library/x509write_crt.c - security/mbedtls - Rivoreo Source Code Repositories

 /*
  *  X.509 certificate writing
  *
  *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
  *
  *  All rights reserved.
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License along
  *  with this program; if not, write to the Free Software Foundation, Inc.,
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 /*
  * References:
  * - certificates: RFC 5280, updated by RFC 6818
  * - CSRs: PKCS#10 v1.7 aka RFC 2986
  * - attributes: PKCS#9 v2.0 aka RFC 2985
  */

 #include "polarssl/config.h"

 #if defined(POLARSSL_X509_CRT_WRITE_C)

 #include "polarssl/x509_crt.h"
 #include "polarssl/oid.h"
 #include "polarssl/asn1write.h"
 #include "polarssl/sha1.h"

 #if defined(POLARSSL_PEM_WRITE_C)
 #include "polarssl/pem.h"
 #endif /* POLARSSL_PEM_WRITE_C */

 void x509write_crt_init( x509write_cert *ctx )
 {
     memset( ctx, 0, sizeof(x509write_cert) );

     mpi_init( &ctx->serial );
     ctx->version = X509_CRT_VERSION_3;
 }

 void x509write_crt_free( x509write_cert *ctx )
 {
     mpi_free( &ctx->serial );

     asn1_free_named_data_list( &ctx->subject );
     asn1_free_named_data_list( &ctx->issuer );
     asn1_free_named_data_list( &ctx->extensions );

     memset( ctx, 0, sizeof(x509write_cert) );
 }

 void x509write_crt_set_version( x509write_cert *ctx, int version )
 {
     ctx->version = version;
 }

 void x509write_crt_set_md_alg( x509write_cert *ctx, md_type_t md_alg )
 {
     ctx->md_alg = md_alg;
 }

 void x509write_crt_set_subject_key( x509write_cert *ctx, pk_context *key )
 {
     ctx->subject_key = key;
 }

 void x509write_crt_set_issuer_key( x509write_cert *ctx, pk_context *key )
 {
     ctx->issuer_key = key;
 }

 int x509write_crt_set_subject_name( x509write_cert *ctx,
                                     const char *subject_name )
 {
     return x509_string_to_names( &ctx->subject, subject_name );
 }

 int x509write_crt_set_issuer_name( x509write_cert *ctx,
                                    const char *issuer_name )
 {
     return x509_string_to_names( &ctx->issuer, issuer_name );
 }

 int x509write_crt_set_serial( x509write_cert *ctx, const mpi *serial )
 {
     int ret;

     if( ( ret = mpi_copy( &ctx->serial, serial ) ) != 0 )
         return( ret );

     return( 0 );
 }

 int x509write_crt_set_validity( x509write_cert *ctx, const char *not_before,
                                 const char *not_after )
 {
     if( strlen(not_before) != X509_RFC5280_UTC_TIME_LEN - 1 ||
         strlen(not_after)  != X509_RFC5280_UTC_TIME_LEN - 1 )
     {
         return( POLARSSL_ERR_X509_BAD_INPUT_DATA );
     }
     strncpy( ctx->not_before, not_before, X509_RFC5280_UTC_TIME_LEN );
     strncpy( ctx->not_after , not_after , X509_RFC5280_UTC_TIME_LEN );
     ctx->not_before[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
     ctx->not_after[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';

     return( 0 );
 }

 int x509write_crt_set_extension( x509write_cert *ctx,
                                  const char *oid, size_t oid_len,
                                  int critical,
                                  const unsigned char *val, size_t val_len )
 {
     return x509_set_extension( &ctx->extensions, oid, oid_len,
                                critical, val, val_len );
 }

 int x509write_crt_set_basic_constraints( x509write_cert *ctx,
                                          int is_ca, int max_pathlen )
 {
     int ret;
     unsigned char buf[9];
     unsigned char *c = buf + sizeof(buf);
     size_t len = 0;

     memset( buf, 0, sizeof(buf) );

     if( is_ca && max_pathlen > 127 )
         return( POLARSSL_ERR_X509_BAD_INPUT_DATA );

     if( is_ca )
     {
         if( max_pathlen >= 0 )
         {
             ASN1_CHK_ADD( len, asn1_write_int( &c, buf, max_pathlen ) );
         }
         ASN1_CHK_ADD( len, asn1_write_bool( &c, buf, 1 ) );
     }

     ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );

     return x509write_crt_set_extension( ctx, OID_BASIC_CONSTRAINTS,
                                         OID_SIZE( OID_BASIC_CONSTRAINTS ),
                                         0, buf + sizeof(buf) - len, len );
 }

 #if defined(POLARSSL_SHA1_C)
 int x509write_crt_set_subject_key_identifier( x509write_cert *ctx )
 {
     int ret;
     unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
     unsigned char *c = buf + sizeof(buf);
     size_t len = 0;

     memset( buf, 0, sizeof(buf));
     ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->subject_key ) );

     sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
     c = buf + sizeof(buf) - 20;
     len = 20;

     ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_OCTET_STRING ) );

     return x509write_crt_set_extension( ctx, OID_SUBJECT_KEY_IDENTIFIER,
                                         OID_SIZE( OID_SUBJECT_KEY_IDENTIFIER ),
                                         0, buf + sizeof(buf) - len, len );
 }

 int x509write_crt_set_authority_key_identifier( x509write_cert *ctx )
 {
     int ret;
     unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
     unsigned char *c = buf + sizeof(buf);
     size_t len = 0;

     memset( buf, 0, sizeof(buf));
     ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->issuer_key ) );

     sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
     c = buf + sizeof(buf) - 20;
     len = 20;

     ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONTEXT_SPECIFIC | 0 ) );

     ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );

     return x509write_crt_set_extension( ctx, OID_AUTHORITY_KEY_IDENTIFIER,
                                    OID_SIZE( OID_AUTHORITY_KEY_IDENTIFIER ),
                                    0, buf + sizeof(buf) - len, len );
 }
 #endif /* POLARSSL_SHA1_C */

 int x509write_crt_set_key_usage( x509write_cert *ctx, unsigned char key_usage )
 {
     unsigned char buf[4];
     unsigned char *c;
     int ret;

     c = buf + 4;

     if( ( ret = asn1_write_bitstring( &c, buf, &key_usage, 7 ) ) != 4 )
         return( ret );

     ret = x509write_crt_set_extension( ctx, OID_KEY_USAGE,
                                        OID_SIZE( OID_KEY_USAGE ),
                                        1, buf, 4 );
     if( ret != 0 )
         return( ret );

     return( 0 );
 }

 int x509write_crt_set_ns_cert_type( x509write_cert *ctx,
                                     unsigned char ns_cert_type )
 {
     unsigned char buf[4];
     unsigned char *c;
     int ret;

     c = buf + 4;

     if( ( ret = asn1_write_bitstring( &c, buf, &ns_cert_type, 8 ) ) != 4 )
         return( ret );

     ret = x509write_crt_set_extension( ctx, OID_NS_CERT_TYPE,
                                        OID_SIZE( OID_NS_CERT_TYPE ),
                                        0, buf, 4 );
     if( ret != 0 )
         return( ret );

     return( 0 );
 }

 static int x509_write_time( unsigned char **p, unsigned char *start,
                             const char *time, size_t size )
 {
     int ret;
     size_t len = 0;

     /*
      * write ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
      */
     if( time[0] == '2' && time[1] == '0' && time [2] < '5' )
     {
         ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
                                              (const unsigned char *) time + 2,
                                              size - 2 ) );
         ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
         ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_UTC_TIME ) );
     }
     else
     {
         ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
                                                   (const unsigned char *) time,
                                                   size ) );
         ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
         ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_GENERALIZED_TIME ) );
     }

     return( (int) len );
 }

 int x509write_crt_der( x509write_cert *ctx, unsigned char *buf, size_t size,
                        int (*f_rng)(void *, unsigned char *, size_t),
                        void *p_rng )
 {
     int ret;
     const char *sig_oid;
     size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
     unsigned char sig[POLARSSL_MPI_MAX_SIZE];
     unsigned char tmp_buf[2048];
     size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
     size_t len = 0;
     pk_type_t pk_alg;

     /*
      * Prepare data to be signed in tmp_buf
      */
     c = tmp_buf + sizeof( tmp_buf );

     /* Signature algorithm needed in TBS, and later for actual signature */
     pk_alg = pk_get_type( ctx->issuer_key );
     if( pk_alg == POLARSSL_PK_ECKEY )
         pk_alg = POLARSSL_PK_ECDSA;

     if( ( ret = oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
                                         &sig_oid, &sig_oid_len ) ) != 0 )
     {
         return( ret );
     }

