A new 2D-ASC chaotic system and its image encryption applications.

In this paper, a new 2D Arnold-sin-coupling (2D-ASC) hyperchaotic map is established and a new image encryption algorithm based on bit-level operations and the ASC hyperchaotic system is proposed. The algorithm first decomposes a normal image into bit-level images by rows, incorporates a sequence of bits generated by a chaotic system to the algorithm to increase randomness and security, and then performs a circular shift of the rows and columns of the bit-level image to obtain a confused intermediate image. Finally, the intermediate image is diffused by our constructed S-box according to the size of each pixel value to obtain a stable and robust encrypted image. Moreover, the initial condition of the chaotic mapping used is calculated from the SHA-256 hash value of the original image, enhancing the correlation of the encryption process with the plaintext image. Through simulation experiments, the image encryption scheme is analyzed in terms of key space, histogram, information entropy, robustness and key sensitivity. The theoretical analysis and experimental findings demonstrate that the algorithm has good performance and sufficient level of security. The information entropy of the encrypted image is above 7.9993, the average NPCR is 99.6440 and the average UACI is 33.4996. [ABSTRACT FROM AUTHOR]