crypto/x509/v3_purp.c - boringssl - Git at Google

 /*
  * Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL project
  * 2001.
  */
 /* ====================================================================
  * Copyright (c) 1999-2004 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
  *
  * 3. All advertising materials mentioning features or use of this
  *    software must display the following acknowledgment:
  *    "This product includes software developed by the OpenSSL Project
  *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
  *
  * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
  *    endorse or promote products derived from this software without
  *    prior written permission. For written permission, please contact
  *    licensing@OpenSSL.org.
  *
  * 5. Products derived from this software may not be called "OpenSSL"
  *    nor may "OpenSSL" appear in their names without prior written
  *    permission of the OpenSSL Project.
  *
  * 6. Redistributions of any form whatsoever must retain the following
  *    acknowledgment:
  *    "This product includes software developed by the OpenSSL Project
  *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
  *
  * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
  * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  * OF THE POSSIBILITY OF SUCH DAMAGE.
  * ====================================================================
  *
  * This product includes cryptographic software written by Eric Young
  * (eay@cryptsoft.com).  This product includes software written by Tim
  * Hudson (tjh@cryptsoft.com). */

 #include <assert.h>
 #include <limits.h>
 #include <string.h>

 #include <openssl/digest.h>
 #include <openssl/err.h>
 #include <openssl/mem.h>
 #include <openssl/obj.h>
 #include <openssl/thread.h>
 #include <openssl/x509.h>

 #include "../internal.h"
 #include "internal.h"

 #define V1_ROOT (EXFLAG_V1 | EXFLAG_SS)
 #define ku_reject(x, usage) \
   (((x)->ex_flags & EXFLAG_KUSAGE) && !((x)->ex_kusage & (usage)))
 #define xku_reject(x, usage) \
   (((x)->ex_flags & EXFLAG_XKUSAGE) && !((x)->ex_xkusage & (usage)))

 static int check_ca(const X509 *x);
 static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
                                     int ca);
 static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                     int ca);
 static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                        int ca);
 static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
                                     int ca);
 static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
                                        int ca);
 static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
                                   int ca);
 static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
                                         int ca);
 static int no_check(const X509_PURPOSE *xp, const X509 *x, int ca);

 static const X509_PURPOSE xstandard[] = {
     {X509_PURPOSE_SSL_CLIENT, X509_TRUST_SSL_CLIENT, 0,
      check_purpose_ssl_client, (char *)"SSL client", (char *)"sslclient", NULL},
     {X509_PURPOSE_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
      check_purpose_ssl_server, (char *)"SSL server", (char *)"sslserver", NULL},
     {X509_PURPOSE_NS_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
      check_purpose_ns_ssl_server, (char *)"Netscape SSL server",
      (char *)"nssslserver", NULL},
     {X509_PURPOSE_SMIME_SIGN, X509_TRUST_EMAIL, 0, check_purpose_smime_sign,
      (char *)"S/MIME signing", (char *)"smimesign", NULL},
     {X509_PURPOSE_SMIME_ENCRYPT, X509_TRUST_EMAIL, 0,
      check_purpose_smime_encrypt, (char *)"S/MIME encryption",
      (char *)"smimeencrypt", NULL},
     {X509_PURPOSE_CRL_SIGN, X509_TRUST_COMPAT, 0, check_purpose_crl_sign,
      (char *)"CRL signing", (char *)"crlsign", NULL},
     {X509_PURPOSE_ANY, X509_TRUST_DEFAULT, 0, no_check, (char *)"Any Purpose",
      (char *)"any", NULL},
     // |X509_PURPOSE_OCSP_HELPER| performs no actual checks. OpenSSL's OCSP
     // implementation relied on the caller performing EKU and KU checks.
     {X509_PURPOSE_OCSP_HELPER, X509_TRUST_COMPAT, 0, no_check,
      (char *)"OCSP helper", (char *)"ocsphelper", NULL},
     {X509_PURPOSE_TIMESTAMP_SIGN, X509_TRUST_TSA, 0,
      check_purpose_timestamp_sign, (char *)"Time Stamp signing",
      (char *)"timestampsign", NULL},
 };

 int X509_check_purpose(X509 *x, int id, int ca) {
   // This differs from OpenSSL, which uses -1 to indicate a fatal error and 0 to
   // indicate an invalid certificate. BoringSSL uses 0 for both.
   if (!x509v3_cache_extensions(x)) {
     return 0;
   }

   if (id == -1) {
     return 1;
   }
   int idx = X509_PURPOSE_get_by_id(id);
   if (idx == -1) {
     return 0;
   }
   // Historically, |check_purpose| implementations other than |X509_PURPOSE_ANY|
   // called |check_ca|. This is redundant with the |X509_V_ERR_INVALID_CA|
   // logic, but |X509_check_purpose| is public API, so we preserve this
   // behavior.
   if (ca && id != X509_PURPOSE_ANY && !check_ca(x)) {
     return 0;
   }
   const X509_PURPOSE *pt = X509_PURPOSE_get0(idx);
   return pt->check_purpose(pt, x, ca);
 }

 int X509_PURPOSE_set(int *p, int purpose) {
   if (X509_PURPOSE_get_by_id(purpose) == -1) {
     OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_PURPOSE);
     return 0;
   }
   *p = purpose;
   return 1;
 }

 int X509_PURPOSE_get_count(void) { return OPENSSL_ARRAY_SIZE(xstandard); }

 const X509_PURPOSE *X509_PURPOSE_get0(int idx) {
   if (idx < 0 || (size_t)idx >= OPENSSL_ARRAY_SIZE(xstandard)) {
     return NULL;
   }
   return xstandard + idx;
 }

