des.c

掌握如何用C来实现各种算法

   **************************************************************************/

   permute(temp, DesTransform, 56);

   /**************************************************************************
   *                                                                         *
   *  Split the key into two 28-bit blocks.                                  *
   *                                                                         *
   **************************************************************************/

   memset(lkey, 0, 4);
   memset(rkey, 0, 4);

   for (j = 0; j < 28; j++)
      bit_set(lkey, j, bit_get(temp, j));

   for (j = 0; j < 28; j++)
      bit_set(rkey, j, bit_get(temp, j + 28));

   /**************************************************************************
   *                                                                         *
   *  Compute the subkeys for each round.                                    *
   *                                                                         *
   **************************************************************************/

   for (i = 0; i < 16; i++) {

      /***********************************************************************
      *                                                                      *
      *  Rotate each block according to its round.                           *
      *                                                                      *
      ***********************************************************************/

      bit_rot_left(lkey, 28, DesRotations[i]);
      bit_rot_left(rkey, 28, DesRotations[i]);

      /***********************************************************************
      *                                                                      *
      *  Concatenate the blocks into a single subkey.                        *
      *                                                                      *
      ***********************************************************************/

      for (j = 0; j < 28; j++)
         bit_set(subkeys[i], j, bit_get(lkey, j));

      for (j = 0; j < 28; j++)
         bit_set(subkeys[i], j + 28, bit_get(rkey, j));

      /***********************************************************************
      *                                                                      *
      *  Do the permuted choice permutation.                                 *
      *                                                                      *
      ***********************************************************************/

      permute(subkeys[i], DesPermuted, 48);

   }

}

/*****************************************************************************
*                                                                            *
*  Make a local copy of the source text.                                     *
*                                                                            *
*****************************************************************************/

memcpy(temp, source, 8);

/*****************************************************************************
*                                                                            *
*  Do the initial permutation.                                               *
*                                                                            *
*****************************************************************************/

permute(temp, DesInitial, 64);

/*****************************************************************************
*                                                                            *
*  Split the source text into a left and right block of 32 bits.             *
*                                                                            *
*****************************************************************************/

memcpy(lblk, &temp[0], 4);
memcpy(rblk, &temp[4], 4);

/*****************************************************************************
*                                                                            *
*  Encipher or decipher the source text.                                     *
*                                                                            *
*****************************************************************************/

for (i = 0; i < 16; i++) {

   /**************************************************************************
   *                                                                         *
   *  Begin the computation of f.                                            *
   *                                                                         *
   **************************************************************************/

   memcpy(fblk, rblk, 4);

   /**************************************************************************
   *                                                                         *
   *  Permute and expand the copy of the right block into 48 bits.           *
   *                                                                         *
   **************************************************************************/

   permute(fblk, DesExpansion, 48);

   /**************************************************************************
   *                                                                         *
   *  Apply the appropriate subkey for the round.                            *
   *                                                                         *
   **************************************************************************/

   if (direction == encipher) {

      /***********************************************************************
      *                                                                      *
      *  For enciphering, subkeys are applied in increasing order.           *
      *                                                                      *
      ***********************************************************************/

      bit_xor(fblk, subkeys[i], xblk, 48);
      memcpy(fblk, xblk, 6);

      }

   else {

      /***********************************************************************
      *                                                                      *
      *  For deciphering, subkeys are applied in decreasing order.           *
      *                                                                      *
      ***********************************************************************/

      bit_xor(fblk, subkeys[15 - i], xblk, 48);
      memcpy(fblk, xblk, 6);

   }

   /**************************************************************************
   *                                                                         *
   *  Do the S-box substitutions.                                            *
   *                                                                         *
   **************************************************************************/

   p = 0;

   for (j = 0; j < 8; j++) {

      /***********************************************************************
      *                                                                      *
      *  Compute a row and column into the S-box tables.                     *
      *                                                                      *
      ***********************************************************************/

      row = (bit_get(fblk, (j * 6)+0) * 2) + (bit_get(fblk, (j * 6)+5) * 1);
      col = (bit_get(fblk, (j * 6)+1) * 8) + (bit_get(fblk, (j * 6)+2) * 4) +
            (bit_get(fblk, (j * 6)+3) * 2) + (bit_get(fblk, (j * 6)+4) * 1);

      /***********************************************************************
      *                                                                      *
      *  Do the S-box substitution for the current six-bit block.            *
      *                                                                      *
      ***********************************************************************/

      sblk = (unsigned char)DesSbox[j][row][col];

      for (k = 4; k < 8; k++) {

         bit_set(fblk, p, bit_get(&sblk, k));
         p++;

      }

   }

   /**************************************************************************
   *                                                                         *
   *  Do the P-box permutation to complete f.                                *
   *                                                                         *
   **************************************************************************/

   permute(fblk, DesPbox, 32);

   /**************************************************************************
   *                                                                         *
   *  Compute the XOR of the left block and f.                               *
   *                                                                         *
   **************************************************************************/

   bit_xor(lblk, fblk, xblk, 32);

   /**************************************************************************
   *                                                                         *
   *  Set the left block for the round.                                      *
   *                                                                         *
   **************************************************************************/

   memcpy(lblk, rblk, 4);

   /**************************************************************************
   *                                                                         *
   *  Set the right block for the round.                                     *
   *                                                                         *
   **************************************************************************/

   memcpy(rblk, xblk, 4);

}

/*****************************************************************************
*                                                                            *
*  Set the target text to the rejoined final right and left blocks.          *
*                                                                            *
*****************************************************************************/

memcpy(&target[0], rblk, 4);
memcpy(&target[4], lblk, 4);

/*****************************************************************************
*                                                                            *
*  Do the final permutation.                                                 *
*                                                                            *
*****************************************************************************/

permute(target, DesFinal, 64);

return 0;

}

/*****************************************************************************
*                                                                            *
*  ----------------------------- des_encipher -----------------------------  *
*                                                                            *
*****************************************************************************/

void des_encipher(const unsigned char *plaintext, unsigned char *ciphertext,
   const unsigned char *key) {

des_main(plaintext, ciphertext, key, encipher);

return;

}

/*****************************************************************************
*                                                                            *
*  ----------------------------- des_decipher -----------------------------  *
*                                                                            *
*****************************************************************************/

void des_decipher(const unsigned char *ciphertext, unsigned char *plaintext,
   const unsigned char *key) {

des_main(ciphertext, plaintext, key, decipher);

return;

}