From Fairness to Full Security in Multiparty Computation

TL;DR

This paper introduces efficient methods to transform fair multiparty computations into fully secure ones, significantly reducing the number of invocations needed and improving security guarantees by using random committees.

Contribution

The authors present novel transformations from fair to fully secure MPC protocols that require fewer invocations and leverage random committees, assuming a constant honest fraction.

Findings

Transformations require super-logarithmic invocations

Reduces the number of parties involved in computation

Enhances security from fairness to full security

Abstract

In the setting of secure multiparty computation (MPC), a set of mutually distrusting parties wish to jointly compute a function, while guaranteeing the privacy of their inputs and the correctness of the output. An MPC protocol is called \emph{fully secure} if no adversary can prevent the honest parties from obtaining their outputs. A protocol is called \emph{fair} if an adversary can prematurely abort the computation, however, only before learning any new information. We present highly efficient transformations from fair computations to fully secure computations, assuming the fraction of honest parties is constant (e.g., $1\%$ of the parties are honest). Compared to previous transformations that require linear invocations (in the number of parties) of the fair computation, our transformations require super-logarithmic, and sometimes even super-constant, such invocations. The main idea is to delegate the computation to chosen random committees that invoke the fair computation. Apart from the benefit of uplifting security, the reduction in the number of parties is also useful, since only committee members are required to work, whereas the remaining parties simply "listen" to the computation over a broadcast channel.