Paper 2014/768

Cut-and-Choose Bilateral Oblivious Transfer and Its Application in Secure Two-party Computation

Han Jiang, Xiaochao Wei, Chuan Zhao, and Qiuliang Xu

Abstract

In secure two-party computation protocols, the cut-and-choose paradigm is used to prevent the malicious party who constructs the garbled circuits from cheating. In previous realization of the cut-and-choose technique on the garbled circuits, the delivery of the random keys is divided into multiple stages. Thus, the round complexity is high and the consistency of cut-and-choose challenge should be proved. In this paper, we introduce a new primitive called cut-and-choose bilateral oblivious transfer, which transfers all necessary keys of garbled circuits in one process. Specifically, in our oblivious transfer protocol, the sender inputs two pairs $(x_0,x_1)$, $(y_0,y_1)$ and a bit $\tau$; the receiver inputs two bits $\sigma$ and $j$. After the protocol execution, the receiver obtains $x_{\tau},y_{\sigma}$ for $j=1$, and $x_0,x_1,y_0,y_1$ for $j=0$. By the introduction of this new primitive, the round complexity of secure two-party computation protocol can be decreased; the cut-and-choose challenge $j$ is no need to be opened anymore, therefore the consistency proof of $j$ is omitted. In addition, the primitive is of independent interest and could be useful in many cut-and-choose scenarios.