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 "hostap_crypt.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 if (!try_module_get(THIS_MODULE))
52 priv = (struct prism2_wep_data *) kmalloc(sizeof(*priv), GFP_ATOMIC);
55 memset(priv, 0, sizeof(*priv));
56 priv->key_idx = keyidx;
58 priv->tfm = crypto_alloc_tfm("arc4", 0);
59 if (priv->tfm == NULL) {
60 printk(KERN_DEBUG "hostap_crypt_wep: could not allocate "
65 /* start WEP IV from a random value */
66 get_random_bytes(&priv->iv, 4);
73 crypto_free_tfm(priv->tfm);
76 module_put(THIS_MODULE);
81 static void prism2_wep_deinit(void *priv)
83 struct prism2_wep_data *_priv = priv;
84 if (_priv && _priv->tfm)
85 crypto_free_tfm(_priv->tfm);
87 module_put(THIS_MODULE);
91 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
92 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
93 * so the payload length increases with 8 bytes.
95 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
97 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
99 struct prism2_wep_data *wep = priv;
101 u8 key[WEP_KEY_LEN + 3];
103 struct scatterlist sg;
105 if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
109 len = skb->len - hdr_len;
110 pos = skb_push(skb, 4);
111 memmove(pos, pos + 4, hdr_len);
114 klen = 3 + wep->key_len;
118 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
119 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
120 * can be used to speedup attacks, so avoid using them. */
121 if ((wep->iv & 0xff00) == 0xff00) {
122 u8 B = (wep->iv >> 16) & 0xff;
123 if (B >= 3 && B < klen)
127 /* Prepend 24-bit IV to RC4 key and TX frame */
128 *pos++ = key[0] = (wep->iv >> 16) & 0xff;
129 *pos++ = key[1] = (wep->iv >> 8) & 0xff;
130 *pos++ = key[2] = wep->iv & 0xff;
131 *pos++ = wep->key_idx << 6;
133 /* Copy rest of the WEP key (the secret part) */
134 memcpy(key + 3, wep->key, wep->key_len);
136 /* Append little-endian CRC32 and encrypt it to produce ICV */
137 crc = ~crc32_le(~0, pos, len);
138 icv = skb_put(skb, 4);
144 crypto_cipher_setkey(wep->tfm, key, klen);
145 sg.page = virt_to_page(pos);
146 sg.offset = offset_in_page(pos);
148 crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
154 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
155 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
156 * ICV (4 bytes). len includes both IV and ICV.
158 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
159 * failure. If frame is OK, IV and ICV will be removed.
161 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
163 struct prism2_wep_data *wep = priv;
165 u8 key[WEP_KEY_LEN + 3];
166 u8 keyidx, *pos, icv[4];
167 struct scatterlist sg;
169 if (skb->len < hdr_len + 8)
172 pos = skb->data + hdr_len;
176 keyidx = *pos++ >> 6;
177 if (keyidx != wep->key_idx)
180 klen = 3 + wep->key_len;
182 /* Copy rest of the WEP key (the secret part) */
183 memcpy(key + 3, wep->key, wep->key_len);
185 /* Apply RC4 to data and compute CRC32 over decrypted data */
186 plen = skb->len - hdr_len - 8;
188 crypto_cipher_setkey(wep->tfm, key, klen);
189 sg.page = virt_to_page(pos);
190 sg.offset = offset_in_page(pos);
191 sg.length = plen + 4;
192 crypto_cipher_decrypt(wep->tfm, &sg, &sg, plen + 4);
194 crc = ~crc32_le(~0, pos, plen);
199 if (memcmp(icv, pos + plen, 4) != 0) {
200 /* ICV mismatch - drop frame */
204 /* Remove IV and ICV */
205 memmove(skb->data + 4, skb->data, hdr_len);
207 skb_trim(skb, skb->len - 4);
213 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
215 struct prism2_wep_data *wep = priv;
217 if (len < 0 || len > WEP_KEY_LEN)
220 memcpy(wep->key, key, len);
227 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
229 struct prism2_wep_data *wep = priv;
231 if (len < wep->key_len)
234 memcpy(key, wep->key, wep->key_len);
240 static char * prism2_wep_print_stats(char *p, void *priv)
242 struct prism2_wep_data *wep = priv;
243 p += sprintf(p, "key[%d] alg=WEP len=%d\n",
244 wep->key_idx, wep->key_len);
249 static struct hostap_crypto_ops hostap_crypt_wep = {
251 .init = prism2_wep_init,
252 .deinit = prism2_wep_deinit,
253 .encrypt_mpdu = prism2_wep_encrypt,
254 .decrypt_mpdu = prism2_wep_decrypt,
255 .encrypt_msdu = NULL,
256 .decrypt_msdu = NULL,
257 .set_key = prism2_wep_set_key,
258 .get_key = prism2_wep_get_key,
259 .print_stats = prism2_wep_print_stats,
260 .extra_prefix_len = 4 /* IV */,
261 .extra_postfix_len = 4 /* ICV */
265 static int __init hostap_crypto_wep_init(void)
267 if (hostap_register_crypto_ops(&hostap_crypt_wep) < 0)
274 static void __exit hostap_crypto_wep_exit(void)
276 hostap_unregister_crypto_ops(&hostap_crypt_wep);
280 module_init(hostap_crypto_wep_init);
281 module_exit(hostap_crypto_wep_exit);