Paper 2025/1642 Original: eprint.iacr.org/2025/1642 ↗

Mixed Arithmetic-Binary Circuits in Fluid MPC Against Honest Majority of 4-Party and Its Applications Against Semi-Honest Adversary

Abstract

Secure multi party computation protocols (MPC) translating between arithmetic and binary data types have recently gained attraction which is introduced by Rotaru and Wood in 2019, called daBit, and improved by Escudero et. al. called edaBits. EdaBits are simply secret shares in arithmetic domain and bit decomposition of the arithmetic share is the binary form the secret shares. These protocols are preprocessing for MPC protocols in order to improve efficiency. Furthermore, fluid MPC setting, introduced by Choudhuri, Goel, Green, Jain and Kaptchuk in 2021, is a framework which the parties, called dynamic parties, do not have be online throughout the whole process. Fluid MPC framework is still has to be worked and conventional protocols and techniques has to be adapted for it. Our work introduces an edaBits protocol specifically designed for the fluid MPC setting under a four-party honest-majority model. The protocol, which consists of eight subprotocols, achieves security against an honest majority and departs slightly from the traditional cut-and-choose paradigm. It attains linear memory and time complexity, as well as constant communication complexity. Finally, we demonstrate two applications that employ edaBits within the fluid MPC framework under the semi-honest adversary model.