1 /* 2 * HKDF implementation -- RFC 5869 3 * 4 * Copyright (C) 2016-2018, ARM Limited, All Rights Reserved 5 * SPDX-License-Identifier: Apache-2.0 6 * 7 * Licensed under the Apache License, Version 2.0 (the "License"); you may 8 * not use this file except in compliance with the License. 9 * You may obtain a copy of the License at 10 * 11 * http://www.apache.org/licenses/LICENSE-2.0 12 * 13 * Unless required by applicable law or agreed to in writing, software 14 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 15 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 * See the License for the specific language governing permissions and 17 * limitations under the License. 18 * 19 * This file is part of mbed TLS (https://tls.mbed.org) 20 */ 21 #if !defined(MBEDTLS_CONFIG_FILE) 22 #include "mbedtls/config.h" 23 #else 24 #include MBEDTLS_CONFIG_FILE 25 #endif 26 27 #if defined(MBEDTLS_HKDF_C) 28 29 #include <string.h> 30 #include "mbedtls/hkdf.h" 31 #include "mbedtls/platform_util.h" 32 33 int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt, 34 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 35 const unsigned char *info, size_t info_len, 36 unsigned char *okm, size_t okm_len ) 37 { 38 int ret; 39 unsigned char prk[MBEDTLS_MD_MAX_SIZE]; 40 41 ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk ); 42 43 if( ret == 0 ) 44 { 45 ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ), 46 info, info_len, okm, okm_len ); 47 } 48 49 mbedtls_platform_zeroize( prk, sizeof( prk ) ); 50 51 return( ret ); 52 } 53 54 int mbedtls_hkdf_extract( const mbedtls_md_info_t *md, 55 const unsigned char *salt, size_t salt_len, 56 const unsigned char *ikm, size_t ikm_len, 57 unsigned char *prk ) 58 { 59 unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' }; 60 61 if( salt == NULL ) 62 { 63 size_t hash_len; 64 65 if( salt_len != 0 ) 66 { 67 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 68 } 69 70 hash_len = mbedtls_md_get_size( md ); 71 72 if( hash_len == 0 ) 73 { 74 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 75 } 76 77 salt = null_salt; 78 salt_len = hash_len; 79 } 80 81 return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) ); 82 } 83 84 int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk, 85 size_t prk_len, const unsigned char *info, 86 size_t info_len, unsigned char *okm, size_t okm_len ) 87 { 88 size_t hash_len; 89 size_t where = 0; 90 size_t n; 91 size_t t_len = 0; 92 size_t i; 93 int ret = 0; 94 mbedtls_md_context_t ctx; 95 unsigned char t[MBEDTLS_MD_MAX_SIZE]; 96 97 if( okm == NULL ) 98 { 99 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 100 } 101 102 hash_len = mbedtls_md_get_size( md ); 103 104 if( prk_len < hash_len || hash_len == 0 ) 105 { 106 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 107 } 108 109 if( info == NULL ) 110 { 111 info = (const unsigned char *) ""; 112 info_len = 0; 113 } 114 115 n = okm_len / hash_len; 116 117 if( (okm_len % hash_len) != 0 ) 118 { 119 n++; 120 } 121 122 /* 123 * Per RFC 5869 Section 2.3, okm_len must not exceed 124 * 255 times the hash length 125 */ 126 if( n > 255 ) 127 { 128 return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA ); 129 } 130 131 mbedtls_md_init( &ctx ); 132 133 if( (ret = mbedtls_md_setup( &ctx, md, 1) ) != 0 ) 134 { 135 goto exit; 136 } 137 138 /* 139 * Compute T = T(1) | T(2) | T(3) | ... | T(N) 140 * Where T(N) is defined in RFC 5869 Section 2.3 141 */ 142 for( i = 1; i <= n; i++ ) 143 { 144 size_t num_to_copy; 145 unsigned char c = i & 0xff; 146 147 ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len ); 148 if( ret != 0 ) 149 { 150 goto exit; 151 } 152 153 ret = mbedtls_md_hmac_update( &ctx, t, t_len ); 154 if( ret != 0 ) 155 { 156 goto exit; 157 } 158 159 ret = mbedtls_md_hmac_update( &ctx, info, info_len ); 160 if( ret != 0 ) 161 { 162 goto exit; 163 } 164 165 /* The constant concatenated to the end of each T(n) is a single octet. 166 * */ 167 ret = mbedtls_md_hmac_update( &ctx, &c, 1 ); 168 if( ret != 0 ) 169 { 170 goto exit; 171 } 172 173 ret = mbedtls_md_hmac_finish( &ctx, t ); 174 if( ret != 0 ) 175 { 176 goto exit; 177 } 178 179 num_to_copy = i != n ? hash_len : okm_len - where; 180 memcpy( okm + where, t, num_to_copy ); 181 where += hash_len; 182 t_len = hash_len; 183 } 184 185 exit: 186 mbedtls_md_free( &ctx ); 187 mbedtls_platform_zeroize( t, sizeof( t ) ); 188 189 return( ret ); 190 } 191 192 #endif /* MBEDTLS_HKDF_C */ 193