Fluctuations of Internal Transmittance in Security of Measurement-Device-Independent Quantum Key Distribution with an Untrusted Source

Measurement-device-independent quantum key distribution(MDI-QKD) is immune to detector side channel attacks, which is a crucial security loophole problem in traditional QKD. In order to relax a key assumption that the sources are trusted in MDI-QKD, an MDI-QKD protocol with an untrusted source has been proposed. For the security of MDI-QKD with an untrusted source, imperfections in the practical experiment should also be taken into account. In this paper, we analyze the effects of fluctuations of internal transmittance on the security of a decoy-state MDI-QKD protocol with an untrusted source. Our numerical results show that both the secret key rate and the maximum secure transmission distance decrease when taken fluctuations of internal transmittance into consideration. Especially, they are more sensitive when Charlie's mean photon number per pulse is smaller. Our results emphasize that the stability of correlative optical devices is important for practical implementations.     

Polarization-Encoding-Based Measurement-Device-Independent Quantum Key Distribution with a Single Untrusted Source

Measurement-device-independent quantum key distribution(MDI-QKD) can be immune to all detector sidechannel attacks and guarantee the information-theoretical security even with uncharacterized single photon detectors.MDI-QKD has been demonstrated in both laboratories and field-tests by using attenuated lasers combined with the decoy-state technique.However,it is a critical assumption that the sources used by legitimate participants are trusted in MDI-QKD.Hence,it is possible that a potential security risk exists.Here we propose a new scheme of polarization-encoding-based MDI-QKD with a single untrusted source,by which the complexity of the synchronization system can be reduced and the success rate of the Bell-state measurement can be improved.Meanwhile,the decoy-state method is employed to avoid the security issues introduced by a non-ideal single photon source.We also derive a security analysis of the proposed system.In addition,it seems to be a promising candidate for the implementation for QKD network in the near future.     

Multi-party Measurement-Device-Independent Quantum Key Distribution Based on Cluster States

We propose a novel multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on cluster states. A four-photon analyzer which can distinguish all the 16 cluster states serves as the measurement device for four-party MDI-QKD. Any two out of four participants can build secure keys after the analyzers obtains successful outputs and the two participants perform post-processing. We derive a security analysis for the protocol, and analyze the key rates under different values of polarization misalignment. The results show that four-party MDI-QKD is feasible over 280 km in the optical fiber channel when the key rate is about 10^??6 with the polarization misalignment parameter 0.015. Moreover, our work takes an important step toward a quantum communication network.     

Measurement-device-independent quantum key distribution of multiple degrees of freedom of a single photon

Measurement-device-independent quantum key distribution(MDI-QKD)provides us a powerful approach to resist all attacks at detection side.Besides the unconditional security,people also seek for high key generation rate,but MDI-QKD has relatively low key generation rate.In this paper,we provide an efficient approach to increase the key generation rate of MDI-QKD by adopting multiple degrees of freedom(DOFs)of single photons to generate keys.Compared with other high-dimension MDI-QKD protocols encoding in one DOF,our protocol is more flexible,for our protocol generating keys in independent subsystems and the detection failure or error in a DOF not affecting the information encoding in other DOFs.Based on above features,our MDI-QKD protocol may have potential application in future quantum comniunication field.     

Asymmetric Decoy State Measurement-Device-Independent Quantum Cryptographic Conferencing

Measurement-device-independent quantum cryptographic conferencing(MDI-QCC) protocol suggsts an important scheme for practical multiparty quantum communication. As far as we know, MDI-QCC or MDI-quantum key distribution protocols always assume that the decoy state strategies used at each user's side are the same.In this study, to mitigate the system complexity and to improve the performance of MDI-QCC protocol in the finite-key case, we propose an asymmetric decoy state method for MDI-QCC protocol, and present security analysis and numerical simulations. From numerical simulations, our protocol can achieve better performance in the finite-key case. That is, with a finite data size of 10~(11), it can achieve nonzero secret key rate over 43.6 km.     

基于不可信光源的量子密钥分配的统计特性研究

通过比较被动系统与主动系统的特性, 得出可信光源、不可信光源主动系统和不可信光源被动系统的密钥生成率随距离的变化关系; 采用标准误差分析法, 得到相应变量的偏离量; 基于诱骗态方案分析不可信光源被动系统暗计数率和光源强度参数波动对系统安全特性的影响, 得出在1310 nm 和1550 nm通信窗口下, 系统最大安全通信距离范围分别为[73.2 km, 96.5 km] 和[104.5 km, 137.9 km]. 这可为实用量子通信实验提供重要的理论参数. 关键词： 量子密钥分配 不可信光源 被动系统 统计波动     

基于量子存储的长距离测量设备无关量子密钥分配研究

针对量子中继器短时间内难以应用于长距离量子密钥分配系统的问题, 提出了基于量子存储的长距离测量设备无关量子密钥分配协议, 分析了其密钥生成率与存储效率、信道传输效率和安全传输距离等参数间的关系, 研究了该协议中量子存储单元的退相干效应对最终密钥生成率的影响, 比较了经典测量设备无关量子密钥分配协议和基于量子存储的测量设备无关量子密钥分配协议的密钥生成率与安全传输距离的关系. 仿真结果表明, 添加量子存储单元后, 协议的安全传输距离由无量子存储的216 km增加至500 km, 且量子存储退相干效应带来的误码对最终的密钥生成率影响较小. 实验中可以采取调节信号光强度的方式提高测量设备无关量子密钥分配系统的密钥生成率, 为实用量子密钥分配实验提供了重要的理论参数.     

