Quantum noise stream cipher (QNSC) is an encryption technique that leverages redundant information obscured by quantum noise to achieve an exponential increase in attack complexity, while continuous-variable quantum key distribution (CV-QKD) can provide such redundant information by generating secret keys. Notably, the optical architectures employed in these two schemes exhibit significant similarities. In this work, we employ polarization division multiplexing (PDM) to enhance channel capacity, enabling simultaneous transmission of signals under two different protocols over a single channel. To mitigate dynamic polarization state variations induced during signal propagation, we implement a polarization-interleaved subcarrier modulation (PISCM) scheme. We demonstrate that at a transmission distance of 20 km, the QKD secure key rate can be maintained at 4.93 Mbps, while the QNSC transmission rate reaches 100 Mbps. The expansion of the key rate from 4 Mbps to 400 Mbps using a linear feedback shift register (LFSR) enables synchronization with the 100 Mbps QNSC signal, realizing a promising pathway toward an integrated communication and encryption system.
Quantum noise stream cipher (QNSC) is an encryption technique that leverages redundant information obscured by quantum noise to achieve an exponential increase in attack complexity, while continuous-variable quantum key distribution (CV-QKD) can provide such redundant information by generating secret keys. Notably, the optical architectures employed in these two schemes exhibit significant similarities. In this work, we employ polarization division multiplexing (PDM) to enhance channel capacity, enabling simultaneous transmission of signals under two different protocols over a single channel. To mitigate dynamic polarization state variations induced during signal propagation, we implement a polarization-interleaved subcarrier modulation (PISCM) scheme. We demonstrate that at a transmission distance of 20 km, the QKD secure key rate can be maintained at 4.93 Mbps, while the QNSC transmission rate reaches 100 Mbps. The expansion of the key rate from 4 Mbps to 400 Mbps using a linear feedback shift register (LFSR) enables synchronization with the 100 Mbps QNSC signal, realizing a promising pathway toward an integrated communication and encryption system.
We have been intensively studying quantum noise stream cipher (QNSC) transmission technique using quadrature amplitude modulation (QAM) with a view to realizing a high-speed and long-distance secure communication system [1]. In this talk, we describe our recent demonstration of an on-line 70 Gbit/s, 128 QAM/QNSC transmission over 100 km with a continuous variable quantum key distribution (CV-QKD) system [2], in which a shared key is transmitted online via the CV-QKD so that the key is shared for a certain time period with absolutely no risk of being eavesdropped.
Quantum Noise Stream Cipher (QNSC) has emerged as a physical-layer encryption technique that exploits quantum noise and non-orthogonal coherent-state modulation to secure optical communication. However, the security of QNSC relies exceedingly on the secrecy and freshness of its seed key. Quantum Key Distribution (QKD), on the other hand, provides information-theoretically secure key exchange rooted in the laws of quantum mechanics. The convergence of these two paradigms, i.e., integrated QKD-QNSC architectures, offers a compelling solution to each of their limitations. In such integrated systems, QKD continuously supplies and refreshes the secret seed key that governs QNSC modulation. Thus, governing a unified security framework that couples provably secure key establishment with high-speed quantum-enhanced physical-layer encryption. This work presents a comprehensive review of QNSC systems, examining their operating principles, security models under various attacks, and their integration with QKD systems. We analyze the security interplay between the key generation and encryption layers and survey experimental demonstrations and architectural progress toward practical deployment. Furthermore, we identify the open challenges and future research directions that must be addressed to realize fully integrated, quantum-secured optical communication networks at a practical scale.
Continuous-variable quantum key distribution (CV-QKD) with local local oscillator (LLO) is well-studied for its security and simplicity, but enhancing performance and interference resistance remains challenging. In this paper, we utilize polarization division multiplexing (PDM) to enhance spectral efficiency and significantly increase the key rate of the CV-QKD system. To address dynamic changes in the state of polarization (SOP) in Gaussian modulated coherent states (GMCS) signals due to polarization impairment effects, we designed a time-division multiplexing pilot scheme to sense and recover changes in SOP in GMCS signals, along with other digital signal processing methods. Experiments over 20 km show that our scheme maintains low excess noise levels (0.062 and 0.043 in shot noise units) and achieves secret key rates of 4.65 Mbps and 5.66 Mbps for the two polarization orientations, totaling 10.31 Mbps. This work confirms the effectiveness of PDM GMCS-CV-QKD and offers technical guidance for high-rate QKD within metropolitan areas.
