A Fast Image Encryption Scheme Based on Simultaneous Permutation-Diffusion

In the traditional image encryption algorithm where permutation and diffusion are performed independently, multiple image scans are required, which reduces the encryption efficiency. In this paper, a fast image encryption scheme based on simultaneous permutation-diffusion is proposed, which performs simultaneous permutation-diffusion row by row and column by column. Firstly, the sorting and cyclic-shift are combined for the permutation. The permutation index sequence of the first row/column is obtained by sorting, and the rest is updated by the cyclic-shift operation related to the plain image, which can resist the chosen-plaintext attack. Secondly, cross-diffusion is performed with dynamic index sequences, which enhances the randomness of the diffusion behavior. Finally, the permutation and diffusion are performed at the same time. Therefore, a round of permutation and diffusion only needs to scan the image once, which improves the encryption efficiency. Note that our scheme only needs to generate and sort chaotic sequences with row/column level length, which reduces the iteration times of the chaotic system and sorting length. In addition, all index sequences are updated at row/column level, which is faster than pixel-level. The simulation results and security analysis show that our scheme has higher encryption efficiency than existing similar methods, and has sufficient security to resist common attacks.