ctr.c

/* ctr.c
 *
 * Cipher counter mode.
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2005 Niels Möller
 *  
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 * 
 * The nettle library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02111-1301, USA.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>
#include <stdlib.h>
#include <string.h>

#include "ctr.h"

#include "macros.h"
#include "memxor.h"
#include "nettle-internal.h"

#define NBLOCKS 4

void
ctr_crypt(void *ctx, nettle_crypt_func *f,
	  size_t block_size, uint8_t *ctr,
	  size_t length, uint8_t *dst,
	  const uint8_t *src)
{
  if (src != dst)
    {
      if (length == block_size)
	{
	  f(ctx, block_size, dst, ctr);
	  INCREMENT(block_size, ctr);
	  memxor(dst, src, block_size);
	}
      else
	{
	  size_t left;
	  uint8_t *p;	  

	  for (p = dst, left = length;
	       left >= block_size;
	       left -= block_size, p += block_size)
	    {
	      memcpy (p, ctr, block_size);
	      INCREMENT(block_size, ctr);
	    }

	  f(ctx, length - left, dst, dst);
	  memxor(dst, src, length - left);

	  if (left)
	    {
	      TMP_DECL(buffer, uint8_t, NETTLE_MAX_CIPHER_BLOCK_SIZE);
	      TMP_ALLOC(buffer, block_size);

	      f(ctx, block_size, buffer, ctr);
	      INCREMENT(block_size, ctr);
	      memxor3(dst + length - left, src + length - left, buffer, left);
	    }
	}
    }
  else
    {
      if (length > block_size)
	{
	  TMP_DECL(buffer, uint8_t, NBLOCKS * NETTLE_MAX_CIPHER_BLOCK_SIZE);
	  size_t chunk = NBLOCKS * block_size;

	  TMP_ALLOC(buffer, chunk);

	  for (; length >= chunk;
	       length -= chunk, src += chunk, dst += chunk)
	    {
	      unsigned n;
	      uint8_t *p;	  
	      for (n = 0, p = buffer; n < NBLOCKS; n++, p += block_size)
		{
		  memcpy (p, ctr, block_size);
		  INCREMENT(block_size, ctr);
		}
	      f(ctx, chunk, buffer, buffer);
	      memxor(dst, buffer, chunk);
	    }

	  if (length > 0)
	    {
	      /* Final, possibly partial, blocks */
	      for (chunk = 0; chunk < length; chunk += block_size)
		{
		  memcpy (buffer + chunk, ctr, block_size);
		  INCREMENT(block_size, ctr);
		}
	      f(ctx, chunk, buffer, buffer);
	      memxor3(dst, src, buffer, length);
	    }
	}
      else if (length > 0)
      	{
	  TMP_DECL(buffer, uint8_t, NETTLE_MAX_CIPHER_BLOCK_SIZE);
	  TMP_ALLOC(buffer, block_size);

	  f(ctx, block_size, buffer, ctr);
	  INCREMENT(block_size, ctr);
	  memxor3(dst, src, buffer, length);
	}
    }
}