Image encryption using chaotic maps

In recent years, a variety of chaos-based image cryptosystems have been proposed. An architecture of such kind of cryptosystems is composed of multiple rounds of substitution and diffusion. In the substitution stage, a two- or higher-dimensional chaotic map is employed to shuffle the image pixels for confusion purpose. In the diffusion process, the pixel values are altered sequentially so that the change made to a particular pixel depends on the accumulated effect of all the previous pixels. The design of this class of chaos-based image cryptosystems, together with the security evaluations, will be discussed in this chapter. In substitution-diffusion type chaos-based image cryptosystems, the confusion and diffusion effects are solely contributed by the substitution and the diffusion stages, respectively. This design leads to the weakness that the two stages are attacked separately. Moreover, the required overall rounds of operations in achieving a certain security level is found more than necessary. A modified architecture is then suggested so that certain diffusion effect is introduced in the substitution stage by simple sequential add-and-shift operations. The resistance to attacks is enhanced. The encryption efficiency is also improved as fewer operation rounds are required. © 2009 Springer-Verlag Berlin Heidelberg.