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15 pages, 11199 KiB

Open AccessArticle

Enhancing Performance of Continuous-Variable Quantum Key Distribution (CV-QKD) and Gaussian Modulation of Coherent States (GMCS) in Free-Space Channels under Individual Attacks with Phase-Sensitive Amplifier (PSA) and Homodyne Detection (HD)

by Nancy Alshaer, Tawfik Ismail and Haitham Mahmoud

Sensors 2024, 24(16), 5201; https://doi.org/10.3390/s24165201 - 11 Aug 2024

Cited by 1 | Viewed by 2807

Abstract

In recent research, there has been a significant focus on establishing robust quantum cryptography using the continuous-variable quantum key distribution (CV-QKD) protocol based on Gaussian modulation of coherent states (GMCS). Unlike more stable fiber channels, one challenge faced in free-space quantum channels is [...] Read more.

In recent research, there has been a significant focus on establishing robust quantum cryptography using the continuous-variable quantum key distribution (CV-QKD) protocol based on Gaussian modulation of coherent states (GMCS). Unlike more stable fiber channels, one challenge faced in free-space quantum channels is the complex transmittance characterized by varying atmospheric turbulence. This complexity poses difficulties in achieving high transmission rates and long-distance communication. In this article, we thoroughly evaluate the performance of the CV-QKD/GMCS system under the effect of individual attacks, considering homodyne detection with both direct and reverse reconciliation techniques. To address the issue of limited detector efficiency, we incorporate the phase-sensitive amplifier (PSA) as a compensating measure. The results show that the CV-QKD/GMCS system with PSA achieves a longer secure distance and a higher key rate compared to the system without PSA, considering both direct and reverse reconciliation algorithms. With an amplifier gain of 10, the reverse reconciliation algorithm achieves a secure distance of 5 km with a secret key rate of

10^{- 1}

bits/pulse. On the other hand, direct reconciliation reaches a secure distance of

2.82

km. Full article

(This article belongs to the Special Issue Quantum Technologies for Communications and Networks Security)

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13 pages, 756 KiB

Open AccessArticle

Underwater Wavelength Attack on Discrete Modulated Continuous-Variable Quantum Key Distribution

by Kangyi Feng, Yijun Wang, Yin Li, Yuang Wang, Zhiyue Zuo and Ying Guo

Entropy 2024, 26(6), 515; https://doi.org/10.3390/e26060515 - 14 Jun 2024

Cited by 1 | Viewed by 1675

Abstract

The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum [...] Read more.

The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) has been researched in both fiber and atmospheric channels. However, the wavelength attack may also pose a threat to the case of ocean turbulent channels, which are vital for the secure communication of both ocean sensor networks and submarines. In this work, we propose two wavelength attack schemes on underwater discrete modulated (DM) CV-QKD protocol, which is effective for the case with and without local oscillator (LO) intensity monitor, respectively. In terms of the transmittance properties of the fused biconical taper (FBT) BS, two sets of wavelengths are determined for Eve’s pulse manipulation, which are all located in the so-called blue–green band. The derived successful criterion shows that both attack schemes can control the estimated excess noise of Alice and Bob close to zero by selecting the corresponding condition parameters based on channel transmittance. Additionally, our numerical analysis shows that Eve can steal more bits when the wavelength attack controls the value of the estimated excess noise closer to zero. Full article

(This article belongs to the Special Issue Quantum Communications Networks: Trends and Challenges)

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10 pages, 478 KiB

Open AccessArticle

Adjusting Optical Polarization with Machine Learning for Enhancing Practical Security of Continuous-Variable Quantum Key Distribution

by Zicheng Zhou and Ying Guo

Electronics 2024, 13(8), 1410; https://doi.org/10.3390/electronics13081410 - 9 Apr 2024

Cited by 2 | Viewed by 1303

Abstract

An available trick to mitigate the interference of environmental noise in quantum communications is to modulate signals with time-polarization multiplexing. Conversely, due to effects of the atmospheric turbulence in free space, the polarization of signals fluctuates randomly, resulting in feasible information leakage when [...] Read more.

