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/* encr-data.c - process an encrypted data packet
* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GnuPG 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "util.h"
#include "memory.h"
#include "packet.h"
#include "mpi.h"
#include "cipher.h"
#include "options.h"
#include "i18n.h"
static int decode_filter( void *opaque, int control, IOBUF a,
byte *buf, size_t *ret_len);
typedef struct {
CIPHER_HANDLE cipher_hd;
} decode_filter_ctx_t;
/****************
* Decrypt the data, specified by ED with the key DEK.
*/
int
decrypt_data( PKT_encrypted *ed, DEK *dek )
{
decode_filter_ctx_t dfx;
byte *p;
int rc, c, i;
byte temp[32];
unsigned blocksize;
unsigned nprefix;
if( opt.verbose ) {
const char *s = cipher_algo_to_string( dek->algo );
if( s )
log_info(_("%s encrypted data\n"), s );
else
log_info(_("encrypted with unknown algorithm %d\n"), dek->algo );
}
if( (rc=check_cipher_algo(dek->algo)) )
return rc;
blocksize = cipher_get_blocksize(dek->algo);
if( !blocksize || blocksize > 16 )
log_fatal("unsupported blocksize %u\n", blocksize );
/* FIXME: remove the kludge for the experimental twofish128 mode:
* we always use the 10 byte prefix and not one depending on the blocksize
*/
nprefix = dek->algo == CIPHER_ALGO_TWOFISH_OLD? blocksize : 8;
if( ed->len && ed->len < (nprefix+2) )
BUG();
dfx.cipher_hd = cipher_open( dek->algo, CIPHER_MODE_AUTO_CFB, 1 );
/*log_hexdump( "thekey", dek->key, dek->keylen );*/
rc = cipher_setkey( dfx.cipher_hd, dek->key, dek->keylen );
if( rc == G10ERR_WEAK_KEY )
log_info(_("WARNING: message was encrypted with "
"a weak key in the symmetric cipher.\n"));
else if( rc )
log_error("key setup failed: %s\n", g10_errstr(rc) );
cipher_setiv( dfx.cipher_hd, NULL );
if( ed->len ) {
for(i=0; i < (nprefix+2) && ed->len; i++, ed->len-- ) {
if( (c=iobuf_get(ed->buf)) == -1 )
break;
else
temp[i] = c;
}
}
else {
for(i=0; i < (nprefix+2); i++ )
if( (c=iobuf_get(ed->buf)) == -1 )
break;
else
temp[i] = c;
}
cipher_decrypt( dfx.cipher_hd, temp, temp, nprefix+2);
cipher_sync( dfx.cipher_hd );
p = temp;
/*log_hexdump( "prefix", temp, nprefix+2 );*/
if( p[nprefix-2] != p[nprefix] || p[nprefix-1] != p[nprefix+1] ) {
cipher_close(dfx.cipher_hd);
return G10ERR_BAD_KEY;
}
iobuf_push_filter( ed->buf, decode_filter, &dfx );
proc_packets(ed->buf);
ed->buf = NULL;
cipher_close(dfx.cipher_hd);
return 0;
}
static int
decode_filter( void *opaque, int control, IOBUF a, byte *buf, size_t *ret_len)
{
decode_filter_ctx_t *fc = opaque;
size_t n, size = *ret_len;
int rc = 0;
int c;
if( control == IOBUFCTRL_UNDERFLOW ) {
assert(a);
for(n=0; n < size; n++ ) {
if( (c = iobuf_get(a)) == -1 )
break;
buf[n] = c;
}
if( n )
cipher_decrypt( fc->cipher_hd, buf, buf, n);
else
rc = -1; /* eof */
*ret_len = n;
}
else if( control == IOBUFCTRL_DESC ) {
*(char**)buf = "decode_filter";
}
return rc;
}
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