gra-projekt/Implementierung/src/md2.c

#include "../lib/md2.h"

// The file "testfile" should lead to this hash:
// fc982e558db259f298b43cd4c1241c66

// Source: https://datatracker.ietf.org/doc/html/rfc1319
static unsigned char PI_SUBST[256] = {
    41,  46,  67,  201, 162, 216, 124, 1,   61,  54,  84,  161, 236, 240, 6,
    19,  98,  167, 5,   243, 192, 199, 115, 140, 152, 147, 43,  217, 188, 76,
    130, 202, 30,  155, 87,  60,  253, 212, 224, 22,  103, 66,  111, 24,  138,
    23,  229, 18,  190, 78,  196, 214, 218, 158, 222, 73,  160, 251, 245, 142,
    187, 47,  238, 122, 169, 104, 121, 145, 21,  178, 7,   63,  148, 194, 16,
    137, 11,  34,  95,  33,  128, 127, 93,  154, 90,  144, 50,  39,  53,  62,
    204, 231, 191, 247, 151, 3,   255, 25,  48,  179, 72,  165, 181, 209, 215,
    94,  146, 42,  172, 86,  170, 198, 79,  184, 56,  210, 150, 164, 125, 182,
    118, 252, 107, 226, 156, 116, 4,   241, 69,  157, 112, 89,  100, 113, 135,
    32,  134, 91,  207, 101, 230, 45,  168, 2,   27,  96,  37,  173, 174, 176,
    185, 246, 28,  70,  97,  105, 52,  64,  126, 15,  85,  71,  163, 35,  221,
    81,  175, 58,  195, 92,  249, 206, 186, 197, 234, 38,  44,  83,  13,  110,
    133, 40,  132, 9,   211, 223, 205, 244, 65,  129, 77,  82,  106, 220, 55,
    200, 108, 193, 171, 250, 36,  225, 123, 8,   12,  189, 177, 74,  120, 136,
    149, 139, 227, 99,  232, 109, 233, 203, 213, 254, 59,  0,   29,  57,  242,
    239, 183, 14,  102, 88,  208, 228, 166, 119, 114, 248, 235, 117, 75,  10,
    49,  68,  80,  180, 143, 237, 31,  26,  219, 153, 141, 51,  159, 17,  131,
    20};

void printBuf(size_t len, uint8_t buf[len]) {
  for (int i = 0; i < len; i++) {
    printf("'%02x',", buf[i]);
  }
  printf("\n");
}

void md2_checksum(size_t len, uint8_t* buf) {
  uint8_t l = 0;

  for (int i = 0; i < len / 16; i++) {
    for (int j = 0; j < 16; j++) {
      u_int8_t c = buf[i * 16 + j];
      l = buf[len + j] = PI_SUBST[c ^ l];
    }
  }
}

void md2_hash(size_t len, const uint8_t buf[len], uint8_t out[16]) {
  // === step 1 ===
  int paddingNeeded = 16 - (len % 16);
  uint8_t originalPadding = paddingNeeded;
  len += paddingNeeded;

  printf("len: %d\n", len);

  // +16 for the checksum
  uint8_t* newBuf = calloc(len + 16, sizeof(uint8_t));
  memcpy(newBuf, buf, len - paddingNeeded);

  while (paddingNeeded > 0) {
    newBuf[len - paddingNeeded] = originalPadding;
    paddingNeeded--;
  }
  printf("buf with padding: ");
  printBuf(len + 16, newBuf);

  // === step 2 ===
  md2_checksum(len, newBuf);

  printf("buf with cecksum: ");
  printBuf(len + 16, newBuf);

  // === step 3 ===
  uint8_t* messageDigestBuf = calloc(48, sizeof(uint8_t));

  // === step 4 ===
  // <= because we need to hash the last block too
  for (int i = 0; i <= (len + 16) / 16 - 1; i++) {
    for (int j = 0; j < 16; j++) {
      messageDigestBuf[16 + j] = newBuf[i * 16 + j];
      messageDigestBuf[32 + j] =
          (messageDigestBuf[16 + j] ^ messageDigestBuf[j]);
    }

    u_int8_t t = 0;

    for (int j = 0; j < 18; j++) {
      for (int k = 0; k < 48; k++) {
        t = messageDigestBuf[k] = messageDigestBuf[k] ^ PI_SUBST[t];
      }
      t = (t + j) % 256;
    }
  }
  printf("messageDigestBuf: \n");
  printBuf(16, messageDigestBuf);

  memcpy(out, messageDigestBuf, 16);

  free(messageDigestBuf);
  free(newBuf);
}