x509_utils.c

 
#include <openssl/objects.h>
#include <openssl/x509v3.h>
#include <openssl/pem.h>
#include <openssl/rsa.h>
#include <openssl/err.h>
 
#include <freerdp/config.h>
 
#include <winpr/crt.h>
#include <winpr/string.h>
#include <winpr/assert.h>
 
#include <freerdp/log.h>
 
#include "x509_utils.h"
 
#define TAG FREERDP_TAG("crypto")
 
BYTE* x509_utils_get_hash(const X509* xcert, const char* hash, size_t* length)
{
  UINT32 fp_len = EVP_MAX_MD_SIZE;
  BYTE* fp = NULL;
  const EVP_MD* md = EVP_get_digestbyname(hash);
  if (!md)
  {
    WLog_ERR(TAG, "System does not support %s hash!", hash);
    return NULL;
  }
  if (!xcert || !length)
  {
    WLog_ERR(TAG, "Invalid arguments: xcert=%p, length=%p", xcert, length);
    return NULL;
  }
 
  fp = calloc(fp_len + 1, sizeof(BYTE));
  if (!fp)
  {
    WLog_ERR(TAG, "could not allocate %" PRIuz " bytes", fp_len);
    return NULL;
  }
 
  if (X509_digest(xcert, md, fp, &fp_len) != 1)
  {
    free(fp);
    WLog_ERR(TAG, "certificate does not have a %s hash!", hash);
    return NULL;
  }
 
  *length = fp_len;
  return fp;
}
 
static char* crypto_print_name(const X509_NAME* name)
{
  char* buffer = NULL;
  BIO* outBIO = BIO_new(BIO_s_mem());
 
  if (X509_NAME_print_ex(outBIO, name, 0, XN_FLAG_ONELINE) > 0)
  {
    UINT64 size = BIO_number_written(outBIO);
    if (size > INT_MAX)
      goto fail;
    buffer = calloc(1, (size_t)size + 1);
 
    if (!buffer)
      goto fail;
 
    ERR_clear_error();
    const int rc = BIO_read(outBIO, buffer, (int)size);
    if (rc <= 0)
    {
      free(buffer);
      buffer = NULL;
      goto fail;
    }
  }
 
fail:
  BIO_free_all(outBIO);
  return buffer;
}
 
char* x509_utils_get_subject(const X509* xcert)
{
  char* subject = NULL;
  if (!xcert)
  {
    WLog_ERR(TAG, "Invalid certificate %p", xcert);
    return NULL;
  }
  subject = crypto_print_name(X509_get_subject_name(xcert));
  if (!subject)
    WLog_WARN(TAG, "certificate does not have a subject!");
  return subject;
}
 
/* GENERAL_NAME type labels */
 
static const char* general_name_type_labels[] = { "OTHERNAME", "EMAIL    ", "DNS      ",
                                                "X400     ", "DIRNAME  ", "EDIPARTY ",
                                                "URI      ", "IPADD    ", "RID      " };
 
static const char* general_name_type_label(int general_name_type)
{
  if ((0 <= general_name_type) &&
      ((size_t)general_name_type < ARRAYSIZE(general_name_type_labels)))
  {
    return general_name_type_labels[general_name_type];
  }
  else
  {
    static char buffer[80] = { 0 };
    (void)snprintf(buffer, sizeof(buffer), "Unknown general name type (%d)", general_name_type);
    return buffer;
  }
}
 
/*
 
map_subject_alt_name(x509,  general_name_type, mapper, data)
 
Call the function mapper with subjectAltNames found in the x509
certificate and data.  if generate_name_type is GEN_ALL,  the the
mapper is called for all the names,  else it's called only for names
of the given type.
 
 
We implement two extractors:
 
 -  a string extractor that can be used to get the subjectAltNames of
    the following types: GEN_URI,  GEN_DNS,  GEN_EMAIL
 
 - a ASN1_OBJECT filter/extractor that can be used to get the
   subjectAltNames of OTHERNAME type.
 
