gnupg/g10/pubkey-enc.c

/* pubkey-enc.c -  public key encoded packet handling
 * Copyright (C) 1998, 1999, 2000, 2001, 2002 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( pkb->pkt->pkt.public_key->selfsigversion > 3
            && 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;
}


/****************
 * 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;
}