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/*

 *  HKDF implementation -- RFC 5869

 *

 *  Copyright (C) 2016-2018, ARM Limited, All Rights Reserved

 *  SPDX-License-Identifier: GPL-2.0

 *

 *  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.

 *

 *  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 

#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 */