Abstract: According that the current color image encryption algorithms of “scrambling- diffusion” mode have many problems,such as the small key space,the tedious encryption process,the security vulnerability and so on,this paper proposed a new color image encryption algorithm based on the hyperchaotic system adopting “transforming- scrambling- diffusion” model.Before scrambling,it first caclulates the number of iterations in accordance with the image itself attri-butes,excutes gray code iterative transformation for all the pixel values of color image,then the chaotic sequence generated from the four-dimensional hyper-chaotic system and pixel matrix converted to gray code are transformed to one dimensional matrixes.The former is sorted and the later change correspondingly to complete the image pixel matrix of the whole domain scrambling.And then,bit operation is executed to complete image diffusion,the ciphertext is obtained by matrix transformation.The key sensitivity histogram information entropy correlation and other evaluation indexes are calculated and analyzed through the simulation experiment,and compared with other algorithms,proving that the encryption algorithm has strong anti-attack ability.

Key words: Adjacent element correlation, Color image encryption, Gray code, Hyper-chaotic system, Key space