Aiming at the problem that hybrid domain image encryption algorithm based on chaos theory has weak encryption strength, a new image encryption algorithm based on the combination of spatial and wavelet domain was proposed. First, one-level two-dimensional discrete wavelet decomposition was performed on the original image to extract the low-frequency wavelet coefficients. Second, using the chaotic sequence generated by 2D Sine Logistic chaotic dynamic system, the low frequency sub-band was scrambled by using chaotic magic transformation, then inverse wavelet transformation was executed on decomposed image.For the scrambled image, a chaotic sequence used for encryption key in spatial domain based on intertwining Logistic map was generated, then the pixels were encrypted by using the combination technology of elemental multiplication in a Galois field with XOR. At the same time, the technology of chaotic disturbance and encryption feedback was introduced to implement one-running key. Theoretical analysis and experimental results show that the proposed algorithm has the advantages of large key space, anti-reconstruction attack, anti-differential attack, feasible encryption efficiency, strong security, and so on.

Abstract: In order to efficiently scramble image, based on skew tent map, a fast random permutation procedure was firstly presented, and then a fast image scrambling algorithm, based on the preceding procedure, was designed. The main idea behind the fast random permutation was position interchange. Its implementation process was, based on geometrical meaning of probability, non-uniform distribution chaos sequence generated by skew tent map was transformed into uniform random sequence, which then drove image element to interchange position. Theory and experiments results demonstrate that the fast random permutation has better efficiency then sorting-based random permutation, the proposed image scrambling method has larger key space and higher running efficiency than sorting-based image scrambling.