sm/certcheck.c

   1 /* certcheck.c - check one certificate
   2  *      Copyright (C) 2001, 2003, 2004 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <config.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <errno.h>
  25 #include <unistd.h>
  26 #include <time.h>
  27 #include <assert.h>
  28
  29 #include "gpgsm.h"
  30 #include <gcrypt.h>
  31 #include <ksba.h>
  32
  33 #include "keydb.h"
  34 #include "i18n.h"
  35
  36
  37 /* Return the number of bits of the Q parameter from the DSA key
  38    KEY.  */
  39 static unsigned int
  40 get_dsa_qbits (gcry_sexp_t key)
  41 {
  42   gcry_sexp_t l1, l2;
  43   gcry_mpi_t q;
  44   unsigned int nbits;
  45
  46   l1 = gcry_sexp_find_token (key, "public-key", 0);
  47   if (!l1)
  48     return 0; /* Does not contain a key object.  */
  49   l2 = gcry_sexp_cadr (l1);
  50   gcry_sexp_release  (l1);
  51   l1 = gcry_sexp_find_token (l2, "q", 1);
  52   gcry_sexp_release (l2);
  53   if (!l1)
  54     return 0; /* Invalid object.  */
  55   q = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
  56   gcry_sexp_release (l1);
  57   if (!q)
  58     return 0; /* Missing value.  */
  59   nbits = gcry_mpi_get_nbits (q);
  60   gcry_mpi_release (q);
  61
  62   return nbits;
  63 }
  64
  65
  66 static int
  67 do_encode_md (gcry_md_hd_t md, int algo, int pkalgo, unsigned int nbits,
  68               gcry_sexp_t pkey, gcry_mpi_t *r_val)
  69 {
  70   int n;
  71   size_t nframe;
  72   unsigned char *frame;
  73
  74   if (pkalgo == GCRY_PK_DSA || pkalgo == GCRY_PK_ECDSA)
  75     {
  76       unsigned int qbits;
  77
  78       if ( pkalgo == GCRY_PK_ECDSA )
  79         qbits = gcry_pk_get_nbits (pkey);
  80       else
  81         qbits = get_dsa_qbits (pkey);
  82
  83       if ( (qbits%8) )
  84         {
  85           log_error(_("DSA requires the hash length to be a"
  86                       " multiple of 8 bits\n"));
  87           return gpg_error (GPG_ERR_INTERNAL);
  88         }
  89
  90       /* Don't allow any Q smaller than 160 bits.  We don't want
  91          someone to issue signatures from a key with a 16-bit Q or
  92          something like that, which would look correct but allow
  93          trivial forgeries.  Yes, I know this rules out using MD5 with
  94          DSA. ;) */
  95       if (qbits < 160)
  96         {
  97           log_error (_("%s key uses an unsafe (%u bit) hash\n"),
  98                      gcry_pk_algo_name (pkalgo), qbits);
  99           return gpg_error (GPG_ERR_INTERNAL);
 100         }
 101
 102       /* Check if we're too short.  Too long is safe as we'll
 103          automatically left-truncate. */
 104       nframe = gcry_md_get_algo_dlen (algo);
 105       if (nframe < qbits/8)
 106         {
 107           log_error (_("a %u bit hash is not valid for a %u bit %s key\n"),
 108                      (unsigned int)nframe*8,
 109                      gcry_pk_get_nbits (pkey),
 110                      gcry_pk_algo_name (pkalgo));
 111           /* FIXME: we need to check the requirements for ECDSA.  */
 112           if (nframe < 20 || pkalgo == GCRY_PK_DSA  )
 113             return gpg_error (GPG_ERR_INTERNAL);
 114         }
 115
 116       frame = xtrymalloc (nframe);
 117       if (!frame)
 118         return out_of_core ();
 119       memcpy (frame, gcry_md_read (md, algo), nframe);
 120       n = nframe;
 121       /* Truncate.  */
 122       if (n > qbits/8)
 123         n = qbits/8;
 124     }
 125   else
 126     {
 127       int i;
 128       unsigned char asn[100];
 129       size_t asnlen;
 130       size_t len;
 131
 132       nframe = (nbits+7) / 8;
 133
 134       asnlen = DIM(asn);
 135       if (!algo || gcry_md_test_algo (algo))
 136         return gpg_error (GPG_ERR_DIGEST_ALGO);
 137       if (gcry_md_algo_info (algo, GCRYCTL_GET_ASNOID, asn, &asnlen))
 138         {
 139           log_error ("no object identifier for algo %d\n", algo);
 140           return gpg_error (GPG_ERR_INTERNAL);
 141         }
 142
 143       len = gcry_md_get_algo_dlen (algo);
 144
 145       if ( len + asnlen + 4  > nframe )
 146         {
 147           log_error ("can't encode a %d bit MD into a %d bits frame\n",
 148                      (int)(len*8), (int)nbits);
 149           return gpg_error (GPG_ERR_INTERNAL);
 150         }
 151
 152       /* We encode the MD in this way:
 153        *
 154        *           0  A PAD(n bytes)   0  ASN(asnlen bytes)  MD(len bytes)
 155        *
 156        * PAD consists of FF bytes.
