Research On Multiple-image Encryption Based On Fractional Fourier Transform

With the rapid development of modern communication technology,the image transmission's security is becoming increasingly important.Optical image encryption techniques can offer fast inherent computing and parallelism,and present a good potential for information protection by providing more key degree of freedom,such as amplitude,phase and wavelength.So it have played an important role in optical information processing.Recently,many image encryption algorithms have been proposed,but most of them are dealing with one or two images.There is some trouble in decryption and transmission for highly correlated and large volume data and images.To solve this problem,some multiple-image encryption algorithms are proposed in this thesis,the main contents are as follows:First of all,a novel technique for multiple-image encryption based on improved theta modulation and double random phase encoding in the fractional Fourier domain is proposed.After being modulated by sinusoidal amplitude grating,each image is performed by filtering procedure and then multiplexed into a complex signal.The complex signal is performed by double random phase encoding in the fractional Fourier domain to obtain the encrypted image with stationary white noise.These images can be retrieved by using the correct keys such as random phase mask and orders of the fractional Fourier transform.This algorithm used the improved theta modulation to overcome the image crosstalk,increase the quality of decrypted image effectively.Second,a multiple-image encryption scheme is proposed by using of improved theta modulation and discrete multiple-parameter fractional Fourier transform.The multiplexing step is the same as the above algorithm's.After operated by a pixel scrambling,the complex signal is multiplied by random phase mask,and then encrypted by discrete multiple-parameter fractional Fourier transform.These images can also be retrieved by using the correct keys such as random phase mask and the parameters in discrete multiple-parameter fractional Fourier transform.This method enhances the key space of the whole system,improves system's efficiency,and further provides a much higher security level.Finally,the encryption algorithm based on improved theta modulation and double random phase encoding in the fractional Fourier domain is simulated in OpenCV to prove its feasibility and effectiveness.Numerical simulation experiments have been carried out to verify the reliability and security of the proposed schemes.These algorithms have less computation,simplified operation and great prospects of application.