 int X509_PURPOSE_get_by_sname(const char *sname) {
   const X509_PURPOSE *xptmp;
   for (int i = 0; i < X509_PURPOSE_get_count(); i++) {
     xptmp = X509_PURPOSE_get0(i);
     if (!strcmp(xptmp->sname, sname)) {
       return i;
     }
   }
   return -1;
 }

 int X509_PURPOSE_get_by_id(int purpose) {
   for (size_t i = 0; i <OPENSSL_ARRAY_SIZE(xstandard); i++) {
     if (xstandard[i].purpose == purpose) {
       static_assert(OPENSSL_ARRAY_SIZE(xstandard) <= INT_MAX,
                     "indices must fit in int");
       return (int)i;
     }
   }
   return -1;
 }

 int X509_PURPOSE_get_id(const X509_PURPOSE *xp) { return xp->purpose; }

 char *X509_PURPOSE_get0_name(const X509_PURPOSE *xp) { return xp->name; }

 char *X509_PURPOSE_get0_sname(const X509_PURPOSE *xp) { return xp->sname; }

 int X509_PURPOSE_get_trust(const X509_PURPOSE *xp) { return xp->trust; }

 int X509_supported_extension(const X509_EXTENSION *ex) {
   int nid = OBJ_obj2nid(X509_EXTENSION_get_object(ex));
   return nid == NID_key_usage ||             //
          nid == NID_subject_alt_name ||      //
          nid == NID_basic_constraints ||     //
          nid == NID_certificate_policies ||  //
          nid == NID_ext_key_usage ||         //
          nid == NID_policy_constraints ||    //
          nid == NID_name_constraints ||      //
          nid == NID_policy_mappings ||       //
          nid == NID_inhibit_any_policy;
 }

 static int setup_dp(X509 *x, DIST_POINT *dp) {
   if (!dp->distpoint || (dp->distpoint->type != 1)) {
     return 1;
   }
   X509_NAME *iname = NULL;
   for (size_t i = 0; i < sk_GENERAL_NAME_num(dp->CRLissuer); i++) {
     GENERAL_NAME *gen = sk_GENERAL_NAME_value(dp->CRLissuer, i);
     if (gen->type == GEN_DIRNAME) {
       iname = gen->d.directoryName;
       break;
     }
   }
   if (!iname) {
     iname = X509_get_issuer_name(x);
   }

   return DIST_POINT_set_dpname(dp->distpoint, iname);
 }

 static int setup_crldp(X509 *x) {
   int j;
   x->crldp = X509_get_ext_d2i(x, NID_crl_distribution_points, &j, NULL);
   if (x->crldp == NULL && j != -1) {
     return 0;
   }
   for (size_t i = 0; i < sk_DIST_POINT_num(x->crldp); i++) {
     if (!setup_dp(x, sk_DIST_POINT_value(x->crldp, i))) {
       return 0;
     }
   }
   return 1;
 }

 int x509v3_cache_extensions(X509 *x) {
   BASIC_CONSTRAINTS *bs;
   ASN1_BIT_STRING *usage;
   EXTENDED_KEY_USAGE *extusage;
   size_t i;
   int j;

   CRYPTO_MUTEX_lock_read(&x->lock);
   const int is_set = x->ex_flags & EXFLAG_SET;
   CRYPTO_MUTEX_unlock_read(&x->lock);

   if (is_set) {
     return (x->ex_flags & EXFLAG_INVALID) == 0;
   }

   CRYPTO_MUTEX_lock_write(&x->lock);
   if (x->ex_flags & EXFLAG_SET) {
     CRYPTO_MUTEX_unlock_write(&x->lock);
     return (x->ex_flags & EXFLAG_INVALID) == 0;
   }

   if (!X509_digest(x, EVP_sha256(), x->cert_hash, NULL)) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   // V1 should mean no extensions ...
   if (X509_get_version(x) == X509_VERSION_1) {
     x->ex_flags |= EXFLAG_V1;
   }
   // Handle basic constraints
   if ((bs = X509_get_ext_d2i(x, NID_basic_constraints, &j, NULL))) {
     if (bs->ca) {
       x->ex_flags |= EXFLAG_CA;
     }
     if (bs->pathlen) {
       if ((bs->pathlen->type == V_ASN1_NEG_INTEGER) || !bs->ca) {
         x->ex_flags |= EXFLAG_INVALID;
         x->ex_pathlen = 0;
       } else {
         // TODO(davidben): |ASN1_INTEGER_get| returns -1 on overflow,
         // which currently acts as if the constraint isn't present. This
         // works (an overflowing path length constraint may as well be
         // infinity), but Chromium's verifier simply treats values above
         // 255 as an error.
         x->ex_pathlen = ASN1_INTEGER_get(bs->pathlen);
       }
     } else {
       x->ex_pathlen = -1;
     }
     BASIC_CONSTRAINTS_free(bs);
     x->ex_flags |= EXFLAG_BCONS;
   } else if (j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   // Handle key usage
   if ((usage = X509_get_ext_d2i(x, NID_key_usage, &j, NULL))) {
     if (usage->length > 0) {
       x->ex_kusage = usage->data[0];
       if (usage->length > 1) {
         x->ex_kusage |= usage->data[1] << 8;
       }
     } else {
       x->ex_kusage = 0;
     }
     x->ex_flags |= EXFLAG_KUSAGE;
     ASN1_BIT_STRING_free(usage);
   } else if (j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   x->ex_xkusage = 0;
   if ((extusage = X509_get_ext_d2i(x, NID_ext_key_usage, &j, NULL))) {
     x->ex_flags |= EXFLAG_XKUSAGE;
     for (i = 0; i < sk_ASN1_OBJECT_num(extusage); i++) {
       switch (OBJ_obj2nid(sk_ASN1_OBJECT_value(extusage, i))) {
         case NID_server_auth:
           x->ex_xkusage |= XKU_SSL_SERVER;
           break;

