Chicago Journal of Theoretical Computer Science

Volume 2009

Article 1

Published by Dept. CS U. Chicago. Copyright 2009 CJTCS and the author.

Legally Enforceable Fairness in Secure Two-Party Communication

Yehuda Lindell
Department of Computer Science.
Bar-Ilan University

June 12, 2009

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 (meanig that fairness is breached) then the party not obtaining output has a digitally signed cheque from the other party. Thus, fairness can be "enforced" int the sense that any breach results in a loss of money by the adversarial party.

Submitted January 16, 2008, revised version submitted June 10 2009, published June 12 2009.

DOI: 10.4086/cjtcs.2009.001
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