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  *  The GNUTLS library is free software; you can redistribute it and/or
   7  *  modify it under the terms of the GNU Lesser General Public
   8  *  License as published by the Free Software Foundation; either
   9  *  version 2.1 of the License, or (at your option) any later version.
  10  *
  11  *  This library 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 GNU
  14  *  Lesser General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU Lesser General Public
  17  *  License along with this library; if not, write to the Free Software
  18  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
  19  *
  20  */
  21
  22 #include "gnutls_int.h"
  23 #include "gnutls_errors.h"
  24 #include "gnutls_cert.h"
  25 #include "x509_asn1.h"
  26 #include "x509_der.h"
  27 #include "gnutls_global.h"
  28 #include "gnutls_num.h"         /* GMAX */
  29 #include <gnutls_sig.h>
  30 #include <gnutls_str.h>
  31
  32
  33 /* Return 0 or INVALID, if the issuer is a CA,
  34  * or not.
  35  */
  36 static int check_if_ca(const gnutls_cert * cert,
  37                        const gnutls_cert * issuer)
  38 {
  39         CertificateStatus ret = GNUTLS_CERT_INVALID;
  40
  41         /* Check if the issuer is the same with the
  42          * certificate. This is added in order for trusted
  43          * certificates to be able to verify themselves.
  44          */
  45         if (cert->raw.size == issuer->raw.size) {
  46                 if (memcmp
  47                     (cert->raw.data, issuer->raw.data,
  48                      cert->raw.size) == 0) {
  49                         return 0;
  50                 }
  51         }
  52
  53         if (issuer->CA == 1) {
  54                 ret = 0;
  55         } else
  56                 gnutls_assert();
  57
  58         return ret;
  59 }
  60
  61
  62
  63 void _gnutls_int2str(int k, char *data);
  64
  65 #define MAX_DN_ELEM 1024
  66
  67 /* This function checks if 'certs' issuer is 'issuer_cert'.
  68  * This does a straight (DER) compare of the issuer/subject fields in
  69  * the given certificates.
  70  *
  71  * FIXME: use a real DN comparison algorithm.
  72  */
  73 static
  74 int compare_dn(gnutls_cert * cert, gnutls_cert * issuer_cert)
  75 {
  76         node_asn *c2, *c3;
  77         int result, len1;
  78         int len2;
  79         char tmpstr[512];
  80         int start1, start2, end1, end2;
  81
  82         /* get the issuer of 'cert'
  83          */
  84         if ((result =
  85              asn1_create_structure(_gnutls_get_pkix(), "PKIX1.Certificate",
  86                                    &c2, "certificate2")) != ASN_OK) {
  87                 gnutls_assert();
  88                 return _gnutls_asn2err(result);
  89         }
  90
  91         result = asn1_get_der(c2, cert->raw.data, cert->raw.size);
  92         if (result != ASN_OK) {
  93                 /* couldn't decode DER */
  94                 gnutls_assert();
  95                 asn1_delete_structure(c2);
  96                 return _gnutls_asn2err(result);
  97         }
  98
  99
 100
 101         /* get the 'subject' info of 'issuer_cert'
 102          */
 103         if ((result =
 104              asn1_create_structure(_gnutls_get_pkix(), "PKIX1.Certificate",
 105                                    &c3, "certificate2")) != ASN_OK) {
 106                 gnutls_assert();
 107                 asn1_delete_structure(c2);
 108                 return _gnutls_asn2err(result);
 109         }
 110
 111         result =
 112             asn1_get_der(c3, issuer_cert->raw.data, issuer_cert->raw.size);
 113         if (result != ASN_OK) {
 114                 /* couldn't decode DER */
 115                 gnutls_assert();
 116                 asn1_delete_structure(c2);
 117                 return _gnutls_asn2err(result);
 118         }
 119
 120
 121         _gnutls_str_cpy(tmpstr, sizeof(tmpstr),
 122                         "certificate2.tbsCertificate.issuer");
 123         result =
 124             asn1_get_start_end_der(c2, cert->raw.data, cert->raw.size,
 125                                    tmpstr, &start1, &end1);
 126         asn1_delete_structure(c2);
 127
 128         if (result != ASN_OK) {
 129                 gnutls_assert();
 130                 asn1_delete_structure(c3);
 131                 return _gnutls_asn2err(result);
 132         }
 133
 134         len1 = end1 - start1 + 1;
 135
 136         _gnutls_str_cpy(tmpstr, sizeof(tmpstr),
 137                         "certificate2.tbsCertificate.subject");
 138         result =
 139             asn1_get_start_end_der(c3, issuer_cert->raw.data,
 140                                    issuer_cert->raw.size, tmpstr, &start2,
 141                                    &end2);
 142         asn1_delete_structure(c3);
 143
 144         if (result != ASN_OK) {
 145                 gnutls_assert();
 146                 return _gnutls_asn2err(result);
 147         }
 148
 149         len2 = end2 - start2 + 1;
 150
 151         /* The error code returned does not really matter
 152          * here.
