Optical cryptosystem for visually meaningful encrypted images based on gyrator transform and Hénon map

A novel image encryption scheme generating visually meaningful encrypted images (VMEIs) is presented based on the gyrator transform (GT) and the Hénon chaotic map. The optical encryption system exploits the polarization degree of freedom to reduce the system complexity by allowing the use of a single GT system to concurrently apply to both the secret image and the VMEI. The cryptosystem yields a VMEI with the same size  as the secret plain image, which is more secure in either storage or transmission. The results demonstrate that even if the identity of the VMEI is unveiled, any attempt to recover the original image from that VMEI −without knowing the whole secret key− will fail. Unlike previous meaningful cryptosystems that are mainly based on steganographic methods like image hiding and watermarking, the proposed optical cryptosystem adopts a non-steganographic approach by assigning an independent VMEI carrying no information related to the original secret image. The cryptosystem is verified robust against occlusion, noise, statistical attacks, as well as the classical attacks including the chosen-plaintext and chosen-ciphertext attacks.