Möbius Transformation and Permutation Based S-Box to Enhance IoT Multimedia Security

In a world of seamless connections, where everyone is connected via smart devices (Internet of Things (IoT)). These smart devices constantly exchange personal multimedia data, which requires maximum protection from unauthorised access. Encryption via ciphers is the traditional way of securing sensitive information and the strength of encryption is dependent on the design of the cipher. However, some encryption algorithms (block ciphers) are found to be vulnerable to data leaking attacks due to the use of an inadequate design of the substitution box (S-box), it fails to prevent attacks in these ciphers. S-boxes are key units of block ciphers that help to resist attacks hence, this paper proposes a non-linear
$8-bits$
S-box design that causes maximum chaos in visual multimedia data by utilising the Möbius transformation and a bit-wise shift permutation. Firstly, the Möbius transformation operation was applied on a finite field (Galois field principle) with an irreducible polynomial and then a permutation was applied on the previous results using a right bitwise shift operation to generate the final S-box. The performance evaluation shows that the proposed S-box has a Non-Linearity value of 112 and a Differential Uniformity of 0.015625 hence making it resistible to the linear and differential attacks respectively. The proposed S-box design produced robust protection when embedded with the Chacha20 (IoT stream cipher) and compared with the state-of-the-art (SOTA) ciphers to secure visual data which proves the proposed S-box can be integrated with any existing cipher to improve its protection on visual data.