library/asn1write.c - third_party/github/ARMmbed/mbedtls - Git at Google

 /*
  * ASN.1 buffer writing functionality
  *
  *  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.
  */

 #include "common.h"

 #if defined(MBEDTLS_ASN1_WRITE_C)

 #include "mbedtls/asn1write.h"
 #include "mbedtls/error.h"

 #include <string.h>

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

 int mbedtls_asn1_write_len( unsigned char **p, const unsigned char *start, size_t len )
 {
     if( len < 0x80 )
     {
         if( *p - start < 1 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = (unsigned char) len;
         return( 1 );
     }

     if( len <= 0xFF )
     {
         if( *p - start < 2 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = (unsigned char) len;
         *--(*p) = 0x81;
         return( 2 );
     }

     if( len <= 0xFFFF )
     {
         if( *p - start < 3 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = MBEDTLS_BYTE_0( len );
         *--(*p) = MBEDTLS_BYTE_1( len );
         *--(*p) = 0x82;
         return( 3 );
     }

     if( len <= 0xFFFFFF )
     {
         if( *p - start < 4 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = MBEDTLS_BYTE_0( len );
         *--(*p) = MBEDTLS_BYTE_1( len );
         *--(*p) = MBEDTLS_BYTE_2( len );
         *--(*p) = 0x83;
         return( 4 );
     }

 #if SIZE_MAX > 0xFFFFFFFF
     if( len <= 0xFFFFFFFF )
 #endif
     {
         if( *p - start < 5 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = MBEDTLS_BYTE_0( len );
         *--(*p) = MBEDTLS_BYTE_1( len );
         *--(*p) = MBEDTLS_BYTE_2( len );
         *--(*p) = MBEDTLS_BYTE_3( len );
         *--(*p) = 0x84;
         return( 5 );
     }

 #if SIZE_MAX > 0xFFFFFFFF
     return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
 #endif
 }

 int mbedtls_asn1_write_tag( unsigned char **p, const unsigned char *start, unsigned char tag )
 {
     if( *p - start < 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

     *--(*p) = tag;

     return( 1 );
 }

 int mbedtls_asn1_write_raw_buffer( unsigned char **p, const unsigned char *start,
                            const unsigned char *buf, size_t size )
 {
     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, buf, len );

     return( (int) len );
 }

 #if defined(MBEDTLS_BIGNUM_C)
 int mbedtls_asn1_write_mpi( unsigned char **p, const unsigned char *start, const mbedtls_mpi *X )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     // Write the MPI
     //
     len = mbedtls_mpi_size( X );

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

     (*p) -= len;
     MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( X, *p, len ) );

     // DER format assumes 2s complement for numbers, so the leftmost bit
     // should be 0 for positive numbers and 1 for negative numbers.
     //
     if( X->s ==1 && **p & 0x80 )
     {
         if( *p - start < 1 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

         *--(*p) = 0x00;
         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_INTEGER ) );

     ret = (int) len;

 cleanup:
     return( ret );
 }
 #endif /* MBEDTLS_BIGNUM_C */

 int mbedtls_asn1_write_null( unsigned char **p, const unsigned char *start )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     // Write NULL
     //
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, 0) );
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_NULL ) );

     return( (int) len );
 }

 int mbedtls_asn1_write_oid( unsigned char **p, const unsigned char *start,
                     const char *oid, size_t oid_len )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
                                   (const unsigned char *) 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_OID ) );

     return( (int) len );
 }

 int mbedtls_asn1_write_algorithm_identifier( unsigned char **p, const unsigned char *start,
                                      const char *oid, size_t oid_len,
                                      size_t par_len )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     if( par_len == 0 )
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_null( p, start ) );
     else
         len += par_len;

     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 ) );

     return( (int) len );
 }

 int mbedtls_asn1_write_bool( unsigned char **p, const unsigned char *start, int boolean )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

