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
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)24 int HKDF(uint8_t *out_key, size_t out_len,
25 const EVP_MD *digest,
26 const uint8_t *secret, size_t secret_len,
27 const uint8_t *salt, size_t salt_len,
28 const uint8_t *info, size_t info_len) {
29 /* https://tools.ietf.org/html/rfc5869#section-2.2 */
30 const size_t digest_len = EVP_MD_size(digest);
31 uint8_t prk[EVP_MAX_MD_SIZE], previous[EVP_MAX_MD_SIZE];
32 size_t n, done = 0;
33 unsigned i, prk_len;
34 int ret = 0;
35 HMAC_CTX hmac;
36
37 /* If salt is not given, HashLength zeros are used. However, HMAC does that
38 * internally already so we can ignore it.*/
39
40 /* Expand key material to desired length. */
41 n = (out_len + digest_len - 1) / digest_len;
42 if (out_len + digest_len < out_len || n > 255) {
43 OPENSSL_PUT_ERROR(HKDF, HKDF_R_OUTPUT_TOO_LARGE);
44 return 0;
45 }
46
47 HMAC_CTX_init(&hmac);
48
49 /* Extract input keying material into pseudorandom key |prk|. */
50 if (HMAC(digest, salt, salt_len, secret, secret_len, prk, &prk_len) == NULL) {
51 goto out;
52 }
53 assert(prk_len == digest_len);
54
55 if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) {
56 goto out;
57 }
58
59 for (i = 0; i < n; i++) {
60 uint8_t ctr = i + 1;
61 size_t todo;
62
63 if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) ||
64 !HMAC_Update(&hmac, previous, digest_len))) {
65 goto out;
66 }
67 if (!HMAC_Update(&hmac, info, info_len) ||
68 !HMAC_Update(&hmac, &ctr, 1) ||
69 !HMAC_Final(&hmac, previous, NULL)) {
70 goto out;
71 }
72
73 todo = digest_len;
74 if (done + todo > out_len) {
75 todo = out_len - done;
76 }
77 memcpy(out_key + done, previous, todo);
78 done += todo;
79 }
80
81 ret = 1;
82
83 out:
84 HMAC_CTX_cleanup(&hmac);
85 if (ret != 1) {
86 OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);
87 }
88 return ret;
89 }
90