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