libtom.libtomcrypt/ofb_encrypt.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.
 *
 * Tom St Denis, [email protected], http://libtomcrypt.org
 */
#include "mycrypt.h"

#ifdef OFB

int ofb_encrypt(const unsigned char *pt, unsigned char *ct, unsigned long len, symmetric_OFB *ofb)
{
   int err;
   _ARGCHK(pt != NULL);
   _ARGCHK(ct != NULL);
   _ARGCHK(ofb != NULL);
   if ((err = cipher_is_valid(ofb->cipher)) != CRYPT_OK) {
       return err;
   }
   
   /* is blocklen/padlen valid? */
   if (ofb->blocklen < 0 || ofb->blocklen > (int)sizeof(ofb->IV) ||
       ofb->padlen   < 0 || ofb->padlen   > (int)sizeof(ofb->IV)) {
      return CRYPT_INVALID_ARG;
   }
   
   while (len-- > 0) {
       if (ofb->padlen == ofb->blocklen) {
          cipher_descriptor[ofb->cipher].ecb_encrypt(ofb->IV, ofb->IV, &ofb->key);
          ofb->padlen = 0;
       }
       *ct++ = *pt++ ^ ofb->IV[ofb->padlen++];
   }
   return CRYPT_OK;
}

#endif