   Note: usually, it's a string, but some type of otherNames can be
   associated with different classes of objects. eg. a KPN may be a
   sequence of realm and principal name, instead of a single string
   object.
 
Not implemented yet: extractors for the types: GEN_X400, GEN_DIRNAME,
GEN_EDIPARTY, GEN_RID, GEN_IPADD (the later can contain nul-bytes).
 
 
mapper(name, data, index, count)
 
The mapper is passed:
 - the GENERAL_NAME selected,
 - the data,
 - the index of the general name in the subjectAltNames,
 - the total number of names in the subjectAltNames.
 
The last parameter let's the mapper allocate arrays to collect objects.
Note: if names are filtered,  not all the indices from 0 to count-1 are
passed to mapper,  only the indices selected.
 
When the mapper returns 0, map_subject_alt_name stops the iteration immediately.
 
*/
 
#define GEN_ALL (-1)
 
typedef int (*general_name_mapper_pr)(GENERAL_NAME* name, void* data, int index, int count);
 
static void map_subject_alt_name(const X509* x509, int general_name_type,
                                 general_name_mapper_pr mapper, void* data)
{
  int num = 0;
  STACK_OF(GENERAL_NAME)* gens = NULL;
  gens = X509_get_ext_d2i(x509, NID_subject_alt_name, NULL, NULL);
 
  if (!gens)
  {
    return;
  }
 
  num = sk_GENERAL_NAME_num(gens);
 
  for (int i = 0; (i < num); i++)
  {
    GENERAL_NAME* name = sk_GENERAL_NAME_value(gens, i);
 
    if (name)
    {
      if ((general_name_type == GEN_ALL) || (general_name_type == name->type))
      {
        if (!mapper(name, data, i, num))
        {
          break;
        }
      }
    }
  }
 
  sk_GENERAL_NAME_pop_free(gens, GENERAL_NAME_free);
}
 
/*
extract_string  --  string extractor
 
- the strings array is allocated lazily, when we first have to store a
  string.
 
- allocated contains the size of the strings array, or -1 if
  allocation failed.
 
- count contains the actual count of strings in the strings array.
 
- maximum limits the number of strings we can store in the strings
  array: beyond, the extractor returns 0 to short-cut the search.
 
extract_string stores in the string list OPENSSL strings,
that must be freed with OPENSSL_free.
 
*/
 
typedef struct string_list
{
  char** strings;
  size_t allocated;
  size_t count;
  size_t maximum;
} string_list;
 
static void string_list_initialize(string_list* list)
{
  list->strings = 0;
  list->allocated = 0;
  list->count = 0;
  list->maximum = INT_MAX;
}
 
static void string_list_allocate(string_list* list, size_t allocate_count)
{
  if (!list->strings && list->allocated == 0)
  {
    list->strings = (char**)calloc(allocate_count, sizeof(char*));
    list->allocated = list->strings ? allocate_count : 0;
    list->count = 0;
  }
}
 
static void string_list_free(string_list* list)
{
  /* Note: we don't free the contents of the strings array: this */
  /* is handled by the caller,  either by returning this */
  /* content,  or freeing it itself. */
  free((void*)list->strings);
}
 
static int extract_string(GENERAL_NAME* name, void* data, int index, int count)
{
  string_list* list = data;
  unsigned char* cstring = 0;
  ASN1_STRING* str = NULL;
 
  WINPR_UNUSED(index);
 
  switch (name->type)
  {
    case GEN_URI:
      str = name->d.uniformResourceIdentifier;
      break;
 
    case GEN_DNS:
      str = name->d.dNSName;
      break;
 
    case GEN_EMAIL:
      str = name->d.rfc822Name;
      break;
 
    default:
      return 1;
  }
 
  if ((ASN1_STRING_to_UTF8(&cstring, str)) < 0)
  {
    WLog_ERR(TAG, "ASN1_STRING_to_UTF8() failed for %s: %s",
             general_name_type_label(name->type), ERR_error_string(ERR_get_error(), NULL));
    return 1;
  }
 
  string_list_allocate(list, WINPR_ASSERTING_INT_CAST(WINPR_CIPHER_TYPE, count));
 
  if (list->allocated <= 0)
  {
    OPENSSL_free(cstring);
    return 0;
  }
 
  list->strings[list->count] = (char*)cstring;
  list->count++;
 
  if (list->count >= list->maximum)
  {
    return 0;
  }
 
  return 1;
}
 
/*
extract_othername_object --  object extractor.
 
