File: cryptoapi.c

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/*
 * Copyright (c) 2004 Peter 'Luna' Runestig <peter@runestig.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modifi-
 * cation, are permitted provided that the following conditions are met:
 *
 *   o  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   o  Redistributions in binary form must reproduce the above copyright no-
 *      tice, this list of conditions and the following disclaimer in the do-
 *      cumentation and/or other materials provided with the distribution.
 *
 *   o  The names of the contributors may not be used to endorse or promote
 *      products derived from this software without specific prior written
 *      permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS 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 REGENTS OR CONTRIBUTORS BE LI-
 * ABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUEN-
 * TIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEV-
 * ER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABI-
 * LITY, 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.
 */
#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>
#include <ctype.h>
#include <assert.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

#ifdef __MINGW32_VERSION
/* MinGW w32api is incomplete when it comes to CryptoAPI, as per version 3.1
 * anyway. This is a hack around that problem. */
#define CALG_SSL3_SHAMD5 (ALG_CLASS_HASH | ALG_TYPE_ANY | ALG_SID_SSL3SHAMD5)
#define CERT_SYSTEM_STORE_LOCATION_SHIFT 16
#define CERT_SYSTEM_STORE_CURRENT_USER_ID 1
#define CERT_SYSTEM_STORE_CURRENT_USER (CERT_SYSTEM_STORE_CURRENT_USER_ID << CERT_SYSTEM_STORE_LOCATION_SHIFT)
#define CERT_STORE_READONLY_FLAG 0x00008000
#define CERT_STORE_OPEN_EXISTING_FLAG 0x00004000
#define CRYPT_ACQUIRE_COMPARE_KEY_FLAG 0x00000004
static HINSTANCE crypt32dll = NULL;
static BOOL WINAPI (*CryptAcquireCertificatePrivateKey) (PCCERT_CONTEXT pCert, DWORD dwFlags,
    void *pvReserved, HCRYPTPROV *phCryptProv, DWORD *pdwKeySpec, BOOL *pfCallerFreeProv) = NULL;
static PCCERT_CONTEXT WINAPI (*CertCreateCertificateContext) (DWORD dwCertEncodingType,
     const BYTE *pbCertEncoded, DWORD cbCertEncoded) = NULL;
#endif

/* Size of an SSL signature: MD5+SHA1 */
#define SSL_SIG_LENGTH	36

/* try to funnel any Windows/CryptoAPI error messages to OpenSSL ERR_... */
#define ERR_LIB_CRYPTOAPI (ERR_LIB_USER + 69)	/* 69 is just a number... */
#define CRYPTOAPIerr(f)   err_put_ms_error(GetLastError(), (f), __FILE__, __LINE__)
#define CRYPTOAPI_F_CERT_OPEN_SYSTEM_STORE		    100
#define CRYPTOAPI_F_CERT_FIND_CERTIFICATE_IN_STORE	    101
#define CRYPTOAPI_F_CRYPT_ACQUIRE_CERTIFICATE_PRIVATE_KEY   102
#define CRYPTOAPI_F_CRYPT_CREATE_HASH			    103
#define CRYPTOAPI_F_CRYPT_GET_HASH_PARAM		    104
#define CRYPTOAPI_F_CRYPT_SET_HASH_PARAM		    105
#define CRYPTOAPI_F_CRYPT_SIGN_HASH			    106
#define CRYPTOAPI_F_LOAD_LIBRARY			    107
#define CRYPTOAPI_F_GET_PROC_ADDRESS			    108
#define CRYPTOAPI_F_CERT_CREATE_CERT_CONTEXT		    109
#define CRYPTOAPI_F_CERT_GET_CERT_CHAIN			    110

