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 
pbkdf2_sha1_f(const char * passphrase,const u8 * ssid,size_t ssid_len,int iterations,unsigned int count,u8 * digest)14 static 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  */
pbkdf2_sha1(const char * passphrase,const u8 * ssid,size_t ssid_len,int iterations,u8 * buf,size_t buflen)72 int 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