- the objects array is allocated lazily, when we first have to store a
  string.
 
- allocated contains the size of the objects array, or -1 if
  allocation failed.
 
- count contains the actual count of objects in the objects array.
 
- maximum limits the number of objects we can store in the objects
  array: beyond, the extractor returns 0 to short-cut the search.
 
extract_othername_objects stores in the objects array ASN1_TYPE *
pointers directly obtained from the GENERAL_NAME.
*/
 
typedef struct object_list
{
  ASN1_OBJECT* type_id;
  char** strings;
  size_t allocated;
  size_t count;
  size_t maximum;
} object_list;
 
static void object_list_initialize(object_list* list)
{
  list->type_id = 0;
  list->strings = 0;
  list->allocated = 0;
  list->count = 0;
  list->maximum = INT_MAX;
}
 
static void object_list_allocate(object_list* list, size_t allocate_count)
{
  if (!list->strings && (list->allocated == 0) && (allocate_count > 0))
  {
    list->strings = (char**)calloc(allocate_count, sizeof(list->strings[0]));
    list->allocated = list->strings ? allocate_count : 0;
    list->count = 0;
  }
}
 
static char* object_string(ASN1_TYPE* object)
{
  char* result = NULL;
  unsigned char* utf8String = NULL;
 
  /* TODO: check that object.type is a string type. */
  const int length = ASN1_STRING_to_UTF8(&utf8String, object->value.asn1_string);
 
  if (length < 0)
  {
    return 0;
  }
 
  result = strndup((char*)utf8String, WINPR_ASSERTING_INT_CAST(size_t, length));
  OPENSSL_free(utf8String);
  return result;
}
 
static void object_list_free(object_list* list)
{
  WINPR_ASSERT(list);
  free((void*)list->strings);
}
 
static int extract_othername_object_as_string(GENERAL_NAME* name, void* data, int index, int count)
{
  object_list* list = data;
  WINPR_UNUSED(index);
 
  if (count < 0)
    return -1;
 
  if (name->type != GEN_OTHERNAME)
  {
    return 1;
  }
 
  if (0 != OBJ_cmp(name->d.otherName->type_id, list->type_id))
  {
    return 1;
  }
 
  object_list_allocate(list, WINPR_ASSERTING_INT_CAST(size_t, count));
 
  if (list->allocated <= 0)
  {
    return 0;
  }
 
  list->strings[list->count] = object_string(name->d.otherName->value);
 
  if (list->strings[list->count])
  {
    list->count++;
  }
 
  if (list->count >= list->maximum)
  {
    return 0;
  }
 
  return 1;
}
 
char* x509_utils_get_email(const X509* x509)
{
  char* result = 0;
  string_list list;
  string_list_initialize(&list);
  list.maximum = 1;
  map_subject_alt_name(x509, GEN_EMAIL, extract_string, &list);
 
  if (list.count == 0)
  {
    string_list_free(&list);
    return 0;
  }
 
  result = _strdup(list.strings[0]);
  OPENSSL_free(list.strings[0]);
  string_list_free(&list);
  return result;
}
 
char* x509_utils_get_upn(const X509* x509)
{
  char* result = 0;
  object_list list = { 0 };
  object_list_initialize(&list);
  list.type_id = OBJ_nid2obj(NID_ms_upn);
  list.maximum = 1;
  map_subject_alt_name(x509, GEN_OTHERNAME, extract_othername_object_as_string, &list);
 
  if (list.count == 0)
  {
    object_list_free(&list);
    return 0;
  }
 
  result = list.strings[0];
  object_list_free(&list);
  return result;
}
 
char* x509_utils_get_date(const X509* x509, BOOL startDate)
{
  WINPR_ASSERT(x509);
 
  const ASN1_TIME* date = startDate ? X509_get0_notBefore(x509) : X509_get0_notAfter(x509);
  if (!date)
    return NULL;
 
