1/*
2 * HMAC-SHA256 KDF (RFC 5295) and HKDF-Expand(SHA256) (RFC 5869)
3 * Copyright (c) 2014-2017, Jouni Malinen <j@w1.fi>
4 *
5 * This software may be distributed under the terms of the BSD license.
6 * See README for more details.
7 */
8
9#include "includes.h"
10
11#include "common.h"
12#include "sha256.h"
13
14
15/**
16 * hmac_sha256_kdf - HMAC-SHA256 based KDF (RFC 5295)
17 * @secret: Key for KDF
18 * @secret_len: Length of the key in bytes
19 * @label: A unique label for each purpose of the KDF or %NULL to select
20 *	RFC 5869 HKDF-Expand() with arbitrary seed (= info)
21 * @seed: Seed value to bind into the key
22 * @seed_len: Length of the seed
23 * @out: Buffer for the generated pseudo-random key
24 * @outlen: Number of bytes of key to generate
25 * Returns: 0 on success, -1 on failure.
26 *
27 * This function is used to derive new, cryptographically separate keys from a
28 * given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2. When used
29 * with label = NULL and seed = info, this matches HKDF-Expand() defined in
30 * RFC 5869, Chapter 2.3.
31 */
32int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
33		    const char *label, const u8 *seed, size_t seed_len,
34		    u8 *out, size_t outlen)
35{
36	u8 T[SHA256_MAC_LEN];
37	u8 iter = 1;
38	const unsigned char *addr[4];
39	size_t len[4];
40	size_t pos, clen;
41
42	addr[0] = T;
43	len[0] = SHA256_MAC_LEN;
44	if (label) {
45		addr[1] = (const unsigned char *) label;
46		len[1] = os_strlen(label) + 1;
47	} else {
48		addr[1] = (const u8 *) "";
49		len[1] = 0;
50	}
51	addr[2] = seed;
52	len[2] = seed_len;
53	addr[3] = &iter;
54	len[3] = 1;
55
56	if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0)
57		return -1;
58
59	pos = 0;
60	for (;;) {
61		clen = outlen - pos;
62		if (clen > SHA256_MAC_LEN)
63			clen = SHA256_MAC_LEN;
64		os_memcpy(out + pos, T, clen);
65		pos += clen;
66
67		if (pos == outlen)
68			break;
69
70		if (iter == 255) {
71			os_memset(out, 0, outlen);
72			forced_memzero(T, SHA256_MAC_LEN);
73			return -1;
74		}
75		iter++;
76
77		if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)
78		{
79			os_memset(out, 0, outlen);
80			forced_memzero(T, SHA256_MAC_LEN);
81			return -1;
82		}
83	}
84
85	forced_memzero(T, SHA256_MAC_LEN);
86	return 0;
87}
88