courierust 1.0.0

//! MD5 message digest (RFC 1321), implemented from the public
//! specification with no unsafe code. Used for JA3 fingerprints.

use alloc::string::String;
use alloc::vec::Vec;

const S: [u32; 64] = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, // round 1
    5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, // round 2
    4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, // round 3
    6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, // round 4
];

/// T[i] = floor(2^32 * |sin(i + 1)|), i = 0..=63 (RFC 1321 §3.4).
const T: [u32; 64] = [
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee, 0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be, 0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05, 0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1, 0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391,
];

/// Compute the MD5 digest of `data`.
pub fn md5(data: &[u8]) -> [u8; 16] {
    let mut a0: u32 = 0x67452301;
    let mut b0: u32 = 0xefcdab89;
    let mut c0: u32 = 0x98badcfe;
    let mut d0: u32 = 0x10325476;

    // Padding: 0x80, zeros, 64-bit little-endian bit length.
    let bit_len = (data.len() as u64).wrapping_mul(8);
    let mut msg = Vec::with_capacity(data.len() + 72);
    msg.extend_from_slice(data);
    msg.push(0x80);
    while msg.len() % 64 != 56 {
        msg.push(0);
    }
    msg.extend_from_slice(&bit_len.to_le_bytes());

    let (chunks, remainder) = msg.as_chunks::<64>();
    assert!(remainder.is_empty(), "MD5 padding must form full blocks");
    for chunk in chunks {
        let mut m = [0u32; 16];
        for (i, w) in m.iter_mut().enumerate() {
            *w = u32::from_le_bytes([
                chunk[i * 4],
                chunk[i * 4 + 1],
                chunk[i * 4 + 2],
                chunk[i * 4 + 3],
            ]);
        }
        let (mut a, mut b, mut c, mut d) = (a0, b0, c0, d0);
        for i in 0..64 {
            let (f, g) = match i / 16 {
                0 => ((b & c) | (!b & d), i),
                1 => ((d & b) | (!d & c), (5 * i + 1) % 16),
                2 => (b ^ c ^ d, (3 * i + 5) % 16),
                _ => (c ^ (b | !d), (7 * i) % 16),
            };
            let tmp = d;
            d = c;
            c = b;
            b = b.wrapping_add(
                a.wrapping_add(f)
                    .wrapping_add(T[i])
                    .wrapping_add(m[g])
                    .rotate_left(S[i]),
            );
            a = tmp;
        }
        a0 = a0.wrapping_add(a);
        b0 = b0.wrapping_add(b);
        c0 = c0.wrapping_add(c);
        d0 = d0.wrapping_add(d);
    }

    let mut out = [0u8; 16];
    out[0..4].copy_from_slice(&a0.to_le_bytes());
    out[4..8].copy_from_slice(&b0.to_le_bytes());
    out[8..12].copy_from_slice(&c0.to_le_bytes());
    out[12..16].copy_from_slice(&d0.to_le_bytes());
    out
}

/// Hex digest (lowercase, 32 chars).
pub fn md5_hex(data: &[u8]) -> String {
    let d = md5(data);
    let mut s = String::with_capacity(32);
    for b in d {
        s.push_str(&format!("{:02x}", b));
    }
    s
}

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

    #[test]
    fn rfc1321_vectors() {
        assert_eq!(md5_hex(b""), "d41d8cd98f00b204e9800998ecf8427e");
        assert_eq!(md5_hex(b"a"), "0cc175b9c0f1b6a831c399e269772661");
        assert_eq!(md5_hex(b"abc"), "900150983cd24fb0d6963f7d28e17f72");
        assert_eq!(
            md5_hex(b"message digest"),
            "f96b697d7cb7938d525a2f31aaf161d0"
        );
        assert_eq!(
            md5_hex(b"abcdefghijklmnopqrstuvwxyz"),
            "c3fcd3d76192e4007dfb496cca67e13b"
        );
        assert_eq!(
            md5_hex(b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"),
            "d174ab98d277d9f5a5611c2c9f419d9f"
        );
        assert_eq!(
            md5_hex(
                b"12345678901234567890123456789012345678901234567890123456789012345678901234567890"
            ),
            "57edf4a22be3c955ac49da2e2107b67a"
        );
    }
}