 157        */
 158       frame = xtrymalloc (nframe);
 159       if (!frame)
 160         return out_of_core ();
 161       n = 0;
 162       frame[n++] = 0;
 163       frame[n++] = 1; /* block type */
 164       i = nframe - len - asnlen -3 ;
 165       assert ( i > 1 );
 166       memset ( frame+n, 0xff, i ); n += i;
 167       frame[n++] = 0;
 168       memcpy ( frame+n, asn, asnlen ); n += asnlen;
 169       memcpy ( frame+n, gcry_md_read(md, algo), len ); n += len;
 170       assert ( n == nframe );
 171     }
 172   if (DBG_CRYPTO)
 173     {
 174       int j;
 175       log_debug ("encoded hash:");
 176       for (j=0; j < nframe; j++)
 177         log_printf (" %02X", frame[j]);
 178       log_printf ("\n");
 179     }
 180
 181   gcry_mpi_scan (r_val, GCRYMPI_FMT_USG, frame, n, &nframe);
 182   xfree (frame);
 183   return 0;
 184 }
 185
 186 /* Return the public key algorithm id from the S-expression PKEY.
 187    FIXME: libgcrypt should provide such a function.  Note that this
 188    implementation uses the names as used by libksba.  */
 189 static int
 190 pk_algo_from_sexp (gcry_sexp_t pkey)
 191 {
 192   gcry_sexp_t l1, l2;
 193   const char *name;
 194   size_t n;
 195   int algo;
 196
 197   l1 = gcry_sexp_find_token (pkey, "public-key", 0);
 198   if (!l1)
 199     return 0; /* Not found.  */
 200   l2 = gcry_sexp_cadr (l1);
 201   gcry_sexp_release (l1);
 202
 203   name = gcry_sexp_nth_data (l2, 0, &n);
 204   if (!name)
 205     algo = 0; /* Not found. */
 206   else if (n==3 && !memcmp (name, "rsa", 3))
 207     algo = GCRY_PK_RSA;
 208   else if (n==3 && !memcmp (name, "dsa", 3))
 209     algo = GCRY_PK_DSA;
 210   /* Because this function is called only for verification we can
 211      assume that ECC actually means ECDSA.  */
 212   else if (n==3 && !memcmp (name, "ecc", 3))
 213     algo = GCRY_PK_ECDSA;
 214   else if (n==13 && !memcmp (name, "ambiguous-rsa", 13))
 215     algo = GCRY_PK_RSA;
 216   else
 217     algo = 0;
 218   gcry_sexp_release (l2);
 219   return algo;
 220 }
 221
 222
 223 /* Check the signature on CERT using the ISSUER-CERT.  This function
 224    does only test the cryptographic signature and nothing else.  It is
 225    assumed that the ISSUER_CERT is valid. */
 226 int
 227 gpgsm_check_cert_sig (ksba_cert_t issuer_cert, ksba_cert_t cert)
 228 {
 229   const char *algoid;
 230   gcry_md_hd_t md;
 231   int rc, algo;
 232   gcry_mpi_t frame;
 233   ksba_sexp_t p;
 234   size_t n;
 235   gcry_sexp_t s_sig, s_hash, s_pkey;
 236
 237   algo = gcry_md_map_name ( (algoid=ksba_cert_get_digest_algo (cert)));
 238   if (!algo)
 239     {
 240       log_error ("unknown hash algorithm `%s'\n", algoid? algoid:"?");
 241       if (algoid
 242           && (  !strcmp (algoid, "1.2.840.113549.1.1.2")
 243                 ||!strcmp (algoid, "1.2.840.113549.2.2")))
