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Breaking the Rate-Distance Limit of Quantum Conference Key Agreement

Hua‐Lei Yin, Zeng‐Bing Chen

Published Jun 18, 2020• 1 citation
OpenAlex

Abstract

Quantum cryptography is anticipated to be a major ingredient of future quantum internet that promises various secure communication tasks. Quantum conference key agreement (CKA) is an important cryptographic primitives of quantum cryptography, which provides the unconditionally secure conference key among multiple users simultaneously. However, it is far from practical application and, more pessimistically, the conference key rate has recently been shown to be limited by Greenberger-Horne-Zeilinger distribution capacity of quantum network. Here, we propose, surprisingly, a quantum CKA of three users to beat the repeaterless capacity even under coherent attacks. Besides, our protocol only requires the phase-randomized weak coherent sources and threshold single-photon detectors, thus can be experimentally demonstrated over 500 km fiber under current technology. Our new type of protocol paves the way towards large-scale quantum CKA network of future quantum internet.

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Quantum cryptography is anticipated to be a major ingredient of future quantum internet that promises various secure communication tasks. Quantum conference key agreement (CKA) is an important cryptographic primitives of quantum cryptography, which provides the unconditionally secure conference key among multiple users simultaneously. However, it is far from practical application and, more pessimistically, the conference key rate has recently been shown to be limited by Greenberger-Horne-Zeilinger distribution capacity of quantum network. Here, we propose, surprisingly, a quantum CKA of three users to beat the repeaterless capacity even under coherent attacks. Besides, our protocol only requires the phase-randomized weak coherent sources and threshold single-photon detectors, thus can be experimentally demonstrated over 500 km fiber under current technology. Our new type of protocol paves the way towards large-scale quantum CKA network of future quantum internet.
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 is anticipated to be experimentally demonstrated over 600 km under current technology. Our scheme can be widely implemented in the approaching large-scale quantum network.
Abstract 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 our protocol, making its experimental demonstration simple.
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 whistle-blowing. In this paper we provide the first protocol for Anonymous Quantum Conference Key Agreement and demonstrate it using four-photon Greenberger-Horne-Zeilinger (GHZ\mathrm{GHZ}GHZ) states.
Abstract Quantum secret sharing (QSS) and conference key agreement (CKA) provide efficient encryption approaches for realizing multi-party secure communication, which are essential components of quantum networks. In this work, a practical, scalable, verifiable ( k , n ) threshold continuous variable QSS protocol secure against eavesdroppers and dishonest players are proposed and demonstrated. The protocol does not require preparing the laser source by each player and phase locking of independent lasers. The parameter evaluation and key extraction can be accomplished by only the dealer and the corresponding player. By using the multiple sideband modulation, a single heterodyne detector can extract the information of multiple players. The practical security of the system is considered. The system is versatile, it can support the CKA protocol by only modifying the classic post-processing and requiring no changes to the underlying hardware architecture. By implementing the QSS and CKA protocols with five parties over 25 km (55 km) single-mode fibers, a key rate of 0.0061 (7.14 × 10 −4 ) bits per pulse is observed. The results significantly reduces the system complexity and paves the way for the practical applications of QSS and CKA with efficient utilization of resources and telecom technologies.
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 protocols, compared to bipartite entangled resources.The existence of secure and anonymous protocols based on multipartite entangled states provides a new insight on their potential as resources and paves the way for further applications.
Sharing multi-partite quantum entanglement between parties allows for diverse secure communication tasks to be performed. Among them, conference key agreement (CKA), an extension of key distribution to multiple parties, has received much attention recently. Interestingly, CKA can also be performed in a way that protects the identities of the participating parties, therefore providing anonymity. In this work, we propose an anonymous CKA protocol for three parties that is implemented in a highly practical network setting. Specifically, a line of quantum repeater nodes is used to build a linear cluster state among all nodes, which is then used to anonymously establish a secret key between any three of them. The nodes need only share maximally entangled pairs with their neighbours, therefore avoiding the necessity of a central server sharing entangled states. This repeater setup makes our protocol an excellent candidate for implementation in future quantum networks. We explicitly prove that our protocol protects the identities of the participants from one another and perform an analysis of the key rate in the finite regime, contributing to the quest of identifying feasible quantum communication tasks for network architectures beyond point-to-point.