7.5.4 PKCS #12 structure generation example

This small program demonstrates the usage of the PKCS #12 API, by generating such a 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 *fp;

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

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

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

	return 0;
}