Practical Security Analysis Of Quantum Random Number Generator Based On Vacuum Fluctuation

Quantum random number generator(QRNG)supports the generation of unpredictable random numbers from the intrinsic uncertainty of quantum processes.It is an ideal and secure random number source in the field of information security,which is of great significance to the information security of national defense,finance and government affairs.Therefore,QRNG is favored by people and has developed continuously in the past two decades,forming two types of schemes with discrete-variable and continuous-variable(CV).The CV-QRNG based on measuring vacuum fluctuation by homodyne detection has attracted much attention due to its notable advantages:easy to prepare vacuum state,insensitive to the detection efficiency,the detected variables can be quantized into multiple bits,and the structure is simple for convenient chip integration,etc.Unpredictable true random numbers can be obtained by QRNG constructed by ideal devices.However,the non-ideal devices in the practical system will greatly reduce the randomness of the final output random number,and even expose loopholes to the eavesdropper.Thus researchers have attached much importance to the practical security of QRNG.In the current researches on the practical security of the vacuum-based QRNG,the main ones focus on the influence of the detector with limited bandwidth on the correlation of generated random numbers and the influence of the sampling range and accuracy of the ADC on the min-entropy,etc.However,it is generally assumed that the local oscillator(LO)is from an ideal laser source,that is,there is no fluctuation in power,and the homodyne detection is balanced.The influence of imbalanced homodyne detection and LO fluctuation on the practical security of vacuum-based QRNG is still lack of research.To study the above practical security problems,the major works of this thesis are as follows:1.Based on the min-entropy basic model and the consideration for LO fluctuation and homodyne detection of imbalance,the practical min-entropy model is established theoretically.Theoretical and experimental results show that the larger the transmittance of the beam splitter,the larger the amplified LO fluctuation noise variance and the total noise variance,and the smaller the amplified quantum variance,i.e.the smaller the practical min-entropy.This means that with the increase of the unbalance of homodyne detection,if the influence of the LO noise is not considered in the calculation of min-entropy,more bits of the generated random sequence will be mastered by the eavesdropper.2.In the experiment,a LO monitoring scheme is proposed to calculate the variance of LO fluctuation noise and calibrate the practical min-entropy of vacuum-based QRNG.Finally,a random number generation rate of more than 350 Mbps is achieved.Besides,the performance of the random number after post-processing is tested,and the results,meet the basic characteristics of the ideal true random number.3.To improve the practical security of the system and get the secure quantum random number,three real-time monitoring schemes are proposed.According to the key parameters of real-time monitoring,such as the practical min-entropy,security parameter and total noise variance,the final generated random sequence is selected.The simple and feasible variance monitoring scheme is applied to the industry-leading high-speed vacuum-based QRNG prototype developed by our research group.