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/*
* HKDF implementation -- RFC 5869
*
* Copyright (C) 2016-2018, 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_HKDF_C)
#include <string.h>
#include "mbedtls/hkdf.h"
#include "mbedtls/platform_util.h"
int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
size_t salt_len, const unsigned char *ikm, size_t ikm_len,
const unsigned char *info, size_t info_len,
unsigned char *okm, size_t okm_len )
{
int ret;
unsigned char prk[MBEDTLS_MD_MAX_SIZE];
ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk );
if( ret == 0 )
{
ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ),
info, info_len, okm, okm_len );
}
mbedtls_platform_zeroize( prk, sizeof( prk ) );
return( ret );
}
int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
const unsigned char *salt, size_t salt_len,
const unsigned char *ikm, size_t ikm_len,
unsigned char *prk )
{
unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' };
if( salt == NULL )
{
size_t hash_len;
if( salt_len != 0 )
{
return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
}
hash_len = mbedtls_md_get_size( md );
if( hash_len == 0 )
{
return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
}
salt = null_salt;
salt_len = hash_len;
}
return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) );
}
int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
size_t prk_len, const unsigned char *info,
size_t info_len, unsigned char *okm, size_t okm_len )
{
size_t hash_len;
size_t where = 0;
size_t n;
size_t t_len = 0;
size_t i;
int ret = 0;
mbedtls_md_context_t ctx;
unsigned char t[MBEDTLS_MD_MAX_SIZE];
if( okm == NULL )
{
return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
}
hash_len = mbedtls_md_get_size( md );
if( prk_len < hash_len || hash_len == 0 )
{
return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
}
if( info == NULL )
{
info = (const unsigned char *) "";
info_len = 0;
}
n = okm_len / hash_len;
if( (okm_len % hash_len) != 0 )
{
n++;
}
/*
* Per RFC 5869 Section 2.3, okm_len must not exceed
* 255 times the hash length
*/
if( n > 255 )
{
return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
}
mbedtls_md_init( &ctx );
if( (ret = mbedtls_md_setup( &ctx, md, 1) ) != 0 )
{
goto exit;
}
/*
* Compute T = T(1) | T(2) | T(3) | ... | T(N)
* Where T(N) is defined in RFC 5869 Section 2.3
*/
for( i = 1; i <= n; i++ )
{
size_t num_to_copy;
unsigned char c = i & 0xff;
ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len );
if( ret != 0 )
{
goto exit;
}
ret = mbedtls_md_hmac_update( &ctx, t, t_len );
if( ret != 0 )
{
goto exit;
}
ret = mbedtls_md_hmac_update( &ctx, info, info_len );
if( ret != 0 )
{
goto exit;
}
/* The constant concatenated to the end of each T(n) is a single octet.
* */
ret = mbedtls_md_hmac_update( &ctx, &c, 1 );
if( ret != 0 )
{
goto exit;
}
ret = mbedtls_md_hmac_finish( &ctx, t );
if( ret != 0 )
{
goto exit;
}
num_to_copy = i != n ? hash_len : okm_len - where;
memcpy( okm + where, t, num_to_copy );
where += hash_len;
t_len = hash_len;
}
exit:
mbedtls_md_free( &ctx );
mbedtls_platform_zeroize( t, sizeof( t ) );
return( ret );
}
#endif /* MBEDTLS_HKDF_C */
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