         case NID_client_auth:
           x->ex_xkusage |= XKU_SSL_CLIENT;
           break;

         case NID_email_protect:
           x->ex_xkusage |= XKU_SMIME;
           break;

         case NID_code_sign:
           x->ex_xkusage |= XKU_CODE_SIGN;
           break;

         case NID_ms_sgc:
         case NID_ns_sgc:
           x->ex_xkusage |= XKU_SGC;
           break;

         case NID_OCSP_sign:
           x->ex_xkusage |= XKU_OCSP_SIGN;
           break;

         case NID_time_stamp:
           x->ex_xkusage |= XKU_TIMESTAMP;
           break;

         case NID_dvcs:
           x->ex_xkusage |= XKU_DVCS;
           break;

         case NID_anyExtendedKeyUsage:
           x->ex_xkusage |= XKU_ANYEKU;
           break;
       }
     }
     sk_ASN1_OBJECT_pop_free(extusage, ASN1_OBJECT_free);
   } else if (j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }

   x->skid = X509_get_ext_d2i(x, NID_subject_key_identifier, &j, NULL);
   if (x->skid == NULL && j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   x->akid = X509_get_ext_d2i(x, NID_authority_key_identifier, &j, NULL);
   if (x->akid == NULL && j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   // Does subject name match issuer ?
   if (!X509_NAME_cmp(X509_get_subject_name(x), X509_get_issuer_name(x))) {
     x->ex_flags |= EXFLAG_SI;
     // If SKID matches AKID also indicate self signed
     if (X509_check_akid(x, x->akid) == X509_V_OK &&
         !ku_reject(x, X509v3_KU_KEY_CERT_SIGN)) {
       x->ex_flags |= EXFLAG_SS;
     }
   }
   x->altname = X509_get_ext_d2i(x, NID_subject_alt_name, &j, NULL);
   if (x->altname == NULL && j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   x->nc = X509_get_ext_d2i(x, NID_name_constraints, &j, NULL);
   if (x->nc == NULL && j != -1) {
     x->ex_flags |= EXFLAG_INVALID;
   }
   if (!setup_crldp(x)) {
     x->ex_flags |= EXFLAG_INVALID;
   }

   for (j = 0; j < X509_get_ext_count(x); j++) {
     const X509_EXTENSION *ex = X509_get_ext(x, j);
     if (!X509_EXTENSION_get_critical(ex)) {
       continue;
     }
     if (!X509_supported_extension(ex)) {
       x->ex_flags |= EXFLAG_CRITICAL;
       break;
     }
   }
   x->ex_flags |= EXFLAG_SET;

   CRYPTO_MUTEX_unlock_write(&x->lock);
   return (x->ex_flags & EXFLAG_INVALID) == 0;
 }

 // check_ca returns one if |x| should be considered a CA certificate and zero
 // otherwise.
 static int check_ca(const X509 *x) {
   // keyUsage if present should allow cert signing
   if (ku_reject(x, X509v3_KU_KEY_CERT_SIGN)) {
     return 0;
   }
   // Version 1 certificates are considered CAs and don't have extensions.
   if ((x->ex_flags & V1_ROOT) == V1_ROOT) {
     return 1;
   }
   // Otherwise, it's only a CA if basicConstraints says so.
   return ((x->ex_flags & EXFLAG_BCONS) && (x->ex_flags & EXFLAG_CA));
 }

 int X509_check_ca(X509 *x) {
   if (!x509v3_cache_extensions(x)) {
     return 0;
   }
   return check_ca(x);
 }

 // check_purpose returns one if |x| is a valid part of a certificate path for
 // extended key usage |required_xku| and at least one of key usages in
 // |required_kus|. |ca| indicates whether |x| is a CA or end-entity certificate.
 static int check_purpose(const X509 *x, int ca, int required_xku,
                          int required_kus) {
   // Check extended key usage on the entire chain.
   if (required_xku != 0 && xku_reject(x, required_xku)) {
     return 0;
   }

   // Check key usages only on the end-entity certificate.
   return ca || !ku_reject(x, required_kus);
 }

 static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
                                     int ca) {
   // We need to do digital signatures or key agreement.
   //
   // TODO(davidben): We do not implement any TLS client certificate modes based
   // on key agreement.
   return check_purpose(x, ca, XKU_SSL_CLIENT,
                        X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_KEY_AGREEMENT);
 }

 // Key usage needed for TLS/SSL server: digital signature, encipherment or
 // key agreement. The ssl code can check this more thoroughly for individual
 // key types.
 #define X509v3_KU_TLS                                         \
   (X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_KEY_ENCIPHERMENT | \
    X509v3_KU_KEY_AGREEMENT)

 static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                     int ca) {
   return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_TLS);
 }

 static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                        int ca) {
   // We need to encipher or Netscape complains.
   return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_KEY_ENCIPHERMENT);
 }

 static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
                                     int ca) {
   return check_purpose(x, ca, XKU_SMIME,
                        X509v3_KU_DIGITAL_SIGNATURE | X509v3_KU_NON_REPUDIATION);
 }

 static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
                                        int ca) {
   return check_purpose(x, ca, XKU_SMIME, X509v3_KU_KEY_ENCIPHERMENT);
 }

 static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
                                   int ca) {
   return check_purpose(x, ca, /*required_xku=*/0, X509v3_KU_CRL_SIGN);
 }

 static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
                                         int ca) {
   if (ca) {
     return 1;
   }

   // Check the optional key usage field:
   // if Key Usage is present, it must be one of digitalSignature
   // and/or nonRepudiation (other values are not consistent and shall
   // be rejected).
   if ((x->ex_flags & EXFLAG_KUSAGE) &&
       ((x->ex_kusage &
         ~(X509v3_KU_NON_REPUDIATION | X509v3_KU_DIGITAL_SIGNATURE)) ||
        !(x->ex_kusage &
          (X509v3_KU_NON_REPUDIATION | X509v3_KU_DIGITAL_SIGNATURE)))) {
     return 0;
   }

