Advanced image encryption and decryption using sandwich phase diffuser and false image along with cryptographical enhancement

The revolution in communication technology facilitates fast and reliable information transfers and is being increasingly used in various fields like scientific, military, civilian and economic. Apart from the speed and reliability, security in transferring the information is gaining much importance now days. Optical data transfer offers several dimensions in which information can be hidden such as phase, polarization, and wavelength, etc., making it possible to encode data more securely. In addition to this, the characteristics of fast computing and the inherent parallelism of optical data transfer make it very useful for real-time applications. This paper focuses on the encryption and decryption of two-dimensional images. The encryption is done by employing a sandwich phase diffuser made by using two speckle patterns, and placed in the Fourier plane of a double random phase encoding system. After phase diffusion another image is fused to the resultant image and then cryptographical enhancement is done which provide an additional security to the system. The used cryptographic technique is derived from the AES cryptosystem in which a modified shift row operation is performed. During decryption first inverse cryptographical enhancement is done, followed by subtraction of fused image. Then further decryption process will be done. Reliability of the technique is evaluated using Mean Square Error (MSE) calculation between the decrypted and original image. In addition to MSE estimation, histogram and correlation coefficient analysis is performed.