1 /*
2 * HKDF implementation -- RFC 5869
3 *
4 * Copyright The Mbed TLS Contributors
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 #include "common.h"
20
21 #if defined(MBEDTLS_HKDF_C)
22
23 #include <string.h>
24 #include "mbedtls/hkdf.h"
25 #include "mbedtls/platform_util.h"
26 #include "mbedtls/error.h"
27
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)28 int mbedtls_hkdf(const mbedtls_md_info_t *md, const unsigned char *salt,
29 size_t salt_len, const unsigned char *ikm, size_t ikm_len,
30 const unsigned char *info, size_t info_len,
31 unsigned char *okm, size_t okm_len)
32 {
33 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
34 unsigned char prk[MBEDTLS_MD_MAX_SIZE];
35
36 ret = mbedtls_hkdf_extract(md, salt, salt_len, ikm, ikm_len, prk);
37
38 if (ret == 0) {
39 ret = mbedtls_hkdf_expand(md, prk, mbedtls_md_get_size(md),
40 info, info_len, okm, okm_len);
41 }
42
43 mbedtls_platform_zeroize(prk, sizeof(prk));
44
45 return ret;
46 }
47
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)48 int mbedtls_hkdf_extract(const mbedtls_md_info_t *md,
49 const unsigned char *salt, size_t salt_len,
50 const unsigned char *ikm, size_t ikm_len,
51 unsigned char *prk)
52 {
53 unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' };
54
55 if (salt == NULL) {
56 size_t hash_len;
57
58 if (salt_len != 0) {
59 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
60 }
61
62 hash_len = mbedtls_md_get_size(md);
63
64 if (hash_len == 0) {
65 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
66 }
67
68 salt = null_salt;
69 salt_len = hash_len;
70 }
71
72 return mbedtls_md_hmac(md, salt, salt_len, ikm, ikm_len, prk);
73 }
74
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)75 int mbedtls_hkdf_expand(const mbedtls_md_info_t *md, const unsigned char *prk,
76 size_t prk_len, const unsigned char *info,
77 size_t info_len, unsigned char *okm, size_t okm_len)
78 {
79 size_t hash_len;
80 size_t where = 0;
81 size_t n;
82 size_t t_len = 0;
83 size_t i;
84 int ret = 0;
85 mbedtls_md_context_t ctx;
86 unsigned char t[MBEDTLS_MD_MAX_SIZE];
87
88 if (okm == NULL) {
89 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
90 }
91
92 hash_len = mbedtls_md_get_size(md);
93
94 if (prk_len < hash_len || hash_len == 0) {
95 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
96 }
97
98 if (info == NULL) {
99 info = (const unsigned char *) "";
100 info_len = 0;
101 }
102
103 n = okm_len / hash_len;
104
105 if (okm_len % hash_len != 0) {
106 n++;
107 }
108
109 /*
110 * Per RFC 5869 Section 2.3, okm_len must not exceed
111 * 255 times the hash length
112 */
113 if (n > 255) {
114 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
115 }
116
117 mbedtls_md_init(&ctx);
118
119 if ((ret = mbedtls_md_setup(&ctx, md, 1)) != 0) {
120 goto exit;
121 }
122
123 memset(t, 0, hash_len);
124
125 /*
126 * Compute T = T(1) | T(2) | T(3) | ... | T(N)
127 * Where T(N) is defined in RFC 5869 Section 2.3
128 */
129 for (i = 1; i <= n; i++) {
130 size_t num_to_copy;
131 unsigned char c = i & 0xff;
132
133 ret = mbedtls_md_hmac_starts(&ctx, prk, prk_len);
134 if (ret != 0) {
135 goto exit;
136 }
137
138 ret = mbedtls_md_hmac_update(&ctx, t, t_len);
139 if (ret != 0) {
140 goto exit;
141 }
142
143 ret = mbedtls_md_hmac_update(&ctx, info, info_len);
144 if (ret != 0) {
145 goto exit;
146 }
147
148 /* The constant concatenated to the end of each T(n) is a single octet.
149 * */
150 ret = mbedtls_md_hmac_update(&ctx, &c, 1);
151 if (ret != 0) {
152 goto exit;
153 }
154
155 ret = mbedtls_md_hmac_finish(&ctx, t);
156 if (ret != 0) {
157 goto exit;
158 }
159
160 num_to_copy = i != n ? hash_len : okm_len - where;
161 memcpy(okm + where, t, num_to_copy);
162 where += hash_len;
163 t_len = hash_len;
164 }
165
166 exit:
167 mbedtls_md_free(&ctx);
168 mbedtls_platform_zeroize(t, sizeof(t));
169
170 return ret;
171 }
172
173 #endif /* MBEDTLS_HKDF_C */
174
