g10/pubkey-enc.c

   1 /* pubkey-enc.c -  public key encoded packet handling
   2  * Copyright (C) 1998, 1999, 2000, 2001, 2002,
   3  *               2003 Free Software Foundation, Inc.
   4  *
   5  * This file is part of GnuPG.
   6  *
   7  * GnuPG is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * GnuPG is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  20  */
  21
  22 #include <config.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <assert.h>
  27
  28 #include "gpg.h"
  29 #include "util.h"
  30 #include "memory.h"
  31 #include "packet.h"
  32 #include "mpi.h"
  33 #include "keydb.h"
  34 #include "trustdb.h"
  35 #include "cipher.h"
  36 #include "status.h"
  37 #include "options.h"
  38 #include "main.h"
  39 #include "i18n.h"
  40 #include "pkglue.h"
  41 #include "call-agent.h"
  42
  43 static int get_it( PKT_pubkey_enc *k,
  44                    DEK *dek, PKT_secret_key *sk, u32 *keyid );
  45
  46
  47 /* check that the given algo is mentioned in one of the valid user IDs */
  48 static int
  49 is_algo_in_prefs ( KBNODE keyblock, preftype_t type, int algo )
  50 {
  51     KBNODE k;
  52
  53     for (k=keyblock; k; k=k->next) {
  54         if (k->pkt->pkttype == PKT_USER_ID) {
  55             PKT_user_id *uid = k->pkt->pkt.user_id;
  56             prefitem_t *prefs = uid->prefs;
  57
  58             if (uid->created && prefs &&
  59                 !uid->is_revoked && !uid->is_expired ) {
  60                 for (; prefs->type; prefs++ )
  61                     if (prefs->type == type && prefs->value == algo)
  62                         return 1;
  63             }
  64         }
  65     }
  66     return 0;
  67 }
  68
  69
  70 /****************
  71  * Get the session key from a pubkey enc packet and return
  72  * it in DEK, which should have been allocated in secure memory.
  73  */
  74 int
  75 get_session_key( PKT_pubkey_enc *k, DEK *dek )
  76 {
  77     PKT_secret_key *sk = NULL;
  78     int rc;
  79
  80     rc = openpgp_pk_test_algo (k->pubkey_algo, PUBKEY_USAGE_ENC);
  81     if( rc )
  82         goto leave;
  83
  84     if( (k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets ) {
  85         sk = xcalloc (1, sizeof *sk );
  86         sk->pubkey_algo = k->pubkey_algo; /* we want a pubkey with this algo*/
  87         if( !(rc = get_seckey( sk, k->keyid )) )
  88             rc = get_it( k, dek, sk, k->keyid );
  89     }
  90     else { /* anonymous receiver: Try all available secret keys */
  91         void *enum_context = NULL;
  92         u32 keyid[2];
  93         char *p;
  94
  95         for(;;) {
  96             if( sk )
  97                 free_secret_key( sk );
  98             sk = xcalloc (1, sizeof *sk );
  99             rc=enum_secret_keys( &enum_context, sk, 1, 0);
 100             if( rc ) {
 101                 rc = GPG_ERR_NO_SECKEY;
 102                 break;
 103             }
 104             if( sk->pubkey_algo != k->pubkey_algo )
 105                 continue;
 106             keyid_from_sk( sk, keyid );
 107             log_info(_("anonymous recipient; trying secret key %08lX ...\n"),
 108                      (ulong)keyid[1] );
 109
 110             if(!opt.try_all_secrets && !is_status_enabled())
 111               {
 112                 p=get_last_passphrase();
 113                 set_next_passphrase(p);
 114                 xfree (p);
 115               }
 116
 117             rc = check_secret_key( sk, opt.try_all_secrets?1:-1 ); /* ask
 118                                                                       only
 119                                                                       once */