static ERR_STRING_DATA CRYPTOAPI_str_functs[] =	{
    { ERR_PACK(ERR_LIB_CRYPTOAPI, 0, 0),				    "microsoft cryptoapi"},
    { ERR_PACK(0, CRYPTOAPI_F_CERT_OPEN_SYSTEM_STORE, 0),		    "CertOpenSystemStore" },
    { ERR_PACK(0, CRYPTOAPI_F_CERT_FIND_CERTIFICATE_IN_STORE, 0),	    "CertFindCertificateInStore" },
    { ERR_PACK(0, CRYPTOAPI_F_CRYPT_ACQUIRE_CERTIFICATE_PRIVATE_KEY, 0),    "CryptAcquireCertificatePrivateKey" },
    { ERR_PACK(0, CRYPTOAPI_F_CRYPT_CREATE_HASH, 0),			    "CryptCreateHash" },
    { ERR_PACK(0, CRYPTOAPI_F_CRYPT_GET_HASH_PARAM, 0),			    "CryptGetHashParam" },
    { ERR_PACK(0, CRYPTOAPI_F_CRYPT_SET_HASH_PARAM, 0),			    "CryptSetHashParam" },
    { ERR_PACK(0, CRYPTOAPI_F_CRYPT_SIGN_HASH, 0),			    "CryptSignHash" },
    { ERR_PACK(0, CRYPTOAPI_F_LOAD_LIBRARY, 0),			    	    "LoadLibrary" },
    { ERR_PACK(0, CRYPTOAPI_F_GET_PROC_ADDRESS, 0),			    "GetProcAddress" },
    { ERR_PACK(0, CRYPTOAPI_F_CERT_CREATE_CERT_CONTEXT, 0),		    "CertCreateCertificateContext" },
    { ERR_PACK(0, CRYPTOAPI_F_CERT_GET_CERT_CHAIN, 0),			    "CertGetCertificateChain" },
    { 0, NULL }
};

typedef struct _CAPI_DATA {
    const CERT_CONTEXT *cert_context;
    HCRYPTPROV crypt_prov;
    DWORD key_spec;
    BOOL free_crypt_prov;
} CAPI_DATA;

static char *ms_error_text(DWORD ms_err)
{
    LPVOID lpMsgBuf = NULL;
    char *rv = NULL;

    FormatMessage(
	FORMAT_MESSAGE_ALLOCATE_BUFFER |
	FORMAT_MESSAGE_FROM_SYSTEM |
	FORMAT_MESSAGE_IGNORE_INSERTS,
	NULL, ms_err,
	MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), /* Default language */
	(LPTSTR) &lpMsgBuf, 0, NULL);
    if (lpMsgBuf) {
	char *p;
	rv = strdup(lpMsgBuf);
	LocalFree(lpMsgBuf);
	/* trim to the left */
	if (rv)
	    for (p = rv + strlen(rv) - 1; p >= rv; p--) {
		if (isspace(*p))
		    *p = '\0';
		else
		    break;
	    }
    }
    return rv;
}

static void err_put_ms_error(DWORD ms_err, int func, const char *file, int line)
{
    static int init = 0;
#   define ERR_MAP_SZ 16
    static struct {
	int err;
	DWORD ms_err;	    /* I don't think we get more than 16 *different* errors */
    } err_map[ERR_MAP_SZ];  /* in here, before we give up the whole thing...        */
    int i;

    if (ms_err == 0)
	/* 0 is not an error */
	return;
    if (!init) {
	ERR_load_strings(ERR_LIB_CRYPTOAPI, CRYPTOAPI_str_functs);
	memset(&err_map, 0, sizeof(err_map));
	init++;
    }
    /* since MS error codes are 32 bit, and the ones in the ERR_... system is
     * only 12, we must have a mapping table between them.  */
    for (i = 0; i < ERR_MAP_SZ; i++) {
	if (err_map[i].ms_err == ms_err) {
	    ERR_PUT_error(ERR_LIB_CRYPTOAPI, func, err_map[i].err, file, line);
	    break;
	} else if (err_map[i].ms_err == 0 ) {
	    /* end of table, add new entry */
	    ERR_STRING_DATA *esd = calloc(2, sizeof(*esd));
	    if (esd == NULL)
		break;
	    err_map[i].ms_err = ms_err;
	    err_map[i].err = esd->error = i + 100;
	    esd->string = ms_error_text(ms_err);
	    ERR_load_strings(ERR_LIB_CRYPTOAPI, esd);
	    ERR_PUT_error(ERR_LIB_CRYPTOAPI, func, err_map[i].err, file, line);
	    break;
	}
    }
}

