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) 2016-2018, 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 #include "md.h" 31 32 /** 33 * \name HKDF Error codes 34 * \{ 35 */ 36 #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 /**< Bad input parameters to function. */ 37 /* \} name */ 38 39 #ifdef __cplusplus 40 extern "C" { 41 #endif 42 43 /** 44 * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function 45 * (HKDF). 46 * 47 * \param md A hash function; md.size denotes the length of the hash 48 * function output in bytes. 49 * \param salt An optional salt value (a non-secret random value); 50 * if the salt is not provided, a string of all zeros of 51 * md.size length is used as the salt. 52 * \param salt_len The length in bytes of the optional \p salt. 53 * \param ikm The input keying material. 54 * \param ikm_len The length in bytes of \p ikm. 55 * \param info An optional context and application specific information 56 * string. This can be a zero-length string. 57 * \param info_len The length of \p info in bytes. 58 * \param okm The output keying material of \p okm_len bytes. 59 * \param okm_len The length of the output keying material in bytes. This 60 * must be less than or equal to 255 * md.size bytes. 61 * 62 * \return 0 on success. 63 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 64 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 65 * MD layer. 66 */ 67 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 68 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 69 const unsigned char *info, size_t info_len, 70 unsigned char *okm, size_t okm_len ); 71 72 /** 73 * \brief Take the input keying material \p ikm and extract from it a 74 * fixed-length pseudorandom key \p prk. 75 * 76 * \warning This function should only be used if the security of it has been 77 * studied and established in that particular context (eg. TLS 1.3 78 * key schedule). For standard HKDF security guarantees use 79 * \c mbedtls_hkdf instead. 80 * 81 * \param md A hash function; md.size denotes the length of the 82 * hash function output in bytes. 83 * \param salt An optional salt value (a non-secret random value); 84 * if the salt is not provided, a string of all zeros 85 * of md.size length is used as the salt. 86 * \param salt_len The length in bytes of the optional \p salt. 87 * \param ikm The input keying material. 88 * \param ikm_len The length in bytes of \p ikm. 89 * \param[out] prk A pseudorandom key of at least md.size bytes. 90 * 91 * \return 0 on success. 92 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 93 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 94 * MD layer. 95 */ 96 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 97 const unsigned char *salt, size_t salt_len, 98 const unsigned char *ikm, size_t ikm_len, 99 unsigned char *prk ); 100 101 /** 102 * \brief Expand the supplied \p prk into several additional pseudorandom 103 * keys, which is the output of the HKDF. 104 * 105 * \warning This function should only be used if the security of it has been 106 * studied and established in that particular context (eg. TLS 1.3 107 * key schedule). For standard HKDF security guarantees use 108 * \c mbedtls_hkdf instead. 109 * 110 * \param md A hash function; md.size denotes the length of the hash 111 * function output in bytes. 112 * \param prk A pseudorandom key of at least md.size bytes. \p prk is 113 * usually the output from the HKDF extract step. 114 * \param prk_len The length in bytes of \p prk. 115 * \param info An optional context and application specific information 116 * string. This can be a zero-length string. 117 * \param info_len The length of \p info in bytes. 118 * \param okm The output keying material of \p okm_len bytes. 119 * \param okm_len The length of the output keying material in bytes. This 120 * must be less than or equal to 255 * md.size bytes. 121 * 122 * \return 0 on success. 123 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 124 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 125 * MD layer. 126 */ 127 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 128 size_t prk_len, const unsigned char *info, 129 size_t info_len, unsigned char *okm, size_t okm_len ); 130 131 #ifdef __cplusplus 132 } 133 #endif 134 135 #endif /* hkdf.h */ 136