library/x509_create.c - mirror/mbed-tls.git - TrustedFirmware Git Browser

 /*
  *  X.509 base functions for creating certificates / CSRs
  *
  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
  *  not use this file except in compliance with the License.
  *  You may obtain a copy of the License at
  *
  *  http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  *
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */

 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif

 #if defined(MBEDTLS_X509_CREATE_C)

 #include "mbedtls/x509.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/oid.h"

 #include <string.h>

 typedef struct {
     const char *name;
     size_t name_len;
     const char*oid;
 } x509_attr_descriptor_t;

 #define ADD_STRLEN( s )     s, sizeof( s ) - 1

 static const x509_attr_descriptor_t x509_attrs[] =
 {
     { ADD_STRLEN( "CN" ),                       MBEDTLS_OID_AT_CN },
     { ADD_STRLEN( "commonName" ),               MBEDTLS_OID_AT_CN },
     { ADD_STRLEN( "C" ),                        MBEDTLS_OID_AT_COUNTRY },
     { ADD_STRLEN( "countryName" ),              MBEDTLS_OID_AT_COUNTRY },
     { ADD_STRLEN( "O" ),                        MBEDTLS_OID_AT_ORGANIZATION },
     { ADD_STRLEN( "organizationName" ),         MBEDTLS_OID_AT_ORGANIZATION },
     { ADD_STRLEN( "L" ),                        MBEDTLS_OID_AT_LOCALITY },
     { ADD_STRLEN( "locality" ),                 MBEDTLS_OID_AT_LOCALITY },
     { ADD_STRLEN( "R" ),                        MBEDTLS_OID_PKCS9_EMAIL },
     { ADD_STRLEN( "OU" ),                       MBEDTLS_OID_AT_ORG_UNIT },
     { ADD_STRLEN( "organizationalUnitName" ),   MBEDTLS_OID_AT_ORG_UNIT },
     { ADD_STRLEN( "ST" ),                       MBEDTLS_OID_AT_STATE },
     { ADD_STRLEN( "stateOrProvinceName" ),      MBEDTLS_OID_AT_STATE },
     { ADD_STRLEN( "emailAddress" ),             MBEDTLS_OID_PKCS9_EMAIL },
     { ADD_STRLEN( "serialNumber" ),             MBEDTLS_OID_AT_SERIAL_NUMBER },
     { ADD_STRLEN( "postalAddress" ),            MBEDTLS_OID_AT_POSTAL_ADDRESS },
     { ADD_STRLEN( "postalCode" ),               MBEDTLS_OID_AT_POSTAL_CODE },
     { ADD_STRLEN( "dnQualifier" ),              MBEDTLS_OID_AT_DN_QUALIFIER },
     { ADD_STRLEN( "title" ),                    MBEDTLS_OID_AT_TITLE },
     { ADD_STRLEN( "surName" ),                  MBEDTLS_OID_AT_SUR_NAME },
     { ADD_STRLEN( "SN" ),                       MBEDTLS_OID_AT_SUR_NAME },
     { ADD_STRLEN( "givenName" ),                MBEDTLS_OID_AT_GIVEN_NAME },
     { ADD_STRLEN( "GN" ),                       MBEDTLS_OID_AT_GIVEN_NAME },
     { ADD_STRLEN( "initials" ),                 MBEDTLS_OID_AT_INITIALS },
     { ADD_STRLEN( "pseudonym" ),                MBEDTLS_OID_AT_PSEUDONYM },
     { ADD_STRLEN( "generationQualifier" ),      MBEDTLS_OID_AT_GENERATION_QUALIFIER },
     { ADD_STRLEN( "domainComponent" ),          MBEDTLS_OID_DOMAIN_COMPONENT },
     { ADD_STRLEN( "DC" ),                       MBEDTLS_OID_DOMAIN_COMPONENT },
     { NULL, 0, NULL }
 };

 static const char *x509_at_oid_from_name( const char *name, size_t name_len )
 {
     const x509_attr_descriptor_t *cur;

     for( cur = x509_attrs; cur->name != NULL; cur++ )
         if( cur->name_len == name_len &&
             strncmp( cur->name, name, name_len ) == 0 )
             break;

     return( cur->oid );
 }

 int mbedtls_x509_string_to_names( mbedtls_asn1_named_data **head, const char *name )
 {
     int ret = 0;
     const char *s = name, *c = s;
     const char *end = s + strlen( s );
     const char *oid = NULL;
     int in_tag = 1;
     char data[MBEDTLS_X509_MAX_DN_NAME_SIZE];
     char *d = data;