/* encrypt */
static int rsa_pub_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
{
    /* I haven't been able to trigger this one, but I want to know if it happens... */
    assert(0);

    return 0;
}

/* verify arbitrary data */
static int rsa_pub_dec(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
{
    /* I haven't been able to trigger this one, but I want to know if it happens... */
    assert(0);

    return 0;
}

/* sign arbitrary data */
static int rsa_priv_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
{
    CAPI_DATA *cd = (CAPI_DATA *) rsa->meth->app_data;
    HCRYPTHASH hash;
    DWORD hash_size, len, i;
    unsigned char *buf;

    if (cd == NULL) {
	RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, ERR_R_PASSED_NULL_PARAMETER);
	return 0;
    }
    if (padding != RSA_PKCS1_PADDING) {
	/* AFAICS, CryptSignHash() *always* uses PKCS1 padding. */
	RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
	return 0;
    }
    /* Unfortunately, there is no "CryptSign()" function in CryptoAPI, that would
     * be way to straightforward for M$, I guess... So we have to do it this
     * tricky way instead, by creating a "Hash", and load the already-made hash
     * from 'from' into it.  */
    /* For now, we only support NID_md5_sha1 */
    if (flen != SSL_SIG_LENGTH) {
	RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, RSA_R_INVALID_MESSAGE_LENGTH);
	return 0;
    }
    if (!CryptCreateHash(cd->crypt_prov, CALG_SSL3_SHAMD5, 0, 0, &hash)) {
	CRYPTOAPIerr(CRYPTOAPI_F_CRYPT_CREATE_HASH);
	return 0;
    }
    len = sizeof(hash_size);
    if (!CryptGetHashParam(hash, HP_HASHSIZE, (BYTE *) &hash_size, &len, 0)) {
	CRYPTOAPIerr(CRYPTOAPI_F_CRYPT_GET_HASH_PARAM);
        CryptDestroyHash(hash);
	return 0;
    }
    if ((int) hash_size != flen) {
	RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, RSA_R_INVALID_MESSAGE_LENGTH);
        CryptDestroyHash(hash);
	return 0;
    }
    if (!CryptSetHashParam(hash, HP_HASHVAL, (BYTE * ) from, 0)) {
	CRYPTOAPIerr(CRYPTOAPI_F_CRYPT_SET_HASH_PARAM);
        CryptDestroyHash(hash);
	return 0;
    }

    len = RSA_size(rsa);
    buf = malloc(len);
    if (buf == NULL) {
	RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, ERR_R_MALLOC_FAILURE);
        CryptDestroyHash(hash);
	return 0;
    }
    if (!CryptSignHash(hash, cd->key_spec, NULL, 0, buf, &len)) {
	CRYPTOAPIerr(CRYPTOAPI_F_CRYPT_SIGN_HASH);
        CryptDestroyHash(hash);
        free(buf);
	return 0;
    }
    /* and now, we have to reverse the byte-order in the result from CryptSignHash()... */
    for (i = 0; i < len; i++)
	to[i] = buf[len - i - 1];
    free(buf);

