Abstract: Combining the Logistic mapping and 3D discrete Lorenz mapping,a new five dimensional discrete chaotic map was constructed.Based on the map,an image encryption algorithm with only two rounds of diffusion operation was proposed.In the first round of the diffusion operation,the key stream is related to the plaintext and the key stream in the second round diffusion operation is related to the ciphertext of first round.Therefore,the final encryption key of the algorithm is related to the plaintext and the relationship among ciphertext,plain text and key becomes complicated.Experimental results and security analysis show that the algorithm has a large key space,good statistical characteristics for ciphertext,high sensitiveness for ciphertext to plaintext and key,resistance to chosen plaintext and ciphertext,fast encryption speed.So,this algorithm has good application prospects in image secure communication and storage applications.

Key words: Five dimensional discrete chaos,Image encryption,Two rounds of diffusion operation,Resistance to choose plain (cipher) text attack