Paper 2017/214

Low Cost Constant Round MPC Combining BMR and Oblivious Transfer

Carmit Hazay, Peter Scholl, and Eduardo Soria-Vazquez

Abstract

In this work, we present two new universally composable, actively secure, constant round multi-party protocols for generating BMR garbled circuits with free-XOR and reduced costs. (1) Our first protocol takes a generic approach using any secret-sharing based MPC protocol for binary circuits, and a correlated oblivious transfer functionality. (2) Our specialized protocol uses secret-sharing based MPC with information-theoretic MACs. This approach is less general, but requires no additional correlated OTs to compute the garbled circuit. In both approaches, the underlying secret-sharing based protocol is only used for one secure $$ multiplication per AND gate. An interesting consequence of this is that, with current techniques, constant round MPC for binary circuits is not much more expensive than practical, non-constant round protocols. We demonstrate the practicality of our second protocol with an implementation, and perform experiments with up to $$ parties securely computing the AES and SHA-256 circuits. Our running times improve upon the best possible performance with previous BMR-based protocols by 60 times.

Note: Fixed minor issues.