A review of indirect authentication in LEO satellite networks: Three decades of progress

Low Earth Orbit (LEO) satellite networks have become the main differentiator in achieving global connectivity, augmenting terrestrial networks through wider coverage, lower latency, and native integration with 5G/6G, the Internet of Things (IoT), and edge services. However, the expansion of LEO constellations introduces substantial security challenges, mainly ensuring robust authentication under dynamic, resource and bandwidth constrained conditions. In many practical architectures, authentication is performed indirectly, with satellites forwarding verification material to ground infrastructure rather than authenticating autonomously. Despite its prevalence, indirect authentication in LEO networks lacks a dedicated, up-to-date survey and a consistent way to compare designs. This paper reviews 69 indirect authentication protocols published between 1996 and 2024 and introduces a role-based taxonomy that distinguishes relay-based schemes from schemes where satellites provide limited assistance prior to ground-based verification. Each protocol is analysed in terms of architecture, cryptographic approach, security properties, validation practices, and efficiency trade-offs. Emerging directions are also synthesised, including blockchain-based designs, quantum security, physical-layer authentication, and Zero Trust-inspired approaches. The survey consolidates fragmented terminology, clarifies design choices and trade-offs, and highlights open research problems toward scalable authentication for future LEO constellations that reflect operational realities.