1 /* 2 * HKDF implementation -- RFC 5869 3 * 4 * Copyright The Mbed TLS Contributors 5 * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later 6 * 7 * This file is provided under the Apache License 2.0, or the 8 * GNU General Public License v2.0 or later. 9 * 10 * ********** 11 * Apache License 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 * ********** 26 * 27 * ********** 28 * GNU General Public License v2.0 or later: 29 * 30 * This program is free software; you can redistribute it and/or modify 31 * it under the terms of the GNU General Public License as published by 32 * the Free Software Foundation; either version 2 of the License, or 33 * (at your option) any later version. 34 * 35 * This program is distributed in the hope that it will be useful, 36 * but WITHOUT ANY WARRANTY; without even the implied warranty of 37 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 38 * GNU General Public License for more details. 39 * 40 * You should have received a copy of the GNU General Public License along 41 * with this program; if not, write to the Free Software Foundation, Inc., 42 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 43 * 44 * ********** 45 */ 46 #if !defined(MBEDTLS_CONFIG_FILE) 47 #include "mbedtls/config.h" 48 #else 49 #include MBEDTLS_CONFIG_FILE 50 #endif 51 52 #if defined(MBEDTLS_HKDF_C) 53 54 #include <string.h> 55 #include "mbedtls/hkdf.h" 56 #include "mbedtls/platform_util.h" 57 58 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 59 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 60 const unsigned char *info, size_t info_len, 61 unsigned char *okm, size_t okm_len ) 62 { 63 int ret; 64 unsigned char prk[MBEDTLS_MD_MAX_SIZE]; 65 66 ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk ); 67 68 if( ret == 0 ) 69 { 70 ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ), 71 info, info_len, okm, okm_len ); 72 } 73 74 mbedtls_platform_zeroize( prk, sizeof( prk ) ); 75 76 return( ret ); 77 } 78 79 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 80 const unsigned char *salt, size_t salt_len, 81 const unsigned char *ikm, size_t ikm_len, 82 unsigned char *prk ) 83 { 84 unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' }; 85 86 if( salt == NULL ) 87 { 88 size_t hash_len; 89 90 if( salt_len != 0 ) 91 { 92 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 93 } 94 95 hash_len = mbedtls_md_get_size( md ); 96 97 if( hash_len == 0 ) 98 { 99 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 100 } 101 102 salt = null_salt; 103 salt_len = hash_len; 104 } 105 106 return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) ); 107 } 108 109 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 110 size_t prk_len, const unsigned char *info, 111 size_t info_len, unsigned char *okm, size_t okm_len ) 112 { 113 size_t hash_len; 114 size_t where = 0; 115 size_t n; 116 size_t t_len = 0; 117 size_t i; 118 int ret = 0; 119 mbedtls_md_context_t ctx; 120 unsigned char t[MBEDTLS_MD_MAX_SIZE]; 121 122 if( okm == NULL ) 123 { 124 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 125 } 126 127 hash_len = mbedtls_md_get_size( md ); 128 129 if( prk_len < hash_len || hash_len == 0 ) 130 { 131 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 132 } 133 134 if( info == NULL ) 135 { 136 info = (const unsigned char *) ""; 137 info_len = 0; 138 } 139 140 n = okm_len / hash_len; 141 142 if( (okm_len % hash_len) != 0 ) 143 { 144 n++; 145 } 146 147 /* 148 * Per RFC 5869 Section 2.3, okm_len must not exceed 149 * 255 times the hash length 150 */ 151 if( n > 255 ) 152 { 153 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 154 } 155 156 mbedtls_md_init( &ctx ); 157 158 if( (ret = mbedtls_md_setup( &ctx, md, 1) ) != 0 ) 159 { 160 goto exit; 161 } 162 163 /* 164 * Compute T = T(1) | T(2) | T(3) | ... | T(N) 165 * Where T(N) is defined in RFC 5869 Section 2.3 166 */ 167 for( i = 1; i <= n; i++ ) 168 { 169 size_t num_to_copy; 170 unsigned char c = i & 0xff; 171 172 ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len ); 173 if( ret != 0 ) 174 { 175 goto exit; 176 } 177 178 ret = mbedtls_md_hmac_update( &ctx, t, t_len ); 179 if( ret != 0 ) 180 { 181 goto exit; 182 } 183 184 ret = mbedtls_md_hmac_update( &ctx, info, info_len ); 185 if( ret != 0 ) 186 { 187 goto exit; 188 } 189 190 /* The constant concatenated to the end of each T(n) is a single octet. 191 * */ 192 ret = mbedtls_md_hmac_update( &ctx, &c, 1 ); 193 if( ret != 0 ) 194 { 195 goto exit; 196 } 197 198 ret = mbedtls_md_hmac_finish( &ctx, t ); 199 if( ret != 0 ) 200 { 201 goto exit; 202 } 203 204 num_to_copy = i != n ? hash_len : okm_len - where; 205 memcpy( okm + where, t, num_to_copy ); 206 where += hash_len; 207 t_len = hash_len; 208 } 209 210 exit: 211 mbedtls_md_free( &ctx ); 212 mbedtls_platform_zeroize( t, sizeof( t ) ); 213 214 return( ret ); 215 } 216 217 #endif /* MBEDTLS_HKDF_C */ 218