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.
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.
In a practical continuous-variable quantum key distribution (CVQKD) system, the optical attenuator can adjust the Gaussian-modulated coherent states and the local oscillator signal to an optimal value for guaranteeing the security of the system and optimizing the performance of the system. However, the performance of the optical attenuator may deteriorate due to the intentional and unintentional damage of the device. In this paper, we investigate the practical security of a CVQKD system with reduced optical attenuation. We find that the secret key rate of the system may be overestimated based on the investigation of parameter estimation under the effects of reduced optical attenuation. This opens a security loophole for Eve to successfully perform an intercept-resend attack in a practical CVQKD system. To close this loophole, we add an optical fuse at Alice's output port and design a scheme to monitor the level of optical attenuation in real time, which can make the secret key rate of the system evaluated precisely. The analysis shows that these countermeasures can effectively resist this potential attack.
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.
Abstract Source monitoring is a matter of vital importance for continuous-variable quantum key distribution (QKD), since it is the first barrier to ensure the practical security. In a practical scenario, the difficulty arises with the existence of the laser intensity fluctuation, which not only contributes to the source noise but also causes the deviation of source monitoring result. We first illustrate the effect of the relative intensity noise (RIN) on the ultimate security by explicitly showing the parameter estimation procedure, and find that the secret key rate is overestimated in this situation. To defend the continuous-variable QKD system against potential attacks utilizing this impairment to conceal itself, a source monitoring scheme is devised by adopting the seminal one-time shot-noise unit calibration approach into the monitor module. It is shown that by using the practical source monitoring scheme the impact of the RIN can be modeled and monitored in real time to circumvent an overestimated secret key rate. This scheme also lowers the system complexity thus is suitable for widespread application.
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.
In a practical continuous-variable quantum key distribution (CVQKD) system, the optical amplifier can be used to improve the performance of the system by compensating for the imperfections of the detectors. However, the eavesdropper Eve can actively utilize a reverse external magnetic field to deteriorate the performance of the optical amplifier, which may affect the practical security of the system. In this paper, we investigate the practical security of a CVQKD system with an optical amplifier under the effect of the reverse external magnetic field. Based on the investigation of the parameter estimation under the above influence, we find that the evaluation of the secret key rate may be overestimated, which will open a security loophole for Eve to successfully launch an intercept-resend attack in the practical CVQKD system with an optical amplifier. In order to close this security loophole, we can monitor the reverse external magnetic field or change the type of the optical isolator to make the secret key rate of the system evaluated exactly.