Quantum secure communication technology, grounded in the principles of quantum mechanics, has revolutionized traditional cryptographic methods, which predominantly rely on mathematical algorithms and logical transformations. Quantum key distribution (QKD) facilitates the secure sharing of symmetric keys between legitimate parties, ensuring the integrity and confidentiality of information in communication channels. Among various QKD schemes, continuous variable quantum key distribution (CV-QKD) has emerged as a viable alternative to the more established discrete variable quantum key distribution (DV-QKD). CV-QKD boasts several advantages, including straightforward deployment, reduced operational costs, and stable signal quality, positioning it as a significant component of the quantum communication landscape. Quantum noise stream cipher (QNSC) represents a technique that employs redundant data streams to encrypt plaintext. Notably, QNSC shares structural similarities with the optical path used in quantum key distribution, allowing for compatibility with existing QKD infrastructure. Furthermore, the keys generated through quantum key distribution ensure absolute security, enabling them to substitute the data streams produced by pseudo-random sequences traditionally used in classical encryption schemes. This substitution enhances the overall security framework of the quantum noise stream encryption approach. The quantum access network (QAN) extends quantum key distribution capabilities from point-to-point connections to point-to-multipoint configurations, thereby becoming an essential component of contemporary network architectures. By interlinking multiple end users with a network backbone, quantum access networks can seamlessly integrate with quantum key distribution protocols. This integration offers a cost-effective and scalable solution for user access to the network. Extensive experimental verifications have demonstrated the viability of downstream access networks, indicating that the merging of quantum access network structures with quantum stream encryption technologies can yield a comprehensive quantum experimental platform. On this platform, security keys are derived through quantum key distribution, which subsequently facilitates the encryption of plaintext information. Notably, experimental validations involving eight users have been successfully executed on this platform, underscoring its practical applicability and effectiveness.
Abstract Quantum cryptography communication encompasses both quantum key distribution (QKD) and the encryption and decryption of plaintext. Continuous-variable QKD (CVQKD) leverages the fundamental principles of physics to enable legitimate parties to share secure keys, while the CVQKD-compatible quantum noise stream cipher (QNSC) exploits quantum fluctuations to further obscure the ciphertext encrypted with these keys. Integrating these two functionalities into a unified system represents a promising developmental trend. However, existing integrated architectures typically rely on multiplexing two separate optical paths and have been demonstrated exclusively over optical fibers. Here, a unified local local oscillator (LLO) quantum cryptography architecture operating over a free-space channel is proposed and experimentally demonstrated. Requiring only simple software-defined switching, our payload-efficient architecture executes both CVQKD and QNSC functionalities utilizing a single optical setup. Over an indoor free-space channel with emulated time-varying atmospheric disturbances, an asymptotic secret key rate of 35.4292 kbps is obtained at a maximum channel attenuation of 19.5054 dB for the CVQKD mode. For the QNSC mode, an encrypted image is successfully transmitted, yielding pixel accuracies of 99.58% and 96.39% under channel attenuations of 10.1690 dB and 12.0620 dB, respectively. This work validates the feasibility of integrated quantum cryptography architectures in complex environments, marking a meaningful step toward constructing payload-constrained quantum communication networks.
Classical communication and quantum key distribution (QKD) share similarities in signal modulation, transmission, and reception, providing a foundation for their integration. This paper proposes a novel protocol for simultaneous quantum and classical communication in short-distance Continuous-Variable QKD (CV-QKD). The protocol employs polarization-state encoding of classical information with weak coherent states, allowing for the concurrent transmission of quantum and classical data without the need for classical optical pulses. A noise model is established to analyze the system’s excess noise under varying modulation variances, along with the performance of both classical and quantum communication. Simulation results indicate that our proposed protocol can achieve a secure key rate of no less than 1.05Mbps over a distance of 20km.