  BIO* bmem = BIO_new(BIO_s_mem());
  if (!bmem)
    return NULL;
 
  char* str = NULL;
  if (ASN1_TIME_print(bmem, date))
  {
    BUF_MEM* bptr = NULL;
 
    BIO_get_mem_ptr(bmem, &bptr);
    str = strndup(bptr->data, bptr->length);
  }
  else
  { // Log error
  }
  BIO_free_all(bmem);
  return str;
}
 
void x509_utils_dns_names_free(size_t count, size_t* lengths, char** dns_names)
{
  free(lengths);
 
  if (dns_names)
  {
    for (size_t i = 0; i < count; i++)
    {
      if (dns_names[i])
      {
        OPENSSL_free(dns_names[i]);
      }
    }
 
    free((void*)dns_names);
  }
}
 
char** x509_utils_get_dns_names(const X509* x509, size_t* count, size_t** lengths)
{
  char** result = 0;
  string_list list = { 0 };
  string_list_initialize(&list);
  map_subject_alt_name(x509, GEN_DNS, extract_string, &list);
  (*count) = list.count;
 
  if (list.count <= 0)
  {
    string_list_free(&list);
    return NULL;
  }
 
  /* lengths are not useful,  since we converted the
     strings to utf-8,  there cannot be nul-bytes in them. */
  result = (char**)calloc(list.count, sizeof(*result));
  (*lengths) = calloc(list.count, sizeof(**lengths));
 
  if (!result || !(*lengths))
  {
    string_list_free(&list);
    free((void*)result);
    free(*lengths);
    (*lengths) = 0;
    (*count) = 0;
    return NULL;
  }
 
  for (size_t i = 0; i < list.count; i++)
  {
    result[i] = list.strings[i];
    (*lengths)[i] = strlen(result[i]);
  }
 
  string_list_free(&list);
  return result;
}
 
char* x509_utils_get_issuer(const X509* xcert)
{
  char* issuer = NULL;
  if (!xcert)
  {
    WLog_ERR(TAG, "Invalid certificate %p", xcert);
    return NULL;
  }
  issuer = crypto_print_name(X509_get_issuer_name(xcert));
  if (!issuer)
    WLog_WARN(TAG, "certificate does not have an issuer!");
  return issuer;
}
 
static int asn1_object_cmp(const ASN1_OBJECT* const* a, const ASN1_OBJECT* const* b)
{
  if (!a || !b)
    return (a == b) ? 0 : (a ? 1 : -1);
 
  if (!*a || !*b)
    return (*a == *b) ? 0 : (*a ? 1 : -1);
 
  return OBJ_cmp(*a, *b);
}
 
BOOL x509_utils_check_eku(const X509* xcert, int nid)
{
  BOOL ret = FALSE;
  STACK_OF(ASN1_OBJECT)* oid_stack = NULL;
  ASN1_OBJECT* oid = NULL;
 
  if (!xcert)
    return FALSE;
 
  oid = OBJ_nid2obj(nid);
  if (!oid)
    return FALSE;
 
  oid_stack = X509_get_ext_d2i(xcert, NID_ext_key_usage, NULL, NULL);
  if (!oid_stack)
    return FALSE;
 
  sk_ASN1_OBJECT_set_cmp_func(oid_stack, asn1_object_cmp);
  if (sk_ASN1_OBJECT_find(oid_stack, oid) >= 0)
    ret = TRUE;
 
  sk_ASN1_OBJECT_pop_free(oid_stack, ASN1_OBJECT_free);
  return ret;
}
 
void x509_utils_print_info(const X509* xcert)
{
  char* fp = NULL;
  char* issuer = NULL;
  char* subject = NULL;
  subject = x509_utils_get_subject(xcert);
  issuer = x509_utils_get_issuer(xcert);
  fp = (char*)x509_utils_get_hash(xcert, "sha256", NULL);
 
  if (!fp)
  {
    WLog_ERR(TAG, "error computing fingerprint");
    goto out_free_issuer;
  }
 
