Review on Color Image Encryption Algorithm based on Pseudorandom Number Key

Abstract

In secure communication, image encryption schemes transform clear images into unintelligible others. The fundamental techniques used to encrypt a block of pixels are substitution and permutation. In recent years focuses on designing of highly robust encryption schemes (i.e., which provide good confusion and diffusion properties, to ensure desired security factor), either using peculiar pixel shuffling methods, or using innovative digital chaos-based ciphers, or by making justified compositions between these different pixel shuffling and ciphering techniques. Almost some encryption schemes based on permutation had already been found insecure against the cipher text-only and known/chosen-plaintext attacks, due to the high information redundancy, and it is quite understandable since the secret permutations can be recovered by comparing the plaintexts and the permuted cipher texts. Generally, chaos-based image encryption algorithms are used more often than others but require high computational cost. Moreover, a chaos system is defined on real numbers while the cryptosystems are defined on finite sets of integers. Furthermore, spatial domain scrambling has defect that the statistical characteristics of image are not changed after scrambling. Therefore, it is not secure to perform scrambling in spatial domain. The image encryption methods based on frequency domain encrypt/decrypt the images by modifying the image frequencies. One can recover the original plain image exactly via a reverse process.