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IEEE photonics journal

Security Analysis of QAM Quantum-Noise Randomized Cipher System

Yukai Chen, Haisong Jiao, Hua Ren Zhou, Jilin Zheng, Tao Pu

Published Jul 15, 2020• 14 citations
Publisher

Abstract

Applying the quadrature amplitude modulation (QAM) format, quantum-noise randomized cipher (QNRC) systems hide the signal states in quantum phase noise and amplitude noise to prevent eavesdropping. In this paper, based on the traditional wire-tap channel model analysis method, the physical-layer security of QAM-QNRC system is investigated quantitatively under the metric of secrecy rate. The general expressions of secrecy rates of the data and key are derived separately. Furthermore, the maximum reachable secrecy rate of a QAM-QNRC system is put forward, under which the data and key are both safe in the view of mutual information evaluation. Finally, the variation trend of secrecy rate with various system parameters is discussed in detail. The simulation results show that we can obtain a higher secrecy rate by setting reasonable parameters, such as the level of ciphertext, mesoscopic signal power, and inner gain at the transmitter. Meanwhile, the security of the key is the main constraint of the maximum reachable secrecy rate.

DOI
10.1109/jphot.2020.3009252

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Applying the quadrature amplitude modulation (QAM) format, quantum-noise randomized cipher (QNRC) systems hide the signal states in quantum phase noise and amplitude noise to prevent eavesdropping. In this paper, based on the traditional wire-tap channel model analysis method, the physical-layer security of QAM-QNRC system is investigated quantitatively under the metric of secrecy rate. The general expressions of secrecy rates of the data and key are derived separately. Furthermore, the maximum reachable secrecy rate of a QAM-QNRC system is put forward, under which the data and key are both safe in the view of mutual information evaluation. Finally, the variation trend of secrecy rate with various system parameters is discussed in detail. The simulation results show that we can obtain a higher secrecy rate by setting reasonable parameters, such as the level of ciphertext, mesoscopic signal power, and inner gain at the transmitter. Meanwhile, the security of the key is the main constraint of the maximum reachable secrecy rate.
The physical-layer security of a quantum-noise randomized cipher (QNRC) system is, for the first time, quantitatively evaluated with secrecy capacity employed as the performance metric. Considering quantum noise as a channel advantage for legitimate parties over eavesdroppers, the specific wire-tap models for both channels of the key and data are built with channel outputs yielded by quantum heterodyne measurement; the general expressions of secrecy capacities for both channels are derived, where the matching codes are proved to be uniformly distributed. The maximal achievable secrecy rate of the system is proposed, under which secrecy of both the key and data is guaranteed. The influences of various system parameters on secrecy capacities are assessed in detail. The results indicate that QNRC combined with proper channel codes is a promising framework of secure communication for long distance with high speed, which can be orders of magnitude higher than the perfect secrecy rates of other encryption systems. Even if the eavesdropper intercepts more signal power than the legitimate receiver, secure communication (up to Gb/s) can still be achievable. Moreover, the secrecy of running key is found to be the main constraint to the systemic maximal secrecy rate.
Quantum-Noise Randomized Cipher (QNRC) is a potentially information-theoretic secure physical-layer encryption method for high-speed and long-distance fiber communications. In order to solve the problem that the modulation and demodulation of M-ary Y-00 ciphertext signal in QNRC system are limited by the ADC chip with high sampling rate and high conversion depth, a novel realization of PSK-QNRC system based on series structure of multiple phase modulators (PM) is proposed, and the performances of the proposed scheme is verified by using commercial simulation software in this paper. The simulation results show that, the 126-PSK QNRC system at 10 Gbit/s over 1000-km optically amplified links is realized based on the series structure of multiple PM. Reducing the mesoscopic power of the ciphertext quantum state can improve the security level of QNRC system, but it will damage the transmission performance of the system at the same time. It is very important to select the appropriate mesoscopic power to optimize the security and reliability of QNRC system.
Quantum-noise randomized cipher (QNRC) is an anti-interception communication technology, which can realize high-speed encryption for data stream in true randomness. In this paper, the characteristics of the phase shift keying (PSK) and quadrature phase shift keying(QPSK) QNRC systems are verified by the simulation system with digital coherent demodulation. The decryption process of the QNRC coherent system is carried out in the optical domain for the first time. Specifically, at the quadrature coupler, the modulated local light is coupled with the received encrypted optical signal. The multi-symbol phase estimation(MSPE) module is employed to eliminate the influence of the phase deviation on the signal decision. Finally, error-free secure transmission is realized at 2.5Gsymbol/s over 500km optically amplified links. We reveal the new fact that the mesoscopic power of QPSK-QNRC system is higher than that of PSK-QNRC system.
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.
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 .
Quantum noise stream cipher where encrypted signals are masked by quantum noise and ASE noise provides a physical layer of security. It requires the transmitter and the receiver to share a stream cipher that is generated from a PRNG. Yet a correlation attack threatens its security due to the mathematical properties of PRNG. This paper discusses the security of QNSC system under correlation attacks. Our experiment results find that the security of the whole system depends on the cycle to refresh the seed key and the correlation between the incepted running key, original running key, and seed key. Furthermore, it is important to provide security for the QNSC system by maintaining low optical power. Besides, this new analytical method provides quantitative security analysis for a QNSC system under a correlation attack.