Paper 2021/795 Original: eprint.iacr.org/2021/795 ↗

Transforming Secure Comparison Protocol from Passive to Active Adversary Model

Abstract

Secure comparison (SC) is an essential primitive in Secure Multiparty Computation (SMC) and a fundamental building block in Privacy-Preserving Data Analytics. Although secure comparison has been studied since the introduction of SMC in the early 80s and many protocols have been proposed, there is still room for improvement, especially providing security against malicious adversaries who form the majority among the participating parties. It is not hard to develop an SC protocol secure against malicious majority based on the current state of the art SPDZ framework. SPDZ is design to work for arbitrary polynomially-bounded functionalities, and it may not provide the most efficient SMC implementation for a specific task, such as SC. In this paper, we propose a novel compiler that is specifically designed to convert most existing SC protocols with semi-honest security into the ones secure against the malicious majority. This compiler provides a flexible and efficient way to achieve both covert and active security for passively secure SC protocols.