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Optical Fiber Technology

Security enhancement of quantum noise stream cipher system based on optical temporal scrambling

Zhaoyun Li, Yukun Zhang, Hai-Yue Pang, Qingsong Luo, Xin Zhang, Yugang Huang, Zhi-Yong Tao, Ya-Xian Fan

Published Jan 19, 2023• 9 citations
Publisher
DOI
10.1016/j.yofte.2023.103245

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【Objective】To further enhance the security of the Intensity Modulated (IM) / Quantum Noise Stream Cipher (QNSC) system, this paper proposes a security enhancement scheme for the IM/QNSC system assisted by chaotic encryption.【Methods】In this scheme, the legitimate transmitter encrypts the low-order 4-level Pulse Amplitude Modulation (PAM-4) signal into an ultra-high-order PAM-256 signal. Then it uses the intensity chaos generated by a nonlinear delayed chaos source to encrypt the ultra-high-order PAM signal, so as to enhance the security of the IM/QNSC system.【Results】This scheme was numerically verified in IM/QNSC dispersion-managed transmission systems with rates of 56 and 112 Gbit/s. The results show that under the 7% Hard Decision-Forward Error Correction (HD-FEC) threshold, the 56 and 112 Gbit/s encrypted systems achieve transmissions of 400 and 300 km. Under the 20% Soft Decision-Forward Error Correction (SD-FEC) threshold, they achieve transmissions of 700 and 600 km. The security analysis of the scheme shows that the Number of Masked Symbols (NMS) and Detection Failure Probability (DFP) of the scheme are higher than those of the original IM/QNSC system.【Conclusion】Chaotic encryption assistance amplifies the eavesdropping noise in the QNSC system. Compared with the original IM/QNSC system, it improves the system security.

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Among physical layer encryption schemes, the quantum noise stream cipher (QNSC) has garnered significant attention due to its compatibility with high-speed commercial fiber-optic communication systems. After careful analysis of the encryption scheme, we reveal that QNSC transmission systems exhibit a security vulnerability in their encoding scheme. This vulnerability limits quantum noise to alerting high-order information bits in plaintext-dependent regions, creating structured ciphertext concealment. Numerical simulation and experimental verification both indicate that an eavesdropper can use quantization-attack to crack this vulnerability. Existing security assessment methods will overestimate the system’s security under quantization-attack. In addition, system security demonstrates a strong linear dependence on the plaintext modulation format, rather than the ciphertext modulation format as is widely presumed. To further enhance system security, the probability distribution is further introduced into the encoding process of ciphertext. The experiment results show that we not only achieved random concealment of ciphertext by quantum noise but also enhanced the eavesdropper’s symbol error rate by ∼86 % and maximally expanded the key space of the QAM-QNSC system by 2 27.2 .

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【Objective】To further enhance the security of the Intensity Modulated (IM) / Quantum Noise Stream Cipher (QNSC) system, this paper proposes a security enhancement scheme for the IM/QNSC system assisted by chaotic encryption.【Methods】In this scheme, the legitimate transmitter encrypts the low-order 4-level Pulse Amplitude Modulation (PAM-4) signal into an ultra-high-order PAM-256 signal. Then it uses the intensity chaos generated by a nonlinear delayed chaos source to encrypt the ultra-high-order PAM signal, so as to enhance the security of the IM/QNSC system.【Results】This scheme was numerically verified in IM/QNSC dispersion-managed transmission systems with rates of 56 and 112 Gbit/s. The results show that under the 7% Hard Decision-Forward Error Correction (HD-FEC) threshold, the 56 and 112 Gbit/s encrypted systems achieve transmissions of 400 and 300 km. Under the 20% Soft Decision-Forward Error Correction (SD-FEC) threshold, they achieve transmissions of 700 and 600 km. The security analysis of the scheme shows that the Number of Masked Symbols (NMS) and Detection Failure Probability (DFP) of the scheme are higher than those of the original IM/QNSC system.【Conclusion】Chaotic encryption assistance amplifies the eavesdropping noise in the QNSC system. Compared with the original IM/QNSC system, it improves the system security.
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.
Among physical layer encryption schemes, the quantum noise stream cipher (QNSC) has garnered significant attention due to its compatibility with high-speed commercial fiber-optic communication systems. After careful analysis of the encryption scheme, we reveal that QNSC transmission systems exhibit a security vulnerability in their encoding scheme. This vulnerability limits quantum noise to alerting high-order information bits in plaintext-dependent regions, creating structured ciphertext concealment. Numerical simulation and experimental verification both indicate that an eavesdropper can use quantization-attack to crack this vulnerability. Existing security assessment methods will overestimate the system’s security under quantization-attack. In addition, system security demonstrates a strong linear dependence on the plaintext modulation format, rather than the ciphertext modulation format as is widely presumed. To further enhance system security, the probability distribution is further introduced into the encoding process of ciphertext. The experiment results show that we not only achieved random concealment of ciphertext by quantum noise but also enhanced the eavesdropper’s symbol error rate by ∼86 % and maximally expanded the key space of the QAM-QNSC system by 2 27.2 .