/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:4;coding:utf-8 -*-│ │vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│ ╞══════════════════════════════════════════════════════════════════════════════╡ │ Copyright The Mbed TLS Contributors │ │ │ │ Licensed under the Apache License, Version 2.0 (the "License"); │ │ you may not use this file except in compliance with the License. │ │ You may obtain a copy of the License at │ │ │ │ http://www.apache.org/licenses/LICENSE-2.0 │ │ │ │ Unless required by applicable law or agreed to in writing, software │ │ distributed under the License is distributed on an "AS IS" BASIS, │ │ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. │ │ See the License for the specific language governing permissions and │ │ limitations under the License. │ ╚─────────────────────────────────────────────────────────────────────────────*/ #include "libc/str/str.h" #include "third_party/mbedtls/common.h" #include "third_party/mbedtls/error.h" #include "third_party/mbedtls/hkdf.h" #include "third_party/mbedtls/platform.h" asm(".ident\t\"\\n\\n\ Mbed TLS (Apache 2.0)\\n\ Copyright ARM Limited\\n\ Copyright Mbed TLS Contributors\""); asm(".include \"libc/disclaimer.inc\""); /* clang-format off */ /** * @fileoverview HKDF implementation (RFC 5869) */ /** * \brief HMAC-based Extract-and-Expand Key Derivation Function * * \param md A hash function; md.size denotes the length of the hash * function output in bytes. * \param salt An optional salt value (a non-secret random value); * if the salt is not provided, a string of all zeros of * md.size length is used as the salt. * \param salt_len The length in bytes of the optional \p salt. * \param ikm The input keying material. * \param ikm_len The length in bytes of \p ikm. * \param info An optional context and application specific information * string. This can be a zero-length string. * \param info_len The length of \p info in bytes. * \param okm The output keying material of \p okm_len bytes. * \param okm_len The length of the output keying material in bytes. This * must be less than or equal to 255 * md.size bytes. * * \return 0 on success. * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying * MD layer. */ int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, size_t salt_len, const unsigned char *ikm, size_t ikm_len, const unsigned char *info, size_t info_len, unsigned char *okm, size_t okm_len ) { int ret = MBEDTLS_ERR_THIS_CORRUPTION; unsigned char prk[MBEDTLS_MD_MAX_SIZE]; ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk ); if( ret == 0 ) { ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ), info, info_len, okm, okm_len ); } mbedtls_platform_zeroize( prk, sizeof( prk ) ); return( ret ); } /** * \brief Takes input keying material \p ikm and extract from it a * fixed-length pseudorandom key \p prk. * * \warning This function should only be used if the security of it has been * studied and established in that particular context (eg. TLS 1.3 * key schedule). For standard HKDF security guarantees use * \c mbedtls_hkdf instead. * * \param md A hash function; md.size denotes the length of the * hash function output in bytes. * \param salt An optional salt value (a non-secret random value); * if the salt is not provided, a string of all zeros * of md.size length is used as the salt. * \param salt_len The length in bytes of the optional \p salt. * \param ikm The input keying material. * \param ikm_len The length in bytes of \p ikm. * \param[out] prk A pseudorandom key of at least md.size bytes. * * \return 0 on success. * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid. * \return An MBEDTLS_ERR_MD_* error for errors returned from the underlying * MD layer. */ int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, const unsigned char *salt, size_t salt_len, const unsigned char *ikm, size_t ikm_len, unsigned char *prk ) { unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' }; if( salt == NULL ) { size_t hash_len; if( salt_len != 0 ) { return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; } hash_len = mbedtls_md_get_size( md ); if( hash_len == 0 ) { return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; } salt = null_salt; salt_len = hash_len; } return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) ); } /** * \brief Expand the supplied \p prk into several additional * pseudorandom keys, which is the output of the HKDF. * * \param md A hash function; md.size denotes the length of the hash * function output in bytes. * \param prk A pseudorandom key of at least md.size bytes. \p prk is * usually the output from the HKDF extract step. * \param prk_len The length in bytes of \p prk. * \param info An optional context and application specific information * string. This can be a zero-length string. * \param info_len The length of \p info in bytes. * \param okm The output keying material of \p okm_len bytes. * \param okm_len The length of the output keying material in bytes. This * must be less than or equal to 255 * md.size bytes. * * \return 0 on success * \return #MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the * parameters are invalid. * \return An MBEDTLS_ERR_MD_* error for errors returned from * the underlying MD layer. * * \warning This function should only be used if its security has * been studied and established in that particular context * (eg. TLS 1.3 key schedule). For standard HKDF security * guarantees use \c mbedtls_hkdf instead. */ int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, size_t prk_len, const unsigned char *info, size_t info_len, unsigned char *okm, size_t okm_len ) { size_t hash_len; size_t where = 0; size_t n; size_t t_len = 0; size_t i; int ret = 0; mbedtls_md_context_t ctx; unsigned char t[MBEDTLS_MD_MAX_SIZE]; if( !okm ) return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); hash_len = mbedtls_md_get_size( md ); if( prk_len < hash_len || hash_len == 0 ) { return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); } if( info == NULL ) { info = (const unsigned char *) ""; info_len = 0; } n = okm_len / hash_len; if( okm_len % hash_len != 0 ) { n++; } /* * Per RFC 5869 Section 2.3, okm_len must not exceed * 255 times the hash length */ if( n > 255 ) return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); mbedtls_md_init( &ctx ); if(( ret = mbedtls_md_setup( &ctx, md, 1 ) )) goto exit; mbedtls_platform_zeroize( t, hash_len ); /* * Compute T = T(1) | T(2) | T(3) | ... | T(N) * Where T(N) is defined in RFC 5869 Section 2.3 */ for( i = 1; i <= n; i++ ) { size_t num_to_copy; unsigned char c = i & 0xff; if(( ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len ) )) goto exit; if(( ret = mbedtls_md_hmac_update( &ctx, t, t_len ) )) goto exit; if(( ret = mbedtls_md_hmac_update( &ctx, info, info_len ) )) goto exit; if(( ret = mbedtls_md_hmac_update( &ctx, &c, 1 ) )) goto exit; if(( ret = mbedtls_md_hmac_finish( &ctx, t ) )) goto exit; num_to_copy = i != n ? hash_len : okm_len - where; memcpy( okm + where, t, num_to_copy ); where += hash_len; t_len = hash_len; } exit: mbedtls_md_free( &ctx ); mbedtls_platform_zeroize( t, sizeof( t ) ); return( ret ); }