International Association
for Cryptologic Research

We present a multi-party computation protocol in the case of dishonest majority which has very low round complexity. Our protocol sits philosophically between Gentry's Fully Homomorphic Encryption based protocol and the SPDZ-BMR protocol of Lindell et al (CRYPTO 2015). Our protocol avoids various inefficiencies of the previous two protocols. Compared to Gentry's protocol we only require Somewhat Homomorphic Encryption (SHE). Whilst in comparison to the SPDZ-BMR protocol we require only a quadratic complexity in the number of players (as opposed to cubic), we have fewer rounds, and we require less proofs of correctness of ciphertexts. In addition we present a variant of our protocol which trades the depth of the required SHE scheme for more homomorphic multiplications.