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ieee80211_crypt_wep.c
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1 /*
2  * Host AP crypt: host-based WEP encryption implementation for Host AP driver
3  *
4  * Copyright (c) 2002-2004, Jouni Malinen <[email protected]>
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. See README and COPYING for
9  * more details.
10  */
11 
12 //#include <linux/config.h>
13 #include <linux/module.h>
14 #include <linux/init.h>
15 #include <linux/slab.h>
16 #include <linux/random.h>
17 #include <linux/skbuff.h>
18 #include <asm/string.h>
19 
20 #include "ieee80211.h"
21 
22 #include <linux/crypto.h>
23 #include <linux/scatterlist.h>
24 #include <linux/crc32.h>
25 
26 MODULE_AUTHOR("Jouni Malinen");
27 MODULE_DESCRIPTION("Host AP crypt: WEP");
28 MODULE_LICENSE("GPL");
29 
30 
31 
34 #define WEP_KEY_LEN 13
40 };
41 
42 
43 static void * prism2_wep_init(int keyidx)
44 {
45  struct prism2_wep_data *priv;
46 
47  priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
48  if (priv == NULL)
49  goto fail;
50  priv->key_idx = keyidx;
51  priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
52  if (IS_ERR(priv->tx_tfm)) {
53  printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
54  "crypto API arc4\n");
55  priv->tx_tfm = NULL;
56  goto fail;
57  }
58  priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
59  if (IS_ERR(priv->rx_tfm)) {
60  printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
61  "crypto API arc4\n");
62  priv->rx_tfm = NULL;
63  goto fail;
64  }
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 
80  return NULL;
81 }
82 
83 
84 static void prism2_wep_deinit(void *priv)
85 {
86  struct prism2_wep_data *_priv = priv;
87 
88  if (_priv) {
89  if (_priv->tx_tfm)
90  crypto_free_blkcipher(_priv->tx_tfm);
91  if (_priv->rx_tfm)
92  crypto_free_blkcipher(_priv->rx_tfm);
93  }
94 
95  kfree(priv);
96 }
97 
98 
99 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
100  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
101  * so the payload length increases with 8 bytes.
102  *
103  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
104  */
105 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
106 {
107  struct prism2_wep_data *wep = priv;
108  struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
109  u32 klen, len;
110  u8 key[WEP_KEY_LEN + 3];
111  u8 *pos;
112  u32 crc;
113  u8 *icv;
114  struct scatterlist sg;
115 
116  if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
117  skb->len < hdr_len)
118  return -1;
119 
120  len = skb->len - hdr_len;
121  pos = skb_push(skb, 4);
122  memmove(pos, pos + 4, hdr_len);
123  pos += hdr_len;
124 
125  klen = 3 + wep->key_len;
126 
127  wep->iv++;
128 
129  /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
130  * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
131  * can be used to speedup attacks, so avoid using them. */
132  if ((wep->iv & 0xff00) == 0xff00) {
133  u8 B = (wep->iv >> 16) & 0xff;
134  if (B >= 3 && B < klen)
135  wep->iv += 0x0100;
136  }
137 
138  /* Prepend 24-bit IV to RC4 key and TX frame */
139  *pos++ = key[0] = (wep->iv >> 16) & 0xff;
140  *pos++ = key[1] = (wep->iv >> 8) & 0xff;
141  *pos++ = key[2] = wep->iv & 0xff;
142  *pos++ = wep->key_idx << 6;
143 
144  /* Copy rest of the WEP key (the secret part) */
145  memcpy(key + 3, wep->key, wep->key_len);
146 
147  /* Append little-endian CRC32 and encrypt it to produce ICV */
148  crc = ~crc32_le(~0, pos, len);
149  icv = skb_put(skb, 4);
150  icv[0] = crc;
151  icv[1] = crc >> 8;
152  icv[2] = crc >> 16;
153  icv[3] = crc >> 24;
154 
155  crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
156  sg_init_one(&sg, pos, len + 4);
157 
158  return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
159 }
160 
161 
162 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
163  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
164  * ICV (4 bytes). len includes both IV and ICV.
165  *
166  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
167  * failure. If frame is OK, IV and ICV will be removed.
168  */
169 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
170 {
171  struct prism2_wep_data *wep = priv;
172  struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
173  u32 klen, plen;
174  u8 key[WEP_KEY_LEN + 3];
175  u8 keyidx, *pos;
176  u32 crc;
177  u8 icv[4];
178  struct scatterlist sg;
179 
180  if (skb->len < hdr_len + 8)
181  return -1;
182 
183  pos = skb->data + hdr_len;
184  key[0] = *pos++;
185  key[1] = *pos++;
186  key[2] = *pos++;
187  keyidx = *pos++ >> 6;
188  if (keyidx != wep->key_idx)
189  return -1;
190 
191  klen = 3 + wep->key_len;
192 
193  /* Copy rest of the WEP key (the secret part) */
194  memcpy(key + 3, wep->key, wep->key_len);
195 
196  /* Apply RC4 to data and compute CRC32 over decrypted data */
197  plen = skb->len - hdr_len - 8;
198 
199  crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
200  sg_init_one(&sg, pos, plen + 4);
201 
202  if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
203  return -7;
204 
205  crc = ~crc32_le(~0, pos, plen);
206  icv[0] = crc;
207  icv[1] = crc >> 8;
208  icv[2] = crc >> 16;
209  icv[3] = crc >> 24;
210 
211  if (memcmp(icv, pos + plen, 4) != 0) {
212  /* ICV mismatch - drop frame */
213  return -2;
214  }
215 
216  /* Remove IV and ICV */
217  memmove(skb->data + 4, skb->data, hdr_len);
218  skb_pull(skb, 4);
219  skb_trim(skb, skb->len - 4);
220  return 0;
221 }
222 
223 
224 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
225 {
226  struct prism2_wep_data *wep = priv;
227 
228  if (len < 0 || len > WEP_KEY_LEN)
229  return -1;
230 
231  memcpy(wep->key, key, len);
232  wep->key_len = len;
233 
234  return 0;
235 }
236 
237 
238 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
239 {
240  struct prism2_wep_data *wep = priv;
241 
242  if (len < wep->key_len)
243  return -1;
244 
245  memcpy(key, wep->key, wep->key_len);
246 
247  return wep->key_len;
248 }
249 
250 
251 static char * prism2_wep_print_stats(char *p, void *priv)
252 {
253  struct prism2_wep_data *wep = priv;
254  p += sprintf(p, "key[%d] alg=WEP len=%d\n",
255  wep->key_idx, wep->key_len);
256  return p;
257 }
258 
259 
260 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
261  .name = "WEP",
262  .init = prism2_wep_init,
263  .deinit = prism2_wep_deinit,
264  .encrypt_mpdu = prism2_wep_encrypt,
265  .decrypt_mpdu = prism2_wep_decrypt,
266  .encrypt_msdu = NULL,
267  .decrypt_msdu = NULL,
268  .set_key = prism2_wep_set_key,
269  .get_key = prism2_wep_get_key,
270  .print_stats = prism2_wep_print_stats,
271  .extra_prefix_len = 4, /* IV */
272  .extra_postfix_len = 4, /* ICV */
273  .owner = THIS_MODULE,
274 };
275 
276 
278 {
279  return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
280 }
281 
282 
284 {
285  ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
286 }
287 
288 
290 {
291 // printk("============>%s()\n", __func__);
292  return;
293 }