Abstract:

 On the basis of compound chaos and affine transformation in finite integer domain, a novel encryption algorithm is proposed, which is embedded in the compression process of color images. Firstly, it scrambles the blocks of 8×8 pixels of red, green and blue components globally in space domain to disarrange the combination relationship among three components, and then proceeds with normal compression. Secondly, it scrambles, self-adaptively replaces and diffuses the frequency domain’s all direct current coefficients universally after quantization. Lastly, it scrambles alternating current coefficients’ value and changes alternating current coefficients’ signs selfadaptively. The scrambling function in it mixes coefficients’ value according to corresponding coordination when changing coefficients’ position, and the self-adaptive function is implemented by introducing image data in the process to disturb the chaos system. The algorithm has huge key space, strong sensitivity and high security. The constructed compoundchaos system, which has a brief form, can be realized parallel conveniently. The ciphertext has almost the same size as original image after direct compression.