   // Only time stamp key usage is permitted and it's required.
   //
   // TODO(davidben): Should we check EKUs up the chain like the other cases?
   if (!(x->ex_flags & EXFLAG_XKUSAGE) || x->ex_xkusage != XKU_TIMESTAMP) {
     return 0;
   }

   // Extended Key Usage MUST be critical
   int i_ext = X509_get_ext_by_NID(x, NID_ext_key_usage, -1);
   if (i_ext >= 0) {
     const X509_EXTENSION *ext = X509_get_ext(x, i_ext);
     if (!X509_EXTENSION_get_critical(ext)) {
       return 0;
     }
   }

   return 1;
 }

 static int no_check(const X509_PURPOSE *xp, const X509 *x, int ca) { return 1; }

 int X509_check_issued(X509 *issuer, X509 *subject) {
   if (X509_NAME_cmp(X509_get_subject_name(issuer),
                     X509_get_issuer_name(subject))) {
     return X509_V_ERR_SUBJECT_ISSUER_MISMATCH;
   }
   if (!x509v3_cache_extensions(issuer) || !x509v3_cache_extensions(subject)) {
     return X509_V_ERR_UNSPECIFIED;
   }

   if (subject->akid) {
     int ret = X509_check_akid(issuer, subject->akid);
     if (ret != X509_V_OK) {
       return ret;
     }
   }

   if (ku_reject(issuer, X509v3_KU_KEY_CERT_SIGN)) {
     return X509_V_ERR_KEYUSAGE_NO_CERTSIGN;
   }
   return X509_V_OK;
 }

 int X509_check_akid(X509 *issuer, const AUTHORITY_KEYID *akid) {
   if (!akid) {
     return X509_V_OK;
   }

   // Check key ids (if present)
   if (akid->keyid && issuer->skid &&
       ASN1_OCTET_STRING_cmp(akid->keyid, issuer->skid)) {
     return X509_V_ERR_AKID_SKID_MISMATCH;
   }
   // Check serial number
   if (akid->serial &&
       ASN1_INTEGER_cmp(X509_get_serialNumber(issuer), akid->serial)) {
     return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
   }
   // Check issuer name
   if (akid->issuer) {
     // Ugh, for some peculiar reason AKID includes SEQUENCE OF
     // GeneralName. So look for a DirName. There may be more than one but
     // we only take any notice of the first.
     GENERAL_NAMES *gens;
     GENERAL_NAME *gen;
     X509_NAME *nm = NULL;
     size_t i;
     gens = akid->issuer;
     for (i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
       gen = sk_GENERAL_NAME_value(gens, i);
       if (gen->type == GEN_DIRNAME) {
         nm = gen->d.dirn;
         break;
       }
     }
     if (nm && X509_NAME_cmp(nm, X509_get_issuer_name(issuer))) {
       return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
     }
   }
   return X509_V_OK;
 }

 uint32_t X509_get_extension_flags(X509 *x) {
   // Ignore the return value. On failure, |x->ex_flags| will include
   // |EXFLAG_INVALID|.
   x509v3_cache_extensions(x);
   return x->ex_flags;
 }

 uint32_t X509_get_key_usage(X509 *x) {
   if (!x509v3_cache_extensions(x)) {
     return 0;
   }
   if (x->ex_flags & EXFLAG_KUSAGE) {
     return x->ex_kusage;
   }
   // If there is no extension, key usage is unconstrained, so set all bits to
   // one. Note that, although we use |UINT32_MAX|, |ex_kusage| only contains the
   // first 16 bits when the extension is present.
   return UINT32_MAX;
 }

 uint32_t X509_get_extended_key_usage(X509 *x) {
   if (!x509v3_cache_extensions(x)) {
     return 0;
   }
   if (x->ex_flags & EXFLAG_XKUSAGE) {
     return x->ex_xkusage;
   }
   // If there is no extension, extended key usage is unconstrained, so set all
   // bits to one.
   return UINT32_MAX;
 }

 const ASN1_OCTET_STRING *X509_get0_subject_key_id(X509 *x509) {
   if (!x509v3_cache_extensions(x509)) {
     return NULL;
   }
   return x509->skid;
 }

 const ASN1_OCTET_STRING *X509_get0_authority_key_id(X509 *x509) {
   if (!x509v3_cache_extensions(x509)) {
     return NULL;
   }
   return x509->akid != NULL ? x509->akid->keyid : NULL;
 }

 const GENERAL_NAMES *X509_get0_authority_issuer(X509 *x509) {
   if (!x509v3_cache_extensions(x509)) {
     return NULL;
   }
   return x509->akid != NULL ? x509->akid->issuer : NULL;
 }

 const ASN1_INTEGER *X509_get0_authority_serial(X509 *x509) {
   if (!x509v3_cache_extensions(x509)) {
     return NULL;
   }
   return x509->akid != NULL ? x509->akid->serial : NULL;
 }

 long X509_get_pathlen(X509 *x509) {
   if (!x509v3_cache_extensions(x509) || (x509->ex_flags & EXFLAG_BCONS) == 0) {
     return -1;
   }
   return x509->ex_pathlen;
 }
	/*
	* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL project
	* 2001.
	*/
	/* ====================================================================
	* Copyright (c) 1999-2004 The OpenSSL Project. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	*
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in
	* the documentation and/or other materials provided with the
	* distribution.
	*
	* 3. All advertising materials mentioning features or use of this
	* software must display the following acknowledgment:
	* "This product includes software developed by the OpenSSL Project
	* for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
	*
	* 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
	* endorse or promote products derived from this software without
	* prior written permission. For written permission, please contact
	* licensing@OpenSSL.org.
	*
	* 5. Products derived from this software may not be called "OpenSSL"
	* nor may "OpenSSL" appear in their names without prior written
	* permission of the OpenSSL Project.
	*
	* 6. Redistributions of any form whatsoever must retain the following
	* acknowledgment:
	* "This product includes software developed by the OpenSSL Project
	* for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
	*
	* THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
	* EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
	* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
	* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
	* OF THE POSSIBILITY OF SUCH DAMAGE.
	* ====================================================================
	*
	* This product includes cryptographic software written by Eric Young
	* (eay@cryptsoft.com). This product includes software written by Tim
	* Hudson (tjh@cryptsoft.com). */

