gnupg/g10/pubkey-enc.c

/* pubkey-enc.c -  public key encoded packet handling
 * Copyright (C) 1998, 1999, 2000, 2001, 2002,
 *               2003 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 "gpg.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"
#include "pkglue.h"
#include "call-agent.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 && prefs &&
		!uid->is_revoked && !uid->is_expired ) {
                for (; prefs->type; prefs++ )
                    if (prefs->type == type && prefs->value == algo)
                        return 1;
            }
        }
    }
    return 0;
}


/****************
 * Get the session key from a pubkey enc packet 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 = openpgp_pk_test_algo (k->pubkey_algo, PUBKEY_USAGE_ENC);
    if( rc )
	goto leave;

    if( (k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets ) {
	sk = xcalloc (1, 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];
	char *p;

	for(;;) {
	    if( sk )
		free_secret_key( sk );
	    sk = xcalloc (1, sizeof *sk );
	    rc=enum_secret_keys( &enum_context, sk, 1, 0);
	    if( rc ) {
		rc = GPG_ERR_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] );

	    if(!opt.try_all_secrets && !is_status_enabled())
	      {
		p=get_last_passphrase();
		set_next_passphrase(p);
		xfree (p);
	      }

	    rc = check_secret_key( sk, opt.try_all_secrets?1:-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, 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;
  gcry_mpi_t plain_dek = NULL;
  byte *frame = NULL;
  unsigned n, nframe;
  u16 csum, csum2;
  int card = 0;

  if (sk->is_protected && sk->protect.s2k.mode == 1002)
    { /* FIXME: Note that we do only support RSA for now. */
      char *rbuf;
      size_t rbuflen;
      char *snbuf;
      unsigned char *indata = NULL;
      unsigned int indatalen;

      snbuf = serialno_and_fpr_from_sk (sk->protect.iv, sk->protect.ivlen, sk);

      if (gcry_mpi_aprint (GCRYMPI_FMT_USG, &indata, &indatalen,
                           enc->data[0]))
        BUG();

      rc = agent_scd_pkdecrypt (snbuf, indata, indatalen, &rbuf, &rbuflen);
      xfree (snbuf);
      xfree (indata);
      if (rc)
        goto leave;

      frame = rbuf;
      nframe = rbuflen;
      card = 1;
    }
  else
    {
      rc = pk_decrypt (sk->pubkey_algo, &plain_dek, enc->data, sk->skey);
      if( rc )
        goto leave;
      if (gcry_mpi_aprint (GCRYMPI_FMT_USG, &frame, &nframe, plain_dek))
        BUG();
      gcry_mpi_release (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_printhex ("DEK frame:", frame, nframe );
  n=0;
  if (!card)
    {
      if( n + 7 > nframe )
        { rc = GPG_ERR_WRONG_SECKEY; goto leave; }
      if( frame[n] == 1 && frame[nframe-1] == 2 ) {
        log_info(_("old encoding of the DEK is not supported\n"));
        rc = GPG_ERR_CIPHER_ALGO;
        goto leave;
      }
      if( frame[n] != 2 )  /* somethink is wrong */
        { rc = GPG_ERR_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 = GPG_ERR_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 = openpgp_cipher_test_algo (dek->algo);
  if( rc ) {
    if( !opt.quiet && gpg_err_code (rc) == GPG_ERR_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 != gcry_cipher_get_algo_keylen (dek->algo) ) {
    rc = GPG_ERR_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 = GPG_ERR_WRONG_SECKEY;
    goto leave;
  }
  if( DBG_CIPHER )
    log_printhex ("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) );
      }
    }

    if ( pk &&  pk->is_revoked ) {
      log_info( _("NOTE: key has been revoked") );
      putc( '\n', log_get_stream() );
      show_revocation_reason( pk, 1 );
    }

    release_kbnode (pkb);
    rc = 0;
  }


 leave:
  gcry_mpi_release (plain_dek);
  xfree (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 GPG_ERR_BAD_KEY;
    dek->algo = atoi(string);
    if ( dek->algo < 1 )
	return GPG_ERR_BAD_KEY;
    if ( !(s = strchr ( string, ':' )) )
	return GPG_ERR_BAD_KEY;
    s++;
    for(i=0; i < DIM(dek->key) && *s; i++, s +=2 ) {
	int c = hextobyte ( s );
	if (c == -1)
	    return GPG_ERR_BAD_KEY;
	dek->key[i] = c;
    }
    if ( *s )
	return GPG_ERR_BAD_KEY;
    dek->keylen = i;
    return 0;
}