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 */
hmac_sha256_kdf(const u8 * secret,size_t secret_len,const char * label,const u8 * seed,size_t seed_len,u8 * out,size_t outlen)32 int 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