 244         log_info (_("(this is the MD2 algorithm)\n"));
 245       return gpg_error (GPG_ERR_GENERAL);
 246     }
 247   rc = gcry_md_open (&md, algo, 0);
 248   if (rc)
 249     {
 250       log_error ("md_open failed: %s\n", gpg_strerror (rc));
 251       return rc;
 252     }
 253   if (DBG_HASHING)
 254     gcry_md_start_debug (md, "hash.cert");
 255
 256   rc = ksba_cert_hash (cert, 1, HASH_FNC, md);
 257   if (rc)
 258     {
 259       log_error ("ksba_cert_hash failed: %s\n", gpg_strerror (rc));
 260       gcry_md_close (md);
 261       return rc;
 262     }
 263   gcry_md_final (md);
 264
 265   p = ksba_cert_get_sig_val (cert);
 266   n = gcry_sexp_canon_len (p, 0, NULL, NULL);
 267   if (!n)
 268     {
 269       log_error ("libksba did not return a proper S-Exp\n");
 270       gcry_md_close (md);
 271       ksba_free (p);
 272       return gpg_error (GPG_ERR_BUG);
 273     }
 274   if (DBG_CRYPTO)
 275     {
 276       int j;
 277       log_debug ("signature value:");
 278       for (j=0; j < n; j++)
 279         log_printf (" %02X", p[j]);
 280       log_printf ("\n");
 281     }
 282
 283   rc = gcry_sexp_sscan ( &s_sig, NULL, (char*)p, n);
 284   ksba_free (p);
 285   if (rc)
 286     {
 287       log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (rc));
 288       gcry_md_close (md);
 289       return rc;
 290     }
 291
 292   p = ksba_cert_get_public_key (issuer_cert);
 293   n = gcry_sexp_canon_len (p, 0, NULL, NULL);
 294   if (!n)
 295     {
 296       log_error ("libksba did not return a proper S-Exp\n");
 297       gcry_md_close (md);
 298       ksba_free (p);
 299       gcry_sexp_release (s_sig);
 300       return gpg_error (GPG_ERR_BUG);
 301     }
 302   rc = gcry_sexp_sscan ( &s_pkey, NULL, (char*)p, n);
 303   ksba_free (p);
 304   if (rc)
 305     {
 306       log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (rc));
 307       gcry_md_close (md);
 308       gcry_sexp_release (s_sig);
 309       return rc;
 310     }
 311
 312   rc = do_encode_md (md, algo, pk_algo_from_sexp (s_pkey),
 313                      gcry_pk_get_nbits (s_pkey), s_pkey, &frame);
 314   if (rc)
 315     {
 316       gcry_md_close (md);
 317       gcry_sexp_release (s_sig);
 318       gcry_sexp_release (s_pkey);
 319       return rc;
 320     }
 321
 322   /* put hash into the S-Exp s_hash */
 323   if ( gcry_sexp_build (&s_hash, NULL, "%m", frame) )
 324     BUG ();
 325   gcry_mpi_release (frame);
 326
 327
 328   rc = gcry_pk_verify (s_sig, s_hash, s_pkey);
 329   if (DBG_X509)
 330       log_debug ("gcry_pk_verify: %s\n", gpg_strerror (rc));
 331   gcry_md_close (md);
 332   gcry_sexp_release (s_sig);
 333   gcry_sexp_release (s_hash);
 334   gcry_sexp_release (s_pkey);
 335   return rc;
 336 }
 337
 338
 339
 340 int
 341 gpgsm_check_cms_signature (ksba_cert_t cert, ksba_const_sexp_t sigval,
