1/*
2 * Software WEP encryption implementation
3 * Copyright 2002, Jouni Malinen <jkmaline@cc.hut.fi>
4 * Copyright 2003, Instant802 Networks, Inc.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 */
10
11#include <linux/netdevice.h>
12#include <linux/types.h>
13#include <linux/random.h>
14#include <linux/compiler.h>
15#include <linux/crc32.h>
16#include <linux/crypto.h>
17#include <linux/err.h>
18#include <linux/mm.h>
19#include <asm/scatterlist.h>
20
21#include <net/mac80211.h>
22#include "ieee80211_i.h"
23#include "wep.h"
24
25
26int ieee80211_wep_init(struct ieee80211_local *local)
27{
28	/* start WEP IV from a random value */
29	get_random_bytes(&local->wep_iv, WEP_IV_LEN);
30
31	local->wep_tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
32						CRYPTO_ALG_ASYNC);
33	if (IS_ERR(local->wep_tx_tfm))
34		return -ENOMEM;
35
36	local->wep_rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0,
37						CRYPTO_ALG_ASYNC);
38	if (IS_ERR(local->wep_rx_tfm)) {
39		crypto_free_blkcipher(local->wep_tx_tfm);
40		return -ENOMEM;
41	}
42
43	return 0;
44}
45
46void ieee80211_wep_free(struct ieee80211_local *local)
47{
48	crypto_free_blkcipher(local->wep_tx_tfm);
49	crypto_free_blkcipher(local->wep_rx_tfm);
50}
51
52static inline int ieee80211_wep_weak_iv(u32 iv, int keylen)
53{
54	/* Fluhrer, Mantin, and Shamir have reported weaknesses in the
55	 * key scheduling algorithm of RC4. At least IVs (KeyByte + 3,
56	 * 0xff, N) can be used to speedup attacks, so avoid using them. */
57	if ((iv & 0xff00) == 0xff00) {
58		u8 B = (iv >> 16) & 0xff;
59		if (B >= 3 && B < 3 + keylen)
60			return 1;
61	}
62	return 0;
63}
64
65
66void ieee80211_wep_get_iv(struct ieee80211_local *local,
67			  struct ieee80211_key *key, u8 *iv)
68{
69	local->wep_iv++;
70	if (ieee80211_wep_weak_iv(local->wep_iv, key->keylen))
71		local->wep_iv += 0x0100;
72
73	if (!iv)
74		return;
75
76	*iv++ = (local->wep_iv >> 16) & 0xff;
77	*iv++ = (local->wep_iv >> 8) & 0xff;
78	*iv++ = local->wep_iv & 0xff;
79	*iv++ = key->keyidx << 6;
80}
81
82
83u8 * ieee80211_wep_add_iv(struct ieee80211_local *local,
84			  struct sk_buff *skb,
85			  struct ieee80211_key *key)
86{
87	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
88	u16 fc;
89	int hdrlen;
90	u8 *newhdr;
91
92	fc = le16_to_cpu(hdr->frame_control);
93	fc |= IEEE80211_FCTL_PROTECTED;
94	hdr->frame_control = cpu_to_le16(fc);
95
96	if ((skb_headroom(skb) < WEP_IV_LEN ||
97	     skb_tailroom(skb) < WEP_ICV_LEN)) {
98		I802_DEBUG_INC(local->tx_expand_skb_head);
99		if (unlikely(pskb_expand_head(skb, WEP_IV_LEN, WEP_ICV_LEN,
100					      GFP_ATOMIC)))
101			return NULL;
102	}
103
104	hdrlen = ieee80211_get_hdrlen(fc);
105	newhdr = skb_push(skb, WEP_IV_LEN);
106	memmove(newhdr, newhdr + WEP_IV_LEN, hdrlen);
107	ieee80211_wep_get_iv(local, key, newhdr + hdrlen);
108	return newhdr + hdrlen;
109}
110
111
112void ieee80211_wep_remove_iv(struct ieee80211_local *local,
113			     struct sk_buff *skb,
114			     struct ieee80211_key *key)
115{
116	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
117	u16 fc;
118	int hdrlen;
119
120	fc = le16_to_cpu(hdr->frame_control);
121	hdrlen = ieee80211_get_hdrlen(fc);
122	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
123	skb_pull(skb, WEP_IV_LEN);
124}
125
126
127/* Perform WEP encryption using given key. data buffer must have tailroom
128 * for 4-byte ICV. data_len must not include this ICV. Note: this function
129 * does _not_ add IV. data = RC4(data | CRC32(data)) */
130void ieee80211_wep_encrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
131				size_t klen, u8 *data, size_t data_len)
132{
133	struct blkcipher_desc desc = { .tfm = tfm };
134	struct scatterlist sg;
135	__le32 *icv;
136
137	icv = (__le32 *)(data + data_len);
138	*icv = cpu_to_le32(~crc32_le(~0, data, data_len));
139
140	crypto_blkcipher_setkey(tfm, rc4key, klen);
141	sg.page = virt_to_page(data);
142	sg.offset = offset_in_page(data);
143	sg.length = data_len + WEP_ICV_LEN;
144	crypto_blkcipher_encrypt(&desc, &sg, &sg, sg.length);
145}
146
147
148/* Perform WEP encryption on given skb. 4 bytes of extra space (IV) in the
149 * beginning of the buffer 4 bytes of extra space (ICV) in the end of the
150 * buffer will be added. Both IV and ICV will be transmitted, so the
151 * payload length increases with 8 bytes.
