/* LibTomCrypt, modular cryptographic library -- Tom St Denis */

/* SPDX-License-Identifier: Unlicense */

#include "tomcrypt_private.h"

/**

  @file ctr_encrypt.c

  CTR implementation, encrypt data, Tom St Denis

*/

#ifdef LTC_CTR_MODE

/**

  CTR encrypt software implementation

  @param pt     Plaintext

  @param ct     [out] Ciphertext

  @param len    Length of plaintext (octets)

  @param ctr    CTR state

  @return CRYPT_OK if successful

*/

static int s_ctr_encrypt(const unsigned char *pt, unsigned char *ct, unsigned long len, symmetric_CTR *ctr)

{

   int x, err;

   while (len) {

      /* is the pad empty? */

      if (ctr->padlen == ctr->blocklen) {

         /* increment counter */

         if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {

            /* little-endian */

            for (x = 0; x < ctr->ctrlen; x++) {

               ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;

               if (ctr->ctr[x] != (unsigned char)0) {

                  break;

               }

            }

         } else {

            /* big-endian */

            for (x = ctr->blocklen-1; x >= ctr->ctrlen; x--) {

               ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;

               if (ctr->ctr[x] != (unsigned char)0) {

                  break;

               }

            }

         }

         /* encrypt it */

         if ((err = cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key)) != CRYPT_OK) {

            return err;

         }

         ctr->padlen = 0;

      }

#ifdef LTC_FAST

      if ((ctr->padlen == 0) && (len >= (unsigned long)ctr->blocklen)) {

         for (x = 0; x < ctr->blocklen; x += sizeof(LTC_FAST_TYPE)) {

            *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)ct + x)) = *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)pt + x)) ^

                                                           *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)ctr->pad + x));

         }

       pt         += ctr->blocklen;

       ct         += ctr->blocklen;

       len        -= ctr->blocklen;

       ctr->padlen = ctr->blocklen;

       continue;

      }

#endif

      *ct++ = *pt++ ^ ctr->pad[ctr->padlen++];

      --len;

   }

   return CRYPT_OK;

}

/**

  CTR encrypt

  @param pt     Plaintext

  @param ct     [out] Ciphertext

  @param len    Length of plaintext (octets)

  @param ctr    CTR state

  @return CRYPT_OK if successful

*/

int ctr_encrypt(const unsigned char *pt, unsigned char *ct, unsigned long len, symmetric_CTR *ctr)

{

   int err, fr;

   LTC_ARGCHK(pt != NULL);

   LTC_ARGCHK(ct != NULL);

   LTC_ARGCHK(ctr != NULL);

   if ((err = cipher_is_valid(ctr->cipher)) != CRYPT_OK) {

       return err;

   }

   /* is blocklen/padlen valid? */

   if ((ctr->blocklen < 1) || (ctr->blocklen > (int)sizeof(ctr->ctr)) ||

       (ctr->padlen   < 0) || (ctr->padlen   > (int)sizeof(ctr->pad))) {

      return CRYPT_INVALID_ARG;

   }

#ifdef LTC_FAST

   if (ctr->blocklen % sizeof(LTC_FAST_TYPE)) {

      return CRYPT_INVALID_ARG;

   }

#endif

   /* handle acceleration only if pad is empty, accelerator is present and length is >= a block size */

   if ((cipher_descriptor[ctr->cipher].accel_ctr_encrypt != NULL) && (len >= (unsigned long)ctr->blocklen)) {

     if (ctr->padlen < ctr->blocklen) {

       fr = ctr->blocklen - ctr->padlen;

       if ((err = s_ctr_encrypt(pt, ct, fr, ctr)) != CRYPT_OK) {

          return err;

       }

       pt += fr;

       ct += fr;

       len -= fr;

     }

     if (len >= (unsigned long)ctr->blocklen) {

       if ((err = cipher_descriptor[ctr->cipher].accel_ctr_encrypt(pt, ct, len/ctr->blocklen, ctr->ctr, ctr->mode, &ctr->key)) != CRYPT_OK) {

          return err;

       }

       pt += (len / ctr->blocklen) * ctr->blocklen;

       ct += (len / ctr->blocklen) * ctr->blocklen;

       len %= ctr->blocklen;

     }

   }

   return s_ctr_encrypt(pt, ct, len, ctr);

}

#endif