     /*
      *  Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
      */
     ASN1_CHK_ADD( len, x509_write_extensions( &c, tmp_buf, ctx->extensions ) );
     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC | ASN1_CONSTRUCTED | 3 ) );

     /*
      *  SubjectPublicKeyInfo
      */
     ASN1_CHK_ADD( pub_len, pk_write_pubkey_der( ctx->subject_key,
                                                 tmp_buf, c - tmp_buf ) );
     c -= pub_len;
     len += pub_len;

     /*
      *  Subject  ::=  Name
      */
     ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->subject ) );

     /*
      *  Validity ::= SEQUENCE {
      *       notBefore      Time,
      *       notAfter       Time }
      */
     sub_len = 0;

     ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_after,
                                             X509_RFC5280_UTC_TIME_LEN ) );

     ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_before,
                                             X509_RFC5280_UTC_TIME_LEN ) );

     len += sub_len;
     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );

     /*
      *  Issuer  ::=  Name
      */
     ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->issuer ) );

     /*
      *  Signature   ::=  AlgorithmIdentifier
      */
     ASN1_CHK_ADD( len, asn1_write_algorithm_identifier( &c, tmp_buf,
                        sig_oid, strlen( sig_oid ), 0 ) );

     /*
      *  Serial   ::=  INTEGER
      */
     ASN1_CHK_ADD( len, asn1_write_mpi( &c, tmp_buf, &ctx->serial ) );

     /*
      *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
      */
     sub_len = 0;
     ASN1_CHK_ADD( sub_len, asn1_write_int( &c, tmp_buf, ctx->version ) );
     len += sub_len;
     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC | ASN1_CONSTRUCTED | 0 ) );

     ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );

     /*
      * Make signature
      */
     md( md_info_from_type( ctx->md_alg ), c, len, hash );

     if( ( ret = pk_sign( ctx->issuer_key, ctx->md_alg, hash, 0, sig, &sig_len,
                          f_rng, p_rng ) ) != 0 )
     {
         return( ret );
     }

     /*
      * Write data to output buffer
      */
     c2 = buf + size;
     ASN1_CHK_ADD( sig_and_oid_len, x509_write_sig( &c2, buf,
                                         sig_oid, sig_oid_len, sig, sig_len ) );

     c2 -= len;
     memcpy( c2, c, len );

     len += sig_and_oid_len;
     ASN1_CHK_ADD( len, asn1_write_len( &c2, buf, len ) );
     ASN1_CHK_ADD( len, asn1_write_tag( &c2, buf, ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );

     return( (int) len );
 }

 #define PEM_BEGIN_CRT           "-----BEGIN CERTIFICATE-----\n"
 #define PEM_END_CRT             "-----END CERTIFICATE-----\n"

 #if defined(POLARSSL_PEM_WRITE_C)
 int x509write_crt_pem( x509write_cert *crt, unsigned char *buf, size_t size,
                        int (*f_rng)(void *, unsigned char *, size_t),
                        void *p_rng )
 {
     int ret;
     unsigned char output_buf[4096];
     size_t olen = 0;

     if( ( ret = x509write_crt_der( crt, output_buf, sizeof(output_buf),
                                    f_rng, p_rng ) ) < 0 )
     {
         return( ret );
     }

     if( ( ret = pem_write_buffer( PEM_BEGIN_CRT, PEM_END_CRT,
                                   output_buf + sizeof(output_buf) - ret,
                                   ret, buf, size, &olen ) ) != 0 )
     {
         return( ret );
     }

     return( 0 );
 }
 #endif /* POLARSSL_PEM_WRITE_C */

 #endif /* POLARSSL_X509_CRT_WRITE_C */
	/*
	* X.509 certificate writing
	*
	* Copyright (C) 2006-2013, Brainspark B.V.
	*
	* This file is part of PolarSSL (http://www.polarssl.org)
	* Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
	*
	* All rights reserved.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
	*/
	/*
	* References:
	* - certificates: RFC 5280, updated by RFC 6818
	* - CSRs: PKCS#10 v1.7 aka RFC 2986
	* - attributes: PKCS#9 v2.0 aka RFC 2985
	*/