  WLog_INFO(TAG, "Certificate details:");
  WLog_INFO(TAG, "\tSubject: %s", subject);
  WLog_INFO(TAG, "\tIssuer: %s", issuer);
  WLog_INFO(TAG, "\tThumbprint: %s", fp);
  WLog_INFO(TAG,
            "The above X.509 certificate could not be verified, possibly because you do not have "
            "the CA certificate in your certificate store, or the certificate has expired. "
            "Please look at the OpenSSL documentation on how to add a private CA to the store.");
  free(fp);
out_free_issuer:
  free(issuer);
  free(subject);
}
 
X509* x509_utils_from_pem(const char* data, size_t len, BOOL fromFile)
{
  X509* x509 = NULL;
  BIO* bio = NULL;
  if (fromFile)
    bio = BIO_new_file(data, "rb");
  else
  {
    if (len > INT_MAX)
      return NULL;
 
    bio = BIO_new_mem_buf(data, (int)len);
  }
 
  if (!bio)
  {
    WLog_ERR(TAG, "BIO_new failed for certificate");
    return NULL;
  }
 
  x509 = PEM_read_bio_X509(bio, NULL, NULL, 0);
  BIO_free_all(bio);
  if (!x509)
    WLog_ERR(TAG, "PEM_read_bio_X509 returned NULL [input length %" PRIuz "]", len);
 
  return x509;
}
 
static WINPR_MD_TYPE hash_nid_to_winpr(int hash_nid)
{
  switch (hash_nid)
  {
    case NID_md2:
      return WINPR_MD_MD2;
    case NID_md4:
      return WINPR_MD_MD4;
    case NID_md5:
      return WINPR_MD_MD5;
    case NID_sha1:
      return WINPR_MD_SHA1;
    case NID_sha224:
      return WINPR_MD_SHA224;
    case NID_sha256:
      return WINPR_MD_SHA256;
    case NID_sha384:
      return WINPR_MD_SHA384;
    case NID_sha512:
      return WINPR_MD_SHA512;
    case NID_ripemd160:
      return WINPR_MD_RIPEMD160;
#if (OPENSSL_VERSION_NUMBER >= 0x1010101fL) && !defined(LIBRESSL_VERSION_NUMBER)
    case NID_sha3_224:
      return WINPR_MD_SHA3_224;
    case NID_sha3_256:
      return WINPR_MD_SHA3_256;
    case NID_sha3_384:
      return WINPR_MD_SHA3_384;
    case NID_sha3_512:
      return WINPR_MD_SHA3_512;
    case NID_shake128:
      return WINPR_MD_SHAKE128;
    case NID_shake256:
      return WINPR_MD_SHAKE256;
#endif
    case NID_undef:
    default:
      return WINPR_MD_NONE;
  }
}
 
static WINPR_MD_TYPE get_rsa_pss_digest(const X509_ALGOR* alg)
{
  WINPR_MD_TYPE ret = WINPR_MD_NONE;
  WINPR_MD_TYPE message_digest = WINPR_MD_NONE;
  WINPR_MD_TYPE mgf1_digest = WINPR_MD_NONE;
  int param_type = 0;
  const void* param_value = NULL;
  const ASN1_STRING* sequence = NULL;
  const unsigned char* inp = NULL;
  RSA_PSS_PARAMS* params = NULL;
  X509_ALGOR* mgf1_digest_alg = NULL;
 
  /* The RSA-PSS digest is encoded in a complex structure, defined in
  https://www.rfc-editor.org/rfc/rfc4055.html. */
  X509_ALGOR_get0(NULL, &param_type, &param_value, alg);
 
