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
28 MODULE_AUTHOR("Jouni Malinen");
29 MODULE_DESCRIPTION("lib80211 crypt: WEP");
30 MODULE_LICENSE("GPL");
31
32 struct 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
lib80211_wep_init(int keyidx)42 static 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
lib80211_wep_deinit(void * priv)78 static 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 */
lib80211_wep_build_iv(struct sk_buff * skb,int hdr_len,u8 * key,int keylen,void * priv)91 static 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 */
lib80211_wep_encrypt(struct sk_buff * skb,int hdr_len,void * priv)133 static 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 */
lib80211_wep_decrypt(struct sk_buff * skb,int hdr_len,void * priv)180 static 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
lib80211_wep_set_key(void * key,int len,u8 * seq,void * priv)231 static 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
lib80211_wep_get_key(void * key,int len,u8 * seq,void * priv)244 static 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
lib80211_wep_print_stats(char * p,void * priv)256 static char *lib80211_wep_print_stats(char *p, void *priv)
257 {
258 struct lib80211_wep_data *wep = priv;
259 p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
260 return p;
261 }
262
263 static struct lib80211_crypto_ops lib80211_crypt_wep = {
264 .name = "WEP",
265 .init = lib80211_wep_init,
266 .deinit = lib80211_wep_deinit,
267 .encrypt_mpdu = lib80211_wep_encrypt,
268 .decrypt_mpdu = lib80211_wep_decrypt,
269 .encrypt_msdu = NULL,
270 .decrypt_msdu = NULL,
271 .set_key = lib80211_wep_set_key,
272 .get_key = lib80211_wep_get_key,
273 .print_stats = lib80211_wep_print_stats,
274 .extra_mpdu_prefix_len = 4, /* IV */
275 .extra_mpdu_postfix_len = 4, /* ICV */
276 .owner = THIS_MODULE,
277 };
278
lib80211_crypto_wep_init(void)279 static int __init lib80211_crypto_wep_init(void)
280 {
281 return lib80211_register_crypto_ops(&lib80211_crypt_wep);
282 }
283
lib80211_crypto_wep_exit(void)284 static void __exit lib80211_crypto_wep_exit(void)
285 {
286 lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
287 }
288
289 module_init(lib80211_crypto_wep_init);
290 module_exit(lib80211_crypto_wep_exit);
291