H. Bechmann-Pasquinucci, A. Pasquinucci
A trusted quantum relay is introduced to enable quantum key distribution links to form the basic legs in a quantum key distribution network. The idea is based on the well-known intercept/resend eavesdropping. The same scheme can be used to make quantum key distribution between several parties. No entanglement is required.
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We propose a QKD protocol for trusted node relays. Our protocol shifts the communication and computational weight of classical post-processing to the end users by reassigning the roles of error correction and privacy amplification, while leaving the exchange of quantum signals untouched. We perform a security analysis for this protocol based on the BB84 protocol on the level of infinite key formulas, taking into account weak coherent implementations involving decoy analysis.
We investigate Quantum Key Distribution (QKD) relaying models. Firstly, we propose a novel quasi-trusted QKD relaying model. The quasi-trusted relays are defined as follows: (i) being honest enough to correctly follow a given multi-party finite-time communication protocol; (ii) however, being under the monitoring of eavesdroppers. We develop a simple 3-party quasi-trusted model, called Quantum Quasi-Trusted Bridge (QQTB) model, to show that we could securely extend up to two times the limited range of single-photon based QKD schemes. We also develop the Quantum Quasi-Trusted Relay (QQTR) model…
A Practical Multi-Protocol Collaborative QKD Networking Scheme
针对QKD网络需平衡强可信中继依赖度与通信能力的问题，提出多协议协同组网单元及基于流模型的最优拓扑设计方法，在保障通信能力的同时降低强可信中继依赖，推动QKD网络实用化。
Quantum utility routing in continuous-variable QKD networks with trusted and untrusted relays
本文提出量子效用路由（QUR）框架，将有限尺寸密钥速率直接纳入路由搜索，平衡瓶颈SKR与资源使用，在CV-QKD网络中实现密码性能与资源消耗的可配置权衡。
Relaxing Trust Assumptions on Quantum Key Distribution Networks
本文针对 QKD 网络必须完全信任中继的限制，划分 FAT、PAT、NAT 三级信任模型，并提出面向无访问信任的集中式与去中心化密钥管理方案。
Quantum cryptography holds the promise to establish an information-theoretically secure global network. All field tests of metropolitan-scale quantum networks to date are based on trusted relays. The security critically relies on the accountability of the trusted relays, which will break down if the relay is dishonest or compromised. Here, we construct a measurement-device-independent quantum key distribution (MDIQKD) network in a star topology over a 200 square kilometers metropolitan area, which is secure against untrustful relays and against all detection attacks. In the field test, our sys…
We show how it is possible to operate end-to-end relays on a QKD network by treating each relay as a trusted eavesdropper operating an intercept/resend strategy. It is shown that, by introducing the concept of bit transport, the key rate compared to that of single-link channels is unaffected. The technique of bit transport extends the capability of QKD networks. We also discuss techniques for reducing the level of trust required in the relays. In particular we demonstrate that it is possible to create a simple quantum key exchange scheme using secret sharing such that by the addition of a sing…
We describe systems and methods for the deployment of global quantum key distribution (QKD) networks covering transoceanic, long-haul, metro, and access segments of the network. A comparative study of the state-of-the-art QKD technologies is carried out, including both terrestrial QKD via optical fibers and free-space optics, as well as spaceborne solutions via satellites. We compare the pros and cons of various existing QKD technologies, including channel loss, potential interference, distance, connection topology, deployment cost and requirements, as well as application scenarios. Technical …
Quantum key distribution from satellites becomes particularly valuable when it can be used on a large network and on-demand to provide a symmetric encryption key to any two nodes. A constellation model is described which enables QKD-derived encryption keys to be established between any two ground stations with low latency. This is achieved through the use of low earth orbit, trusted-node QKD satellites which create a buffer of keys with the ground stations they pass over, and geostationary relay satellites to transfer secure combinations of the keys to the ground stations. Regional and global …
