Compact optical asymmetric cryptosystem based on unequal modulus decomposition of multiple color images

In this paper, a silhouette-free and crosstalk-free multiple-color-image cryptosystem is presented based on unequal modulus decomposition (UMD) in the gyrator transform (GT) domains. To the best of our knowledge, it is the first time that the use of cascaded GT, UMD, and inverse-GT operations is demonstrated which features four-orders-of-magnitude higher sensitivity relative to the known GT-UMD cryptosystems. This significantly enlarges its key space. It is demonstrated that this method eliminates the silhouette and cross-talk problems which are well-known in previous interference-based and multiple-image cryptosystems. The polarization and time degrees of freedom (DoFs) are harnessed to realize the proposed cryptosystem using a compact optical system. Also for more compactness, the inverse-GT operation is performed by propagating the beam carrying the image in the reverse direction through the optical GT system. The cryptosystem is verified robust against occlusion, noise, statistical attacks, as well as the chosen-plaintext attack. The quality of the output images is found unaffected by the number of encrypted images which offers ultimately high multiplexing capacity.