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/* 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., 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 "macros.h"
#include "memxor.h"
#include "nettle-internal.h"
#define NBLOCKS 4
void
ctr_crypt(void *ctx, nettle_crypt_func *f,
unsigned block_size, uint8_t *ctr,
unsigned 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
{
unsigned 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, 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);
}
else
{
TMP_DECL(buffer, uint8_t, NBLOCKS * NETTLE_MAX_CIPHER_BLOCK_SIZE);
unsigned 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);
}
}
}
}
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