 153          */
 154         if (len1 != len2) {
 155                 gnutls_assert();
 156                 return GNUTLS_E_UNKNOWN_ERROR;
 157         }
 158         if (memcmp(&issuer_cert->raw.data[start2],
 159                    &cert->raw.data[start1], len1) != 0) {
 160                 gnutls_assert();
 161                 return GNUTLS_E_UNKNOWN_ERROR;
 162         }
 163
 164         /* they match */
 165         return 0;
 166
 167 }
 168
 169 static gnutls_cert *find_issuer(gnutls_cert * cert,
 170                                 gnutls_cert * trusted_cas, int tcas_size)
 171 {
 172         int i;
 173
 174         /* this is serial search.
 175          */
 176
 177         for (i = 0; i < tcas_size; i++) {
 178                 if (compare_dn(cert, &trusted_cas[i]) == 0)
 179                         return &trusted_cas[i];
 180         }
 181
 182         gnutls_assert();
 183         return NULL;
 184 }
 185
 186 /* ret_trust is the value to return when the certificate chain is ok
 187  * ret_else is the value to return otherwise.
 188  */
 189 int gnutls_verify_certificate2(gnutls_cert * cert,
 190                                gnutls_cert * trusted_cas, int tcas_size,
 191                                void *CRLs, int crls_size, int ret_trust,
 192                                int ret_else)
 193 {
 194 /* CRL is ignored for now */
 195
 196         gnutls_cert *issuer;
 197         int ret;
 198
 199         if (tcas_size >= 1)
 200                 issuer = find_issuer(cert, trusted_cas, tcas_size);
 201         else {
 202                 gnutls_assert();
 203                 return ret_else;
 204         }
 205
 206         /* issuer is not in trusted certificate
 207          * authorities.
 208          */
 209         if (issuer == NULL) {
 210                 gnutls_assert();
 211                 return ret_else;
 212         }
 213
 214         ret = check_if_ca(cert, issuer);
 215         if (ret != 0) {
 216                 gnutls_assert();
 217                 return ret_else | GNUTLS_CERT_INVALID;
 218         }
 219
 220         ret = gnutls_x509_verify_signature(cert, issuer);
 221         if (ret != 0) {
 222                 gnutls_assert();
 223                 return ret_else | GNUTLS_CERT_INVALID;
 224         }
 225
 226         /* FIXME: Check CRL --not done yet.
 227          */
 228
 229
 230         return ret_trust;
 231 }
 232
 233 /* The algorithm used is:
 234  * 1. Check the certificate chain given by the peer, if it is ok.
 235  * 2. If any certificate in the chain are revoked, not
 236  *    valid, or they are not CAs then the certificate is invalid.
 237  * 3. If 1 is ok, then find a certificate in the trusted CAs file
 238  *    that has the DN of the issuer field in the last certificate
 239  *    in the peer's certificate chain.
 240  * 4. If it does exist then verify it. If verification is ok then
 241  *    it is trusted. Otherwise it is just valid (but not trusted).
 242  */
 243 /* This function verifies a X.509 certificate list. The certificate list should
 244  * lead to a trusted CA in order to be trusted.
 245  */
 246 int _gnutls_x509_verify_certificate(gnutls_cert * certificate_list,
 247                                     int clist_size,
 248                                     gnutls_cert * trusted_cas,
 249                                     int tcas_size, void *CRLs,
 250                                     int crls_size)
 251 {
 252         int i = 0, ret;
 253         CertificateStatus status = 0;
 254
 255         if (clist_size == 0) {
 256                 return GNUTLS_E_NO_CERTIFICATE_FOUND;
 257         }
 258
 259         /* Verify the certificate path */
 260         for (i = 0; i < clist_size; i++) {
 261                 if (i + 1 >= clist_size)
 262                         break;
 263
 264                 if ((ret =
 265                      gnutls_verify_certificate2(&certificate_list[i],
 266                                                 &certificate_list[i + 1],
 267                                                 1, NULL, 0, 0,
 268                                                 GNUTLS_CERT_INVALID)) !=
 269                     0) {
 270                         /*
 271                            * We only accept the first certificate to be
 272                            * expired, revoked etc. If any of the certificates in the
 273                            * certificate chain is expired then the certificate
 274                            * is not valid.
 275                          */
 276                         if (ret > 0) {
 277                                 gnutls_assert();
 278                                 status |= ret;
 279                         } else {
 280                                 gnutls_assert();
 281                                 return ret;
 282                         }
 283                 }
 284         }
 285
 286         if (status > 0) { /* If there is any problem in the
 287                            * certificate chain then mark as not trusted
 288                            * and return immediately.
 289                            */
 290                 return (status | GNUTLS_CERT_NOT_TRUSTED);
 291         }
 292
 293         /* Now verify the last certificate in the certificate path
 294          * against the trusted CA certificate list.
 295          *
 296          * If no CAs are present returns NOT_TRUSTED. Thus works
 297          * in self signed etc certificates.
 298          */
 299         ret =
 300             gnutls_verify_certificate2(&certificate_list[i], trusted_cas,
 301                                        tcas_size, CRLs, crls_size, 0,
 302                                        GNUTLS_CERT_NOT_TRUSTED);
 303
 304         if (ret > 0) {
 305                 /* if the last certificate in the certificate
 306                  * list is invalid, then the certificate is not
 307                  * trusted.
 308                  */
 309                 gnutls_assert();
 310                 status |= ret;
 311         }
 312
 313         if (ret < 0) {
 314                 gnutls_assert();
 315                 return ret;
 316         }
 317
 318         /* if we got here, then it's trusted.
 319          */
 320         return status;
 321 }