Between a Rock and a Hard Place: Interpolating between MPC and FHE

We present a computationally secure MPC protocol for threshold adversaries which is parametrized by a value L. When L = 2 we obtain a classical form of MPC protocol in which interaction is required for multiplications, as L increases interaction is reduced in that one requires interaction only after computing a higher degree function. When L approaches infinity one obtains the FHE based protocol of Gentry, which requires no interaction. Thus one can trade communication for computation in a simple way. Our protocol is based on an interactive protocol for “bootstrapping” a somewhat homomorphic encryption scheme. The key contribution is that our presented protocol is highly communication efficient enabling us to obtain reduced communication when compared to traditional MPC protocols for relatively small values of L.