     /* Clear existing chain if present */
     mbedtls_asn1_free_named_data_list( head );

     while( c <= end )
     {
         if( in_tag && *c == '=' )
         {
             if( ( oid = x509_at_oid_from_name( s, c - s ) ) == NULL )
             {
                 ret = MBEDTLS_ERR_X509_UNKNOWN_OID;
                 goto exit;
             }

             s = c + 1;
             in_tag = 0;
             d = data;
         }

         if( !in_tag && *c == '\\' && c != end )
         {
             c++;

             /* Check for valid escaped characters */
             if( c == end || *c != ',' )
             {
                 ret = MBEDTLS_ERR_X509_INVALID_NAME;
                 goto exit;
             }
         }
         else if( !in_tag && ( *c == ',' || c == end ) )
         {
             if( mbedtls_asn1_store_named_data( head, oid, strlen( oid ),
                                        (unsigned char *) data,
                                        d - data ) == NULL )
             {
                 return( MBEDTLS_ERR_X509_ALLOC_FAILED );
             }

             while( c < end && *(c + 1) == ' ' )
                 c++;

             s = c + 1;
             in_tag = 1;
         }

         if( !in_tag && s != c + 1 )
         {
             *(d++) = *c;

             if( d - data == MBEDTLS_X509_MAX_DN_NAME_SIZE )
             {
                 ret = MBEDTLS_ERR_X509_INVALID_NAME;
                 goto exit;
             }
         }

         c++;
     }

 exit:

     return( ret );
 }

 /* The first byte of the value in the mbedtls_asn1_named_data structure is reserved
  * to store the critical boolean for us
  */
 int mbedtls_x509_set_extension( mbedtls_asn1_named_data **head, const char *oid, size_t oid_len,
                         int critical, const unsigned char *val, size_t val_len )
 {
     mbedtls_asn1_named_data *cur;

     if( ( cur = mbedtls_asn1_store_named_data( head, oid, oid_len,
                                        NULL, val_len + 1 ) ) == NULL )
     {
         return( MBEDTLS_ERR_X509_ALLOC_FAILED );
     }

     cur->val.p[0] = critical;
     memcpy( cur->val.p + 1, val, val_len );

     return( 0 );
 }

 /*
  *  RelativeDistinguishedName ::=
  *    SET OF AttributeTypeAndValue
  *
  *  AttributeTypeAndValue ::= SEQUENCE {
  *    type     AttributeType,
  *    value    AttributeValue }
  *
  *  AttributeType ::= OBJECT IDENTIFIER
  *
  *  AttributeValue ::= ANY DEFINED BY AttributeType
  */
 static int x509_write_name( unsigned char **p, unsigned char *start,
                             const char *oid, size_t oid_len,
                             const unsigned char *name, size_t name_len )
 {
     int ret;
     size_t len = 0;

     // Write PrintableString for all except MBEDTLS_OID_PKCS9_EMAIL
     //
     if( MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_EMAIL ) == oid_len &&
         memcmp( oid, MBEDTLS_OID_PKCS9_EMAIL, oid_len ) == 0 )
     {
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_ia5_string( p, start,
                                                   (const char *) name,
                                                   name_len ) );
     }
     else
     {
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_printable_string( p, start,
                                                         (const char *) name,
                                                         name_len ) );
     }

     // Write OID
     //
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( p, start, oid, oid_len ) );

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED |
                                                  MBEDTLS_ASN1_SEQUENCE ) );

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED |
                                                  MBEDTLS_ASN1_SET ) );

     return( (int) len );
 }

 int mbedtls_x509_write_names( unsigned char **p, unsigned char *start,
                       mbedtls_asn1_named_data *first )
 {
     int ret;
     size_t len = 0;
     mbedtls_asn1_named_data *cur = first;

     while( cur != NULL )
     {
         MBEDTLS_ASN1_CHK_ADD( len, x509_write_name( p, start, (char *) cur->oid.p,
                                             cur->oid.len,
                                             cur->val.p, cur->val.len ) );
         cur = cur->next;
     }

