AES, Serpent or Twofish in C example?

Question

I found a lot of implementations of AES, Twofish and Serpent in C. But I don\'t really understand the examples. I only understand that some where provided with examples to i

Answer 1

Trying to answer the -still unanswered- question of killercode, here is my attempt of achieving the same thing:

• Download this TwoFish code (thanks go to Schneier et al.): https://www.schneier.com/code/twofish-reference-c.zip

• Use this code (at your own risk of course):

  int mode = MODE_CBC;
  int keySize = 256;
  int result = 0;
  
  keyInstance    ki;          /* key information, including tables */
  cipherInstance ci;          /* keeps mode (ECB, CBC) and IV */
  BYTE  plainText[MAX_BLK_CNT*(BLOCK_SIZE / 8)]; // 64 in size!
  BYTE cipherText[MAX_BLK_CNT*(BLOCK_SIZE / 8)];
  BYTE decryptOut[MAX_BLK_CNT*(BLOCK_SIZE / 8)];
  BYTE iv[BLOCK_SIZE / 8];
  int  i;
  
  
  /* select number of bytes to encrypt (multiple of block) */
  /* e.g., byteCnt = 16, 32, 48, 64 */
  //byteCnt = (BLOCK_SIZE / 8) * (1 + (rand() % MAX_BLK_CNT));
  
  /* generate test data */;
  int plainTextLength = 65;
  for (i = 0; i < min(plainTextLength, MAX_BLK_CNT*(BLOCK_SIZE / 8)); i++)
      plainText[i] = (BYTE)rand();
  
  if (plainTextLength > MAX_BLK_CNT * BLOCK_SIZE / 8) {
      ::MessageBox(NULL, _T("You need to increase your MAX_BLK_CNT for the plain-text to fit in one call."), _T("Error"), MB_OK);
      return;
  }
  
  int byteCnt = ceil((double)plainTextLength / (BLOCK_SIZE / 8.0)) * (BLOCK_SIZE / 8);
  
  /* ----------------------- */
  
  /* 'dummy' setup for a 128-bit key */
  if (makeKey(&ki, DIR_ENCRYPT, keySize, NULL) != TRUE)
      result = 1;
  
  /* ----------------------- */
  
  /* 'dummy' setup for cipher */
  if (cipherInit(&ci, mode, NULL) != TRUE)
      result = 1;
  
  /* select key bits */
  for (i = 0; i < keySize / 32; i++)
      ki.key32[i] = 0x10003 * rand();
  
  /* run the key schedule */
  reKey(&ki);
  
  /* set up random iv (if needed)*/
  if (mode != MODE_ECB)
  {
      for (i = 0; i < sizeof(iv); i++)
          iv[i] = (BYTE)rand();
  
      /* copy the IV to ci */
      memcpy(ci.iv32, iv, sizeof(ci.iv32));
  }
  
  /* encrypt the bytes */
  if (blockEncrypt(&ci, &ki, plainText, byteCnt * 8, cipherText) != byteCnt * 8)
      result = 1;
  
  /* ----------------------- */
  
  /* decrypt the bytes */
  if (mode != MODE_ECB)       /* first re-init the IV (if needed) */
      memcpy(ci.iv32, iv, sizeof(ci.iv32));
  
  if (blockDecrypt(&ci, &ki, cipherText, byteCnt * 8, decryptOut) != byteCnt * 8)
      result = 1;
  
  /* make sure the decrypt output matches original plaintext */
  if (memcmp(plainText, decryptOut, byteCnt))
      result = 1;
  
  if (result == 0) ::MessageBox(NULL, _T("Success"), _T("SUCCESS"), MB_OK);
  

That was my attempt and it seems working quite good.

It is using CBC mode.

I am open to suggestions, if anyone has any.

Of course you might like to make MAX_BLK_CNT a variable and increase it accordingly, to be able to encrypt a variety of data lengths. Although I am not 100% sure if that is its normal usage.

Cheer! :)