152 *
153 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
154 */
155int ieee80211_wep_encrypt(struct ieee80211_local *local, struct sk_buff *skb,
156			  struct ieee80211_key *key)
157{
158	u32 klen;
159	u8 *rc4key, *iv;
160	size_t len;
161
162	if (!key || key->alg != ALG_WEP)
163		return -1;
164
165	klen = 3 + key->keylen;
166	rc4key = kmalloc(klen, GFP_ATOMIC);
167	if (!rc4key)
168		return -1;
169
170	iv = ieee80211_wep_add_iv(local, skb, key);
171	if (!iv) {
172		kfree(rc4key);
173		return -1;
174	}
175
176	len = skb->len - (iv + WEP_IV_LEN - skb->data);
177
178	/* Prepend 24-bit IV to RC4 key */
179	memcpy(rc4key, iv, 3);
180
181	/* Copy rest of the WEP key (the secret part) */
182	memcpy(rc4key + 3, key->key, key->keylen);
183
184	/* Add room for ICV */
185	skb_put(skb, WEP_ICV_LEN);
186
187	ieee80211_wep_encrypt_data(local->wep_tx_tfm, rc4key, klen,
188				   iv + WEP_IV_LEN, len);
189
190	kfree(rc4key);
191
192	return 0;
193}
194
195
196/* Perform WEP decryption using given key. data buffer includes encrypted
197 * payload, including 4-byte ICV, but _not_ IV. data_len must not include ICV.
198 * Return 0 on success and -1 on ICV mismatch. */
199int ieee80211_wep_decrypt_data(struct crypto_blkcipher *tfm, u8 *rc4key,
200			       size_t klen, u8 *data, size_t data_len)
201{
202	struct blkcipher_desc desc = { .tfm = tfm };
203	struct scatterlist sg;
204	__le32 crc;
205
206	crypto_blkcipher_setkey(tfm, rc4key, klen);
207	sg.page = virt_to_page(data);
208	sg.offset = offset_in_page(data);
209	sg.length = data_len + WEP_ICV_LEN;
210	crypto_blkcipher_decrypt(&desc, &sg, &sg, sg.length);
211
212	crc = cpu_to_le32(~crc32_le(~0, data, data_len));
213	if (memcmp(&crc, data + data_len, WEP_ICV_LEN) != 0)
214		/* ICV mismatch */
215		return -1;
216
217	return 0;
218}
219
220
221/* Perform WEP decryption on given skb. Buffer includes whole WEP part of
222 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
223 * ICV (4 bytes). skb->len includes both IV and ICV.
224 *
225 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
226 * failure. If frame is OK, IV and ICV will be removed, i.e., decrypted payload
227 * is moved to the beginning of the skb and skb length will be reduced.
228 */
229int ieee80211_wep_decrypt(struct ieee80211_local *local, struct sk_buff *skb,
230			  struct ieee80211_key *key)
231{
232	u32 klen;
233	u8 *rc4key;
234	u8 keyidx;
235	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
236	u16 fc;
237	int hdrlen;
238	size_t len;
239	int ret = 0;
240
241	fc = le16_to_cpu(hdr->frame_control);
242	if (!(fc & IEEE80211_FCTL_PROTECTED))
243		return -1;
244
245	hdrlen = ieee80211_get_hdrlen(fc);
246
247	if (skb->len < 8 + hdrlen)
248		return -1;
249
250	len = skb->len - hdrlen - 8;
251
252	keyidx = skb->data[hdrlen + 3] >> 6;
253
254	if (!key || keyidx != key->keyidx || key->alg != ALG_WEP)
255		return -1;
256
257	klen = 3 + key->keylen;
258
259	rc4key = kmalloc(klen, GFP_ATOMIC);
260	if (!rc4key)
261		return -1;
262
263	/* Prepend 24-bit IV to RC4 key */
264	memcpy(rc4key, skb->data + hdrlen, 3);
265
266	/* Copy rest of the WEP key (the secret part) */
267	memcpy(rc4key + 3, key->key, key->keylen);
268
269	if (ieee80211_wep_decrypt_data(local->wep_rx_tfm, rc4key, klen,
270				       skb->data + hdrlen + WEP_IV_LEN,
271				       len)) {
272		printk(KERN_DEBUG "WEP decrypt failed (ICV)\n");
273		ret = -1;
274	}
275
276	kfree(rc4key);
277
278	/* Trim ICV */
279	skb_trim(skb, skb->len - WEP_ICV_LEN);
280
281	/* Remove IV */
282	memmove(skb->data + WEP_IV_LEN, skb->data, hdrlen);
283	skb_pull(skb, WEP_IV_LEN);
284
285	return ret;
286}
287
288
289int ieee80211_wep_get_keyidx(struct sk_buff *skb)
290{
291	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
292	u16 fc;
293	int hdrlen;
294
295	fc = le16_to_cpu(hdr->frame_control);
296	if (!(fc & IEEE80211_FCTL_PROTECTED))
297		return -1;
298
299	hdrlen = ieee80211_get_hdrlen(fc);
300
301	if (skb->len < 8 + hdrlen)
302		return -1;
303
304	return skb->data[hdrlen + 3] >> 6;
305}
306
307
308u8 * ieee80211_wep_is_weak_iv(struct sk_buff *skb, struct ieee80211_key *key)
309{
310	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
311	u16 fc;
312	int hdrlen;
313	u8 *ivpos;
314	u32 iv;
315
316	fc = le16_to_cpu(hdr->frame_control);
317	if (!(fc & IEEE80211_FCTL_PROTECTED))
318		return NULL;
319
320	hdrlen = ieee80211_get_hdrlen(fc);
321	ivpos = skb->data + hdrlen;
322	iv = (ivpos[0] << 16) | (ivpos[1] << 8) | ivpos[2];
323
324	if (ieee80211_wep_weak_iv(iv, key->keylen))
325		return ivpos;
326
327	return NULL;
328}
329