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED |
                                                  MBEDTLS_ASN1_SEQUENCE ) );

     return( (int) len );
 }

 int mbedtls_x509_write_sig( unsigned char **p, unsigned char *start,
                     const char *oid, size_t oid_len,
                     unsigned char *sig, size_t size )
 {
     int ret;
     size_t len = 0;

     if( *p < start || (size_t)( *p - start ) < size )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

     len = size;
     (*p) -= len;
     memcpy( *p, sig, len );

     if( *p - start < 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

     *--(*p) = 0;
     len += 1;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BIT_STRING ) );

     // Write OID
     //
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_algorithm_identifier( p, start, oid,
                                                         oid_len, 0 ) );

     return( (int) len );
 }

 static int x509_write_extension( unsigned char **p, unsigned char *start,
                                  mbedtls_asn1_named_data *ext )
 {
     int ret;
     size_t len = 0;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, ext->val.p + 1,
                                               ext->val.len - 1 ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, ext->val.len - 1 ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OCTET_STRING ) );

     if( ext->val.p[0] != 0 )
     {
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_bool( p, start, 1 ) );
     }

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, ext->oid.p,
                                               ext->oid.len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, ext->oid.len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OID ) );

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED |
                                                  MBEDTLS_ASN1_SEQUENCE ) );

     return( (int) len );
 }

 /*
  * Extension  ::=  SEQUENCE  {
  *     extnID      OBJECT IDENTIFIER,
  *     critical    BOOLEAN DEFAULT FALSE,
  *     extnValue   OCTET STRING
  *                 -- contains the DER encoding of an ASN.1 value
  *                 -- corresponding to the extension type identified
  *                 -- by extnID
  *     }
  */
 int mbedtls_x509_write_extensions( unsigned char **p, unsigned char *start,
                            mbedtls_asn1_named_data *first )
 {
     int ret;
     size_t len = 0;
     mbedtls_asn1_named_data *cur_ext = first;

     while( cur_ext != NULL )
     {
         MBEDTLS_ASN1_CHK_ADD( len, x509_write_extension( p, start, cur_ext ) );
         cur_ext = cur_ext->next;
     }

     return( (int) len );
 }

 #endif /* MBEDTLS_X509_CREATE_C */
	/*
	* X.509 base functions for creating certificates / CSRs
	*
	* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
	* SPDX-License-Identifier: Apache-2.0
	*
	* Licensed under the Apache License, Version 2.0 (the "License"); you may
	* not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
	* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*
	* This file is part of mbed TLS (https://tls.mbed.org)
	*/

	#if !defined(MBEDTLS_CONFIG_FILE)
	#include "mbedtls/config.h"
	#else
	#include MBEDTLS_CONFIG_FILE
	#endif

	#if defined(MBEDTLS_X509_CREATE_C)

	#include "mbedtls/x509.h"
	#include "mbedtls/asn1write.h"
	#include "mbedtls/oid.h"

	#include <string.h>

	typedef struct {
	const char *name;
	size_t name_len;
	const char*oid;
	} x509_attr_descriptor_t;