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

     *--(*p) = (boolean) ? 255 : 0;
     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_BOOLEAN ) );

     return( (int) len );
 }

 static int asn1_write_tagged_int( unsigned char **p, const unsigned char *start, int val, int tag )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     do
     {
         if( *p - start < 1 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
         len += 1;
         *--(*p) = val & 0xff;
         val >>= 8;
     }
     while( val > 0 );

     if( **p & 0x80 )
     {
         if( *p - start < 1 )
             return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
         *--(*p) = 0x00;
         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, tag ) );

     return( (int) len );
 }

 int mbedtls_asn1_write_int( unsigned char **p, const unsigned char *start, int val )
 {
     return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_INTEGER ) );
 }

 int mbedtls_asn1_write_enum( unsigned char **p, const unsigned char *start, int val )
 {
     return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_ENUMERATED ) );
 }

 int mbedtls_asn1_write_tagged_string( unsigned char **p, const unsigned char *start, int tag,
     const char *text, size_t text_len )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
         (const unsigned char *) text, text_len ) );

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

     return( (int) len );
 }

 int mbedtls_asn1_write_utf8_string( unsigned char **p, const unsigned char *start,
     const char *text, size_t text_len )
 {
     return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_UTF8_STRING, text, text_len) );
 }

 int mbedtls_asn1_write_printable_string( unsigned char **p, const unsigned char *start,
                                  const char *text, size_t text_len )
 {
     return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_PRINTABLE_STRING, text, text_len) );
 }

 int mbedtls_asn1_write_ia5_string( unsigned char **p, const unsigned char *start,
                            const char *text, size_t text_len )
 {
     return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_IA5_STRING, text, text_len) );
 }

 int mbedtls_asn1_write_named_bitstring( unsigned char **p,
                                         const unsigned char *start,
                                         const unsigned char *buf,
                                         size_t bits )
 {
     size_t unused_bits, byte_len;
     const unsigned char *cur_byte;
     unsigned char cur_byte_shifted;
     unsigned char bit;

     byte_len = ( bits + 7 ) / 8;
     unused_bits = ( byte_len * 8 ) - bits;

     /*
      * Named bitstrings require that trailing 0s are excluded in the encoding
      * of the bitstring. Trailing 0s are considered part of the 'unused' bits
      * when encoding this value in the first content octet
      */
     if( bits != 0 )
     {
         cur_byte = buf + byte_len - 1;
         cur_byte_shifted = *cur_byte >> unused_bits;

         for( ; ; )
         {
             bit = cur_byte_shifted & 0x1;
             cur_byte_shifted >>= 1;

             if( bit != 0 )
                 break;

             bits--;
             if( bits == 0 )
                 break;

             if( bits % 8 == 0 )
                 cur_byte_shifted = *--cur_byte;
         }
     }

     return( mbedtls_asn1_write_bitstring( p, start, buf, bits ) );
 }

 int mbedtls_asn1_write_bitstring( unsigned char **p, const unsigned char *start,
                           const unsigned char *buf, size_t bits )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;
     size_t unused_bits, byte_len;

     byte_len = ( bits + 7 ) / 8;
     unused_bits = ( byte_len * 8 ) - bits;

     if( *p < start || (size_t)( *p - start ) < byte_len + 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

     len = byte_len + 1;

     /* Write the bitstring. Ensure the unused bits are zeroed */
     if( byte_len > 0 )
     {
         byte_len--;
         *--( *p ) = buf[byte_len] & ~( ( 0x1 << unused_bits ) - 1 );
         ( *p ) -= byte_len;
         memcpy( *p, buf, byte_len );
     }

     /* Write unused bits */
     *--( *p ) = (unsigned char)unused_bits;

     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 ) );

     return( (int) len );
 }

 int mbedtls_asn1_write_octet_string( unsigned char **p, const unsigned char *start,
                              const unsigned char *buf, size_t size )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len = 0;

     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, buf, size ) );

