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Optics Letters

Weak randomness impacts the security of reference-frame-independent quantum key distribution

Chun-Mei Zhang, Wenbo Wang, Hong-Wei Li, Qin Wang

Published Feb 25, 2019• 21 citations
Publisher

Abstract

Perfect randomness is of great significance in various quantum key distribution (QKD) protocols. In this Letter, we investigate the effect of weak randomness on the state preparation in reference-frame-independent QKD (RFI-QKD), which may be implemented with imperfect random numbers or quantum-state encoding devices. In the scenario of weak randomness, the maximal amount of information the eavesdropper can acquire should be carefully evaluated. With practical experimental parameters, we demonstrate that even a small proportion of weak randomness will impact the security of RFI-QKD seriously. Furthermore, we briefly study the side effect of weak randomness on RFI measurement-device-independent QKD (RFI-MDI-QKD), and simulation results show that weak randomness damages the performance of RFI-MDI-QKD more critically than that of RFI-QKD.

DOI
10.1364/ol.44.001226

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Perfect randomness is of great significance in various quantum key distribution (QKD) protocols. In this Letter, we investigate the effect of weak randomness on the state preparation in reference-frame-independent QKD (RFI-QKD), which may be implemented with imperfect random numbers or quantum-state encoding devices. In the scenario of weak randomness, the maximal amount of information the eavesdropper can acquire should be carefully evaluated. With practical experimental parameters, we demonstrate that even a small proportion of weak randomness will impact the security of RFI-QKD seriously. Furthermore, we briefly study the side effect of weak randomness on RFI measurement-device-independent QKD (RFI-MDI-QKD), and simulation results show that weak randomness damages the performance of RFI-MDI-QKD more critically than that of RFI-QKD.
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.
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.
Abstract Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) can remove all potential detector side-channel attacks and the requirement of real-time alignment of reference frames. However, all previous RFI-MDI-QKD implementations assume the perfect state preparation in sources, which is impractical and may lead to security loopholes. Here, we propose an RFI-MDI-QKD protocol which is robust against state preparation flaws. Comparing to the conventional six-state RFI-MDI-QKD, our scheme can be realized with only four flawed states, which improves the practical security of RFI-MDI-QKD and simplifies the experimental implementation. In addition, simulation results demonstrate that source flaws in Z basis have adverse effect on the performance of RFI-MDI-QKD while the source flaws in X and Y bases have almost no effect. We hope that this work could provide a valuable reference for practical implementations of RFI-MDI-QKD.
Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) is immune to both detector side channel attacks and slow drifts of reference frames, and thus possesses a high level of security. In the traditional protocol of RFI-MDI-QKD, each legitimate user, Alice or Bob, has to prepare six encoding states in three orthogonal bases (X,YX, YX,Y, and ZZZ), which are sent to the untrusted third party, Charlie. Then all the successful counting events are utilized for parameter estimations, which suffer from a severe finite-size effect. In this paper, we propose a scheme on RFI-MDI-QKD with fewer states and demonstrate that it can be secured and made useful by utilizing semidefinite programming. Numerical simulation results reveal the equivalence between those groups of different monitoring states from Alice and Bob. In addition, when considering practical experimental conditions and taking finite-size effects into account, our proposal can achieve a better performance than the traditional six-state RFI-MDI scheme, which provides a resource-saving and simpler state-preparation approach for practical implementations without sacrificing key rates.
Reference-frame-independent measurement-deviceindependent quantum key distribution (RFI-MDI-QKD) can eschew the alignment of reference frames in practical systems and defeat all potential detector side channel attacks. Here, we propose the decoy-state RFI-MDI-QKD protocol with biased bases. In this protocol, two legitimate parties Alice and Bob prepare signal states in Z, X, and Y bases and decoy states in X and Y bases, which avoids the futility in Z basis for decoy states and simplifies the operation of existing systems. Considering the security against coherent attacks with statistical fluctuations, we investigate the performance of the decoy-state RFI-MDI-QKD protocol with biased bases in the environment of unknown and slowly drifting reference frames and make comparisons with the original decoy-state RFI-MDI-QKD protocol under the same conditions. Simulation results show that the proposed protocol can increase the achievable secret key rate and transmission distance obviously compared with the original protocol, which is very promising in real-life QKD systems.
Abstract Reference-frame-independent measurement-device-independent QKD (RFI-MDI-QKD), immune to both the slow unknown drift of reference frames and detector side channel attacks, can generate information-theoretic secure keys. Despite its natural resistance to the slow drift of reference frames, the performance of practical RFI-MDI-QKD systems descends with the increasing drift of reference frames. In this paper, we demonstrate the worst relative rotation of reference frames for practical RFI-MDI-QKD systems, and investigate their performance against the worst-case scenario, both of which are unclear to date. Simulation results show that, practical RFI-MDI-QKD systems can achieve quite good performance even against the worst-case scenario, which clearly demonstrates that it is possible to implement practical MDI-QKD systems with freely drifting reference frames.