	#include "polarssl/config.h"

	#if defined(POLARSSL_X509_CRT_WRITE_C)

	#include "polarssl/x509_crt.h"
	#include "polarssl/oid.h"
	#include "polarssl/asn1write.h"
	#include "polarssl/sha1.h"

	#if defined(POLARSSL_PEM_WRITE_C)
	#include "polarssl/pem.h"
	#endif /* POLARSSL_PEM_WRITE_C */

	void x509write_crt_init( x509write_cert *ctx )
	{
	memset( ctx, 0, sizeof(x509write_cert) );

	mpi_init( &ctx->serial );
	ctx->version = X509_CRT_VERSION_3;
	}

	void x509write_crt_free( x509write_cert *ctx )
	{
	mpi_free( &ctx->serial );

	asn1_free_named_data_list( &ctx->subject );
	asn1_free_named_data_list( &ctx->issuer );
	asn1_free_named_data_list( &ctx->extensions );

	memset( ctx, 0, sizeof(x509write_cert) );
	}

	void x509write_crt_set_version( x509write_cert *ctx, int version )
	{
	ctx->version = version;
	}

	void x509write_crt_set_md_alg( x509write_cert *ctx, md_type_t md_alg )
	{
	ctx->md_alg = md_alg;
	}

	void x509write_crt_set_subject_key( x509write_cert ctx, pk_context key )
	{
	ctx->subject_key = key;
	}

	void x509write_crt_set_issuer_key( x509write_cert ctx, pk_context key )
	{
	ctx->issuer_key = key;
	}

	int x509write_crt_set_subject_name( x509write_cert *ctx,
	const char *subject_name )
	{
	return x509_string_to_names( &ctx->subject, subject_name );
	}

	int x509write_crt_set_issuer_name( x509write_cert *ctx,
	const char *issuer_name )
	{
	return x509_string_to_names( &ctx->issuer, issuer_name );
	}

	int x509write_crt_set_serial( x509write_cert ctx, const mpi serial )
	{
	int ret;

	if( ( ret = mpi_copy( &ctx->serial, serial ) ) != 0 )
	return( ret );

	return( 0 );
	}

	int x509write_crt_set_validity( x509write_cert ctx, const char not_before,
	const char *not_after )
	{
	if( strlen(not_before) != X509_RFC5280_UTC_TIME_LEN - 1 \|\|
	strlen(not_after) != X509_RFC5280_UTC_TIME_LEN - 1 )
	{
	return( POLARSSL_ERR_X509_BAD_INPUT_DATA );
	}
	strncpy( ctx->not_before, not_before, X509_RFC5280_UTC_TIME_LEN );
	strncpy( ctx->not_after , not_after , X509_RFC5280_UTC_TIME_LEN );
	ctx->not_before[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';
	ctx->not_after[X509_RFC5280_UTC_TIME_LEN - 1] = 'Z';

	return( 0 );
	}

	int x509write_crt_set_extension( x509write_cert *ctx,
	const char *oid, size_t oid_len,
	int critical,
	const unsigned char *val, size_t val_len )
	{
	return x509_set_extension( &ctx->extensions, oid, oid_len,
	critical, val, val_len );
	}

	int x509write_crt_set_basic_constraints( x509write_cert *ctx,
	int is_ca, int max_pathlen )
	{
	int ret;
	unsigned char buf[9];
	unsigned char *c = buf + sizeof(buf);
	size_t len = 0;

	memset( buf, 0, sizeof(buf) );

	if( is_ca && max_pathlen > 127 )
	return( POLARSSL_ERR_X509_BAD_INPUT_DATA );

	if( is_ca )
	{
	if( max_pathlen >= 0 )
	{
	ASN1_CHK_ADD( len, asn1_write_int( &c, buf, max_pathlen ) );
	}
	ASN1_CHK_ADD( len, asn1_write_bool( &c, buf, 1 ) );
	}

	ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );

	return x509write_crt_set_extension( ctx, OID_BASIC_CONSTRAINTS,
	OID_SIZE( OID_BASIC_CONSTRAINTS ),
	0, buf + sizeof(buf) - len, len );
	}

