2 * Host AP crypt: host-based WEP encryption implementation for Host AP driver
4 * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
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
12 #include <linux/err.h>
13 #include <linux/module.h>
14 #include <linux/init.h>
15 #include <linux/slab.h>
16 #include <linux/random.h>
17 #include <linux/scatterlist.h>
18 #include <linux/skbuff.h>
20 #include <asm/string.h>
22 #include <net/ieee80211.h>
24 #include <linux/crypto.h>
25 #include <linux/scatterlist.h>
26 #include <linux/crc32.h>
28 MODULE_AUTHOR("Jouni Malinen");
29 MODULE_DESCRIPTION("Host AP crypt: WEP");
30 MODULE_LICENSE("GPL");
32 struct prism2_wep_data
{
34 #define WEP_KEY_LEN 13
35 u8 key
[WEP_KEY_LEN
+ 1];
38 struct crypto_blkcipher
*tx_tfm
;
39 struct crypto_blkcipher
*rx_tfm
;
42 static void *prism2_wep_init(int keyidx
)
44 struct prism2_wep_data
*priv
;
46 priv
= kzalloc(sizeof(*priv
), GFP_ATOMIC
);
49 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 "
59 priv
->rx_tfm
= crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC
);
60 if (IS_ERR(priv
->rx_tfm
)) {
61 printk(KERN_DEBUG
"ieee80211_crypt_wep: could not allocate "
66 /* start WEP IV from a random value */
67 get_random_bytes(&priv
->iv
, 4);
74 crypto_free_blkcipher(priv
->tx_tfm
);
76 crypto_free_blkcipher(priv
->rx_tfm
);
82 static void prism2_wep_deinit(void *priv
)
84 struct prism2_wep_data
*_priv
= priv
;
87 crypto_free_blkcipher(_priv
->tx_tfm
);
89 crypto_free_blkcipher(_priv
->rx_tfm
);
94 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
95 static int prism2_wep_build_iv(struct sk_buff
*skb
, int hdr_len
,
96 u8
*key
, int keylen
, void *priv
)
98 struct prism2_wep_data
*wep
= priv
;
102 if (skb_headroom(skb
) < 4 || skb
->len
< hdr_len
)
105 len
= skb
->len
- hdr_len
;
106 pos
= skb_push(skb
, 4);
107 memmove(pos
, pos
+ 4, hdr_len
);
110 klen
= 3 + wep
->key_len
;
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
)
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;
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.
136 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
138 static int prism2_wep_encrypt(struct sk_buff
*skb
, int hdr_len
, void *priv
)
140 struct prism2_wep_data
*wep
= priv
;
141 struct blkcipher_desc desc
= { .tfm
= wep
->tx_tfm
};
144 struct scatterlist sg
;
145 u8 key
[WEP_KEY_LEN
+ 3];
147 /* other checks are in prism2_wep_build_iv */
148 if (skb_tailroom(skb
) < 4)
151 /* add the IV to the frame */
152 if (prism2_wep_build_iv(skb
, hdr_len
, NULL
, 0, priv
))
155 /* Copy the IV into the first 3 bytes of the key */
156 skb_copy_from_linear_data_offset(skb
, hdr_len
, key
, 3);
158 /* Copy rest of the WEP key (the secret part) */
159 memcpy(key
+ 3, wep
->key
, wep
->key_len
);
161 len
= skb
->len
- hdr_len
- 4;
162 pos
= skb
->data
+ hdr_len
+ 4;
163 klen
= 3 + wep
->key_len
;
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);
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);
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.
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.
185 static int prism2_wep_decrypt(struct sk_buff
*skb
, int hdr_len
, void *priv
)
187 struct prism2_wep_data
*wep
= priv
;
188 struct blkcipher_desc desc
= { .tfm
= wep
->rx_tfm
};
190 u8 key
[WEP_KEY_LEN
+ 3];
191 u8 keyidx
, *pos
, icv
[4];
192 struct scatterlist sg
;
194 if (skb
->len
< hdr_len
+ 8)
197 pos
= skb
->data
+ hdr_len
;
201 keyidx
= *pos
++ >> 6;
202 if (keyidx
!= wep
->key_idx
)
205 klen
= 3 + wep
->key_len
;
207 /* Copy rest of the WEP key (the secret part) */
208 memcpy(key
+ 3, wep
->key
, wep
->key_len
);
210 /* Apply RC4 to data and compute CRC32 over decrypted data */
211 plen
= skb
->len
- hdr_len
- 8;
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))
218 crc
= ~crc32_le(~0, pos
, plen
);
223 if (memcmp(icv
, pos
+ plen
, 4) != 0) {
224 /* ICV mismatch - drop frame */
228 /* Remove IV and ICV */
229 memmove(skb
->data
+ 4, skb
->data
, hdr_len
);
231 skb_trim(skb
, skb
->len
- 4);
236 static int prism2_wep_set_key(void *key
, int len
, u8
* seq
, void *priv
)
238 struct prism2_wep_data
*wep
= priv
;
240 if (len
< 0 || len
> WEP_KEY_LEN
)
243 memcpy(wep
->key
, key
, len
);
249 static int prism2_wep_get_key(void *key
, int len
, u8
* seq
, void *priv
)
251 struct prism2_wep_data
*wep
= priv
;
253 if (len
< wep
->key_len
)
256 memcpy(key
, wep
->key
, wep
->key_len
);
261 static char *prism2_wep_print_stats(char *p
, void *priv
)
263 struct prism2_wep_data
*wep
= priv
;
264 p
+= sprintf(p
, "key[%d] alg=WEP len=%d\n", wep
->key_idx
, wep
->key_len
);
268 static struct ieee80211_crypto_ops ieee80211_crypt_wep
= {
270 .init
= prism2_wep_init
,
271 .deinit
= prism2_wep_deinit
,
272 .build_iv
= prism2_wep_build_iv
,
273 .encrypt_mpdu
= prism2_wep_encrypt
,
274 .decrypt_mpdu
= prism2_wep_decrypt
,
275 .encrypt_msdu
= NULL
,
276 .decrypt_msdu
= NULL
,
277 .set_key
= prism2_wep_set_key
,
278 .get_key
= prism2_wep_get_key
,
279 .print_stats
= prism2_wep_print_stats
,
280 .extra_mpdu_prefix_len
= 4, /* IV */
281 .extra_mpdu_postfix_len
= 4, /* ICV */
282 .owner
= THIS_MODULE
,
285 static int __init
ieee80211_crypto_wep_init(void)
287 return ieee80211_register_crypto_ops(&ieee80211_crypt_wep
);
290 static void __exit
ieee80211_crypto_wep_exit(void)
292 ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep
);
295 module_init(ieee80211_crypto_wep_init
);
296 module_exit(ieee80211_crypto_wep_exit
);