    CryptDestroyHash(hash);
    return len;
}

/* decrypt */
static int rsa_priv_dec(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
{
    /* I haven't been able to trigger this one, but I want to know if it happens... */
    assert(0);

    return 0;
}

/* called at RSA_new */
static int init(RSA *rsa)
{

    return 0;
}

/* called at RSA_free */
static int finish(RSA *rsa)
{
    CAPI_DATA *cd = (CAPI_DATA *) rsa->meth->app_data;

    if (cd == NULL)
	return 0;
    if (cd->crypt_prov && cd->free_crypt_prov)
	CryptReleaseContext(cd->crypt_prov, 0);
    if (cd->cert_context)
	CertFreeCertificateContext(cd->cert_context);
    free(rsa->meth->app_data);
    free((char *) rsa->meth);
    rsa->meth = NULL;
    return 1;
}

static const CERT_CONTEXT *find_certificate_in_store(const char *cert_prop, HCERTSTORE cert_store)
{
    /* Find, and use, the desired certificate from the store. The
     * 'cert_prop' certificate search string can look like this:
     * SUBJ:<certificate substring to match>
     * THUMB:<certificate thumbprint hex value>, e.g.
     *     THUMB:f6 49 24 41 01 b4 fb 44 0c ce f4 36 ae d0 c4 c9 df 7a b6 28
     */
    const CERT_CONTEXT *rv = NULL;

    if (!strncmp(cert_prop, "SUBJ:", 5)) {
	/* skip the tag */
	cert_prop += 5;
	rv = CertFindCertificateInStore(cert_store, X509_ASN_ENCODING | PKCS_7_ASN_ENCODING,
		0, CERT_FIND_SUBJECT_STR_A, cert_prop, NULL);

    } else if (!strncmp(cert_prop, "THUMB:", 6)) {
	unsigned char hash[255];
	char *p;
	int i, x = 0;
	CRYPT_HASH_BLOB blob;

	/* skip the tag */
	cert_prop += 6;
	for (p = (char *) cert_prop, i = 0; *p && i < sizeof(hash); i++) {
	    if (*p >= '0' && *p <= '9')
		x = (*p - '0') << 4;
	    else if (*p >= 'A' && *p <= 'F')
		x = (*p - 'A' + 10) << 4;
	    else if (*p >= 'a' && *p <= 'f')
		x = (*p - 'a' + 10) << 4;
	    if (!*++p)	/* unexpected end of string */
		break;
	    if (*p >= '0' && *p <= '9')
		x += *p - '0';
	    else if (*p >= 'A' && *p <= 'F')
		x += *p - 'A' + 10;
	    else if (*p >= 'a' && *p <= 'f')
		x += *p - 'a' + 10;
	    hash[i] = x;
	    /* skip any space(s) between hex numbers */
	    for (p++; *p && *p == ' '; p++);
	}
	blob.cbData = i;
	blob.pbData = (unsigned char *) &hash;
	rv = CertFindCertificateInStore(cert_store, X509_ASN_ENCODING | PKCS_7_ASN_ENCODING,
		0, CERT_FIND_HASH, &blob, NULL);

    }

    return rv;
}

int SSL_CTX_use_CryptoAPI_certificate(SSL_CTX *ssl_ctx, const char *cert_prop)
{
    HCERTSTORE cs;
    X509 *cert = NULL;
    RSA *rsa = NULL, *pub_rsa;
    CAPI_DATA *cd = calloc(1, sizeof(*cd));
    RSA_METHOD *my_rsa_method = calloc(1, sizeof(*my_rsa_method));

    if (cd == NULL || my_rsa_method == NULL) {
	SSLerr(SSL_F_SSL_CTX_USE_CERTIFICATE_FILE, ERR_R_MALLOC_FAILURE);
	goto err;
    }
    /* search CURRENT_USER first, then LOCAL_MACHINE */
    cs = CertOpenStore((LPCSTR) CERT_STORE_PROV_SYSTEM, 0, 0, CERT_SYSTEM_STORE_CURRENT_USER |
		       CERT_STORE_OPEN_EXISTING_FLAG | CERT_STORE_READONLY_FLAG, L"MY");
    if (cs == NULL) {
	CRYPTOAPIerr(CRYPTOAPI_F_CERT_OPEN_SYSTEM_STORE);
	goto err;
    }
    cd->cert_context = find_certificate_in_store(cert_prop, cs);
    CertCloseStore(cs, 0);
    if (!cd->cert_context) {
	cs = CertOpenStore((LPCSTR) CERT_STORE_PROV_SYSTEM, 0, 0, CERT_SYSTEM_STORE_LOCAL_MACHINE |
			   CERT_STORE_OPEN_EXISTING_FLAG | CERT_STORE_READONLY_FLAG, L"MY");
	if (cs == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_CERT_OPEN_SYSTEM_STORE);
	    goto err;
	}
	cd->cert_context = find_certificate_in_store(cert_prop, cs);
	CertCloseStore(cs, 0);
	if (cd->cert_context == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_CERT_FIND_CERTIFICATE_IN_STORE);
	    goto err;
	}
    }