Free Space Measurement Device Independent Quantum Key Distribution with Modulating Retro-Reflectors under Correlated Turbulent Channel

Modulating retro-reflector (MRR), originally introduced to support laser communication, relieves most of the weight, power, and pointing requirements to the ground station. In this paper, a plug-and-play measurement device independent quantum key distribution (MDI-QKD) scheme with MRR is proposed not only to eliminate detector side channels and allow an untrusted satellite relay between two users, but also to simplify the requirements set-ups in practical flexible moving scenarios. The plug-and-play architecture compensates for the polarization drift during the transmission to provide superior performance in implementing the MDI-QKD on a free-space channel, and the MRR device is adopted to relax the requirements on both communication terminals. A double-pass correlated turbulent channel model is presented to investigate the complex and unstable channel characteristics caused by the atmospheric turbulence. Furthermore, the security of the modified MDI-QKD scheme is analyzed under some classical attacks and the simulation results indicate the feasibility under the situation that the system performance deteriorates with the increase of fading correlation coefficient and the turbulence intensity, which provides a meaningful step towards an MDI-QKD based on the moving platforms to join a dynamic quantum network with untrusted relays.     

一种K分布强湍流下的测量设备无关量子密钥分发方案

研究了K分布强湍流下自由空间测量设备无关量子密钥分发协议模型,采用阈值后选择方法来减少大气湍流对密钥生成率的影响,对比分析了使用阈值后选择方法前后协议的密钥率和湍流强度之间的关系.仿真结果表明,使用阈值后选择方法可以有效地提高协议的密钥生成率,尤其是在高损耗和强湍流区域,而且其最佳阈值与湍流强度、信道平均损耗有关,对实际搭建性能较好的自由空间测量设备无关量子密钥分发协议系统具有一定的参考价值.     

The Performance of Satellite-Based Links for Measurement-Device-Independent Quantum Key Distribution

Measurement-device-independent quantum key distribution (MDI-QKD) protocol has high practical value. Satellite-based links are useful to build long-distance quantum communication network. The model of satellite-based links for MDI-QKD was proposed but it lacks practicality. This work further analyzes the performance of it. First, MDI-QKD and satellite-based links model are introduced. Then considering the operation of the satellite the performance of their combination is studied under different weather conditions. The results may provide important references for combination of optical-fiber-based links on the ground and satellite-based links in space, which is helpful for large-scale quantum communication network.     

Decoy-state measurement-device-independent quantum key distribution with mismatched-basis statistics

Measurement-device-independent quantum key distribution(MDI-QKD) is aimed at removing all detector side channel attacks,while its security relies on the assumption that the encoding systems including sources are fully characterized by the two legitimate parties. By exploiting the mismatched-basis statistics in the security analysis, MDI-QKD even with uncharacterized qubits can generate secret keys. In this paper, considering the finite size effect, we study the decoy-state MDI-QKD protocol with mismatchedbasis events statistics by performing full parameter optimization, and the simulation result shows that this scheme is very practical.     

A practical two-way system of quantum key distribution with untrusted source

The most severe problem of a two-way "plug-and-play" (p & p) quantum key distribution system is that the source can be controlled by the eavesdropper. This kind of source is defined as an üntrusted source". This paper discusses the effects of the fluctuation of internal transmittance on the final key generation rate and the transmission distance. The security of the standard BB84 protocol, one-decoy state protocol, and weak+vacuum decoy state protocol, with untrusted sources and the fluctuation of internal transmittance are studied. It is shown that the one-decoy state is sensitive to the statistical fluctuation but weak+vacuum decoy state is only slightly affected by the fluctuation. It is also shown that both the maximum secure transmission distance and final key generation rate are reduced when Alice's laboratory transmittance fluctuation is considered.     

Measurement-device-independent quantum key distribution with hyper-encoding

Measurement device-independent quantum key distribution(MDI-QKD) protocols are immune to all possible attacks on the photon detectors during quantum communication, but their key generation rates are low compared with those of other QKD schemes.Increasing each individual photon's channel capacity is an efficient way to increase the key generation rate, and high-dimensional(HD) encoding is a powerful tool for increasing the channel capacity of photons. In this paper, we propose an HD MDI-QKD protocol with qudits hyper-encoded in spatial mode and polarization degrees of freedom(DOFs). In the proposed protocol, keys can be generated using the spatial mode and polarization DOFs simultaneously. The proposed protocol is unconditionally secure,even for weak coherent pulses with decoy states. The proposed MDI-QKD protocol may be useful for future quantum secure communication applications.     

