1 /*
2  * SHA256-based PRF (IEEE 802.11r)
3  * Copyright (c) 2003-2016, 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 #include "crypto.h"
14 
15 
16 /**
17  * sha256_prf - SHA256-based Pseudo-Random Function (IEEE 802.11r, 8.5.1.5.2)
18  * @key: Key for PRF
19  * @key_len: Length of the key in bytes
20  * @label: A unique label for each purpose of the PRF
21  * @data: Extra data to bind into the key
22  * @data_len: Length of the data
23  * @buf: Buffer for the generated pseudo-random key
24  * @buf_len: 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.
29  */
sha256_prf(const u8 * key,size_t key_len,const char * label,const u8 * data,size_t data_len,u8 * buf,size_t buf_len)30 int sha256_prf(const u8 *key, size_t key_len, const char *label,
31 		const u8 *data, size_t data_len, u8 *buf, size_t buf_len)
32 {
33 	return sha256_prf_bits(key, key_len, label, data, data_len, buf,
34 			       buf_len * 8);
35 }
36 
37 
38 /**
39  * sha256_prf_bits - IEEE Std 802.11-2012, 11.6.1.7.2 Key derivation function
40  * @key: Key for KDF
41  * @key_len: Length of the key in bytes
42  * @label: A unique label for each purpose of the PRF
43  * @data: Extra data to bind into the key
44  * @data_len: Length of the data
45  * @buf: Buffer for the generated pseudo-random key
46  * @buf_len: Number of bits of key to generate
47  * Returns: 0 on success, -1 on failure
48  *
49  * This function is used to derive new, cryptographically separate keys from a
50  * given key. If the requested buf_len is not divisible by eight, the least
51  * significant 1-7 bits of the last octet in the output are not part of the
52  * requested output.
53  */
sha256_prf_bits(const u8 * key,size_t key_len,const char * label,const u8 * data,size_t data_len,u8 * buf,size_t buf_len_bits)54 int sha256_prf_bits(const u8 *key, size_t key_len, const char *label,
55 		    const u8 *data, size_t data_len, u8 *buf,
56 		    size_t buf_len_bits)
57 {
58 	u16 counter = 1;
59 	size_t pos, plen;
60 	u8 hash[SHA256_MAC_LEN];
61 	const u8 *addr[4];
62 	size_t len[4];
63 	u8 counter_le[2], length_le[2];
64 	size_t buf_len = (buf_len_bits + 7) / 8;
65 
66 	addr[0] = counter_le;
67 	len[0] = 2;
68 	addr[1] = (u8 *) label;
69 	len[1] = os_strlen(label);
70 	addr[2] = data;
71 	len[2] = data_len;
72 	addr[3] = length_le;
73 	len[3] = sizeof(length_le);
74 
75 	WPA_PUT_LE16(length_le, buf_len_bits);
76 	pos = 0;
77 	while (pos < buf_len) {
78 		plen = buf_len - pos;
79 		WPA_PUT_LE16(counter_le, counter);
80 		if (plen >= SHA256_MAC_LEN) {
81 			if (hmac_sha256_vector(key, key_len, 4, addr, len,
82 					       &buf[pos]) < 0)
83 				return -1;
84 			pos += SHA256_MAC_LEN;
85 		} else {
86 			if (hmac_sha256_vector(key, key_len, 4, addr, len,
87 					       hash) < 0)
88 				return -1;
89 			os_memcpy(&buf[pos], hash, plen);
90 			pos += plen;
91 			break;
92 		}
93 		counter++;
94 	}
95 
96 	/*
97 	 * Mask out unused bits in the last octet if it does not use all the
98 	 * bits.
99 	 */
100 	if (buf_len_bits % 8) {
101 		u8 mask = 0xff << (8 - buf_len_bits % 8);
102 		buf[pos - 1] &= mask;
103 	}
104 
105 	forced_memzero(hash, sizeof(hash));
106 
107 	return 0;
108 }
109