    /* cert_context->pbCertEncoded is the cert X509 DER encoded. */
    cert = d2i_X509(NULL, (const unsigned char **) &cd->cert_context->pbCertEncoded,
		    cd->cert_context->cbCertEncoded);
    if (cert == NULL) {
	SSLerr(SSL_F_SSL_CTX_USE_CERTIFICATE_FILE, ERR_R_ASN1_LIB);
	goto err;
    }

    /* set up stuff to use the private key */
#ifdef __MINGW32_VERSION
    /* MinGW w32api is incomplete when it comes to CryptoAPI, as per version 3.1
     * anyway. This is a hack around that problem. */
    if (crypt32dll == NULL) {
	crypt32dll = LoadLibrary("crypt32");
	if (crypt32dll == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_LOAD_LIBRARY);
	    goto err;
	}
    }
    if (CryptAcquireCertificatePrivateKey == NULL) {
	CryptAcquireCertificatePrivateKey = GetProcAddress(crypt32dll,
		"CryptAcquireCertificatePrivateKey");
	if (CryptAcquireCertificatePrivateKey == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_GET_PROC_ADDRESS);
	    goto err;
	}
    }
#endif
    if (!CryptAcquireCertificatePrivateKey(cd->cert_context, CRYPT_ACQUIRE_COMPARE_KEY_FLAG,
	    NULL, &cd->crypt_prov, &cd->key_spec, &cd->free_crypt_prov)) {
	/* if we don't have a smart card reader here, and we try to access a
	 * smart card certificate, we get:
	 * "Error 1223: The operation was canceled by the user." */
	CRYPTOAPIerr(CRYPTOAPI_F_CRYPT_ACQUIRE_CERTIFICATE_PRIVATE_KEY);
	goto err;
    }
    /* here we don't need to do CryptGetUserKey() or anything; all necessary key
     * info is in cd->cert_context, and then, in cd->crypt_prov.  */

    my_rsa_method->name = "Microsoft CryptoAPI RSA Method";
    my_rsa_method->rsa_pub_enc = rsa_pub_enc;
    my_rsa_method->rsa_pub_dec = rsa_pub_dec;
    my_rsa_method->rsa_priv_enc = rsa_priv_enc;
    my_rsa_method->rsa_priv_dec = rsa_priv_dec;
    /* my_rsa_method->init = init; */
    my_rsa_method->finish = finish;
    my_rsa_method->flags = RSA_METHOD_FLAG_NO_CHECK;
    my_rsa_method->app_data = (char *) cd;

    rsa = RSA_new();
    if (rsa == NULL) {
	SSLerr(SSL_F_SSL_CTX_USE_CERTIFICATE_FILE, ERR_R_MALLOC_FAILURE);
	goto err;
    }

    /* cert->cert_info->key->pkey is NULL until we call SSL_CTX_use_certificate(),
     * so we do it here then...  */
    if (!SSL_CTX_use_certificate(ssl_ctx, cert))
	goto err;
    /* the public key */
    pub_rsa = cert->cert_info->key->pkey->pkey.rsa;
    /* SSL_CTX_use_certificate() increased the reference count in 'cert', so
     * we decrease it here with X509_free(), or it will never be cleaned up. */
    X509_free(cert);
    cert = NULL;

