object-hash 0.3.0

//! MD5, for callers who must match a system that already uses it.
//!
//! MD5 is broken as a security primitive and is not used as one here: it names a
//! value, the same job SHA-1 does in this crate. It is included because the
//! reference package offers it and a cache key or ETag already in the field may
//! be an MD5, and matching an existing digest is the whole point.

const S: [u32; 64] = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9,
    14, 20, 5, 9, 14, 20, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 6, 10, 15,
    21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21,
];

/// The MD5 digest of `data`.
pub(crate) fn digest(data: &[u8]) -> [u8; 16] {
    const K: [u32; 64] = [
        0xd76a_a478,
        0xe8c7_b756,
        0x2420_70db,
        0xc1bd_ceee,
        0xf57c_0faf,
        0x4787_c62a,
        0xa830_4613,
        0xfd46_9501,
        0x6980_98d8,
        0x8b44_f7af,
        0xffff_5bb1,
        0x895c_d7be,
        0x6b90_1122,
        0xfd98_7193,
        0xa679_438e,
        0x49b4_0821,
        0xf61e_2562,
        0xc040_b340,
        0x265e_5a51,
        0xe9b6_c7aa,
        0xd62f_105d,
        0x0244_1453,
        0xd8a1_e681,
        0xe7d3_fbc8,
        0x21e1_cde6,
        0xc337_07d6,
        0xf4d5_0d87,
        0x455a_14ed,
        0xa9e3_e905,
        0xfcef_a3f8,
        0x676f_02d9,
        0x8d2a_4c8a,
        0xfffa_3942,
        0x8771_f681,
        0x6d9d_6122,
        0xfde5_380c,
        0xa4be_ea44,
        0x4bde_cfa9,
        0xf6bb_4b60,
        0xbebf_bc70,
        0x289b_7ec6,
        0xeaa1_27fa,
        0xd4ef_3085,
        0x0488_1d05,
        0xd9d4_d039,
        0xe6db_99e5,
        0x1fa2_7cf8,
        0xc4ac_5665,
        0xf429_2244,
        0x432a_ff97,
        0xab94_23a7,
        0xfc93_a039,
        0x655b_59c3,
        0x8f0c_cc92,
        0xffef_f47d,
        0x8584_5dd1,
        0x6fa8_7e4f,
        0xfe2c_e6e0,
        0xa301_4314,
        0x4e08_11a1,
        0xf753_7e82,
        0xbd3a_f235,
        0x2ad7_d2bb,
        0xeb86_d391,
    ];

    let mut state: [u32; 4] = [0x6745_2301, 0xefcd_ab89, 0x98ba_dcfe, 0x1032_5476];
    let bit_length = (data.len() as u64).wrapping_mul(8);

    let mut message = data.to_vec();
    message.push(0x80);
    while message.len() % 64 != 56 {
        message.push(0);
    }
    message.extend_from_slice(&bit_length.to_le_bytes());

    for block in message.as_chunks::<64>().0 {
        let mut m = [0u32; 16];
        for (index, word) in m.iter_mut().enumerate() {
            let start = index * 4;
            *word = u32::from_le_bytes([
                block[start],
                block[start + 1],
                block[start + 2],
                block[start + 3],
            ]);
        }

        let [mut a, mut b, mut c, mut d] = state;
        for index in 0..64 {
            let (f, g) = match index {
                0..=15 => ((b & c) | ((!b) & d), index),
                16..=31 => ((d & b) | ((!d) & c), (5 * index + 1) % 16),
                32..=47 => (b ^ c ^ d, (3 * index + 5) % 16),
                _ => (c ^ (b | (!d)), (7 * index) % 16),
            };
            let temp = d;
            d = c;
            c = b;
            let sum = a.wrapping_add(f).wrapping_add(K[index]).wrapping_add(m[g]);
            b = b.wrapping_add(sum.rotate_left(S[index]));
            a = temp;
        }

        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);
    }

    let mut out = [0u8; 16];
    for (chunk, word) in out.as_chunks_mut::<4>().0.iter_mut().zip(state) {
        chunk.copy_from_slice(&word.to_le_bytes());
    }
    out
}

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

    /// The digest as lowercase hexadecimal, for the published vectors.
    fn hex(data: &[u8]) -> String {
        let mut out = String::new();
        for byte in digest(data) {
            out.push(char::from_digit(u32::from(byte >> 4), 16).expect("nibble"));
            out.push(char::from_digit(u32::from(byte & 0x0f), 16).expect("nibble"));
        }
        out
    }

    #[test]
    fn the_published_test_vectors_match() {
        // The vectors from RFC 1321.
        assert_eq!(hex(b""), "d41d8cd98f00b204e9800998ecf8427e");
        assert_eq!(hex(b"abc"), "900150983cd24fb0d6963f7d28e17f72");
        assert_eq!(hex(b"message digest"), "f96b697d7cb7938d525a2f31aaf161d0");
        assert_eq!(
            hex(b"abcdefghijklmnopqrstuvwxyz"),
            "c3fcd3d76192e4007dfb496cca67e13b"
        );
        assert_eq!(
            hex(b"The quick brown fox jumps over the lazy dog"),
            "9e107d9d372bb6826bd81d3542a419d6"
        );
    }

    #[test]
    fn a_longer_message_spanning_many_blocks_matches() {
        // The eighty-digit ASCII vector from RFC 1321.
        let data =
            b"12345678901234567890123456789012345678901234567890123456789012345678901234567890";
        assert_eq!(hex(data), "57edf4a22be3c955ac49da2e2107b67a");
    }
}