  /* param_type and param_value the parameter in ASN1_TYPE form, but split into two parameters. A
  SEQUENCE is has type V_ASN1_SEQUENCE, and the value is an ASN1_STRING with the encoded
  structure. */
  if (param_type != V_ASN1_SEQUENCE)
    goto end;
  sequence = param_value;
 
  /* Decode the structure. */
  inp = ASN1_STRING_get0_data(sequence);
  params = d2i_RSA_PSS_PARAMS(NULL, &inp, ASN1_STRING_length(sequence));
  if (params == NULL)
    goto end;
 
  /* RSA-PSS uses two hash algorithms, a message digest and also an MGF function which is, itself,
  parameterized by a hash function. Both fields default to SHA-1, so we must also check for the
  value being NULL. */
  message_digest = WINPR_MD_SHA1;
  if (params->hashAlgorithm != NULL)
  {
    const ASN1_OBJECT* obj = NULL;
    X509_ALGOR_get0(&obj, NULL, NULL, params->hashAlgorithm);
    message_digest = hash_nid_to_winpr(OBJ_obj2nid(obj));
    if (message_digest == WINPR_MD_NONE)
      goto end;
  }
 
  mgf1_digest = WINPR_MD_SHA1;
  if (params->maskGenAlgorithm != NULL)
  {
    const ASN1_OBJECT* obj = NULL;
    int mgf_param_type = 0;
    const void* mgf_param_value = NULL;
    const ASN1_STRING* mgf_param_sequence = NULL;
    /* First, check this is MGF-1, the only one ever defined. */
    X509_ALGOR_get0(&obj, &mgf_param_type, &mgf_param_value, params->maskGenAlgorithm);
    if (OBJ_obj2nid(obj) != NID_mgf1)
      goto end;
 
    /* MGF-1 is, itself, parameterized by a hash function, encoded as an AlgorithmIdentifier. */
    if (mgf_param_type != V_ASN1_SEQUENCE)
      goto end;
    mgf_param_sequence = mgf_param_value;
    inp = ASN1_STRING_get0_data(mgf_param_sequence);
    mgf1_digest_alg = d2i_X509_ALGOR(NULL, &inp, ASN1_STRING_length(mgf_param_sequence));
    if (mgf1_digest_alg == NULL)
      goto end;
 
    /* Finally, extract the digest. */
    X509_ALGOR_get0(&obj, NULL, NULL, mgf1_digest_alg);
    mgf1_digest = hash_nid_to_winpr(OBJ_obj2nid(obj));
    if (mgf1_digest == WINPR_MD_NONE)
      goto end;
  }
 
  /* If the two digests do not match, it is ambiguous which to return. tls-server-end-point leaves
  it undefined, so return none.
  https://www.rfc-editor.org/rfc/rfc5929.html#section-4.1 */
  if (message_digest != mgf1_digest)
    goto end;
  ret = message_digest;
 
end:
  RSA_PSS_PARAMS_free(params);
  X509_ALGOR_free(mgf1_digest_alg);
  return ret;
}
 
WINPR_MD_TYPE x509_utils_get_signature_alg(const X509* xcert)
{
  WINPR_ASSERT(xcert);
 
  const int nid = X509_get_signature_nid(xcert);
 
  if (nid == NID_rsassaPss)
  {
    const X509_ALGOR* alg = NULL;
    X509_get0_signature(NULL, &alg, xcert);
    return get_rsa_pss_digest(alg);
  }
 
  int hash_nid = 0;
  if (OBJ_find_sigid_algs(nid, &hash_nid, NULL) != 1)
    return WINPR_MD_NONE;
 
  return hash_nid_to_winpr(hash_nid);
}
 
char* x509_utils_get_common_name(const X509* xcert, size_t* plength)
{
  X509_NAME* subject_name = X509_get_subject_name(xcert);
  if (subject_name == NULL)
    return NULL;
 
  const int index = X509_NAME_get_index_by_NID(subject_name, NID_commonName, -1);
  if (index < 0)
    return NULL;
 
  const X509_NAME_ENTRY* entry = X509_NAME_get_entry(subject_name, index);
  if (entry == NULL)
    return NULL;
 
  const ASN1_STRING* entry_data = X509_NAME_ENTRY_get_data(entry);
  if (entry_data == NULL)
    return NULL;
 
