Sublinear GMW-Style Compiler for MPC with Preprocessing

We consider the efficiency of protocols for secure multiparty computation (MPC) with a dishonest majority. A popular approach for the design of such protocols is to employ preprocessing. Before the inputs are known, the parties generate correlated secret randomness, which is consumed by a fast and possibly “information-theoretic” online protocol. A powerful technique for securing such protocols against malicious parties uses homomorphic MACs to authenticate the values produced by the online protocol. Compared to a baseline protocol, which is only secure against semi-honest parties, this involves a significant increase in the size of the correlated randomness, by a factor of up to a statistical security parameter. Different approaches for partially mitigating this extra storage cost come at the expense of increasing the online communication. In this work we propose a new technique for protecting MPC with preprocessing against malicious parties. We show that for circuit evaluation protocols that satisfy mild security and structural requirements, that are met by many standard protocols with semi-honest security, the extra additive storage and online communication costs are both logarithmic in the circuit size. This applies to Boolean circuits and to arithmetic circuits over fields or rings, and to both information-theoretic and computationally secure protocols. Our protocol can be viewed as a sublinear information-theoretic variant of the celebrated “GMW compiler” that applies to natural protocols for MPC with preprocessing. Our compiler makes a novel use of the techniques of Boneh et al. (Crypto 2019) for sublinear distributed zero knowledge, which were previously only used in the setting of honest-majority MPC.