     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_OCTET_STRING ) );

     return( (int) len );
 }


 /* This is a copy of the ASN.1 parsing function mbedtls_asn1_find_named_data(),
  * which is replicated to avoid a dependency ASN1_WRITE_C on ASN1_PARSE_C. */
 static mbedtls_asn1_named_data *asn1_find_named_data(
                                                mbedtls_asn1_named_data *list,
                                                const char *oid, size_t len )
 {
     while( list != NULL )
     {
         if( list->oid.len == len &&
             memcmp( list->oid.p, oid, len ) == 0 )
         {
             break;
         }

         list = list->next;
     }

     return( list );
 }

 mbedtls_asn1_named_data *mbedtls_asn1_store_named_data(
                                         mbedtls_asn1_named_data **head,
                                         const char *oid, size_t oid_len,
                                         const unsigned char *val,
                                         size_t val_len )
 {
     mbedtls_asn1_named_data *cur;

     if( ( cur = asn1_find_named_data( *head, oid, oid_len ) ) == NULL )
     {
         // Add new entry if not present yet based on OID
         //
         cur = (mbedtls_asn1_named_data*)mbedtls_calloc( 1,
                                             sizeof(mbedtls_asn1_named_data) );
         if( cur == NULL )
             return( NULL );

         cur->oid.len = oid_len;
         cur->oid.p = mbedtls_calloc( 1, oid_len );
         if( cur->oid.p == NULL )
         {
             mbedtls_free( cur );
             return( NULL );
         }

         memcpy( cur->oid.p, oid, oid_len );

         cur->val.len = val_len;
         if( val_len != 0 )
         {
             cur->val.p = mbedtls_calloc( 1, val_len );
             if( cur->val.p == NULL )
             {
                 mbedtls_free( cur->oid.p );
                 mbedtls_free( cur );
                 return( NULL );
             }
         }

         cur->next = *head;
         *head = cur;
     }
     else if( val_len == 0 )
     {
         mbedtls_free( cur->val.p );
         cur->val.p = NULL;
     }
     else if( cur->val.len != val_len )
     {
         /*
          * Enlarge existing value buffer if needed
          * Preserve old data until the allocation succeeded, to leave list in
          * a consistent state in case allocation fails.
          */
         void *p = mbedtls_calloc( 1, val_len );
         if( p == NULL )
             return( NULL );

         mbedtls_free( cur->val.p );
         cur->val.p = p;
         cur->val.len = val_len;
     }

     if( val != NULL )
         memcpy( cur->val.p, val, val_len );

     return( cur );
 }
 #endif /* MBEDTLS_ASN1_WRITE_C */
	/*
	* ASN.1 buffer writing functionality
	*
	* 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.
	*/

	#include "common.h"

	#if defined(MBEDTLS_ASN1_WRITE_C)

	#include "mbedtls/asn1write.h"
	#include "mbedtls/error.h"

	#include <string.h>

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

	int mbedtls_asn1_write_len( unsigned char *p, const unsigned char start, size_t len )
	{
	if( len < 0x80 )
	{
	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = (unsigned char) len;
	return( 1 );
	}

	if( len <= 0xFF )
	{
	if( *p - start < 2 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = (unsigned char) len;
	--(p) = 0x81;
	return( 2 );
	}

	if( len <= 0xFFFF )
	{
	if( *p - start < 3 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = MBEDTLS_BYTE_0( len );
	--(p) = MBEDTLS_BYTE_1( len );
	--(p) = 0x82;
	return( 3 );
	}

	if( len <= 0xFFFFFF )
	{
	if( *p - start < 4 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = MBEDTLS_BYTE_0( len );
	--(p) = MBEDTLS_BYTE_1( len );
	--(p) = MBEDTLS_BYTE_2( len );
	--(p) = 0x83;
	return( 4 );
	}

	#if SIZE_MAX > 0xFFFFFFFF
	if( len <= 0xFFFFFFFF )
	#endif
	{
	if( *p - start < 5 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = MBEDTLS_BYTE_0( len );
	--(p) = MBEDTLS_BYTE_1( len );
	--(p) = MBEDTLS_BYTE_2( len );
	--(p) = MBEDTLS_BYTE_3( len );
	--(p) = 0x84;
	return( 5 );
	}

