A novel one-dimensional Cosine within Sine chaotic map and novel permutation–diffusion based medical image encryption

With the rapid advancement of multimedia technology, exchange of digital images has significantly increased. This advancement of information exchange in the form of digital images comes with its own challenge of securing them, from being altered during storage or transmission. In health care sector, medical professionals often need to share medical images such as X-ray, MRI, CT-Scan etc., with other specialists or healthcare facilities for correct disease diagnosis and treatment planning. Encryption allows secure sharing of these images over insecure network, by maintaining the integrity of medical data, which is essential as these medical images contain the personal data of patients. For encryption, chaotic maps have become a popular approach due to their significant characteristics such as sensitivity to initial conditions and ergodicity. In this paper, a novel One-dimensional Cosine within Sine (1D-CwS) chaotic map has been proposed. The proposed novel 1D-CwS chaotic map has been evaluated using Bifurcation diagram, Shannon Entropy and Lyapunov Exponent parameters, to prove that the proposed chaotic map is more complex in behaviour, more random in nature and provides larger chaotic range than many existing chaotic maps. Also, the work in this paper discusses a novel method of permutation and diffusion to propose a new medical image encryption (MIE) technique that uses the novel 1D-CwS chaotic map. The MIE scheme is divided into three major phases. In first phase, padding is done, if the given image dimensions are not square. In second phase, pixel level permutation is performed to reposition the pixels by generating unique random numbers, and by applying division and modulus operations on these unique random numbers. In final phase, diffusion process is performed to change the pixel values, which uses chaotic sequence generated by the novel 1D-CwS map. The proposed MIE has been analysed using standard parameters, which demonstrate that the proposed cryptosystem is resistant to various types of attacks.