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Optica

Robust countermeasure against detector control attack in a practical quantum key distribution system: comment

Zhihao Wu, Anqi Huang, Xiaogang Qiang, Jiangfang Ding, Ping Xu, Xiang Fu, Junjie Wu

Published Jun 30, 2020• 6 citations
Publisher

Abstract

The physical imperfections of quantum key distribution systems compromise their information-theoretic security. By exploiting the imperfections on the detection unit, an eavesdropper can launch various detector-control attacks to steal the secret key. Recently, in Optica 6 , 1178 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.001178 entitled “Robust countermeasure against detector control attack in a practical quantum key distribution system,” Qian et al. proposed a countermeasure using variable attenuators in the detection unit that was claimed to be effective against detector-control attacks with or without blinding light. We comment on this paper, disputing this countermeasure by showing that their assumptions for proving this effectiveness are unrealistic.

DOI
10.1364/optica.391325

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In real-life implementations of quantum key distribution (QKD), the physical systems with unwanted imperfections would be exploited by an eavesdropper. Based on imperfections in the detectors, detector control attacks have been successfully launched on several QKD systems, and attracted widespread concerns. Here, we propose a robust countermeasure against these attacks just by introducing a variable attenuator in front of the detector. This countermeasure is not only effective against the attacks with blinding light, but also robust against the attacks without blinding light which are more concealed and threatening. Different from previous technical improvements, the single photon detector in our countermeasure model is treated as a blackbox, and the eavesdropper can be detected by statistics of the detection and error rates of the QKD system. Besides theoretical proof, the countermeasure is also supported by an experimental demonstration. Our countermeasure is general in sense that it is independent of the technical details of the detector, and can be easily applied to the existing QKD systems.

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Robust countermeasure against detector control attack in a practical quantum key distribution system: reply

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We reply to the comment on our robust countermeasure against the detector control attack [ Optica 6 , 1178 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.001178 ] and explain that the concerns arising from an over-interpretation of our countermeasure are one-sided and untenable.

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The physical imperfections of quantum key distribution systems compromise their information-theoretic security. By exploiting the imperfections on the detection unit, an eavesdropper can launch various detector-control attacks to steal the secret key. Recently, in Optica 6 , 1178 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.001178 entitled “Robust countermeasure against detector control attack in a practical quantum key distribution system,” Qian et al. proposed a countermeasure using variable attenuators in the detection unit that was claimed to be effective against detector-control attacks with or without blinding light. We comment on this paper, disputing this countermeasure by showing that their assumptions for proving this effectiveness are unrealistic.
In real-life implementations of quantum key distribution (QKD), the physical systems with unwanted imperfections would be exploited by an eavesdropper. Based on imperfections in the detectors, detector control attacks have been successfully launched on several QKD systems, and attracted widespread concerns. Here, we propose a robust countermeasure against these attacks just by introducing a variable attenuator in front of the detector. This countermeasure is not only effective against the attacks with blinding light, but also robust against the attacks without blinding light which are more concealed and threatening. Different from previous technical improvements, the single photon detector in our countermeasure model is treated as a blackbox, and the eavesdropper can be detected by statistics of the detection and error rates of the QKD system. Besides theoretical proof, the countermeasure is also supported by an experimental demonstration. Our countermeasure is general in sense that it is independent of the technical details of the detector, and can be easily applied to the existing QKD systems.
Abstract Quantum key distribution (QKD), rooted in quantum mechanics, offers information-theoretic security. However, practical systems open security threats due to imperfections, notably bright-light blinding attacks targeting single-photon detectors. Here, we propose a concise, robust defense strategy for protecting single-photon detectors in QKD systems against blinding attacks. Our strategy uses a dual approach: detecting the bias current of the avalanche photodiode (APD) to defend against continuous-wave blinding attacks, and monitoring the avalanche amplitude to protect against pulsed blinding attacks. By integrating these two branches, the proposed solution effectively identifies and mitigates a wide range of bright light injection attempts, significantly enhancing the resilience of QKD systems against various bright-light blinding attacks. This method fortifies the safeguards of quantum communications and offers a crucial contribution to the field of quantum information security.
In a practical quantum key distribution(QKD) system, imperfect equipment, especially the single-photon detector,can be eavesdropped on by a blinding attack. However, the original blinding attack may be discovered by directly detecting the current. In this paper, we propose a probabilistic blinding attack model, where Eve probabilistically applies a blinding attack without being caught by using only an existing intuitive countermeasure. More precisely, our countermeasure solves the problem of how to define the bound in the limitation of precision of current detection, and then we prove security of the practical system by considering the current parameter. Meanwhile, we discuss the bound of the quantum bit error rate(QBER) introduced by Eve, by which Eve can acquire information without the countermeasure.
In the recent decade, it has been discovered that QKD systems are extremely vulnerable to side-channel attacks. In particular, by exploiting the internal working knowledge of practical detectors, it is possible to bring them to an operating region whereby only certain target detectors are sensitive to detections. Crucially, the adversary can use this loophole to learn everything about the secret key without introducing any error to the quantum channel. In this paper, as a step toward overcoming detector blinding attacks, we focus on an experimentally convenient countermeasure, where the efficiency of the detectors is randomly varied.
A homodyne detector, which is also a common element in current telecommunication, is a core component of continuous-variable quantum key distribution (CV-QKD) since it is considered the simplest setup for the distinguishing of coherent states with minimum error. However, the theoretical security of CV-QKD is based on the assumption that the responses of the homodyne detector are always linear with respect to the input, which is impossible in practice. In the real world, a homodyne detector has a finite linear domain, so the linearity assumption is broken when the input is too large. Regarding this security vulnerability, the eavesdropper Eve can perform the so-called homodyne detector-blinding attack by saturating the homodyne detector and then stealing key information without being detected by the legitimate users. In this paper, we propose a countermeasure for the homodyne detector-blinding attack by using an adjustable optical attenuator with a feedback structure. Specifically, we estimate the suitable attenuation value in the data processing of CV-QKD and feed it back to the adjustable optical attenuator before the detector in real time. Numerical simulation shows that the proposed countermeasure can effectively defend against homodyne detector-blinding attacks and ensure the security of the Gaussian-modulated coherent state protocol with finite-size effect.