typebit 0.1.8

//! SHA-256 (FIPS 180-4) — required by BitTorrent v2 (BEP-52), receipt
//! content commitment and Merkle helpers. Pure `no_std`, zero `unsafe`.

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,
];

/// Incremental SHA-256 hasher.
#[derive(Clone)]
pub struct Sha256 {
    state: [u32; 8],
    len: u64,
    block: [u8; 64],
    n: usize,
}

impl Default for Sha256 {
    fn default() -> Self {
        Self::new()
    }
}

impl Sha256 {
    /// New hasher.
    pub fn new() -> Self {
        Sha256 {
            state: [
                0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
                0x5be0cd19,
            ],
            len: 0,
            block: [0u8; 64],
            n: 0,
        }
    }

    /// Absorb `data`.
    pub fn update(&mut self, data: &[u8]) {
        self.len = self.len.wrapping_add(data.len() as u64);
        let mut off = 0usize;
        if self.n > 0 && self.n + data.len() >= 64 {
            let take = 64 - self.n;
            self.block[self.n..].copy_from_slice(&data[..take]);
            compress(&mut self.state, &self.block);
            self.n = 0;
            off = take;
        }
        while off + 64 <= data.len() {
            let mut b = [0u8; 64];
            b.copy_from_slice(&data[off..off + 64]);
            compress(&mut self.state, &b);
            off += 64;
        }
        let rem = data.len() - off;
        if rem > 0 {
            self.block[self.n..self.n + rem].copy_from_slice(&data[off..]);
            self.n += rem;
        }
    }

    /// Finalize into a 32-byte digest.
    pub fn finalize(mut self) -> [u8; 32] {
        let bit_len = self.len.wrapping_mul(8);
        self.update(&[0x80]);
        while self.n != 56 {
            self.update(&[0]);
        }
        self.block[56..64].copy_from_slice(&bit_len.to_be_bytes());
        compress(&mut self.state, &self.block);
        let mut out = [0u8; 32];
        for (i, s) in self.state.iter().enumerate() {
            out[i * 4..i * 4 + 4].copy_from_slice(&s.to_be_bytes());
        }
        out
    }

    /// One-shot SHA-256.
    pub fn digest(data: &[u8]) -> [u8; 32] {
        let mut h = Sha256::new();
        h.update(data);
        h.finalize()
    }

    /// Two-input one-shot (avoids a temporary concatenation).
    pub fn digest2(a: &[u8], b: &[u8]) -> [u8; 32] {
        let mut h = Sha256::new();
        h.update(a);
        h.update(b);
        h.finalize()
    }

    /// Three-input one-shot.
    pub fn digest3(a: &[u8], b: &[u8], c: &[u8]) -> [u8; 32] {
        let mut h = Sha256::new();
        h.update(a);
        h.update(b);
        h.update(c);
        h.finalize()
    }
}

fn compress(state: &mut [u32; 8], block: &[u8; 64]) {
    let mut w = [0u32; 64];
    for i in 0..16 {
        w[i] = u32::from_be_bytes([
            block[i * 4],
            block[i * 4 + 1],
            block[i * 4 + 2],
            block[i * 4 + 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, mut b, mut c, mut d, mut e, mut f, mut g, mut h) = (
        state[0], state[1], state[2], state[3], state[4], state[5], state[6], state[7],
    );
    for i in 0..64 {
        let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
        let ch = (e & f) ^ ((!e) & g);
        let t1 = h
            .wrapping_add(s1)
            .wrapping_add(ch)
            .wrapping_add(K[i])
            .wrapping_add(w[i]);
        let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
        let maj = (a & b) ^ (a & c) ^ (b & c);
        let t2 = s0.wrapping_add(maj);
        h = g;
        g = f;
        f = e;
        e = d.wrapping_add(t1);
        d = c;
        c = b;
        b = a;
        a = t1.wrapping_add(t2);
    }
    state[0] = state[0].wrapping_add(a);
    state[1] = state[1].wrapping_add(b);
    state[2] = state[2].wrapping_add(c);
    state[3] = state[3].wrapping_add(d);
    state[4] = state[4].wrapping_add(e);
    state[5] = state[5].wrapping_add(f);
    state[6] = state[6].wrapping_add(g);
    state[7] = state[7].wrapping_add(h);
}

#[cfg(test)]
mod tests {
    use super::*;
    use alloc::string::String;

    fn hex(d: [u8; 32]) -> String {
        let mut s = String::new();
        for b in d {
            s.push_str(&format!("{:02x}", b));
        }
        s
    }

    #[test]
    fn fips_vectors() {
        assert_eq!(
            hex(Sha256::digest(b"abc")),
            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
        );
        assert_eq!(
            hex(Sha256::digest(b"")),
            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
        );
        assert_eq!(
            hex(Sha256::digest(
                b"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"
            )),
            "248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1"
        );
    }

    #[test]
    fn incremental_matches_oneshot() {
        let mut h = Sha256::new();
        let data = b"TypeBit incremental SHA-256 test, split into odd chunks!";
        for c in data.chunks(5) {
            h.update(c);
        }
        assert_eq!(h.finalize(), Sha256::digest(data));
    }
}