Chaotic image encryption based on circular substitution box and key stream buffer

• A new image encryption scheme based on substitution–diffusion structure is proposed.
• The circular S-box is introduced for substituting the pixels depending on image.
• The key stream buffer is used to generate the key stream varying for different images.
• The proposed encryption scheme has high security and significant speed advantage.

A new image encryption algorithm based on spatiotemporal chaotic system is proposed, in which the circular S-box and the key stream buffer are introduced to increase the security. This algorithm is comprised of a substitution process and a diffusion process. In the substitution process, the S-box is considered as a circular sequence with a head pointer, and each image pixel is replaced with an element of S-box according to both the pixel value and the head pointer, while the head pointer varies with the previous substituted pixel. In the diffusion process, the key stream buffer is used to cache the random numbers generated by the chaotic system, and each image pixel is then enciphered by incorporating the previous cipher pixel and a random number dependently chosen from the key stream buffer. A series of experiments and security analysis results demonstrate that this new encryption algorithm is highly secure and more efficient for most of the real image encryption practices.