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 The Mbed TLS Contributors 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 #ifndef MBEDTLS_HKDF_H 26 #define MBEDTLS_HKDF_H 27 28 #if !defined(MBEDTLS_CONFIG_FILE) 29 #include "mbedtls/config.h" 30 #else 31 #include MBEDTLS_CONFIG_FILE 32 #endif 33 34 #include "mbedtls/md.h" 35 36 /** 37 * \name HKDF Error codes 38 * \{ 39 */ 40 #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 /**< Bad input parameters to function. */ 41 /* \} name */ 42 43 #ifdef __cplusplus 44 extern "C" { 45 #endif 46 47 /** 48 * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function 49 * (HKDF). 50 * 51 * \param md A hash function; md.size denotes the length of the hash 52 * function output in bytes. 53 * \param salt An optional salt value (a non-secret random value); 54 * if the salt is not provided, a string of all zeros of 55 * md.size length is used as the salt. 56 * \param salt_len The length in bytes of the optional \p salt. 57 * \param ikm The input keying material. 58 * \param ikm_len The length in bytes of \p ikm. 59 * \param info An optional context and application specific information 60 * string. This can be a zero-length string. 61 * \param info_len The length of \p info in bytes. 62 * \param okm The output keying material of \p okm_len bytes. 63 * \param okm_len The length of the output keying material in bytes. This 64 * must be less than or equal to 255 * md.size bytes. 65 * 66 * \return 0 on success. 67 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 68 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 69 * MD layer. 70 */ 71 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 72 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 73 const unsigned char *info, size_t info_len, 74 unsigned char *okm, size_t okm_len ); 75 76 /** 77 * \brief Take the input keying material \p ikm and extract from it a 78 * fixed-length pseudorandom key \p prk. 79 * 80 * \warning This function should only be used if the security of it has been 81 * studied and established in that particular context (eg. TLS 1.3 82 * key schedule). For standard HKDF security guarantees use 83 * \c mbedtls_hkdf instead. 84 * 85 * \param md A hash function; md.size denotes the length of the 86 * hash function output in bytes. 87 * \param salt An optional salt value (a non-secret random value); 88 * if the salt is not provided, a string of all zeros 89 * of md.size length is used as the salt. 90 * \param salt_len The length in bytes of the optional \p salt. 91 * \param ikm The input keying material. 92 * \param ikm_len The length in bytes of \p ikm. 93 * \param[out] prk A pseudorandom key of at least md.size bytes. 94 * 95 * \return 0 on success. 96 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 97 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 98 * MD layer. 99 */ 100 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 101 const unsigned char *salt, size_t salt_len, 102 const unsigned char *ikm, size_t ikm_len, 103 unsigned char *prk ); 104 105 /** 106 * \brief Expand the supplied \p prk into several additional pseudorandom 107 * keys, which is the output of the HKDF. 108 * 109 * \warning This function should only be used if the security of it has been 110 * studied and established in that particular context (eg. TLS 1.3 111 * key schedule). For standard HKDF security guarantees use 112 * \c mbedtls_hkdf instead. 113 * 114 * \param md A hash function; md.size denotes the length of the hash 115 * function output in bytes. 116 * \param prk A pseudorandom key of at least md.size bytes. \p prk is 117 * usually the output from the HKDF extract step. 118 * \param prk_len The length in bytes of \p prk. 119 * \param info An optional context and application specific information 120 * string. This can be a zero-length string. 121 * \param info_len The length of \p info in bytes. 122 * \param okm The output keying material of \p okm_len bytes. 123 * \param okm_len The length of the output keying material in bytes. This 124 * must be less than or equal to 255 * md.size bytes. 125 * 126 * \return 0 on success. 127 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 128 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 129 * MD layer. 130 */ 131 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 132 size_t prk_len, const unsigned char *info, 133 size_t info_len, unsigned char *okm, size_t okm_len ); 134 135 #ifdef __cplusplus 136 } 137 #endif 138 139 #endif /* hkdf.h */ 140