We prove the security of the Bennett-Brassard (BB84) quantum key distribution protocol in the case where the key information is encoded in the relative phase of a coherent-state reference pulse and a weak coherent-state signal pulse, as in some practical implementations of the protocol. In contrast to previous work, our proof applies even if the eavesdropper knows the phase of the reference pulse, provided that this phase is not modulated by the source, and even if the reference pulse is bright. The proof also applies to the case where the key is encoded in the photon polarization of a weak coherent-state pulse with a known phase, but only if the phases of the four BB84 signal states are judiciously chosen. The achievable key generation rate scales quadratically with the transmission in the channel, just as for BB84 with phase-randomized weak coherent-state signals (when decoy states are not used). For the case where the phase of the reference pulse is strongly modulated by the source, we exhibit an explicit attack that allows the eavesdropper to learn every key bit in a parameter regime where a protocol using phase-randomized signals is provably secure.
Experimental Coherent One-Way Quantum Key Distribution with Simplicity and Practical Security
National Laboratory of Solid State Microstructures and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学固体微结构物理国家重点实验室和物理学院，先进微结构协同创新中心）；School of Physics and Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Renmin University of China（中国人民大学物理学院与量子态构建与操控教育部重点实验室）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）
Security-proof framework for two-way Gaussian quantum-key-distribution protocols
双向高斯协议具有将量子密钥分发（QKD）协议的密钥速率提高几个数量级的潜力。修订版~ A { \bf 94}，012322（2016）]。然而，双向协议的安全性证明目前还不发达。在本文中，我们建立了一个安全性证明框架的一般一致攻击双向高斯协议的渐近制度。我们首先证明了所有双向QKD协议的一致攻击安全性都可以归结为集体攻击安全性。接下来，我们确定了两个不同的约束，每个提供入侵参数，绑定窃听者的相干攻击信息增益的任何双向高斯QKD协议。最后，我们将我们的结果应用到两个这样的协议。
The performance of quantum key distribution (QKD) is severely limited by multi-photon pulses emitted by laser sources due to the photon-number splitting attack. Coherent-one-way (COW) QKD has been introduced as a promising solution to overcome this limitation, and thus extend the achievable distance of practical QKD. Indeed, thanks to its experimental simplicity, the COW protocol is already used in commercial applications. Here, we derive simple upper security bounds on its secret key rate, which demonstrate that it scales at most quadratically with the system's transmittance, thus solving a l…
Finite-key security against coherent attacks in quantum key distribution
Christandl，König和Renner [Phys. Rev. Lett. 102，020504（2009）]特别提供了研究所有离散变量协议的有限密钥机制中的无条件安全性的可能性。我们从他们的一般形式主义中阐明这个界限。然后，我们将其应用于最近提出的协议的研究[Laing等人，A82，012304（2010）]。当Alice和Bob的参考系的对准未被监视并且可能随时间变化时，该协议是有意义的。在这种情况下，渐近密钥速率的概念几乎没有任何操作意义，因为如果等待太长时间，平均相关性就会模糊，无法推断出安全性。因此，有限密钥分析是必要的，以找到最大可实现的密钥速率和相应的最佳信号数。
Security of Binary-Modulated Optical Key Distribution Against Quantum-Enhanced Coherent Eavesdropping
Centre for Quantum Optical Technologies, Centre of New Technologies, University of Warsaw（华沙大学新技术中心量子光学技术研究中心）；Faculty of Physics, University of Warsaw（华沙大学物理学院）；Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano（米兰大学阿尔多·庞特罗莫利物理系）；Istituto Nazionale di Fisica Nucleare, Sezione di Milano（意大利国家核物理研究所米兰分部）
The coherent one-way (COW) quantum key distribution (QKD) is a highly practical quantum communication protocol that is currently deployed in off-the-shelves products. However, despite its simplicity and widespread use, the security of COW-QKD is still an open problem. This is largely due to its unique security feature based on inter-signal phase distribution, which makes it very difficult to analyze using standard security proof techniques. Here, to overcome this problem, we present a simple variant of COW-QKD and prove its security in the infinite-key limit. The proposed modifications only in…
A quantum key distribution (QKD) system must fulfill the requirement of universal composability to ensure that any cryptographic application (using the QKD system) is also secure. Furthermore, the theoretical proof responsible for security analysis and key generation should cater to the number $N$ of the distributed quantum states being finite in practice. Continuous-variable (CV) QKD based on coherent states, despite being a suitable candidate for integration in the telecom infrastructure, has so far been unable to demonstrate composability as existing proofs require a rather large $N$ for su…
In comparison to conventional discrete-variable (DV) quantum key distribution (QKD), continuous-variable (CV) QKD with homodyne/heterodyne measurements has distinct advantages of lower-cost implementation and affinity to wavelength division multiplexing. On the other hand, its continuous nature makes it harder to accommodate to practical signal processing, which is always discretized, leading to lack of complete security proofs so far. Here we propose a tight and robust method of estimating fidelity of an optical pulse to a coherent state via heterodyne measurements. We then construct a binary…
