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Physical Review A

Defending against a laser-seeding attack on continuous-variable quantum key distribution using an improved optical power limiter

Qingquan Peng, Binwu Gao, Dongyang Wang, Qin Liao, Zhiyue Zuo, Hai Zhong, Anqi Huang, Ying Guo

Published Nov 27, 2023• 17 citations
Publisher

Abstract

Laser-seeding attack enables an attacker to control the source output and eavesdrops on the key information, compromising the security of the continuous-variable (CV) quantum key distribution (QKD) system. In this paper, we suggest an improved optical power limiter (OPL) to defend against a laser-seeding attack on CV QKD systems. The proposed OPL utilizes a temperature monitor to detect Eve's attacks through temperature changes, providing an effective optical component for improving the security and reliability of the CV QKD system in practical environments, which is called an OPL-T scheme. In particular, we consider the security threats of a laser-seeding attack on two common CV QKD systems and prove their theoretical security degradation. Experiments are conducted to verify the effective OPL-T, and the results show that this defense scheme has an advantage in resisting the laser-seeding attack. Numerical simulations demonstrate the security analysis on CV QKD equipped with an OPL-T, which further confirms the effectiveness of our scheme. This work provides a practical solution for the security enhancements of continuous-variable quantum communication in practical applications.

DOI
10.1103/physreva.108.052616

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Laser-seeding attack enables an attacker to control the source output and eavesdrops on the key information, compromising the security of the continuous-variable (CV) quantum key distribution (QKD) system. In this paper, we suggest an improved optical power limiter (OPL) to defend against a laser-seeding attack on CV QKD systems. The proposed OPL utilizes a temperature monitor to detect Eve's attacks through temperature changes, providing an effective optical component for improving the security and reliability of the CV QKD system in practical environments, which is called an OPL-T scheme. In particular, we consider the security threats of a laser-seeding attack on two common CV QKD systems and prove their theoretical security degradation. Experiments are conducted to verify the effective OPL-T, and the results show that this defense scheme has an advantage in resisting the laser-seeding attack. Numerical simulations demonstrate the security analysis on CV QKD equipped with an OPL-T, which further confirms the effectiveness of our scheme. This work provides a practical solution for the security enhancements of continuous-variable quantum communication in practical applications.
Here, we investigate the security of the practical one-way CVQKD and CV-MDI-QKD systems under laser seeding attack. In particular, Eve can inject a suitable light into the laser diodes of the light source modules in the two kinds of practical CVQKD systems, which results in the increased intensity of the generated optical signal. The parameter estimation under laser seeding attack shows that the secret key rates of these two schemes may be overestimated, which indicates that this attack can open a security loophole for Eve to successfully obtain information about secret key in these practical CVQKD systems. To close this loophole, we propose a real-time monitoring scheme to precisely evaluate the secret key rates of these schemes. The analysis results indicate the implementation of the proposed monitoring scheme can effectively resist this potential attack.
Continuous-variable measurement-device-independent quantum key distribution (CV-MDI QKD) can defend all detection-side attacks effectively. Therefore, the source side is the final battlefield for performing quantum hacking attacks. This paper investigates the practical security of a CV-MDI QKD system under a light-injection attack. Here, we first describe two different light-injection attacks, i.e., the induced-photorefractive attack and the strong-power injection attack. Then, we consider three attack cases where Eve only attacks one of the parties or both parties of the CV-MDI QKD system. Based on the analysis of the parameter estimation, we find that the legitimate communication parties will overestimate the secret key rate of the system under the effect of a light-injection attack. This opens a security loophole for Eve to successfully obtain secret key information in a practical CV-MDI QKD system. In particular, compared to the laser-damage attack, the above attacks use a lower power of injected light and have a more serious effect on the security of the system. To eliminate the above effects, we can enhance the practical security of the system by doping the lithium niobate material with various impurities or by using protective devices, such as optical isolators, circulators, optical power limiters, and narrow-band filters. Apart from these, we can also use an intensity monitor or a photodetector to detect the light-injection attack.
