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
22 #include "hkdf.h"
23
mbedtls_hkdf(const mbedtls_md_info_t * md,const uint8_t * salt,size_t salt_len,const uint8_t * ikm,size_t ikm_len,const uint8_t * info,size_t info_len,uint8_t * okm,size_t okm_len)24 int32_t mbedtls_hkdf(const mbedtls_md_info_t *md, const uint8_t *salt,
25 size_t salt_len, const uint8_t *ikm, size_t ikm_len,
26 const uint8_t *info, size_t info_len,
27 uint8_t *okm, size_t okm_len)
28 {
29 int32_t ret;
30 uint8_t prk[MBEDTLS_MD_MAX_SIZE];
31
32 ret = mbedtls_hkdf_extract(md, salt, salt_len, ikm, ikm_len, prk);
33
34 if (ret == 0) {
35 ret = mbedtls_hkdf_expand(md, prk, (size_t)mbedtls_md_get_size(md),
36 info, info_len, okm, okm_len);
37 }
38
39 (void)mbedtls_platform_zeroize(prk, sizeof(prk));
40
41 return ret;
42 }
43
mbedtls_hkdf_extract(const mbedtls_md_info_t * md,const uint8_t * salt,size_t salt_len,const uint8_t * ikm,size_t ikm_len,uint8_t * prk)44 int32_t mbedtls_hkdf_extract(const mbedtls_md_info_t *md,
45 const uint8_t *salt, size_t salt_len,
46 const uint8_t *ikm, size_t ikm_len,
47 uint8_t *prk)
48 {
49 int32_t ret = 0;
50 size_t tmp_salt_len = salt_len;
51 const uint8_t *tmp_salt = salt;
52 uint8_t null_salt[MBEDTLS_MD_MAX_SIZE] = { 0U };
53
54 if (tmp_salt == NULL) {
55 size_t hash_len;
56
57 if (tmp_salt_len != 0U) {
58 ret = MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
59 } else {
60
61 hash_len = mbedtls_md_get_size(md);
62
63 if (hash_len == 0U) {
64 ret = MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
65 } else {
66 tmp_salt = null_salt;
67 tmp_salt_len = hash_len;
68 }
69 }
70 }
71
72 if (ret == 0) {
73 ret = mbedtls_md_hmac(md, tmp_salt, tmp_salt_len, ikm, ikm_len, prk);
74 }
75
76 return ret;
77 }
78
mbedtls_hkdf_expand(const mbedtls_md_info_t * md,const uint8_t * prk,size_t prk_len,const uint8_t * info,size_t info_len,uint8_t * okm,size_t okm_len)79 int32_t mbedtls_hkdf_expand(const mbedtls_md_info_t *md, const uint8_t *prk,
80 size_t prk_len, const uint8_t *info,
81 size_t info_len, uint8_t *okm, size_t okm_len)
82 {
83 size_t hash_len;
84 size_t where = 0;
85 size_t n;
86 size_t t_len = 0;
87 size_t tmp_info_len = info_len;
88 const uint8_t *tmp_info = info;
89 size_t i;
90 int32_t ret = 0;
91 mbedtls_md_context_t ctx;
92 uint8_t t[MBEDTLS_MD_MAX_SIZE];
93
94 hash_len = mbedtls_md_get_size(md);
95
96 if ((okm == NULL) || (prk_len < hash_len) || (hash_len == 0U)) {
97 ret = MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
98 } else {
99
100 if (tmp_info == NULL) {
101 tmp_info = (const uint8_t *) "";
102 tmp_info_len = 0U;
103 }
104
105 n = okm_len / hash_len;
106
107 if ((okm_len % hash_len) != 0U) {
108 n++;
109 }
110
111 /*
112 * Per RFC 5869 Section 2.3, okm_len must not exceed
113 * 255 times the hash length
114 */
115 if (n > 255U) {
116 ret = MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
117 } else {
118 mbedtls_md_init(&ctx);
119
120 ret = mbedtls_md_setup(&ctx, md);
121 if (ret == 0) {
122
123 /*
124 * Compute T = T(1) | T(2) | T(3) | ... | T(N)
125 * Where T(N) is defined in RFC 5869 Section 2.3
126 */
127 for (i = 1U; i <= n; i++) {
128 size_t num_to_copy;
129 uint8_t c = (uint8_t)(i & 0xffU);
130
131 ret = mbedtls_md_hmac_starts(&ctx, prk, prk_len);
132 if (ret == 0) {
133 ret = mbedtls_md_hmac_update(&ctx, t, t_len);
134 }
135
136 if (ret == 0) {
137 ret = mbedtls_md_hmac_update(&ctx, tmp_info, tmp_info_len);
138 }
139
140 /* The constant concatenated to the end of each T(n) is a single octet.
141 * */
142 if (ret == 0) {
143 ret = mbedtls_md_hmac_update(&ctx, &c, 1);
144 }
145
146 if (ret == 0) {
147 ret = mbedtls_md_hmac_finish(&ctx, t);
148 }
149
150 if (ret != 0) {
151 break;
152 }
153
154 num_to_copy = (i != n) ? hash_len : (okm_len - where);
155 (void)memcpy_s(okm + where, num_to_copy, t, num_to_copy);
156 where += hash_len;
157 t_len = hash_len;
158 }
159 }
160
161 mbedtls_md_free(&ctx);
162 }
163 }
164
165 (void)mbedtls_platform_zeroize(t, sizeof(t));
166
167 return ret;
168 }
169