/* 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, tomstdenis@gmail.com, http://libtomcrypt.com */#include "tomcrypt.h"/**   @file ctr_start.c   CTR implementation, start chain, Tom St Denis*/#ifdef LTC_CTR_MODE/**   Initialize a CTR context   @param cipher      The index of the cipher desired   @param IV          The initial vector   @param key         The secret key    @param keylen      The length of the secret key (octets)   @param num_rounds  Number of rounds in the cipher desired (0 for default)   @param ctr_mode    The counter mode (CTR_COUNTER_LITTLE_ENDIAN or CTR_COUNTER_BIG_ENDIAN)   @param ctr         The CTR state to initialize   @return CRYPT_OK if successful*/int ctr_start(               int   cipher,               const unsigned char *IV,               const unsigned char *key,       int keylen,                              int  num_rounds, int ctr_mode,                   symmetric_CTR *ctr){   int x, err;   LTC_ARGCHK(IV  != NULL);   LTC_ARGCHK(key != NULL);   LTC_ARGCHK(ctr != NULL);   /* bad param? */   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {      return err;   }   /* setup cipher */   if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ctr->key)) != CRYPT_OK) {      return err;   }   /* copy ctr */   ctr->blocklen = cipher_descriptor[cipher].block_length;   ctr->cipher   = cipher;   ctr->padlen   = 0;   ctr->mode     = ctr_mode & 1;   for (x = 0; x < ctr->blocklen; x++) {       ctr->ctr[x] = IV[x];   }   if (ctr_mode & LTC_CTR_RFC3686) {      /* increment the IV as per RFC 3686 */      if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {         /* little-endian */         for (x = 0; x < ctr->blocklen; 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 >= 0; x--) {             ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;             if (ctr->ctr[x] != (unsigned char)0) {                break;             }         }      }   }   return cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key); }#endif/* $Source: /cvs/libtom/libtomcrypt/src/modes/ctr/ctr_start.c,v $ *//* $Revision: 1.11 $ *//* $Date: 2006/11/05 01:46:35 $ */