Unauthorized light injection has always been a vital threat to the practical security of a quantum-key-distribution (QKD) system. An optical-power limiter (OPL) based on the thermo-optical defocusing effect has been proposed and implemented, limiting the injected hacking light. As a hardware countermeasure, the performance of the OPL under various light-injection attacks will be tested to clarify the security boundary before it is widely deployed. To investigate the security boundary of the OPL in quantum cryptography, we comprehensively test and analyze the behavior of the OPL under continuous-wave (cw) light-injection attacks and pulse-illumination attacks with pulse repetition rates of 0.50.50.5 Hz, 404040 MHz, and 111 GHz. The test results illuminate the security boundary of the OPL, which allows one to properly employ the OPL in use cases. The methodology of testing and analysis proposed here is applicable to other power-limitation components in a QKD system.
Due to possible imperfect implementation of laser sources and coherent detectors, continuous-variable quantum key distribution (CV-QKD) in optical networks is vulnerable to quantum attacks, which would significantly degrade the secret key rate (SKR) and compromise the security of the quantum keys. The attackers may steal the data encrypted with the compromised keys, leading to service failure and resource wastage. To tackle it, we propose a quantum attack mitigation resource allocation scheme (QAM-RA) for CV-QKD over optical networks. It corrects the biased channel parameters of the compromised quantum channels by conducting appropriate countermeasures, re-analyzes the SKR, and allocates additional quantum resources to compensate for the loss of SKR. A deep reinforcement learning (DRL) framework based on the Asynchronous Advantage Actor-Critic (A3C) algorithm is developed to determine QAM-RA solutions intelligently. Extensive simulations have been conducted to evaluate the performance of the DRL-assisted QAM-RA scheme in two test networks. Simulation results have confirmed the effectiveness of the proposed scheme in mitigating quantum attacks and reducing user request blocking probabilities.
Continuous variable quantum key distribution is a information system that uses quantum physics to share secret keys among legitimate participants, where a variable optical attenuator (VOA) plays a crucial role in managing the intensity of light transmitted between the participants. However, minor changes in light intensity can have an impact on its security. In this paper, we suggest an attack strategy called the laser damage attack targeting the VOA of the continuous variable (CV) measurement-device-independent (MDI) quantum key distribution (QKD) system. This attack can damage the VOA, leading to incorrect secret key rate calculations by legitimate participants and enabling an eavesdropper to steal partial secret key information. Numerical simulations show its potential impact on the practical security of the CV-MDI-QKD system.
Abstract In a practical continuous‐variable quantum key distribution (CVQKD) system, a new security loophole opened by the photorefractive effect of lithium niobate‐based (LN‐based) modulators is explored. Exploiting this loophole, a quantum hacking strategy called the induced‐photorefraction attack is proposed. This strategy utilizes the induced photorefraction on the LN‐based modulators to conceal a classical intercept‐resend attack. Specifically, the induced photorefraction biases the response curve of the LN‐based modulator, which affects the intensity of the modulated signal. Based on the investigation of channel parameter estimation and the analysis of the secret key rate of the practical CVQKD system, the simulation results show that the communication parties overestimate the secret key rate, which reveals that Eve can actively open a security loophole via the induced‐photorefraction attack to obtain secret key information. To defend against this attack, a random monitoring scheme for modulation variance is proposed to detect the attack, along with an improved optical power limiter to mitigate the irradiation beam. Additionally, a Sagnac‐based IM is suggested to stabilize the practical CVQKD system. Furthermore, the impact of this attack is analyzed on continuous‐variable measurement‐device‐independent QKD systems ((CV‐MDI‐QKD) and on local‐local‐oscillator (LLO) systems and propose countermeasures for each. Finally, the passive‐state‐preparation CVQKD protocol is proposed to fundamentally close the security loopholes originating from the modulators.