[398] | 1 | /*
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| 2 | * HKDF implementation -- RFC 5869
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| 3 | *
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| 4 | * Copyright (C) 2016-2018, ARM Limited, All Rights Reserved
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| 5 | * SPDX-License-Identifier: Apache-2.0
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| 6 | *
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| 7 | * Licensed under the Apache License, Version 2.0 (the "License"); you may
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| 8 | * not use this file except in compliance with the License.
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| 9 | * You may obtain a copy of the License at
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| 10 | *
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| 11 | * http://www.apache.org/licenses/LICENSE-2.0
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| 12 | *
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| 13 | * Unless required by applicable law or agreed to in writing, software
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| 14 | * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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| 15 | * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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| 16 | * See the License for the specific language governing permissions and
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| 17 | * limitations under the License.
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| 18 | *
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| 19 | * This file is part of mbed TLS (https://tls.mbed.org)
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| 20 | */
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| 21 | #if !defined(MBEDTLS_CONFIG_FILE)
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| 22 | #include "mbedtls/config.h"
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| 23 | #else
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| 24 | #include MBEDTLS_CONFIG_FILE
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| 25 | #endif
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| 26 |
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| 27 | #if defined(MBEDTLS_HKDF_C)
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| 28 |
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| 29 | #include <string.h>
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| 30 | #include "mbedtls/hkdf.h"
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| 31 | #include "mbedtls/platform_util.h"
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| 32 |
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| 33 | int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
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| 34 | size_t salt_len, const unsigned char *ikm, size_t ikm_len,
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| 35 | const unsigned char *info, size_t info_len,
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| 36 | unsigned char *okm, size_t okm_len )
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| 37 | {
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| 38 | int ret;
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| 39 | unsigned char prk[MBEDTLS_MD_MAX_SIZE];
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| 40 |
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| 41 | ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk );
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| 42 |
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| 43 | if( ret == 0 )
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| 44 | {
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| 45 | ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ),
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| 46 | info, info_len, okm, okm_len );
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| 47 | }
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| 48 |
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| 49 | mbedtls_platform_zeroize( prk, sizeof( prk ) );
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| 50 |
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| 51 | return( ret );
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| 52 | }
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| 53 |
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| 54 | int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
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| 55 | const unsigned char *salt, size_t salt_len,
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| 56 | const unsigned char *ikm, size_t ikm_len,
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| 57 | unsigned char *prk )
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| 58 | {
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| 59 | unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' };
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| 60 |
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| 61 | if( salt == NULL )
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| 62 | {
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| 63 | size_t hash_len;
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| 64 |
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| 65 | if( salt_len != 0 )
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| 66 | {
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| 67 | return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
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| 68 | }
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| 69 |
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| 70 | hash_len = mbedtls_md_get_size( md );
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| 71 |
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| 72 | if( hash_len == 0 )
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| 73 | {
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| 74 | return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
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| 75 | }
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| 76 |
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| 77 | salt = null_salt;
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| 78 | salt_len = hash_len;
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| 79 | }
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| 80 |
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| 81 | return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) );
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| 82 | }
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| 83 |
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| 84 | int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
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| 85 | size_t prk_len, const unsigned char *info,
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| 86 | size_t info_len, unsigned char *okm, size_t okm_len )
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| 87 | {
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| 88 | size_t hash_len;
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| 89 | size_t where = 0;
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| 90 | size_t n;
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| 91 | size_t t_len = 0;
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| 92 | size_t i;
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| 93 | int ret = 0;
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| 94 | mbedtls_md_context_t ctx;
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| 95 | unsigned char t[MBEDTLS_MD_MAX_SIZE];
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| 96 |
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| 97 | if( okm == NULL )
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| 98 | {
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| 99 | return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
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| 100 | }
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| 101 |
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| 102 | hash_len = mbedtls_md_get_size( md );
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| 103 |
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| 104 | if( prk_len < hash_len || hash_len == 0 )
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| 105 | {
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| 106 | return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
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| 107 | }
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| 108 |
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| 109 | if( info == NULL )
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| 110 | {
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| 111 | info = (const unsigned char *) "";
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| 112 | info_len = 0;
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| 113 | }
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| 114 |
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| 115 | n = okm_len / hash_len;
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| 116 |
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| 117 | if( (okm_len % hash_len) != 0 )
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| 118 | {
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| 119 | n++;
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| 120 | }
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| 121 |
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| 122 | /*
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| 123 | * Per RFC 5869 Section 2.3, okm_len must not exceed
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| 124 | * 255 times the hash length
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| 125 | */
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| 126 | if( n > 255 )
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| 127 | {
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| 128 | return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
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| 129 | }
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| 130 |
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| 131 | mbedtls_md_init( &ctx );
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| 132 |
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| 133 | if( (ret = mbedtls_md_setup( &ctx, md, 1) ) != 0 )
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| 134 | {
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| 135 | goto exit;
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| 136 | }
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| 137 |
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| 138 | /*
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| 139 | * Compute T = T(1) | T(2) | T(3) | ... | T(N)
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| 140 | * Where T(N) is defined in RFC 5869 Section 2.3
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| 141 | */
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| 142 | for( i = 1; i <= n; i++ )
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| 143 | {
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| 144 | size_t num_to_copy;
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| 145 | unsigned char c = i & 0xff;
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| 146 |
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| 147 | ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len );
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| 148 | if( ret != 0 )
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| 149 | {
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| 150 | goto exit;
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| 151 | }
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| 152 |
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| 153 | ret = mbedtls_md_hmac_update( &ctx, t, t_len );
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| 154 | if( ret != 0 )
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| 155 | {
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| 156 | goto exit;
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| 157 | }
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| 158 |
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| 159 | ret = mbedtls_md_hmac_update( &ctx, info, info_len );
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| 160 | if( ret != 0 )
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| 161 | {
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| 162 | goto exit;
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| 163 | }
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| 164 |
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| 165 | /* The constant concatenated to the end of each T(n) is a single octet.
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| 166 | * */
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| 167 | ret = mbedtls_md_hmac_update( &ctx, &c, 1 );
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| 168 | if( ret != 0 )
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| 169 | {
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| 170 | goto exit;
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| 171 | }
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| 172 |
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| 173 | ret = mbedtls_md_hmac_finish( &ctx, t );
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| 174 | if( ret != 0 )
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| 175 | {
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| 176 | goto exit;
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| 177 | }
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| 178 |
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| 179 | num_to_copy = i != n ? hash_len : okm_len - where;
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| 180 | memcpy( okm + where, t, num_to_copy );
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| 181 | where += hash_len;
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| 182 | t_len = hash_len;
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| 183 | }
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| 184 |
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| 185 | exit:
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| 186 | mbedtls_md_free( &ctx );
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| 187 | mbedtls_platform_zeroize( t, sizeof( t ) );
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| 188 |
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| 189 | return( ret );
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| 190 | }
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| 191 |
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| 192 | #endif /* MBEDTLS_HKDF_C */
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