Paper 2025/487 Original: eprint.iacr.org/2025/487 ↗

webSPDZ: Versatile MPC on the Web

Abstract

Multi-party computation (MPC) has become increasingly practical in the last two decades, solving privacy and security issues in various domains, such as healthcare, finance, and machine learning. One big caveat is that MPC sometimes lacks usability since the knowledge barrier for regular users can be high. Users have to deal with, e.g., various CLI tools, private networks, and sometimes even must install many dependencies, which are often hardware-dependent. A solution to improve the usability of MPC is to build browser-based MPC engines where each party runs within a browser window. Two examples of such an MPC web engine are JIFF and the web variant of MPyC. Both support an honest majority with passive corruptions. $\texttt{webSPDZ}$: Our work brings one of the most performant and versatile general-purpose MPC engines, MP-SPDZ, to the web. MP-SPDZ supports ≥40 MPC protocols with different security models, enabling many security models on the web. To port MP-SPDZ to the web, we use Emscripten to compile MP-SPDZ’s C++ BackEnd to WebAssembly and upgrade the party communication for the browser (WebRTC or WebSockets). We call the new MPC web engine webSPDZ. As with the native versions of the mentioned MPC web engines, MPyC-Web and JIFF, webSPDZ outperforms them in our end-to-end experiments. We believe that webSPDZ brings forth many interesting and practically relevant use cases. Thus, webSPDZ pushes the boundaries of practical MPC: making MPC more usable and enabling it for a broader community.