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arXiv:1907.09661 · Applied Physics Letters

Asymmetric delay attack on an entanglement-based bidirectional clock synchronization protocol

Jianwei Lee, Lijiong Shen, Alessandro Cerè, James E. Troupe, Antia Lamas-Linares, Christian Kurtsiefer

Published Sep 30, 2019• 23 citations
arXivHTMLPDF

Abstract

We demonstrate an attack on a clock synchronization protocol that attempts to detect tampering of the synchronization channel using polarization-entangled photon pairs. The protocol relies on a symmetrical channel, where propagation delays do not depend on the propagation direction, for correctly deducing the offset between clocks—a condition that could be manipulated using optical circulators, which rely on static magnetic fields to break the reciprocity of propagating electromagnetic fields. Despite the polarization transformation induced within a set of circulators, our attack creates an error in time synchronization while evading detection.

DOI
10.1063/1.5121489

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We demonstrate an attack on a clock synchronization protocol that attempts to detect tampering of the synchronization channel using polarization-entangled photon pairs. The protocol relies on a symmetrical channel, where propagation delays do not depend on the propagation direction, for correctly deducing the offset between clocks—a condition that could be manipulated using optical circulators, which rely on static magnetic fields to break the reciprocity of propagating electromagnetic fields. Despite the polarization transformation induced within a set of circulators, our attack creates an error in time synchronization while evading detection.
Quantum clock synchronization achieves picosecond-level precision by compensating for channel delays based on reciprocity, which is intrinsically vulnerable to asymmetric delay attacks. In this Letter, we propose a slow and persistent asymmetric channel delay strategy that superimposes delays onto the channel, thereby producing a subtle, time-varying clock-offset error that can remain concealed within intrinsic timing fluctuations. In a 50 km round-trip quantum clock synchronization experiment, we demonstrate that the proposed attack successfully evades both threshold alarms and sliding window anomaly detection under varying delay intensities and modulation periods. This work uncovers key vulnerabilities in synchronization protocols under customizable attacks and provides a foundation for developing secure and resilient quantum clock synchronization systems.
Quantum technologies, leveraging the principles of quantum mechanics, are rapidly advancing and offer transformative benefits in secure communication, computation, and sensing. While quantum communication systems provide unprecedented data security, the implementation security of quantum communication protocols still needs investigation. In this regard, the security of Quantum Key Distribution (QKD) is well studied, while there is limited research on quantum communication protocols beyond QKD. In this work, we study time-delay attacks on generic entanglement distribution quantum communication networks. These networks rely heavily on precise time synchronization between detection stations and a preset coincidence window for accurate identification of distributed entangled pairs. An eavesdropper can exploit this reliance on correct photon arrival timing by introducing a time delay, causing genuine entangled pairs to fall outside the coincidence window. This leads to missed detections, potential false pair identifications, or denial-of-service (DoS) conditions. To mitigate this vulnerability, we propose photon arrival-time monitoring and threshold-based time-delay detection, enabling adaptive coincidence window adjustment. By dynamically centering the coincidence window on the mean photon arrival time, valid entangled pairs can still be accurately identified, even in the presence of a time-delay attack. We simulate the quantum measurement process under different time-delay insertion values in the quantum channel, assuming perfectly synchronized remote detection stations. Our results show the impact of time-delay attacks on entangled pair detection rates, detection accuracy, and fidelity of the reconstructed Bell state. The effectiveness of our proposed countermeasure is demonstrated in simulation, showing that it maintains both the photon count rate and the fidelity at high levels, even when an eavesdropper introduces time delays in the quantum channel.
Quantum technologies, leveraging the principles of quantum mechanics, are rapidly advancing and offer transformative benefits in secure communication, computation, and sensing. While quantum communication systems provide unprecedented data security, the implementation security of quantum communication protocols still needs investigation. In this regard, the security of Quantum Key Distribution (QKD) is well studied, while there is limited research on quantum communication protocols beyond QKD. In this work, we study time-delay attacks on generic entanglement distribution quantum communication networks. These networks rely heavily on precise time synchronization between detection stations and a preset coincidence window for accurate identification of distributed entangled pairs. An eavesdropper can exploit this reliance on correct photon arrival timing by introducing a time delay, causing genuine entangled pairs to fall outside the coincidence window. This leads to missed detections, potential false pair identifications, or denial-of-service (DoS) conditions. To mitigate this vulnerability, we propose photon arrival-time monitoring and threshold-based time-delay detection, enabling adaptive coincidence window adjustment. By dynamically centering the coincidence window on the mean photon arrival time, valid entangled pairs can still be accurately identified, even in the presence of a time-delay attack. We simulate the quantum measurement process under different time-delay insertion values in the quantum channel, assuming perfectly synchronized remote detection stations. Our results show the impact of time-delay attacks on entangled pair detection rates, detection accuracy, and fidelity of the reconstructed Bell state. The effectiveness of our proposed countermeasure is demonstrated in simulation, showing that it maintains both the photon count rate and the fidelity at high levels, even when an eavesdropper introduces time delays in the quantum channel.