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rtllib_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/module.h>
13 #include <linux/init.h>
14 #include <linux/slab.h>
15 #include <linux/random.h>
16 #include <linux/skbuff.h>
17 #include <linux/string.h>
18 #include "rtllib.h"
19 
20 #include <linux/crypto.h>
21 
22 #include <linux/scatterlist.h>
23 #include <linux/crc32.h>
24 
25 struct prism2_wep_data {
26  u32 iv;
27 #define WEP_KEY_LEN 13
28  u8 key[WEP_KEY_LEN + 1];
29  u8 key_len;
30  u8 key_idx;
31  struct crypto_blkcipher *tx_tfm;
32  struct crypto_blkcipher *rx_tfm;
33 };
34 
35 
36 static void *prism2_wep_init(int keyidx)
37 {
38  struct prism2_wep_data *priv;
39 
40  priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
41  if (priv == NULL)
42  goto fail;
43  priv->key_idx = keyidx;
44 
45  priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
46  if (IS_ERR(priv->tx_tfm)) {
47  printk(KERN_DEBUG "rtllib_crypt_wep: could not allocate "
48  "crypto API arc4\n");
49  priv->tx_tfm = NULL;
50  goto fail;
51  }
52  priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
53  if (IS_ERR(priv->rx_tfm)) {
54  printk(KERN_DEBUG "rtllib_crypt_wep: could not allocate "
55  "crypto API arc4\n");
56  priv->rx_tfm = NULL;
57  goto fail;
58  }
59 
60  /* start WEP IV from a random value */
61  get_random_bytes(&priv->iv, 4);
62 
63  return priv;
64 
65 fail:
66  if (priv) {
67  if (priv->tx_tfm)
68  crypto_free_blkcipher(priv->tx_tfm);
69  if (priv->rx_tfm)
70  crypto_free_blkcipher(priv->rx_tfm);
71  kfree(priv);
72  }
73  return NULL;
74 }
75 
76 
77 static void prism2_wep_deinit(void *priv)
78 {
79  struct prism2_wep_data *_priv = priv;
80 
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 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
91  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
92  * so the payload length increases with 8 bytes.
93  *
94  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
95  */
96 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
97 {
98  struct prism2_wep_data *wep = priv;
99  u32 klen, len;
100  u8 key[WEP_KEY_LEN + 3];
101  u8 *pos;
102  struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb +
104  struct blkcipher_desc desc = {.tfm = wep->tx_tfm};
105  u32 crc;
106  u8 *icv;
107  struct scatterlist sg;
108  if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
109  skb->len < hdr_len){
110  printk(KERN_ERR "Error!!! headroom=%d tailroom=%d skblen=%d"
111  " hdr_len=%d\n", skb_headroom(skb), skb_tailroom(skb),
112  skb->len, hdr_len);
113  return -1;
114  }
115  len = skb->len - hdr_len;
116  pos = skb_push(skb, 4);
117  memmove(pos, pos + 4, hdr_len);
118  pos += hdr_len;
119 
120  klen = 3 + wep->key_len;
121 
122  wep->iv++;
123 
124  /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
125  * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
126  * can be used to speedup attacks, so avoid using them. */
127  if ((wep->iv & 0xff00) == 0xff00) {
128  u8 B = (wep->iv >> 16) & 0xff;
129  if (B >= 3 && B < klen)
130  wep->iv += 0x0100;
131  }
132 
133  /* Prepend 24-bit IV to RC4 key and TX frame */
134  *pos++ = key[0] = (wep->iv >> 16) & 0xff;
135  *pos++ = key[1] = (wep->iv >> 8) & 0xff;
136  *pos++ = key[2] = wep->iv & 0xff;
137  *pos++ = wep->key_idx << 6;
138 
139  /* Copy rest of the WEP key (the secret part) */
140  memcpy(key + 3, wep->key, wep->key_len);
141 
142  if (!tcb_desc->bHwSec) {
143 
144  /* Append little-endian CRC32 and encrypt it to produce ICV */
145  crc = ~crc32_le(~0, pos, len);
146  icv = skb_put(skb, 4);
147  icv[0] = crc;
148  icv[1] = crc >> 8;
149  icv[2] = crc >> 16;
150  icv[3] = crc >> 24;
151 
152  sg_init_one(&sg, pos, len+4);
153  crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
154  return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
155  }
156 
157  return 0;
158 }
159 
160 
161 /* Perform WEP decryption on given struct buffer. Buffer includes whole WEP
162  * part of the frame: IV (4 bytes), encrypted payload (including SNAP header),
163  * ICV (4 bytes). len includes both IV and ICV.
164  *
165  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
166  * failure. If frame is OK, IV and ICV will be removed.
167  */
168 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
169 {
170  struct prism2_wep_data *wep = priv;
171  u32 klen, plen;
172  u8 key[WEP_KEY_LEN + 3];
173  u8 keyidx, *pos;
174  struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb +
176  struct blkcipher_desc desc = {.tfm = wep->rx_tfm};
177  u32 crc;
178  u8 icv[4];
179  struct scatterlist sg;
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  if (!tcb_desc->bHwSec) {
200  sg_init_one(&sg, pos, plen+4);
201  crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
202  if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
203  return -7;
204  crc = ~crc32_le(~0, pos, plen);
205  icv[0] = crc;
206  icv[1] = crc >> 8;
207  icv[2] = crc >> 16;
208  icv[3] = crc >> 24;
209  if (memcmp(icv, pos + plen, 4) != 0) {
210  /* ICV mismatch - drop frame */
211  return -2;
212  }
213  }
214  /* Remove IV and ICV */
215  memmove(skb->data + 4, skb->data, hdr_len);
216  skb_pull(skb, 4);
217  skb_trim(skb, skb->len - 4);
218 
219  return 0;
220 }
221 
222 
223 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
224 {
225  struct prism2_wep_data *wep = priv;
226 
227  if (len < 0 || len > WEP_KEY_LEN)
228  return -1;
229 
230  memcpy(wep->key, key, len);
231  wep->key_len = len;
232 
233  return 0;
234 }
235 
236 
237 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
238 {
239  struct prism2_wep_data *wep = priv;
240 
241  if (len < wep->key_len)
242  return -1;
243 
244  memcpy(key, wep->key, wep->key_len);
245 
246  return wep->key_len;
247 }
248 
249 
250 static char *prism2_wep_print_stats(char *p, void *priv)
251 {
252  struct prism2_wep_data *wep = priv;
253  p += sprintf(p, "key[%d] alg=WEP len=%d\n",
254  wep->key_idx, wep->key_len);
255  return p;
256 }
257 
258 static struct lib80211_crypto_ops rtllib_crypt_wep = {
259  .name = "R-WEP",
260  .init = prism2_wep_init,
261  .deinit = prism2_wep_deinit,
262  .encrypt_mpdu = prism2_wep_encrypt,
263  .decrypt_mpdu = prism2_wep_decrypt,
264  .encrypt_msdu = NULL,
265  .decrypt_msdu = NULL,
266  .set_key = prism2_wep_set_key,
267  .get_key = prism2_wep_get_key,
268  .print_stats = prism2_wep_print_stats,
269  .extra_mpdu_prefix_len = 4, /* IV */
270  .extra_mpdu_postfix_len = 4, /* ICV */
271  .owner = THIS_MODULE,
272 };
273 
274 
276 {
277  return lib80211_register_crypto_ops(&rtllib_crypt_wep);
278 }
279 
280 
282 {
283  lib80211_unregister_crypto_ops(&rtllib_crypt_wep);
284 }
285 
288 
289 MODULE_LICENSE("GPL");