drivers/net/wireless/hostap/hostap_crypt_wep.c

   1 /*
   2  * Host AP crypt: host-based WEP encryption implementation for Host AP driver
   3  *
   4  * Copyright (c) 2002-2004, Jouni Malinen <jkmaline@cc.hut.fi>
   5  *
   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
   9  * more details.
  10  */
  11
  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>
  20
  21 #include "hostap_crypt.h"
  22 #include "hostap_config.h"
  23
  24 #ifndef CONFIG_CRYPTO
  25 #error CONFIG_CRYPTO is required to build this module.
  26 #endif
  27 #include <linux/crypto.h>
  28 #include <asm/scatterlist.h>
  29 #include <linux/crc32.h>
  30
  31 MODULE_AUTHOR("Jouni Malinen");
  32 MODULE_DESCRIPTION("Host AP crypt: WEP");
  33 MODULE_LICENSE("GPL");
  34 MODULE_VERSION(PRISM2_VERSION);
  35
  36
  37 struct prism2_wep_data {
  38         u32 iv;
  39 #define WEP_KEY_LEN 13
  40         u8 key[WEP_KEY_LEN + 1];
  41         u8 key_len;
  42         u8 key_idx;
  43         struct crypto_tfm *tfm;
  44 };
  45
  46
  47 static void * prism2_wep_init(int keyidx)
  48 {
  49         struct prism2_wep_data *priv;
  50
  51         if (!try_module_get(THIS_MODULE))
  52                 return NULL;
  53
  54         priv = (struct prism2_wep_data *) kmalloc(sizeof(*priv), GFP_ATOMIC);
  55         if (priv == NULL)
  56                 goto fail;
  57         memset(priv, 0, sizeof(*priv));
  58         priv->key_idx = keyidx;
  59
  60         priv->tfm = crypto_alloc_tfm("arc4", 0);
  61         if (priv->tfm == NULL) {
  62                 printk(KERN_DEBUG "hostap_crypt_wep: could not allocate "
  63                        "crypto API arc4\n");
  64                 goto fail;
  65         }
  66
  67         /* start WEP IV from a random value */
  68         get_random_bytes(&priv->iv, 4);
  69
  70         return priv;
  71
  72 fail:
  73         if (priv) {
  74                 if (priv->tfm)
  75                         crypto_free_tfm(priv->tfm);
  76                 kfree(priv);
  77         }
  78         module_put(THIS_MODULE);
  79         return NULL;
  80 }
  81
  82
  83 static void prism2_wep_deinit(void *priv)
  84 {
  85         struct prism2_wep_data *_priv = priv;
  86         if (_priv && _priv->tfm)
  87                 crypto_free_tfm(_priv->tfm);
  88         kfree(priv);
  89         module_put(THIS_MODULE);
  90 }
  91
  92
  93 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
  94  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
  95  * so the payload length increases with 8 bytes.
  96  *
  97  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
  98  */
  99 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 100 {
 101         struct prism2_wep_data *wep = priv;
 102         u32 crc, klen, len;
 103         u8 key[WEP_KEY_LEN + 3];
 104         u8 *pos, *icv;
 105         struct scatterlist sg;
 106
 107         if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
 108             skb->len < hdr_len)
 109                 return -1;
 110
 111         len = skb->len - hdr_len;
 112         pos = skb_push(skb, 4);
 113         memmove(pos, pos + 4, hdr_len);
 114         pos += hdr_len;
 115
 116         klen = 3 + wep->key_len;
 117
 118         wep->iv++;
 119
 120         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 121          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 122          * can be used to speedup attacks, so avoid using them. */
 123         if ((wep->iv & 0xff00) == 0xff00) {
 124                 u8 B = (wep->iv >> 16) & 0xff;
 125                 if (B >= 3 && B < klen)
 126                         wep->iv += 0x0100;
 127         }
 128
 129         /* Prepend 24-bit IV to RC4 key and TX frame */
 130         *pos++ = key[0] = (wep->iv >> 16) & 0xff;
 131         *pos++ = key[1] = (wep->iv >> 8) & 0xff;
 132         *pos++ = key[2] = wep->iv & 0xff;
 133         *pos++ = wep->key_idx << 6;
 134
 135         /* Copy rest of the WEP key (the secret part) */
 136         memcpy(key + 3, wep->key, wep->key_len);
 137
 138         /* Append little-endian CRC32 and encrypt it to produce ICV */
 139         crc = ~crc32_le(~0, pos, len);
 140         icv = skb_put(skb, 4);
 141         icv[0] = crc;
 142         icv[1] = crc >> 8;
 143         icv[2] = crc >> 16;
 144         icv[3] = crc >> 24;
 145
 146         crypto_cipher_setkey(wep->tfm, key, klen);
 147         sg.page = virt_to_page(pos);
 148         sg.offset = offset_in_page(pos);
 149         sg.length = len + 4;
 150         crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
 151
 152         return 0;
 153 }
 154
 155
 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.