	#if defined(POLARSSL_SHA1_C)
	int x509write_crt_set_subject_key_identifier( x509write_cert *ctx )
	{
	int ret;
	unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
	unsigned char *c = buf + sizeof(buf);
	size_t len = 0;

	memset( buf, 0, sizeof(buf));
	ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->subject_key ) );

	sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
	c = buf + sizeof(buf) - 20;
	len = 20;

	ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_OCTET_STRING ) );

	return x509write_crt_set_extension( ctx, OID_SUBJECT_KEY_IDENTIFIER,
	OID_SIZE( OID_SUBJECT_KEY_IDENTIFIER ),
	0, buf + sizeof(buf) - len, len );
	}

	int x509write_crt_set_authority_key_identifier( x509write_cert *ctx )
	{
	int ret;
	unsigned char buf[POLARSSL_MPI_MAX_SIZE * 2 + 20]; /* tag, length + 2xMPI */
	unsigned char *c = buf + sizeof(buf);
	size_t len = 0;

	memset( buf, 0, sizeof(buf));
	ASN1_CHK_ADD( len, pk_write_pubkey( &c, buf, ctx->issuer_key ) );

	sha1( buf + sizeof(buf) - len, len, buf + sizeof(buf) - 20 );
	c = buf + sizeof(buf) - 20;
	len = 20;

	ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONTEXT_SPECIFIC \| 0 ) );

	ASN1_CHK_ADD( len, asn1_write_len( &c, buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );

	return x509write_crt_set_extension( ctx, OID_AUTHORITY_KEY_IDENTIFIER,
	OID_SIZE( OID_AUTHORITY_KEY_IDENTIFIER ),
	0, buf + sizeof(buf) - len, len );
	}
	#endif /* POLARSSL_SHA1_C */

	int x509write_crt_set_key_usage( x509write_cert *ctx, unsigned char key_usage )
	{
	unsigned char buf[4];
	unsigned char *c;
	int ret;

	c = buf + 4;

	if( ( ret = asn1_write_bitstring( &c, buf, &key_usage, 7 ) ) != 4 )
	return( ret );

	ret = x509write_crt_set_extension( ctx, OID_KEY_USAGE,
	OID_SIZE( OID_KEY_USAGE ),
	1, buf, 4 );
	if( ret != 0 )
	return( ret );

	return( 0 );
	}

	int x509write_crt_set_ns_cert_type( x509write_cert *ctx,
	unsigned char ns_cert_type )
	{
	unsigned char buf[4];
	unsigned char *c;
	int ret;

	c = buf + 4;

	if( ( ret = asn1_write_bitstring( &c, buf, &ns_cert_type, 8 ) ) != 4 )
	return( ret );

	ret = x509write_crt_set_extension( ctx, OID_NS_CERT_TYPE,
	OID_SIZE( OID_NS_CERT_TYPE ),
	0, buf, 4 );
	if( ret != 0 )
	return( ret );

	return( 0 );
	}

	static int x509_write_time( unsigned char *p, unsigned char start,
	const char *time, size_t size )
	{
	int ret;
	size_t len = 0;

	/*
	* write ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
	*/
	if( time[0] == '2' && time[1] == '0' && time [2] < '5' )
	{
	ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
	(const unsigned char *) time + 2,
	size - 2 ) );
	ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_UTC_TIME ) );
	}
	else
	{
	ASN1_CHK_ADD( len, asn1_write_raw_buffer( p, start,
	(const unsigned char *) time,
	size ) );
	ASN1_CHK_ADD( len, asn1_write_len( p, start, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( p, start, ASN1_GENERALIZED_TIME ) );
	}

	return( (int) len );
	}

	int x509write_crt_der( x509write_cert ctx, unsigned char buf, size_t size,
	int (f_rng)(void , unsigned char *, size_t),
	void *p_rng )
	{
	int ret;
	const char *sig_oid;
	size_t sig_oid_len = 0;
	unsigned char c, c2;
	unsigned char hash[64];
	unsigned char sig[POLARSSL_MPI_MAX_SIZE];
	unsigned char tmp_buf[2048];
	size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
	size_t len = 0;
	pk_type_t pk_alg;

	/*
	* Prepare data to be signed in tmp_buf
	*/
	c = tmp_buf + sizeof( tmp_buf );

