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
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)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
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)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
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)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