	#include <assert.h>
	#include <limits.h>
	#include <string.h>

	#include <openssl/digest.h>
	#include <openssl/err.h>
	#include <openssl/mem.h>
	#include <openssl/obj.h>
	#include <openssl/thread.h>
	#include <openssl/x509.h>

	#include "../internal.h"
	#include "internal.h"

	#define V1_ROOT (EXFLAG_V1 \| EXFLAG_SS)
	#define ku_reject(x, usage) \
	(((x)->ex_flags & EXFLAG_KUSAGE) && !((x)->ex_kusage & (usage)))
	#define xku_reject(x, usage) \
	(((x)->ex_flags & EXFLAG_XKUSAGE) && !((x)->ex_xkusage & (usage)))

	static int check_ca(const X509 *x);
	static int check_purpose_ssl_client(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_ssl_server(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_ns_ssl_server(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_smime_sign(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_smime_encrypt(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_crl_sign(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int check_purpose_timestamp_sign(const X509_PURPOSE xp, const X509 x,
	int ca);
	static int no_check(const X509_PURPOSE xp, const X509 x, int ca);

	static const X509_PURPOSE xstandard[] = {
	{X509_PURPOSE_SSL_CLIENT, X509_TRUST_SSL_CLIENT, 0,
	check_purpose_ssl_client, (char )"SSL client", (char )"sslclient", NULL},
	{X509_PURPOSE_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
	check_purpose_ssl_server, (char )"SSL server", (char )"sslserver", NULL},
	{X509_PURPOSE_NS_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
	check_purpose_ns_ssl_server, (char *)"Netscape SSL server",
	(char *)"nssslserver", NULL},
	{X509_PURPOSE_SMIME_SIGN, X509_TRUST_EMAIL, 0, check_purpose_smime_sign,
	(char )"S/MIME signing", (char )"smimesign", NULL},
	{X509_PURPOSE_SMIME_ENCRYPT, X509_TRUST_EMAIL, 0,
	check_purpose_smime_encrypt, (char *)"S/MIME encryption",
	(char *)"smimeencrypt", NULL},
	{X509_PURPOSE_CRL_SIGN, X509_TRUST_COMPAT, 0, check_purpose_crl_sign,
	(char )"CRL signing", (char )"crlsign", NULL},
	{X509_PURPOSE_ANY, X509_TRUST_DEFAULT, 0, no_check, (char *)"Any Purpose",
	(char *)"any", NULL},
	// \|X509_PURPOSE_OCSP_HELPER\| performs no actual checks. OpenSSL's OCSP
	// implementation relied on the caller performing EKU and KU checks.
	{X509_PURPOSE_OCSP_HELPER, X509_TRUST_COMPAT, 0, no_check,
	(char )"OCSP helper", (char )"ocsphelper", NULL},
	{X509_PURPOSE_TIMESTAMP_SIGN, X509_TRUST_TSA, 0,
	check_purpose_timestamp_sign, (char *)"Time Stamp signing",
	(char *)"timestampsign", NULL},
	};

	int X509_check_purpose(X509 *x, int id, int ca) {
	// This differs from OpenSSL, which uses -1 to indicate a fatal error and 0 to
	// indicate an invalid certificate. BoringSSL uses 0 for both.
	if (!x509v3_cache_extensions(x)) {
	return 0;
	}

	if (id == -1) {
	return 1;
	}
	int idx = X509_PURPOSE_get_by_id(id);
	if (idx == -1) {
	return 0;
	}
	// Historically, \|check_purpose\| implementations other than \|X509_PURPOSE_ANY\|
	// called \|check_ca\|. This is redundant with the \|X509_V_ERR_INVALID_CA\|
	// logic, but \|X509_check_purpose\| is public API, so we preserve this
	// behavior.
	if (ca && id != X509_PURPOSE_ANY && !check_ca(x)) {
	return 0;
	}
	const X509_PURPOSE *pt = X509_PURPOSE_get0(idx);
	return pt->check_purpose(pt, x, ca);
	}

	int X509_PURPOSE_set(int *p, int purpose) {
	if (X509_PURPOSE_get_by_id(purpose) == -1) {
	OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_PURPOSE);
	return 0;
	}
	*p = purpose;
	return 1;
	}

	int X509_PURPOSE_get_count(void) { return OPENSSL_ARRAY_SIZE(xstandard); }

	const X509_PURPOSE *X509_PURPOSE_get0(int idx) {
	if (idx < 0 \|\| (size_t)idx >= OPENSSL_ARRAY_SIZE(xstandard)) {
	return NULL;
	}
	return xstandard + idx;
	}

	int X509_PURPOSE_get_by_sname(const char *sname) {
	const X509_PURPOSE *xptmp;
	for (int i = 0; i < X509_PURPOSE_get_count(); i++) {
	xptmp = X509_PURPOSE_get0(i);
	if (!strcmp(xptmp->sname, sname)) {
	return i;
	}
	}
	return -1;
	}