	#if SIZE_MAX > 0xFFFFFFFF
	return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
	#endif
	}

	int mbedtls_asn1_write_tag( unsigned char *p, const unsigned char start, unsigned char tag )
	{
	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = tag;

	return( 1 );
	}

	int mbedtls_asn1_write_raw_buffer( unsigned char *p, const unsigned char start,
	const unsigned char *buf, size_t size )
	{
	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, buf, len );

	return( (int) len );
	}

	#if defined(MBEDTLS_BIGNUM_C)
	int mbedtls_asn1_write_mpi( unsigned char *p, const unsigned char start, const mbedtls_mpi *X )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	// Write the MPI
	//
	len = mbedtls_mpi_size( X );

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

	(*p) -= len;
	MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( X, *p, len ) );

	// DER format assumes 2s complement for numbers, so the leftmost bit
	// should be 0 for positive numbers and 1 for negative numbers.
	//
	if( X->s ==1 && **p & 0x80 )
	{
	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	--(p) = 0x00;
	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_INTEGER ) );

	ret = (int) len;

	cleanup:
	return( ret );
	}
	#endif /* MBEDTLS_BIGNUM_C */

	int mbedtls_asn1_write_null( unsigned char *p, const unsigned char start )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	// Write NULL
	//
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, 0) );
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_NULL ) );

	return( (int) len );
	}

	int mbedtls_asn1_write_oid( unsigned char *p, const unsigned char start,
	const char *oid, size_t oid_len )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
	(const unsigned char *) 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_OID ) );

	return( (int) len );
	}

	int mbedtls_asn1_write_algorithm_identifier( unsigned char *p, const unsigned char start,
	const char *oid, size_t oid_len,
	size_t par_len )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	if( par_len == 0 )
	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_null( p, start ) );
	else
	len += par_len;

	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 ) );

	return( (int) len );
	}

	int mbedtls_asn1_write_bool( unsigned char *p, const unsigned char start, int boolean )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

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

	--(p) = (boolean) ? 255 : 0;
	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_BOOLEAN ) );

	return( (int) len );
	}

	static int asn1_write_tagged_int( unsigned char *p, const unsigned char start, int val, int tag )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	do
	{
	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
	len += 1;
	--(p) = val & 0xff;
	val >>= 8;
	}
	while( val > 0 );

	if( **p & 0x80 )
	{
	if( *p - start < 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
	--(p) = 0x00;
	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, tag ) );

	return( (int) len );
	}

	int mbedtls_asn1_write_int( unsigned char *p, const unsigned char start, int val )
	{
	return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_INTEGER ) );
	}

	int mbedtls_asn1_write_enum( unsigned char *p, const unsigned char start, int val )
	{
	return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_ENUMERATED ) );
	}

	int mbedtls_asn1_write_tagged_string( unsigned char *p, const unsigned char start, int tag,
	const char *text, size_t text_len )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
	(const unsigned char *) text, text_len ) );

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

	return( (int) len );
	}

	int mbedtls_asn1_write_utf8_string( unsigned char *p, const unsigned char start,
	const char *text, size_t text_len )
	{
	return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_UTF8_STRING, text, text_len) );
	}

	int mbedtls_asn1_write_printable_string( unsigned char *p, const unsigned char start,
	const char *text, size_t text_len )
	{
	return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_PRINTABLE_STRING, text, text_len) );
	}

	int mbedtls_asn1_write_ia5_string( unsigned char *p, const unsigned char start,
	const char *text, size_t text_len )
	{
	return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_IA5_STRING, text, text_len) );
	}

	int mbedtls_asn1_write_named_bitstring( unsigned char **p,
	const unsigned char *start,
	const unsigned char *buf,
	size_t bits )
	{
	size_t unused_bits, byte_len;
	const unsigned char *cur_byte;
	unsigned char cur_byte_shifted;
	unsigned char bit;

	byte_len = ( bits + 7 ) / 8;
	unused_bits = ( byte_len * 8 ) - bits;

