Globally Secure Satellite QKD with Distributed Trust

Abstract

This thesis aims to evaluate the feasibility of a global key distribution architecture without localizing the relay nodes entirely by investigating space geometry and a constraints-aware framework for satellite-based Twin-Field quantum key distribution (TF–QKD). The investigation concentrates on the inter-satellite link (ISL) and uplink (UL) segments in the context of realistic orbital dynamics. Under these conditions, the availability and quality of the link are jointly influenced by elevation, slant range, and line of sight. Geometric sizing of the Tx/Rx telescope apertures, Beer-Lambert atmospheric extinction, beam pointing instability, background scattering due to Sun/Moon radiation and synchronization penalties are all included in channel efficiency models, and they are all treated stochastically to reflect scalability with fidelity. XOR-based key forwarding is employed to evaluate end-to-end secure key generation on top of these physical layers. Path Routing and scheduling are guaranteed by graph based networks and numerical calculations.

Various routing strategies are evaluated, such as key rate-aware optimization, distance weighed shortest path (KSP), and k-disjoint parallel chains. Performance across service-level metrics is quantified by simulation campaigns that span month-long orbital cycles, including delivered keys per pass, continuity curves, outage probability, time-to-key, throughput and k-disjoint availability. The findings indicate that the primary network design choices include uplink elevation and short, repeatable ISLs. By raising elevation masks and coordinating orbital phasing, narrow peaks in synchronous-key transmission are transformed into wide plateaus with a high secret key rate. The system maintained 12.3 Gbit/month of end-to-end keys under conservative XOR bottlenecks in the Sun-synchronous orbit (SSO) con stellation scenario that was demonstrated. It also accomplished median multi-path SKR in the tens of kbps with near-zero outages and provided three disjoint paths for virtually the entire run due to a calculated resource-intensive network.

For a practical architectural candidate for global-scale quantum networks, these findings agree on satellite TF–QKD with XOR forwarding. The framework demonstrates how non-localized trust can be maintained without sacrificing continuity by utilizing orbital repeatability and impairment-aware scheduling. This work parallelize industry friendly post-quantum cryptography and advances the field of quantum communication.