Realistic vulnerabilities of decoy-state quantum key distribution

• URL: http://arxiv.org/abs/2507.15446v1
• Date: Mon, 21 Jul 2025 09:58:01 GMT
• Title: Realistic vulnerabilities of decoy-state quantum key distribution
• Authors: I. S. Sushchev, K. E. Bugai, S. N. Molotkov, D. S. Bulavkin, A. S. Sidelnikova, D. M. Melkonian, V. M. Vakhrusheva, R. Yu. Lokhmatov, D. A. Dvoretskiy,
• Abstract summary: decoy-state quantum key distribution (QKD) is designed to protect against photon-number-splitting and beam-splitting attacks.<n>We analyze realistic vulnerabilities of QKD arising from the combination of laser damage attack (LDA) and unambiguous state discrimination (USD)
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We analyze realistic vulnerabilities of decoy-state quantum key distribution (QKD) arising from the combination of laser damage attack (LDA) and unambiguous state discrimination (USD). While decoy-state QKD is designed to protect against photon-number-splitting and beam-splitting attacks by accurately estimating the single-photon fraction, it relies on stable attenuation to prepare pulses with fixed mean-photon numbers. An eavesdropper (Eve) can exploit LDA to irreversibly alter the optical components on Alice's side, effectively increasing the mean-photon numbers beyond the decoy-state security regime. We show that once the alteration exceeds a critical threshold - on the order of 10--20 dB - Eve can implement an efficient USD-based intercept-resend strategy using current off-the-shelf technology, thus obtaining the entire secret key. Numerical simulations confirm that for sufficiently elevated mean-photon numbers, Eve's conclusive measurement outcomes skew the decoy-state statistics, yet remain undetected by standard security checks. We further demonstrate how a modified USD setup employing an additional beam splitter can reduce the required threshold, facilitating Eve's attack. Our findings emphasize the need for robust safeguards against high-power laser damage in QKD systems, including careful hardware selection, rigorous testing under high-power illumination, and real-time monitoring to ensure the integrity of the decoy-state protocol.

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