An available trick to mitigate the interference of environmental noise in quantum communications is to modulate signals with time-polarization multiplexing. Conversely, due to effects of the atmospheric turbulence in free space, the polarization of signals fluctuates randomly, resulting in feasible information leakage when direct polarization demultiplexing is carried out at the receiver, drowning out the noise-contained signals. For enhancing the practical security of the continuous-variable quantum key distribution (CVQKD), we propose a machine learning (ML) approach for optimization of the dynamic polarization control (DPC) of signals transmitted through atmospheric turbulence. An optimal DPC scheme can be adaptively adjusted with ML algorithms, which is based on the received signals at the receiver for solving the loophole problem of information leakage since it provides an accurate response to the polarization changes regarding the anamorphic signals. The performance of the CVQKD system can be increased in terms of secret key rates and maximal transmission distance as well. Numerical simulation shows the positive effect of the ML-based DPC while taking into account the secret key rate of the CVQKD system. The ML-based DPC effectively reduces the feasibility of information leakage and hence results in an increased secret key rate of the practical CVQKD system. Full article

(This article belongs to the Special Issue Quantum Computation and Its Applications)

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10 pages, 11180 KiB

Open AccessArticle

Note about Passive Continuous Variable Quantum Key Distribution over Turbulent Atmospheric Channel

by Yun Mao, Yiwu Zhu, Yijun Wang and Ying Guo

Symmetry 2022, 14(10), 2128; https://doi.org/10.3390/sym14102128 - 13 Oct 2022

Viewed by 1701

Abstract

Continuous variable quantum key distribution (CVQKD) has been implemented over the atmospheric channels over free space. However, atmospheric turbulence weakens the quality of the transmitting quantum signals and hence decreases the secret key rate of the system. Here, we suggest an atmospheric turbulence [...] Read more.

Continuous variable quantum key distribution (CVQKD) has been implemented over the atmospheric channels over free space. However, atmospheric turbulence weakens the quality of the transmitting quantum signals and hence decreases the secret key rate of the system. Here, we suggest an atmospheric turbulence channel model that involves atmospheric turbulence bubbles and demonstrates the implementation feasibility of passive CVQKD with spectrum resources in the terahertz band over the atmospheric turbulence channel. We achieve the channel transmittance characterized by the refractive index and the wavefront distortions. Moreover, an adaptive optics (AO) unit is used for performance improvement while considering the effect of the thermal noise and excess noise on the atmospheric turbulence bubble-modeled channel. Numerical simulations show that the AO-involved detection scheme can result in reductions in excess noise when being faced with the floating clouds and mist in atmospheric turbulence, which results in performance improvements in terms of secret key rate, which confirms the utility of the high-rate and long-distance CVQKD in terahertz (THz) for practical implementations. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry in Quantum Cryptography)

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17 pages, 801 KiB

Open AccessArticle

Noiseless Attenuation for Continuous-Variable Quantum Key Distribution over Ground-Satellite Uplink

by Shengjie Xu, Yin Li, Yijun Wang, Yun Mao, Zhiyue Zuo, Xinchao Ruan and Ying Guo

Appl. Sci. 2021, 11(23), 11289; https://doi.org/10.3390/app112311289 - 29 Nov 2021

Cited by 4 | Viewed by 1882

Abstract

Satellite-based quantum key distribution (QKD) has lately received considerable attention due to its potential to establish a secure global network. Associated with its application is a turbulent atmosphere that sets a notable restriction to the transmission efficiency, which is especially challenging for ground-to-satellite [...] Read more.

Satellite-based quantum key distribution (QKD) has lately received considerable attention due to its potential to establish a secure global network. Associated with its application is a turbulent atmosphere that sets a notable restriction to the transmission efficiency, which is especially challenging for ground-to-satellite uplink scenarios. Here, we propose a novel noiseless attenuation (NA) scheme involving a zero-photon catalysis operation for source preparation to improve the performance of continuous-variable (CV) QKD over uplink. Numerical analysis shows that the NA-based CV-QKD, under attenuation optimization, outperforms the traditional CV-QKD, which is embodied in extending the allowable zenith angle while improving the effective communication time. Attributing to characteristics of the attenuation optimization, we find that the NA-involved source preparation improves the security bound by relatively reducing the amount of information available to eavesdroppers. Taking the finite-size effect into account, we achieve a tighter bond of security, which is more practical compared with the asymptotic limit. Full article

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13 pages, 1886 KiB

Open AccessArticle

High-Rate Continuous-Variable Quantum Key Distribution with Orbital Angular Momentum Multiplexing

by Xinchao Ruan, Wenhao Shi, Guojun Chen, Wei Zhao, Hang Zhang and Ying Guo

Entropy 2021, 23(9), 1187; https://doi.org/10.3390/e23091187 - 9 Sep 2021

Cited by 3 | Viewed by 2807

Abstract

The secret key rate is one of the main obstacles to the practical application of continuous-variable quantum key distribution (CVQKD). In this paper, we propose a multiplexing scheme to increase the secret key rate of the CVQKD system with orbital angular momentum (OAM). [...] Read more.

