lib/x509_verify.c

   1 /*
   2  * Copyright (C) 2001,2002 Nikos Mavroyanopoulos <nmav@hellug.gr>
   3  *
   4  * This file is part of GNUTLS.
   5  *
   6  * GNUTLS 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 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GNUTLS 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, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include "gnutls_int.h"
  22 #include "gnutls_errors.h"
  23 #include "gnutls_cert.h"
  24 #include "x509_asn1.h"
  25 #include "x509_der.h"
  26 #include "gnutls_global.h"
  27 #include "gnutls_num.h"         /* GMAX */
  28 #include <gnutls_sig.h>
  29 #include <gnutls_str.h>
  30
  31
  32 /* Return 0 or INVALID, if the issuer is a CA,
  33  * or not.
  34  */
  35 static int check_if_ca(const gnutls_cert * cert,
  36                        const gnutls_cert * issuer)
  37 {
  38         CertificateStatus ret = GNUTLS_CERT_INVALID;
  39
  40         /* Check if the issuer is the same with the
  41          * certificate. This is added in order for trusted
  42          * certificates to be able to verify themselves.
  43          */
  44         if (cert->raw.size == issuer->raw.size) {
  45                 if (memcmp
  46                     (cert->raw.data, issuer->raw.data,
  47                      cert->raw.size) == 0) {
  48                         return 0;
  49                 }
  50         }
  51
  52         if (issuer->CA == 1) {
  53                 ret = 0;
  54         } else
  55                 gnutls_assert();
  56
  57         return ret;
  58 }
  59
  60
  61
  62 void _gnutls_int2str(int k, char *data);
  63
  64 #define MAX_DN_ELEM 1024
  65
  66 /* This function checks if 'certs' issuer is 'issuer_cert'.
  67  * This does a straight (DER) compare of the issuer/subject fields in
  68  * the given certificates.
  69  *
  70  * FIXME: use a real DN comparison algorithm.
  71  */
  72 static
  73 int compare_dn(gnutls_cert * cert, gnutls_cert * issuer_cert)
  74 {
  75         node_asn *c2, *c3;
  76         int result, len1;
  77         int len2;
  78         char tmpstr[512];
  79         int start1, start2, end1, end2;
  80
  81         /* get the issuer of 'cert'
  82          */
  83         if ((result =
  84              asn1_create_structure(_gnutls_get_pkix(), "PKIX1.Certificate",
  85                                    &c2, "certificate2")) != ASN_OK) {
  86                 gnutls_assert();
  87                 return _gnutls_asn2err(result);
  88         }
  89
  90         result = asn1_get_der(c2, cert->raw.data, cert->raw.size);
  91         if (result != ASN_OK) {
  92                 /* couldn't decode DER */
  93                 gnutls_assert();
  94                 asn1_delete_structure(c2);
  95                 return _gnutls_asn2err(result);
  96         }
  97
  98
  99
 100         /* get the 'subject' info of 'issuer_cert'
 101          */
 102         if ((result =
 103              asn1_create_structure(_gnutls_get_pkix(), "PKIX1.Certificate",
 104                                    &c3, "certificate2")) != ASN_OK) {
 105                 gnutls_assert();
 106                 asn1_delete_structure(c2);
 107                 return _gnutls_asn2err(result);
 108         }
 109
 110         result =
 111             asn1_get_der(c3, issuer_cert->raw.data, issuer_cert->raw.size);
 112         if (result != ASN_OK) {
 113                 /* couldn't decode DER */
 114                 gnutls_assert();
 115                 asn1_delete_structure(c2);
 116                 return _gnutls_asn2err(result);
 117         }
 118
 119
 120         _gnutls_str_cpy(tmpstr, sizeof(tmpstr),
 121                         "certificate2.tbsCertificate.issuer");
 122         result =
 123             asn1_get_start_end_der(c2, cert->raw.data, cert->raw.size,
 124                                    tmpstr, &start1, &end1);
 125         asn1_delete_structure(c2);
 126
 127         if (result != ASN_OK) {
 128                 gnutls_assert();
 129                 asn1_delete_structure(c3);
 130                 return _gnutls_asn2err(result);
 131         }
 132
 133         len1 = end1 - start1 + 1;
 134
 135         _gnutls_str_cpy(tmpstr, sizeof(tmpstr),
 136                         "certificate2.tbsCertificate.subject");
 137         result =
 138             asn1_get_start_end_der(c3, issuer_cert->raw.data,
 139                                    issuer_cert->raw.size, tmpstr, &start2,
 140                                    &end2);
 141         asn1_delete_structure(c3);
 142
 143         if (result != ASN_OK) {
 144                 gnutls_assert();
 145                 return _gnutls_asn2err(result);
 146         }
 147
 148         len2 = end2 - start2 + 1;
 149
 150         /* The error code returned does not really matter
 151          * here.
 152          */
 153         if (len1 != len2) {
 154                 gnutls_assert();
 155                 return GNUTLS_E_UNKNOWN_ERROR;
 156         }
 157         if (memcmp(&issuer_cert->raw.data[start2],
 158                    &cert->raw.data[start1], len1) != 0) {
 159                 gnutls_assert();
 160                 return GNUTLS_E_UNKNOWN_ERROR;
 161         }
 162
 163         /* they match */
 164         return 0;
 165
 166 }
 167
 168 static gnutls_cert *find_issuer(gnutls_cert * cert,
 169                                 gnutls_cert * trusted_cas, int tcas_size)
 170 {
 171         int i;
 172
 173         /* this is serial search.
