Cryptanalyzing a Color Image Encryption Scheme Based on Hybrid Hyper-Chaotic System and Cellular Automata

Recently, a new color image encryption scheme based on hybrid hyper-chaotic system and cellular automata was proposed. In order to generate different key streams according to different plaintexts, the sum of pixel values of each component of the original color image apart from the secret keys is used to determine the initial value of logistic map for encryption. It was claimed that the scheme can resist kinds of attacks. However, this paper found out three security drawbacks about the original encryption scheme and proposed an effective attack method using chosen-plaintext attack by cryptanalysis. The equivalent permutation key stream can be obtained by adjusting individual pixel values of the chosen plaintexts while keeping the sum of pixel values of each color channel unchanged, and all 256 possibilities of equivalent diffusion key streams can be obtained by using 512 specific chosen plaintexts. In addition, the main stages of the proposed attack method, including breaking diffusion and breaking permutation, are exchangeable. The effectiveness of our method is supported by both theoretical analyses and experimental results.