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/* ctr.c
*
* Cipher counter mode.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2005 Niels Mller
*
* 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., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include "ctr.h"
#include "memxor.h"
#include "nettle-internal.h"
#define INCREMENT(size, counter, i) \
do { \
if (++(ctr)[(size) - 1] == 0) \
{ \
unsigned i = size - 1; \
while (i > 0 && ++(ctr)[--i] == 0) \
; \
} \
} while (0)
void
ctr_crypt(void *ctx, nettle_crypt_func f,
unsigned block_size, uint8_t *ctr,
unsigned length, uint8_t *dst,
const uint8_t *src)
{
TMP_DECL(buffer, uint8_t, NETTLE_MAX_CIPHER_BLOCK_SIZE);
TMP_ALLOC(buffer, block_size);
if (src != dst)
{
for (; length >= block_size; length -= block_size, src += block_size, dst += block_size)
{
f(ctx, block_size, dst, ctr);
memxor(dst, src, block_size);
INCREMENT(block_size, ctr, i);
}
}
else
{
for (; length >= block_size; length -= block_size, src += block_size, dst += block_size)
{
f(ctx, block_size, buffer, ctr);
memxor3(dst, src, buffer, block_size);
INCREMENT(block_size, ctr, i);
}
}
if (length > 0)
{
/* A final partial block */
f(ctx, block_size, buffer, ctr);
memxor3(dst, src, buffer, length);
INCREMENT(block_size, ctr, i);
}
}