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Journal of Optical Communications and Networking

CDMA-based quantum noise stream cipher for passive optical networks

Yuchao Liu, Tao Wang, Lang Li, Yuehan Xu, Xu Liu, Yankai Xu, Beibei Zhang, Peng Huang, Guihua Zeng

Published Jan 7, 2026• 0 citations
Publisher

Abstract

The quantum noise stream cipher (QNSC) scheme, grounded in Heisenberg’s uncertainty principle, can facilitate secure communication by employing noise to obfuscate multi-base encrypted signals. The current research primarily focuses on point-to-point performance, while studies on point-to-multipoint schemes remain limited due to compatibility issues with multiple access technologies. This study presents a QNSC scheme for passive optical networks based on code-division multiple access (CDMA). In our scheme, different user datasets are combined into one dataset via CDMA and then encrypted using the QNSC protocol. Each user can recover their corresponding dataset from the encrypted signal by employing the same security keys along with a distinct pseudo-noise code (PN code). Through simulation studies, we found that under the condition of being able to decode correctly, as the number of users increases, the optical signal-to-noise ratio (OSNR) at the receiver decreases, which leads to a gradual rise in the eavesdropper’s detection failure probability (DFP). Furthermore, the network capacity is correlated with the number of modulation bits, as the increase in modulation bits directly translates to an enhancement in the data’s carrying capability. We have conducted verification experiments, and the results confirmed that four users can acquire 64 QAM/QNSC plaintext data with an average transmission rate of 600 Mbit/s over a transmission distance of 20 km. These data were encrypted in the constellation with 64×64 symbols, achieving a DFP of up to 99.3%, and each user successfully decoded them via CDMA. We have successfully extended the fundamental point-to-point QNSC scheme to accommodate point-to-multipoint passive optical networks, establishing the foundational framework for the future large-scale deployment of quantum networks.

DOI
10.1364/jocn.565150

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The quantum noise stream cipher (QNSC) scheme, grounded in Heisenberg’s uncertainty principle, can facilitate secure communication by employing noise to obfuscate multi-base encrypted signals. The current research primarily focuses on point-to-point performance, while studies on point-to-multipoint schemes remain limited due to compatibility issues with multiple access technologies. This study presents a QNSC scheme for passive optical networks based on code-division multiple access (CDMA). In our scheme, different user datasets are combined into one dataset via CDMA and then encrypted using the QNSC protocol. Each user can recover their corresponding dataset from the encrypted signal by employing the same security keys along with a distinct pseudo-noise code (PN code). Through simulation studies, we found that under the condition of being able to decode correctly, as the number of users increases, the optical signal-to-noise ratio (OSNR) at the receiver decreases, which leads to a gradual rise in the eavesdropper’s detection failure probability (DFP). Furthermore, the network capacity is correlated with the number of modulation bits, as the increase in modulation bits directly translates to an enhancement in the data’s carrying capability. We have conducted verification experiments, and the results confirmed that four users can acquire 64 QAM/QNSC plaintext data with an average transmission rate of 600 Mbit/s over a transmission distance of 20 km. These data were encrypted in the constellation with 64×64 symbols, achieving a DFP of up to 99.3%, and each user successfully decoded them via CDMA. We have successfully extended the fundamental point-to-point QNSC scheme to accommodate point-to-multipoint passive optical networks, establishing the foundational framework for the future large-scale deployment of quantum networks.
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In the era of large models and big data, the security of optical fiber communication backbone networks has garnered significant attention. Quantum noise stream cipher (QNSC) stands as a crucial method for safeguarding the physical layer security of optical fiber communications, yet the current schemes lag behind the rate capabilities of existing 400G optical fiber backbone networks. In this paper, we introduce deep learning into QNSC and propose an end-to-end quantum noise stream cipher (E2E-QNSC) scheme, which encrypts 16 quadrature amplitude modulation (QAM) into E2E-65536QAM/QNSC. Our experiments successfully demonstrate secure optical communication with a single-channel rate of 400 Gbps, a total capacity of 8.4 Tbps, and a transmission distance of 1520 km. Even in the most extreme scenarios, the detection failure probability (DFP) of the scheme remains at an excellent level greater than 0.9999, proving the security of the approach. The experimental results presented herein represent the highest rate-distance product record of QNSC secure transmission systems, to the best of our knowledge.
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 .
With the use of a 40 Gbit/s quantum noise stream cipher (QNSC) transmitter and receiver, we succeed in the first secure optical transmission exceeding 1 Tbit/s/λ over 560 km by combining 29 optical carriers generated from a single light source. In addition to amplitude and phase encryption, time-domain masking is newly introduced to further enhance the security of the random sequence used for encryption. This three-dimensional QNSC scheme employs irregular mapping of the QAM constellation, together with symbol order shuffling in the time domain. As a result of the time-domain shuffling, the BER at an eavesdropper reaches 0.5 for each bit within a symbol, even when the irregular mapping is decrypted.
With the use of a 40 Gbit/s quantum noise stream cipher (QNSC) transmitter and receiver, we succeed in the first secure optical transmission exceeding 1 Tbit/s/λ over 560 km by combining 29 optical carriers generated from a single light source. In addition to amplitude and phase encryption, time-domain masking is newly introduced to further enhance the security of the random sequence used for encryption. This three-dimensional QNSC scheme employs irregular mapping of the QAM constellation, together with symbol order shuffling in the time domain. As a result of the time-domain shuffling, the BER at an eavesdropper reaches 0.5 for each bit within a symbol, even when the irregular mapping is decrypted.
A ciphertext mapping method based on Gray code is proposed to improve the security of quantum noise stream cipher (QNSC). The experiment is conducted in 1024 × 1024 -quadrature amplitude modulation (QAM) coherent optical communication system over 300 km. Experimental results verify that the proposed scheme does not affect the transmission performance. Meanwhile, the performance analysis reveals that the attacker's bit error rate (BER) increases to about 0.5 per bit position per symbol. The advantage of proposed scheme is that QNSC makes use of basis with fewer bits for encryption/decryption.