+
−/* 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 $ */