An encryption scheme for images based on the DWT and a chaotic cipher

A partial encryption system based on the chaotic stream cipher Elknz is presented in this paper. After the image goes through a single-level discrete 2-dimensional wavelet transform (2-D DWT), the lowest frequency band is encrypted by the Elknz cipher. The other subbands are scrambled using the same basic Elknz algorithm. The Elknz algorithm hops between eight chaotic maps to generate the scrambling pattern. Each map has 16 orbits. Two other chaotic maps are used to produce random map and orbit hopping patterns. The system is able to reduce encryption to one quarter of the image information. Yet it provides a high level of security by sufficiently scrambling the rest of the image information. The system is explained in detail and examples are given to show that complete perceptual encryption is accomplished in all subbands as well as in the image as a whole.