An Asymmetric Optical Cryptosystem of Double Image Encryption Based on Optical Vortex Phase Mask Using Gyrator Transform Domain

Abstract

Background: Optical Vortex (OV) has attracted attention amongst many researchers. Paper proposes a nonlinear scheme of image encryption based on Optical Vortex (OV) and Double Random Phase Encoding (DRPE) in the Gyrator Transform (GT) domain under phase truncation operations. Objective: The amplitude and phase truncation operation in the image encryption generates two decryption keys and convert the method to nonlinear. It has also been proposed opto-electronically. Original image can only be decrypted with correct values of OV, GT rotation angles and Decryption Keys (DKs). Methods: A novel asymmetric image encryption scheme, using optical vortex mask has been proposed in view of amplitude and phase truncation operation. The scheme becomes more strengthened by the parameters used in the Optical Vortex (OV) and by taking the (n)th power operation in the encryption path and (n)th root operation in the decryption path. Results: It shows that for each of the encryption parameters, binary image has greater sensitivity as compared to the grayscale image. This scheme inflates the security by making use of OV-based Structured Phase Mask (SPM) as it expands the key space. The scheme has also been investigated for its robustness and its sensitivity against various attacks such as noise and occlusion attacks under number of iterations. Conclusion: This scheme provides solution to the problem of key space with the use of GT rotational angles and OV phase mask thus enhances the security. The scheme has been verified based on various security parameters such as occlusion, noise attacks, CC, entropy etc.