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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 "ath.h"
#include "./cipher-internal.h"
gcry_err_code_t
_gcry_cipher_ofb_encrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, unsigned int outbuflen,
const unsigned char *inbuf, unsigned int inbuflen)
{
unsigned char *ivp;
size_t blocksize = c->cipher->blocksize;
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 */
for (ivp=c->u_iv.iv+c->cipher->blocksize - c->unused;
inbuflen;
inbuflen--, c->unused-- )
*outbuf++ = (*ivp++ ^ *inbuf++);
return 0;
}
if( c->unused )
{
inbuflen -= c->unused;
for(ivp=c->u_iv.iv+blocksize - c->unused; c->unused; c->unused-- )
*outbuf++ = (*ivp++ ^ *inbuf++);
}
/* Now we can process complete blocks. */
while ( inbuflen >= blocksize )
{
int i;
/* Encrypt the IV (and save the current one). */
memcpy( c->lastiv, c->u_iv.iv, blocksize );
c->cipher->encrypt ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
for (ivp=c->u_iv.iv,i=0; i < blocksize; i++ )
*outbuf++ = (*ivp++ ^ *inbuf++);
inbuflen -= blocksize;
}
if ( inbuflen )
{ /* process the remaining bytes */
memcpy( c->lastiv, c->u_iv.iv, blocksize );
c->cipher->encrypt ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
c->unused = blocksize;
c->unused -= inbuflen;
for(ivp=c->u_iv.iv; inbuflen; inbuflen-- )
*outbuf++ = (*ivp++ ^ *inbuf++);
}
return 0;
}
gcry_err_code_t
_gcry_cipher_ofb_decrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, unsigned int outbuflen,
const unsigned char *inbuf, unsigned int inbuflen)
{
unsigned char *ivp;
size_t blocksize = c->cipher->blocksize;
if (outbuflen < inbuflen)
return GPG_ERR_BUFFER_TOO_SHORT;
if( inbuflen <= c->unused )
{
/* Short enough to be encoded by the remaining XOR mask. */
for (ivp=c->u_iv.iv+blocksize - c->unused; inbuflen; inbuflen--,c->unused--)
*outbuf++ = *ivp++ ^ *inbuf++;
return 0;
}
if ( c->unused )
{
inbuflen -= c->unused;
for (ivp=c->u_iv.iv+blocksize - c->unused; c->unused; c->unused-- )
*outbuf++ = *ivp++ ^ *inbuf++;
}
/* Now we can process complete blocks. */
while ( inbuflen >= blocksize )
{
int i;
/* Encrypt the IV (and save the current one). */
memcpy( c->lastiv, c->u_iv.iv, blocksize );
c->cipher->encrypt ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
for (ivp=c->u_iv.iv,i=0; i < blocksize; i++ )
*outbuf++ = *ivp++ ^ *inbuf++;
inbuflen -= blocksize;
}
if ( inbuflen )
{ /* Process the remaining bytes. */
/* Encrypt the IV (and save the current one). */
memcpy( c->lastiv, c->u_iv.iv, blocksize );
c->cipher->encrypt ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
c->unused = blocksize;
c->unused -= inbuflen;
for (ivp=c->u_iv.iv; inbuflen; inbuflen-- )
*outbuf++ = *ivp++ ^ *inbuf++;
}
return 0;
}
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