zenith-float-num 1.0.2

//! SHA-2, HMAC-SHA-256, and constant-time byte compare. Integer only.

/// SHA-256 of `data`.
pub fn sha256(data: &[u8]) -> [u8; 32] {
    let mut h = SHA256_IV;
    let (n_full, tail) = padded_blocks::<64>(data, 8);
    for i in 0..n_full {
        sha256_compress(&mut h, &block64(data, i));
    }
    for blk in &tail {
        sha256_compress(&mut h, blk);
    }
    let mut out = [0u8; 32];
    for (i, w) in h.iter().enumerate() {
        out[i * 4..(i + 1) * 4].copy_from_slice(&w.to_be_bytes());
    }
    out
}

/// SHA-512 of `data`.
pub fn sha512(data: &[u8]) -> [u8; 64] {
    let mut h = SHA512_IV;
    let (n_full, tail) = padded_blocks::<128>(data, 16);
    for i in 0..n_full {
        sha512_compress(&mut h, &block128(data, i));
    }
    for blk in &tail {
        sha512_compress(&mut h, blk);
    }
    let mut out = [0u8; 64];
    for (i, w) in h.iter().enumerate() {
        out[i * 8..(i + 1) * 8].copy_from_slice(&w.to_be_bytes());
    }
    out
}

/// HMAC-SHA-256 (`key`, `data`).
pub fn hmac_sha256(key: &[u8], data: &[u8]) -> [u8; 32] {
    let mut k = [0u8; 64];
    if key.len() > 64 {
        k[..32].copy_from_slice(&sha256(key));
    } else {
        k[..key.len()].copy_from_slice(key);
    }
    let mut ipad = [0x36u8; 64];
    let mut opad = [0x5cu8; 64];
    for i in 0..64 {
        ipad[i] ^= k[i];
        opad[i] ^= k[i];
    }
    let mut inner = alloc::vec![0u8; 64 + data.len()];
    inner[..64].copy_from_slice(&ipad);
    inner[64..].copy_from_slice(data);
    let ih = sha256(&inner);
    let mut outer = [0u8; 96];
    outer[..64].copy_from_slice(&opad);
    outer[64..].copy_from_slice(&ih);
    sha256(&outer)
}

/// Timing-safe equality: always scans both slices; length mismatch is `false`.
pub fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
    let mut diff = (a.len() ^ b.len()) as u8;
    let n = a.len().min(b.len());
    for i in 0..n {
        diff |= a[i] ^ b[i];
    }
    if a.len() != b.len() {
        for &x in &a[n..] {
            diff |= x;
        }
        for &x in &b[n..] {
            diff |= x;
        }
    }
    diff == 0
}

fn block64(data: &[u8], i: usize) -> [u8; 64] {
    let mut b = [0u8; 64];
    b.copy_from_slice(&data[i * 64..(i + 1) * 64]);
    b
}

fn block128(data: &[u8], i: usize) -> [u8; 128] {
    let mut b = [0u8; 128];
    b.copy_from_slice(&data[i * 128..(i + 1) * 128]);
    b
}

/// Full unpadded blocks, then one or two padded tail blocks.
fn padded_blocks<const B: usize>(
    data: &[u8],
    len_bytes: usize,
) -> (usize, alloc::vec::Vec<[u8; B]>) {
    let n_full = data.len() / B;
    let rem = data.len() % B;
    let bit_len = (data.len() as u128).wrapping_mul(8);
    let mut tail = alloc::vec::Vec::new();
    let mut blk = [0u8; B];
    blk[..rem].copy_from_slice(&data[n_full * B..]);
    blk[rem] = 0x80;
    let need = rem + 1 + len_bytes;
    if need > B {
        tail.push(blk);
        blk = [0u8; B];
    }
    write_be_len(&mut blk[B - len_bytes..], bit_len, len_bytes);
    tail.push(blk);
    (n_full, tail)
}

fn write_be_len(dst: &mut [u8], bit_len: u128, len_bytes: usize) {
    if len_bytes == 8 {
        dst.copy_from_slice(&(bit_len as u64).to_be_bytes());
    } else {
        dst.copy_from_slice(&bit_len.to_be_bytes());
    }
}

