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arXiv:1601.06385 · Physical Review A

Trustworthiness of measurement devices in round-robin differential-phase-shift quantum key distribution

Zhu Cao, Zhen−Qiang Yin, Zheng‐Fu Han

Published Feb 8, 2016• 8 citations
arXivHTMLPDF

Abstract

Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) has been proposed to raise the noise tolerability of the channel. However, in practice, the measurement device in RRDPS QKD may be imperfect. Here, we show that, with these imperfections, the security of RRDPS may be damaged by proposing two attacks for RRDPS systems with uncharacterized measurement devices. One is valid even for a system with unit total efficiency, while the other is valid even when a single-photon state is sent. To prevent these attacks, either security arguments need to be fundamentally revised or further practical assumptions on the measurement device should be put.

DOI
10.1103/physreva.93.022310

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Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) has been proposed to raise the noise tolerability of the channel. However, in practice, the measurement device in RRDPS QKD may be imperfect. Here, we show that, with these imperfections, the security of RRDPS may be damaged by proposing two attacks for RRDPS systems with uncharacterized measurement devices. One is valid even for a system with unit total efficiency, while the other is valid even when a single-photon state is sent. To prevent these attacks, either security arguments need to be fundamentally revised or further practical assumptions on the measurement device should be put.
Recently, a new type of quantum key distribution, called the round-robin differential-phase-shift (RRDPS) protocol [T. Sasaki et al., Nature (London) 509, 475 (2014)], was proposed, where the security can be guaranteed without monitoring any statistics. In this Rapid Communication, we investigate source imperfections and side-channel attacks on the source of this protocol. We show that only three assumptions are needed for the security, and no detailed characterizations of the source or the side-channel attacks are needed. This high robustness is another striking advantage of the RRDPS protocol over other protocols.
The round-robin-differential-phase-shift (RRDPS) quantum key distribution (QKD) protocol has attracted intensive study due to its distinct security characteristics; e.g., information leakage is bounded without learning the error rate of key bits. Nevertheless, its practicality and performance are still not satisfactory. Here, by observing the phase randomization of the encoding states and its connection with eavesdropper's attack, we develop an improved bound on information leakage. Interestingly, our theory is especially useful for implementations with short trains of pulses, and running without monitoring signal disturbance is still available. As a result, the practicality and performance of RRDPS are improved. Furthermore, we realize a proof-of-principle experiment with up to 140 km of fiber, which has been the longest achievable distance of RRDPS until now, whereas the original theory predicted that no secret key could be generated in our experiment. Our results will help in bringing practical RRDPS closer to practical implementations.
Round-robin-differential-phase (RRDPS) quantum key distribution (QKD) protocol has attracted intensive studies due to its distinct security characteristic, e.g., information leakage in RRDPS can be bounded without learning error rate of key bits. Nevertheless, its implementation is still far from practical due to the complication of its measurement device. Moreover, on the theoretical side, its security is still not clear in view of error rate. Here, by observing a potential phase randomization in the encoding states, we develop a theory to bound information leakage quite tightly and differently. Besides, the error rate is incorporated to improve the secret key rate, which is significant for the understanding of RRDPS. Based on our novel security proof, the practicality and performance of RRDPS can be both improved dramatically. Furthermore, we realize an experiment up to 140km fiber distance which is the longest achievable distance of RRDPS system until now, while the original security proof predicts no secret key can be generated in our experiment. Our results pave an avenue towards practical RRDPS.
By introducing four-phase modulations into round-robin-differential-phase-shift (RRDPS) quantum key distribution (QKD) protocol, the round-robin-differential-quadrature-phase-shift (RRDQPS) protocol is proposed. According to the security proof of RRDQPS protocol, it is able to tolerate a higher error rate of key bits. However, its performance with a practical weak coherent source is still unknown since that security proof only applies to a single photon source. In this article, we give the security proof for the general nnn-photon RRDQPS protocol, by which RRDQPS with a practical weak coherent source becomes feasible in the experiment. Through numerical simulation, it is verified that RRDQPS protocol has an advantage over RRDPS protocol on transmission distance, especially when the pulse number is small.
Recently, a new type of protocol named Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) was proposed, where the security can be guaranteed without monitoring conventional signal disturbances. The active decoy state method can be used in this protocol to overcome the imperfections of the source. But, it may lead to side channel attacks and break the security of QKD systems. In this paper, we apply the passive decoy state method to the RRDPS QKD protocol. Not only can the more environment disturbance be tolerated, but in addition it can overcome side channel attacks on the sources. Importantly, we derive a new key generation rate formula for our RRDPS protocol using passive decoy states and enhance the key generation rate. We also compare the performance of our RRDPS QKD to that using the active decoy state method and the original RRDPS QKD without any decoy states. From numerical simulations, the performance improvement of the RRDPS QKD by our new method can be seen.
Among various quantum-key-distribution (QKD) protocols, the round-robin differential-phase- shift (RRDPS) protocol has a unique feature where its security is guaranteed without monitoring the signal disturbance. Moreover, this protocol has the remarkable property of being robust against source imperfections, assuming that the emitted pulses are independent. Unfortunately, some experiments with high-speed QKD systems confirmed the violation of the independence due to pulse correlations, and therefore the lack of a security proof, without taking into account this effect is an obstacle for guaranteeing the implementation security. In this paper, we show that the RRDPS protocol is secure against any source imperfections by establishing a security proof with the pulse correlations. The proof is simple in the sense that we make only three experimentally simple assumptions on the source. Our numerical simulation based on the proof shows that the long-range pulse correlation does not cause a significant impact on the key rate, which reveals another striking feature of the RRDPS protocol. Our security proof is thus effective and applicable to a wide range of practical sources and paves the way to realizing truly secure QKD in high-speed systems.