In this paper we explore how recent technologies can improve the security of optical networks. In particular, we study how to use quantum key distribution (QKD) in common optical network infrastructures and propose a method to overcome its distance limitations. QKD is the first technology offering information theoretic secret-key distribution that relies only on the fundamental principles of quantum physics. Point-to-point QKD devices have reached a mature industrial state; however, these devices are severely limited in distance, since signals at the quantum level (e.g. single photons) are hig…
We consider two remote parties connected to a relay by two quantum channels. To generate a secret key, they transmit coherent states to the relay, where the states are subject to a continuous-variable (CV) Bell detection. We study the ideal case where Alice's channel is lossless, i.e., the relay is locally situated in her lab and the Bell detection is performed with unit efficiency. This configuration allows us to explore the optimal performances achievable by CV measurement-device-independent (MDI) quantum key distribution (QKD). This corresponds to the limit of a trusted local relay, where t…
Present-day quantum communication predominantly depends on trusted relays (e.g., quantum repeaters, low-Earth-orbit satellite) connected by optical fiber cables to transmit information. However, recent evidence supports a decades-old concept that quantum entanglement, harnessed by current quantum communication systems, does not necessarily rely on a physical relay medium. In modern quantum communication networks, this trusted relay infrastructure is (1) susceptible to security attacks, (2) limited by the channel capacity, (3) subject to decoherence loss, and (4) expensive to set up. The instan…
A Quantum Key Distribution (QKD) network is an infrastructure capable of performing long-distance and high-rate secret key agreement with information-theoretic security. In this paper we study security properties of QKD networks based on trusted repeater nodes. Such networks can already be deployed, based on current technology. We present an example of a trusted repeater QKD network, developed within the SECOQC project. The main focus is put on the study of secure key agreement over a trusted repeater QKD network, when some nodes are corrupted. We propose an original method, able to ensure the…
Secure Quantum Relay Networks Using Distributed Entanglement without Classical Authentication
针对当前量子通信协议依赖经典认证易受攻击的问题，本研究提出一种利用预分布纠缠图和非经典关联辅助解码的安全量子中继网络框架，无需经典认证即可实现消息独家检索，保证量子前向 secrecy 和端到端来源完整性。
Quantum key distribution (QKD) network has recently attracted growing attentions. Due to the special characteristics of quantum information, to build a full-connectivity QKD network without trusted relays is a stimulating challenge. In this letter, we report on the first realization of QKD network without trusted relays which covers metropolis in the commercial backbone optical fiber networks. The star topology four-user QKD network automatically addresses the quantum signal with a quantum router (QR) and every user in the network can receive and distribute quantum keys to any others simultane…
The ping-pong protocol adapted for quantum key distribution is studied in the trusted quantum noise scenario, wherein the legitimate parties can add noise locally. For a well-studied attack model, we show how non-unital quantum non-Markovianity of the added noise can improve the key rate. We also point out that this noise-induced advantage cannot be obtained by Alice and Bob by adding local classical noise to their post-measurement data.
One of the obstacles to deployment of QKD solutions has been the distance limitation. Solutions using relays have been proposed but these rely on link-by-link key establishment. We present a new technique to extend the distance of a quantum key distribution channel using an active relay. Each relay acts as an intercept/resend device and allows the establishment of an end-to-end key. It has been argued that such relays cannot be used to extend the distance, but we show that with a suitable adaptation of the protocol the effective key distribution distance can be increased.
