Legally-Enforceable Fairness in Secure Two-Party Computation

Yehuda Lindell


In the setting of secure multiparty computation, a set of mutually distrustful parties wish to securely compute some joint function of their private inputs. The computation should be carried out in a secure way, meaning that the properties privacy, correctness, independence of inputs, fairness and guaranteed output delivery should all be preserved. Unfortunately, in the case of no honest majority -- and specifically in the important two-party case -- it is impossible to achieve fairness and guaranteed output delivery. In this paper, we show how a legal infrastructure that respects digital signatures can be used to enforce fairness in two-party computation. Our protocol has the property that if one party obtains output while the other does not (meaning that fairness is breached), then the party not obtaining output has a digitally signed cheque from the other party. Thus, fairness can be ``enforced'' in the sense that any breach results in a loss of money by the adversarial party.


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