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Bulletin of the Russian Academy of Sciences Physics

Improving Estimates of the Length of a Secret Key in the Channel of an Earth Satellite

Egor I. Ivchenko, A. V. Khmelev, V. L. Kurochkin

Published Jun 1, 2024• 1 citation
Publisher

Abstract

Abstract The length of a secret sequence is studied and optimized, depending on the communication session’s splitting of intervals the quantum distribution of the key between a satellite and the ground station. The proposed technique can greatly increase the rate of key generation, due to dynamically changing channel parameters.
DOI
10.1134/s1062873824706883

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Establishing information-theoretically secure communication between arbitrary locations on Earth is a central goal of quantum networking, for which space-based distribution of quantum entanglement is a leading approach. Modelling and analysis of the performance of satellite entanglement pair distribution is therefore important for the architecture and design of future constellations and space systems. However, entanglement-based quantum key distribution in the absence of quantum repeaters, is especially prone to finite-key effects due to low coincident count rates compared to trusted-node single-path links. Quantifying these effects under realistic orbital conditions is therefore essential for the design of practical satellite quantum communication systems. Here, we develop a high-fidelity model of pair distribution from a low-Earth-orbit satellite that captures orbital dynamics, elevation-dependent loss, background noise, and extraneous detector effects. Integrating this with a finite-key security framework for the BBM92 protocol, we optimise the secret key length across different overpass geometries, orbital altitudes, and optical ground station (OGS) separations. We show that secure key generation remains feasible in early clear daytime conditions using baseline parameters representative of current technologies, while showing that modest system improvements could further extend daytime operation. Finally, we evaluate the annual secret key performance for representative intercity-scale OGS pairings. Our results provide quantitative performance bounds and practical design guidelines for near-term entanglement-based satellite QKD, enabling informed trade-offs between satellite payload complexity, ground infrastructure, and achievable secure key throughput.