The secret key rate is one of the main obstacles to the practical application of continuous-variable quantum key distribution (CVQKD). In this paper, we propose a multiplexing scheme to increase the secret key rate of the CVQKD system with orbital angular momentum (OAM). The propagation characteristics of a typical vortex beam, involving the Laguerre–Gaussian (LG) beam, are analyzed in an atmospheric channel for the Kolmogorov turbulence model. Discrete modulation is utilized to extend the maximal transmission distance. We show the effect of the transmittance of the beam over the turbulent channel on the secret key rate and the transmission distance. Numerical simulations indicate that the OAM multiplexing scheme can improve the performance of the CVQKD system and hence has potential use for practical high-rate quantum communications. Full article

(This article belongs to the Special Issue Practical Quantum Communication)

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11 pages, 1005 KiB

Open AccessArticle

Performance Analysis of the Shore-to-Reef Atmospheric Continuous-Variable Quantum Key Distribution

by Shujing Zhang, Chen Xiao, Chun Zhou, Xiang Wang, Jianshu Yao, Hailong Zhang and Wansu Bao

Appl. Sci. 2019, 9(24), 5285; https://doi.org/10.3390/app9245285 - 4 Dec 2019

Cited by 2 | Viewed by 1860

Abstract

The effects of sea salt concluded in oceanic atmosphere are ubiquitous in practical wireless optical links. Here a shore-to-reef atmospheric continuous-variable quantum key distribution (CVQKD) model is established on the basis of Mie scattering theory, with the aim to characterize the complex case [...] Read more.

The effects of sea salt concluded in oceanic atmosphere are ubiquitous in practical wireless optical links. Here a shore-to-reef atmospheric continuous-variable quantum key distribution (CVQKD) model is established on the basis of Mie scattering theory, with the aim to characterize the complex case of beam propagation in the atmosphere caused by sea salt particles. The effects on performance of shore-to-reef atmospheric CVQKD under the sea salt particles and relative humidity are also studied. Simulation results show that the increase of particle radius and relative humidity will lead to the degeneration of secret key rate. Extending the channel distance also reduces the secret key rate. This paper provides a basis for the establishment of practical shore-to-reef atmospheric CVQKD model. The research of this paper also gives momentous reference for the study of optical communication channel models with other suspended particles over the ocean. Full article

(This article belongs to the Special Issue Quantum Communications and Quantum Networks)

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17 pages, 909 KiB

Open AccessArticle

Parameter Optimization Based BPNN of Atmosphere Continuous-Variable Quantum Key Distribution

by Yu Su, Ying Guo and Duan Huang

Entropy 2019, 21(9), 908; https://doi.org/10.3390/e21090908 - 18 Sep 2019

Cited by 11 | Viewed by 3262

Abstract

The goal of continuous variable quantum key distribution (CVQKD) is to be diffusely used and adopted in diverse scenarios, so the adhibition of atmospheric channel will play a crucial part in constituting global secure quantum communications. Atmospheric channel transmittance is affected by many [...] Read more.

The goal of continuous variable quantum key distribution (CVQKD) is to be diffusely used and adopted in diverse scenarios, so the adhibition of atmospheric channel will play a crucial part in constituting global secure quantum communications. Atmospheric channel transmittance is affected by many factors and does not vary linearly, leading to great changes in signal-to-noise ratio. It is crucial to choose the appropriate modulation variance under different turbulence intensities to acquire the optimal secret key rate. In this paper, the four-state protocol, back-propagation neural network (BPNN) algorithm was discussed in the proposed scheme. We employ BPNN to CVQKD, which could adjust the modulation variance to an optimum value for ensuring the system security and making the system performance optimal. The numerical results show that the proposed scheme is equipped to improve the secret key rate efficiently. Full article

(This article belongs to the Special Issue Quantum Information Processing)

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