xcbc_init.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */
#include "tomcrypt.h"

/**
  @file xcbc_init.c
  XCBC Support, start an XCBC state
*/

#ifdef LTC_XCBC

/** Initialize XCBC-MAC state
  @param xcbc    [out] XCBC state to initialize
  @param cipher  Index of cipher to use
  @param key     [in]  Secret key
  @param keylen  Length of secret key in octets
  Return CRYPT_OK on success
*/
int xcbc_init(xcbc_state *xcbc, int cipher, const unsigned char *key, unsigned long keylen)
{
   int            x, y, err;
   symmetric_key *skey;
   unsigned long  k1;

   LTC_ARGCHK(xcbc != NULL);
   LTC_ARGCHK(key  != NULL);

   /* schedule the key */
   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
      return err;
   }

#ifdef LTC_FAST
   if (cipher_descriptor[cipher].block_length % sizeof(LTC_FAST_TYPE)) {
       return CRYPT_INVALID_ARG;
   }
#endif

   skey = NULL;

   /* are we in pure XCBC mode with three keys? */
   if (keylen & LTC_XCBC_PURE) {
      keylen &= ~LTC_XCBC_PURE;

      if (keylen < 2UL*cipher_descriptor[cipher].block_length) {
         return CRYPT_INVALID_ARG;
      }

      k1      = keylen - 2*cipher_descriptor[cipher].block_length;
      XMEMCPY(xcbc->K[0], key, k1);
      XMEMCPY(xcbc->K[1], key+k1, cipher_descriptor[cipher].block_length);
      XMEMCPY(xcbc->K[2], key+k1 + cipher_descriptor[cipher].block_length, cipher_descriptor[cipher].block_length);
   } else {
      /* use the key expansion */
      k1      = cipher_descriptor[cipher].block_length;

      /* schedule the user key */
      skey = XCALLOC(1, sizeof(*skey));
      if (skey == NULL) {
         return CRYPT_MEM;
      }

      if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, skey)) != CRYPT_OK) {
         goto done;
      }

      /* make the three keys */
      for (y = 0; y < 3; y++) {
        for (x = 0; x < cipher_descriptor[cipher].block_length; x++) {
           xcbc->K[y][x] = y + 1;
        }
        cipher_descriptor[cipher].ecb_encrypt(xcbc->K[y], xcbc->K[y], skey);
      }
   }

   /* setup K1 */
   err = cipher_descriptor[cipher].setup(xcbc->K[0], k1, 0, &xcbc->key);

   /* setup struct */
   zeromem(xcbc->IV, cipher_descriptor[cipher].block_length);
   xcbc->blocksize = cipher_descriptor[cipher].block_length;
   xcbc->cipher    = cipher;
   xcbc->buflen    = 0;
done:
   cipher_descriptor[cipher].done(skey);
   if (skey != NULL) {
#ifdef LTC_CLEAN_STACK
      zeromem(skey, sizeof(*skey));
#endif
      XFREE(skey);
   }
   return err;
}

#endif