Gláucia Murta, Federico Grasselli, Hermann Kampermann, Dagmar Bruß
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15 pages, 4 figures. Contribution to special issue "Advancing quantum technologies - chances and challenges" of Advanced Quantum Technologies. v2: small changes, new citations included, close to the published version
Conference key agreement (CKA), or multipartite key distribution, is a cryptographic task where more than two parties wish to establish a common secret key. A composition of bipartite quantum key distribution protocols can accomplish this task. However, the existence of multipartite quantum correlations allows for new and potentially more efficient protocols, to be applied in future quantum networks. Here, we review the existing quantum CKA protocols based on multipartite entanglement, both in the device-dependent and the device-independent scenario.
Quantum Conference Key Agreement (QCKA) protocols are designed to allow multiple parties to agree on a shared secret key, secure against computationally unbounded adversaries. In this paper, we consider a high-dimensional QCKA protocol and prove its information theoretic security against arbitrary, general, attacks in the finite-key scenario. Our proof technique may be useful for other high-dimensional multi-party quantum cryptographic protocols. Finally, we evaluate the protocol in a variety of settings, showing that high-dimensional states can greatly benefit QCKA protocols.
In this manuscript we discuss the device-independent conference key agreement (DICKA) protocol [Phys. Rev. A 97, 022307 (2018)]. We show that the suggested honest implementation fails, because perfect correlated measurement results and the required Bell-inequality violation cannot be achieved simultaneously, in contradiction to what is claimed. We further show via semidefinite programming that there cannot exist any suitable honest implementation in the tripartite setting, rendering the DICKA protocol incomplete.
Quantum cryptography is a major ingredient of the future quantum internet that promises various secure communication tasks. Quantum conference key agreement (CKA) is an important cryptographic primitive of quantum cryptography, which provides the conference key among multiple users simultaneously. However, quantum CKA is currently far from practical application due to the low conference key rate. Here, we propose a quantum CKA protocol of three users with information-theoretic security. Our protocol only requires phase-randomized weak coherent sources and threshold single-photon detectors, and…
Quantum Conference Key Agreement (CKA) is a cryptographic effort of multiple parties to establish a shared secret key. While bipartite quantum key distribution protocols are also useful in the context of CKA, multipartite protocols allow for a more efficient generation of the necessary correlations and are therefore viewed favorably in the context of quantum networks. In future quantum networks, generating secret keys in an anonymous way is of tremendous importance for parties that do not only want to keep their shared key secret but also protect their own identity, e.g. in the context of whis…
Conference key agreement (CKA) is an information processing task where more than two parties want to share a common secret key. Here, we present a loss-resilient protocol for CKA, based on redundant encoding and error correction. Our protocol provides a speed-up in transmission rate over the existing lossy CKA protocol. However, encoding and error correction come with extra cost. We show that, using photon sources with creation probability p > 0.3, our protocol's secret key rate can overcome the existing protocol's. Hence, high probability entangled photon sources are required for realistic im…
Entanglement plays a crucial role in the security of quantum key distribution. A secret key can only be obtained by two parties if there exists a corresponding entanglement-based description of the protocol in which entanglement is witnessed, as shown by Curty et al (2004). Here we investigate the role of entanglement for the generalization of quantum key distribution to the multipartite scenario, namely conference key agreement. In particular, we ask whether the strongest form of multipartite entanglement, namely genuine multipartite entanglement, is necessary to establish a conference key. W…
In this work, we present a new class of genuine multipartite Bell inequalities, that is particularly designed for multipartite device-independent (DI) quantum key distribution (QKD), also called DI conference key agreement. We prove the classical bounds of this inequality, discuss how to maximally violate it and show its usefulness by calculating achievable conference key rates via the violation of this Bell inequality. To this end, semidefinite programming techniques based on [Nat. Commun. 2, 238 (2011)] are employed and extended to the multipartite scenario. Our Bell inequality represents a …
The generation of GHZ states in quantum networks is a key element for the realization of several quantum information tasks. Given the complexity of the implementation of such generation, it is not easy to find an unambigous proof for an optimal protocol. Motivated by recent improvements in NV center manipulation, we present and compare an extensive list of protocols for generating GHZ states using realistic parameters. Furthermore, in order to establish the goodness of the various protocols, we test them on a specific application, i.e. conference key agreement. We show that for an high number …
