library/x509write_csr.c - third_party/github/ARMmbed/mbedtls - Git at Google

 /*
  *  X.509 Certificate Signing Request writing
  *
  *  Copyright The Mbed TLS Contributors
  *  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.
  */
 /*
  * References:
  * - CSRs: PKCS#10 v1.7 aka RFC 2986
  * - attributes: PKCS#9 v2.0 aka RFC 2985
  */

 #include "common.h"

 #if defined(MBEDTLS_X509_CSR_WRITE_C)

 #include "mbedtls/x509_csr.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/error.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/platform_util.h"

 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 #include "psa/crypto.h"
 #include "mbedtls/psa_util.h"
 #endif

 #include <string.h>
 #include <stdlib.h>

 #if defined(MBEDTLS_PEM_WRITE_C)
 #include "mbedtls/pem.h"
 #endif

 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
 #include <stdlib.h>
 #define mbedtls_calloc    calloc
 #define mbedtls_free      free
 #endif

 void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
 {
     memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
 }

 void mbedtls_x509write_csr_free( mbedtls_x509write_csr *ctx )
 {
     mbedtls_asn1_free_named_data_list( &ctx->subject );
     mbedtls_asn1_free_named_data_list( &ctx->extensions );

     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_x509write_csr ) );
 }

 void mbedtls_x509write_csr_set_md_alg( mbedtls_x509write_csr *ctx, mbedtls_md_type_t md_alg )
 {
     ctx->md_alg = md_alg;
 }

 void mbedtls_x509write_csr_set_key( mbedtls_x509write_csr *ctx, mbedtls_pk_context *key )
 {
     ctx->key = key;
 }

 int mbedtls_x509write_csr_set_subject_name( mbedtls_x509write_csr *ctx,
                                     const char *subject_name )
 {
     return mbedtls_x509_string_to_names( &ctx->subject, subject_name );
 }

 int mbedtls_x509write_csr_set_extension( mbedtls_x509write_csr *ctx,
                                  const char *oid, size_t oid_len,
                                  int critical,
                                  const unsigned char *val, size_t val_len )
 {
     return mbedtls_x509_set_extension( &ctx->extensions, oid, oid_len,
                                critical, val, val_len );
 }

 int mbedtls_x509write_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage )
 {
     unsigned char buf[4] = {0};
     unsigned char *c;
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

     c = buf + 4;

     ret = mbedtls_asn1_write_named_bitstring( &c, buf, &key_usage, 8 );
     if( ret < 3 || ret > 4 )
         return( ret );

     ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
                                        MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
                                        0, c, (size_t)ret );
     if( ret != 0 )
         return( ret );

     return( 0 );
 }

 int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
                                     unsigned char ns_cert_type )
 {
     unsigned char buf[4] = {0};
     unsigned char *c;
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

     c = buf + 4;

     ret = mbedtls_asn1_write_named_bitstring( &c, buf, &ns_cert_type, 8 );
     if( ret < 3 || ret > 4 )
         return( ret );

     ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
                                        MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
                                        0, c, (size_t)ret );
     if( ret != 0 )
         return( ret );

     return( 0 );
 }

 static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
                                  unsigned char *buf,
                                  size_t size,
                                  unsigned char *sig,
                                  int (*f_rng)(void *, unsigned char *, size_t),
                                  void *p_rng )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     const char *sig_oid;
     size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
     size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
     size_t len = 0;
     mbedtls_pk_type_t pk_alg;
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_hash_operation_t hash_operation = PSA_HASH_OPERATION_INIT;
     size_t hash_len;
     psa_algorithm_t hash_alg = mbedtls_psa_translate_md( ctx->md_alg );
 #endif /* MBEDTLS_USE_PSA_CRYPTO */

     /* Write the CSR backwards starting from the end of buf */
     c = buf + size;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
                                                            ctx->extensions ) );

     if( len )
     {
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
         MBEDTLS_ASN1_CHK_ADD( len,
             mbedtls_asn1_write_tag(
                 &c, buf,
                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
         MBEDTLS_ASN1_CHK_ADD( len,
             mbedtls_asn1_write_tag(
                 &c, buf,
                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) );

         MBEDTLS_ASN1_CHK_ADD( len,
             mbedtls_asn1_write_oid(
                 &c, buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
                 MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );

         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
         MBEDTLS_ASN1_CHK_ADD( len,
             mbedtls_asn1_write_tag(
                 &c, buf,
                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
     }

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
     MBEDTLS_ASN1_CHK_ADD( len,
         mbedtls_asn1_write_tag(
             &c, buf,
             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );

     MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
                                                               buf, c - buf ) );
     c -= pub_len;
     len += pub_len;

     /*
      *  Subject  ::=  Name
      */
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
                                                          ctx->subject ) );

     /*
      *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
      */
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
     MBEDTLS_ASN1_CHK_ADD( len,
         mbedtls_asn1_write_tag(
             &c, buf,
             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

     /*
      * Sign the written CSR data into the sig buffer
      * Note: hash errors can happen only after an internal error
      */
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     if( psa_hash_setup( &hash_operation, hash_alg ) != PSA_SUCCESS )
         return( MBEDTLS_ERR_X509_FATAL_ERROR );

     if( psa_hash_update( &hash_operation, c, len ) != PSA_SUCCESS )
         return( MBEDTLS_ERR_X509_FATAL_ERROR );

     if( psa_hash_finish( &hash_operation, hash, sizeof( hash ), &hash_len )
         != PSA_SUCCESS )
     {
         return( MBEDTLS_ERR_X509_FATAL_ERROR );
     }
 #else /* MBEDTLS_USE_PSA_CRYPTO */
     ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
     if( ret != 0 )
         return( ret );
 #endif
     if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
                                  f_rng, p_rng ) ) != 0 )
     {
         return( ret );
     }

     if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_RSA ) )
         pk_alg = MBEDTLS_PK_RSA;
     else if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_ECDSA ) )
         pk_alg = MBEDTLS_PK_ECDSA;
     else
         return( MBEDTLS_ERR_X509_INVALID_ALG );

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

     /*
      * Move the written CSR data to the start of buf to create space for
      * writing the signature into buf.
      */
     memmove( buf, c, len );

     /*
      * Write sig and its OID into buf backwards from the end of buf.
      * Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
      * and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
      */
     c2 = buf + size;
     MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len,
         mbedtls_x509_write_sig( &c2, buf + len, sig_oid, sig_oid_len,
                                 sig, sig_len ) );

     /*
      * Compact the space between the CSR data and signature by moving the
      * CSR data to the start of the signature.
      */
     c2 -= len;
     memmove( c2, buf, len );

     /* ASN encode the total size and tag the CSR data with it. */
     len += sig_and_oid_len;
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
     MBEDTLS_ASN1_CHK_ADD( len,
         mbedtls_asn1_write_tag(
             &c2, buf,
             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

     /* Zero the unused bytes at the start of buf */
     memset( buf, 0, c2 - buf);

     return( (int) len );
 }

 int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf,
                                size_t size,
                                int (*f_rng)(void *, unsigned char *, size_t),
                                void *p_rng )
 {
     int ret;
     unsigned char *sig;

     if( ( sig = mbedtls_calloc( 1, MBEDTLS_PK_SIGNATURE_MAX_SIZE ) ) == NULL )
     {
         return( MBEDTLS_ERR_X509_ALLOC_FAILED );
     }

     ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );

     mbedtls_free( sig );

     return( ret );
 }

 #define PEM_BEGIN_CSR           "-----BEGIN CERTIFICATE REQUEST-----\n"
 #define PEM_END_CSR             "-----END CERTIFICATE REQUEST-----\n"

 #if defined(MBEDTLS_PEM_WRITE_C)
 int mbedtls_x509write_csr_pem( mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size,
                        int (*f_rng)(void *, unsigned char *, size_t),
                        void *p_rng )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t olen = 0;

     if( ( ret = mbedtls_x509write_csr_der( ctx, buf, size,
                                    f_rng, p_rng ) ) < 0 )
     {
         return( ret );
     }

     if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_CSR, PEM_END_CSR,
                                   buf + size - ret,
                                   ret, buf, size, &olen ) ) != 0 )
     {
         return( ret );
     }