	/*
	* Named bitstrings require that trailing 0s are excluded in the encoding
	* of the bitstring. Trailing 0s are considered part of the 'unused' bits
	* when encoding this value in the first content octet
	*/
	if( bits != 0 )
	{
	cur_byte = buf + byte_len - 1;
	cur_byte_shifted = *cur_byte >> unused_bits;

	for( ; ; )
	{
	bit = cur_byte_shifted & 0x1;
	cur_byte_shifted >>= 1;

	if( bit != 0 )
	break;

	bits--;
	if( bits == 0 )
	break;

	if( bits % 8 == 0 )
	cur_byte_shifted = *--cur_byte;
	}
	}

	return( mbedtls_asn1_write_bitstring( p, start, buf, bits ) );
	}

	int mbedtls_asn1_write_bitstring( unsigned char *p, const unsigned char start,
	const unsigned char *buf, size_t bits )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;
	size_t unused_bits, byte_len;

	byte_len = ( bits + 7 ) / 8;
	unused_bits = ( byte_len * 8 ) - bits;

	if( p < start \|\| (size_t)( p - start ) < byte_len + 1 )
	return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

	len = byte_len + 1;

	/* Write the bitstring. Ensure the unused bits are zeroed */
	if( byte_len > 0 )
	{
	byte_len--;
	--( p ) = buf[byte_len] & ~( ( 0x1 << unused_bits ) - 1 );
	( *p ) -= byte_len;
	memcpy( *p, buf, byte_len );
	}

	/* Write unused bits */
	--( p ) = (unsigned char)unused_bits;

	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 ) );

	return( (int) len );
	}

	int mbedtls_asn1_write_octet_string( unsigned char *p, const unsigned char start,
	const unsigned char *buf, size_t size )
	{
	int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
	size_t len = 0;

	MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, buf, size ) );

	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_OCTET_STRING ) );

	return( (int) len );
	}


	/* This is a copy of the ASN.1 parsing function mbedtls_asn1_find_named_data(),
	* which is replicated to avoid a dependency ASN1_WRITE_C on ASN1_PARSE_C. */
	static mbedtls_asn1_named_data *asn1_find_named_data(
	mbedtls_asn1_named_data *list,
	const char *oid, size_t len )
	{
	while( list != NULL )
	{
	if( list->oid.len == len &&
	memcmp( list->oid.p, oid, len ) == 0 )
	{
	break;
	}

	list = list->next;
	}

	return( list );
	}

	mbedtls_asn1_named_data *mbedtls_asn1_store_named_data(
	mbedtls_asn1_named_data **head,
	const char *oid, size_t oid_len,
	const unsigned char *val,
	size_t val_len )
	{
	mbedtls_asn1_named_data *cur;

	if( ( cur = asn1_find_named_data( *head, oid, oid_len ) ) == NULL )
	{
	// Add new entry if not present yet based on OID
	//
	cur = (mbedtls_asn1_named_data*)mbedtls_calloc( 1,
	sizeof(mbedtls_asn1_named_data) );
	if( cur == NULL )
	return( NULL );

	cur->oid.len = oid_len;
	cur->oid.p = mbedtls_calloc( 1, oid_len );
	if( cur->oid.p == NULL )
	{
	mbedtls_free( cur );
	return( NULL );
	}

	memcpy( cur->oid.p, oid, oid_len );

	cur->val.len = val_len;
	if( val_len != 0 )
	{
	cur->val.p = mbedtls_calloc( 1, val_len );
	if( cur->val.p == NULL )
	{
	mbedtls_free( cur->oid.p );
	mbedtls_free( cur );
	return( NULL );
	}
	}

	cur->next = *head;
	*head = cur;
	}
	else if( val_len == 0 )
	{
	mbedtls_free( cur->val.p );
	cur->val.p = NULL;
	}
	else if( cur->val.len != val_len )
	{
	/*
	* Enlarge existing value buffer if needed
	* Preserve old data until the allocation succeeded, to leave list in
	* a consistent state in case allocation fails.
	*/
	void *p = mbedtls_calloc( 1, val_len );
	if( p == NULL )
	return( NULL );

	mbedtls_free( cur->val.p );
	cur->val.p = p;
	cur->val.len = val_len;
	}

	if( val != NULL )
	memcpy( cur->val.p, val, val_len );

	return( cur );
	}
	#endif /* MBEDTLS_ASN1_WRITE_C */