Universally-Composable Two-Party Computation in Two Rounds

14 years 5 months ago

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Round complexity is a central measure of eﬃciency, and characterizing the round complexity of various cryptographic tasks is of both theoretical and practical importance. We show here a universallycomposable (UC) protocol (in the common reference string model) for two-party computation of any functionality, where both parties receive output, using only two rounds. (This assumes honest parties are allowed to transmit messages simultaneously in any given round; we obtain a three-round protocol when parties are required to alternate messages.) Our results match the obvious lower bounds for the round complexity of secure two-party computation under any reasonable deﬁnition of security, regardless of what setup is used. Thus, our results establish that secure two-party computation can be obtained under a commonly-used setup assumption with maximal security (i.e., security under general composition) in a minimal number of rounds. To give but one example of the power of our general result...

Omer Horvitz, Jonathan Katz

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