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High-rate quantum conferencing and secret sharing

Carlo Ottaviani, Cosmo Lupo, Riccardo Laurenza, Stefano Pirandola

Published Sep 20, 2017• 1 citation
OpenAlex

Abstract

We introduce a measurement-device independent star network which is conveniently based on continuous variable systems and standard linear optics. Here an arbitrary number of users send modulated coherent states to an untrusted relay where a generalized Bell detection creates multi-partite secret correlations. These correlations are then distilled into a shared secret key to implement a completely-secure quantum conference or, alternatively, a protocol of quantum secret-sharing. Our scheme is composably secure and able to achieve high rates with cheap optical implementation.

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Communications in Theoretical Physics•Aug 1, 2017•3 citations
We introduce a measurement-device independent star network which is conveniently based on continuous variable systems and standard linear optics. Here an arbitrary number of users send modulated coherent states to an untrusted relay where a generalized Bell detection creates multi-partite secret correlations. These correlations are then distilled into a shared secret key to implement a completely-secure quantum conference or, alternatively, a protocol of quantum secret-sharing. Our scheme is composably secure and able to achieve high rates with cheap optical implementation.
Abstract One of the main open problems in quantum communication is the design of efficient quantum-secured networks. This is a challenging goal, because it requires protocols that guarantee both unconditional security and high communication rates, while increasing the number of users. In this scenario, continuous-variable systems provide an ideal platform where high rates can be achieved by using off-the-shelf optical components. At the same time, the measurement-device independent architecture is also appealing for its feature of removing a substantial portion of practical weaknesses. Driven by these ideas, here we introduce a modular design of continuous-variable network where each individual module is a measurement-device-independent star network. In each module, the users send modulated coherent states to an untrusted relay, creating multipartite secret correlations via a generalized Bell detection. Using one-time pad between different modules, the network users may share a quantum-secure conference key over arbitrary distances at constant rate.
Future quantum communication networks will conceivably support cryptographic tasks that require entanglement among more than two users. Quantum secret sharing is a prime example where entanglement provides a direct means to coordinate untrusted parties with security from eavesdropping in a multi-party setting. However, the canonical GHZ-based protocols can be vulnerable to participant attacks, in which untrusted parties try to learn the secret without collaborating. Here, we experimentally evaluate a discrete-variable (n,n)(n,n)(n,n)-threshold quantum secret-sharing protocol whose finite-key analysis provides composable security against general attacks, including participant attacks. Using two domain-engineered entangled photon pair sources, we generate 4-qubit GHZ states at rates above 5×1035\times10^35×103 fourfold events per second and a maximum asymptotic secret key rate of 750±10750 \pm 10750±10 bits per second. We then distribute the state through a 4-arm star network comprising 20km of fibre in total. From the measured event rates and error statistics, we infer that a randomised 24-hour execution with the optimised basis probability would yield a composable finite-key lower bound of 8.7 Mbits, under the assumption that the measured source and device statistics remain stationary.
Quantum cryptography has undergone substantial growth and development within the multi-disciplinary field of quantum information in recent years. The field is constantly advancing with new protocols being developed, security measures being improved, and the first practical applications of these technologies being deployed in optical fibers and free space optical beams. In this paper, we present a comprehensive review of a cutting-edge metropolitan-scale protocol for continuous-variable quantum cryptography. The protocol allows an arbitrary number of users to send modulated coherent states to a relay, where a generalised Bell detection creates secure multipartite correlations. These correlations are then distilled into a shared secret key, providing a secure method for quantum secret-sharing. This novel approach to quantum cryptography has the potential to offer high-rate secure multipartite communication using readily available optical components, making it a promising advancement in the field.
We suggest a continuous variable quantum conferencing network scheme with an entangled source in the middle. Here, the source generates a multipartite entangled state and distributes the modes of the state to an arbitrary number of legitimate network users. The entangled modes that were received and measured by the users share mutual information, which is utilized to generate secure conferencing key between users. The scheme is proven secure against collective attacks on both the untrusted source in the middle and all the quantum links. Simulation results show that the presented scheme can achieve high rate secure conferencing for 100 users within a 400 m-radius community or factory area.
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.
Abstract The developing tendency of continuous-variable (CV) measurement-device-independent (MDI) quantum cryptography is to cope with the practical issue of implementing scalable quantum networks. Up to now, most theoretical and experimental researches on CV-MDI QKD are focused on two-party protocols. However, we suggest a CV-MDI multipartite quantum secret sharing (QSS) protocol use the EPR states coupled with optical amplifiers. More remarkable, QSS is the real application in multipartite CV-MDI QKD, in other words, is the concrete implementation method of multipartite CV-MDI QKD. It can implement a practical quantum network scheme, under which the legal participants create the secret correlations by using EPR states connecting to an untrusted relay via insecure links and applying the multi-entangled Greenberger–Horne–Zeilinger (GHZ) state analysis at relay station. Even if there is a possibility that the relay may be completely tampered, the legal participants are still able to extract a secret key from network communication. The numerical simulation indicates that the quantum network communication can be achieved in an asymmetric scenario, fulfilling the demands of a practical quantum network. Additionally, we illustrate that the use of optical amplifiers can compensate the partial inherent imperfections of detectors and increase the transmission distance of the CV-MDI quantum system .