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/* pubkey-enc.c - public key encoded packet handling
* Copyright (C) 1998 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 "keydb.h"
#include "trustdb.h"
#include "cipher.h"
#include "status.h"
#include "i18n.h"
/****************
* Get the session key from a pubkey enc paket and return
* it in DEK, which should have been allocated in secure memory.
*/
int
get_session_key( PKT_pubkey_enc *k, DEK *dek )
{
int rc = 0;
MPI plain_dek = NULL;
byte *frame = NULL;
unsigned n, nframe;
u16 csum, csum2;
PKT_secret_key *sk = m_alloc_clear( sizeof *sk );
if( is_RSA(k->pubkey_algo) ) /* warn about that */
write_status(STATUS_RSA_OR_IDEA);
rc=check_pubkey_algo( k->pubkey_algo );
if( rc )
goto leave;
sk->pubkey_algo = k->pubkey_algo; /* we want a pubkey with this algo*/
if( (rc = get_seckey( sk, k->keyid )) )
goto leave;
rc = pubkey_decrypt(k->pubkey_algo, &plain_dek, k->data, sk->skey );
if( rc )
goto leave;
free_secret_key( sk ); sk = NULL;
frame = mpi_get_buffer( plain_dek, &nframe, NULL );
mpi_free( plain_dek ); plain_dek = NULL;
/* Now get the DEK (data encryption key) from the frame
*
* Old versions encode the DEK in in this format (msb is left):
*
* 0 1 DEK(16 bytes) CSUM(2 bytes) 0 RND(n bytes) 2
*
* Later versions encode the DEK like this:
*
* 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes)
*
* (mpi_get_buffer already removed the leading zero).
*
* RND are non-zero randow bytes.
* A is the cipher algorithm
* DEK is the encryption key (session key) with length k
* CSUM
*/
if( DBG_CIPHER )
log_hexdump("DEK frame:", frame, nframe );
n=0;
if( n + 7 > nframe )
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
if( frame[n] == 1 && frame[nframe-1] == 2 ) {
log_error("old encoding of DEK is not supported\n");
rc = G10ERR_CIPHER_ALGO;
goto leave;
}
if( frame[n] != 2 ) /* somethink is wrong */
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
for(n++; n < nframe && frame[n]; n++ ) /* skip the random bytes */
;
n++; /* and the zero byte */
if( n + 4 > nframe )
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
dek->keylen = nframe - (n+1) - 2;
dek->algo = frame[n++];
if( dek->algo == CIPHER_ALGO_IDEA )
write_status(STATUS_RSA_OR_IDEA);
rc = check_cipher_algo( dek->algo );
if( rc ) {
dek->algo = 0;
goto leave;
}
if( (dek->keylen*8) != cipher_get_keylen( dek->algo ) ) {
rc = G10ERR_WRONG_SECKEY;
goto leave;
}
/* copy the key to DEK and compare the checksum */
csum = frame[nframe-2] << 8;
csum |= frame[nframe-1];
memcpy( dek->key, frame+n, dek->keylen );
for( csum2=0, n=0; n < dek->keylen; n++ )
csum2 += dek->key[n];
if( csum != csum2 ) {
rc = G10ERR_WRONG_SECKEY;
goto leave;
}
if( DBG_CIPHER )
log_hexdump("DEK is:", dek->key, dek->keylen );
/* check that the algo is in the preferences */
{
PKT_public_key *pk = m_alloc_clear( sizeof *pk );
if( (rc = get_pubkey( pk, k->keyid )) )
log_error("public key problem: %s\n", g10_errstr(rc) );
else if( !pk->local_id && query_trust_record(pk) )
log_error("can't check algorithm against preferences\n");
else if( dek->algo != CIPHER_ALGO_3DES
&& !is_algo_in_prefs( pk->local_id, PREFTYPE_SYM, dek->algo ) )
log_info(_("note: cipher algorithm %d not found in preferences\n"),
dek->algo );
free_public_key( pk );
rc = 0;
}
leave:
mpi_free(plain_dek);
m_free(frame);
if( sk )
free_secret_key( sk );
return rc;
}
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