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Intensity Modulated Quantum Noise Stream Cipher System Assisted by Optical Chaos

Gu Sijia, JIANG Lin, Yan Lianshan, Sun Jihui, FENG Jiacheng, 易安林 Yi Anlin, PAN Wei

Published Dec 1, 2025• 0 citations
OpenAlex

Abstract

【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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Photonics Research•Oct 21, 2025•2 citations
【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.
An ultra-high-order QAM quantum noise stream cipher (QNSC) scheme assisted by intensity and phase chaotic encryption is proposed. In this scheme, the legal transmitter (Alice) first encrypts the original low-order QAM signal into an ultra-high-order QAM signal according to the pre-shared seed key based on the Y-00 protocol, and then conceals the intensity and phase information of the ultra-high-order QAM signal through the intensity and phase chaos generated from a nonlinear delay chaotic source for enhancing the security. The intensity and phase chaotic carrier can be eliminated by the open-loop chaotic synchronization module at the legal receiver (Bob). The scheme was numerically verified in 112 Gbit/s (28 GBaud 16QAM plaintext) and 168 Gbit/s (28 GBaud 64QAM plaintext) 65536QAM/QNSC systems, which can achieve 600 km and 150 km transmission at 7% HD-FEC threshold, and 1000 km and 350 km transmission at 20% SD-FEC threshold, respectively. Meanwhile, the number of masked signals (NMS) and the detection failure probability (DFP) in the scheme are obviously higher than in the original QAM/QNSC system. We believe that the proposed scheme is a promising strategy for enhancing the security of QAM/QNSC transmission systems.
Abstract Data security is a key feature of future communications networks. Physical layer introduces rich physical mechanisms to increase the complexity of deciphering and provides extensive protection, but faces challenges in compatibility with commercial systems. Quantum noise stream cipher (QNSC) has been proposed as a promising solution to overcome this problem by fusing the stream cryptography regime with the quantum noise masking physical mechanism. However, it has limitations in terms of digital to analog conversion and clock data synchronization of ultra-high-order ciphertext as well as flexible control of masking noise. Here we report a 147.9-Gbps device-compatible quadrature amplitude modulation (QAM) QNSC secure scheme over 75-km fiber. Thanks to delta-sigma modulator, the transmission of 220 × 220-order QAM-QNSC signal are established through the low-order digital signal. We develop a theoretical model for flexibly regulating the transmission rate and security performance. Broadband optical chaos introduces true randomness and acts on the masking noise.
A quantum noise stream cipher scheme (QNSC) based on triangular quadrature amplitude modulation (TQAM) and the secret probabilistic shaping (SPS) is studied. Compared with rectangular quadrature amplitude modulation (QAM), TQAM is a more compact symmetrical structure, which results in better transmission performance and greater noise masking number. Then, SPS is realized, where the probabilistic shaping information as the secret key is masked into noise and transmitted with the encrypted signal simultaneously. The combination of SPS and QNSC makes it impossible for an attacker to obtain the ciphertext, which enhances the security of QNSC scheme without introducing additional key. TQAM and probabilistic shaping improve the transmission performance of QNSC scheme. Under 7% forward error correction (FEC) threshold in back-to-back system, compared with QAM/QNSC systems, TQAM/QNSC provides an OSNR gain of ∼ 0.6 dB, and SPS-TQAM/QNSC provides an OSNR gain of ∼ 1.2 dB. The proposed scheme is demonstrated with the net data rate of 34.28 Gbit/s over 140 km single-span standard single mode fiber.
A probabilistic shaping (PS) quadrature amplitude modulation (QAM) based on Y-00 quantum noise stream cipher (QNSC) has been proposed. We experimentally demonstrated this scheme with data rate of 201.6Gbit/s over a 1200-km standard single mode fiber (SSMF) under a 20% SD-FEC threshold. Accounting for the 20% FEC and 6.25% pilot overhead, the achieved net data rate is ∼160Gbit/s. In the proposed scheme, a mathematical cipher (Y-00 protocol) is utilized to convert the original low-order modulation PS-16 (2 2 × 2 2 ) QAM into ultra-dense high-order modulation PS-65536 (2 8 × 2 8 ) QAM. Then, the physical randomness of quantum (shot) noise at photodetection and amplified spontaneous emission (ASE) noise from optical amplifiers are employed to mask the encrypted ultra-dense high-order signal for further improving the security. We further analyze the security performance by two metrics known in the reported QNSC systems, namely the number of masked signals (NMS) of noise and the detection failure probability (DFP). Experimental results show it is difficult or even impossible to extract transmission signals from quantum or ASE noise for an eavesdropper (Eve). We believe that the proposed PS-QAM/QNSC secure transmission scheme has the potential to be compatible with existing high-speed long-distance optical fiber communication systems.
In the quantum noise stream cipher (QNSC) system, the low-order plaintext is encrypted by pre-shared keys into high-order ciphertext. However, high-speed optical communication systems have a huge demand for pre-shared keys. On the other hand, the separation of the secure communications sub-system from the secure key distribution (SKD) sub-system increases potential security risks and introduces additional resources overhead. In this letter, we propose an artificial amplitude noise-based SKD scheme (AAN-SKD) in QAM/QNSC to generate secret key for legal parties accordingly. The two orthogonal PAM symbols are superimposed to generate QAM symbols. Thus, the AAN-SKD can also be implemented in PAM modulation. In addition, the data transmission and AAN-SKD are completed in the same channel. Experimental results indicate that the key generation rate and key consistency ratio of the proposed scheme can reach188.22Mbit/s188.22Mbit/s188.22Mbit/sand 91%, respectively. Compared with quantum key distribution, the AAN-SKD has the advantage of lower cost, better compatibility, and a higher key rate.
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 .