Paper 2003/100

Protocols for Bounded-Concurrent Secure Two-Party Computation in the Plain Model

Yehuda Lindell

Abstract

Until recently, most research on the topic of secure computation focused on the stand-alone model, where a single protocol execution takes place. In this paper, we construct protocols for the setting of {\em bounded-concurrent self composition}, where a (single) secure protocol is run many times concurrently, and there is a predetermined bound on the number of concurrent executions. In short, we show that {\em any} two-party functionality can be securely computed under bounded-concurrent self composition, in the {\sf plain model} (where the only setup assumption made is that the parties communicate via authenticated channels). Our protocol provides the first feasibility result for general two-party computation in the plain model, {\em for any model of concurrency}. All previous protocols assumed a trusted setup phase in order to obtain a common reference string. On the downside, the number of rounds of communication in our protocol is super-linear in the bound on the number of concurrent executions. However, we believe that our constructions will lead to more efficient protocols for this task.

Note: This paper contains the upper bound from the STOC'03 paper entitled "Bounded-Concurrent Secure Two-Party Computation Without Setup Assumptions". The lower bound from this paper will be posted shortly in a separate paper. (Meanwhile, the proceedings version has quite a full presentation of the lower bound.)