A secure encryption scheme using a Composite Logistic Sine Map (CLSM) and SHA-256

We present an algorithm for image encryption for secure transmission and storage of images over insecure public networks. Our algorithm uses Composite Logistic Sine Map (CLSM) and Secure Hash Algorithm-256 (SHA-256). The algorithm first scrambles the pixels of the plain image based on pseudo random number sequence (PRNS) generated by the CLSM. This is followed by diffusing the pixel values by using values generated by SHA-256. The initial conditions and parameters of the CLSM together with a nonce chosen by the user act as key for the algorithm. The nonce is used to initialize the SHA-256 that generates hash values for the diffusion phase. The algorithm has a very wide key space to defeat any brute force or guessing attack. The proposed algorithm was tested with several images of different characteristics against nine security measures. The tests results show that the scheme is robust, scalable and capable of providing strong security to data. The lightweight arithmetic and logical operations involved in the used chaotic map and in permutation-substitution steps enable it to have fast speed due to low computational overhead. This makes it suitable for low power battery operated devices equipped with inexpensive processors having limited computing speed.