 120             if( !rc )
 121                 rc = get_it( k, dek, sk, keyid );
 122             if( !rc ) {
 123                 log_info(_("okay, we are the anonymous recipient.\n") );
 124                 break;
 125             }
 126         }
 127         enum_secret_keys( &enum_context, NULL, 0, 0 ); /* free context */
 128     }
 129
 130   leave:
 131     if( sk )
 132         free_secret_key( sk );
 133     return rc;
 134 }
 135
 136
 137 static int
 138 get_it( PKT_pubkey_enc *enc, DEK *dek, PKT_secret_key *sk, u32 *keyid )
 139 {
 140   int rc;
 141   gcry_mpi_t plain_dek = NULL;
 142   byte *frame = NULL;
 143   unsigned n, nframe;
 144   u16 csum, csum2;
 145   int card = 0;
 146
 147   if (sk->is_protected && sk->protect.s2k.mode == 1002)
 148     { /* FIXME: Note that we do only support RSA for now. */
 149       char *rbuf;
 150       size_t rbuflen;
 151       char *snbuf;
 152       unsigned char *indata = NULL;
 153       unsigned int indatalen;
 154
 155       snbuf = serialno_and_fpr_from_sk (sk->protect.iv, sk->protect.ivlen, sk);
 156
 157       if (gcry_mpi_aprint (GCRYMPI_FMT_USG, &indata, &indatalen,
 158                            enc->data[0]))
 159         BUG();
 160
 161       rc = agent_scd_pkdecrypt (snbuf, indata, indatalen, &rbuf, &rbuflen);
 162       xfree (snbuf);
 163       xfree (indata);
 164       if (rc)
 165         goto leave;
 166
 167       frame = rbuf;
 168       nframe = rbuflen;
 169       card = 1;
 170     }
 171   else
 172     {
 173       rc = pk_decrypt (sk->pubkey_algo, &plain_dek, enc->data, sk->skey);
 174       if( rc )
 175         goto leave;
 176       if (gcry_mpi_aprint (GCRYMPI_FMT_USG, &frame, &nframe, plain_dek))
 177         BUG();
 178       gcry_mpi_release (plain_dek); plain_dek = NULL;
 179     }
 180
 181
 182   /* Now get the DEK (data encryption key) from the frame
 183    *
 184    * Old versions encode the DEK in in this format (msb is left):
 185    *
 186    *       0  1  DEK(16 bytes)  CSUM(2 bytes)  0  RND(n bytes) 2
 187    *
 188    * Later versions encode the DEK like this:
 189    *
 190    *       0  2  RND(n bytes)  0  A  DEK(k bytes)  CSUM(2 bytes)
 191    *
 192    * (mpi_get_buffer already removed the leading zero).
 193    *
 194    * RND are non-zero randow bytes.
 195    * A   is the cipher algorithm
 196    * DEK is the encryption key (session key) with length k
 197    * CSUM
 198    */
 199   if( DBG_CIPHER )
 200     log_printhex ("DEK frame:", frame, nframe );
 201   n=0;
 202   if (!card)
 203     {
 204       if( n + 7 > nframe )
 205         { rc = GPG_ERR_WRONG_SECKEY; goto leave; }
 206       if( frame[n] == 1 && frame[nframe-1] == 2 ) {
 207         log_info(_("old encoding of the DEK is not supported\n"));
 208         rc = GPG_ERR_CIPHER_ALGO;
 209         goto leave;
 210       }
 211       if( frame[n] != 2 )  /* somethink is wrong */
 212         { rc = GPG_ERR_WRONG_SECKEY; goto leave; }
 213       for(n++; n < nframe && frame[n]; n++ ) /* skip the random bytes */
 214         ;
 215       n++; /* and the zero byte */
 216     }
 217
 218   if( n + 4 > nframe )
 219     { rc = GPG_ERR_WRONG_SECKEY; goto leave; }
 220   dek->keylen = nframe - (n+1) - 2;
 221   dek->algo = frame[n++];
 222   if( dek->algo ==  CIPHER_ALGO_IDEA )
 223     write_status(STATUS_RSA_OR_IDEA);
 224   rc = openpgp_cipher_test_algo (dek->algo);
 225   if( rc ) {
 226     if( !opt.quiet && gpg_err_code (rc) == GPG_ERR_CIPHER_ALGO ) {
 227       log_info(_("cipher algorithm %d%s is unknown or disabled\n"),
 228                dek->algo, dek->algo == CIPHER_ALGO_IDEA? " (IDEA)":"");
