7.5.4 PKCS #12 Structure Generation

The following example is about generating a PKCS #12 structure.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>
#include <gnutls/pkcs12.h>

#include "examples.h"

#define OUTFILE "out.p12"

/* This function will write a pkcs12 structure into a file.
 * cert: is a DER encoded certificate
 * pkcs8_key: is a PKCS #8 encrypted key (note that this must be
 *  encrypted using a PKCS #12 cipher, or some browsers will crash)
 * password: is the password used to encrypt the PKCS #12 packet.
 */
int
write_pkcs12 (const gnutls_datum_t * cert,
	      const gnutls_datum_t * pkcs8_key, const char *password)
{
  gnutls_pkcs12_t pkcs12;
  int ret, bag_index;
  gnutls_pkcs12_bag_t bag, key_bag;
  char pkcs12_struct[10 * 1024];
  size_t pkcs12_struct_size;
  FILE *fd;

  /* A good idea might be to use gnutls_x509_privkey_get_key_id()
   * to obtain a unique ID.
   */
  gnutls_datum_t key_id = { (char*) "\x00\x00\x07", 3 };

  gnutls_global_init ();

  /* Firstly we create two helper bags, which hold the certificate,
   * and the (encrypted) key.
   */

  gnutls_pkcs12_bag_init (&bag);
  gnutls_pkcs12_bag_init (&key_bag);

  ret = gnutls_pkcs12_bag_set_data (bag, GNUTLS_BAG_CERTIFICATE, cert);
  if (ret < 0)
    {
      fprintf (stderr, "ret: %s\n", gnutls_strerror (ret));
      return 1;
    }

  /* ret now holds the bag's index.
   */
  bag_index = ret;

  /* Associate a friendly name with the given certificate. Used
   * by browsers.
   */
  gnutls_pkcs12_bag_set_friendly_name (bag, bag_index, "My name");

  /* Associate the certificate with the key using a unique key
   * ID.
   */
  gnutls_pkcs12_bag_set_key_id (bag, bag_index, &key_id);

  /* use weak encryption for the certificate. 
   */
  gnutls_pkcs12_bag_encrypt (bag, password, GNUTLS_PKCS_USE_PKCS12_RC2_40);

  /* Now the key.
   */

  ret = gnutls_pkcs12_bag_set_data (key_bag,
				    GNUTLS_BAG_PKCS8_ENCRYPTED_KEY,
				    pkcs8_key);
  if (ret < 0)
    {
      fprintf (stderr, "ret: %s\n", gnutls_strerror (ret));
      return 1;
    }

  /* Note that since the PKCS #8 key is already encrypted we don't
   * bother encrypting that bag.
   */
  bag_index = ret;

  gnutls_pkcs12_bag_set_friendly_name (key_bag, bag_index, "My name");

  gnutls_pkcs12_bag_set_key_id (key_bag, bag_index, &key_id);


  /* The bags were filled. Now create the PKCS #12 structure.
   */
  gnutls_pkcs12_init (&pkcs12);

  /* Insert the two bags in the PKCS #12 structure.
   */

  gnutls_pkcs12_set_bag (pkcs12, bag);
  gnutls_pkcs12_set_bag (pkcs12, key_bag);


  /* Generate a message authentication code for the PKCS #12
   * structure.
   */
  gnutls_pkcs12_generate_mac (pkcs12, password);

  pkcs12_struct_size = sizeof (pkcs12_struct);
  ret =
    gnutls_pkcs12_export (pkcs12, GNUTLS_X509_FMT_DER, pkcs12_struct,
			  &pkcs12_struct_size);
  if (ret < 0)
    {
      fprintf (stderr, "ret: %s\n", gnutls_strerror (ret));
      return 1;
    }

  fd = fopen (OUTFILE, "w");
  if (fd == NULL)
    {
      fprintf (stderr, "cannot open file\n");
      return 1;
    }
  fwrite (pkcs12_struct, 1, pkcs12_struct_size, fd);
  fclose (fd);

  gnutls_pkcs12_bag_deinit (bag);
  gnutls_pkcs12_bag_deinit (key_bag);
  gnutls_pkcs12_deinit (pkcs12);

  return 0;
}