https://blog.amuralmanji.com/categories/implementation/Recent content in Implementation onHugoenFri, 18 Apr 2025 14:00:00 +0400https://blog.amuralmanji.com/posts/clefia_sbox_normal_basis/Fri, 18 Apr 2025 14:00:00 +0400https://blog.amuralmanji.com/posts/clefia_sbox_normal_basis/<p>A few years ago, I explored one of my favorite cryptographic building blocks: the substitution box (S-box). Back then, I came across the elegant paper <em>A Very Compact Rijndael S-box</em>, which showed how to eliminate lookup tables by leveraging <strong>normal basis representation</strong> and logical operations in $F_{2^{8}}$. That approach deeply resonated with me—compact, efficient, and mathematically sound.</p> <p>Recently, I decided to revisit that work—but this time with a new challenge: re-implementing the <strong>CLEFIA S-box</strong> using the same principles. CLEFIA, Sony’s lightweight block cipher, uses two $8 \times 8$ S-boxes ($S_0$ and $S_1$), and I focused on reconstructing <strong>S₁</strong> using field inversion and affine transformations—all without tables.</p>