 174          */
 175
 176         for (i = 0; i < tcas_size; i++) {
 177                 if (compare_dn(cert, &trusted_cas[i]) == 0)
 178                         return &trusted_cas[i];
 179         }
 180
 181         gnutls_assert();
 182         return NULL;
 183 }
 184
 185 /* ret_trust is the value to return when the certificate chain is ok
 186  * ret_else is the value to return otherwise.
 187  */
 188 int gnutls_verify_certificate2(gnutls_cert * cert,
 189                                gnutls_cert * trusted_cas, int tcas_size,
 190                                void *CRLs, int crls_size, int ret_trust,
 191                                int ret_else)
 192 {
 193 /* CRL is ignored for now */
 194
 195         gnutls_cert *issuer;
 196         int ret;
 197
 198         if (tcas_size >= 1)
 199                 issuer = find_issuer(cert, trusted_cas, tcas_size);
 200         else {
 201                 gnutls_assert();
 202                 return ret_else;
 203         }
 204
 205         /* issuer is not in trusted certificate
 206          * authorities.
 207          */
 208         if (issuer == NULL) {
 209                 gnutls_assert();
 210                 return ret_else;
 211         }
 212
 213         ret = check_if_ca(cert, issuer);
 214         if (ret != 0) {
 215                 gnutls_assert();
 216                 return ret_else | GNUTLS_CERT_INVALID;
 217         }
 218
 219         ret = gnutls_x509_verify_signature(cert, issuer);
 220         if (ret != 0) {
 221                 gnutls_assert();
 222                 return ret_else | GNUTLS_CERT_INVALID;
 223         }
 224
 225         /* FIXME: Check CRL --not done yet.
 226          */
 227
 228
 229         return ret_trust;
 230 }
 231
 232 /* The algorithm used is:
 233  * 1. Check the certificate chain given by the peer, if it is ok.
 234  * 2. If any certificate in the chain are revoked, not
 235  *    valid, or they are not CAs then the certificate is invalid.
 236  * 3. If 1 is ok, then find a certificate in the trusted CAs file
 237  *    that has the DN of the issuer field in the last certificate
 238  *    in the peer's certificate chain.
 239  * 4. If it does exist then verify it. If verification is ok then
 240  *    it is trusted. Otherwise it is just valid (but not trusted).
 241  */
 242 /* This function verifies a X.509 certificate list. The certificate list should
 243  * lead to a trusted CA in order to be trusted.
 244  */
 245 int _gnutls_x509_verify_certificate(gnutls_cert * certificate_list,
 246                                     int clist_size,
 247                                     gnutls_cert * trusted_cas,
 248                                     int tcas_size, void *CRLs,
 249                                     int crls_size)
 250 {
 251         int i = 0, ret;
 252         CertificateStatus status = 0;
 253
 254         if (clist_size == 0) {
 255                 return GNUTLS_E_NO_CERTIFICATE_FOUND;
 256         }
 257
 258         /* Verify the certificate path */
 259         for (i = 0; i < clist_size; i++) {
 260                 if (i + 1 >= clist_size)
 261                         break;
 262
 263                 if ((ret =
 264                      gnutls_verify_certificate2(&certificate_list[i],
 265                                                 &certificate_list[i + 1],
 266                                                 1, NULL, 0, 0,
 267                                                 GNUTLS_CERT_INVALID)) !=
 268                     0) {
 269                         /*
 270                            * We only accept the first certificate to be
 271                            * expired, revoked etc. If any of the certificates in the
 272                            * certificate chain is expired then the certificate
 273                            * is not valid.
 274                          */
 275                         if (ret > 0) {
 276                                 gnutls_assert();
 277                                 status |= ret;
 278                         } else {
 279                                 gnutls_assert();
 280                                 return ret;
 281                         }
 282                 }
 283         }
 284
 285         if (status > 0) { /* If there is any problem in the
 286                            * certificate chain then mark as not trusted
 287                            * and return immediately.
 288                            */
 289                 return (status | GNUTLS_CERT_NOT_TRUSTED);
 290         }
 291
 292         /* Now verify the last certificate in the certificate path
 293          * against the trusted CA certificate list.
 294          *
 295          * If no CAs are present returns NOT_TRUSTED. Thus works
 296          * in self signed etc certificates.
 297          */
 298         ret =
 299             gnutls_verify_certificate2(&certificate_list[i], trusted_cas,
 300                                        tcas_size, CRLs, crls_size, 0,
 301                                        GNUTLS_CERT_NOT_TRUSTED);
 302
 303         if (ret > 0) {
 304                 /* if the last certificate in the certificate
 305                  * list is invalid, then the certificate is not
 306                  * trusted.
 307                  */
 308                 gnutls_assert();
 309                 status |= ret;
 310         }
 311
 312         if (ret < 0) {
 313                 gnutls_assert();
 314                 return ret;
 315         }
 316
 317         /* if we got here, then it's trusted.
 318          */
 319         return status;
 320 }