fn rotr32(x: u32, n: u32) -> u32 {
    x.rotate_right(n)
}

fn rotr64(x: u64, n: u32) -> u64 {
    x.rotate_right(n)
}

fn sha256_compress(h: &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 = rotr32(w[i - 15], 7) ^ rotr32(w[i - 15], 18) ^ (w[i - 15] >> 3);
        let s1 = rotr32(w[i - 2], 17) ^ rotr32(w[i - 2], 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[0];
    let mut b = h[1];
    let mut c = h[2];
    let mut d = h[3];
    let mut e = h[4];
    let mut f = h[5];
    let mut g = h[6];
    let mut hh = h[7];
    for i in 0..64 {
        let s1 = rotr32(e, 6) ^ rotr32(e, 11) ^ rotr32(e, 25);
        let ch = (e & f) ^ ((!e) & g);
        let t1 = hh
            .wrapping_add(s1)
            .wrapping_add(ch)
            .wrapping_add(SHA256_K[i])
            .wrapping_add(w[i]);
        let s0 = rotr32(a, 2) ^ rotr32(a, 13) ^ rotr32(a, 22);
        let maj = (a & b) ^ (a & c) ^ (b & c);
        let t2 = s0.wrapping_add(maj);
        hh = g;
        g = f;
        f = e;
        e = d.wrapping_add(t1);
        d = c;
        c = b;
        b = a;
        a = t1.wrapping_add(t2);
    }
    h[0] = h[0].wrapping_add(a);
    h[1] = h[1].wrapping_add(b);
    h[2] = h[2].wrapping_add(c);
    h[3] = h[3].wrapping_add(d);
    h[4] = h[4].wrapping_add(e);
    h[5] = h[5].wrapping_add(f);
    h[6] = h[6].wrapping_add(g);
    h[7] = h[7].wrapping_add(hh);
}

fn sha512_compress(h: &mut [u64; 8], block: &[u8; 128]) {
    let mut w = [0u64; 80];
    for i in 0..16 {
        w[i] = u64::from_be_bytes([
            block[i * 8],
            block[i * 8 + 1],
            block[i * 8 + 2],
            block[i * 8 + 3],
            block[i * 8 + 4],
            block[i * 8 + 5],
            block[i * 8 + 6],
            block[i * 8 + 7],
        ]);
    }
    for i in 16..80 {
        let s0 = rotr64(w[i - 15], 1) ^ rotr64(w[i - 15], 8) ^ (w[i - 15] >> 7);
        let s1 = rotr64(w[i - 2], 19) ^ rotr64(w[i - 2], 61) ^ (w[i - 2] >> 6);
        w[i] = w[i - 16]
            .wrapping_add(s0)
            .wrapping_add(w[i - 7])
            .wrapping_add(s1);
    }
    let mut a = h[0];
    let mut b = h[1];
    let mut c = h[2];
    let mut d = h[3];
    let mut e = h[4];
    let mut f = h[5];
    let mut g = h[6];
    let mut hh = h[7];
    for i in 0..80 {
        let s1 = rotr64(e, 14) ^ rotr64(e, 18) ^ rotr64(e, 41);
        let ch = (e & f) ^ ((!e) & g);
        let t1 = hh
            .wrapping_add(s1)
            .wrapping_add(ch)
            .wrapping_add(SHA512_K[i])
            .wrapping_add(w[i]);
        let s0 = rotr64(a, 28) ^ rotr64(a, 34) ^ rotr64(a, 39);
        let maj = (a & b) ^ (a & c) ^ (b & c);
        let t2 = s0.wrapping_add(maj);
        hh = g;
        g = f;
        f = e;
        e = d.wrapping_add(t1);
        d = c;
        c = b;
        b = a;
        a = t1.wrapping_add(t2);
    }
    h[0] = h[0].wrapping_add(a);
    h[1] = h[1].wrapping_add(b);
    h[2] = h[2].wrapping_add(c);
    h[3] = h[3].wrapping_add(d);
    h[4] = h[4].wrapping_add(e);
    h[5] = h[5].wrapping_add(f);
    h[6] = h[6].wrapping_add(g);
    h[7] = h[7].wrapping_add(hh);
}

const SHA256_IV: [u32; 8] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

const SHA256_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,
];

const SHA512_IV: [u64; 8] = [
    0x6a09e667f3bcc908,
    0xbb67ae8584caa73b,
    0x3c6ef372fe94f82b,
    0xa54ff53a5f1d36f1,
    0x510e527fade682d1,
    0x9b05688c2b3e6c1f,
    0x1f83d9abfb41bd6b,
    0x5be0cd19137e2179,
];

