We propose a quantum-cryptography network based on a continuous-variable graph state along with its corresponding quantum key distribution (QKD) protocol. It allows two arbitrary parties in the graph state to share a secret Gaussian key (any-to-any QKD). A mathematical model is established to determine an arbitrary graph state'!`\ifmmode\bar\else\textasciimacron\fi{}s properties, including the possibility of QKD and the relevant criteria. The general entangling cloner attack strategy is analyzed in detail employing Shannon information theory. Results show that the proposed network is secure against such attack if the graph state meets certain criteria.
We propose a quantum-cryptography network based on a continuous-variable graph state along with its corresponding quantum key distribution (QKD) protocol. It allows two arbitrary parties in the graph state to share a secret Gaussian key (any-to-any QKD). A mathematical model is established to determine an arbitrary graph state'!`\ifmmode\bar\else\textasciimacron\fi{}s properties, including the possibility of QKD and the relevant criteria. The general entangling cloner attack strategy is analyzed in detail employing Shannon information theory. Results show that the proposed network is secure against such attack if the graph state meets certain criteria.
In the rapidly developing field of quantum cryptography, graph theory provides a useful mathematical foundation for complex relationships and structures.Applications for it are becoming more and more common.Vertices, edges, connectivity, and graph states, all components of graph theory help illustrate multi-party entanglement, network connection, and protocol designs in quantum cryptography systems.The connection between graph theory and quantum cryptography is examined in this article.It shows that, graph theory and quantum cryptography design can be used to create scalable, reliable quantum secure networks.The basics of graph theory, including network modeling and graph-state entanglement, are covered.It then gives a summary of modern graph-based quantum cryptography methods, including those used for secure computing, secret sharing, and key distribution.The study highlights current issues while contrasting their approaches and resource requirements.Graph states are used in current methods for secret sharing and multi-party key agreement.Additionally, they use graph structures for protocol creation and graph networks for routing in quantum key distribution (QKD).However, significant obstacles remain, such as the experimental construction of large graph-state networks, securing against different types of assaults, and using sophisticated graphtheoretic methods.Novel graph structures such as hypergraphs and quotient graphs should be the focus of future research.It should also develop graph-based solutions for post-quantum and multi-party cryptographic primitives and include classical-quantum network analysis.
We consider the continuous-variable protocol of Pirandola et al. [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 strategies against the quantum links explicitly showing that, at fixed transmissivity and thermal noise, two-mode coherent attacks are optimal, manifestly outperforming one-mode collective attacks based on independent entangling cloners. Such an advantage is shown both in terms of security threshold and secret-key rate.
Abstract Multipartite quantum key distribution (QKD) is crucial for quantum communicating and may link massive private information to the complex quantum network protocols. In this paper, we tackle one of the difficulties in multipartite quantum communications by designing a quantum key distribution scheme with improved secret key rates. We suggest an entanglement-based tripartite continuous variable quantum key distribution (CVQKD) scheme for quantum network, where the source in the middle generates tripartite state and distributes the modes of the state to legitimate parties, respectively. We analyze the mutual information among the distributed modes of the tripartite state of protocols involving different attack strategies of the eavesdropper in varied circumstances. Numeric simulation results show that the CVQKD system enables the generations of secret keys against optimal coherent attacks.
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 proxy servers. Our theory is confirmed by an experiment generating key-rates which are orders of magnitude higher than those achievable with discrete-variable protocols. Thus, using the cheapest possible quantum resources, we experimentally show the possibility of high-rate quantum key distribution in network topologies where direct links are missing between end-users and intermediate relays cannot be trusted.
Secret sharing is a multiparty cryptographic primitive that can be applied to a network of partially distrustful parties for encrypting data that is both sensitive (it must remain secure) and important (it must not be lost or destroyed).When sharing classical secrets (as opposed to quantum states), one can distinguish between protocols that leverage bipartite quantum key distribution (QKD) and those that exploit multipartite entanglement.The latter class are known to be vulnerable to so-called participant attacks and, while progress has been made recently, there is currently no analysis that quantifies their performance in the composable, finite-size regime, which has become the gold standard for QKD security.Given this-and the fact that distributing multipartite entanglement is typically challenging-one might well ask is there any virtue in pursuing multipartite entanglement-based schemes?Here, we answer this question in the affirmative for a class of secret-sharing protocols based on continuous-variable graph states.We establish security in a composable framework and identify a network topology, specifically a bottleneck network of lossy channels, and parameter regimes within the reach of present-day experiments for which a multipartite scheme outperforms the corresponding QKD-based method in the asymptotic and finite-size setting.Finally, we establish experimental parameters where the multipartite schemes outperform any possible QKD-based protocol.This is one of the first concrete compelling examples of multipartite entangled resources achieving a genuine advantage over point-to-point protocols for quantum communication and represents a rigorous, operational benchmark to assess the usefulness of such resources.
The need for secrecy and security is essential in communication. Secret sharing is a conventional protocol to distribute a secret message to a group of parties, who cannot access it individually but need to cooperate in order to decode it. While several variants of this protocol have been investigated, including realizations using quantum systems, the security of quantum secret sharing schemes still remains unproven almost two decades after their original conception. Here we establish an unconditional security proof for entanglement-based continuous-variable quantum secret sharing schemes, in the limit of asymptotic keys and for an arbitrary number of players. We tackle the problem by resorting to the recently developed one-sided device-independent approach to quantum key distribution. We demonstrate theoretically the feasibility of our scheme, which can be implemented by Gaussian states and homodyne measurements, with no need for ideal single-photon sources or quantum memories. Our results contribute to validating quantum secret sharing as a viable primitive for quantum technologies.