    /* I'm not sure about what we have to fill in in the RSA, trying out stuff... */
    /* rsa->n indicates the key size */
    rsa->n = BN_dup(pub_rsa->n);
    rsa->flags |= RSA_FLAG_EXT_PKEY;
    if (!RSA_set_method(rsa, my_rsa_method))
	goto err;

    if (!SSL_CTX_use_RSAPrivateKey(ssl_ctx, rsa))
	goto err;
    /* SSL_CTX_use_RSAPrivateKey() increased the reference count in 'rsa', so
     * we decrease it here with RSA_free(), or it will never be cleaned up. */
    RSA_free(rsa);
    return 1;

  err:
    if (cert)
	X509_free(cert);
    if (rsa)
	RSA_free(rsa);
    else {
	if (my_rsa_method)
	    free(my_rsa_method);
	if (cd) {
	    if (cd->free_crypt_prov && cd->crypt_prov)
		CryptReleaseContext(cd->crypt_prov, 0);
	    if (cd->cert_context)
		CertFreeCertificateContext(cd->cert_context);
	    free(cd);
	}
    }
    return 0;
}

int CryptoAPI_verify_certificate(X509 *x509)
{
  int ret = -1;
  int len;
  unsigned char *buf = NULL;

  PCCERT_CONTEXT pCertContext = NULL;
  PCCERT_CHAIN_CONTEXT pChainContext = NULL;
  CERT_ENHKEY_USAGE EnhkeyUsage;
  CERT_USAGE_MATCH CertUsage;  
  CERT_CHAIN_PARA ChainPara;

  /* Convert from internal X509 format to DER */
  len = i2d_X509(x509, &buf);
  if (len < 0) {
	SSLerr(SSL_F_SSL_CTX_USE_CERTIFICATE_FILE, ERR_R_ASN1_LIB);
	goto err;
  }

#ifdef __MINGW32_VERSION
    /* MinGW w32api is incomplete when it comes to CryptoAPI, as per version 3.1
     * anyway. This is a hack around that problem. */
    if (crypt32dll == NULL) {
	crypt32dll = LoadLibrary("crypt32");
	if (crypt32dll == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_LOAD_LIBRARY);
	    goto err;
	}
    }
    if (CertCreateCertificateContext == NULL) {
	CertCreateCertificateContext = GetProcAddress(crypt32dll,
		"CertCreateCertificateContext");
	if (CertCreateCertificateContext == NULL) {
	    CRYPTOAPIerr(CRYPTOAPI_F_GET_PROC_ADDRESS);
	    goto err;
	}
    }
#endif

  /* Create a certificate context based on the above certificate */
  pCertContext = CertCreateCertificateContext(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING,
  	buf, len);
  if (pCertContext == NULL) {
	CRYPTOAPIerr(CRYPTOAPI_F_CERT_CREATE_CERT_CONTEXT);
	goto err;
  }

  /* Create an empty issuer list */
  EnhkeyUsage.cUsageIdentifier = 0;
  EnhkeyUsage.rgpszUsageIdentifier = NULL;
  CertUsage.dwType = USAGE_MATCH_TYPE_AND;
  CertUsage.Usage  = EnhkeyUsage;

  /* Searching and matching criteria to be used when building the chain */
  ChainPara.cbSize = sizeof(CERT_CHAIN_PARA);
  ChainPara.RequestedUsage = CertUsage;

  /* Get the certificate chain of our certificate */
  if (!CertGetCertificateChain(NULL, pCertContext, NULL, NULL, &ChainPara,
	0, NULL, &pChainContext)) {
	CRYPTOAPIerr(CRYPTOAPI_F_CERT_GET_CERT_CHAIN);
	goto err;
  }

  /* return 1 when the certificate is trusted, 0 when it's not; -1 on error */
  ret = (pChainContext->TrustStatus.dwErrorStatus == CERT_TRUST_NO_ERROR);

  err:
    if (buf)
	OPENSSL_free(buf);
    if (pChainContext)
	CertFreeCertificateChain(pChainContext);
    if (pCertContext)
	CertFreeCertificateContext(pCertContext);

  return ret;
}