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/* pubkey-enc.c - public key encoded packet handling
* Copyright (c) 1997 by Werner Koch (dd9jn)
*
* This file is part of G10.
*
* G10 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.
*
* G10 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 "cipher.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_cert *skc = m_alloc_clear( sizeof *skc );
skc->pubkey_algo = k->pubkey_algo; /* we want a pubkey with this algo*/
if( (rc = get_seckey( skc, k->keyid )) )
goto leave;
if( k->pubkey_algo == PUBKEY_ALGO_ELGAMAL ) {
ELG_secret_key skey;
if( DBG_CIPHER ) {
log_mpidump("Encr DEK a:", k->d.elg.a );
log_mpidump(" DEK b:", k->d.elg.b );
}
skey.p = skc->d.elg.p;
skey.g = skc->d.elg.g;
skey.y = skc->d.elg.y;
skey.x = skc->d.elg.x;
plain_dek = mpi_alloc_secure( mpi_get_nlimbs(skey.p) );
elg_decrypt( plain_dek, k->d.elg.a, k->d.elg.b, &skey );
memset( &skey, 0, sizeof skey );
}
#ifdef HAVE_RSA_CIPHER
else if( k->pubkey_algo == PUBKEY_ALGO_RSA ) {
RSA_secret_key skey;
if( DBG_CIPHER )
log_mpidump("Encr DEK frame:", k->d.rsa.rsa_integer );
skey.e = skc->d.rsa.rsa_e;
skey.n = skc->d.rsa.rsa_n;
skey.p = skc->d.rsa.rsa_p;
skey.q = skc->d.rsa.rsa_q;
skey.d = skc->d.rsa.rsa_d;
skey.u = skc->d.rsa.rsa_u;
plain_dek = mpi_alloc_secure( mpi_get_nlimbs(skey.n) );
rsa_secret( plain_dek, k->d.rsa.rsa_integer, &skey );
memset( &skey, 0, sizeof skey );
}
#endif/*HAVE_RSA_CIPHER*/
else {
rc = G10ERR_PUBKEY_ALGO; /* unsupported algorithm */
goto leave;
}
free_secret_cert( skc ); skc = 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)
*
* 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 );
for(n=0; n < nframe && !frame[n]; n++ ) /* skip leading zeroes */
;
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++];
switch( dek->algo ) {
case CIPHER_ALGO_IDEA:
rc = G10ERR_NI_CIPHER;
goto leave;
case CIPHER_ALGO_BLOWFISH:
if( dek->keylen != 20 )
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
break;
case CIPHER_ALGO_BLOWFISH128:
if( dek->keylen != 16 )
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
break;
case CIPHER_ALGO_CAST:
if( dek->keylen < 5 || dek->keylen > 16 )
{ rc = G10ERR_WRONG_SECKEY; goto leave; }
break;
default:
dek->algo = 0;
rc = G10ERR_CIPHER_ALGO;
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 );
leave:
mpi_free(plain_dek);
m_free(frame);
if( skc )
free_secret_cert( skc );
return rc;
}
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