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      1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
      2  *
      3  * LibTomCrypt is a library that provides various cryptographic
      4  * algorithms in a highly modular and flexible manner.
      5  *
      6  * The library is free for all purposes without any express
      7  * guarantee it works.
      8  *
      9  * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com
     10  */
     11 #include "tomcrypt.h"
     12 
     13 /**
     14   @file ctr_encrypt.c
     15   CTR implementation, encrypt data, Tom St Denis
     16 */
     17 
     18 
     19 #ifdef LTC_CTR_MODE
     20 
     21 /**
     22   CTR encrypt
     23   @param pt     Plaintext
     24   @param ct     [out] Ciphertext
     25   @param len    Length of plaintext (octets)
     26   @param ctr    CTR state
     27   @return CRYPT_OK if successful
     28 */
     29 int ctr_encrypt(const unsigned char *pt, unsigned char *ct, unsigned long len, symmetric_CTR *ctr)
     30 {
     31    int x, err;
     32 
     33    LTC_ARGCHK(pt != NULL);
     34    LTC_ARGCHK(ct != NULL);
     35    LTC_ARGCHK(ctr != NULL);
     36 
     37    if ((err = cipher_is_valid(ctr->cipher)) != CRYPT_OK) {
     38        return err;
     39    }
     40 
     41    /* is blocklen/padlen valid? */
     42    if (ctr->blocklen < 1 || ctr->blocklen > (int)sizeof(ctr->ctr) ||
     43        ctr->padlen   < 0 || ctr->padlen   > (int)sizeof(ctr->pad)) {
     44       return CRYPT_INVALID_ARG;
     45    }
     46 
     47 #ifdef LTC_FAST
     48    if (ctr->blocklen % sizeof(LTC_FAST_TYPE)) {
     49       return CRYPT_INVALID_ARG;
     50    }
     51 #endif
     52 
     53    /* handle acceleration only if pad is empty, accelerator is present and length is >= a block size */
     54    if ((ctr->padlen == ctr->blocklen) && cipher_descriptor[ctr->cipher].accel_ctr_encrypt != NULL && (len >= (unsigned long)ctr->blocklen)) {
     55       if ((err = cipher_descriptor[ctr->cipher].accel_ctr_encrypt(pt, ct, len/ctr->blocklen, ctr->ctr, ctr->mode, &ctr->key)) != CRYPT_OK) {
     56          return err;
     57       }
     58       len %= ctr->blocklen;
     59    }
     60 
     61    while (len) {
     62       /* is the pad empty? */
     63       if (ctr->padlen == ctr->blocklen) {
     64          /* increment counter */
     65          if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {
     66             /* little-endian */
     67             for (x = 0; x < ctr->blocklen; x++) {
     68                ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
     69                if (ctr->ctr[x] != (unsigned char)0) {
     70                   break;
     71                }
     72             }
     73          } else {
     74             /* big-endian */
     75             for (x = ctr->blocklen-1; x >= 0; x--) {
     76                ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
     77                if (ctr->ctr[x] != (unsigned char)0) {
     78                   break;
     79                }
     80             }
     81          }
     82 
     83          /* encrypt it */
     84          if ((err = cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key)) != CRYPT_OK) {
     85             return err;
     86          }
     87          ctr->padlen = 0;
     88       }
     89 #ifdef LTC_FAST
     90       if (ctr->padlen == 0 && len >= (unsigned long)ctr->blocklen) {
     91          for (x = 0; x < ctr->blocklen; x += sizeof(LTC_FAST_TYPE)) {
     92             *((LTC_FAST_TYPE*)((unsigned char *)ct + x)) = *((LTC_FAST_TYPE*)((unsigned char *)pt + x)) ^
     93                                                            *((LTC_FAST_TYPE*)((unsigned char *)ctr->pad + x));
     94          }
     95        pt         += ctr->blocklen;
     96        ct         += ctr->blocklen;
     97        len        -= ctr->blocklen;
     98        ctr->padlen = ctr->blocklen;
     99        continue;
    100       }
    101 #endif
    102       *ct++ = *pt++ ^ ctr->pad[ctr->padlen++];
    103       --len;
    104    }
    105    return CRYPT_OK;
    106 }
    107 
    108 #endif
    109 
    110 /* $Source: /cvs/libtom/libtomcrypt/src/modes/ctr/ctr_encrypt.c,v $ */
    111 /* $Revision: 1.20 $ */
    112 /* $Date: 2006/11/21 00:18:23 $ */
    113