Abstract: This paper suggests a new fast colour image cipher to meet the increasing demand for secure online image communication applications. Unlike most other existing approaches using a permutation-substitution network, the proposed algorithm consists of only a single substitution part. The keystream sequence is generated from a 4-D hyperchaotic system, whose initial conditions are determined by both the secret key and the SHA-224 cryptographic hash value of the plain-image. Favoured by the avalanche effect of hash functions, totally different keystream sequences will be generated for different images. Consequently, desired diffusion effect can be achieved after only a single round of substitution operation, whereas at least two encryption rounds are required by the state-of-the-art permutation-substitution type image ciphers. We also demonstrate the computational efficiency of the proposed algorithm by comparing it with the AES encryption algorithm. A thorough security analysis is carried out in detail, demonstrating the satisfactory security of the proposed algorithm.
