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Physical Review A

Passive continuous-variable quantum secret sharing using a thermal source

Xiaodong Wu, Yijun Wang, Duan Huang

Published Feb 3, 2020• 62 citations
Publisher

Abstract

We propose a continuous-variable quantum secret sharing (CV-QSS) protocol in which the quantum states are prepared passively using a thermal source. In our protocol, one player splits the output of a thermal source into two spatial modes with the help of a beam splitter, then he (or she) measures one of the correlated thermal states and sends the others to the secure station of the adjacent player in sequence after using appropriate optical attenuation, which waives the necessity of employment of high extinction ratio modulators with good stability. Therefore, the proposed protocol provides convenient implementation in QSS framework. Moreover, our scheme is immune to Trojan horse attacks. We derive the security bounds for our protocol against both eavesdroppers and dishonest players. Furthermore, we can achieve tighter bound of QSS distance by considering the finite-size effect, which is more practical than that obtained in the asymptotic limit.

DOI
10.1103/physreva.101.022301

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We propose a continuous-variable quantum secret sharing (CV-QSS) protocol in which the quantum states are prepared passively using a thermal source. In our protocol, one player splits the output of a thermal source into two spatial modes with the help of a beam splitter, then he (or she) measures one of the correlated thermal states and sends the others to the secure station of the adjacent player in sequence after using appropriate optical attenuation, which waives the necessity of employment of high extinction ratio modulators with good stability. Therefore, the proposed protocol provides convenient implementation in QSS framework. Moreover, our scheme is immune to Trojan horse attacks. We derive the security bounds for our protocol against both eavesdroppers and dishonest players. Furthermore, we can achieve tighter bound of QSS distance by considering the finite-size effect, which is more practical than that obtained in the asymptotic limit.
Secret sharing allows a trusted party (the dealer) to distribute a secret to a group of players, who can only access the secret cooperatively. Quantum secret sharing (QSS) protocols could provide unconditional security based on fundamental laws in physics. While the general security proof has been established recently in an entanglement-based QSS protocol, the tolerable channel loss is unfortunately rather small. Here we propose a continuous variable QSS protocol using conventional laser sources and homodyne detectors. In this protocol, a Gaussian-modulated coherent state (GMCS) prepared by one player passes through the secure stations of the other players sequentially, and each of the other players injects a locally prepared, independent GMCS into the circulating optical mode. Finally, the dealer measures both the amplitude and the phase quadratures of the receiving optical mode using double homodyne detectors. Collectively, the players can use their encoded random numbers to estimate the measurement results of the dealer and further generate a shared key. We prove the unconditional security of the proposed protocol against both eavesdroppers and dishonest players in the presence of high channel loss, and discuss various practical issues.
Quantum secret sharing (QSS) allows multiple players to achieve unconditional secure communication through an unsecure quantum channel; however, the actual implementation requires a modulator with a high extinction ratio, which means high system expense and miniaturization and commercialization difficulties. In this paper, we propose a continuous variable QSS scheme that can replace the traditional lasers and modulators with directly modulated lasers (DML). Each player prepares quantum states through a DML and sends the signal light to the dealer through a beam splitter into a quantum channel. The method provides a new way for realizing secret key sharing. Moreover, we introduce the chirp estimation algorithm to realize the phase modulation, which can achieve a two-dimensional modulation scheme under a single laser.
We propose a continuous-variable quantum secret sharing (CVQSS) scheme based on thermal terahertz (THz) sources in inter-satellite wireless links (THz-CVQSS). In this scheme, firstly, each player locally preforms Gaussian modulation to prepare a thermal THz state, and then couples it into a circulating spatiotemporal mode using a highly asymmetric beam splitter. At the end, the dealer measures the quadrature components of the received spatiotemporal mode through performing the heterodyne detection to share secure keys with all the players of a group. This design enables that the key can be recovered only by the whole group players' knowledge in cooperation and neither a single player nor any subset of the players in the group can recover the key correctly. We analyze both the security and the performance of THz-CVQSS in inter-satellite links. Results show that a long-distance inter-satellite THz-CVQSS scheme with multiple players is feasible. This work will provide an effective way for building an inter-satellite quantum communication network.
Abstract Although continuous-variable quantum secret sharing (CVQSS) has been theoretically proven to be secure, it may still be vulnerable to various local oscillator (LO) attacks. To close this loophole, here we propose a practical CVQSS scheme using local LO (LLO-CVQSS), where LO is no longer generated by each user but is locally generated by the legitimate dealer. This waives the necessity that all LOs have to be transmitted through untrusted channels, making CVQSS system naturally immune to all LO-aimed attacks and enhancing its practical security. We also develop a dedicated phase compensation method for LLO-CVQSS to control the phase noise, and construct a noise model that derives its security bound against both eavesdroppers and dishonest users. Finally, numerical simulation shows that LLO-CVQSS can support 30 users at the same time and the maximal transmission distance reaches 112 km, revealing its potential for building large-scale practical quantum communication networks.
Recently, several continuous-variable quantum secret sharing (CV-QSS) protocols were proposed, while most of them are limited to the fiber channel systems with a relatively stable transmissivity. However, by means of complex channels, the transmissivity fluctuates dramatically in time with a probability distribution, which will lead to a fast-fluctuating attack. Therefore, the security analysis of CV-QSS in fiber channels may not apply to CV-QSS in complex channels. In this paper, we study the CV-QSS protocol in the absence of uniform fast-fluctuating channels whose transmissivity changes with respect to a uniform probability distribution. We give a lower bound of secret key rate to provide security analysis against the fast-fluctuating attack for the CV-QSS protocol. In particular, the realistic highly asymmetric beam splitter (HABS) in CV-QSS protocol is investigated in detail here for the first time, and numerical simulation shows that the security bound is overestimated when the HABS is treated as the perfect device.
Continuous-variable quantum secret sharing (CVQSS) allows a legitimate user, i.e., the dealer, to share a string of secret keys with multiple distant users. These users cannot individually recover the dealer's secret key unless they work cooperatively. Although the theoretical security proof of CVQSS has been well established, its practical security and implementation still face challenges. In this paper, we suggest a practical scheme for CVQSS using plug-and-play (P&P) configuration and dual-phase-modulated coherent state (DPMCS). The proposed scheme, called P&P DPM-based CVQSS, waives the necessity that each user has to prepare respective coherent states with their own lasers, thereby eliminating synchronous loopholes caused by different lasers and reducing the complexity of deployment of the user's stations. Moreover, the local oscillator (LO) can be generated locally by the dealer so that the whole CVQSS system could be naturally immune to all LO-aimed attacks. We derive the security bounds for P&P DPM-based CVQSS by properly making most of the existing security analysis techniques of continuous-variable quantum key distribution (CVQKD). In addition, an experimental concept of P&P DPM-based CVQSS is also presented, which can be deemed a guideline for future implementation.