A novel ToCC map and two-level scrambling-based medical image encryption technique

Since the past few decades, various methods for diagnosis of different diseases have been introduced in the area of medical science. One such invention is the use of digital images to detect different types of diseases. Images obtained from X-rays, CT scans and MRI scans are the most common examples. These images contain a lot of data that need protection from unauthorised access. To avoid this unauthorized access, different types of encryption schemes are used. Chaos mechanism has gained popularity because of its randomness and initial sensitivity properties. In this research paper, a new one-dimensional Tangent over Cosine Cosine (ToCC) chaos map along with a two-stage scrambling technique to encrypt medical images is proposed. The method mainly comprises of four phases. First, padding is performed on the input image to hide the original dimension. The second stage involves generation of two different chaotic sequences using the ToCC and Chebyshev-Chebyshev chaotic maps, respectively. In the third stage, modified High-Efficiency Scrambling (mHES) that uses the ToCC chaotic map-generated sequence to perform first level scrambling, is applied. At last, modified Simultaneous Permutation and Diffusion Operation (mSPDO) that exploits the Chebyshev-Chebyshev chaotic map to implement second level scrambling to obtain the final encrypted image is applied. The strength of the proposed chaos map has been checked by plotting Bifurcation Diagram, Lyapunov Exponent and Shannon Entropy metrics. We have also analysed the proposed image encryption scheme using parameters like Unified Averaged Changed Intensity (UACI), Number of Changing Pixel Rate (NPCR), Correlation Coefficient (CC), Avalanche effect, Peak Signal to Noise Ratio (PSNR), and Entropy. The obtained results suggest that the proposed scheme is resistant to various known attacks on medical images.