	int X509_PURPOSE_get_by_id(int purpose) {
	for (size_t i = 0; i <OPENSSL_ARRAY_SIZE(xstandard); i++) {
	if (xstandard[i].purpose == purpose) {
	static_assert(OPENSSL_ARRAY_SIZE(xstandard) <= INT_MAX,
	"indices must fit in int");
	return (int)i;
	}
	}
	return -1;
	}

	int X509_PURPOSE_get_id(const X509_PURPOSE *xp) { return xp->purpose; }

	char X509_PURPOSE_get0_name(const X509_PURPOSE xp) { return xp->name; }

	char X509_PURPOSE_get0_sname(const X509_PURPOSE xp) { return xp->sname; }

	int X509_PURPOSE_get_trust(const X509_PURPOSE *xp) { return xp->trust; }

	int X509_supported_extension(const X509_EXTENSION *ex) {
	int nid = OBJ_obj2nid(X509_EXTENSION_get_object(ex));
	return nid == NID_key_usage \|\| //
	nid == NID_subject_alt_name \|\| //
	nid == NID_basic_constraints \|\| //
	nid == NID_certificate_policies \|\| //
	nid == NID_ext_key_usage \|\| //
	nid == NID_policy_constraints \|\| //
	nid == NID_name_constraints \|\| //
	nid == NID_policy_mappings \|\| //
	nid == NID_inhibit_any_policy;
	}

	static int setup_dp(X509 x, DIST_POINT dp) {
	if (!dp->distpoint \|\| (dp->distpoint->type != 1)) {
	return 1;
	}
	X509_NAME *iname = NULL;
	for (size_t i = 0; i < sk_GENERAL_NAME_num(dp->CRLissuer); i++) {
	GENERAL_NAME *gen = sk_GENERAL_NAME_value(dp->CRLissuer, i);
	if (gen->type == GEN_DIRNAME) {
	iname = gen->d.directoryName;
	break;
	}
	}
	if (!iname) {
	iname = X509_get_issuer_name(x);
	}

	return DIST_POINT_set_dpname(dp->distpoint, iname);
	}

	static int setup_crldp(X509 *x) {
	int j;
	x->crldp = X509_get_ext_d2i(x, NID_crl_distribution_points, &j, NULL);
	if (x->crldp == NULL && j != -1) {
	return 0;
	}
	for (size_t i = 0; i < sk_DIST_POINT_num(x->crldp); i++) {
	if (!setup_dp(x, sk_DIST_POINT_value(x->crldp, i))) {
	return 0;
	}
	}
	return 1;
	}

	int x509v3_cache_extensions(X509 *x) {
	BASIC_CONSTRAINTS *bs;
	ASN1_BIT_STRING *usage;
	EXTENDED_KEY_USAGE *extusage;
	size_t i;
	int j;

	CRYPTO_MUTEX_lock_read(&x->lock);
	const int is_set = x->ex_flags & EXFLAG_SET;
	CRYPTO_MUTEX_unlock_read(&x->lock);

	if (is_set) {
	return (x->ex_flags & EXFLAG_INVALID) == 0;
	}

	CRYPTO_MUTEX_lock_write(&x->lock);
	if (x->ex_flags & EXFLAG_SET) {
	CRYPTO_MUTEX_unlock_write(&x->lock);
	return (x->ex_flags & EXFLAG_INVALID) == 0;
	}

	if (!X509_digest(x, EVP_sha256(), x->cert_hash, NULL)) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	// V1 should mean no extensions ...
	if (X509_get_version(x) == X509_VERSION_1) {
	x->ex_flags \|= EXFLAG_V1;
	}
	// Handle basic constraints
	if ((bs = X509_get_ext_d2i(x, NID_basic_constraints, &j, NULL))) {
	if (bs->ca) {
	x->ex_flags \|= EXFLAG_CA;
	}
	if (bs->pathlen) {
	if ((bs->pathlen->type == V_ASN1_NEG_INTEGER) \|\| !bs->ca) {
	x->ex_flags \|= EXFLAG_INVALID;
	x->ex_pathlen = 0;
	} else {
	// TODO(davidben): \|ASN1_INTEGER_get\| returns -1 on overflow,
	// which currently acts as if the constraint isn't present. This
	// works (an overflowing path length constraint may as well be
	// infinity), but Chromium's verifier simply treats values above
	// 255 as an error.
	x->ex_pathlen = ASN1_INTEGER_get(bs->pathlen);
	}
	} else {
	x->ex_pathlen = -1;
	}
	BASIC_CONSTRAINTS_free(bs);
	x->ex_flags \|= EXFLAG_BCONS;
	} else if (j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	// Handle key usage
	if ((usage = X509_get_ext_d2i(x, NID_key_usage, &j, NULL))) {
	if (usage->length > 0) {
	x->ex_kusage = usage->data[0];
	if (usage->length > 1) {
	x->ex_kusage \|= usage->data[1] << 8;
	}
	} else {
	x->ex_kusage = 0;
	}
	x->ex_flags \|= EXFLAG_KUSAGE;
	ASN1_BIT_STRING_free(usage);
	} else if (j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	x->ex_xkusage = 0;
	if ((extusage = X509_get_ext_d2i(x, NID_ext_key_usage, &j, NULL))) {
	x->ex_flags \|= EXFLAG_XKUSAGE;
	for (i = 0; i < sk_ASN1_OBJECT_num(extusage); i++) {
	switch (OBJ_obj2nid(sk_ASN1_OBJECT_value(extusage, i))) {
	case NID_server_auth:
	x->ex_xkusage \|= XKU_SSL_SERVER;
	break;

	case NID_client_auth:
	x->ex_xkusage \|= XKU_SSL_CLIENT;
	break;

	case NID_email_protect:
	x->ex_xkusage \|= XKU_SMIME;
	break;

	case NID_code_sign:
	x->ex_xkusage \|= XKU_CODE_SIGN;
	break;

