otp-auth 0.1.0

//! # Sources: <https://datatracker.ietf.org/doc/html/rfc6234>

#[rustfmt::skip]
const 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,
];

/// # Example:
/// ```rust
/// use otp::Algorithm;
///
/// let alg = Algorithm::SHA512;
///
/// let empty_hash = alg.hash_hex(b"");
/// assert_eq!("cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e", &empty_hash);
///
/// let hash = alg.hash_hex(b"The quick brown fox jumps over the lazy dog");
/// assert_eq!("07e547d9586f6a73f73fbac0435ed76951218fb7d0c8d788a309d785436bbb642e93a252a954f23912547d1e8a3b5ed6e1bfd7097821233fa0538f3db854fee6", &hash);
/// ```
pub fn sha512(input: &[u8]) -> [u8; 64] {
    #[rustfmt::skip]
    let mut state: [u64; 8] = [
        0x6a09e667f3bcc908,
        0xbb67ae8584caa73b,
        0x3c6ef372fe94f82b,
        0xa54ff53a5f1d36f1,
        0x510e527fade682d1,
        0x9b05688c2b3e6c1f,
        0x1f83d9abfb41bd6b,
        0x5be0cd19137e2179,
    ];

    const BLOCK_SIZE: usize = 128;
    const PREP_ROUNDS: usize = 16;
    const EXTENSION_ROUNDS: usize = 80;
    const COMPRESSION_ROUNDS: usize = 80;

    let bit_len = (input.len() as u128) * 8;

    let mut padded = input.to_vec();

    // mark of the end of the original message.
    padded.push(0x80);

    // pad with zeroes until the length mod 128 is = 112.
    padded.resize(((padded.len() + 128) & !127_usize) - 16, 0x00);

    // reserves the last 16 bytes for the bit-length field.
    padded.extend_from_slice(&(bit_len.to_be_bytes()));

    for chunk in padded.chunks(BLOCK_SIZE) {
        let mut words = [0_u64; COMPRESSION_ROUNDS];

        // w[0..16]: schedule preparation
        for i in 0..PREP_ROUNDS {
            words[i] = u64::from_be_bytes([
                chunk[i * 8],
                chunk[i * 8 + 1],
                chunk[i * 8 + 2],
                chunk[i * 8 + 3],
                chunk[i * 8 + 4],
                chunk[i * 8 + 5],
                chunk[i * 8 + 6],
                chunk[i * 8 + 7],
            ]);
        }

        // w[16..80]: schedule extension
        for i in PREP_ROUNDS..EXTENSION_ROUNDS {
            #[rustfmt::skip]
            let s0 = words[i - 15].rotate_right(1) ^ words[i - 15].rotate_right(8) ^ (words[i - 15] >> 7);

            #[rustfmt::skip]
            let s1 = words[i - 2].rotate_right(19) ^ words[i - 2].rotate_right(61) ^ (words[i - 2] >> 6);

            words[i] = words[i - 16]
                .wrapping_add(s0)
                .wrapping_add(words[i - 7])
                .wrapping_add(s1);
        }

        let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = state;

        for i in 0..COMPRESSION_ROUNDS {
            let s1 = e.rotate_right(14) ^ e.rotate_right(18) ^ e.rotate_right(41);
            let ch = (e & f) ^ ((!e) & g);
            let temp1 = h
                .wrapping_add(s1)
                .wrapping_add(ch)
                .wrapping_add(K[i])
                .wrapping_add(words[i]);
            let s0 = a.rotate_right(28) ^ a.rotate_right(34) ^ a.rotate_right(39);
            let maj = (a & b) ^ (a & c) ^ (b & c);
            let temp2 = s0.wrapping_add(maj);

            h = g;
            g = f;
            f = e;
            e = d.wrapping_add(temp1);
            d = c;
            c = b;
            b = a;
            a = temp1.wrapping_add(temp2);
        }

        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);
    }

    let mut digest = [0_u8; 64];
    for (i, word) in state.iter().enumerate() {
        digest[i * 8..(i + 1) * 8].copy_from_slice(&word.to_be_bytes());
    }

    digest
}