Dual-link agile QKD for LEO and terrestrial FSO links: a crypto-adaptive, channel-aware design

We present a crypto-adaptive quantum key distribution (QKD) framework for dual-use ground stations capable of operating over both LEO satellite and terrestrial free-space optical (FSO) links. Our approach introduces three key innovations. First, we develop aquantum-native, system-aware channel modelthat integrates both channel-induced impairments and design-dependent system long-term lossses and short/medium-term fluctuations, where the latter are resolved into temporal (synchronization failures) and spatial (pointing and tracking errors). Second, we extend two-tier key distillation by explicitly incorporatingtrusted erasures, which remove non-adversarial intervals prior to estimation, yielding more accurate and conservative operational key rates. Third, we formalizecryptoadaptivity: a policy that adjusts in real time both key length andc-security budget under a global target. This ensures that, at any instant, the system outputs either (i) a provisional hybrid key fused with a post-quantum key encapsulation mechanism (PQKEM), whose security relies solely on computational assumptions, or (ii) a universally composable QKD key with information-theoretic security when finite-key conditions are met. Numerical analysis show the effect of trusted erasures as well as how synchronization in a representative satellite pass governs the availability of composable keys versus hybrid fallback, and how operators can balance security and availability through thec-budget. These results provide a concrete step toward agile, commercially deployable dual-link QKD terminals resilient to real-world dynamics.