NIST compliant Difference of Sine-Cosine based Non-linear Modulated Signal Chaotic Map Driven Medical Image Encryption Defender of Statistical and Differential Attacks

Abstract

This article proposes a Difference of Sine-Cosine based Non-linear Modulated Signal based chaotic map driven encryption technique designed for medical images, which are vital in disease diagnosis, treatment planning, and patient monitoring. Since medical images are classified as protected health information, they require strong encryption to ensure confidentiality and prevent unauthorized access. The proposed method uses a chaotic system sensitive to initial conditions, making small changes in the input image or key result in completely different encrypted outputs. This property significantly strengthens resistance against differential attacks. The chaotic map enhances confusion and diffusion, producing cipher images that pass all statistical randomness tests by National Institute of Standards and Technology (NIST) and exhibit no discernible patterns, thus protecting against cryptanalysis. In this approach, the image is first converted into a one-dimensional vector, which is then divided into two segments and diffusion is applied. The combined diffused data subsequently undergoes chaotic sequence based permutation, followed by six layers of diffusion both using chaotic and pseudo random sequences. The technique is evaluated using entropy analysis, correlation coefficients, key space analysis,  and histogram uniformity with Number of Pixel Change Rate (NPCR) > 99.59% and Unified Average Change in Intensity (UACI) >33.33% but lower then derived theoretical upper bound limit, results confirm the schemes robustness and effectiveness in securing sensitive medical images,  especially for telemedicine and cloud storage applications.