Design of 256-Bit Block Cipher and Enhanced Non-Linear Substitution

In today's digital era, the need for advanced encryption techniques is paramount to ensure secure and resilient information exchange. This project proposes the design of a custom 256bit block cipher, inspired by the Advanced Encryption Standard (AES), with structural and functional enhancements aimed at addressing emerging security challenges. The cipher operates on a 256bit data block structured as a 4×8 matrix doubling the block size of standard AES and introduces compatibility with MIMD (Multiple Instruction, Multiple Data) architectures, in contrast to AES's SIMD-friendly nature. While preserving AES's core operations (Sub Bytes, Shift Rows, Mix Columns, and Add Round Key), the design incorporates multiple nonlinear S-boxes, row-wise spatial substitution, and parallelism-friendly optimizations. These modifications enhance both confusion and diffusion properties, aiming to offer improved resistance against classical and quantum cryptanalytic techniques. The proposed cipher represents a step toward future-ready symmetric encryption aligned with post-quantum security requirements.