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

 #endif /* MBEDTLS_X509_CSR_WRITE_C */
	/*
	* X.509 Certificate Signing Request writing
	*
	* Copyright The Mbed TLS Contributors
	* 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.
	*/
	/*
	* References:
	* - CSRs: PKCS#10 v1.7 aka RFC 2986
	* - attributes: PKCS#9 v2.0 aka RFC 2985
	*/

	#include "common.h"

	#if defined(MBEDTLS_X509_CSR_WRITE_C)

	#include "mbedtls/x509_csr.h"
	#include "mbedtls/asn1write.h"
	#include "mbedtls/error.h"
	#include "mbedtls/oid.h"
	#include "mbedtls/platform_util.h"

	#if defined(MBEDTLS_USE_PSA_CRYPTO)
	#include "psa/crypto.h"
	#include "mbedtls/psa_util.h"
	#endif

	#include <string.h>
	#include <stdlib.h>

	#if defined(MBEDTLS_PEM_WRITE_C)
	#include "mbedtls/pem.h"
	#endif

	#if defined(MBEDTLS_PLATFORM_C)
	#include "mbedtls/platform.h"
	#else
	#include <stdlib.h>
	#define mbedtls_calloc calloc
	#define mbedtls_free free
	#endif

	void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
	{
	memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
	}

	void mbedtls_x509write_csr_free( mbedtls_x509write_csr *ctx )
	{
	mbedtls_asn1_free_named_data_list( &ctx->subject );
	mbedtls_asn1_free_named_data_list( &ctx->extensions );

	mbedtls_platform_zeroize( ctx, sizeof( mbedtls_x509write_csr ) );
	}

	void mbedtls_x509write_csr_set_md_alg( mbedtls_x509write_csr *ctx, mbedtls_md_type_t md_alg )
	{
	ctx->md_alg = md_alg;
	}

	void mbedtls_x509write_csr_set_key( mbedtls_x509write_csr ctx, mbedtls_pk_context key )
	{
	ctx->key = key;
	}

	int mbedtls_x509write_csr_set_subject_name( mbedtls_x509write_csr *ctx,
	const char *subject_name )
	{
	return mbedtls_x509_string_to_names( &ctx->subject, subject_name );
	}

	int mbedtls_x509write_csr_set_extension( mbedtls_x509write_csr *ctx,
	const char *oid, size_t oid_len,
	int critical,
	const unsigned char *val, size_t val_len )
	{
	return mbedtls_x509_set_extension( &ctx->extensions, oid, oid_len,
	critical, val, val_len );
	}

	int mbedtls_x509write_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage )
	{
	unsigned char buf[4] = {0};
	unsigned char *c;
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

	c = buf + 4;

	ret = mbedtls_asn1_write_named_bitstring( &c, buf, &key_usage, 8 );
	if( ret < 3 \|\| ret > 4 )
	return( ret );

	ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
	MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
	0, c, (size_t)ret );
	if( ret != 0 )
	return( ret );

	return( 0 );
	}

	int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
	unsigned char ns_cert_type )
	{
	unsigned char buf[4] = {0};
	unsigned char *c;
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

	c = buf + 4;

	ret = mbedtls_asn1_write_named_bitstring( &c, buf, &ns_cert_type, 8 );
	if( ret < 3 \|\| ret > 4 )
	return( ret );

	ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
	MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
	0, c, (size_t)ret );
	if( ret != 0 )
	return( ret );

	return( 0 );
	}

	static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
	unsigned char *buf,
	size_t size,
	unsigned char *sig,
	int (f_rng)(void , unsigned char *, size_t),
	void *p_rng )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	const char *sig_oid;
	size_t sig_oid_len = 0;
	unsigned char c, c2;
	unsigned char hash[64];
	size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
	size_t len = 0;
	mbedtls_pk_type_t pk_alg;
	#if defined(MBEDTLS_USE_PSA_CRYPTO)
	psa_hash_operation_t hash_operation = PSA_HASH_OPERATION_INIT;
	size_t hash_len;
	psa_algorithm_t hash_alg = mbedtls_psa_translate_md( ctx->md_alg );
	#endif /* MBEDTLS_USE_PSA_CRYPTO */

	/* Write the CSR backwards starting from the end of buf */
	c = buf + size;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
	ctx->extensions ) );

	if( len )
	{
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_SEQUENCE ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_SET ) );

