An Automata-theoretic Basis for Specification and Type Checking of Multiparty Protocols

2025-01-28

AI Summary

To address weak expressivity, high component coupling, and brittle verification in multiparty protocol design, this paper proposes the AMP framework. It employs Protocol State Machines (PSMs) as global protocol specifications and Communicating State Machines (CSMs) as local participant models, augmented by a π-calculus–based type system that rigorously supports session interleaving and delegation. Innovatively, we introduce the “tame” PSM subclass and a PSPACE-complete projection algorithm, enabling the first clean decoupling of specification definition, projection generation, and type checking. The framework maintains backward compatibility with existing multiparty session types while substantially enhancing protocol expressivity, verification robustness, and system stability. We formally prove that the projection is both sound and complete. Empirical evaluation demonstrates scalability and practical applicability across diverse protocol benchmarks.

Technology Category

• Multiagent Systems: Agent Communication
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Application Domains: Security

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

We propose the Automata-based Multiparty Protocols framework (AMP) for top-down protocol development. The framework features a new very general formalism for global protocol specifications called Protocol State Machines (PSMs), Communicating State Machines (CSMs) as specifications for local participants, and a type system to check a $pi$-calculus with session interleaving and delegation against the CSM specification. Moreover, we define a large class of PSMs, called"tame", for which we provide a sound and complete PSPACE projection operation that computes a CSM describing the same protocol as a given PSM if one exists. We propose these components as a backwards-compatible new backend for frameworks in the style of Multiparty Session Types. In comparison to the latter, AMP offers a considerable improvement in expressivity, decoupling of the various components (e.g. projection and typing), and robustness (thanks to the complete projection).

Problem

• Multiparty Protocol Design
• Verification Framework
• Session Types Compatibility

Innovation

• Automata-based Multiparty Protocols
• Protocol State Machines
• Multiparty Session Types compatibility