Abstract: A new self-adaptive colour image encryption scheme based on spatiotemporal chaotic system was introduced,and it operates at the bit level.Firstly,plain image is converted to R,G,B three vectors,and then a self-adaptive method is employed to encrypt the image.The method is as follows:B vector image is used to encrypt R vector image,and R′is given;R′ is used to encrypt G vector image,and G′ is given;G′ is used to encrypt B vector image,and B′ is gotten;B′ is used to encrypt R′,and R″ is attained,then cipher image appears after one turn.Encryption schemes are composed of confusion process and diffusion process.Spatiotemporal chaotic system——coupled map lattices(CML) is used to permute the positions of the image pixels at the bit level,and logistic chaotic system is adopted to diffuse the shuffled bit image.The initial values of chaotic systems are influenced by the plain image,and the method is sensitive to the plain image.Tests and analyses of key space,image histogram,key sensitivity,correlation,information entropy,plain image sensitivity and steganogram attack were carried out and the results demonstrate the superior security and high efficiency of the proposed scheme.Moreover,the encryption scheme has huge application potential in image secure communication field.

Key words: Secure communication,Colour image encryption,Spatiotemporal chaotic system,Self-adaptive,Bit level