An efficient chosen-plaintext attack and improvement on an image encryption algorithm based on cyclicshift and multiple chaotic map

This paper proposes a more efficient attack method on an image encryption algorithm with permutation-cyclic shift-pixel diffusion structure. After in-depth analysis, it was found that the security of the original algorithm completely depends on the equivalent key streams: index matrix indexB, cyclic shift sequence D and diffusion sequences Z and M. But the generation of these equivalent keys has nothing to do with the plaintext image or the corresponding ciphertext image, so the equivalent keys can be decoded by the chosen-plaintext attack, in which only 2 + ceil(log256m) special plaintext images and their corresponding cipher images are required. (m represent the height of the target ciphertext image). When cracking the chaotic sequences Z and M, only one plaintext image with all pixel values of 0 is used. When cracking the cyclic shift sequence D, only one plaintext image with all pixel values of 15 is used. Finally, ceil(log256m) plaintext image is used to crack the index matrix for scrambling. Theoretical analysis and simulation experiments verify the feasibility of chosen-plaintext attack strategy. At the same time, the original algorithm is improved on the basis of being loyal to the original algorithm as much as possible.