The assumption that detection and/or state-preparation devices used for continuous-variable quantum key distribution (CV-QKD) are beyond influence of potential eavesdroppers leads to a significant performance enhancement in terms of achievable key rate and transmission distance. We provide a detailed and comprehensible derivation of the Holevo bound in this so-called trusted-device scenario. Modelling an entangling-cloner attack and using some basic algebraic matrix transformations, we show that the computation of the Holevo bound can be reduced to the solution of a quadratic equation. As an a…
Quantum key distribution (QKD) networks is expected to provide information-theoretical secured (ITS) communication over long distances. QKD networks based trusted relay architecture are now the most widely used scheme in practice. However, it is an unrealistic assumption that all relays are fully trustable in complex networks. In the past, only a few studies have theoretically analyzed the case of passive eavesdropping attack by dishonest relays and corresponding defense method. However, we have found that active attacks by dishonest relays can be more threatening. With the consideration of pa…
The maximum distance of quantum communication is limited due to the photon loss and detector noise. Exploiting entanglement swapping, quantum relay could offer ways to extend the achievable distance by increasing the signal to noise ratio. In this letter we present an experimental simulation of long distance quantum communication, in which the superiority of quantum relay is demonstrated. Assisted by quantum relay, we greatly extend the distance limit of unconditional secure quantum communication.
Quantum Secure Anonymous Communication Networks
针对Tor依赖RSA与Diffie-Hellman分发密钥而面临量子攻击的问题，本文提出无需可信节点的QKD协议与网络架构，以构建量子安全匿名通信网络。
Quantum correlation between two particles and among three particles show nonclassic properties that can be used for providing secure transmission of information. In this paper, we propose two quantum key distribution schemes for quantum cryptographic network, which use the correlation properties of two and three particles. One is implemented by the Greenberger-Horne-Zeilinger state, and another is implemented by the Bell states. These schemes need a trusted information center like that in the classic cryptography. The optimal efficiency of the proposed protocols are higher than that in the pre…
Discrete-modulated continuous-variable quantum key distribution protocols are promising candidates for large-scale deployment due to the large technological overlap with deployed modern optical communication devices. The security of discrete modulation schemes has previously analyzed in the ideal detector scenario in the asymptotic limit. In this work, we calculate asymptotic key rates against collective attacks in the trusted detector noise scenario. Our results show that we can thus cut out most of the effect of detector noise and obtain asymptotic key rates similar to those had we access to…
Absorption, scattering, and turbulence experienced in underwater channels severely limit the range of quantum communications. In this paper, to overcome range limitations, we investigate a multi-hop underwater quantum key distribution (QKD) where intermediate nodes help the key distribution between the source and destination nodes. We consider deployment of passive-relays which simply redirect the qubits to the next relay node or receiver without any measurement. Based on near-field analysis, we present the performance of relay-assisted QKD scheme in clear ocean under different atmospheric con…
We show how QKD on a multi-user, multi-path, network can be used to establish a key between any two end users in an asynchronous fashion using the technique of bit-transport. By a suitable adaptation of our previous secret-sharing scheme we show that an attacker has to compromise all of the intermediate relays on the network in order to obtain the key. Thus, two end users can establish a secret key provided they trust at least one of the network relays.
We address the role of the phase-insensitive trusted preparation and detection noise in the security of a continuous-variable quantum key distribution, considering the Gaussian protocols on the basis of coherent and squeezed states and studying them in the conditions of Gaussian lossy and noisy channels. The influence of such a noise on the security of Gaussian quantum cryptography can be crucial, even despite the fact that a noise is trusted, due to a strongly nonlinear behavior of the quantum entropies involved in the security analysis. We recapitulate the known effect of the preparation noi…
Finite Key Security of Simplified Trusted Node Networks
本文研究了简化可信节点（STN）量子密钥分发网络的有限密钥安全性，推导了新的有限密钥安全证明，并提出了成本函数以评估STN相比常规TN的计算优势。
Parallel trusted node approach for satellite quantum key distribution
针对卫星QKD依赖单一可信卫星的问题，提出由多颗QKD卫星并行中介密钥分发的可信节点方法，以分散信任、消除单点故障并降低信任假设。
In this paper, using the full security framework for continuous variable quantum key distribution (CV-QKD), we provide a composable security proof for the CV-QKD system in a realistic implementation. We take into account equipment losses and contributions from various components of excess noise and evaluate performance against collective and coherent attacks assuming trusted hardware noise. The calculation showed that the system remains operable at channel losses up to 10.2 dB in the presence of collective attacks and up to 7.5 dB in the presence of coherent ones.
