From Fairness to Full Security in Multiparty Computation
This work addresses the efficiency bottleneck in secure multiparty computation for distributed systems, offering a significant reduction in computational overhead.
The paper tackles the problem of transforming fair multiparty computation protocols into fully secure ones with improved efficiency, achieving transformations that require only super-logarithmic or super-constant invocations of fair computations, compared to previous linear invocations, assuming a constant fraction of honest parties.
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.