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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