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 */
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)29 int 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 os_memset(T, 0, SHA256_MAC_LEN);
65 return -1;
66 }
67 iter++;
68
69 if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)
70 {
71 os_memset(out, 0, outlen);
72 os_memset(T, 0, SHA256_MAC_LEN);
73 return -1;
74 }
75 }
76
77 os_memset(T, 0, SHA256_MAC_LEN);
78 return 0;
79 }
80