	/* Signature algorithm needed in TBS, and later for actual signature */
	pk_alg = pk_get_type( ctx->issuer_key );
	if( pk_alg == POLARSSL_PK_ECKEY )
	pk_alg = POLARSSL_PK_ECDSA;

	if( ( ret = oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
	&sig_oid, &sig_oid_len ) ) != 0 )
	{
	return( ret );
	}

	/*
	* Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
	*/
	ASN1_CHK_ADD( len, x509_write_extensions( &c, tmp_buf, ctx->extensions ) );
	ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );
	ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC \| ASN1_CONSTRUCTED \| 3 ) );

	/*
	* SubjectPublicKeyInfo
	*/
	ASN1_CHK_ADD( pub_len, pk_write_pubkey_der( ctx->subject_key,
	tmp_buf, c - tmp_buf ) );
	c -= pub_len;
	len += pub_len;

	/*
	* Subject ::= Name
	*/
	ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->subject ) );

	/*
	* Validity ::= SEQUENCE {
	* notBefore Time,
	* notAfter Time }
	*/
	sub_len = 0;

	ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_after,
	X509_RFC5280_UTC_TIME_LEN ) );

	ASN1_CHK_ADD( sub_len, x509_write_time( &c, tmp_buf, ctx->not_before,
	X509_RFC5280_UTC_TIME_LEN ) );

	len += sub_len;
	ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );

	/*
	* Issuer ::= Name
	*/
	ASN1_CHK_ADD( len, x509_write_names( &c, tmp_buf, ctx->issuer ) );

	/*
	* Signature ::= AlgorithmIdentifier
	*/
	ASN1_CHK_ADD( len, asn1_write_algorithm_identifier( &c, tmp_buf,
	sig_oid, strlen( sig_oid ), 0 ) );

	/*
	* Serial ::= INTEGER
	*/
	ASN1_CHK_ADD( len, asn1_write_mpi( &c, tmp_buf, &ctx->serial ) );

	/*
	* Version ::= INTEGER { v1(0), v2(1), v3(2) }
	*/
	sub_len = 0;
	ASN1_CHK_ADD( sub_len, asn1_write_int( &c, tmp_buf, ctx->version ) );
	len += sub_len;
	ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, sub_len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONTEXT_SPECIFIC \| ASN1_CONSTRUCTED \| 0 ) );

	ASN1_CHK_ADD( len, asn1_write_len( &c, tmp_buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c, tmp_buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );

	/*
	* Make signature
	*/
	md( md_info_from_type( ctx->md_alg ), c, len, hash );

	if( ( ret = pk_sign( ctx->issuer_key, ctx->md_alg, hash, 0, sig, &sig_len,
	f_rng, p_rng ) ) != 0 )
	{
	return( ret );
	}

	/*
	* Write data to output buffer
	*/
	c2 = buf + size;
	ASN1_CHK_ADD( sig_and_oid_len, x509_write_sig( &c2, buf,
	sig_oid, sig_oid_len, sig, sig_len ) );

	c2 -= len;
	memcpy( c2, c, len );

	len += sig_and_oid_len;
	ASN1_CHK_ADD( len, asn1_write_len( &c2, buf, len ) );
	ASN1_CHK_ADD( len, asn1_write_tag( &c2, buf, ASN1_CONSTRUCTED \| ASN1_SEQUENCE ) );

	return( (int) len );
	}

	#define PEM_BEGIN_CRT "-----BEGIN CERTIFICATE-----\n"
	#define PEM_END_CRT "-----END CERTIFICATE-----\n"

	#if defined(POLARSSL_PEM_WRITE_C)
	int x509write_crt_pem( x509write_cert crt, unsigned char buf, size_t size,
	int (f_rng)(void , unsigned char *, size_t),
	void *p_rng )
	{
	int ret;
	unsigned char output_buf[4096];
	size_t olen = 0;

	if( ( ret = x509write_crt_der( crt, output_buf, sizeof(output_buf),
	f_rng, p_rng ) ) < 0 )
	{
	return( ret );
	}

	if( ( ret = pem_write_buffer( PEM_BEGIN_CRT, PEM_END_CRT,
	output_buf + sizeof(output_buf) - ret,
	ret, buf, size, &olen ) ) != 0 )
	{
	return( ret );
	}

	return( 0 );
	}
	#endif /* POLARSSL_PEM_WRITE_C */

	#endif /* POLARSSL_X509_CRT_WRITE_C */