 229       if(dek->algo==CIPHER_ALGO_IDEA)
 230         idea_cipher_warn(0);
 231     }
 232     dek->algo = 0;
 233     goto leave;
 234   }
 235   if( dek->keylen != gcry_cipher_get_algo_keylen (dek->algo) ) {
 236     rc = GPG_ERR_WRONG_SECKEY;
 237     goto leave;
 238   }
 239
 240   /* copy the key to DEK and compare the checksum */
 241   csum  = frame[nframe-2] << 8;
 242   csum |= frame[nframe-1];
 243   memcpy( dek->key, frame+n, dek->keylen );
 244   for( csum2=0, n=0; n < dek->keylen; n++ )
 245     csum2 += dek->key[n];
 246   if( csum != csum2 ) {
 247     rc = GPG_ERR_WRONG_SECKEY;
 248     goto leave;
 249   }
 250   if( DBG_CIPHER )
 251     log_printhex ("DEK is:", dek->key, dek->keylen );
 252   /* check that the algo is in the preferences and whether it has expired */
 253   {
 254     PKT_public_key *pk = NULL;
 255     KBNODE pkb = get_pubkeyblock (keyid);
 256
 257     if( !pkb ) {
 258       rc = -1;
 259       log_error("oops: public key not found for preference check\n");
 260     }
 261     else if( pkb->pkt->pkt.public_key->selfsigversion > 3
 262              && dek->algo != CIPHER_ALGO_3DES
 263              && !is_algo_in_prefs( pkb, PREFTYPE_SYM, dek->algo ) ) {
 264       /* Don't print a note while we are not on verbose mode,
 265        * the cipher is blowfish and the preferences have twofish
 266        * listed */
 267       if( opt.verbose || dek->algo != CIPHER_ALGO_BLOWFISH
 268           || !is_algo_in_prefs( pkb, PREFTYPE_SYM, CIPHER_ALGO_TWOFISH))
 269         log_info(_(
 270                    "NOTE: cipher algorithm %d not found in preferences\n"),
 271                  dek->algo );
 272     }
 273
 274     if (!rc) {
 275       KBNODE k;
 276
 277       for (k=pkb; k; k = k->next) {
 278         if (k->pkt->pkttype == PKT_PUBLIC_KEY
 279             || k->pkt->pkttype == PKT_PUBLIC_SUBKEY){
 280           u32 aki[2];
 281           keyid_from_pk(k->pkt->pkt.public_key, aki);
 282
 283           if (aki[0]==keyid[0] && aki[1]==keyid[1]) {
 284             pk = k->pkt->pkt.public_key;
 285             break;
 286           }
 287         }
 288       }
 289       if (!pk)
 290         BUG ();
 291       if ( pk->expiredate && pk->expiredate <= make_timestamp() ) {
 292         log_info(_("NOTE: secret key %08lX expired at %s\n"),
 293                  (ulong)keyid[1], asctimestamp( pk->expiredate) );
 294       }
 295     }
 296
 297     if ( pk &&  pk->is_revoked ) {
 298       log_info( _("NOTE: key has been revoked") );
 299       putc( '\n', log_get_stream() );
 300       show_revocation_reason( pk, 1 );
 301     }
 302
 303     release_kbnode (pkb);
 304     rc = 0;
 305   }
 306
 307
 308  leave:
 309   gcry_mpi_release (plain_dek);
 310   xfree (frame);
 311   return rc;
 312 }
 313
 314
 315 /****************
 316  * Get the session key from the given string.
 317  * String is supposed to be formatted as this:
 318  *  <algo-id>:<even-number-of-hex-digits>
 319  */
 320 int
 321 get_override_session_key( DEK *dek, const char *string )
 322 {
 323     const char *s;
 324     int i;
 325
 326     if ( !string )
 327         return GPG_ERR_BAD_KEY;
 328     dek->algo = atoi(string);
 329     if ( dek->algo < 1 )
 330         return GPG_ERR_BAD_KEY;
 331     if ( !(s = strchr ( string, ':' )) )
 332         return GPG_ERR_BAD_KEY;
 333     s++;
 334     for(i=0; i < DIM(dek->key) && *s; i++, s +=2 ) {
 335         int c = hextobyte ( s );
 336         if (c == -1)
 337             return GPG_ERR_BAD_KEY;
 338         dek->key[i] = c;
 339     }
 340     if ( *s )
 341         return GPG_ERR_BAD_KEY;
 342     dek->keylen = i;
 343     return 0;
 344 }
 345