2 * Host AP crypt: host-based WEP encryption implementation for Host AP driver
4 * Copyright (c) 2002-2004, Jouni Malinen <jkmaline@cc.hut.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/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>
19 #include "ieee80211.h"
21 #include <crypto/skcipher.h>
22 #include <linux/scatterlist.h>
23 #include <linux/crc32.h>
25 MODULE_AUTHOR("Jouni Malinen");
26 MODULE_DESCRIPTION("Host AP crypt: WEP");
27 MODULE_LICENSE("GPL");
29 struct prism2_wep_data {
31 #define WEP_KEY_LEN 13
32 u8 key[WEP_KEY_LEN + 1];
35 struct crypto_skcipher *tx_tfm;
36 struct crypto_skcipher *rx_tfm;
40 static void *prism2_wep_init(int keyidx)
42 struct prism2_wep_data *priv;
44 priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
47 priv->key_idx = keyidx;
49 priv->tx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
50 if (IS_ERR(priv->tx_tfm))
52 priv->rx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
53 if (IS_ERR(priv->rx_tfm))
56 /* start WEP IV from a random value */
57 get_random_bytes(&priv->iv, 4);
61 crypto_free_skcipher(priv->tx_tfm);
68 static void prism2_wep_deinit(void *priv)
70 struct prism2_wep_data *_priv = priv;
73 crypto_free_skcipher(_priv->tx_tfm);
74 crypto_free_skcipher(_priv->rx_tfm);
79 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
80 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
81 * so the payload length increases with 8 bytes.
83 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
85 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
87 struct prism2_wep_data *wep = priv;
89 u8 key[WEP_KEY_LEN + 3];
91 cb_desc *tcb_desc = (cb_desc *)(skb->cb + MAX_DEV_ADDR_SIZE);
94 struct scatterlist sg;
97 if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
101 len = skb->len - hdr_len;
102 pos = skb_push(skb, 4);
103 memmove(pos, pos + 4, hdr_len);
106 klen = 3 + wep->key_len;
110 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
111 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
112 * can be used to speedup attacks, so avoid using them. */
113 if ((wep->iv & 0xff00) == 0xff00) {
114 u8 B = (wep->iv >> 16) & 0xff;
116 if (B >= 3 && B < klen)
120 /* Prepend 24-bit IV to RC4 key and TX frame */
121 *pos++ = key[0] = (wep->iv >> 16) & 0xff;
122 *pos++ = key[1] = (wep->iv >> 8) & 0xff;
123 *pos++ = key[2] = wep->iv & 0xff;
124 *pos++ = wep->key_idx << 6;
126 /* Copy rest of the WEP key (the secret part) */
127 memcpy(key + 3, wep->key, wep->key_len);
129 if (!tcb_desc->bHwSec) {
130 SKCIPHER_REQUEST_ON_STACK(req, wep->tx_tfm);
132 /* Append little-endian CRC32 and encrypt it to produce ICV */
133 crc = ~crc32_le(~0, pos, len);
134 icv = skb_put(skb, 4);
140 crypto_skcipher_setkey(wep->tx_tfm, key, klen);
141 sg_init_one(&sg, pos, len+4);
143 skcipher_request_set_tfm(req, wep->tx_tfm);
144 skcipher_request_set_callback(req, 0, NULL, NULL);
145 skcipher_request_set_crypt(req, &sg, &sg, len + 4, NULL);
147 err = crypto_skcipher_encrypt(req);
148 skcipher_request_zero(req);
156 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
157 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
158 * ICV (4 bytes). len includes both IV and ICV.
160 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
161 * failure. If frame is OK, IV and ICV will be removed.
163 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
165 struct prism2_wep_data *wep = priv;
167 u8 key[WEP_KEY_LEN + 3];
169 cb_desc *tcb_desc = (cb_desc *)(skb->cb + MAX_DEV_ADDR_SIZE);
172 struct scatterlist sg;
175 if (skb->len < hdr_len + 8)
178 pos = skb->data + hdr_len;
182 keyidx = *pos++ >> 6;
183 if (keyidx != wep->key_idx)
186 klen = 3 + wep->key_len;
188 /* Copy rest of the WEP key (the secret part) */
189 memcpy(key + 3, wep->key, wep->key_len);
191 /* Apply RC4 to data and compute CRC32 over decrypted data */
192 plen = skb->len - hdr_len - 8;
194 if (!tcb_desc->bHwSec) {
195 SKCIPHER_REQUEST_ON_STACK(req, wep->rx_tfm);
197 crypto_skcipher_setkey(wep->rx_tfm, key, klen);
198 sg_init_one(&sg, pos, plen+4);
200 skcipher_request_set_tfm(req, wep->rx_tfm);
201 skcipher_request_set_callback(req, 0, NULL, NULL);
202 skcipher_request_set_crypt(req, &sg, &sg, plen + 4, NULL);
204 err = crypto_skcipher_decrypt(req);
205 skcipher_request_zero(req);
209 crc = ~crc32_le(~0, pos, plen);
214 if (memcmp(icv, pos + plen, 4) != 0) {
215 /* ICV mismatch - drop frame */
219 /* Remove IV and ICV */
220 memmove(skb->data + 4, skb->data, hdr_len);
222 skb_trim(skb, skb->len - 4);
228 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
230 struct prism2_wep_data *wep = priv;
232 if (len < 0 || len > WEP_KEY_LEN)
235 memcpy(wep->key, key, len);
242 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
244 struct prism2_wep_data *wep = priv;
246 if (len < wep->key_len)
249 memcpy(key, wep->key, wep->key_len);
255 static char *prism2_wep_print_stats(char *p, void *priv)
257 struct prism2_wep_data *wep = priv;
259 p += sprintf(p, "key[%d] alg=WEP len=%d\n",
260 wep->key_idx, wep->key_len);
265 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
267 .init = prism2_wep_init,
268 .deinit = prism2_wep_deinit,
269 .encrypt_mpdu = prism2_wep_encrypt,
270 .decrypt_mpdu = prism2_wep_decrypt,
271 .encrypt_msdu = NULL,
272 .decrypt_msdu = NULL,
273 .set_key = prism2_wep_set_key,
274 .get_key = prism2_wep_get_key,
275 .print_stats = prism2_wep_print_stats,
276 .extra_prefix_len = 4, /* IV */
277 .extra_postfix_len = 4, /* ICV */
278 .owner = THIS_MODULE,
281 int __init ieee80211_crypto_wep_init(void)
283 return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
286 void __exit ieee80211_crypto_wep_exit(void)
288 ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);