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Physical Review A

Security of practical quantum key distribution with weak-randomness basis selection

Hong-Wei Li, Zheng-Mao Xu, Zhen−Qiang Yin, Qing-yu Cai

Published Aug 10, 2020• 10 citations
Publisher

Abstract

The security of the perfect quantum key distribution protocol can be guaranteed by applying the fundamental laws of quantum mechanics, but the practical quantum key distribution system may be attacked by utilizing imperfect state preparation and measurement devices. In this work, we analyze the security of the practical quantum key distribution system with weak-randomness basis selection, where the basis selection may be partly controlled by the eavesdropper due to the imperfect quantum devices. We propose the parameter $\ensuremath{\epsilon}$ to quantify the deviation value between the practical basis selection probability and the perfect basis selection probability, and the secret key rate of the practical quantum key distribution system is obtained under different $\ensuremath{\epsilon}$ values. By applying the practical experimental parameters, the analysis result demonstrates that the maximal transmission distance will be reduced from 142 to 139 km if $\ensuremath{\epsilon}\ensuremath{\le}0.1$, but no secret key can be generated in the case of $\ensuremath{\epsilon}\ensuremath{\ge}0.34$.

DOI
10.1103/physreva.102.022605

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Quantum secure direct communication (QSDC) enables the user to directly transmit secret messages through quantum channels without pre-shared keys. However, the imperfection of devices brings a security loophole to QSDC. The weak-random basis selection attack is a strong attack mode, where the eavesdropper can manipulate users’ basis selection probability distribution, and thus reduce the error rate caused by her eavesdropping. In this paper, we propose the first, to the best of our knowledge, general quantitative security analysis model for the practical QSDC system under the weak-randomness basis selection attack. We characterize the imperfect basis selection by the parameter ε . The simulation results show that when ε increases from 0 to 0.1, the maximal secure communication distance reduces from 34 km to 24 km. When ε > 0.32, the maximal secure communication distance reduces to 0. Our work indicates the importance of inspecting the QSDC system’s security loopholes from the weak-randomness basis selection attack and contributes to enhancing its practical security under real experimental conditions.
Quantum key distribution protocol requires true random numbers to prepare and measure quantum states, but the randomness may be weakened by applying the imperfect input random numbers or imperfect quantum devices. In this work, we propose the randomness attack model in the practical quantum key distribution system, and we analyze the final secret key rate under the randomness attack. The security analysis result demonstrates that the imperfect randomness can be amplified by considering the signal loss, thus the quantum key distribution system may be attacked even if the randomness has very small part of imperfection. Combining the practical experimental parameters with the small nonrandom probability parameters 0.10.1%0.1 and 11%1, we prove that the maximal transmission distance will be sharply reduced from 140 km to 60 and 12 km, respectively.
The ideal quantum key distribution (QKD) protocol requires perfect random numbers for bit encoding and basis selecting. Perfect randomness is of great significance to the practical QKD system. However, due to the imperfection of practical quantum devices, an eavesdropper (Eve) may acquire some random numbers, thus affecting the security of practical systems. In this paper, we analyze the effects of the weak randomness in the measurement-device-independent QKD (MDI-QKD) with finite resources. We analytically derive concise formulas for estimating the lower bound of the single-photon yield and the upper bound of the phase error rate in the case of the weak randomness. The simulation demonstrates that the final secret key rate of MDI-QKD with finite resources is sensitive to state preparation, even with a small proportion of weak randomness, the secure key rate has a noticeable fluctuation. Therefore, the weak randomness of the state preparation may bring additional security risks. In order to ensure the practical security of the QKD system, we are supposed to strengthen the protection of state preparation devices.
Quantum key distribution (QKD) offers an approach for secure communication over quantum channels, based on the principles of quantum mechanics. However, the inevitable imperfections in QKD systems can introduce critical vulnerabilities, posing significant challenges to the deployment of QKD in terms of both practical security and performance. In this work, we present a comprehensive security analysis of QKD in the practical scenarios involving imperfections in modulation spaces. Specifically, our analysis focuses on the imperfections related to encoding, intensity modulation, and their characterization. We provide a unified framework based on the operator dominance method to overcome these issues and achieve a tight estimation of the secret key rate (SKR). The simulation results show that the SKR in practical scenarios, with parameters characterized from commercial QKD systems, closely matches the SKR under ideal conditions. In the finite case, the maximum transmission distance can reach up to 250 km with total pulse number N=1012N=10^{12}N=1012 and the SKR closely approaches the asymptotic limit up to 250 km with N=1014N=10^{14}N=1014. This validates the robustness of our method against imperfections in state preparation and characterization. Furthermore, the feasibility and robustness of method in measurement-device-independent (MDI) QKD have also been demonstrated. Our analysis not only promotes advancements in enhancing practical security and performance but also highlights the feasibility of deploying QKD for actual applications.
ABSTRACT Quantum key distribution (QKD) enables long‐distance secret keys transmission with information‐theoretic security. However, weak‐randomness obviously limits the security of practical QKD systems. This may leak the key information by considering the imperfect devices. In this work, we proposed a practical security analysis model that simultaneously considers the bit‐weak‐randomness and the basis‐weak‐randomness parameters, which we refer to as the weak‐randomness model. First, we establish a novel bit‐weak‐randomness model based on the virtual mutually unbiased bases method. Subsequently, under the framework of information‐theoretic security proof, we proposed a comprehensive weak‐randomness model by incorporating the basis‐weak‐randomness model. Then, we characterize the relationship between typical quantum attacking strategies and weak‐randomness parameters. Based on our proposed weak‐randomness model, we perform a security analysis against these attacks. Finally, we perform numerical simulations of the weak‐randomness model based on the advantage distillation method, considering both single photon sources and weak coherent sources. Our results can provide a model capable of characterizing security parameters to simultaneously account for the impacts of both imperfect devices and quantum hacking. This enables a unified standard for evaluating the security levels of practical QKD systems and offers a theoretical foundation for QKD system testing and assessment.
Abstract Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) is considered one of the most promising protocols, as it can generate secret keys without reference frame alignment and defeat all attacks on the measurement side. A fundamental assumption for the security of RFI-MDI-QKD is that both senders can prepare their quantum states with perfect randomness. However, in practical implementations, this assumption may be violated, primarily due to limitations in the imperfect random numbers and quantum device imperfections. In this work, we investigate the effect of weak randomness on the state preparation in practical decoy-state RFI-MDI-QKD, demonstrating that even a small proportion of weak randomness severely compromises the security of RFI-MDI-QKD. Furthermore, we apply the advantage distillation (AD) method to counteract the performance degradation caused by weak randomness in RFI-MDI-QKD. Simulation results demonstrate that AD can significantly improve both the secret key rate and the maximum transmission distance for practical decoy-state RFI-MDI-QKD under weak randomness conditions. These results represent a critical advance toward the development of secure, long-distance, multi-node quantum communication networks.