1/*
2 * lib80211 crypt: host-based WEP encryption implementation for lib80211
3 *
4 * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
5 * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation. See README and COPYING for
10 * more details.
11 */
12
13#include <linux/err.h>
14#include <linux/module.h>
15#include <linux/init.h>
16#include <linux/slab.h>
17#include <linux/random.h>
18#include <linux/scatterlist.h>
19#include <linux/skbuff.h>
20#include <linux/mm.h>
21#include <asm/string.h>
22
23#include <net/lib80211.h>
24
25#include <linux/crypto.h>
26#include <linux/crc32.h>
27
28MODULE_AUTHOR("Jouni Malinen");
29MODULE_DESCRIPTION("lib80211 crypt: WEP");
30MODULE_LICENSE("GPL");
31
32struct lib80211_wep_data {
33	u32 iv;
34#define WEP_KEY_LEN 13
35	u8 key[WEP_KEY_LEN + 1];
36	u8 key_len;
37	u8 key_idx;
38	struct crypto_blkcipher *tx_tfm;
39	struct crypto_blkcipher *rx_tfm;
40};
41
42static void *lib80211_wep_init(int keyidx)
43{
44	struct lib80211_wep_data *priv;
45
46	priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
47	if (priv == NULL)
48		goto fail;
49	priv->key_idx = keyidx;
50
51	priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
52	if (IS_ERR(priv->tx_tfm)) {
53		priv->tx_tfm = NULL;
54		goto fail;
55	}
56
57	priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
58	if (IS_ERR(priv->rx_tfm)) {
59		priv->rx_tfm = NULL;
60		goto fail;
61	}
62	/* start WEP IV from a random value */
63	get_random_bytes(&priv->iv, 4);
64
65	return priv;
66
67      fail:
68	if (priv) {
69		if (priv->tx_tfm)
70			crypto_free_blkcipher(priv->tx_tfm);
71		if (priv->rx_tfm)
72			crypto_free_blkcipher(priv->rx_tfm);
73		kfree(priv);
74	}
75	return NULL;
76}
77
78static void lib80211_wep_deinit(void *priv)
79{
80	struct lib80211_wep_data *_priv = priv;
81	if (_priv) {
82		if (_priv->tx_tfm)
83			crypto_free_blkcipher(_priv->tx_tfm);
84		if (_priv->rx_tfm)
85			crypto_free_blkcipher(_priv->rx_tfm);
86	}
87	kfree(priv);
88}
89
90/* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
91static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
92			       u8 *key, int keylen, void *priv)
93{
94	struct lib80211_wep_data *wep = priv;
95	u32 klen;
96	u8 *pos;
97
98	if (skb_headroom(skb) < 4 || skb->len < hdr_len)
99		return -1;
100
101	pos = skb_push(skb, 4);
102	memmove(pos, pos + 4, hdr_len);
103	pos += hdr_len;
104
105	klen = 3 + wep->key_len;
106
107	wep->iv++;
108
109	/* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
110	 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
111	 * can be used to speedup attacks, so avoid using them. */
112	if ((wep->iv & 0xff00) == 0xff00) {
113		u8 B = (wep->iv >> 16) & 0xff;
114		if (B >= 3 && B < klen)
115			wep->iv += 0x0100;
116	}
117
118	/* Prepend 24-bit IV to RC4 key and TX frame */
119	*pos++ = (wep->iv >> 16) & 0xff;
120	*pos++ = (wep->iv >> 8) & 0xff;
121	*pos++ = wep->iv & 0xff;
122	*pos++ = wep->key_idx << 6;
123
124	return 0;
125}
126
127/* Perform WEP encryption on given skb that has at least 4 bytes of headroom
128 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
129 * so the payload length increases with 8 bytes.
