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307
g10/pubkey-enc.c
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307
g10/pubkey-enc.c
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/* pubkey-enc.c - public key encoded packet handling
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* Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* GnuPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "util.h"
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#include "memory.h"
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#include "packet.h"
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#include "mpi.h"
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#include "keydb.h"
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#include "trustdb.h"
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#include "cipher.h"
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#include "status.h"
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#include "options.h"
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#include "main.h"
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#include "i18n.h"
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static int get_it( PKT_pubkey_enc *k,
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DEK *dek, PKT_secret_key *sk, u32 *keyid );
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/* check that the given algo is mentioned in one of the valid user IDs */
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static int
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is_algo_in_prefs ( KBNODE keyblock, preftype_t type, int algo )
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{
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KBNODE k;
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for (k=keyblock; k; k=k->next) {
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if (k->pkt->pkttype == PKT_USER_ID) {
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PKT_user_id *uid = k->pkt->pkt.user_id;
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prefitem_t *prefs = uid->prefs;
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if (uid->created && prefs &&
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!uid->is_revoked && !uid->is_expired ) {
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for (; prefs->type; prefs++ )
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if (prefs->type == type && prefs->value == algo)
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return 1;
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}
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}
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}
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return 0;
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}
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/****************
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* Get the session key from a pubkey enc packet and return
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* it in DEK, which should have been allocated in secure memory.
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*/
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int
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get_session_key( PKT_pubkey_enc *k, DEK *dek )
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{
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PKT_secret_key *sk = NULL;
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int rc;
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rc = check_pubkey_algo2 (k->pubkey_algo, PUBKEY_USAGE_ENC);
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if( rc )
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goto leave;
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if( (k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets ) {
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sk = m_alloc_clear( sizeof *sk );
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sk->pubkey_algo = k->pubkey_algo; /* we want a pubkey with this algo*/
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if( !(rc = get_seckey( sk, k->keyid )) )
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rc = get_it( k, dek, sk, k->keyid );
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}
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else { /* anonymous receiver: Try all available secret keys */
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void *enum_context = NULL;
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u32 keyid[2];
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char *p;
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for(;;) {
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if( sk )
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free_secret_key( sk );
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sk = m_alloc_clear( sizeof *sk );
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rc=enum_secret_keys( &enum_context, sk, 1, 0);
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if( rc ) {
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rc = G10ERR_NO_SECKEY;
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break;
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}
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if( sk->pubkey_algo != k->pubkey_algo )
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continue;
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keyid_from_sk( sk, keyid );
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log_info(_("anonymous recipient; trying secret key %08lX ...\n"),
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(ulong)keyid[1] );
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if(!opt.try_all_secrets && !is_status_enabled())
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{
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p=get_last_passphrase();
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set_next_passphrase(p);
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m_free(p);
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}
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rc = check_secret_key( sk, opt.try_all_secrets?1:-1 ); /* ask
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only
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once */
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if( !rc )
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rc = get_it( k, dek, sk, keyid );
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if( !rc ) {
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log_info(_("okay, we are the anonymous recipient.\n") );
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break;
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}
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}
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enum_secret_keys( &enum_context, NULL, 0, 0 ); /* free context */
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}
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leave:
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if( sk )
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free_secret_key( sk );
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return rc;
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}
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static int
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get_it( PKT_pubkey_enc *enc, DEK *dek, PKT_secret_key *sk, u32 *keyid )
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{
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int rc;
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MPI plain_dek = NULL;
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byte *frame = NULL;
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unsigned n, nframe;
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u16 csum, csum2;
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rc = pubkey_decrypt(sk->pubkey_algo, &plain_dek, enc->data, sk->skey );
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if( rc )
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goto leave;
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frame = mpi_get_buffer( plain_dek, &nframe, NULL );
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mpi_free( plain_dek ); plain_dek = NULL;
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/* Now get the DEK (data encryption key) from the frame
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*
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* Old versions encode the DEK in in this format (msb is left):
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*
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* 0 1 DEK(16 bytes) CSUM(2 bytes) 0 RND(n bytes) 2
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*
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* Later versions encode the DEK like this:
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*
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* 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes)
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*
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* (mpi_get_buffer already removed the leading zero).
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*
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* RND are non-zero randow bytes.