  BYTE* common_name_raw = NULL;
  const int length = ASN1_STRING_to_UTF8(&common_name_raw, entry_data);
  if (length < 0)
    return NULL;
 
  if (plength)
    *plength = (size_t)length;
 
  char* common_name = _strdup((char*)common_name_raw);
  OPENSSL_free(common_name_raw);
  return common_name;
}
 
static int verify_cb(int ok, X509_STORE_CTX* csc)
{
  if (ok != 1)
  {
    WINPR_ASSERT(csc);
    int err = X509_STORE_CTX_get_error(csc);
    int derr = X509_STORE_CTX_get_error_depth(csc);
    X509* where = X509_STORE_CTX_get_current_cert(csc);
    const char* what = X509_verify_cert_error_string(err);
    char* name = x509_utils_get_subject(where);
 
    WLog_WARN(TAG, "Certificate verification failure '%s (%d)' at stack position %d", what, err,
              derr);
    WLog_WARN(TAG, "%s", name);
 
    free(name);
  }
  return ok;
}
 
BOOL x509_utils_verify(X509* xcert, STACK_OF(X509) * chain, const char* certificate_store_path)
{
  const int purposes[3] = { X509_PURPOSE_SSL_SERVER, X509_PURPOSE_SSL_CLIENT, X509_PURPOSE_ANY };
  X509_STORE_CTX* csc = NULL;
  BOOL status = FALSE;
  X509_LOOKUP* lookup = NULL;
 
  if (!xcert)
    return FALSE;
 
  X509_STORE* cert_ctx = X509_STORE_new();
 
  if (cert_ctx == NULL)
    goto end;
 
#if OPENSSL_VERSION_NUMBER < 0x10100000L || defined(LIBRESSL_VERSION_NUMBER)
  OpenSSL_add_all_algorithms();
#else
  OPENSSL_init_crypto(OPENSSL_INIT_ADD_ALL_CIPHERS | OPENSSL_INIT_ADD_ALL_DIGESTS |
                          OPENSSL_INIT_LOAD_CONFIG,
                      NULL);
#endif
 
  if (X509_STORE_set_default_paths(cert_ctx) != 1)
    goto end;
 
  lookup = X509_STORE_add_lookup(cert_ctx, X509_LOOKUP_hash_dir());
 
  if (lookup == NULL)
    goto end;
 
  X509_LOOKUP_add_dir(lookup, NULL, X509_FILETYPE_DEFAULT);
 
  if (certificate_store_path != NULL)
  {
    X509_LOOKUP_add_dir(lookup, certificate_store_path, X509_FILETYPE_PEM);
  }
 
  X509_STORE_set_flags(cert_ctx, 0);
 
  for (size_t i = 0; i < ARRAYSIZE(purposes); i++)
  {
    int err = -1;
    int rc = -1;
    int purpose = purposes[i];
    csc = X509_STORE_CTX_new();
 
    if (csc == NULL)
      goto skip;
    if (!X509_STORE_CTX_init(csc, cert_ctx, xcert, chain))
      goto skip;
 
    X509_STORE_CTX_set_purpose(csc, purpose);
    X509_STORE_CTX_set_verify_cb(csc, verify_cb);
 
    rc = X509_verify_cert(csc);
    err = X509_STORE_CTX_get_error(csc);
  skip:
    X509_STORE_CTX_free(csc);
    if (rc == 1)
    {
      status = TRUE;
      break;
    }
    else if (err != X509_V_ERR_INVALID_PURPOSE)
      break;
  }
 
  X509_STORE_free(cert_ctx);
end:
  return status;
}