On Definitions for Semi-Honest Secure Multiparty Computation

Secure multiparty computation (MPC) is a cryptographic technology to perform some computation on multiple parties' input data while concealing the individual inputs from other parties. For the case of semi-honest adversaries, the security definition in Goldreich's famous book is widely used as a standard definition. In this paper, however, we point out that there is an MPC protocol where a semi-honest adversary receives only a ciphertext of one-time pad with unknown key but the protocol is not secure under the standard security definition, which may look inconsistent with the perfect secrecy of one-time pad that its ciphertext leaks no information at all. We propose a variant of the security definition that resolves this issue. We also show that a somewhat restrictive version of the Composition Theorem holds for our modified security definition.