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
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)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
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)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
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)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