The huge discrepancies between actual devices and theoretical assumptions severely threaten the security of quantum key distribution. Recently, a general new framework called the reference technique has attracted wide attention in defending against the imperfect sources of quantum key distribution. Here, the state preparation flaws, the side channels of mode dependencies, the Trojan horse attacks, and the pulse classical correlations are studied by using the reference technique on the phase-matching protocol. Our simulation results highlight the importance of the actual secure parameters choice for transmitters, which is necessary to achieve secure communication. Increasing the single actual secure parameter will reduce the secure key rate. However, as long as the parameters are set properly, the secure key rate is still high. Considering the influences of multiple actual secure parameters will significantly reduce the secure key rate. These actual secure parameters must be considered when scientists calibrate transmitters. This work is an important step towards the practical and secure implementation of phase-matching protocol. In the future, it is essential to study the main parameters, find out their maximum and general values, classify the multiple parameters as the same parameter, and give countermeasures.
The huge discrepancies between actual devices and theoretical assumptions severely threaten the security of quantum key distribution. Recently, a general new framework called the reference technique has attracted wide attention in defending against the imperfect sources of quantum key distribution. Here, the state preparation flaws, the side channels of mode dependencies, the Trojan horse attacks, and the pulse classical correlations are studied by using the reference technique on the phase-matching protocol. Our simulation results highlight the importance of the actual secure parameters choice for transmitters, which is necessary to achieve secure communication. Increasing the single actual secure parameter will reduce the secure key rate. However, as long as the parameters are set properly, the secure key rate is still high. Considering the influences of multiple actual secure parameters will significantly reduce the secure key rate. These actual secure parameters must be considered when scientists calibrate transmitters. This work is an important step towards the practical and secure implementation of phase-matching protocol. In the future, it is essential to study the main parameters, find out their maximum and general values, classify the multiple parameters as the same parameter, and give countermeasures.
The security of quantum key distribution (QKD) is severely threatened by discrepancies between realistic devices and theoretical assumptions. Recently, a significant framework called the reference technique was proposed to provide security against arbitrary source flaws under current technology such as state preparation flaws, side channels caused by mode dependencies, the Trojan horse attacks and pulse correlations. Here, we adopt the reference technique to prove security of an efficient four-phase measurement-device-independent QKD using laser pulses against potential source imperfections. We present a characterization of source flaws and connect them to experiments, together with a finite-key analysis against coherent attacks. In addition, we demonstrate the feasibility of our protocol through a proof-of-principle experimental implementation and achieve a secure key rate of 253 bps with a 20 dB channel loss. Compared with previous QKD protocols with imperfect devices, our study considerably improves both the secure key rate and the transmission distance, and shows application potential in the practical deployment of secure QKD with device imperfections.
Abstract In theory, quantum key distribution (QKD) allows secure communications between two parties based on physical laws. However, most of the security proofs of QKD today make unrealistic assumptions and neglect many relevant device imperfections. As a result, they cannot guarantee the security of the practical implementations. Recently, the loss-tolerant protocol (K. Tamaki et al., Phys. Rev. A, 90, 052314, 2014) was proposed to make QKD robust against state preparation flaws. This protocol relies on the emission of qubit systems, which, unfortunately, is difficult to achieve in practice. In this work, we remove such qubit assumption and generalise the loss-tolerant protocol to accommodate multiple optical modes in the emitted signals. These multiple optical modes could arise, e.g., from Trojan horse attacks and/or device imperfections. Our security proof determines some dominant device parameter regimes needed for achieving secure communication and, therefore, it can serve as a guideline to characterise QKD transmitters. Furthermore, we compare our approach with that of H.-K. Lo et al. (Quantum Inf. Comput., 7, 431–458, 2007) and identify which method provides the highest secret key generation rate as a function of the device imperfections. Our work constitutes an important step towards the best practical and secure implementation for QKD.
In theory, quantum key distribution (QKD) offers information-theoretic security. In practice, however, it does not due to the discrepancies between the assumptions used in the security proofs and the behavior of the real apparatuses. Recent years have witnessed a tremendous effort to fill the gap, but the treatment of correlations among pulses has remained a major elusive problem. Here, we close this gap by introducing a simple yet general method to prove the security of QKD with arbitrarily long-range pulse correlations. Our method is compatible with those security proofs that accommodate all the other typical device imperfections, thus paving the way toward achieving implementation security in QKD with arbitrary flawed devices. Moreover, we introduce a new framework for security proofs, which we call the reference technique. This framework includes existing security proofs as special cases, and it can be widely applied to a number of QKD protocols.
Quantum key distribution (QKD) enables the establishment of shared keys between two distant users, Alice and Bob, based on the fundamental principles of quantum mechanics, and it has proven to possess information-theoretic security. In most of QKD systems, Alice and Bob require a shared reference frame, and real-time calibration of the reference frame increases system costs and reduces its performance. Fortunately, the reference-frame-independent QKD protocol has been proposed, overcoming reference-frame drift issues and receiving widespread attention. However, in practical QKD systems, the non-ideal characteristics of realistic devices introduce certain inconsistency between the theory and the practice. In real-world quantum key distribution systems, device imperfections can lead to security vulnerabilities, thereby reducing system security. For example, imperfections in the encoding apparatus at the source end may result in errors in the quantum states. The inherent defects in the detection part may cause after-pulse effects and dead-time effects, thus reducing the key rate. Therefore, in this work, we propose a practical state-preparation error tolerant reference-frame-independent quantum key distribution protocol by taking imperfections in both the source and the detectors into account. Moreover, a three-intensity decoy-state scheme for modeling analysis and numerical simulations is employed. In this protocol, we reduce the influence of state-preparation errors on the key rate by utilizing virtual state methods to precisely estimate the phase-error rate. Furthermore, by characterizing the effects of after-pulses and dead-time on the key rate, our protocol exhibits higher robustness and can effectively address issues related to detector imperfections. This approach can also be extended to other quantum key distribution protocols with higher security levels, such as measurement-device-independent quantum key distribution protocol and twin-field quantum key distribution, further mitigating the influence of device imperfections on practical implementation of QKD system. Therefore, our present work provide important reference value for putting the quantum key distributions into practical application.
Decoy-state quantum key distribution (QKD) is the most widely adopted approach for overcoming the limitations of imperfect single-photon sources. However, existing security proofs typically either neglect important device imperfections or rely on assumptions that are difficult to justify in realistic high-speed implementations, such as the independent and identically distributed nature of the emitted signals. In this work, we combine and extend several recent theoretical advances to provide a comprehensive analytical finite-key security proof for decoy-state QKD that simultaneously incorporates multiple practically relevant transmitter and receiver imperfections, including state-preparation flaws, bit and basis side-channel leakage and correlations, setting-independent intensity fluctuations, and detection-efficiency mismatches.
Recently, reference-frame-independent quantum key distribution (RFI-QKD) has attracted more attention, since no active calibration of the reference frame is required. Thus, it has potential advantages in practical applications, especially for QKD with a mobile-platform-based quantum channel. However, due to the imperfections of devices, practical security is still one of the main bottlenecks for the application of RFI-QKD. Although, based on ``qubit'' assumption, RFI-QKD with the inaccuracy of encoded state was analyzed and demonstrated, this assumption is hard to be guaranteed in practical situations, and some source flaws could not be considered. In this paper we evaluate the security of RFI-QKD with general source flaws, in which the qubit assumption is removed. Then, almost all the source flaws (not only the inaccuracy of encoded state, but also the side channel, the Trojan horse, and so on) can be considered together.