Paper 2024/1653

AD-MPC: Fully Asynchronous Dynamic MPC with Guaranteed Output Delivery

Abstract

Traditional secure multiparty computation (MPC) protocols presuppose a fixed set of participants throughout the computational process. To address this limitation, Fluid MPC [CRYPTO 2021] presents a dynamic MPC model that allows parties to join or exit during circuit evaluation dynamically. However, existing dynamic MPC protocols can guarantee safety but not liveness within asynchronous networks. This paper introduces ΠAD-MPC, a fully asynchronous dynamic MPC protocol. ΠAD-MPC ensures both safety and liveness with optimal resilience, capable of tolerating t (n=3t+1) corrupted participants. To achieve this, we develop a novel asynchronous transfer protocol ΠTrans and a preprocessing protocol ΠAprep specifically tailored for dynamic environments. In contrast to most dynamic MPC protocols that achieve security with abort in synchronous networks, ΠAD-MPC guarantees output delivery in asynchronous networks with optimal resilience, thus enhancing robustness. We provide a formal security proof of ΠAD-MPC under the Universal Composability (UC) framework. Furthermore, an extensive evaluation involving up to 20 geographically distributed nodes demonstrates the protocol’s practical performance and its ability to reliably deliver outputs in asynchronous dynamic settings. Compared to the state-of-the-art Fluid MPC, ΠAD-MPC achieves comparable performance while offering significantly enhanced security guarantees.