	#define ADD_STRLEN( s ) s, sizeof( s ) - 1

	static const x509_attr_descriptor_t x509_attrs[] =
	{
	{ ADD_STRLEN( "CN" ), MBEDTLS_OID_AT_CN },
	{ ADD_STRLEN( "commonName" ), MBEDTLS_OID_AT_CN },
	{ ADD_STRLEN( "C" ), MBEDTLS_OID_AT_COUNTRY },
	{ ADD_STRLEN( "countryName" ), MBEDTLS_OID_AT_COUNTRY },
	{ ADD_STRLEN( "O" ), MBEDTLS_OID_AT_ORGANIZATION },
	{ ADD_STRLEN( "organizationName" ), MBEDTLS_OID_AT_ORGANIZATION },
	{ ADD_STRLEN( "L" ), MBEDTLS_OID_AT_LOCALITY },
	{ ADD_STRLEN( "locality" ), MBEDTLS_OID_AT_LOCALITY },
	{ ADD_STRLEN( "R" ), MBEDTLS_OID_PKCS9_EMAIL },
	{ ADD_STRLEN( "OU" ), MBEDTLS_OID_AT_ORG_UNIT },
	{ ADD_STRLEN( "organizationalUnitName" ), MBEDTLS_OID_AT_ORG_UNIT },
	{ ADD_STRLEN( "ST" ), MBEDTLS_OID_AT_STATE },
	{ ADD_STRLEN( "stateOrProvinceName" ), MBEDTLS_OID_AT_STATE },
	{ ADD_STRLEN( "emailAddress" ), MBEDTLS_OID_PKCS9_EMAIL },
	{ ADD_STRLEN( "serialNumber" ), MBEDTLS_OID_AT_SERIAL_NUMBER },
	{ ADD_STRLEN( "postalAddress" ), MBEDTLS_OID_AT_POSTAL_ADDRESS },
	{ ADD_STRLEN( "postalCode" ), MBEDTLS_OID_AT_POSTAL_CODE },
	{ ADD_STRLEN( "dnQualifier" ), MBEDTLS_OID_AT_DN_QUALIFIER },
	{ ADD_STRLEN( "title" ), MBEDTLS_OID_AT_TITLE },
	{ ADD_STRLEN( "surName" ), MBEDTLS_OID_AT_SUR_NAME },
	{ ADD_STRLEN( "SN" ), MBEDTLS_OID_AT_SUR_NAME },
	{ ADD_STRLEN( "givenName" ), MBEDTLS_OID_AT_GIVEN_NAME },
	{ ADD_STRLEN( "GN" ), MBEDTLS_OID_AT_GIVEN_NAME },
	{ ADD_STRLEN( "initials" ), MBEDTLS_OID_AT_INITIALS },
	{ ADD_STRLEN( "pseudonym" ), MBEDTLS_OID_AT_PSEUDONYM },
	{ ADD_STRLEN( "generationQualifier" ), MBEDTLS_OID_AT_GENERATION_QUALIFIER },
	{ ADD_STRLEN( "domainComponent" ), MBEDTLS_OID_DOMAIN_COMPONENT },
	{ ADD_STRLEN( "DC" ), MBEDTLS_OID_DOMAIN_COMPONENT },
	{ NULL, 0, NULL }
	};

	static const char x509_at_oid_from_name( const char name, size_t name_len )
	{
	const x509_attr_descriptor_t *cur;

	for( cur = x509_attrs; cur->name != NULL; cur++ )
	if( cur->name_len == name_len &&
	strncmp( cur->name, name, name_len ) == 0 )
	break;

	return( cur->oid );
	}

	int mbedtls_x509_string_to_names( mbedtls_asn1_named_data *head, const char name )
	{
	int ret = 0;
	const char s = name, c = s;
	const char *end = s + strlen( s );
	const char *oid = NULL;
	int in_tag = 1;
	char data[MBEDTLS_X509_MAX_DN_NAME_SIZE];
	char *d = data;

	/* Clear existing chain if present */
	mbedtls_asn1_free_named_data_list( head );

	while( c <= end )
	{
	if( in_tag && *c == '=' )
	{
	if( ( oid = x509_at_oid_from_name( s, c - s ) ) == NULL )
	{
	ret = MBEDTLS_ERR_X509_UNKNOWN_OID;
	goto exit;
	}

	s = c + 1;
	in_tag = 0;
	d = data;
	}

	if( !in_tag && *c == '\\' && c != end )
	{
	c++;

	/* Check for valid escaped characters */
	if( c == end \|\| *c != ',' )
	{
	ret = MBEDTLS_ERR_X509_INVALID_NAME;
	goto exit;
	}
	}
	else if( !in_tag && ( *c == ',' \|\| c == end ) )
	{
	if( mbedtls_asn1_store_named_data( head, oid, strlen( oid ),
	(unsigned char *) data,
	d - data ) == NULL )
	{
	return( MBEDTLS_ERR_X509_ALLOC_FAILED );
	}

	while( c < end && *(c + 1) == ' ' )
	c++;

	s = c + 1;
	in_tag = 1;
	}

	if( !in_tag && s != c + 1 )
	{
	(d++) = c;

	if( d - data == MBEDTLS_X509_MAX_DN_NAME_SIZE )
	{
	ret = MBEDTLS_ERR_X509_INVALID_NAME;
	goto exit;
	}
	}

	c++;
	}

	exit:

