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中国物理B：英文版

Countermeasure against probabilistic blinding attack in practical quantum key distribution systems

钱泳君, 李宏伟, 何德勇, 银振强, 张春梅, 陈巍, 王双, Han Fu

Published Jan 1, 2015• 0 citations
OpenAlex

Abstract

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.

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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 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.
Abstract In practical quantum key distribution (QKD) systems, a single photon-detector (SPD) is one of the most vulnerable components. Faint after-gate attack is a universal attack against the detector. However, the original faint after-gate attack can be discovered by monitoring the photocurrent. This paper presents a probabilistic generalization of the attack, which we refer to as probabilistic faint after-gate attack, by introducing probability control modules. Previous countermeasures for photocurrent monitoring may fail in detecting the eavesdropper under some specific probabilities. To mitigate this threat, we provide a method to determine the detectable boundary in the limitation of precision of photocurrent monitoring, and investigate the security of QKD systems under such boundaries using the weak randomness model.
Quantum technologies are driving more and more interest both in academia and industry thanks to their promising performances in terms of security. In reality, practical systems suffer from imperfections compared to theoretical models which could be exploited by an eavesdropper if no protection is implemented. Bridging the gap between theory and practice is therefore one of the main challenges of this field today. During this thesis, I worked on different aspects of the practical security of quantum technologies. This ranges from the modeling of the entropy source of a quantum random number generator (QNRG) to the study of the vulnerabilities of quantum key distribution (QKD) implementations against hacking. In the first part, I focus on the modeling of a commercial QRNG chip from ID Quantique. More specifically, I present the model we developed for the quantum entropy source of the device. We estimate that this fully integrated device can provide a quantum min-entropy of 0.98 per bit. Importantly, this near-unity quantum entropy is achievable without post-processing reducing the power consumption of the chip, making it suitable for mobile devices. Moreover, we show that this high-quality entropy is robust against imperfections. On the side of QKD security, I begin by studying the behavior of negative-feedback avalanche diode (NFAD) detectors under a blinding attack. After showing their vulnerability to this attack and testing the resilience of a countermeasure based on the monitoring of the mean photocurrent, I present an improved countermeasure. This allows Bob to detect more advanced blinding strategies where Eve modulates her blinding power to reduce her impact on the mean photocurrent. In the last part of this thesis, I present a novel method to prevent the blinding attack based on statistical measurements with a multi-pixel detector. Through this approach, we can estimate an upper bound on Eve's information on the key exchanged. An analysis of the finite-key effects estimates that this countermeasure can be effective for distances up to 250km. The applicability of this countermeasure with current technology is shown with a 2-pixel superconducting detector.
In the last decade, efforts have been made to reconcile theoretical security with realistic imperfect implementations of quantum key distribution (QKD). Implementable countermeasures are proposed to patch the discovered loopholes. However, certain countermeasures are not as robust as would be expected. In this paper, we present a concrete example of ID Quantique's random-detector-efficiency countermeasure against detector blinding attacks. As a third-party tester, we have found that the first industrial implementation of this countermeasure is effective against the original blinding attack, but not immune to a modified blinding attack. Then, we implement and test a later full version of this countermeasure containing a security proof [C. C. W. Lim et al., IEEE Journal of Selected Topics in Quantum Electronics, 21, 6601305 (2015)]. We find that it is still vulnerable against the modified blinding attack, because an assumption about hardware characteristics on which the proof relies fails in practice.
Quantum key distribution (QKD) has been proved to be information-theoretically secure in theory. Unfortunately, the imperfect devices in practice compromise its security. Thus, to improve the security property of practical QKD systems, a commonly used method is to patch the loopholes in the existing QKD systems. However, in this work, we show an adversary's capability of exploiting the imperfection of the patch itself to bypass the patch. Specifically, we experimentally demonstrate that, in the detector under test, the patch of photocurrent monitor against the detector blinding attack can be defeated by the pulse illumination attack proposed in this paper. We also analyze the secret key rate under the pulse illumination attack, which theoretically confirmed that Eve can conduct the attack to learn the secret key. This work indicates the importance of inspecting the security loopholes in a detection unit to further understand their impacts on a QKD system. The method of pulse illumination attack can be a general testing item in the security evaluation standard of QKD.