/*
 * 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 <stdio.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/x509v3.h>

#include "../internal.h"
#include "../x509/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)))
#define ns_reject(x, usage) \
  (((x)->ex_flags & EXFLAG_NSCERT) && !((x)->ex_nscert & (usage)))

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 purpose_smime(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 int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca);

static int xp_cmp(const X509_PURPOSE **a, const X509_PURPOSE **b);
static void xptable_free(X509_PURPOSE *p);

static 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, X509_TRUST_COMPAT, 0, ocsp_helper,
     (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},
};

#define X509_PURPOSE_COUNT (sizeof(xstandard) / sizeof(X509_PURPOSE))

static STACK_OF(X509_PURPOSE) *xptable = NULL;

static int xp_cmp(const X509_PURPOSE **a, const X509_PURPOSE **b) {
  return (*a)->purpose - (*b)->purpose;
}

// As much as I'd like to make X509_check_purpose use a "const" X509* I
// really can't because it does recalculate hashes and do other non-const
// things.
int X509_check_purpose(X509 *x, int id, int ca) {
  int idx;
  const X509_PURPOSE *pt;
  if (!x509v3_cache_extensions(x)) {
    return -1;
  }

  if (id == -1) {
    return 1;
  }
  idx = X509_PURPOSE_get_by_id(id);
  if (idx == -1) {
    return -1;
  }
  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) {
  if (!xptable) {
    return X509_PURPOSE_COUNT;
  }
  return sk_X509_PURPOSE_num(xptable) + X509_PURPOSE_COUNT;
}

X509_PURPOSE *X509_PURPOSE_get0(int idx) {
  if (idx < 0) {
    return NULL;
  }
  if (idx < (int)X509_PURPOSE_COUNT) {
    return xstandard + idx;
  }
  return sk_X509_PURPOSE_value(xptable, idx - X509_PURPOSE_COUNT);
}

int X509_PURPOSE_get_by_sname(char *sname) {
  int i;
  X509_PURPOSE *xptmp;
  for (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) {
  X509_PURPOSE tmp;
  size_t idx;

  if ((purpose >= X509_PURPOSE_MIN) && (purpose <= X509_PURPOSE_MAX)) {
    return purpose - X509_PURPOSE_MIN;
  }
  tmp.purpose = purpose;
  if (!xptable) {
    return -1;
  }

  sk_X509_PURPOSE_sort(xptable);
  if (!sk_X509_PURPOSE_find(xptable, &idx, &tmp)) {
    return -1;
  }
  return idx + X509_PURPOSE_COUNT;
}

int X509_PURPOSE_add(int id, int trust, int flags,
                     int (*ck)(const X509_PURPOSE *, const X509 *, int),
                     char *name, char *sname, void *arg) {
  int idx;
  X509_PURPOSE *ptmp;
  char *name_dup, *sname_dup;

  // This is set according to what we change: application can't set it
  flags &= ~X509_PURPOSE_DYNAMIC;
  // This will always be set for application modified trust entries
  flags |= X509_PURPOSE_DYNAMIC_NAME;
  // Get existing entry if any
  idx = X509_PURPOSE_get_by_id(id);
  // Need a new entry
  if (idx == -1) {
    if (!(ptmp = OPENSSL_malloc(sizeof(X509_PURPOSE)))) {
      return 0;
    }
    ptmp->flags = X509_PURPOSE_DYNAMIC;
  } else {
    ptmp = X509_PURPOSE_get0(idx);
  }

  // Duplicate the supplied names.
  name_dup = OPENSSL_strdup(name);
  sname_dup = OPENSSL_strdup(sname);
  if (name_dup == NULL || sname_dup == NULL) {
    if (name_dup != NULL) {
      OPENSSL_free(name_dup);
    }
    if (sname_dup != NULL) {
      OPENSSL_free(sname_dup);
    }
    if (idx == -1) {
      OPENSSL_free(ptmp);
    }
    return 0;
  }

  // OPENSSL_free existing name if dynamic
  if (ptmp->flags & X509_PURPOSE_DYNAMIC_NAME) {
    OPENSSL_free(ptmp->name);
    OPENSSL_free(ptmp->sname);
  }
  // dup supplied name
  ptmp->name = name_dup;
  ptmp->sname = sname_dup;
  // Keep the dynamic flag of existing entry
  ptmp->flags &= X509_PURPOSE_DYNAMIC;
  // Set all other flags
  ptmp->flags |= flags;

  ptmp->purpose = id;
  ptmp->trust = trust;
  ptmp->check_purpose = ck;
  ptmp->usr_data = arg;

