Cyber-Physical Systems (CPSs) rely on distributed embedded devices that often must communicate securely over buses. Ensuring message integrity and authenticity on these buses typically requires group-shared keys for Message Authentication Codes (MACs). To avoid insecure fixed pre-shared keys and trust-on-first-use concepts, a Group Key Agreement (GKA) protocol is needed to dynamically agree on a key amongst the devices. Yet existing GKA protocols lack adaptability to constrained CPS buses. This paper targets authenticated, fully distributed GKA suitable for bus topologies under constraints of industrial and cyber-physical systems, including broadcast-only links, half-duplex operation, resource limits, dynamic membership (including unannounced leaves), a long device lifetime, and a strong Dolev-Yao adversary capable of partitioning the bus. We first systematise existing protocols, then derive the requirements necessary for an authenticated and fully distributed GKA on bus systems. Finally, we design, implement, and evaluate a custom GKA protocol based on TreeKEM.

翻译：信息物理系统依赖于分布式嵌入式设备，这些设备通常需要通过总线进行安全通信。为确保这些总线上消息的完整性与真实性，通常需要为消息认证码使用群组共享密钥。为避免使用不安全的固定预共享密钥及首次使用信任机制，需要一种群组密钥协商协议来使设备间动态协商密钥。然而，现有的群组密钥协商协议缺乏对受限信息物理系统总线的适应性。本文旨在设计一种适用于总线拓扑、经过认证且完全分布式的群组密钥协商协议，以满足工业与信息物理系统的约束条件，包括：仅广播链路、半双工操作、资源限制、动态成员关系（含未声明的离开）、设备长生命周期以及能够分割总线的强Dolev-Yao攻击者。我们首先系统化梳理现有协议，进而推导出总线系统上实现认证且完全分布式群组密钥协商的必要条件。最后，我们基于TreeKEM设计、实现并评估了一种定制化的群组密钥协商协议。