Designing permutation-substitution image encryption networks with Henon map

In traditional permutation-substitution architecture type image cipher, the permutation and substitution generally are two independent parts, and the diffusion performed by substitution is more like the cipher block chaining mode of operation. However, such operation approaches clearly downgrade the encryption efficiency because the pixel values need to be modified one by one for 2-4 overall rounds and images are scanned twice for permutation and substitution in each round. To improve the encryption efficiency, a new two-point diffusion strategy realized by discrete Henon map is proposed in this paper, which can significantly accelerate the diffusion process if there is more than one processing unit. Besides, the permutation and substitution are no longer two independent parts and they intermingle with each other so that the image required to be scanned just one time. To achieve the better ability of resisting chosen-plaintext or known-plaintext attack, the substitution keystream generated in our method is dependent on the plain image. Consequently, different plain images produce the distinct keystream for substitution. The results of various security analyses prove that our proposed image cryptosystem owns superior security, meanwhile, time complexity analysis shows that it can achieve faster encryption speed than most typical image encryption schemes.