High-Bit Multi-Ary Quantum Noise Random Encryption System Based on Cascade Modulation

Objective A large -capacity, high -security quantum noise random cryption (QNRC) system requires high-speed, high -resolution pseudo-multi-ary signal waveforms. However, the generation of pseudo-multi-ary signal waveforms requires a high-speed, high -resolution digital -analog converter/analog-to-digital converter (DAC/ADC). Therefore, a high-speed, high -resolution DAC/ADC plays a crucial role in the performance of QNRC systems. However, owing to the performance limitations of the current high-speed, high -resolution DAC/ADC, the performance of the QNRC system is limited. Our suggested approach is motivated by the need to utilize a new method based on low speed and low resolution to avoid the usage of high-speed, high -resolution DAC in the QNRC system, hence eliminating the performance constraint of QNRC systems owing to the DAC bottleneck. Therefore, the potential of??Methods In this study, a flexible multi-ary PSK-QNRC system based on a low -speed, low -resolution DAC combined with cascaded phase modulators is proposed. The proposed system is optical domain decryption based on coherent detection, which is simple and easy to implement. At the transmitter of the system, the encryption mapping of a 12 bit running sub -key with an n bit plaintext signal is performed on a bit -by -bit basis (if n<4, we only need to place (4-n) digits with "0" in front of them), where the first group of four -bit -DAC is used to modulate the first phase modulator, the second group of four -bit -DAC is used to modulate the second phase modulator, and so on. Four phase modulators are used in our experimental system, which are connected by 100 ps delay lines. The cascaded modulated signal output is attenuated to a mesoscopic coherent state, which has a power of-20 dBm, by an optical attenuator and then sent to the transmission link of the PSK-QNRC system. At the receiver end, the optical signal carrying the decryption information of the running sub -key is used as the reference light (LO, local oscillator) for coherent demodulation, and the ciphertext signal transmitted through a span of the optical fiber with dispersion compensation is used as the signal light (SIG) for coherent demodulation. These two optical signals are then simultaneously sent to the coherent receiver for decryption after time -delay matching. The output signals from the coherent receiver include an in -phase branch (I) signal and a quadrature branch (Q) signal. The I and Q branch signals are then sent to a real-time oscilloscope, where signal phase estimation is performed. Finally, bit error rate estimation is performed based on the results of the signal phase estimation. Through theoretical and experimental analyses of the PSK- QNRC encryption system, the feasibility of the proposed scheme for a large -capacity, long-distance quantum -noise random -encryption transmission system is verified. Results and Discussions To evaluate the proposed scheme, we established an experimental optical PSK-QNRC system (Fig. 3) and a corresponding computer simulation system based on VPI9.1 software (Fig. 4). All the parameter configurations are listed in Table 1. Taking the transmission of the binary plaintext signal (1+12) as an example, the simulation results are shown in Fig. 5. After the ciphertext signal is transmitted and decrypted over a long distance, the signal is restored to a binary signal, and a clear eye diagram is obtained. A legitimate receiver can accurately obtain the plaintext information, whereas an illegal eavesdropper cannot obtain the transmitted signals from the encrypted signal. We discussed and analyzed the performance of the proposed scheme and compared it with a traditional scheme using high-speed and high -resolution ADC/DAC under binary plaintext. Additionally, we analyzed the security performance of the proposed system under binary and multi-ary decryption. The system transmission performance of the proposed scheme is analyzed under a multi-ary decryption setting and compared with the traditional scheme. Figure 6 shows the power penalty comparison curve between this scheme and the 16 bit high-speed, high -resolution DAC scheme under a binary plaintext setting. The results show that the proposed system can retain the performance of the traditional scheme while avoiding the performance limits of the high-speed QNRC transmission system imposed by the DAC resolution limits and can significantly reduce the system cost. Figure 7 shows the evaluation results of the system s security performance. It can be clearly observed that the NMS (number of quantum state) values under the binary decryption and multi-ary decryption schemes (where 4-ary, 6-ary, and 8-ary are considered) are 2.33, 4.66, 9.33, and 18.66, respectively, which can meet the security performance requirements of the system in both binary and multi-ary decryption settings. Figure 8 shows the time -domain waveforms, eye diagrams, and constellation diagrams of the decrypted signals when the plaintext is quaternary. It can be observed that after decryption, both the binary and multi-ary signals are successfully recovered, and the eye diagram is clearly visible. A legitimate receiver can obtain the corresponding original plaintext signal under each condition after signal decryption; however, an illegal receiver cannot obtain the original plaintext information from the encrypted signals. Figure 9 depicts the system bit error rate curve of the proposed scheme with a 10 km signal transmission under multi-ary settings. The results confirm the feasibility of the proposed scheme for multi-ary decryption system applications. Conclusions To solve the performance limitation of high-speed and high -resolution DAC on the performance of the QNRC system, this study proposed a scheme for designing a high -bit QNRC transmission system based on a low -speed, low -resolution DAC combined with cascaded phase modulators. The proposed scheme not only overcomes the transmission performance constraint imposed by the DAC bottleneck in cascaded PSK-QNRC systems but also significantly reduces the system cost. Moreover, the proposed scheme can be adapted for multi-ary transmission applications. First, the proposed scheme was discussed, analyzed, and compared with the traditional 16 bit high-speed scheme with a high -resolution DAC in terms of the power penalty. Subsequently, the feasibility of the proposed scheme was verified. Second, this study applied this scheme to a multi-ary transmission setting and conducted a comparative analysis of the system s performance under various multi-ary transmission conditions. The feasibility of the future QNRC system adapting to a multi-ary transmission system was verified. Third, the domestication of DAC with a 4 bit resolution and 30 Gb/s transmission rate used in the proposed system has already been realized, which can bypass the dependence on the imported high-speed, high -resolution DACs, thus providing a feasible solution for realizing domestic QNRC systems with low system costs. Notably, the system proposed in this study is scalable because the maximum number of ciphertext states in the transmission is not limited to 16 bit. When necessary, it can be upgraded by cascading more low -speed DACs at the end of the transceiver or a few higher -resolution DACs to increase the transmitted ciphertext state of the QNRC system.