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/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/skbuff.h>
18 #include <asm/string.h>
20 #include <net/ieee80211.h>
22 #include <linux/crypto.h>
23 #include <asm/scatterlist.h>
24 #include <linux/crc32.h>
26 MODULE_AUTHOR("Jouni Malinen");
27 MODULE_DESCRIPTION("Host AP crypt: WEP");
28 MODULE_LICENSE("GPL");
30 struct prism2_wep_data {
32 #define WEP_KEY_LEN 13
33 u8 key[WEP_KEY_LEN + 1];
36 struct crypto_blkcipher *tx_tfm;
37 struct crypto_blkcipher *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_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
50 if (IS_ERR(priv->tx_tfm)) {
51 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
57 priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
58 if (IS_ERR(priv->rx_tfm)) {
59 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
63 /* start WEP IV from a random value */
64 get_random_bytes(&priv->iv, 4);
71 crypto_free_blkcipher(priv->tx_tfm);
73 crypto_free_blkcipher(priv->rx_tfm);
79 static void prism2_wep_deinit(void *priv)
81 struct prism2_wep_data *_priv = priv;
84 crypto_free_blkcipher(_priv->tx_tfm);
86 crypto_free_blkcipher(_priv->rx_tfm);
91 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
92 static int prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,
93 u8 *key, int keylen, void *priv)
95 struct prism2_wep_data *wep = priv;
99 if (skb_headroom(skb) < 4 || skb->len < hdr_len)
102 len = skb->len - hdr_len;
103 pos = skb_push(skb, 4);
104 memmove(pos, pos + 4, hdr_len);
107 klen = 3 + wep->key_len;
111 /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
112 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
113 * can be used to speedup attacks, so avoid using them. */
114 if ((wep->iv & 0xff00) == 0xff00) {
115 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++ = (wep->iv >> 16) & 0xff;
122 *pos++ = (wep->iv >> 8) & 0xff;
123 *pos++ = wep->iv & 0xff;
124 *pos++ = wep->key_idx << 6;
129 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
130 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
131 * so the payload length increases with 8 bytes.
133 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
135 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
137 struct prism2_wep_data *wep = priv;
138 struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
141 struct scatterlist sg;
142 u8 key[WEP_KEY_LEN + 3];
144 /* other checks are in prism2_wep_build_iv */
145 if (skb_tailroom(skb) < 4)
148 /* add the IV to the frame */
149 if (prism2_wep_build_iv(skb, hdr_len, NULL, 0, priv))
152 /* Copy the IV into the first 3 bytes of the key */
153 memcpy(key, skb->data + hdr_len, 3);
155 /* Copy rest of the WEP key (the secret part) */
156 memcpy(key + 3, wep->key, wep->key_len);
158 len = skb->len - hdr_len - 4;
159 pos = skb->data + hdr_len + 4;
160 klen = 3 + wep->key_len;
162 /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
163 crc = ~crc32_le(~0, pos, len);
164 icv = skb_put(skb, 4);
170 crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
171 sg.page = virt_to_page(pos);
172 sg.offset = offset_in_page(pos);
174 return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
177 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
178 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
179 * ICV (4 bytes). len includes both IV and ICV.
181 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
182 * failure. If frame is OK, IV and ICV will be removed.
184 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
186 struct prism2_wep_data *wep = priv;
187 struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
189 u8 key[WEP_KEY_LEN + 3];
190 u8 keyidx, *pos, icv[4];
191 struct scatterlist sg;
193 if (skb->len < hdr_len + 8)
196 pos = skb->data + hdr_len;
200 keyidx = *pos++ >> 6;
201 if (keyidx != wep->key_idx)
204 klen = 3 + wep->key_len;
206 /* Copy rest of the WEP key (the secret part) */
207 memcpy(key + 3, wep->key, wep->key_len);
209 /* Apply RC4 to data and compute CRC32 over decrypted data */
210 plen = skb->len - hdr_len - 8;
212 crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
213 sg.page = virt_to_page(pos);
214 sg.offset = offset_in_page(pos);
215 sg.length = plen + 4;
216 if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
219 crc = ~crc32_le(~0, pos, plen);
224 if (memcmp(icv, pos + plen, 4) != 0) {
225 /* ICV mismatch - drop frame */
229 /* Remove IV and ICV */
230 memmove(skb->data + 4, skb->data, hdr_len);
232 skb_trim(skb, skb->len - 4);
237 static int prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)
239 struct prism2_wep_data *wep = priv;
241 if (len < 0 || len > WEP_KEY_LEN)
244 memcpy(wep->key, key, len);
250 static int prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)
252 struct prism2_wep_data *wep = priv;
254 if (len < wep->key_len)
257 memcpy(key, wep->key, wep->key_len);
262 static char *prism2_wep_print_stats(char *p, void *priv)
264 struct prism2_wep_data *wep = priv;
265 p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
269 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
271 .init = prism2_wep_init,
272 .deinit = prism2_wep_deinit,
273 .build_iv = prism2_wep_build_iv,
274 .encrypt_mpdu = prism2_wep_encrypt,
275 .decrypt_mpdu = prism2_wep_decrypt,
276 .encrypt_msdu = NULL,
277 .decrypt_msdu = NULL,
278 .set_key = prism2_wep_set_key,
279 .get_key = prism2_wep_get_key,
280 .print_stats = prism2_wep_print_stats,
281 .extra_mpdu_prefix_len = 4, /* IV */
282 .extra_mpdu_postfix_len = 4, /* ICV */
283 .owner = THIS_MODULE,
286 static int __init ieee80211_crypto_wep_init(void)
288 return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
291 static void __exit ieee80211_crypto_wep_exit(void)
293 ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
296 module_init(ieee80211_crypto_wep_init);
297 module_exit(ieee80211_crypto_wep_exit);