 159  *
 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.
 162  */
 163 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 164 {
 165         struct prism2_wep_data *wep = priv;
 166         u32 crc, klen, plen;
 167         u8 key[WEP_KEY_LEN + 3];
 168         u8 keyidx, *pos, icv[4];
 169         struct scatterlist sg;
 170
 171         if (skb->len < hdr_len + 8)
 172                 return -1;
 173
 174         pos = skb->data + hdr_len;
 175         key[0] = *pos++;
 176         key[1] = *pos++;
 177         key[2] = *pos++;
 178         keyidx = *pos++ >> 6;
 179         if (keyidx != wep->key_idx)
 180                 return -1;
 181
 182         klen = 3 + wep->key_len;
 183
 184         /* Copy rest of the WEP key (the secret part) */
 185         memcpy(key + 3, wep->key, wep->key_len);
 186
 187         /* Apply RC4 to data and compute CRC32 over decrypted data */
 188         plen = skb->len - hdr_len - 8;
 189
 190         crypto_cipher_setkey(wep->tfm, key, klen);
 191         sg.page = virt_to_page(pos);
 192         sg.offset = offset_in_page(pos);
 193         sg.length = plen + 4;
 194         crypto_cipher_decrypt(wep->tfm, &sg, &sg, plen + 4);
 195
 196         crc = ~crc32_le(~0, pos, plen);
 197         icv[0] = crc;
 198         icv[1] = crc >> 8;
 199         icv[2] = crc >> 16;
 200         icv[3] = crc >> 24;
 201         if (memcmp(icv, pos + plen, 4) != 0) {
 202                 /* ICV mismatch - drop frame */
 203                 return -2;
 204         }
 205
 206         /* Remove IV and ICV */
 207         memmove(skb->data + 4, skb->data, hdr_len);
 208         skb_pull(skb, 4);
 209         skb_trim(skb, skb->len - 4);
 210
 211         return 0;
 212 }
 213
 214
 215 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
 216 {
 217         struct prism2_wep_data *wep = priv;
 218
 219         if (len < 0 || len > WEP_KEY_LEN)
 220                 return -1;
 221
 222         memcpy(wep->key, key, len);
 223         wep->key_len = len;
 224
 225         return 0;
 226 }
 227
 228
 229 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
 230 {
 231         struct prism2_wep_data *wep = priv;
 232
 233         if (len < wep->key_len)
 234                 return -1;
 235
 236         memcpy(key, wep->key, wep->key_len);
 237
 238         return wep->key_len;
 239 }
 240
 241
 242 static char * prism2_wep_print_stats(char *p, void *priv)
 243 {
 244         struct prism2_wep_data *wep = priv;
 245         p += sprintf(p, "key[%d] alg=WEP len=%d\n",
 246                      wep->key_idx, wep->key_len);
 247         return p;
 248 }
 249
 250
 251 static struct hostap_crypto_ops hostap_crypt_wep = {
 252         .name                   = "WEP",
 253         .init                   = prism2_wep_init,
 254         .deinit                 = prism2_wep_deinit,
 255         .encrypt_mpdu           = prism2_wep_encrypt,
 256         .decrypt_mpdu           = prism2_wep_decrypt,
 257         .encrypt_msdu           = NULL,
 258         .decrypt_msdu           = NULL,
 259         .set_key                = prism2_wep_set_key,
 260         .get_key                = prism2_wep_get_key,
 261         .print_stats            = prism2_wep_print_stats,
 262         .extra_prefix_len       = 4 /* IV */,
 263         .extra_postfix_len      = 4 /* ICV */
 264 };
 265
 266
 267 static int __init hostap_crypto_wep_init(void)
 268 {
 269         if (hostap_register_crypto_ops(&hostap_crypt_wep) < 0)
 270                 return -1;
 271
 272         return 0;
 273 }
 274
 275
 276 static void __exit hostap_crypto_wep_exit(void)
 277 {
 278         hostap_unregister_crypto_ops(&hostap_crypt_wep);
 279 }
 280
 281
 282 module_init(hostap_crypto_wep_init);
 283 module_exit(hostap_crypto_wep_exit);