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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 <gcrypt.h>
#include "util.h"
#include "packet.h"
#include "dummy-cipher.h"
#include "options.h"
#include "i18n.h"
static int decode_filter( void *opaque, int control, IOBUF a,
byte *buf, size_t *ret_len);
static int mdc_decode_filter( void *opaque, int control, IOBUF a,
byte *buf, size_t *ret_len);
typedef struct {
GCRY_CIPHER_HD cipher_hd;
GCRY_MD_HD mdc_hash;
char defer[20];
int defer_filled;
int eof_seen;
} decode_filter_ctx_t;
/****************
* Decrypt the data, specified by ED with the key DEK.
*/
int
decrypt_data( void *procctx, PKT_encrypted *ed, DEK *dek )
{
decode_filter_ctx_t dfx;
byte *p;
int rc=0, c, i;
byte temp[32];
int blocksize;
unsigned nprefix;
memset( &dfx, 0, sizeof dfx );
if( gcry_cipher_test_algo( dek->algo ) ) {
if( opt.verbose )
log_info(_("encrypted with unknown algorithm %d\n"), dek->algo );
rc = G10ERR_CIPHER_ALGO;
goto leave;
}
if( opt.verbose )
log_info(_("%s encrypted data\n"), gcry_cipher_algo_name( dek->algo ) );
blocksize = gcry_cipher_get_algo_blklen( dek->algo );
if( blocksize < 1 || blocksize > 16 )
log_fatal("unsupported blocksize %u\n", blocksize );
nprefix = blocksize;
if( ed->len && ed->len < (nprefix+2) )
BUG();
if( ed->mdc_method ) {
dfx.mdc_hash = gcry_md_open( ed->mdc_method, 0 );
if( !dfx.mdc_hash )
BUG();
}
if( !(dfx.cipher_hd = gcry_cipher_open( dek->algo,
GCRY_CIPHER_MODE_CFB,
GCRY_CIPHER_SECURE
| (dek->algo >= 100 ?
0 : GCRY_CIPHER_ENABLE_SYNC) ))
) {
/* we should never get an error here cause we already checked, that
* the algorithm is available. What about a flag to let the function
* die in this case? */
BUG();
}
/* log_hexdump( "thekey", dek->key, dek->keylen );*/
rc = gcry_cipher_setkey( dfx.cipher_hd, dek->key, dek->keylen );
if( rc == GCRYERR_WEAK_KEY ) {
log_info(_("WARNING: message was encrypted with "
"a weak key in the symmetric cipher.\n"));
rc = 0;
}
else if( rc ) {
log_error("key setup failed: %s\n", gcry_strerror(rc) );
goto leave;
}
gcry_cipher_setiv( dfx.cipher_hd, NULL, 0 );
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;
}
gcry_cipher_decrypt( dfx.cipher_hd, temp, nprefix+2, NULL, 0 );
if( dfx.mdc_hash )
gcry_md_write( dfx.mdc_hash, temp, nprefix+2 );
gcry_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] ) {
rc = G10ERR_BAD_KEY;
goto leave;
}
if( ed->mdc_method )
iobuf_push_filter( ed->buf, mdc_decode_filter, &dfx );
else
iobuf_push_filter( ed->buf, decode_filter, &dfx );
proc_packets( procctx, ed->buf);
ed->buf = NULL;
if( ed->mdc_method && dfx.eof_seen == 2 )
rc = G10ERR_INVALID_PACKET;
else if( ed->mdc_method ) { /* check the mdc */
int datalen = gcry_md_get_algo_dlen( ed->mdc_method );
if( datalen != 20
|| memcmp(gcry_md_read( dfx.mdc_hash, 0 ), dfx.defer, datalen) )
rc = G10ERR_BAD_SIGN;
log_hexdump("MDC calculated:", gcry_md_read( dfx.mdc_hash, 0), datalen);
log_hexdump("MDC message :", dfx.defer, 20);
}
leave:
gcry_cipher_close(dfx.cipher_hd);
gcry_md_close( dfx.mdc_hash );
return rc;
}
/* I think we should merge this with cipher_filter */
static int
mdc_decode_filter( void *opaque, int control, IOBUF a,
byte *buf, size_t *ret_len)
{
decode_filter_ctx_t *dfx = opaque;
size_t n, size = *ret_len;
int rc = 0;
int c;
if( control == IOBUFCTRL_UNDERFLOW && dfx->eof_seen ) {
*ret_len = 0;
rc = -1;
}
else if( control == IOBUFCTRL_UNDERFLOW ) {
assert(a);
assert( size > 40 );
/* get at least 20 bytes and put it somewhere ahead in the buffer */
for(n=20; n < 40 ; n++ ) {
if( (c = iobuf_get(a)) == -1 )
break;
buf[n] = c;
}
if( n == 40 ) {
/* we have enough stuff - flush the deferred stuff */
/* (we have asserted that the buffer is large enough */
if( !dfx->defer_filled ) /* the first time */
memcpy(buf, buf+20, 20 );
else
memcpy(buf, dfx->defer, 20 );
/* now fill up */
for(; n < size; n++ ) {
if( (c = iobuf_get(a)) == -1 )
break;
buf[n] = c;
}
/* move the last 20 bytes back to the defer buffer */
/* (okay, we are wasting 20 bytes of supplied buffer) */
n -= 20;
memcpy( dfx->defer, buf+n, 20 );
dfx->defer_filled = 1;
}
else if( !dfx->defer_filled ) { /* eof seen buf empty defer */
/* this is very bad because there is an incomplete hash */
n -= 20;
memcpy(buf, buf+20, n );
dfx->eof_seen = 2; /* eof with incomplete hash */
}
else { /* eof seen */
memcpy(buf, dfx->defer, 20 );
n -= 20;
memcpy( dfx->defer, buf+n, 20 );
dfx->eof_seen = 1; /* normal eof */
}
if( n ) {
gcry_cipher_decrypt( dfx->cipher_hd, buf, n, NULL, 0);
gcry_md_write( dfx->mdc_hash, buf, n );
}
else {
assert( dfx->eof_seen );
rc = -1; /* eof */
}
*ret_len = n;
}
else if( control == IOBUFCTRL_DESC ) {
*(char**)buf = "mdc_decode_filter";
}
return rc;
}
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;
if( control == IOBUFCTRL_UNDERFLOW ) {
assert(a);
n = iobuf_read( a, buf, size );
if( n == -1 ) n = 0;
if( n )
gcry_cipher_decrypt( fc->cipher_hd, buf, n, NULL, 0);
else
rc = -1; /* eof */
*ret_len = n;
}
else if( control == IOBUFCTRL_DESC ) {
*(char**)buf = "decode_filter";
}
return rc;
}
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