Joanna Sliwa

Quantum Key Distribution (QKD) provides information-theoretic security for key establishment, but its security guarantees rely on the authentication of the classical communication channel. Although this requirement is well understood at the protocol level, its implications for large-scale and operational QKD networks, particularly satellite-based QKD (SatQKD), remain insufficiently explored. In this work, we analyse authentication mechanisms and trust assumptions in satellite QKD networks from a system-level perspective. We compare symmetric-key authentication and post-quantum digital signatures and examine how they affect both resource consumption and security guarantees. A structured analysis of trust boundaries in SatQKD architectures is provided, comparing trusted-node relay configurations with end-to-end approaches. We show that practical deployments introduce implicit trust assumptions that are not captured in idealised QKD security models. Our results highlight that authentication and trust are key design parameters in operational and dual-use QKD systems.