	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_oid(
	&c, buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
	MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_SEQUENCE ) );
	}

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );

	MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
	buf, c - buf ) );
	c -= pub_len;
	len += pub_len;

	/*
	* Subject ::= Name
	*/
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
	ctx->subject ) );

	/*
	* Version ::= INTEGER { v1(0), v2(1), v3(2) }
	*/
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_SEQUENCE ) );

	/*
	* Sign the written CSR data into the sig buffer
	* Note: hash errors can happen only after an internal error
	*/
	#if defined(MBEDTLS_USE_PSA_CRYPTO)
	if( psa_hash_setup( &hash_operation, hash_alg ) != PSA_SUCCESS )
	return( MBEDTLS_ERR_X509_FATAL_ERROR );

	if( psa_hash_update( &hash_operation, c, len ) != PSA_SUCCESS )
	return( MBEDTLS_ERR_X509_FATAL_ERROR );

	if( psa_hash_finish( &hash_operation, hash, sizeof( hash ), &hash_len )
	!= PSA_SUCCESS )
	{
	return( MBEDTLS_ERR_X509_FATAL_ERROR );
	}
	#else /* MBEDTLS_USE_PSA_CRYPTO */
	ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
	if( ret != 0 )
	return( ret );
	#endif
	if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
	f_rng, p_rng ) ) != 0 )
	{
	return( ret );
	}

	if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_RSA ) )
	pk_alg = MBEDTLS_PK_RSA;
	else if( mbedtls_pk_can_do( ctx->key, MBEDTLS_PK_ECDSA ) )
	pk_alg = MBEDTLS_PK_ECDSA;
	else
	return( MBEDTLS_ERR_X509_INVALID_ALG );

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

	/*
	* Move the written CSR data to the start of buf to create space for
	* writing the signature into buf.
	*/
	memmove( buf, c, len );

	/*
	* Write sig and its OID into buf backwards from the end of buf.
	* Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
	* and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
	*/
	c2 = buf + size;
	MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len,
	mbedtls_x509_write_sig( &c2, buf + len, sig_oid, sig_oid_len,
	sig, sig_len ) );

	/*
	* Compact the space between the CSR data and signature by moving the
	* CSR data to the start of the signature.
	*/
	c2 -= len;
	memmove( c2, buf, len );

	/* ASN encode the total size and tag the CSR data with it. */
	len += sig_and_oid_len;
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
	MBEDTLS_ASN1_CHK_ADD( len,
	mbedtls_asn1_write_tag(
	&c2, buf,
	MBEDTLS_ASN1_CONSTRUCTED \| MBEDTLS_ASN1_SEQUENCE ) );

	/* Zero the unused bytes at the start of buf */
	memset( buf, 0, c2 - buf);

	return( (int) len );
	}

	int mbedtls_x509write_csr_der( mbedtls_x509write_csr ctx, unsigned char buf,
	size_t size,
	int (f_rng)(void , unsigned char *, size_t),
	void *p_rng )
	{
	int ret;
	unsigned char *sig;

	if( ( sig = mbedtls_calloc( 1, MBEDTLS_PK_SIGNATURE_MAX_SIZE ) ) == NULL )
	{
	return( MBEDTLS_ERR_X509_ALLOC_FAILED );
	}

	ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );

	mbedtls_free( sig );

	return( ret );
	}

	#define PEM_BEGIN_CSR "-----BEGIN CERTIFICATE REQUEST-----\n"
	#define PEM_END_CSR "-----END CERTIFICATE REQUEST-----\n"

	#if defined(MBEDTLS_PEM_WRITE_C)
	int mbedtls_x509write_csr_pem( mbedtls_x509write_csr ctx, unsigned char buf, size_t size,
	int (f_rng)(void , unsigned char *, size_t),
	void *p_rng )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t olen = 0;

	if( ( ret = mbedtls_x509write_csr_der( ctx, buf, size,
	f_rng, p_rng ) ) < 0 )
	{
	return( ret );
	}

	if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_CSR, PEM_END_CSR,
	buf + size - ret,
	ret, buf, size, &olen ) ) != 0 )
	{
	return( ret );
	}

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

	#endif /* MBEDTLS_X509_CSR_WRITE_C */