md5Convert function

List<int> md5Convert(Uint8List data)

Minimal MD5 implementation for PDF encryption.

Implementation

List<int> md5Convert(Uint8List data) {
  // Using dart:convert's built-in doesn't include md5, so we implement it
  // Constants
  const s = <int>[
    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,
  ];
  const k = <int>[
    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,
  ];

  // Pre-processing: add padding
  final msgLen = data.length;
  final bitLen = msgLen * 8;
  final padded = <int>[...data, 0x80];
  while (padded.length % 64 != 56) {
    padded.add(0);
  }
  // Append original length as 64-bit LE
  for (int i = 0; i < 8; i++) {
    padded.add((bitLen >> (i * 8)) & 0xFF);
  }

  int a0 = 0x67452301;
  int b0 = 0xefcdab89;
  int c0 = 0x98badcfe;
  int d0 = 0x10325476;

  int leftRotate(int x, int c) =>
      ((x << c) | ((x & 0xFFFFFFFF) >> (32 - c))) & 0xFFFFFFFF;

  for (int chunk = 0; chunk < padded.length; chunk += 64) {
    final m = List<int>.filled(16, 0);
    for (int i = 0; i < 16; i++) {
      final offset = chunk + i * 4;
      m[i] = padded[offset] |
          (padded[offset + 1] << 8) |
          (padded[offset + 2] << 16) |
          (padded[offset + 3] << 24);
    }

    int a = a0, b = b0, c = c0, d = d0;

    for (int i = 0; i < 64; i++) {
      int f, g;
      if (i < 16) {
        f = (b & c) | ((~b & 0xFFFFFFFF) & d);
        g = i;
      } else if (i < 32) {
        f = (d & b) | ((~d & 0xFFFFFFFF) & c);
        g = (5 * i + 1) % 16;
      } else if (i < 48) {
        f = b ^ c ^ d;
        g = (3 * i + 5) % 16;
      } else {
        f = c ^ (b | (~d & 0xFFFFFFFF));
        g = (7 * i) % 16;
      }

      f = (f + a + k[i] + m[g]) & 0xFFFFFFFF;
      a = d;
      d = c;
      c = b;
      b = (b + leftRotate(f, s[i])) & 0xFFFFFFFF;
    }

    a0 = (a0 + a) & 0xFFFFFFFF;
    b0 = (b0 + b) & 0xFFFFFFFF;
    c0 = (c0 + c) & 0xFFFFFFFF;
    d0 = (d0 + d) & 0xFFFFFFFF;
  }

  final digest = Uint8List(16);
  for (int i = 0; i < 4; i++) {
    digest[i] = (a0 >> (i * 8)) & 0xFF;
    digest[i + 4] = (b0 >> (i * 8)) & 0xFF;
    digest[i + 8] = (c0 >> (i * 8)) & 0xFF;
    digest[i + 12] = (d0 >> (i * 8)) & 0xFF;
  }
  return digest.toList();
}