130 *
131 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
132 */
133static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
134{
135	struct lib80211_wep_data *wep = priv;
136	struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
137	u32 crc, klen, len;
138	u8 *pos, *icv;
139	struct scatterlist sg;
140	u8 key[WEP_KEY_LEN + 3];
141
142	/* other checks are in lib80211_wep_build_iv */
143	if (skb_tailroom(skb) < 4)
144		return -1;
145
146	/* add the IV to the frame */
147	if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
148		return -1;
149
150	/* Copy the IV into the first 3 bytes of the key */
151	skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
152
153	/* Copy rest of the WEP key (the secret part) */
154	memcpy(key + 3, wep->key, wep->key_len);
155
156	len = skb->len - hdr_len - 4;
157	pos = skb->data + hdr_len + 4;
158	klen = 3 + wep->key_len;
159
160	/* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
161	crc = ~crc32_le(~0, pos, len);
162	icv = skb_put(skb, 4);
163	icv[0] = crc;
164	icv[1] = crc >> 8;
165	icv[2] = crc >> 16;
166	icv[3] = crc >> 24;
167
168	crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
169	sg_init_one(&sg, pos, len + 4);
170	return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
171}
172
173/* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
174 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
175 * ICV (4 bytes). len includes both IV and ICV.
176 *
177 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
178 * failure. If frame is OK, IV and ICV will be removed.
179 */
180static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
181{
182	struct lib80211_wep_data *wep = priv;
183	struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
184	u32 crc, klen, plen;
185	u8 key[WEP_KEY_LEN + 3];
186	u8 keyidx, *pos, icv[4];
187	struct scatterlist sg;
188
189	if (skb->len < hdr_len + 8)
190		return -1;
191
192	pos = skb->data + hdr_len;
193	key[0] = *pos++;
194	key[1] = *pos++;
195	key[2] = *pos++;
196	keyidx = *pos++ >> 6;
197	if (keyidx != wep->key_idx)
198		return -1;
199
200	klen = 3 + wep->key_len;
201
202	/* Copy rest of the WEP key (the secret part) */
203	memcpy(key + 3, wep->key, wep->key_len);
204
205	/* Apply RC4 to data and compute CRC32 over decrypted data */
206	plen = skb->len - hdr_len - 8;
207
208	crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
209	sg_init_one(&sg, pos, plen + 4);
210	if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
211		return -7;
212
213	crc = ~crc32_le(~0, pos, plen);
214	icv[0] = crc;
215	icv[1] = crc >> 8;
216	icv[2] = crc >> 16;
217	icv[3] = crc >> 24;
218	if (memcmp(icv, pos + plen, 4) != 0) {
219		/* ICV mismatch - drop frame */
220		return -2;
221	}
222
223	/* Remove IV and ICV */
224	memmove(skb->data + 4, skb->data, hdr_len);
225	skb_pull(skb, 4);
226	skb_trim(skb, skb->len - 4);
227
228	return 0;
229}
230
231static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
232{
233	struct lib80211_wep_data *wep = priv;
234
235	if (len < 0 || len > WEP_KEY_LEN)
236		return -1;
237
238	memcpy(wep->key, key, len);
239	wep->key_len = len;
240
241	return 0;
242}
243
244static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
245{
246	struct lib80211_wep_data *wep = priv;
247
248	if (len < wep->key_len)
249		return -1;
250
251	memcpy(key, wep->key, wep->key_len);
252
253	return wep->key_len;
254}
255
256static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
257{
258	struct lib80211_wep_data *wep = priv;
259	seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
260}
261
262static struct lib80211_crypto_ops lib80211_crypt_wep = {
263	.name = "WEP",
264	.init = lib80211_wep_init,
265	.deinit = lib80211_wep_deinit,
266	.encrypt_mpdu = lib80211_wep_encrypt,
267	.decrypt_mpdu = lib80211_wep_decrypt,
268	.encrypt_msdu = NULL,
269	.decrypt_msdu = NULL,
270	.set_key = lib80211_wep_set_key,
271	.get_key = lib80211_wep_get_key,
272	.print_stats = lib80211_wep_print_stats,
273	.extra_mpdu_prefix_len = 4,	/* IV */
274	.extra_mpdu_postfix_len = 4,	/* ICV */
275	.owner = THIS_MODULE,
276};
277
278static int __init lib80211_crypto_wep_init(void)
279{
280	return lib80211_register_crypto_ops(&lib80211_crypt_wep);
281}
282
283static void __exit lib80211_crypto_wep_exit(void)
284{
285	lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
286}
287
288module_init(lib80211_crypto_wep_init);
289module_exit(lib80211_crypto_wep_exit);
290