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cipher-ctr.c
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/* cipher-ctr.c - Generic CTR mode implementation
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
* 2005, 2007, 2008, 2009, 2011 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt 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.
*
* Libgcrypt 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 this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "g10lib.h"
#include "cipher.h"
#include "bufhelp.h"
#include "./cipher-internal.h"
gcry_err_code_t
_gcry_cipher_ctr_encrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, size_t outbuflen,
const unsigned char *inbuf, size_t inbuflen)
{
size_t n;
int i;
gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
unsigned int blocksize = c->spec->blocksize;
size_t nblocks;
unsigned int burn, nburn;
if (outbuflen < inbuflen)
return GPG_ERR_BUFFER_TOO_SHORT;
burn = 0;
/* First process a left over encrypted counter. */
if (c->unused)
{
gcry_assert (c->unused < blocksize);
i = blocksize - c->unused;
n = c->unused > inbuflen ? inbuflen : c->unused;
buf_xor(outbuf, inbuf, &c->lastiv[i], n);
c->unused -= n;
inbuf += n;
outbuf += n;
inbuflen -= n;
}
/* Use a bulk method if available. */
nblocks = inbuflen / blocksize;
if (nblocks && c->bulk.ctr_enc)
{
c->bulk.ctr_enc (&c->context.c, c->u_ctr.ctr, outbuf, inbuf, nblocks);
inbuf += nblocks * blocksize;
outbuf += nblocks * blocksize;
inbuflen -= nblocks * blocksize;
}
/* If we don't have a bulk method use the standard method. We also
use this method for the a remaining partial block. */
if (inbuflen)
{
unsigned char tmp[MAX_BLOCKSIZE];
do {
nburn = enc_fn (&c->context.c, tmp, c->u_ctr.ctr);
burn = nburn > burn ? nburn : burn;
for (i = blocksize; i > 0; i--)
{
c->u_ctr.ctr[i-1]++;
if (c->u_ctr.ctr[i-1] != 0)
break;
}
n = blocksize < inbuflen ? blocksize : inbuflen;
buf_xor(outbuf, inbuf, tmp, n);
inbuflen -= n;
outbuf += n;
inbuf += n;
} while (inbuflen);
/* Save the unused bytes of the counter. */
c->unused = blocksize - n;
if (c->unused)
buf_cpy (c->lastiv+n, tmp+n, c->unused);
wipememory (tmp, sizeof tmp);
}
if (burn > 0)
_gcry_burn_stack (burn + 4 * sizeof(void *));
return 0;
}

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