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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 | .encrypt_mpdu = lib80211_wep_encrypt, |
273 | .decrypt_mpdu = lib80211_wep_decrypt, |
274 | .encrypt_msdu = NULL, |
275 | .decrypt_msdu = NULL, |
276 | .set_key = lib80211_wep_set_key, |
277 | .get_key = lib80211_wep_get_key, |
278 | .print_stats = lib80211_wep_print_stats, |
279 | .extra_mpdu_prefix_len = 4, /* IV */ |
280 | .extra_mpdu_postfix_len = 4, /* ICV */ |
281 | .owner = THIS_MODULE, |
282 | }; |
283 | |
284 | static int __init lib80211_crypto_wep_init(void) |
285 | { |
286 | return lib80211_register_crypto_ops(&lib80211_crypt_wep); |
287 | } |
288 | |
289 | static void __exit lib80211_crypto_wep_exit(void) |
290 | { |
291 | lib80211_unregister_crypto_ops(&lib80211_crypt_wep); |
292 | } |
293 | |
294 | module_init(lib80211_crypto_wep_init); |
295 | module_exit(lib80211_crypto_wep_exit); |
296 |
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