Quantum Key Distribution with Efficient Post-Quantum Cryptography-Secured Trusted Node on a Quantum Network
提出一种利用后量子密码技术降低可信节点隐私要求的高效方案，并在巴黎地区部署的光纤量子通信网络上实现了量子密钥分发。
Trusted source noise model of discrete-modulated continuous-variable quantum key distribution
针对离散调制连续变量量子密钥分发中不完美源引入噪声的问题，提出可信源噪声模型并升级安全性分析，有效减轻了源噪声对系统性能的负面影响，提升了实际部署的密钥率与安全性。
Quantum Cryptography is on the verge of commercial application. One of its greatest limitations is over long distance - secret key rates are low and the longest fibre over which any key has been exchanged is currently 100 km. We investigate the quantum relay, which can increase the maximum distance at which quantum cryptography is possible. The relay splits the channel into sections, and sends a different photon across each section, increasing the signal to noise ratio. The photons are linked as in teleportation, with entangled photon pairs and Bell measurements. We show that such a scheme cou…
We show that partially trusting the phase noise associated with estimation uncertainty in a LLO CVQKD system allows one to exchange higher secure key rates than in the case of untrusted phase noise. However, this opens a security loophole through the manipulation of the reference pulse amplitude. We label this as "reference pulse attack" which is applicable to all LLO-CVQKD systems if the phase noise is trusted. We show that, at the optimal reference pulse intensity level, Eve achieves unity attack efficiency at 23.8km and 32.0km while using lossless and 0.14dB/km loss channels, respectively, …
A recently published patent (https://www.ipo.gov.uk/p-ipsum/Case/PublicationNumber/GB2590064) has claimed the development of a novel quantum key distribution protocol purporting to achieve long-range quantum security without trusted nodes and without use of quantum repeaters. Here we present a straightforward analysis of this claim, and reach the conclusion that it is largely unfounded.
Quantum cryptography makes it possible to expand a short shared key (of e.g. 256 bits[1]) into an arbitrary long shared key. The novelty of quantum cryptography is that whenever a spy tries to eavesdrop the communication he causes disturbances in the transmission of the message. Ultimately this unavoidable disturbance is a consequence of Heisenberg's uncertainty principle that limits the joint knowledge of complementary observables. Now, a problem remains: in order to initialize quantum key distribution, Alice and Bob need to share a short shared key in order to be able to identify each other …
Quantum digital signature based on single-qubit without a trusted third-party
本文提出一种无需可信第三方的量子数字签名协议，利用量子态不可克隆性构造量子单向函数，以经典私钥与量子公钥组成密钥，并证明其具备信息论不可伪造性、非对称性、不可否认性和可扩展性。
Quantum key distribution (QKD) networks hold promise for sharing secure randomness over multi-partities. Most existing QKD network schemes and demonstrations are based on trusted relays or limited to point-to-point scenario. Here, we propose a flexible and extensible scheme named as open-destination measurement-device-independent QKD network. The scheme enjoys security against untrusted relays and all detector side-channel attacks. Particularly, any users can accomplish key distribution under assistance of others in the network. As an illustration, we show in detail a four-user network where t…
We propose a quantum k-means algorithm based on quantum cloud computing that effectively solves the problem that the client can not afford to execute the same quantum subroutine repeatedly in the face of large training samples. In the quantum k-means algorithm, the core subroutine is the Quantum minimization algorithm (GroverOptim), the client needs to repeat several Grover searches to find the minimum value in each iteration to find a new clustering center, so we use quantum homomorphic encryption scheme (QHE) to encrypt the data and upload it to the cloud for computing. After calculation, th…
General treatment of Gaussian trusted noise in continuous variable quantum key distribution
本文提出一种基于噪声-损耗等价性的通用方法，通过对含噪声零差/外差探测器输出重新标定，将高斯可信噪声等效为微小附加损耗，从而适用于各类CV-QKD协议、有限码长情形及现有和未来的安全证明技术。
We extend the field of continuous-variable quantum cryptography to a network formulation where two honest parties connect to an untrusted relay by insecure quantum links. To generate secret correlations, they transmit coherent states to the relay where a continuous-variable Bell detection is performed and the outcome broadcast. Even though the detection could be fully corrupted and the links subject to optimal coherent attacks, the honest parties can still extract a secret key, achieving high rates when the relay is proximal to one party, as typical in public networks with access points or pro…
Enhancing Long-distance Continuous-variable Quantum-key-distribution with an Error-correcting Relay
本研究通过结合噪声less线性放大器和单位元平均协议，提升长距离连续变量量子密钥分发的性能，突破无中继系统的根本速率-距离限制。
