1 /* Copyright (c) 2014, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/hkdf.h>
16
17 #include <assert.h>
18 #include <string.h>
19
20 #include <openssl/err.h>
21 #include <openssl/hmac.h>
22
23 #include "../internal.h"
24
25
HKDF(uint8_t * out_key,size_t out_len,const EVP_MD * digest,const uint8_t * secret,size_t secret_len,const uint8_t * salt,size_t salt_len,const uint8_t * info,size_t info_len)26 int HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
27 const uint8_t *secret, size_t secret_len, const uint8_t *salt,
28 size_t salt_len, const uint8_t *info, size_t info_len) {
29 // https://tools.ietf.org/html/rfc5869#section-2
30 uint8_t prk[EVP_MAX_MD_SIZE];
31 size_t prk_len;
32
33 if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt,
34 salt_len) ||
35 !HKDF_expand(out_key, out_len, digest, prk, prk_len, info, info_len)) {
36 return 0;
37 }
38
39 return 1;
40 }
41
HKDF_extract(uint8_t * out_key,size_t * out_len,const EVP_MD * digest,const uint8_t * secret,size_t secret_len,const uint8_t * salt,size_t salt_len)42 int HKDF_extract(uint8_t *out_key, size_t *out_len, const EVP_MD *digest,
43 const uint8_t *secret, size_t secret_len, const uint8_t *salt,
44 size_t salt_len) {
45 // https://tools.ietf.org/html/rfc5869#section-2.2
46
47 // If salt is not given, HashLength zeros are used. However, HMAC does that
48 // internally already so we can ignore it.
49 unsigned len;
50 if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == NULL) {
51 OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);
52 return 0;
53 }
54 *out_len = len;
55 assert(*out_len == EVP_MD_size(digest));
56 return 1;
57 }
58
HKDF_expand(uint8_t * out_key,size_t out_len,const EVP_MD * digest,const uint8_t * prk,size_t prk_len,const uint8_t * info,size_t info_len)59 int HKDF_expand(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
60 const uint8_t *prk, size_t prk_len, const uint8_t *info,
61 size_t info_len) {
62 // https://tools.ietf.org/html/rfc5869#section-2.3
63 const size_t digest_len = EVP_MD_size(digest);
64 uint8_t previous[EVP_MAX_MD_SIZE];
65 size_t n, done = 0;
66 unsigned i;
67 int ret = 0;
68 HMAC_CTX hmac;
69
70 // Expand key material to desired length.
71 n = (out_len + digest_len - 1) / digest_len;
72 if (out_len + digest_len < out_len || n > 255) {
73 OPENSSL_PUT_ERROR(HKDF, HKDF_R_OUTPUT_TOO_LARGE);
74 return 0;
75 }
76
77 HMAC_CTX_init(&hmac);
78 if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) {
79 goto out;
80 }
81
82 for (i = 0; i < n; i++) {
83 uint8_t ctr = i + 1;
84 size_t todo;
85
86 if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) ||
87 !HMAC_Update(&hmac, previous, digest_len))) {
88 goto out;
89 }
90 if (!HMAC_Update(&hmac, info, info_len) ||
91 !HMAC_Update(&hmac, &ctr, 1) ||
92 !HMAC_Final(&hmac, previous, NULL)) {
93 goto out;
94 }
95
96 todo = digest_len;
97 if (done + todo > out_len) {
98 todo = out_len - done;
99 }
100 OPENSSL_memcpy(out_key + done, previous, todo);
101 done += todo;
102 }
103
104 ret = 1;
105
106 out:
107 HMAC_CTX_cleanup(&hmac);
108 if (ret != 1) {
109 OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);
110 }
111 return ret;
112 }
113