Both the game theory approach and the distributed computing approach have something to recommend them. In fact, for many applications, it is important to take both fault tolerance and strategic behavior into account. That is, we are interested in solution concepts that consider strategic behavior while maintaining a level of fault tolerance. In this paper, we briefly review the approaches to combine these concerns taken in two papers, [1] and [4], and discuss more generally the question of