1 /** 2 * \file hkdf.h 3 * 4 * \brief This file contains the HKDF interface. 5 * 6 * The HMAC-based Extract-and-Expand Key Derivation Function (HKDF) is 7 * specified by RFC 5869. 8 */ 9 /* 10 * Copyright (C) 2016-2019, ARM Limited, All Rights Reserved 11 * SPDX-License-Identifier: Apache-2.0 12 * 13 * Licensed under the Apache License, Version 2.0 (the "License"); you may 14 * not use this file except in compliance with the License. 15 * You may obtain a copy of the License at 16 * 17 * http://www.apache.org/licenses/LICENSE-2.0 18 * 19 * Unless required by applicable law or agreed to in writing, software 20 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 21 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 22 * See the License for the specific language governing permissions and 23 * limitations under the License. 24 * 25 * This file is part of mbed TLS (https://tls.mbed.org) 26 */ 27 #ifndef MBEDTLS_HKDF_H 28 #define MBEDTLS_HKDF_H 29 30 #if !defined(MBEDTLS_CONFIG_FILE) 31 #include "config.h" 32 #else 33 #include MBEDTLS_CONFIG_FILE 34 #endif 35 36 #include "md.h" 37 38 /** 39 * \name HKDF Error codes 40 * \{ 41 */ 42 #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 /**< Bad input parameters to function. */ 43 /* \} name */ 44 45 #ifdef __cplusplus 46 extern "C" { 47 #endif 48 49 /** 50 * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function 51 * (HKDF). 52 * 53 * \param md A hash function; md.size denotes the length of the hash 54 * function output in bytes. 55 * \param salt An optional salt value (a non-secret random value); 56 * if the salt is not provided, a string of all zeros of 57 * md.size length is used as the salt. 58 * \param salt_len The length in bytes of the optional \p salt. 59 * \param ikm The input keying material. 60 * \param ikm_len The length in bytes of \p ikm. 61 * \param info An optional context and application specific information 62 * string. This can be a zero-length string. 63 * \param info_len The length of \p info in bytes. 64 * \param okm The output keying material of \p okm_len bytes. 65 * \param okm_len The length of the output keying material in bytes. This 66 * must be less than or equal to 255 * md.size bytes. 67 * 68 * \return 0 on success. 69 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 70 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 71 * MD layer. 72 */ 73 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 74 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 75 const unsigned char *info, size_t info_len, 76 unsigned char *okm, size_t okm_len ); 77 78 /** 79 * \brief Take the input keying material \p ikm and extract from it a 80 * fixed-length pseudorandom key \p prk. 81 * 82 * \warning This function should only be used if the security of it has been 83 * studied and established in that particular context (eg. TLS 1.3 84 * key schedule). For standard HKDF security guarantees use 85 * \c mbedtls_hkdf instead. 86 * 87 * \param md A hash function; md.size denotes the length of the 88 * hash function output in bytes. 89 * \param salt An optional salt value (a non-secret random value); 90 * if the salt is not provided, a string of all zeros 91 * of md.size length is used as the salt. 92 * \param salt_len The length in bytes of the optional \p salt. 93 * \param ikm The input keying material. 94 * \param ikm_len The length in bytes of \p ikm. 95 * \param[out] prk A pseudorandom key of at least md.size bytes. 96 * 97 * \return 0 on success. 98 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 99 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 100 * MD layer. 101 */ 102 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 103 const unsigned char *salt, size_t salt_len, 104 const unsigned char *ikm, size_t ikm_len, 105 unsigned char *prk ); 106 107 /** 108 * \brief Expand the supplied \p prk into several additional pseudorandom 109 * keys, which is the output of the HKDF. 110 * 111 * \warning This function should only be used if the security of it has been 112 * studied and established in that particular context (eg. TLS 1.3 113 * key schedule). For standard HKDF security guarantees use 114 * \c mbedtls_hkdf instead. 115 * 116 * \param md A hash function; md.size denotes the length of the hash 117 * function output in bytes. 118 * \param prk A pseudorandom key of at least md.size bytes. \p prk is 119 * usually the output from the HKDF extract step. 120 * \param prk_len The length in bytes of \p prk. 121 * \param info An optional context and application specific information 122 * string. This can be a zero-length string. 123 * \param info_len The length of \p info in bytes. 124 * \param okm The output keying material of \p okm_len bytes. 125 * \param okm_len The length of the output keying material in bytes. This 126 * must be less than or equal to 255 * md.size bytes. 127 * 128 * \return 0 on success. 129 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 130 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 131 * MD layer. 132 */ 133 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 134 size_t prk_len, const unsigned char *info, 135 size_t info_len, unsigned char *okm, size_t okm_len ); 136 137 #ifdef __cplusplus 138 } 139 #endif 140 141 #endif /* hkdf.h */ 142