Nonlinear optical double image encryption using random-optical vortex in fractional Hartley transform domain

This paper proposed an enhanced asymmetric cryptosystem scheme for optical image encryption in the fractional Hartley transform domain. Grayscale and binary images have been encrypted separately using double random phase encoding. Phase masks based on optical vortex and random phase masks have been jointly used in spatial as well as in the Fourier planes. The images to be encrypted are first multiplied by optical vortex and random phase mask and then transformed with direct and inverse fractional Hartley transform for obtaining the encrypted images. The images are recovered from their corresponding encrypted images by using the correct parameters of the fractional Hartley transform and optical vortex, whose digital implementation has been performed using MATLAB 7.6.0 (R2008a). The random phase masks, optical vortex and transform orders associated with the fractional Hartley transform are extra keys that cause difficulty to an unauthorized user. Thus, the proposed asymmetric scheme is more secure as compared to conventional techniques. The efficacy of the proposed asymmetric scheme is verified by computing the mean squared error between recovered and the original images. The sensitivity of the asymmetric scheme is also verified with encryption parameters, noise and occlusion attacks. Numerical simulation results demonstrate the effectiveness and security performance of the proposed system.