sha256.c revision 8d520ff1dc2da35cdca849e982051b86468016d8 
1/*
2 * SHA-256 hash implementation and interface functions
3 * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 *
9 * Alternatively, this software may be distributed under the terms of BSD
10 * license.
11 *
12 * See README and COPYING for more details.
13 */
14
15#include "includes.h"
16
17#include "common.h"
18#include "sha256.h"
19#include "crypto.h"
20
21
22/**
23 * hmac_sha256_vector - HMAC-SHA256 over data vector (RFC 2104)
24 * @key: Key for HMAC operations
25 * @key_len: Length of the key in bytes
26 * @num_elem: Number of elements in the data vector
27 * @addr: Pointers to the data areas
28 * @len: Lengths of the data blocks
29 * @mac: Buffer for the hash (32 bytes)
30 */
31void hmac_sha256_vector(const u8 *key, size_t key_len, size_t num_elem,
32			const u8 *addr[], const size_t *len, u8 *mac)
33{
34	unsigned char k_pad[64]; /* padding - key XORd with ipad/opad */
35	unsigned char tk[32];
36	const u8 *_addr[6];
37	size_t _len[6], i;
38
39	if (num_elem > 5) {
40		/*
41		 * Fixed limit on the number of fragments to avoid having to
42		 * allocate memory (which could fail).
43		 */
44		return;
45	}
46
47        /* if key is longer than 64 bytes reset it to key = SHA256(key) */
48        if (key_len > 64) {
49		sha256_vector(1, &key, &key_len, tk);
50		key = tk;
51		key_len = 32;
52        }
53
54	/* the HMAC_SHA256 transform looks like:
55	 *
56	 * SHA256(K XOR opad, SHA256(K XOR ipad, text))
57	 *
58	 * where K is an n byte key
59	 * ipad is the byte 0x36 repeated 64 times
60	 * opad is the byte 0x5c repeated 64 times
61	 * and text is the data being protected */
62
63	/* start out by storing key in ipad */
64	os_memset(k_pad, 0, sizeof(k_pad));
65	os_memcpy(k_pad, key, key_len);
66	/* XOR key with ipad values */
67	for (i = 0; i < 64; i++)
68		k_pad[i] ^= 0x36;
69
70	/* perform inner SHA256 */
71	_addr[0] = k_pad;
72	_len[0] = 64;
73	for (i = 0; i < num_elem; i++) {
74		_addr[i + 1] = addr[i];
75		_len[i + 1] = len[i];
76	}
77	sha256_vector(1 + num_elem, _addr, _len, mac);
78
79	os_memset(k_pad, 0, sizeof(k_pad));
80	os_memcpy(k_pad, key, key_len);
81	/* XOR key with opad values */
82	for (i = 0; i < 64; i++)
83		k_pad[i] ^= 0x5c;
84
85	/* perform outer SHA256 */
86	_addr[0] = k_pad;
87	_len[0] = 64;
88	_addr[1] = mac;
89	_len[1] = SHA256_MAC_LEN;
90	sha256_vector(2, _addr, _len, mac);
91}
92
93
94/**
95 * hmac_sha256 - HMAC-SHA256 over data buffer (RFC 2104)
96 * @key: Key for HMAC operations
97 * @key_len: Length of the key in bytes
98 * @data: Pointers to the data area
99 * @data_len: Length of the data area
100 * @mac: Buffer for the hash (20 bytes)
101 */
102void hmac_sha256(const u8 *key, size_t key_len, const u8 *data,
103		 size_t data_len, u8 *mac)
104{
105	hmac_sha256_vector(key, key_len, 1, &data, &data_len, mac);
106}
107
108
109/**
110 * sha256_prf - SHA256-based Pseudo-Random Function (IEEE 802.11r, 8.5.1.5.2)
111 * @key: Key for PRF
112 * @key_len: Length of the key in bytes
113 * @label: A unique label for each purpose of the PRF
114 * @data: Extra data to bind into the key
115 * @data_len: Length of the data
116 * @buf: Buffer for the generated pseudo-random key
117 * @buf_len: Number of bytes of key to generate
118 *
119 * This function is used to derive new, cryptographically separate keys from a
120 * given key.
121 */
122void sha256_prf(const u8 *key, size_t key_len, const char *label,
123		const u8 *data, size_t data_len, u8 *buf, size_t buf_len)
124{
125	u16 counter = 1;
126	size_t pos, plen;
127	u8 hash[SHA256_MAC_LEN];
128	const u8 *addr[4];
129	size_t len[4];
130	u8 counter_le[2], length_le[2];
131
132	addr[0] = counter_le;
133	len[0] = 2;
134	addr[1] = (u8 *) label;
135	len[1] = os_strlen(label);
136	addr[2] = data;
137	len[2] = data_len;
138	addr[3] = length_le;
139	len[3] = sizeof(length_le);
140
141	WPA_PUT_LE16(length_le, buf_len * 8);
142	pos = 0;
143	while (pos < buf_len) {
144		plen = buf_len - pos;
145		WPA_PUT_LE16(counter_le, counter);
146		if (plen >= SHA256_MAC_LEN) {
147			hmac_sha256_vector(key, key_len, 4, addr, len,
148					   &buf[pos]);
149			pos += SHA256_MAC_LEN;
150		} else {
151			hmac_sha256_vector(key, key_len, 4, addr, len, hash);
152			os_memcpy(&buf[pos], hash, plen);
153			break;
154		}
155		counter++;
156	}
157}
158