const SHA512_K: [u64; 80] = [
    0x428a2f98d728ae22,
    0x7137449123ef65cd,
    0xb5c0fbcfec4d3b2f,
    0xe9b5dba58189dbbc,
    0x3956c25bf348b538,
    0x59f111f1b605d019,
    0x923f82a4af194f9b,
    0xab1c5ed5da6d8118,
    0xd807aa98a3030242,
    0x12835b0145706fbe,
    0x243185be4ee4b28c,
    0x550c7dc3d5ffb4e2,
    0x72be5d74f27b896f,
    0x80deb1fe3b1696b1,
    0x9bdc06a725c71235,
    0xc19bf174cf692694,
    0xe49b69c19ef14ad2,
    0xefbe4786384f25e3,
    0x0fc19dc68b8cd5b5,
    0x240ca1cc77ac9c65,
    0x2de92c6f592b0275,
    0x4a7484aa6ea6e483,
    0x5cb0a9dcbd41fbd4,
    0x76f988da831153b5,
    0x983e5152ee66dfab,
    0xa831c66d2db43210,
    0xb00327c898fb213f,
    0xbf597fc7beef0ee4,
    0xc6e00bf33da88fc2,
    0xd5a79147930aa725,
    0x06ca6351e003826f,
    0x142929670a0e6e70,
    0x27b70a8546d22ffc,
    0x2e1b21385c26c926,
    0x4d2c6dfc5ac42aed,
    0x53380d139d95b3df,
    0x650a73548baf63de,
    0x766a0abb3c77b2a8,
    0x81c2c92e47edaee6,
    0x92722c851482353b,
    0xa2bfe8a14cf10364,
    0xa81a664bbc423001,
    0xc24b8b70d0f89791,
    0xc76c51a30654be30,
    0xd192e819d6ef5218,
    0xd69906245565a910,
    0xf40e35855771202a,
    0x106aa07032bbd1b8,
    0x19a4c116b8d2d0c8,
    0x1e376c085141ab53,
    0x2748774cdf8eeb99,
    0x34b0bcb5e19b48a8,
    0x391c0cb3c5c95a63,
    0x4ed8aa4ae3418acb,
    0x5b9cca4f7763e373,
    0x682e6ff3d6b2b8a3,
    0x748f82ee5defb2fc,
    0x78a5636f43172f60,
    0x84c87814a1f0ab72,
    0x8cc702081a6439ec,
    0x90befffa23631e28,
    0xa4506cebde82bde9,
    0xbef9a3f7b2c67915,
    0xc67178f2e372532b,
    0xca273eceea26619c,
    0xd186b8c721c0c207,
    0xeada7dd6cde0eb1e,
    0xf57d4f7fee6ed178,
    0x06f067aa72176fba,
    0x0a637dc5a2c898a6,
    0x113f9804bef90dae,
    0x1b710b35131c471b,
    0x28db77f523047d84,
    0x32caab7b40c72493,
    0x3c9ebe0a15c9bebc,
    0x431d67c49c100d4c,
    0x4cc5d4becb3e42b6,
    0x597f299cfc657e2a,
    0x5fcb6fab3ad6faec,
    0x6c44198c4a475817,
];

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

    fn hex32(s: &str) -> [u8; 32] {
        let mut o = [0u8; 32];
        for i in 0..32 {
            o[i] = u8::from_str_radix(&s[i * 2..i * 2 + 2], 16).unwrap();
        }
        o
    }

    #[test]
    fn hash_sha256_hmac_ct() {
        assert_eq!(
            sha256(b""),
            hex32("e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855")
        );
        assert_eq!(
            sha256(b"abc"),
            hex32("ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad")
        );
        let mut key = [0u8; 20];
        key.fill(0x0b);
        assert_eq!(
            hmac_sha256(&key, b"Hi There"),
            hex32("b0344c61d8db38535ca8afceaf0bf12b881dc200c9833da726e9376c2e32cff7")
        );
        assert!(constant_time_eq(b"abc", b"abc"));
        assert!(!constant_time_eq(b"abc", b"abx"));
        assert_eq!(
            constant_time_eq(&[0, 1, 0], &[1, 0, 0]),
            constant_time_eq(&[0, 0, 1], &[0, 1, 0])
        );
        assert!(!constant_time_eq(&[0, 1, 0], &[1, 0, 0]));
        assert!(!constant_time_eq(b"ab", b"abc"));
        assert_eq!(
            sha512(b""),
            [
                0xcf, 0x83, 0xe1, 0x35, 0x7e, 0xef, 0xb8, 0xbd, 0xf1, 0x54, 0x28, 0x50, 0xd6, 0x6d,
                0x80, 0x07, 0xd6, 0x20, 0xe4, 0x05, 0x0b, 0x57, 0x15, 0xdc, 0x83, 0xf4, 0xa9, 0x21,
                0xd3, 0x6c, 0xe9, 0xce, 0x47, 0xd0, 0xd1, 0x3c, 0x5d, 0x85, 0xf2, 0xb0, 0xff, 0x83,
                0x18, 0xd2, 0x87, 0x7e, 0xec, 0x2f, 0x63, 0xb9, 0x31, 0xbd, 0x47, 0x41, 0x7a, 0x81,
                0xa5, 0x38, 0x32, 0x7a, 0xf9, 0x27, 0xda, 0x3e,
            ]
        );
    }
}