Conference Key Agreement (CKA) is a cryptographic effort of multiple parties to establish a shared secret key. In future quantum networks, generating secret keys in an anonymous way is of tremendous importance for parties that want to keep their shared key secret and at the same time protect their own identity. We provide a definition of anonymity for general protocols and present a CKA protocol that is provably anonymous under realistic adversarial scenarios. We base our protocol on shared Greenberger-Horne-Zeilinger states, which have been proposed as more efficient resources for CKA protoco…
Quantum networks will provide multi-node entanglement over long distances to enable secure communication on a global scale. Traditional quantum communication protocols consume pair-wise entanglement, which is sub-optimal for distributed tasks involving more than two users. Here we demonstrate quantum conference key agreement, a quantum communication protocol that exploits multi-partite entanglement to efficiently create identical keys between N users with up to N-1 rate advantage in constrained networks. We distribute four-photon Greenberger-Horne-Zeilinger (GHZ) states generated by high-brigh…
Strategy optimization for quantum conference key agreement in asymmetric star networks
Technische Universität Berlin（柏林工业大学）；Heinrich Heine University Düsseldorf（杜塞尔多夫大学）；Freie Universität Berlin（柏林自由大学）；Helmholtz-Zentrum Berlin für Materialien und Energie（亥姆霍兹柏林材料与能源中心）；Universität Innsbruck（因斯布鲁克大学）
The intense research activity on Twin-Field (TF) quantum key distribution (QKD) is motivated by the fact that two users can establish a secret key by relying on single-photon interference in an untrusted node. Thanks to this feature, variants of the protocol have been proven to beat the point-to-point private capacity of a lossy quantum channel. Here we generalize the main idea of the TF-QKD protocol introduced by Curty et al. to the multipartite scenario, by devising a conference key agreement (CKA) where the users simultaneously distill a secret conference key through single-photon interfere…
We present the first security analysis of conference key agreement (CKA) in the most adversarial model of device independence (DI). Our protocol can be implemented {by any experimental setup} that is capable of performing Bell tests (specifically, we introduce the "Parity-CHSH" inequality), and security can in principle be obtained for any violation of the Parity-CHSH inequality. We use a direct connection between the $N$-partite Parity-CHSH inequality and the CHSH inequality. Namely, the Parity-CHSH inequality can be considered as a CHSH inequality or another CHSH inequality (equivalent up to…
As an essential ingredient of quantum networks, quantum conference key agreement (QCKA) provides unconditional secret keys among multiple parties, which enables only legitimate users to decrypt the encrypted message. Recently, some QCKA protocols employing twin-field was proposed to promote transmission distance. These protocols, however, suffer from relatively low conference key rate and short transmission distance over asymmetric channels, which demands a prompt solution in practice. Here, we consider a tripartite QCKA protocol utilizing the idea of sending-or-not-sending twin-field scheme a…
Quantum conference key agreement (CKA) enables key sharing among multiple trusted users with information-theoretic security. Currently, the key rates of most quantum CKA protocols suffer from the limit of the total efficiency among quantum channels. Inspired by the coherent one-way and twin-field quantum key distribution (QKD) protocols, we propose a quantum CKA protocol of three users. Exploiting coherent states with intensity 0 and $μ$ to encode logic bits, our protocol can break the limit. Additionally, the requirements of phase randomization and multiple intensity modulation are removed in…
We provide several general upper bounds on the rate of a key secure against a quantum adversary in the device-independent conference key agreement (DI-CKA) scenario. They include bounds by reduced entanglement measures and those based on multipartite secrecy monotones such as a multipartite squashed entanglement-based measure, which we refer to as reduced c-squashed entanglement. We compare the latter bound with the known lower bound for the protocol of conference key distillation based on the parity Clauser-Horne-Shimony-Holt game. We also show that the gap between the DI-CKA rate and the dev…
Improving the Loss Tolerance of Heralded Photonic GHZ States for Long-Distance Device-Independent Conference Key Agreement
Imperial College London（帝国理工学院）；Keio University（庆应义塾大学）；Curtin University（科廷大学）；University of Oxford（牛津大学）；National Institute of Information and Communications Technology (NICT)（信息通信研究机构）
Performance Analysis of Multiparty GHZ-State Quantum Conference Key Agreement over Optical Fiber Channel
Indian Institute of Technology Delhi（印度德里理工学院）；Centre for Applied Research in Electronics (CARE)（电子应用研究中心）；Bharti School of Telecommunication Technology and Management（Bharti电信技术与管理学院）；University of Melbourne（墨尔本大学）
Pauli Error Composition Determines the Multipartite Advantage in Conference Key Agreement
The Coding School dba Frontier Technology Institute（Frontier Technology Institute）；Department of Computer Science, University of Maryland, College Park, Maryland, USA（马里兰大学）
该研究通过精确模拟不同噪声下的 GHZ 会议密钥协商协议，发现 Pauli 错误组成决定其相对 BB84 的多体优势，并推导闭式速率证明噪声分散优于集中。
