1 | /**
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2 | * \file hkdf.h
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3 | *
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4 | * \brief This file contains the HKDF interface.
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5 | *
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6 | * The HMAC-based Extract-and-Expand Key Derivation Function (HKDF) is
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7 | * specified by RFC 5869.
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8 | */
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9 | /*
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10 | * Copyright (C) 2016-2018, ARM Limited, All Rights Reserved
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11 | * SPDX-License-Identifier: Apache-2.0
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12 | *
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13 | * Licensed under the Apache License, Version 2.0 (the "License"); you may
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14 | * not use this file except in compliance with the License.
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15 | * You may obtain a copy of the License at
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16 | *
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17 | * http://www.apache.org/licenses/LICENSE-2.0
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18 | *
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19 | * Unless required by applicable law or agreed to in writing, software
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20 | * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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21 | * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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22 | * See the License for the specific language governing permissions and
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23 | * limitations under the License.
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24 | *
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25 | * This file is part of mbed TLS (https://tls.mbed.org)
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26 | */
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27 | #ifndef MBEDTLS_HKDF_H
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28 | #define MBEDTLS_HKDF_H
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29 |
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30 | #if !defined(MBEDTLS_CONFIG_FILE)
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31 | #include "config.h"
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32 | #else
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33 | #include MBEDTLS_CONFIG_FILE
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34 | #endif
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35 |
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36 | #include "md.h"
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37 |
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38 | /**
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39 | * \name HKDF Error codes
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40 | * \{
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41 | */
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42 | #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 /**< Bad input parameters to function. */
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43 | /* \} name */
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44 |
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45 | #ifdef __cplusplus
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46 | extern "C" {
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47 | #endif
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48 |
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49 | /**
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50 | * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function
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51 | * (HKDF).
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52 | *
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53 | * \param md A hash function; md.size denotes the length of the hash
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54 | * function output in bytes.
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55 | * \param salt An optional salt value (a non-secret random value);
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56 | * if the salt is not provided, a string of all zeros of
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57 | * md.size length is used as the salt.
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58 | * \param salt_len The length in bytes of the optional \p salt.
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59 | * \param ikm The input keying material.
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60 | * \param ikm_len The length in bytes of \p ikm.
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61 | * \param info An optional context and application specific information
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62 | * string. This can be a zero-length string.
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63 | * \param info_len The length of \p info in bytes.
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64 | * \param okm The output keying material of \p okm_len bytes.
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65 | * \param okm_len The length of the output keying material in bytes. This
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66 | * must be less than or equal to 255 * md.size bytes.
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67 | *
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68 | * \return 0 on success.
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69 | * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.
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70 | * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
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71 | * MD layer.
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72 | */
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73 | int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
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74 | size_t salt_len, const unsigned char *ikm, size_t ikm_len,
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75 | const unsigned char *info, size_t info_len,
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76 | unsigned char *okm, size_t okm_len );
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77 |
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78 | /**
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79 | * \brief Take the input keying material \p ikm and extract from it a
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80 | * fixed-length pseudorandom key \p prk.
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81 | *
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82 | * \warning This function should only be used if the security of it has been
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83 | * studied and established in that particular context (eg. TLS 1.3
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84 | * key schedule). For standard HKDF security guarantees use
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85 | * \c mbedtls_hkdf instead.
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86 | *
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87 | * \param md A hash function; md.size denotes the length of the
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88 | * hash function output in bytes.
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89 | * \param salt An optional salt value (a non-secret random value);
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90 | * if the salt is not provided, a string of all zeros
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91 | * of md.size length is used as the salt.
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92 | * \param salt_len The length in bytes of the optional \p salt.
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93 | * \param ikm The input keying material.
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94 | * \param ikm_len The length in bytes of \p ikm.
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95 | * \param[out] prk A pseudorandom key of at least md.size bytes.
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96 | *
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97 | * \return 0 on success.
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98 | * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.
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99 | * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
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100 | * MD layer.
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101 | */
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102 | int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
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103 | const unsigned char *salt, size_t salt_len,
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104 | const unsigned char *ikm, size_t ikm_len,
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105 | unsigned char *prk );
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106 |
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107 | /**
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108 | * \brief Expand the supplied \p prk into several additional pseudorandom
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109 | * keys, which is the output of the HKDF.
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110 | *
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111 | * \warning This function should only be used if the security of it has been
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112 | * studied and established in that particular context (eg. TLS 1.3
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113 | * key schedule). For standard HKDF security guarantees use
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114 | * \c mbedtls_hkdf instead.
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115 | *
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116 | * \param md A hash function; md.size denotes the length of the hash
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117 | * function output in bytes.
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118 | * \param prk A pseudorandom key of at least md.size bytes. \p prk is
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119 | * usually the output from the HKDF extract step.
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120 | * \param prk_len The length in bytes of \p prk.
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121 | * \param info An optional context and application specific information
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122 | * string. This can be a zero-length string.
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123 | * \param info_len The length of \p info in bytes.
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124 | * \param okm The output keying material of \p okm_len bytes.
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125 | * \param okm_len The length of the output keying material in bytes. This
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126 | * must be less than or equal to 255 * md.size bytes.
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127 | *
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128 | * \return 0 on success.
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129 | * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.
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130 | * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying
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131 | * MD layer.
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132 | */
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133 | int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
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134 | size_t prk_len, const unsigned char *info,
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135 | size_t info_len, unsigned char *okm, size_t okm_len );
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136 |
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137 | #ifdef __cplusplus
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138 | }
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139 | #endif
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140 |
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141 | #endif /* hkdf.h */
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