Sender-controlled measurement-device-independent multiparty quantum communication

Multiparty quantum communication is an important branch of quantum networks. It enables private information transmission with information-theoretic security among legitimate parties. We propose a sender-controlled measurement-device-independent multiparty quantum communication protocol. The sender Alice divides a private message into several parts and delivers them to different receivers for secret sharing with imperfect measurement devices and untrusted ancillary nodes. Furthermore, Alice acts as an active controller and checks the security of quantum channels and the reliability of each receiver before she encodes her private message for secret sharing, which makes the protocol convenient for multiparity quantum communication.     

利用纠缠GHZ态实现受控的量子确定性安全通讯(英文)

提出一个受控的量子确定性安全通信方案,在通信过程中,纠缠GHZ态用作量子信道,秘密信息的编码和破解是通过受控的量子纠缠交换和局域酉变换实现的.此方案是安全的.关于此方案安全性的证明和两步方案[Phys.Rev.A 68 042317]的安全性是一样的.此方案也可以推广到有多方控制者参与的情形.     

Free-space measurement-device-independent quantum-key-distribution protocol using decoy states with orbital angular momentum

In this paper, we propose a measurement-device-independent quantum-key-distribution(MDI-QKD) protocol using orbital angular momentum(OAM) in free space links, named the OAM-MDI-QKD protocol. In the proposed protocol,the OAM states of photons, instead of polarization states, are used as the information carriers to avoid the reference frame alignment, the decoy-state is adopted to overcome the security loophole caused by the weak coherent pulse source, and the high efficient OAM-sorter is adopted as the measurement tool for Charlie to obtain the output OAM state. Here, Charlie may be an untrusted third party. The results show that the authorized users, Alice and Bob, could distill a secret key with Charlie's successful measurements, and the key generation performance is slightly better than that of the polarization-based MDI-QKD protocol in the two-dimensional OAM cases. Simultaneously, Alice and Bob can reduce the number of flipping the bits in the secure key distillation. It is indicated that a higher key generation rate performance could be obtained by a high dimensional OAM-MDI-QKD protocol because of the unlimited degree of freedom on OAM states. Moreover,the results show that the key generation rate and the transmission distance will decrease as the growth of the strength of atmospheric turbulence(AT) and the link attenuation. In addition, the decoy states used in the proposed protocol can get a considerable good performance without the need for an ideal source.     

Measurement-device-independent quantum secret sharing with hyper-encoding

Quantum secret sharing (QSS) is a typical multi-party quantum communication mode, in which the key sender splits a key into several parts and the participants can obtain the key by cooperation. Measurement-device-independent quantum secret sharing (MDI-QSS) is immune to all possible attacks from measurement devices and can greatly enhance QSS's security in practical applications. However, previous MDI-QSS's key generation rate is relatively low. Here, we adopt the polarization-spatial-mode hyper-encoding technology in the MDI-QSS, which can increase single photon's channel capacity. Meanwhile, we use the cross-Kerr nonlinearity to realize the complete hyper-entangled Greenberger—Horne—Zeilinger state analysis. Both above factors can increase MDI-QSS's key generation rate by about 10³. The proposed hyper-encoded MDI-QSS protocol may be useful for future multiparity quantum communication applications.     

Performance Improvement of Atmospheric Continuous-Variable Quantum Key Distribution with Untrusted Source

Atmospheric continuous-variable quantum key distribution (ACVQKD) has been proven to be secure theoretically with the assumption that the signal source is well protected by the sender so that it cannot be compromised. However, this assumption is quite unpractical in realistic quantum communication system. In this work, we investigate a practical situation in which the signal source is no longer protected by the legitimate parts, but is exposed to the untrusted atmospheric channel. We show that the performance of ACVQKD is reduced by removing the assumption, especially when putting the untrusted source at the middle of the channel. To improve the performance of the ACVQKD with the untrusted source, a non-Gaussian operation, called photon subtraction, is subsequently introduced. Numerical analysis shows that the performance of ACVQKD with an untrusted source can be improved by properly adopting the photon subtraction operation. Moreover, a special situation where the untrusted source is located in the middle of the atmospheric channel is also considered. Under direct reconciliation, we find that its performance can be significantly improved when the photon subtraction operation is manipulated by the sender.     

The Decoy-State Measurement-Device-Independent Quantum Key Distribution with Heralded Single-Photon Source

Based on heralded single-photon source (HSPS), a decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed in this paper. The MDI-QKD protocol mainly uses orbital angular momentum (OAM) states and pulse position modulation (PPM) technology to realize the coding of the signal states in heralded single-photon source. The three-intensity decoy states are used to avoid the attacks against the light source. Moreover, the formula of key generation rate is given by computing the lower bound of the yield of single-photon pairs and the upper bound of the error rate of single-photon pairs. Numerical simulation shows that the new MDI-QKD protocol has high key generation rate and low error rate. Moreover, the secure communication distance can be up to 450 km.