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 /** Bad input parameters to function. */ 41 #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 42 /* \} name */ 43 44 #ifdef __cplusplus 45 extern "C" { 46 #endif 47 48 /** 49 * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function 50 * (HKDF). 51 * 52 * \param md A hash function; md.size denotes the length of the hash 53 * function output in bytes. 54 * \param salt An optional salt value (a non-secret random value); 55 * if the salt is not provided, a string of all zeros of 56 * md.size length is used as the salt. 57 * \param salt_len The length in bytes of the optional \p salt. 58 * \param ikm The input keying material. 59 * \param ikm_len The length in bytes of \p ikm. 60 * \param info An optional context and application specific information 61 * string. This can be a zero-length string. 62 * \param info_len The length of \p info in bytes. 63 * \param okm The output keying material of \p okm_len bytes. 64 * \param okm_len The length of the output keying material in bytes. This 65 * must be less than or equal to 255 * md.size bytes. 66 * 67 * \return 0 on success. 68 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 69 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 70 * MD layer. 71 */ 72 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 73 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 74 const unsigned char *info, size_t info_len, 75 unsigned char *okm, size_t okm_len ); 76 77 /** 78 * \brief Take the input keying material \p ikm and extract from it a 79 * fixed-length pseudorandom key \p prk. 80 * 81 * \warning This function should only be used if the security of it has been 82 * studied and established in that particular context (eg. TLS 1.3 83 * key schedule). For standard HKDF security guarantees use 84 * \c mbedtls_hkdf instead. 85 * 86 * \param md A hash function; md.size denotes the length of the 87 * hash function output in bytes. 88 * \param salt An optional salt value (a non-secret random value); 89 * if the salt is not provided, a string of all zeros 90 * of md.size length is used as the salt. 91 * \param salt_len The length in bytes of the optional \p salt. 92 * \param ikm The input keying material. 93 * \param ikm_len The length in bytes of \p ikm. 94 * \param[out] prk A pseudorandom key of at least md.size bytes. 95 * 96 * \return 0 on success. 97 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 98 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 99 * MD layer. 100 */ 101 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 102 const unsigned char *salt, size_t salt_len, 103 const unsigned char *ikm, size_t ikm_len, 104 unsigned char *prk ); 105 106 /** 107 * \brief Expand the supplied \p prk into several additional pseudorandom 108 * keys, which is the output of the HKDF. 109 * 110 * \warning This function should only be used if the security of it has been 111 * studied and established in that particular context (eg. TLS 1.3 112 * key schedule). For standard HKDF security guarantees use 113 * \c mbedtls_hkdf instead. 114 * 115 * \param md A hash function; md.size denotes the length of the hash 116 * function output in bytes. 117 * \param prk A pseudorandom key of at least md.size bytes. \p prk is 118 * usually the output from the HKDF extract step. 119 * \param prk_len The length in bytes of \p prk. 120 * \param info An optional context and application specific information 121 * string. This can be a zero-length string. 122 * \param info_len The length of \p info in bytes. 123 * \param okm The output keying material of \p okm_len bytes. 124 * \param okm_len The length of the output keying material in bytes. This 125 * must be less than or equal to 255 * md.size bytes. 126 * 127 * \return 0 on success. 128 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 129 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 130 * MD layer. 131 */ 132 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 133 size_t prk_len, const unsigned char *info, 134 size_t info_len, unsigned char *okm, size_t okm_len ); 135 136 #ifdef __cplusplus 137 } 138 #endif 139 140 #endif /* hkdf.h */ 141
