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/config.h>
13 #include <linux/version.h>
14 #include <linux/module.h>
15 #include <linux/init.h>
16 #include <linux/slab.h>
17 #include <linux/random.h>
18 #include <linux/skbuff.h>
19 #include <asm/string.h>
21 #include "ieee80211.h"
24 #error CONFIG_CRYPTO is required to build this module.
26 #include <linux/crypto.h>
27 #include <asm/scatterlist.h>
28 #include <linux/crc32.h>
30 MODULE_AUTHOR("Jouni Malinen");
31 MODULE_DESCRIPTION("Host AP crypt: WEP");
32 MODULE_LICENSE("GPL");
35 struct prism2_wep_data {
37 #define WEP_KEY_LEN 13
38 u8 key[WEP_KEY_LEN + 1];
41 struct crypto_tfm *tfm;
45 static void * prism2_wep_init(int keyidx)
47 struct prism2_wep_data *priv;
49 priv = kmalloc(sizeof(*priv), GFP_ATOMIC);
52 memset(priv, 0, sizeof(*priv));
53 priv->key_idx = keyidx;
55 priv->tfm = crypto_alloc_tfm("arc4", 0);
56 if (priv->tfm == NULL) {
57 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
62 /* start WEP IV from a random value */
63 get_random_bytes(&priv->iv, 4);
70 crypto_free_tfm(priv->tfm);
77 static void prism2_wep_deinit(void *priv)
79 struct prism2_wep_data *_priv = priv;
80 if (_priv && _priv->tfm)
81 crypto_free_tfm(_priv->tfm);
86 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
87 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
88 * so the payload length increases with 8 bytes.
90 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
92 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
94 struct prism2_wep_data *wep = priv;
96 u8 key[WEP_KEY_LEN + 3];
98 struct scatterlist sg;
100 if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
104 len = skb->len - hdr_len;
105 pos = skb_push(skb, 4);
106 memmove(pos, pos + 4, hdr_len);
109 klen = 3 + wep->key_len;
113 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
114 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
115 * can be used to speedup attacks, so avoid using them. */
116 if ((wep->iv & 0xff00) == 0xff00) {
117 u8 B = (wep->iv >> 16) & 0xff;
118 if (B >= 3 && B < klen)
122 /* Prepend 24-bit IV to RC4 key and TX frame */
123 *pos++ = key[0] = (wep->iv >> 16) & 0xff;
124 *pos++ = key[1] = (wep->iv >> 8) & 0xff;
125 *pos++ = key[2] = wep->iv & 0xff;
126 *pos++ = wep->key_idx << 6;
128 /* Copy rest of the WEP key (the secret part) */
129 memcpy(key + 3, wep->key, wep->key_len);
131 /* Append little-endian CRC32 and encrypt it to produce ICV */
132 crc = ~crc32_le(~0, pos, len);
133 icv = skb_put(skb, 4);
139 crypto_cipher_setkey(wep->tfm, key, klen);
140 sg.page = virt_to_page(pos);
141 sg.offset = offset_in_page(pos);
143 crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
149 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
150 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
151 * ICV (4 bytes). len includes both IV and ICV.
153 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
154 * failure. If frame is OK, IV and ICV will be removed.
156 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
158 struct prism2_wep_data *wep = priv;
160 u8 key[WEP_KEY_LEN + 3];
161 u8 keyidx, *pos, icv[4];
162 struct scatterlist sg;
164 if (skb->len < hdr_len + 8)
167 pos = skb->data + hdr_len;
171 keyidx = *pos++ >> 6;
172 if (keyidx != wep->key_idx)
175 klen = 3 + wep->key_len;
177 /* Copy rest of the WEP key (the secret part) */
178 memcpy(key + 3, wep->key, wep->key_len);
180 /* Apply RC4 to data and compute CRC32 over decrypted data */
181 plen = skb->len - hdr_len - 8;
183 crypto_cipher_setkey(wep->tfm, key, klen);
184 sg.page = virt_to_page(pos);
185 sg.offset = offset_in_page(pos);
186 sg.length = plen + 4;
187 crypto_cipher_decrypt(wep->tfm, &sg, &sg, plen + 4);
189 crc = ~crc32_le(~0, pos, plen);
194 if (memcmp(icv, pos + plen, 4) != 0) {
195 /* ICV mismatch - drop frame */
199 /* Remove IV and ICV */
200 memmove(skb->data + 4, skb->data, hdr_len);
202 skb_trim(skb, skb->len - 4);
208 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
210 struct prism2_wep_data *wep = priv;
212 if (len < 0 || len > WEP_KEY_LEN)
215 memcpy(wep->key, key, len);
222 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
224 struct prism2_wep_data *wep = priv;
226 if (len < wep->key_len)
229 memcpy(key, wep->key, wep->key_len);
235 static char * prism2_wep_print_stats(char *p, void *priv)
237 struct prism2_wep_data *wep = priv;
238 p += sprintf(p, "key[%d] alg=WEP len=%d\n",
239 wep->key_idx, wep->key_len);
244 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
246 .init = prism2_wep_init,
247 .deinit = prism2_wep_deinit,
248 .encrypt_mpdu = prism2_wep_encrypt,
249 .decrypt_mpdu = prism2_wep_decrypt,
250 .encrypt_msdu = NULL,
251 .decrypt_msdu = NULL,
252 .set_key = prism2_wep_set_key,
253 .get_key = prism2_wep_get_key,
254 .print_stats = prism2_wep_print_stats,
255 .extra_prefix_len = 4, /* IV */
256 .extra_postfix_len = 4, /* ICV */
257 .owner = THIS_MODULE,
261 static int __init ieee80211_crypto_wep_init(void)
263 if (ieee80211_register_crypto_ops(&ieee80211_crypt_wep) < 0)
270 static void __exit ieee80211_crypto_wep_exit(void)
272 ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
276 module_init(ieee80211_crypto_wep_init);
277 module_exit(ieee80211_crypto_wep_exit);