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Asia Communications and Photonics Conference

Ciphertext Mapping Method based on Bitwise NOT Operation in Quantum Noise Stream Cipher

Kai Wang, Yajie Li, Xiaokun Yang, Yongli Zhao, Jie Zhang

Published Oct 1, 2018• 1 citation
Publisher

Abstract

The effect of quantum noise on different bit positions of ciphertext is different in Quantum Noise Stream Cipher. This feature makes the QNSC system vulnerable to different attacks, e.g. fast correlation attack. To balance the effect of quantum noise on different bit positions, this paper proposes a ciphertext mapping method based on Bitwise NOT Operation (BNO). The performance of BNO-based 16QAM/QNSC is investigated with different intensity noises and basis states. The simulation results demonstrate that bit error rate in different bit positions of ciphertext is close to 0.5 by using BNO-based 16QAM/QNSC. In addition, the proposed method has little influence on symbol error rate of Bob.

DOI
10.1109/acp.2018.8596069

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The effect of quantum noise on different bit positions of ciphertext is different in Quantum Noise Stream Cipher. This feature makes the QNSC system vulnerable to different attacks, e.g. fast correlation attack. To balance the effect of quantum noise on different bit positions, this paper proposes a ciphertext mapping method based on Bitwise NOT Operation (BNO). The performance of BNO-based 16QAM/QNSC is investigated with different intensity noises and basis states. The simulation results demonstrate that bit error rate in different bit positions of ciphertext is close to 0.5 by using BNO-based 16QAM/QNSC. In addition, the proposed method has little influence on symbol error rate of Bob.
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.
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 .
We propose a probabilistic shaping-assisted base precoding quantum noise stream cipher (PSABP QNSC) scheme to effectively alleviate the encryption penalty in QAM QNSC systems. In contrast to the uniformly distributed bases adopted in traditional QNSC, Gaussian distributed bases can provide shaping gain. We theoretically analyze the underlying gain mechanism of Gaussian distributed bases in the PSABP QNSC scheme. Experimental results of 160 km reveal that the encryption penalties of QPSK and 16QAM are reduced by 0.44 dB and 0.27 dB, in terms of OSNR. Moreover, the security is quantified through the number of masked signals as a primary key metric. To mitigate the impact of base precoding, we propose the effective bases and effective ciphertext symbol points to refine the security evaluation. Moreover, the security is estimated in terms of mutual information leakage, with 2.2×10−4 bits of QPSK and 1.85×10−4 bits of 16QAM. The results indicate that the PSABP QNSC scheme provides effective protection against eavesdropping.
In this letter, we conduct an experiment of quantum noise stream cipher scheme based on 3-channel-QAM mapping and DFTs-OFDM in optical back-to-back and 160km standard single mode fiber. The fusion of 3D mapping and DFTs-OFDM offers sufficient security for QAM/QNSC within the dual polarization I/Q modulator system. Notably, the proposed 3D-mapping approach demonstrates improved minimum Euclidean distance and bit error rate performance compared to conventional 2D mapping. Experimental results confirm that our 3-channel-QAM/QNSC system achieves better transmission and higher security performance at the same base length than conventional QAM/QNSC.
Abstract An implementation method of quantum noise stream cipher with optical digital to analog converter is proposed and demonstrated. The proof-of-principle experiment for quantum noise stream cipher system has been designed to transmit 16-level signal with the baud rate of 10 Gbps by means of 4-bit port. So, the encrypted signal is obtained by weighting the intensities of multiple optical wavelengths and summing them according to plaintext signal and secret key, that makes the adjacent level of the signals are covered with the fluctuation of quantum noise. Experimental results show that the legitimate user can successfully recover the QNSC signal by the decryption with a very low probability of error with 2.19×10–11. However, the eavesdropper cannot distinguish the distinct bits due to the disturbance of quantum noise, which it is giving a very high probability of error with 0.425 due to the disturbance of quantum noise.