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Free Space Security Analysis of CV-QKD Transmission in Ground-to-HAP under Collective Attack

Nancy Alshaer, Tawfik Ismail

Published Nov 20, 2023• 0 citations
Publisher

Abstract

Abstract In the contemporary digital era, ensuring the security of sensitive data and communication is of paramount significance. Encryption methods have been widely employed to safeguard data transmission over public channels. However, the exponential growth in computational power has led to concerns regarding the potential vulnerability of encryption methods. Consequently, breaking encryption poses a significant threat to data privacy. In response to these challenges, the field of quantum cryptography has emerged as a promising solution, offering a fundamentally unbreakable approach to secure communication. One of the key advancements in quantum cryptography is quantum key distribution (QKD). This secure communication mechanism relies on the principles of quantum mechanics to generate encryption keys, enabling secure information exchange between parties. This paper focuses on analysis of the quantum channel between the optical ground station (OGS) and the high-altitude platform System (HAPS). The research involves a meticulous examination and optimization of various system parameters such as performance secret key rate (SKR), electronic noise, modulation variance, and zenith angle. Remarkably, the SKR for a HAPS operating at a vertical altitude of 20 km, with a zenith angle of 20 degrees and a pulse generation rate of 500 MHz, is approximately 84 Mb/s and 44.5 Mb/s for homodyne and heterodyne detection, respectively. This information highlights the potential of quantum cryptography in providing secure communication channels that are resilient to cryptographic attacks.

