Abstract: In the paper,a self-adaptive color image encryption algorithm using the hyperchaotic system was introduced,and we operated it at the bit level.Firstly,chaotic sequences produced by Chen hyperchaotic system are used to confused and diffused R,G,B components of the plain image.Moreover,self-adaptive encryption algorithm is adopted,namely,the higher four bit images are used to encrypt the lower four bit images,and the encrypted lower four bit images are used to encrypt the higher four bit images conversely.Then,the encrypted three base color components are combined horizontally and encrypted simultaneously,and this reduces the correlations of the three base color components.The encryption algorithm makes the relationship between the ciphered image and the plain image,keys more complex,some keys depend on the plain image,and the algorithm is more sensitive to the plain image.Tests and analyses of key space,key sensitivity,image histogram,correlation,information entropy and plain image sensitivity were carried out.The results demonstrate the superior security and high efficiency of the proposed scheme,and the encryption scheme has huge application in image secure communication field.

Key words: Secure communication,Hyperchaotic system,Self-adaptive,Bit level,Combined encryption