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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Experimental Anonymous Conference Key Agreement

Jonathan Webb, Joseph Ho, Federico Grasselli, Gláucia Murta, Alexander Pickston, Andrés Ulibarrena, Alessandro Fedrizzi

Published Jun 26, 2023• 0 citations
Publisher

Abstract

Quantum conference key agreement (QCKA) generalises the traditional two-party quantum key distribution (QKD) paradigm to multiple users, enabling them to share a common quantum-safe key. Deriving quantum conference keys from multi-partite entanglement can have significant resource advantages over two-party schemes [1]. Anonymous quantum key agreement (AQCKA) is a related protocol which has been theoretically shown to obtain an even more substantial reduction in network resources when multi-partite entanglement is available and incorporated into the protocol. The addition of anonymity can be useful in circumstances where users require guaranteed secrecy, e.g. for electronic voting, or for whistle blowers.

DOI
10.1109/cleo/europe-eqec57999.2023.10232078

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Quantum conference key agreement (QCKA) generalises the traditional two-party quantum key distribution (QKD) paradigm to multiple users, enabling them to share a common quantum-safe key. Deriving quantum conference keys from multi-partite entanglement can have significant resource advantages over two-party schemes [1]. Anonymous quantum key agreement (AQCKA) is a related protocol which has been theoretically shown to obtain an even more substantial reduction in network resources when multi-partite entanglement is available and incorporated into the protocol. The addition of anonymity can be useful in circumstances where users require guaranteed secrecy, e.g. for electronic voting, or for whistle blowers.
Anonymous quantum conference key agreement (AQCKA) allows a group of users within a network to establish a shared cryptographic key without revealing their participation. Although this can be achieved using bipartite primitives alone, it is costly in the number of network rounds required. By allowing the use of multi-partite entanglement, there is a substantial efficiency improvement. We experimentally implement the AQCKA task in a six-user quantum network using Greenberger–Horne–Zeilinger (GHZ)-state entanglement and obtain a significant resource cost reduction in line with theory when compared to a bipartite-only approach. We also demonstrate that the protocol retains an advantage in a four-user scenario with finite key effects taken into account.
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 conference key agreement (QCKA) allows multiple users to establish a secure key from a shared multi-partite entangled state. In a quantum network, this protocol can be efficiently implemented using a single copy of a N-qubit Greenberger-Horne-Zeilinger (GHZ) state to distil a secure N-user conference key bit, whereas up to N-1 entanglement pairs are consumed in the traditional pair-wise protocol. We demonstrate the advantage provided by GHZ states in a testbed consisting of a photonic six-user quantum network, where four users can distil either a GHZ state or the required number of Bell pairs for QCKA using network routing techniques. In the asymptotic limit, we report a more than two-fold enhancement of the conference key rate when comparing the two protocols. We extrapolate our data set to show that the resource advantage for the GHZ protocol persists when taking into account finite-key effects.
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 linear chain 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.
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.