DOI
10.21203/rs.3.rs-3618757/v1

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Abstract In the contemporary digital era, ensuring the security of sensitive data and communication is of paramount significance. Encryption methods have been widely employed to safeguard data transmission over public channels. However, the exponential growth in computational power has led to concerns regarding the potential vulnerability of encryption methods. Consequently, breaking encryption poses a significant threat to data privacy. In response to these challenges, the field of quantum cryptography has emerged as a promising solution, offering a fundamentally unbreakable approach to secure communication. One of the key advancements in quantum cryptography is quantum key distribution (QKD). This secure communication mechanism relies on the principles of quantum mechanics to generate encryption keys, enabling secure information exchange between parties. This paper focuses on analysis of the quantum channel between the optical ground station (OGS) and the high-altitude platform System (HAPS). The research involves a meticulous examination and optimization of various system parameters such as performance secret key rate (SKR), electronic noise, modulation variance, and zenith angle. Remarkably, the SKR for a HAPS operating at a vertical altitude of 20 km, with a zenith angle of 20 degrees and a pulse generation rate of 500 MHz, is approximately 84 Mb/s and 44.5 Mb/s for homodyne and heterodyne detection, respectively. This information highlights the potential of quantum cryptography in providing secure communication channels that are resilient to cryptographic attacks.
In the contemporary digital era, ensuring the security of sensitive data and communication is of paramount significance. Encryption methods have been widely employed to safeguard data transmission over public channels. However the exponential growth in computational power has led to concerns regarding the potential vulnerability of encryption methods. Consequently, breaking encryption poses a significant threat to data privacy. In response to these challenges, the field of quantum cryptography has emerged as a promising solution, offering a fundamentally unbreakable approach to secure communication. One of the key advancements in quantum cryptography is quantum key distribution (QKD). This secure communication mechanism relies on the principles of quantum mechanics to generate encryption keys, enabling secure information exchange between parties. This paper focuses on analysis of the quantum channel between the optical ground station (OGS) and the high-altitude platform System (HAPS). The research involves a meticulous examination and optimization of various system parameters such as performance secret key rate (SKR), electronic noise, modulation variance, and zenith angle. Remarkably, the SKR for a HAPS operating at a vertical altitude of 20 km, with a zenith angle of 20 degrees and a pulse generation rate of 500MHz500 \mathbf{M H z}500MHz, is approximately 84 Mb/s84 \mathbf{~ M b} / \mathbf{s}84 Mb/s and 44.5 Mb/s\mathbf{M b} / \mathbf{s}Mb/s for homodyne and heterodyne detection, respectively. This information highlights the potential of quantum cryptography in providing secure communication channels that are resilient to cryptographic attacks.
The encryption process is essential for ensuring data protection and privacy. However, breaking the encrypted data becomes feasible as computational power grows exponentially. This leads to insecure data transmission over a public channel. Quantum key distribution is a secure communication mechanism that allows shared parties to exchange encryption keys periodically. Furthermore, it has the ability to detect eavesdropping since the error level becomes higher when she attempts to access the communication channel. This paper studies and analysis the performance of the uplink quantum channel between the ground station and the high-altitude platform system (HAPS). In order to achieve optimal performance, the system parameters, such as modulation variance, receiver aperture, and zenith angle influence, are tuned with consideration to the effects of weather conditions and beam wandering. For a HAP at vertical altitude 20 km and with 20° zenith angle and 100 MHz pulse generation rate, a raw key rate of 57 Mb/s and 63 Mb/s is estimated for homodyne and heterodyne detection schemes, respectively.
Unmanned aerial vehicles (UAV) based on free-space optical (FSO) systems combine the benefits of both the high data rate of the FSO and the mobility of UAV. However, cumulative effects of laser beam divergence and turbulence-induced fading on the received irradiance in the FSO link might allow an external eavesdropper located near the authorized receiver to break the transmission under certain conditions. Quantum key distribution (QKD) is a technique of secure communication that employs quantum mechanics-based cryptography principles. A combination of a continuous-variable quantum key distribution (CV-QKD) and Gaussian modulation of quantum coherent states (GMCS) enables a relatively secure communication system against collective attacks over FSO transmission links. However, the performance is restricted and degraded due to the influence of atmospheric turbulence and excess noise. This paper aims to evaluate the performance of a secured UAV-based FSO system utilizing prepare and measure CV-QKD protocol based on GMCS under collective attack in terms of quantum bit error rate (QBER), outage probability, and secret key rate (SKR) considering the impairments of the FSO channel, link budget, deviations in the position and attitude angles of the UAV, channel fluctuating transmittance, and excess noise. The system parameters, including transmit power, receiver’s field-of-view, and beam divergence angle, are optimized to satisfy the system’s design criteria of threshold-QBER=10−3=10^{-3}=10−3and threshold outage probability=10−2=10^{-2}=10−2. The proposed system tolerates boresight displacement up to 7 cm with the optimized values. The Closed-form expressions and analytical results are confirmed by Monte-Carlo simulations.
Quantum key distribution (QKD) is one of the most mature quantum technologies and can provide quantum-safe security in future communication networks. Since QKD in fiber is limited to a range of few hundred kilometers, one approach to bridge continental scale distances may be the use of high altitude pseudo satellites (HAPS) as mobile trusted nodes in the stratosphere. In parallel, free-space laser communication for high rate data transmission has been a subject of research and development for several decades and its commercialization is progressing rapidly. Important synergies exist between classical free-space communication and QKD systems since the quantum states are often implemented using the same degrees of freedom such as polarization or field amplitude and phase. These synergies can be used to benefit from the progress in classical free-space laser communication in QKD applications. In this paper, the use case of QKD in a stratospheric environment is described wherein HAPS may serve as relay station of secret keys and encrypted data. The mission scenario and HAPS capabilities are analyzed to derive special requirements on the stratospheric laser terminal, the link geometry and the ground segment with respect to a feasibility demonstration. To obtain a flexible and compatible system, discrete variable and continuous variable QKD protocols are considered to be implemented side by side in the HAPS payload. Depending on the system parameters, it can be beneficial to use the one or the other kind of protocol. Thus, a direct comparison of both in one and the same system is of scientific interest. Each of the protocols has particular requirements on coupling efficiency and implementation. Link budget calculations are performed to analyze possible distances, key rates and data transmission rates for the different schemes. In case of the QKD system, the mean coupling efficiency is of main interest, i.e. signal fluctuations arising from atmospheric turbulence must be taken into account in the security proof, but the buffered key generation relaxes real-time requirements. This is different to classical communications, where the corresponding fading loss must be assessed. A system architecture is presented that comprises the optical aircraft terminal, the optical ground terminal and the most important subsystems that enable implementation of the considered QKD protocols. The aircraft terminal is interfaced with the dedicated quantum transmitter module (Alice) and the ground station with the dedicated quantum receiver module (Bob). The optical interfaces are SMF couplings which put high requirements on the receiving optics, in particular the need for wave-front correction with adaptive optics. The findings of the system study are reviewed and necessary next steps pointed out.
Abstract High-altitude platforms (HAPs) offer enhanced channel transmissivity compared to satellite-based links for free-space continuous-variable quantum key distribution. However, the inherent non-stationarity of the atmospheric channel, dominated by turbulence-induced fading, poses significant challenges to link stability and the consistent maximization of the secret key rate (SKR). To address this, real-time dynamic optimization of system parameters is essential for adapting to channel fluctuations. This study establishes a comprehensive physical transmission model for HAP uplinks to elucidate the impact mechanisms of the initial beam waist and transmitter modulation variance on the SKR. We quantitatively evaluate the performance gains yielded by single-parameter independent optimization versus dual-parameter joint optimization strategies. while joint parameter optimization yields the theoretical performance upper bound, dynamic regulation of the modulation variance emerges as the decisive factor in improving the signal-to-noise ratio and maximizing the SKR. Given the high hardware complexity and response latency associated with adaptive optical zooming mechanisms, we demonstrate that the ‘modulation variance-only’ optimization strategy constitutes the optimal engineering solution. This approach achieves quasi-optimal performance comparable to the joint strategy while significantly reducing implementation complexity, providing a robust and feasible design paradigm for future HAP-based quantum networks.
This research explores the fundamental principles of quantum computing and their application in enhancing communication security through Quantum Key Distribution (QKD) in free-space channels. Classical cryptographic methods face inherent limitations, particularly with the advent of quantum computational capabilities. Quantum mechanics, specifically the principles of superposition and entanglement, offers a robust framework for secure communication, ensuring that any attempt at eavesdropping inevitably perturbs the quantum state, thus revealing the intruder's presence. Through comprehensive simulations, this study analyzes the performance of QKD systems in free-space communication. Key parameters such as transmittance efficiency ( ), Quantum Bit Error Rate (QBER), and Secret Key Rate (SKR) are evaluated. Results indicate that transmittance efficiency in free space generally decreases with increasing zenith angle, with downlink scenarios (day and night) exhibiting higher efficiencies compared to uplink during the night. For all protocols, simulations demonstrate an increase in QBER and a corresponding decrease in SKR as the zenith angle increases, with downlink performance consistently surpassing uplink in terms of a higher SKR and a lower QBER