An Encryption Algorithm for Image Based on Affine and Composed Chaos

With the popular application of multimedia, the security of digital image becomes more and more important. According to the feature of digital image and on the basis of three-dimension affine transformation and chaos, a novel spatial domain encryption algorithm is proposed. Firstly, it scrambles pixel position and confuses pixel value according to the corresponding coordination. Secondly, it takes a series of nonlinear diffusion and substitution in turn for all lines. The algorithm proceeds with the above two steps for at least 3 times, and it can be conveniently converted to the frequency domain algorithm while replacing the processed data in the spatial domain with quantized coefficients in the frequency domain. In the process of substitution, pixel value is introduced to perturb multiple chaos systems that are coupled together for self-adaptive encryption. In the encryption process, the scrambling parameters are generated by chaos systems automatically, and the scrambling function is compatible with images at any ratio of length to width without any preprocessing. Theoretical analysis shows that the algorithm has huge key space to defend against violent attack, the mapping relation between the plaintext and the ciphertext is complex enough to resist chosen plaintext attack efficiently, and the algorithm using simple chaos systems is designed modularly in order to be realized parallelly conveniently. Experimental results show that the algorithm takes good encryption result, gets strong sensitivity, conforms to confusion and diffusion principles in cryptography, and achieves high security.