2 * HMAC-SHA256 KDF (RFC 5295)
3 * Copyright (c) 2014, Jouni Malinen <j@w1.fi>
5 * This software may be distributed under the terms of the BSD license.
6 * See README for more details.
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.
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.
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)
35 const unsigned char *addr[4];
40 len[0] = SHA256_MAC_LEN;
41 addr[1] = (const unsigned char *) label;
42 len[1] = os_strlen(label) + 1;
48 if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0)
54 if (clen > SHA256_MAC_LEN)
55 clen = SHA256_MAC_LEN;
56 os_memcpy(out + pos, T, clen);
63 os_memset(out, 0, outlen);
64 os_memset(T, 0, SHA256_MAC_LEN);
69 if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)
71 os_memset(out, 0, outlen);
72 os_memset(T, 0, SHA256_MAC_LEN);
77 os_memset(T, 0, SHA256_MAC_LEN);