In this paper we estimate how introduction of additional connections between trusted nodes through one, two and so on (i.e. connection density) to a quantum network with serial connection of trusted nodes affects its security. We provide proper scaling of failure probability of authentication and quantum key distribution protocols to the level of the whole quantum network. Expressions of the failure probability dependent on the total number of connected nodes between users and connection density for given mean failure probability of each element are derived. The result provides explicit trade-…
Challenges facing the deployment of quantum key distribution (QKD) systems in critical infrastructure protection applications include the optical loss-key rate tradeoff, addition of network clients, and interoperability of vendor-specific QKD hardware. Here, we address these challenges and present results from a recent field demonstration of three QKD systems on a real-world electric utility optical fiber network.
We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ~kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive OR operations between the two keys and relays the result to one of the ground stations. That …
Quantum key distribution (QKD) is the most used protocol in the context of quantum cryptography for sharing a private encryption key between two parties. Covid-19 pandemic has raised the ever-increasing need for online communications a lot; this requires enhanced security protocols. QKD has the potential to meet a global scale network's security requirements. Despite considerable progress, all ground-based QKD approaches have distance limitations due to atmospheric or fiber attenuation. A global network scheme can use intersatellite links to establish a trusted node network with constellations…
Advantage of the key relay protocol over secure network coding
本文严格比较KRP与SNC，证明在同一图上某些KRP具有更高安全性，并揭示KRP等价于加入免费公共信道后的广义SNC。
Topological optimization of hybrid quantum key distribution networks
本研究针对QKD网络拓扑设计的复杂难题，首次从拓扑角度研究混合QKD网络，提出成本约束下优化设备部署与不可信中继选择的解析模型，仿真验证了混合组网的性能优势与模型的有效性。
Preprocessing noise in finite-size quantum key distribution
本文研究有限规模量子密钥分发中预处理噪声的影响，通过优化Rényi熵计算密钥率，发现信任噪声在特定alpha区间内提升密钥率，并确定块大小与可容忍QBER的关系。
We report the results of the implementation of a quantum key distribution (QKD) network using standard fibre communication lines in Moscow. The developed QKD network is based on the paradigm of trusted repeaters and allows a common secret key to be generated between users via an intermediate trusted node. The main feature of the network is the integration of the setups using two types of encoding, i.e. polarisation encoding and phase encoding. One of the possible applications of the developed QKD network is the continuous key renewal in existing symmetric encryption devices with a key refresh …
This paper presents a hybrid cryptographic protocol, using quantum and classical resources, for authentication and authorization in a network. One or more trusted servers distribute streams of entangled photons to individual resources that seek to communicate. It is assumed that each resource shares a previously distributed secret key with the trusted server, and that resources can communicate with the server using both classical and quantum channels. Resources do not share secret keys with each other, so that the key distribution problem for the network is reduced from O(n^2) to O(n). Some ad…
We consider the continuous-variable protocol of Pirandola et al. [Nature Photonics 9, 397-402 (2015), see also arXiv.1312.4104] where the secret-key is established by the measurement of an untrusted relay. In this network protocol, two authorized parties are connected to an untrusted relay by insecure quantum links. Secret correlations are generated by a continuous-variable Bell detection performed on incoming coherent states. In the present work we provide a detailed study of the symmetric configuration, where the relay is midway between the parties. We analyze symmetric eavesdropping strateg…
In this paper, we consider quantum key distribution (QKD) in a quantum network with both quantum repeaters and a small number of trusted nodes. In contrast to current QKD networks with only trusted nodes and the true Quantum Internet with only quantum repeaters, such networks represent a middle ground, serving as near-future QKD networks. In this setting, QKD can be efficiently and practically deployed, while providing insights for the future true Quantum Internet. To significantly improve the key generation efficiency in such networks, we develop a new dynamic routing strategy that makes rout…
We present a simple new technique to secure quantum key distribution relay networks using secret sharing. Previous techniques have relied on creating distinct physical paths in order to create the shares. We show, however, how this can be achieved on a single physical path by creating distinct logical channels. The technique utilizes a random 'drop-out' scheme to ensure that an attacker must compromise all of the relays on the channel in order to access the key.
