1/*
2 * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25#include "inner.h"
26
27const unsigned char br_hkdf_no_salt = 0;
28
29/* see bearssl_kdf.h */
30void
31br_hkdf_init(br_hkdf_context *hc, const br_hash_class *digest_vtable,
32	const void *salt, size_t salt_len)
33{
34	br_hmac_key_context kc;
35	unsigned char tmp[64];
36
37	if (salt == BR_HKDF_NO_SALT) {
38		salt = tmp;
39		salt_len = br_digest_size(digest_vtable);
40		memset(tmp, 0, salt_len);
41	}
42	br_hmac_key_init(&kc, digest_vtable, salt, salt_len);
43	br_hmac_init(&hc->u.hmac_ctx, &kc, 0);
44	hc->dig_len = br_hmac_size(&hc->u.hmac_ctx);
45}
46
47/* see bearssl_kdf.h */
48void
49br_hkdf_inject(br_hkdf_context *hc, const void *ikm, size_t ikm_len)
50{
51	br_hmac_update(&hc->u.hmac_ctx, ikm, ikm_len);
52}
53
54/* see bearssl_kdf.h */
55void
56br_hkdf_flip(br_hkdf_context *hc)
57{
58	unsigned char tmp[64];
59
60	br_hmac_out(&hc->u.hmac_ctx, tmp);
61	br_hmac_key_init(&hc->u.prk_ctx,
62		br_hmac_get_digest(&hc->u.hmac_ctx), tmp, hc->dig_len);
63	hc->ptr = hc->dig_len;
64	hc->chunk_num = 0;
65}
66
67/* see bearssl_kdf.h */
68size_t
69br_hkdf_produce(br_hkdf_context *hc,
70	const void *info, size_t info_len, void *out, size_t out_len)
71{
72	size_t tlen;
73
74	tlen = 0;
75	while (out_len > 0) {
76		size_t clen;
77
78		if (hc->ptr == hc->dig_len) {
79			br_hmac_context hmac_ctx;
80			unsigned char x;
81
82			hc->chunk_num ++;
83			if (hc->chunk_num == 256) {
84				return tlen;
85			}
86			x = hc->chunk_num;
87			br_hmac_init(&hmac_ctx, &hc->u.prk_ctx, 0);
88			if (x != 1) {
89				br_hmac_update(&hmac_ctx, hc->buf, hc->dig_len);
90			}
91			br_hmac_update(&hmac_ctx, info, info_len);
92			br_hmac_update(&hmac_ctx, &x, 1);
93			br_hmac_out(&hmac_ctx, hc->buf);
94			hc->ptr = 0;
95		}
96		clen = hc->dig_len - hc->ptr;
97		if (clen > out_len) {
98			clen = out_len;
99		}
100		memcpy(out, hc->buf + hc->ptr, clen);
101		out = (unsigned char *)out + clen;
102		out_len -= clen;
103		hc->ptr += clen;
104		tlen += clen;
105	}
106	return tlen;
107}
108