sha256-kdf.c revision 281681 
1/*
2 * HMAC-SHA256 KDF (RFC 5295)
3 * Copyright (c) 2014, 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
20 * @seed: Seed value to bind into the key
21 * @seed_len: Length of the seed
22 * @out: Buffer for the generated pseudo-random key
23 * @outlen: Number of bytes of key to generate
24 * Returns: 0 on success, -1 on failure.
25 *
26 * This function is used to derive new, cryptographically separate keys from a
27 * given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2.
28 */
29int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
30		    const char *label, const u8 *seed, size_t seed_len,
31		    u8 *out, size_t outlen)
32{
33	u8 T[SHA256_MAC_LEN];
34	u8 iter = 1;
35	const unsigned char *addr[4];
36	size_t len[4];
37	size_t pos, clen;
38
39	addr[0] = T;
40	len[0] = SHA256_MAC_LEN;
41	addr[1] = (const unsigned char *) label;
42	len[1] = os_strlen(label) + 1;
43	addr[2] = seed;
44	len[2] = seed_len;
45	addr[3] = &iter;
46	len[3] = 1;
47
48	if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0)
49		return -1;
50
51	pos = 0;
52	for (;;) {
53		clen = outlen - pos;
54		if (clen > SHA256_MAC_LEN)
55			clen = SHA256_MAC_LEN;
56		os_memcpy(out + pos, T, clen);
57		pos += clen;
58
59		if (pos == outlen)
60			break;
61
62		if (iter == 255) {
63			os_memset(out, 0, outlen);
64			return -1;
65		}
66		iter++;
67
68		if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)
69		{
70			os_memset(out, 0, outlen);
71			return -1;
72		}
73	}
74
75	return 0;
76}
77