An authentic digital signature scheme based on the correlation of Greenberger-Horne-Zeilinger (GHZ) states was presented. In this scheme, by performing a local unitary operation on the third particles of each GHZ triplet, Alice can encode message M and get its signature S. Bob performs CNOT operation on the combined GHZ triplets can recovery the message M and directly authenticates Alice's signature S. Our scheme was designed to use quantum secret key to guaranteed unconditional security, as well as use quantum fingerprinting to avoid trick attacks and reduce communication complexity.
The role of the side channels in the continuous-variable quantum key distribution is studied. It is shown how the information leakage through a side channel from the trusted sender station increases the vulnerability of the protocols to the eavesdropping in the main quantum communication channel. Moreover, the untrusted noise infusion by an eavesdropper on the trusted receiving side breaks the security even for a purely attenuating main quantum channel. As a method to compensate for the effect of the side-channel leakage on the sender side, we suggest several types of manipulations on the side…
We address security of the quantum key distribution scheme based on the noisy modulation of coherent states and investigate how it is robust against noise in the modulation regardless of the particular technical implementation. As the trusted preparation noise is shown to be security breaking even for purely lossy channels, we reveal the essential difference between two types of trusted noise, namely sender-side preparation noise and receiver-side detection noise, the latter being security preserving. We consider the method of sender-side state purification to compensate the preparation noise …
As quantum key distribution becomes increasingly practical, questions of how to effectively employ it in large-scale networks and over large distances becomes increasingly important. To that end, in this work, we model the performance of the E91 entanglement based QKD protocol when operating in a network consisting of both quantum repeaters and trusted nodes. We propose a number of routing protocols for this network and compare their performance under different usage scenarios. Through our modeling, we investigate optimal placement and number of trusted nodes versus repeaters depending on devi…
A long distance quantum teleportation experiment with a fiber-delayed Bell State Measurement (BSM) is reported. The source creating the qubits to be teleported and the source creating the necessary entangled state are connected to the beam splitter realizing the BSM by two 2 km long optical fibers. In addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm are teleported onto photons at 1550 nm. The fidelity is of 77%, above the maximal value obtainable without entanglement. This is the first re…
In practical continuous-variable quantum key distribution system using local local oscillator (LLO CV-QKD), the phase noise related to coherent detection and phase-reference pulse intensity that can be locally calibrated at the receiver side is considered to be trusted noise to improve the performance. However, if the intensity of the phase-reference pulse is not monitored precisely in real-time, a security loophole will be opened for the eavesdropper to launch attacks. To this end, we propose two practical phase-reference pulse intensity attack strategies, where Eve can reduce the trusted pha…
We consider a quantum relay which is used by two parties to perform several continuous-variable protocols: Entanglement swapping, distillation, quantum teleportation, and quantum key distribution. The theory of these protocols is extended to a non-Markovian model of decoherence characterized by correlated Gaussian noise. Even if bipartite entanglement is completely lost at the relay, we show that the various protocols can progressively be reactivated by the separable noise-correlations of the environment. In fact, above a critical amount, these correlations are able to restore the distribution…
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