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arXiv:2311.14158 · Optica

Experimental anonymous quantum conferencing

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

Published May 7, 2024• 13 citations
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Abstract

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.

DOI
10.1364/optica.514362

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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 (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.
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.
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.
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.
Multipartite entanglement enables secure and anonymous key exchange between multiple parties in a network. Greenberger-Horne-Zeilinger states have been introduced as resource states for anonymous key exchange protocols, in which an anonymous subset of parties within a larger network establishes a secret key. However, the use of other types of multipartite entanglement for such protocols remains relatively unexplored. Here, we demonstrate that linear cluster states can serve as a versatile and potentially scalable resource in such applications. We implemented an anonymous key exchange protocol with four photons in a linear cluster state and established a shared key between three parties in our network. We show how to optimize the protocol parameters to account for noise and to maximize the finite key rate under realistic conditions. As cluster states have been established as a flexible resource in quantum computation, we expect that our demonstration provides a first step towards their hybrid use for networked computing and communication.
Multipartite entanglement enables secure and anonymous key exchange between multiple parties in a network. Greenberger-Horne-Zeilinger states have been introduced as resource states for anonymous key exchange protocols, in which an anonymous subset of parties within a larger network establishes a secret key. However, the use of other types of multipartite entanglement for such protocols remains relatively unexplored. Here, we demonstrate that linear cluster states can serve as a versatile and potentially scalable resource in such applications. We implemented an anonymous key exchange protocol with four photons in a linear cluster state and established a shared key between three parties in our network. We show how to optimize the protocol parameters to account for noise and to maximize the finite key rate under realistic conditions. As cluster states have been established as a flexible resource in quantum computation, we expect that our demonstration provides a first step towards their hybrid use for networked computing and communication.