	case NID_ms_sgc:
	case NID_ns_sgc:
	x->ex_xkusage \|= XKU_SGC;
	break;

	case NID_OCSP_sign:
	x->ex_xkusage \|= XKU_OCSP_SIGN;
	break;

	case NID_time_stamp:
	x->ex_xkusage \|= XKU_TIMESTAMP;
	break;

	case NID_dvcs:
	x->ex_xkusage \|= XKU_DVCS;
	break;

	case NID_anyExtendedKeyUsage:
	x->ex_xkusage \|= XKU_ANYEKU;
	break;
	}
	}
	sk_ASN1_OBJECT_pop_free(extusage, ASN1_OBJECT_free);
	} else if (j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}

	x->skid = X509_get_ext_d2i(x, NID_subject_key_identifier, &j, NULL);
	if (x->skid == NULL && j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	x->akid = X509_get_ext_d2i(x, NID_authority_key_identifier, &j, NULL);
	if (x->akid == NULL && j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	// Does subject name match issuer ?
	if (!X509_NAME_cmp(X509_get_subject_name(x), X509_get_issuer_name(x))) {
	x->ex_flags \|= EXFLAG_SI;
	// If SKID matches AKID also indicate self signed
	if (X509_check_akid(x, x->akid) == X509_V_OK &&
	!ku_reject(x, X509v3_KU_KEY_CERT_SIGN)) {
	x->ex_flags \|= EXFLAG_SS;
	}
	}
	x->altname = X509_get_ext_d2i(x, NID_subject_alt_name, &j, NULL);
	if (x->altname == NULL && j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	x->nc = X509_get_ext_d2i(x, NID_name_constraints, &j, NULL);
	if (x->nc == NULL && j != -1) {
	x->ex_flags \|= EXFLAG_INVALID;
	}
	if (!setup_crldp(x)) {
	x->ex_flags \|= EXFLAG_INVALID;
	}

	for (j = 0; j < X509_get_ext_count(x); j++) {
	const X509_EXTENSION *ex = X509_get_ext(x, j);
	if (!X509_EXTENSION_get_critical(ex)) {
	continue;
	}
	if (!X509_supported_extension(ex)) {
	x->ex_flags \|= EXFLAG_CRITICAL;
	break;
	}
	}
	x->ex_flags \|= EXFLAG_SET;

	CRYPTO_MUTEX_unlock_write(&x->lock);
	return (x->ex_flags & EXFLAG_INVALID) == 0;
	}

	// check_ca returns one if \|x\| should be considered a CA certificate and zero
	// otherwise.
	static int check_ca(const X509 *x) {
	// keyUsage if present should allow cert signing
	if (ku_reject(x, X509v3_KU_KEY_CERT_SIGN)) {
	return 0;
	}
	// Version 1 certificates are considered CAs and don't have extensions.
	if ((x->ex_flags & V1_ROOT) == V1_ROOT) {
	return 1;
	}
	// Otherwise, it's only a CA if basicConstraints says so.
	return ((x->ex_flags & EXFLAG_BCONS) && (x->ex_flags & EXFLAG_CA));
	}

	int X509_check_ca(X509 *x) {
	if (!x509v3_cache_extensions(x)) {
	return 0;
	}
	return check_ca(x);
	}

	// check_purpose returns one if \|x\| is a valid part of a certificate path for
	// extended key usage \|required_xku\| and at least one of key usages in
	// \|required_kus\|. \|ca\| indicates whether \|x\| is a CA or end-entity certificate.
	static int check_purpose(const X509 *x, int ca, int required_xku,
	int required_kus) {
	// Check extended key usage on the entire chain.
	if (required_xku != 0 && xku_reject(x, required_xku)) {
	return 0;
	}

	// Check key usages only on the end-entity certificate.
	return ca \|\| !ku_reject(x, required_kus);
	}

	static int check_purpose_ssl_client(const X509_PURPOSE xp, const X509 x,
	int ca) {
	// We need to do digital signatures or key agreement.
	//
	// TODO(davidben): We do not implement any TLS client certificate modes based
	// on key agreement.
	return check_purpose(x, ca, XKU_SSL_CLIENT,
	X509v3_KU_DIGITAL_SIGNATURE \| X509v3_KU_KEY_AGREEMENT);
	}

	// Key usage needed for TLS/SSL server: digital signature, encipherment or
	// key agreement. The ssl code can check this more thoroughly for individual
	// key types.
	#define X509v3_KU_TLS \
	(X509v3_KU_DIGITAL_SIGNATURE \| X509v3_KU_KEY_ENCIPHERMENT \| \
	X509v3_KU_KEY_AGREEMENT)

	static int check_purpose_ssl_server(const X509_PURPOSE xp, const X509 x,
	int ca) {
	return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_TLS);
	}

	static int check_purpose_ns_ssl_server(const X509_PURPOSE xp, const X509 x,
	int ca) {
	// We need to encipher or Netscape complains.
	return check_purpose(x, ca, XKU_SSL_SERVER, X509v3_KU_KEY_ENCIPHERMENT);
	}

	static int check_purpose_smime_sign(const X509_PURPOSE xp, const X509 x,
	int ca) {
	return check_purpose(x, ca, XKU_SMIME,
	X509v3_KU_DIGITAL_SIGNATURE \| X509v3_KU_NON_REPUDIATION);
	}

	static int check_purpose_smime_encrypt(const X509_PURPOSE xp, const X509 x,
	int ca) {
	return check_purpose(x, ca, XKU_SMIME, X509v3_KU_KEY_ENCIPHERMENT);
	}

	static int check_purpose_crl_sign(const X509_PURPOSE xp, const X509 x,
	int ca) {
	return check_purpose(x, ca, /required_xku=/0, X509v3_KU_CRL_SIGN);
	}

	static int check_purpose_timestamp_sign(const X509_PURPOSE xp, const X509 x,
	int ca) {
	if (ca) {
	return 1;
	}