	return( ret );
	}

	/* The first byte of the value in the mbedtls_asn1_named_data structure is reserved
	* to store the critical boolean for us
	*/
	int mbedtls_x509_set_extension( mbedtls_asn1_named_data *head, const char oid, size_t oid_len,
	int critical, const unsigned char *val, size_t val_len )
	{
	mbedtls_asn1_named_data *cur;

	if( ( cur = mbedtls_asn1_store_named_data( head, oid, oid_len,
	NULL, val_len + 1 ) ) == NULL )
	{
	return( MBEDTLS_ERR_X509_ALLOC_FAILED );
	}

	cur->val.p[0] = critical;
	memcpy( cur->val.p + 1, val, val_len );

	return( 0 );
	}

	/*
	* RelativeDistinguishedName ::=
	* SET OF AttributeTypeAndValue
	*
	* AttributeTypeAndValue ::= SEQUENCE {
	* type AttributeType,
	* value AttributeValue }
	*
	* AttributeType ::= OBJECT IDENTIFIER
	*
	* AttributeValue ::= ANY DEFINED BY AttributeType
	*/
	static int x509_write_name( unsigned char *p, unsigned char start,
	const char *oid, size_t oid_len,
	const unsigned char *name, size_t name_len )
	{
	int ret;
	size_t len = 0;

	// Write PrintableString for all except MBEDTLS_OID_PKCS9_EMAIL
	//
	if( MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_EMAIL ) == oid_len &&
	memcmp( oid, MBEDTLS_OID_PKCS9_EMAIL, oid_len ) == 0 )
	{
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_ia5_string( p, start,
	(const char *) name,
	name_len ) );
	}
	else
	{
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_printable_string( p, start,
	(const char *) name,
	name_len ) );
	}

	// Write OID
	//
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( p, start, oid, oid_len ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SET ) );

	return( (int) len );
	}

	int mbedtls_x509_write_names( unsigned char *p, unsigned char start,
	mbedtls_asn1_named_data *first )
	{
	int ret;
	size_t len = 0;
	mbedtls_asn1_named_data *cur = first;

	while( cur != NULL )
	{
	MBEDTLS_ASN1_CHK_ADD( len, x509_write_name( p, start, (char *) cur->oid.p,
	cur->oid.len,
	cur->val.p, cur->val.len ) );
	cur = cur->next;
	}

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE ) );

	return( (int) len );
	}

	int mbedtls_x509_write_sig( unsigned char *p, unsigned char start,
	const char *oid, size_t oid_len,
	unsigned char *sig, size_t size )
	{
	int ret;
	size_t len = 0;

	if( p < start \|\| (size_t)( p - start ) < size )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	len = size;
	(*p) -= len;
	memcpy( *p, sig, len );

	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = 0;
	len += 1;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BIT_STRING ) );

	// Write OID
	//
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_algorithm_identifier( p, start, oid,
	oid_len, 0 ) );

	return( (int) len );
	}

	static int x509_write_extension( unsigned char *p, unsigned char start,
	mbedtls_asn1_named_data *ext )
	{
	int ret;
	size_t len = 0;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, ext->val.p + 1,
	ext->val.len - 1 ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, ext->val.len - 1 ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OCTET_STRING ) );

	if( ext->val.p[0] != 0 )
	{
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_bool( p, start, 1 ) );
	}

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, ext->oid.p,
	ext->oid.len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, ext->oid.len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OID ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED \|
	MBEDTLS_ASN1_SEQUENCE ) );

	return( (int) len );
	}

	/*
	* Extension ::= SEQUENCE {
	* extnID OBJECT IDENTIFIER,
	* critical BOOLEAN DEFAULT FALSE,
	* extnValue OCTET STRING
	* -- contains the DER encoding of an ASN.1 value
	* -- corresponding to the extension type identified
	* -- by extnID
	* }
	*/
	int mbedtls_x509_write_extensions( unsigned char *p, unsigned char start,
	mbedtls_asn1_named_data *first )
	{
	int ret;
	size_t len = 0;
	mbedtls_asn1_named_data *cur_ext = first;

	while( cur_ext != NULL )
	{
	MBEDTLS_ASN1_CHK_ADD( len, x509_write_extension( p, start, cur_ext ) );
	cur_ext = cur_ext->next;
	}

	return( (int) len );
	}

	#endif /* MBEDTLS_X509_CREATE_C */