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
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 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate "
54 "crypto API arc4\n");
55 priv->tx_tfm = NULL;
56 goto fail;
57 }
58
59 priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
60 if (IS_ERR(priv->rx_tfm)) {
61 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate "
62 "crypto API arc4\n");
63 priv->rx_tfm = NULL;
64 goto fail;
65 }
66 /* start WEP IV from a random value */
67 get_random_bytes(&priv->iv, 4);
68
69 return priv;
70
71 fail:
72 if (priv) {
73 if (priv->tx_tfm)
74 crypto_free_blkcipher(priv->tx_tfm);
75 if (priv->rx_tfm)
76 crypto_free_blkcipher(priv->rx_tfm);
77 kfree(priv);
78 }
79 return NULL;
80 }
81
82 static void lib80211_wep_deinit(void *priv)
83 {
84 struct lib80211_wep_data *_priv = priv;
85 if (_priv) {
86 if (_priv->tx_tfm)
87 crypto_free_blkcipher(_priv->tx_tfm);
88 if (_priv->rx_tfm)
89 crypto_free_blkcipher(_priv->rx_tfm);
90 }
91 kfree(priv);
92 }
93
94 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
95 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
96 u8 *key, int keylen, void *priv)
97 {
98 struct lib80211_wep_data *wep = priv;
99 u32 klen, len;
100 u8 *pos;
101
102 if (skb_headroom(skb) < 4 || skb->len < hdr_len)
103 return -1;
104
105 len = skb->len - hdr_len;
106 pos = skb_push(skb, 4);
107 memmove(pos, pos + 4, hdr_len);
108 pos += hdr_len;
109
110 klen = 3 + wep->key_len;
111
112 wep->iv++;
113
114 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
115 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
116 * can be used to speedup attacks, so avoid using them. */
117 if ((wep->iv & 0xff00) == 0xff00) {
118 u8 B = (wep->iv >> 16) & 0xff;
119 if (B >= 3 && B < klen)
120 wep->iv += 0x0100;
121 }
122
123 /* Prepend 24-bit IV to RC4 key and TX frame */
124 *pos++ = (wep->iv >> 16) & 0xff;
125 *pos++ = (wep->iv >> 8) & 0xff;
126 *pos++ = wep->iv & 0xff;
127 *pos++ = wep->key_idx << 6;
128
129 return 0;
130 }
131
132 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
133 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
134 * so the payload length increases with 8 bytes.
135 *
136 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
137 */
138 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
139 {
140 struct lib80211_wep_data *wep = priv;
141 struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
142 u32 crc, klen, len;
143 u8 *pos, *icv;
144 struct scatterlist sg;
145 u8 key[WEP_KEY_LEN + 3];
146
147 /* other checks are in lib80211_wep_build_iv */
148 if (skb_tailroom(skb) < 4)
149 return -1;
150
151 /* add the IV to the frame */
152 if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
153 return -1;
154
155 /* Copy the IV into the first 3 bytes of the key */
156 skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
157
158 /* Copy rest of the WEP key (the secret part) */
159 memcpy(key + 3, wep->key, wep->key_len);
160
161 len = skb->len - hdr_len - 4;
162 pos = skb->data + hdr_len + 4;
163 klen = 3 + wep->key_len;
164
165 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
166 crc = ~crc32_le(~0, pos, len);
167 icv = skb_put(skb, 4);
168 icv[0] = crc;
169 icv[1] = crc >> 8;
170 icv[2] = crc >> 16;
171 icv[3] = crc >> 24;
172
173 crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
174 sg_init_one(&sg, pos, len + 4);
175 return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
176 }
177
178 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
179 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
180 * ICV (4 bytes). len includes both IV and ICV.
181 *
182 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
183 * failure. If frame is OK, IV and ICV will be removed.
184 */
185 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
186 {
187 struct lib80211_wep_data *wep = priv;
188 struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
189 u32 crc, klen, plen;
190 u8 key[WEP_KEY_LEN + 3];
191 u8 keyidx, *pos, icv[4];
192 struct scatterlist sg;
193
194 if (skb->len < hdr_len + 8)
195 return -1;
196
197 pos = skb->data + hdr_len;
198 key[0] = *pos++;
199 key[1] = *pos++;
200 key[2] = *pos++;
201 keyidx = *pos++ >> 6;
202 if (keyidx != wep->key_idx)
203 return -1;
204
205 klen = 3 + wep->key_len;
206
207 /* Copy rest of the WEP key (the secret part) */
208 memcpy(key + 3, wep->key, wep->key_len);
209
210 /* Apply RC4 to data and compute CRC32 over decrypted data */
211 plen = skb->len - hdr_len - 8;
212
213 crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
214 sg_init_one(&sg, pos, plen + 4);
215 if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
216 return -7;
217
218 crc = ~crc32_le(~0, pos, plen);
219 icv[0] = crc;
220 icv[1] = crc >> 8;
221 icv[2] = crc >> 16;
222 icv[3] = crc >> 24;
223 if (memcmp(icv, pos + plen, 4) != 0) {
224 /* ICV mismatch - drop frame */
225 return -2;
226 }
227
228 /* Remove IV and ICV */
229 memmove(skb->data + 4, skb->data, hdr_len);
230 skb_pull(skb, 4);
231 skb_trim(skb, skb->len - 4);
232
233 return 0;
234 }
235
236 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
237 {
238 struct lib80211_wep_data *wep = priv;
239
240 if (len < 0 || len > WEP_KEY_LEN)
241 return -1;
242
243 memcpy(wep->key, key, len);
244 wep->key_len = len;
245
246 return 0;
247 }
248
249 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
250 {
251 struct lib80211_wep_data *wep = priv;
252
253 if (len < wep->key_len)
254 return -1;
255
256 memcpy(key, wep->key, wep->key_len);
257
258 return wep->key_len;
259 }
260
261 static char *lib80211_wep_print_stats(char *p, void *priv)
262 {
263 struct lib80211_wep_data *wep = priv;
264 p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
265 return p;
266 }
267
268 static struct lib80211_crypto_ops lib80211_crypt_wep = {
269 .name = "WEP",
270 .init = lib80211_wep_init,
271 .deinit = lib80211_wep_deinit,
272 .build_iv = lib80211_wep_build_iv,
273 .encrypt_mpdu = lib80211_wep_encrypt,
274 .decrypt_mpdu = lib80211_wep_decrypt,
275 .encrypt_msdu = NULL,
276 .decrypt_msdu = NULL,
277 .set_key = lib80211_wep_set_key,
278 .get_key = lib80211_wep_get_key,
279 .print_stats = lib80211_wep_print_stats,
280 .extra_mpdu_prefix_len = 4, /* IV */
281 .extra_mpdu_postfix_len = 4, /* ICV */
282 .owner = THIS_MODULE,
283 };
284
285 static int __init lib80211_crypto_wep_init(void)
286 {
287 return lib80211_register_crypto_ops(&lib80211_crypt_wep);
288 }
289
290 static void __exit lib80211_crypto_wep_exit(void)
291 {
292 lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
293 }
294
295 module_init(lib80211_crypto_wep_init);
296 module_exit(lib80211_crypto_wep_exit);
297
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