ofb.c

#include "mycrypt.h"

#ifdef OFB

int ofb_start(int cipher, const unsigned char *IV, const unsigned char *key, 
              int keylen, int num_rounds, symmetric_OFB *ofb)
{
   int x, err;

   _ARGCHK(IV != NULL);
   _ARGCHK(key != NULL);
   _ARGCHK(ofb != NULL);

   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
      return err;
   }

   /* copy details */
   ofb->cipher = cipher;
   ofb->blocklen = cipher_descriptor[cipher].block_length;
   for (x = 0; x < ofb->blocklen; x++) {
       ofb->IV[x] = IV[x];
   }

   /* init the cipher */
   ofb->padlen = ofb->blocklen;
   return cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ofb->key);
}

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;
}

int ofb_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_OFB *ofb)
{
   _ARGCHK(pt != NULL);
   _ARGCHK(ct != NULL);
   _ARGCHK(ofb != NULL);
   return ofb_encrypt(ct, pt, len, ofb);
}


#endif