1/*
2 * SHA1-based key derivation function (PBKDF2) for IEEE 802.11i
3 * Copyright (c) 2003-2005, 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 "sha1.h"
13
14static int pbkdf2_sha1_f(const char *passphrase, const u8 *ssid,
15			 size_t ssid_len, int iterations, unsigned int count,
16			 u8 *digest)
17{
18	unsigned char tmp[SHA1_MAC_LEN], tmp2[SHA1_MAC_LEN];
19	int i, j;
20	unsigned char count_buf[4];
21	const u8 *addr[2];
22	size_t len[2];
23	size_t passphrase_len = os_strlen(passphrase);
24
25	addr[0] = ssid;
26	len[0] = ssid_len;
27	addr[1] = count_buf;
28	len[1] = 4;
29
30	/* F(P, S, c, i) = U1 xor U2 xor ... Uc
31	 * U1 = PRF(P, S || i)
32	 * U2 = PRF(P, U1)
33	 * Uc = PRF(P, Uc-1)
34	 */
35
36	count_buf[0] = (count >> 24) & 0xff;
37	count_buf[1] = (count >> 16) & 0xff;
38	count_buf[2] = (count >> 8) & 0xff;
39	count_buf[3] = count & 0xff;
40	if (hmac_sha1_vector((u8 *) passphrase, passphrase_len, 2, addr, len,
41			     tmp))
42		return -1;
43	os_memcpy(digest, tmp, SHA1_MAC_LEN);
44
45	for (i = 1; i < iterations; i++) {
46		if (hmac_sha1((u8 *) passphrase, passphrase_len, tmp,
47			      SHA1_MAC_LEN, tmp2))
48			return -1;
49		os_memcpy(tmp, tmp2, SHA1_MAC_LEN);
50		for (j = 0; j < SHA1_MAC_LEN; j++)
51			digest[j] ^= tmp2[j];
52	}
53
54	return 0;
55}
56
57
58/**
59 * pbkdf2_sha1 - SHA1-based key derivation function (PBKDF2) for IEEE 802.11i
60 * @passphrase: ASCII passphrase
61 * @ssid: SSID
62 * @ssid_len: SSID length in bytes
63 * @iterations: Number of iterations to run
64 * @buf: Buffer for the generated key
65 * @buflen: Length of the buffer in bytes
66 * Returns: 0 on success, -1 of failure
67 *
68 * This function is used to derive PSK for WPA-PSK. For this protocol,
69 * iterations is set to 4096 and buflen to 32. This function is described in
70 * IEEE Std 802.11-2004, Clause H.4. The main construction is from PKCS#5 v2.0.
71 */
72int pbkdf2_sha1(const char *passphrase, const u8 *ssid, size_t ssid_len,
73		int iterations, u8 *buf, size_t buflen)
74{
75	unsigned int count = 0;
76	unsigned char *pos = buf;
77	size_t left = buflen, plen;
78	unsigned char digest[SHA1_MAC_LEN];
79
80	while (left > 0) {
81		count++;
82		if (pbkdf2_sha1_f(passphrase, ssid, ssid_len, iterations,
83				  count, digest))
84			return -1;
85		plen = left > SHA1_MAC_LEN ? SHA1_MAC_LEN : left;
86		os_memcpy(pos, digest, plen);
87		pos += plen;
88		left -= plen;
89	}
90
91	return 0;
92}
93