Research On Multi-image Encryption Technology Based On Joint Fractional Fourier Transform And Phase Coding

Optical image encryption technology uses light as information carrier to compile image information from various aspects such as amplitude,phase,and wavelength of light.Encrypting information provides a more efficient,stable and secure encryption method for image information transmission and storage,thus playing an important role in image security field.Simply speaking,image encryption can be divided into three parts,encryption,transmission and decryption.It is often affected by channel noise,channel environment and malicious attacks during transmission.How to improve the image's anti-attack performance and the quality of the decrypted image is a key issue in image encryption technology while keeping the image information intact.This topic aims to improve the image encryption performance,the number of encryption at the same time,the anti-attack capability of the encrypted ciphertext and the recovery quality of the decrypted image,and finally achieve the purpose of simultaneous transmission of multiple information with high sensitivity,high anti-interference ability and high efficiency.The specific research contents are as follows:Firstly,based on the theory of fundamental optics,the image encryption technology of joint transform converter based on fractional Fourier transform is studied.Due to the existence of autocorrelation and cross-correlation,the quality of decrypted image is greatly disturbed.In this paper,the pre-storage of autocorrelation items is used to remove the zero-order term and nonlinear term,which greatly improves the quality of the decrypted image.Secondly,the phase encoding technique is introduced into the joint fractional Fourier transform encryption system,and a joint fractional Fourier transform encryption technique based on phase encoding technology is proposed.The phase encoding technique is used to remove the linear relationship between the original image and the encrypted ciphertext,and the quality of the restored image is improved.Therefore,the scrambling technology is introduced,which boosts the key space by preprocessing the original image.Finally,the frequency domain information of the image is analyzed,and combined with discrete cosine transform,a multi-image encryption technology based on phase-encoding combined fractional Fourier transform is proposed to realize simultaneous encryption of multiple images.At the same time,the chaos theory is studied.The chaotic parameters are used to generate random numbers instead of random phase plates,which reduces the number of transmissions and improves the transmission efficiency.