Developer Rebuilds SHA-256 Using Only Lookup Tables, Verifies Results Against FIPS Vectors

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A developer known as Abraham A. conducted an independent experiment to reimagine SHA-256 by replacing all arithmetic operations — rotations, XOR, and modular addition — with precomputed lookup tables, dubbing the result LUT-SHA256. The core challenge was handling 32-bit addition without actual math, solved by splitting words into 4 bytes and chaining carries through a 131,072-entry table, reducing all 64 rounds to roughly 14,000 memory lookups. The implementation was validated against Python's hashlib across FIPS test vectors, BIP39 exercises, long messages, and block boundaries, with all digests matching exactly. The author also built a documented "vulnerability ladder" showing how side-channel leakage from observable memory accesses — not the algorithm's math — could allow message reconstruction, with one variant solved by the Z3 solver in 68 seconds. While unsuitable for GPU mining due to non-coalescing memory access patterns, the approach is presented as potentially valuable for FPGAs, secure elements, and compute-in-memory architectures where logic minimization matters.

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