S-Box based Nibble-Swapping Encryption Scheme to Enhance the Security of Digital Images

Sensitive information, such as financial data, military intelligence, and medical records, is communicated using images. The need for safe digital image encryption techniques has grown as digital photographs are used and transmitted over the internet more and more. In this context, the use of Substitution Box (S-box) combined with dynamic step has proven to be a dependable scheme for image encryption. In S-Box based scheme, a substitution method is employed to replace an image’s original pixel values with new values generated from a predefined table. A key-sensitive variable step and bit swapping techniques further encrypt the substituted pixel values. This work examines the algorithm's efficacy using metrics like Entropy and the Number of Pixel Change Rate (NPCR).