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 OR GPL-2.0-or-later 12 */ 13 #ifndef MBEDTLS_HKDF_H 14 #define MBEDTLS_HKDF_H 15 16 #if !defined(MBEDTLS_CONFIG_FILE) 17 #include "mbedtls/config.h" 18 #else 19 #include MBEDTLS_CONFIG_FILE 20 #endif 21 22 #include "mbedtls/md.h" 23 24 /** 25 * \name HKDF Error codes 26 * \{ 27 */ 28 /** Bad input parameters to function. */ 29 #define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80 30 /** \} name */ 31 32 #ifdef __cplusplus 33 extern "C" { 34 #endif 35 36 /** 37 * \brief This is the HMAC-based Extract-and-Expand Key Derivation Function 38 * (HKDF). 39 * 40 * \param md A hash function; md.size denotes the length of the hash 41 * function output in bytes. 42 * \param salt An optional salt value (a non-secret random value); 43 * if the salt is not provided, a string of all zeros of 44 * md.size length is used as the salt. 45 * \param salt_len The length in bytes of the optional \p salt. 46 * \param ikm The input keying material. 47 * \param ikm_len The length in bytes of \p ikm. 48 * \param info An optional context and application specific information 49 * string. This can be a zero-length string. 50 * \param info_len The length of \p info in bytes. 51 * \param okm The output keying material of \p okm_len bytes. 52 * \param okm_len The length of the output keying material in bytes. This 53 * must be less than or equal to 255 * md.size bytes. 54 * 55 * \return 0 on success. 56 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 57 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 58 * MD layer. 59 */ 60 int mbedtls_hkdf(const mbedtls_md_info_t *md, const unsigned char *salt, 61 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 62 const unsigned char *info, size_t info_len, 63 unsigned char *okm, size_t okm_len); 64 65 /** 66 * \brief Take the input keying material \p ikm and extract from it a 67 * fixed-length pseudorandom key \p prk. 68 * 69 * \warning This function should only be used if the security of it has been 70 * studied and established in that particular context (eg. TLS 1.3 71 * key schedule). For standard HKDF security guarantees use 72 * \c mbedtls_hkdf instead. 73 * 74 * \param md A hash function; md.size denotes the length of the 75 * hash function output in bytes. 76 * \param salt An optional salt value (a non-secret random value); 77 * if the salt is not provided, a string of all zeros 78 * of md.size length is used as the salt. 79 * \param salt_len The length in bytes of the optional \p salt. 80 * \param ikm The input keying material. 81 * \param ikm_len The length in bytes of \p ikm. 82 * \param[out] prk A pseudorandom key of at least md.size bytes. 83 * 84 * \return 0 on success. 85 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 86 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 87 * MD layer. 88 */ 89 int mbedtls_hkdf_extract(const mbedtls_md_info_t *md, 90 const unsigned char *salt, size_t salt_len, 91 const unsigned char *ikm, size_t ikm_len, 92 unsigned char *prk); 93 94 /** 95 * \brief Expand the supplied \p prk into several additional pseudorandom 96 * keys, which is the output of the HKDF. 97 * 98 * \warning This function should only be used if the security of it has been 99 * studied and established in that particular context (eg. TLS 1.3 100 * key schedule). For standard HKDF security guarantees use 101 * \c mbedtls_hkdf instead. 102 * 103 * \param md A hash function; md.size denotes the length of the hash 104 * function output in bytes. 105 * \param prk A pseudorandom key of at least md.size bytes. \p prk is 106 * usually the output from the HKDF extract step. 107 * \param prk_len The length in bytes of \p prk. 108 * \param info An optional context and application specific information 109 * string. This can be a zero-length string. 110 * \param info_len The length of \p info in bytes. 111 * \param okm The output keying material of \p okm_len bytes. 112 * \param okm_len The length of the output keying material in bytes. This 113 * must be less than or equal to 255 * md.size bytes. 114 * 115 * \return 0 on success. 116 * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. 117 * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying 118 * MD layer. 119 */ 120 int mbedtls_hkdf_expand(const mbedtls_md_info_t *md, const unsigned char *prk, 121 size_t prk_len, const unsigned char *info, 122 size_t info_len, unsigned char *okm, size_t okm_len); 123 124 #ifdef __cplusplus 125 } 126 #endif 127 128 #endif /* hkdf.h */ 129