Experimental Study of Random Secret Key Extraction From Atmospheric Optical Channels

Utilizing reciprocal atmospheric turbulence as a physical entropy source for extracting random secret key is an effective means to achieve physical layer security in wireless channels. To study the impact of turbulence intensity on secret key extraction rate in atmospheric optical channels, this paper conducted a bi-directional synchronous atmospheric channel laser transmission experiment, analyzed the experimental data from three different time periods, and tested the Kolmogorov-Smirnov (KS) fitting efficiency values for five types of probability distribution normalized received signals. Comparative analysis shows that Johnson SB and Log-Normal distributions have the most ideal fitting effects on data. Based on these distribution parameters, a theoretical model of key capacity was constructed. The Monte Carlo method was used to simulate the secret key extraction rates under different turbulence intensities and different probability distribution models. The analysis results show that under weak turbulence conditions, using Johnson SB distribution yields about 87% higher average maximum secret key extraction rate than using Log-Normal distribution; under medium turbulence conditions, there is no significant difference in secret key extraction rates between the two distribution models. Compared with Log-Normal distribution, Johnson SB distribution is more suitable for secret key extraction under medium to weak turbulence intensities.