  // If its a new entry manage the dynamic table
  if (idx == -1) {
    if (!xptable && !(xptable = sk_X509_PURPOSE_new(xp_cmp))) {
      xptable_free(ptmp);
      return 0;
    }
    if (!sk_X509_PURPOSE_push(xptable, ptmp)) {
      xptable_free(ptmp);
      return 0;
    }
  }
  return 1;
}

static void xptable_free(X509_PURPOSE *p) {
  if (!p) {
    return;
  }
  if (p->flags & X509_PURPOSE_DYNAMIC) {
    if (p->flags & X509_PURPOSE_DYNAMIC_NAME) {
      OPENSSL_free(p->name);
      OPENSSL_free(p->sname);
    }
    OPENSSL_free(p);
  }
}

void X509_PURPOSE_cleanup(void) {
  unsigned int i;
  sk_X509_PURPOSE_pop_free(xptable, xptable_free);
  for (i = 0; i < X509_PURPOSE_COUNT; i++) {
    xptable_free(xstandard + i);
  }
  xptable = NULL;
}

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; }

static int nid_cmp(const void *void_a, const void *void_b) {
  const int *a = void_a, *b = void_b;

  return *a - *b;
}

int X509_supported_extension(const X509_EXTENSION *ex) {
  // This table is a list of the NIDs of supported extensions: that is
  // those which are used by the verify process. If an extension is
  // critical and doesn't appear in this list then the verify process will
  // normally reject the certificate. The list must be kept in numerical
  // order because it will be searched using bsearch.

  static const int supported_nids[] = {
      NID_netscape_cert_type,    // 71
      NID_key_usage,             // 83
      NID_subject_alt_name,      // 85
      NID_basic_constraints,     // 87
      NID_certificate_policies,  // 89
      NID_ext_key_usage,         // 126
      NID_policy_constraints,    // 401
      NID_name_constraints,      // 666
      NID_policy_mappings,       // 747
      NID_inhibit_any_policy     // 748
  };

  int ex_nid = OBJ_obj2nid(X509_EXTENSION_get_object(ex));

  if (ex_nid == NID_undef) {
    return 0;
  }

  if (bsearch(&ex_nid, supported_nids, sizeof(supported_nids) / sizeof(int),
              sizeof(int), nid_cmp) != NULL) {
    return 1;
  }
  return 0;
}

static int setup_dp(X509 *x, DIST_POINT *dp) {
  X509_NAME *iname = NULL;
  size_t i;
  if (dp->reasons) {
    if (dp->reasons->length > 0) {
      dp->dp_reasons = dp->reasons->data[0];
    }
    if (dp->reasons->length > 1) {
      dp->dp_reasons |= (dp->reasons->data[1] << 8);
    }
    dp->dp_reasons &= CRLDP_ALL_REASONS;
  } else {
    dp->dp_reasons = CRLDP_ALL_REASONS;
  }
  if (!dp->distpoint || (dp->distpoint->type != 1)) {
    return 1;
  }
  for (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;
  ASN1_BIT_STRING *ns;
  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;
  }

  if ((ns = X509_get_ext_d2i(x, NID_netscape_cert_type, &j, NULL))) {
    if (ns->length > 0) {
      x->ex_nscert = ns->data[0];
    } else {
      x->ex_nscert = 0;
    }
    x->ex_flags |= EXFLAG_NSCERT;
    ASN1_BIT_STRING_free(ns);
  } 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, 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 (OBJ_obj2nid(X509_EXTENSION_get_object(ex)) == NID_freshest_crl) {
      x->ex_flags |= EXFLAG_FRESHEST;
    }
    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, 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);
}

static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
                                    int ca) {
  if (xku_reject(x, XKU_SSL_CLIENT)) {
    return 0;
  }
  if (ca) {
    return check_ca(x);
  }
  // We need to do digital signatures or key agreement
  if (ku_reject(x, KU_DIGITAL_SIGNATURE | KU_KEY_AGREEMENT)) {
    return 0;
  }
  // nsCertType if present should allow SSL client use
  if (ns_reject(x, NS_SSL_CLIENT)) {
    return 0;
  }
  return 1;
}

