soft3/mudra/src/proof/sha256.rs

// ---
// tags: mudra, rust
// crystal-type: source
// crystal-domain: comp
// ---
//! SHA-256 as a word-operation circuit (part of milestone 2d).
//!
//! ECDSA verification needs two hashes: the ADR-036 digest `z = sha256(doc)` and
//! the Cosmos account id `ripemd160(sha256(pubkey))`. Both must run in-circuit
//! for the whole claim check to be provable.
//!
//! SHA-256 is built from 32-bit word operations, each a nox pattern: `and`,
//! `xor`, `not`, `shl` (tags 12/11/13/14) directly; addition mod 2³² is a
//! Goldilocks `add` followed by a 32-bit range-check (operands `< 2³²`, sum
//! `< 2³³`, so the field add is exact); right-shift and right-rotate are
//! range-decompositions (`x = hi·2ⁿ + lo`) — the same range-check gadget. This
//! reference uses native `u32` ops; the mapping is what 2e emits.

const H0: [u32; 8] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

const K: [u32; 64] = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
];

/// The SHA-256 digest of `input`.
pub fn hash(input: &[u8]) -> [u8; 32] {
    let mut h = H0;

    // padding: append 0x80, then zeros, then the 64-bit big-endian bit length
    let bit_len = (input.len() as u64) * 8;
    let mut msg = input.to_vec();
    msg.push(0x80);
    while msg.len() % 64 != 56 {
        msg.push(0);
    }
    msg.extend_from_slice(&bit_len.to_be_bytes());

    for block in msg.chunks_exact(64) {
        let mut w = [0u32; 64];
        for (i, word) in block.chunks_exact(4).enumerate() {
            w[i] = u32::from_be_bytes([word[0], word[1], word[2], word[3]]);
        }
        for i in 16..64 {
            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
            w[i] = w[i - 16]
                .wrapping_add(s0)
                .wrapping_add(w[i - 7])
                .wrapping_add(s1);
        }

        let mut a = h;
        for i in 0..64 {
            let s1 = a[4].rotate_right(6) ^ a[4].rotate_right(11) ^ a[4].rotate_right(25);
            let ch = (a[4] & a[5]) ^ ((!a[4]) & a[6]);
            let t1 = a[7]
                .wrapping_add(s1)
                .wrapping_add(ch)
                .wrapping_add(K[i])
                .wrapping_add(w[i]);
            let s0 = a[0].rotate_right(2) ^ a[0].rotate_right(13) ^ a[0].rotate_right(22);
            let maj = (a[0] & a[1]) ^ (a[0] & a[2]) ^ (a[1] & a[2]);
            let t2 = s0.wrapping_add(maj);
            a = [
                t1.wrapping_add(t2),
                a[0],
                a[1],
                a[2],
                a[3].wrapping_add(t1),
                a[4],
                a[5],
                a[6],
            ];
        }
        for i in 0..8 {
            h[i] = h[i].wrapping_add(a[i]);
        }
    }

    let mut out = [0u8; 32];
    for (i, word) in h.iter().enumerate() {
        out[i * 4..i * 4 + 4].copy_from_slice(&word.to_be_bytes());
    }
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use sha2::{Digest, Sha256};

    fn reference(input: &[u8]) -> [u8; 32] {
        Sha256::digest(input).into()
    }

    #[test]
    fn matches_sha2_on_edge_lengths() {
        // empty, one block boundary cases, and lengths that force extra padding blocks
        for len in [0usize, 1, 3, 55, 56, 57, 63, 64, 65, 100, 128, 191, 200] {
            let input: Vec<u8> = (0..len).map(|i| (i * 31 + 7) as u8).collect();
            assert_eq!(hash(&input), reference(&input), "sha256 mismatch at len {len}");
        }
    }

    #[test]
    fn matches_sha2_known_vector() {
        // "abc" → the canonical SHA-256 test vector
        assert_eq!(
            hash(b"abc"),
            hex_lit("ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"),
        );
    }

    fn hex_lit(s: &str) -> [u8; 32] {
        let mut out = [0u8; 32];
        for (i, byte) in out.iter_mut().enumerate() {
            *byte = u8::from_str_radix(&s[i * 2..i * 2 + 2], 16).unwrap();
        }
        out
    }
}