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cipher-ofb.c
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/* cipher-ofb.c - Generic OFB 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_ofb_encrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, size_t outbuflen,
const unsigned char *inbuf, size_t inbuflen)
{
unsigned char *ivp;
gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
size_t blocksize = c->spec->blocksize;
unsigned int burn, nburn;
/* Tell compiler that we require a cipher with a 64bit or 128 bit block
* length, to allow better optimization of this function. */
if (blocksize > 16 || blocksize < 8 || blocksize & (8 - 1))
return GPG_ERR_INV_LENGTH;
if (outbuflen < inbuflen)
return GPG_ERR_BUFFER_TOO_SHORT;
if ( inbuflen <= c->unused )
{
/* Short enough to be encoded by the remaining XOR mask. */
/* XOR the input with the IV */
ivp = c->u_iv.iv + blocksize - c->unused;
buf_xor(outbuf, ivp, inbuf, inbuflen);
c->unused -= inbuflen;
return 0;
}
burn = 0;
if( c->unused )
{
inbuflen -= c->unused;
ivp = c->u_iv.iv + blocksize - c->unused;
buf_xor(outbuf, ivp, inbuf, c->unused);
outbuf += c->unused;
inbuf += c->unused;
c->unused = 0;
}
/* Now we can process complete blocks. */
while ( inbuflen >= blocksize )
{
/* Encrypt the IV (and save the current one). */
nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
burn = nburn > burn ? nburn : burn;
buf_xor(outbuf, c->u_iv.iv, inbuf, blocksize);
outbuf += blocksize;
inbuf += blocksize;
inbuflen -= blocksize;
}
if ( inbuflen )
{ /* process the remaining bytes */
nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
burn = nburn > burn ? nburn : burn;
c->unused = blocksize;
c->unused -= inbuflen;
buf_xor(outbuf, c->u_iv.iv, inbuf, inbuflen);
outbuf += inbuflen;
inbuf += inbuflen;
inbuflen = 0;
}
if (burn > 0)
_gcry_burn_stack (burn + 4 * sizeof(void *));
return 0;
}

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Mon, Dec 23, 5:04 PM (10 h, 25 m)
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