// 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 KU_TLS (KU_DIGITAL_SIGNATURE | KU_KEY_ENCIPHERMENT | KU_KEY_AGREEMENT)

static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                    int ca) {
  if (xku_reject(x, XKU_SSL_SERVER)) {
    return 0;
  }
  if (ca) {
    return check_ca(x);
  }

  if (ns_reject(x, NS_SSL_SERVER)) {
    return 0;
  }
  if (ku_reject(x, KU_TLS)) {
    return 0;
  }

  return 1;
}

static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                       int ca) {
  int ret;
  ret = check_purpose_ssl_server(xp, x, ca);
  if (!ret || ca) {
    return ret;
  }
  // We need to encipher or Netscape complains
  if (ku_reject(x, KU_KEY_ENCIPHERMENT)) {
    return 0;
  }
  return ret;
}

// purpose_smime returns one if |x| is a valid S/MIME leaf (|ca| is zero) or CA
// (|ca| is one) certificate, and zero otherwise.
static int purpose_smime(const X509 *x, int ca) {
  if (xku_reject(x, XKU_SMIME)) {
    return 0;
  }
  if (ca) {
    // check nsCertType if present
    if ((x->ex_flags & EXFLAG_NSCERT) && (x->ex_nscert & NS_SMIME_CA) == 0) {
      return 0;
    }

    return check_ca(x);
  }
  if (x->ex_flags & EXFLAG_NSCERT) {
    return (x->ex_nscert & NS_SMIME) == NS_SMIME;
  }
  return 1;
}

static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
                                    int ca) {
  int ret;
  ret = purpose_smime(x, ca);
  if (!ret || ca) {
    return ret;
  }
  if (ku_reject(x, KU_DIGITAL_SIGNATURE | KU_NON_REPUDIATION)) {
    return 0;
  }
  return ret;
}

static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
                                       int ca) {
  int ret;
  ret = purpose_smime(x, ca);
  if (!ret || ca) {
    return ret;
  }
  if (ku_reject(x, KU_KEY_ENCIPHERMENT)) {
    return 0;
  }
  return ret;
}

static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
                                  int ca) {
  if (ca) {
    return check_ca(x);
  }
  if (ku_reject(x, KU_CRL_SIGN)) {
    return 0;
  }
  return 1;
}

// OCSP helper: this is *not* a full OCSP check. It just checks that each CA
// is valid. Additional checks must be made on the chain.

static int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca) {
  if (ca) {
    return check_ca(x);
  }
  // leaf certificate is checked in OCSP_verify()
  return 1;
}

static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
                                        int ca) {
  int i_ext;

  // If ca is true we must return if this is a valid CA certificate.
  if (ca) {
    return check_ca(x);
  }

  // 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 & ~(KU_NON_REPUDIATION | KU_DIGITAL_SIGNATURE)) ||
       !(x->ex_kusage & (KU_NON_REPUDIATION | KU_DIGITAL_SIGNATURE)))) {
    return 0;
  }

  // Only time stamp key usage is permitted and it's required.
  if (!(x->ex_flags & EXFLAG_XKUSAGE) || x->ex_xkusage != XKU_TIMESTAMP) {
    return 0;
  }

  // Extended Key Usage MUST be critical
  i_ext = X509_get_ext_by_NID((X509 *)x, NID_ext_key_usage, -1);
  if (i_ext >= 0) {
    const X509_EXTENSION *ext = X509_get_ext((X509 *)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; }

// Various checks to see if one certificate issued the second. This can be
// used to prune a set of possible issuer certificates which have been looked
// up using some simple method such as by subject name. These are: 1. Check
// issuer_name(subject) == subject_name(issuer) 2. If akid(subject) exists
// check it matches issuer 3. If key_usage(issuer) exists check it supports
// certificate signing returns 0 for OK, positive for reason for mismatch,
// reasons match codes for X509_verify_cert()

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, KU_KEY_CERT_SIGN)) {
    return X509_V_ERR_KEYUSAGE_NO_CERTSIGN;
  }
  return X509_V_OK;
}

int X509_check_akid(X509 *issuer, 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;
  }
  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;
  }
  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;
}