 342                            gcry_md_hd_t md, int mdalgo, int *r_pkalgo)
 343 {
 344   int rc;
 345   ksba_sexp_t p;
 346   gcry_mpi_t frame;
 347   gcry_sexp_t s_sig, s_hash, s_pkey;
 348   size_t n;
 349   int pkalgo;
 350
 351   if (r_pkalgo)
 352     *r_pkalgo = 0;
 353
 354   n = gcry_sexp_canon_len (sigval, 0, NULL, NULL);
 355   if (!n)
 356     {
 357       log_error ("libksba did not return a proper S-Exp\n");
 358       return gpg_error (GPG_ERR_BUG);
 359     }
 360   rc = gcry_sexp_sscan (&s_sig, NULL, (char*)sigval, n);
 361   if (rc)
 362     {
 363       log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (rc));
 364       return rc;
 365     }
 366
 367   p = ksba_cert_get_public_key (cert);
 368   n = gcry_sexp_canon_len (p, 0, NULL, NULL);
 369   if (!n)
 370     {
 371       log_error ("libksba did not return a proper S-Exp\n");
 372       ksba_free (p);
 373       gcry_sexp_release (s_sig);
 374       return gpg_error (GPG_ERR_BUG);
 375     }
 376   if (DBG_CRYPTO)
 377     log_printhex ("public key: ", p, n);
 378
 379   rc = gcry_sexp_sscan ( &s_pkey, NULL, (char*)p, n);
 380   ksba_free (p);
 381   if (rc)
 382     {
 383       log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (rc));
 384       gcry_sexp_release (s_sig);
 385       return rc;
 386     }
 387
 388   pkalgo = pk_algo_from_sexp (s_pkey);
 389   if (r_pkalgo)
 390     *r_pkalgo = pkalgo;
 391   rc = do_encode_md (md, mdalgo, pkalgo,
 392                      gcry_pk_get_nbits (s_pkey), s_pkey, &frame);
 393   if (rc)
 394     {
 395       gcry_sexp_release (s_sig);
 396       gcry_sexp_release (s_pkey);
 397       return rc;
 398     }
 399   /* put hash into the S-Exp s_hash */
 400   if ( gcry_sexp_build (&s_hash, NULL, "%m", frame) )
 401     BUG ();
 402   gcry_mpi_release (frame);
 403
 404   rc = gcry_pk_verify (s_sig, s_hash, s_pkey);
 405   if (DBG_X509)
 406       log_debug ("gcry_pk_verify: %s\n", gpg_strerror (rc));
 407   gcry_sexp_release (s_sig);
 408   gcry_sexp_release (s_hash);
 409   gcry_sexp_release (s_pkey);
 410   return rc;
 411 }
 412
 413
 414
 415 int
 416 gpgsm_create_cms_signature (ctrl_t ctrl, ksba_cert_t cert,
 417                             gcry_md_hd_t md, int mdalgo,
 418                             unsigned char **r_sigval)
 419 {
 420   int rc;
 421   char *grip, *desc;
 422   size_t siglen;
 423
 424   grip = gpgsm_get_keygrip_hexstring (cert);
 425   if (!grip)
 426     return gpg_error (GPG_ERR_BAD_CERT);
 427
 428   desc = gpgsm_format_keydesc (cert);
 429
 430   rc = gpgsm_agent_pksign (ctrl, grip, desc, gcry_md_read(md, mdalgo),
 431                            gcry_md_get_algo_dlen (mdalgo), mdalgo,
 432                            r_sigval, &siglen);
 433   xfree (desc);
 434   xfree (grip);
 435   return rc;
 436 }
 437
 438
 439