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gnupg/g10/pubkey-enc.c
David Shaw e8936126af Much stricter checking of the keyserver URI 
IDEA warning for pk messages encrypted with IDEA (symmetric is already done)
Print IDEA warning for each occurance except for secret key protection and
unknown cipher from an encrypted message.
2001-12-18 23:10:46 +00:00

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/* pubkey-enc.c - public key encoded packet handling
* Copyright (C) 1998, 1999, 2000, 2001 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 "options.h"
#include "main.h"
#include "i18n.h"
static int get_it( PKT_pubkey_enc *k,
DEK *dek, PKT_secret_key *sk, u32 *keyid );
/* check that the given algo is mentioned in one of the valid user IDs */
static int
is_algo_in_prefs ( KBNODE keyblock, preftype_t type, int algo )
{
KBNODE k;
for (k=keyblock; k; k=k->next) {
if (k->pkt->pkttype == PKT_USER_ID) {
PKT_user_id *uid = k->pkt->pkt.user_id;
prefitem_t *prefs = uid->prefs;
if (uid->created && !uid->is_revoked && prefs ) {
for (; prefs->type; prefs++ )
if (prefs->type == type && prefs->value == algo)
return 1;
}
}
}
return 0;
}
/****************
* 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 )
{
PKT_secret_key *sk = NULL;
int rc;
rc = check_pubkey_algo2 (k->pubkey_algo, PUBKEY_USAGE_ENC);
if( rc )
goto leave;
if( (k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets ) {
sk = m_alloc_clear( sizeof *sk );
sk->pubkey_algo = k->pubkey_algo; /* we want a pubkey with this algo*/
if( !(rc = get_seckey( sk, k->keyid )) )
rc = get_it( k, dek, sk, k->keyid );
}
else { /* anonymous receiver: Try all available secret keys */
void *enum_context = NULL;
u32 keyid[2];
for(;;) {
if( sk )
free_secret_key( sk );
sk = m_alloc_clear( sizeof *sk );
rc=enum_secret_keys( &enum_context, sk, 1);
if( rc ) {
rc = G10ERR_NO_SECKEY;
break;
}
if( sk->pubkey_algo != k->pubkey_algo )
continue;
keyid_from_sk( sk, keyid );
log_info(_("anonymous recipient; trying secret key %08lX ...\n"),
(ulong)keyid[1] );
rc = check_secret_key( sk, 1 ); /* ask only once */
if( !rc )
rc = get_it( k, dek, sk, keyid );
if( !rc ) {
log_info(_("okay, we are the anonymous recipient.\n") );
break;
}
}
enum_secret_keys( &enum_context, NULL, 0 ); /* free context */
}
leave:
if( sk )
free_secret_key( sk );
return rc;
}
static int
get_it( PKT_pubkey_enc *enc, DEK *dek, PKT_secret_key *sk, u32 *keyid )
{
int rc;
MPI plain_dek = NULL;
byte *frame = NULL;
unsigned n, nframe;
u16 csum, csum2;
rc = pubkey_decrypt(sk->pubkey_algo, &plain_dek, enc->data, sk->skey );
if( rc )
goto leave;
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_info(_("old encoding of the 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 ) {
if( !opt.quiet && rc == G10ERR_CIPHER_ALGO ) {
log_info(_("cipher algorithm %d%s is unknown or disabled\n"),
dek->algo, dek->algo == CIPHER_ALGO_IDEA? " (IDEA)":"");
if(dek->algo==CIPHER_ALGO_IDEA)
idea_cipher_warn(0);
}
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 and whether it has expired */
{
PKT_public_key *pk = NULL;
KBNODE pkb = get_pubkeyblock (keyid);
if( !pkb ) {
rc = -1;
log_error("oops: public key not found for preference check\n");
}
else if( dek->algo != CIPHER_ALGO_3DES
&& !is_algo_in_prefs( pkb, PREFTYPE_SYM, dek->algo ) ) {
/* Don't print a note while we are not on verbose mode,
* the cipher is blowfish and the preferences have twofish
* listed */
if( opt.verbose || dek->algo != CIPHER_ALGO_BLOWFISH
|| !is_algo_in_prefs( pkb, PREFTYPE_SYM, CIPHER_ALGO_TWOFISH))
log_info(_(
"NOTE: cipher algorithm %d not found in preferences\n"),
dek->algo );
}
if (!rc) {
KBNODE k;
for (k=pkb; k; k = k->next) {
if (k->pkt->pkttype == PKT_PUBLIC_KEY
|| k->pkt->pkttype == PKT_PUBLIC_SUBKEY){
u32 aki[2];
keyid_from_pk(k->pkt->pkt.public_key, aki);
if (aki[0]==keyid[0] && aki[1]==keyid[1]) {
pk = k->pkt->pkt.public_key;
break;
}
}
}
if (!pk)
BUG ();
if ( pk->expiredate && pk->expiredate <= make_timestamp() ) {
log_info(_("NOTE: secret key %08lX expired at %s\n"),
(ulong)keyid[1], asctimestamp( pk->expiredate) );
}
}
/* FIXME: check wheter the key has been revoked and display
* the revocation reason. Actually the user should know this himself,
* but the sender might not know already and therefor the user
* should get a notice that an revoked key has been used to decode
* the message. The user can than watch out for snakes send by
* one of those Eves outside his paradise :-)
*/
release_kbnode (pkb);
rc = 0;
}
leave:
mpi_free(plain_dek);
m_free(frame);
return rc;
}
static int
hextobyte( const char *s )
{
int c;
if( *s >= '0' && *s <= '9' )
c = 16 * (*s - '0');
else if( *s >= 'A' && *s <= 'F' )
c = 16 * (10 + *s - 'A');
else if( *s >= 'a' && *s <= 'f' )
c = 16 * (10 + *s - 'a');
else
return -1;
s++;
if( *s >= '0' && *s <= '9' )
c += *s - '0';
else if( *s >= 'A' && *s <= 'F' )
c += 10 + *s - 'A';
else if( *s >= 'a' && *s <= 'f' )
c += 10 + *s - 'a';
else
return -1;
return c;
}
/****************
* Get the session key from the given string.
* String is supposed to be formatted as this:
* <algo-id>:<even-number-of-hex-digits>
*/
int
get_override_session_key( DEK *dek, const char *string )
{
const char *s;
int i;
if ( !string )
return G10ERR_BAD_KEY;
dek->algo = atoi(string);
if ( dek->algo < 1 )
return G10ERR_BAD_KEY;
if ( !(s = strchr ( string, ':' )) )
return G10ERR_BAD_KEY;
s++;
for(i=0; i < DIM(dek->key) && *s; i++, s +=2 ) {
int c = hextobyte ( s );
if (c == -1)
return G10ERR_BAD_KEY;
dek->key[i] = c;
}
if ( *s )
return G10ERR_BAD_KEY;
dek->keylen = i;
return 0;
}
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