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* A is the cipher algorithm
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* DEK is the encryption key (session key) with length k
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* CSUM
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*/
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if( DBG_CIPHER )
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log_hexdump("DEK frame:", frame, nframe );
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n=0;
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if( n + 7 > nframe )
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{ rc = G10ERR_WRONG_SECKEY; goto leave; }
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if( frame[n] == 1 && frame[nframe-1] == 2 ) {
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log_info(_("old encoding of the DEK is not supported\n"));
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rc = G10ERR_CIPHER_ALGO;
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goto leave;
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}
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if( frame[n] != 2 ) /* somethink is wrong */
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{ rc = G10ERR_WRONG_SECKEY; goto leave; }
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for(n++; n < nframe && frame[n]; n++ ) /* skip the random bytes */
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;
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n++; /* and the zero byte */
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if( n + 4 > nframe )
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{ rc = G10ERR_WRONG_SECKEY; goto leave; }
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dek->keylen = nframe - (n+1) - 2;
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dek->algo = frame[n++];
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if( dek->algo == CIPHER_ALGO_IDEA )
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write_status(STATUS_RSA_OR_IDEA);
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rc = check_cipher_algo( dek->algo );
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if( rc ) {
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if( !opt.quiet && rc == G10ERR_CIPHER_ALGO ) {
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log_info(_("cipher algorithm %d%s is unknown or disabled\n"),
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dek->algo, dek->algo == CIPHER_ALGO_IDEA? " (IDEA)":"");
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if(dek->algo==CIPHER_ALGO_IDEA)
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idea_cipher_warn(0);
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}
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dek->algo = 0;
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goto leave;
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}
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if( (dek->keylen*8) != cipher_get_keylen( dek->algo ) ) {
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rc = G10ERR_WRONG_SECKEY;
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goto leave;
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}
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/* copy the key to DEK and compare the checksum */
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csum = frame[nframe-2] << 8;
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csum |= frame[nframe-1];
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memcpy( dek->key, frame+n, dek->keylen );
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for( csum2=0, n=0; n < dek->keylen; n++ )
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csum2 += dek->key[n];
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if( csum != csum2 ) {
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rc = G10ERR_WRONG_SECKEY;
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goto leave;
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}
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if( DBG_CIPHER )
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log_hexdump("DEK is:", dek->key, dek->keylen );
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/* check that the algo is in the preferences and whether it has expired */
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{
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PKT_public_key *pk = NULL;
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KBNODE pkb = get_pubkeyblock (keyid);
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if( !pkb ) {
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rc = -1;
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log_error("oops: public key not found for preference check\n");
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}
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else if( pkb->pkt->pkt.public_key->selfsigversion > 3
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&& dek->algo != CIPHER_ALGO_3DES
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&& !is_algo_in_prefs( pkb, PREFTYPE_SYM, dek->algo ) ) {
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/* Don't print a note while we are not on verbose mode,
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* the cipher is blowfish and the preferences have twofish
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* listed */
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if( opt.verbose || dek->algo != CIPHER_ALGO_BLOWFISH
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|| !is_algo_in_prefs( pkb, PREFTYPE_SYM, CIPHER_ALGO_TWOFISH))
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log_info(_(
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"NOTE: cipher algorithm %d not found in preferences\n"),
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dek->algo );
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}
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if (!rc) {
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KBNODE k;
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for (k=pkb; k; k = k->next) {
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if (k->pkt->pkttype == PKT_PUBLIC_KEY
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|| k->pkt->pkttype == PKT_PUBLIC_SUBKEY){
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u32 aki[2];
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keyid_from_pk(k->pkt->pkt.public_key, aki);
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if (aki[0]==keyid[0] && aki[1]==keyid[1]) {
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pk = k->pkt->pkt.public_key;
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break;
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}
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}
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}
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if (!pk)
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BUG ();
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if ( pk->expiredate && pk->expiredate <= make_timestamp() ) {
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log_info(_("NOTE: secret key %08lX expired at %s\n"),
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(ulong)keyid[1], asctimestamp( pk->expiredate) );
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}
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}
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if ( pk && pk->is_revoked ) {
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log_info( _("NOTE: key has been revoked") );
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putc( '\n', log_stream() );
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show_revocation_reason( pk, 1 );
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}
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release_kbnode (pkb);
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rc = 0;
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}
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leave:
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mpi_free(plain_dek);
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m_free(frame);
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return rc;
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}
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/****************
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* Get the session key from the given string.
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* String is supposed to be formatted as this:
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* <algo-id>:<even-number-of-hex-digits>
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*/
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int
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get_override_session_key( DEK *dek, const char *string )
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{
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const char *s;
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int i;
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if ( !string )
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return G10ERR_BAD_KEY;
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dek->algo = atoi(string);
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if ( dek->algo < 1 )
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return G10ERR_BAD_KEY;
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if ( !(s = strchr ( string, ':' )) )
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return G10ERR_BAD_KEY;
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s++;
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for(i=0; i < DIM(dek->key) && *s; i++, s +=2 ) {
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int c = hextobyte ( s );
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if (c == -1)
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return G10ERR_BAD_KEY;
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dek->key[i] = c;
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}
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if ( *s )
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return G10ERR_BAD_KEY;
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dek->keylen = i;
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return 0;
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}
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