	// Check the optional key usage field:
	// if Key Usage is present, it must be one of digitalSignature
	// and/or nonRepudiation (other values are not consistent and shall
	// be rejected).
	if ((x->ex_flags & EXFLAG_KUSAGE) &&
	((x->ex_kusage &
	~(X509v3_KU_NON_REPUDIATION \| X509v3_KU_DIGITAL_SIGNATURE)) \|\|
	!(x->ex_kusage &
	(X509v3_KU_NON_REPUDIATION \| X509v3_KU_DIGITAL_SIGNATURE)))) {
	return 0;
	}

	// Only time stamp key usage is permitted and it's required.
	//
	// TODO(davidben): Should we check EKUs up the chain like the other cases?
	if (!(x->ex_flags & EXFLAG_XKUSAGE) \|\| x->ex_xkusage != XKU_TIMESTAMP) {
	return 0;
	}

	// Extended Key Usage MUST be critical
	int i_ext = X509_get_ext_by_NID(x, NID_ext_key_usage, -1);
	if (i_ext >= 0) {
	const X509_EXTENSION *ext = X509_get_ext(x, i_ext);
	if (!X509_EXTENSION_get_critical(ext)) {
	return 0;
	}
	}

	return 1;
	}

	static int no_check(const X509_PURPOSE xp, const X509 x, int ca) { return 1; }

	int X509_check_issued(X509 issuer, X509 subject) {
	if (X509_NAME_cmp(X509_get_subject_name(issuer),
	X509_get_issuer_name(subject))) {
	return X509_V_ERR_SUBJECT_ISSUER_MISMATCH;
	}
	if (!x509v3_cache_extensions(issuer) \|\| !x509v3_cache_extensions(subject)) {
	return X509_V_ERR_UNSPECIFIED;
	}

	if (subject->akid) {
	int ret = X509_check_akid(issuer, subject->akid);
	if (ret != X509_V_OK) {
	return ret;
	}
	}

	if (ku_reject(issuer, X509v3_KU_KEY_CERT_SIGN)) {
	return X509_V_ERR_KEYUSAGE_NO_CERTSIGN;
	}
	return X509_V_OK;
	}

	int X509_check_akid(X509 issuer, const AUTHORITY_KEYID akid) {
	if (!akid) {
	return X509_V_OK;
	}

	// Check key ids (if present)
	if (akid->keyid && issuer->skid &&
	ASN1_OCTET_STRING_cmp(akid->keyid, issuer->skid)) {
	return X509_V_ERR_AKID_SKID_MISMATCH;
	}
	// Check serial number
	if (akid->serial &&
	ASN1_INTEGER_cmp(X509_get_serialNumber(issuer), akid->serial)) {
	return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
	}
	// Check issuer name
	if (akid->issuer) {
	// Ugh, for some peculiar reason AKID includes SEQUENCE OF
	// GeneralName. So look for a DirName. There may be more than one but
	// we only take any notice of the first.
	GENERAL_NAMES *gens;
	GENERAL_NAME *gen;
	X509_NAME *nm = NULL;
	size_t i;
	gens = akid->issuer;
	for (i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
	gen = sk_GENERAL_NAME_value(gens, i);
	if (gen->type == GEN_DIRNAME) {
	nm = gen->d.dirn;
	break;
	}
	}
	if (nm && X509_NAME_cmp(nm, X509_get_issuer_name(issuer))) {
	return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
	}
	}
	return X509_V_OK;
	}

	uint32_t X509_get_extension_flags(X509 *x) {
	// Ignore the return value. On failure, \|x->ex_flags\| will include
	// \|EXFLAG_INVALID\|.
	x509v3_cache_extensions(x);
	return x->ex_flags;
	}

	uint32_t X509_get_key_usage(X509 *x) {
	if (!x509v3_cache_extensions(x)) {
	return 0;
	}
	if (x->ex_flags & EXFLAG_KUSAGE) {
	return x->ex_kusage;
	}
	// If there is no extension, key usage is unconstrained, so set all bits to
	// one. Note that, although we use \|UINT32_MAX\|, \|ex_kusage\| only contains the
	// first 16 bits when the extension is present.
	return UINT32_MAX;
	}

	uint32_t X509_get_extended_key_usage(X509 *x) {
	if (!x509v3_cache_extensions(x)) {
	return 0;
	}
	if (x->ex_flags & EXFLAG_XKUSAGE) {
	return x->ex_xkusage;
	}
	// If there is no extension, extended key usage is unconstrained, so set all
	// bits to one.
	return UINT32_MAX;
	}

	const ASN1_OCTET_STRING X509_get0_subject_key_id(X509 x509) {
	if (!x509v3_cache_extensions(x509)) {
	return NULL;
	}
	return x509->skid;
	}

	const ASN1_OCTET_STRING X509_get0_authority_key_id(X509 x509) {
	if (!x509v3_cache_extensions(x509)) {
	return NULL;
	}
	return x509->akid != NULL ? x509->akid->keyid : NULL;
	}

	const GENERAL_NAMES X509_get0_authority_issuer(X509 x509) {
	if (!x509v3_cache_extensions(x509)) {
	return NULL;
	}
	return x509->akid != NULL ? x509->akid->issuer : NULL;
	}

	const ASN1_INTEGER X509_get0_authority_serial(X509 x509) {
	if (!x509v3_cache_extensions(x509)) {
	return NULL;
	}
	return x509->akid != NULL ? x509->akid->serial : NULL;
	}

	long X509_get_pathlen(X509 *x509) {
	if (!x509v3_cache_extensions(x509) \|\| (x509->ex_flags & EXFLAG_BCONS) == 0) {
	return -1;
	}
	return x509->ex_pathlen;
	}