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
  23 #ifndef CONFIG_CRYPTO
  24 #error CONFIG_CRYPTO is required to build this module.
  25 #endif
  26 #include <linux/crypto.h>
  27 #include <asm/scatterlist.h>
  28 #include <linux/crc32.h>
  29
  30 MODULE_AUTHOR("Jouni Malinen");
  31 MODULE_DESCRIPTION("Host AP crypt: WEP");
  32 MODULE_LICENSE("GPL");
  33
  34
  35 struct prism2_wep_data {
  36         u32 iv;
  37 #define WEP_KEY_LEN 13
  38         u8 key[WEP_KEY_LEN + 1];
  39         u8 key_len;
  40         u8 key_idx;
  41         struct crypto_tfm *tfm;
  42 };
  43
  44
  45 static void * prism2_wep_init(int keyidx)
  46 {
  47         struct prism2_wep_data *priv;
  48
  49         if (!try_module_get(THIS_MODULE))
  50                 return NULL;
  51
  52         priv = (struct prism2_wep_data *) kmalloc(sizeof(*priv), GFP_ATOMIC);
  53         if (priv == NULL)
  54                 goto fail;
  55         memset(priv, 0, sizeof(*priv));
  56         priv->key_idx = keyidx;
  57
  58         priv->tfm = crypto_alloc_tfm("arc4", 0);
  59         if (priv->tfm == NULL) {
  60                 printk(KERN_DEBUG "hostap_crypt_wep: could not allocate "
  61                        "crypto API arc4\n");
  62                 goto fail;
  63         }
  64
  65         /* start WEP IV from a random value */
  66         get_random_bytes(&priv->iv, 4);
  67
  68         return priv;
  69
  70 fail:
  71         if (priv) {
  72                 if (priv->tfm)
  73                         crypto_free_tfm(priv->tfm);
  74                 kfree(priv);
  75         }
  76         module_put(THIS_MODULE);
  77         return NULL;
  78 }
  79
  80
  81 static void prism2_wep_deinit(void *priv)
  82 {
  83         struct prism2_wep_data *_priv = priv;
  84         if (_priv && _priv->tfm)
  85                 crypto_free_tfm(_priv->tfm);
  86         kfree(priv);
  87         module_put(THIS_MODULE);
  88 }
  89
  90
  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.
  94  *
  95  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
  96  */
  97 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
  98 {
  99         struct prism2_wep_data *wep = priv;
 100         u32 crc, klen, len;
 101         u8 key[WEP_KEY_LEN + 3];
 102         u8 *pos, *icv;
 103         struct scatterlist sg;
 104
 105         if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
 106             skb->len < hdr_len)
 107                 return -1;
 108
 109         len = skb->len - hdr_len;
 110         pos = skb_push(skb, 4);
 111         memmove(pos, pos + 4, hdr_len);
 112         pos += hdr_len;
 113
 114         klen = 3 + wep->key_len;
 115
 116         wep->iv++;
 117
 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)
 124                         wep->iv += 0x0100;
 125         }
 126
 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;
 132
 133         /* Copy rest of the WEP key (the secret part) */
 134         memcpy(key + 3, wep->key, wep->key_len);
 135
 136         /* Append little-endian CRC32 and encrypt it to produce ICV */
 137         crc = ~crc32_le(~0, pos, len);
 138         icv = skb_put(skb, 4);
 139         icv[0] = crc;
 140         icv[1] = crc >> 8;
 141         icv[2] = crc >> 16;
 142         icv[3] = crc >> 24;
 143
 144         crypto_cipher_setkey(wep->tfm, key, klen);
 145         sg.page = virt_to_page(pos);
 146         sg.offset = offset_in_page(pos);
 147         sg.length = len + 4;
 148         crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
 149
 150         return 0;
 151 }
 152
 153
 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.
 157  *
 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.
 160  */
 161 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 162 {
 163         struct prism2_wep_data *wep = priv;
 164         u32 crc, klen, plen;
 165         u8 key[WEP_KEY_LEN + 3];
 166         u8 keyidx, *pos, icv[4];
 167         struct scatterlist sg;
 168
 169         if (skb->len < hdr_len + 8)
 170                 return -1;
 171
 172         pos = skb->data + hdr_len;
 173         key[0] = *pos++;
 174         key[1] = *pos++;
 175         key[2] = *pos++;
 176         keyidx = *pos++ >> 6;
 177         if (keyidx != wep->key_idx)
 178                 return -1;
 179
 180         klen = 3 + wep->key_len;
 181
 182         /* Copy rest of the WEP key (the secret part) */
 183         memcpy(key + 3, wep->key, wep->key_len);
 184
 185         /* Apply RC4 to data and compute CRC32 over decrypted data */
 186         plen = skb->len - hdr_len - 8;
 187
 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);
 193
 194         crc = ~crc32_le(~0, pos, plen);
 195         icv[0] = crc;
 196         icv[1] = crc >> 8;
 197         icv[2] = crc >> 16;
 198         icv[3] = crc >> 24;
 199         if (memcmp(icv, pos + plen, 4) != 0) {
 200                 /* ICV mismatch - drop frame */
 201                 return -2;
 202         }
 203
 204         /* Remove IV and ICV */
 205         memmove(skb->data + 4, skb->data, hdr_len);
 206         skb_pull(skb, 4);
 207         skb_trim(skb, skb->len - 4);
 208
 209         return 0;
 210 }
 211
 212
 213 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
 214 {
 215         struct prism2_wep_data *wep = priv;
 216
 217         if (len < 0 || len > WEP_KEY_LEN)
 218                 return -1;
 219
 220         memcpy(wep->key, key, len);
 221         wep->key_len = len;
 222
 223         return 0;
 224 }
 225
 226
 227 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
 228 {
 229         struct prism2_wep_data *wep = priv;
 230
 231         if (len < wep->key_len)
 232                 return -1;
 233
 234         memcpy(key, wep->key, wep->key_len);
 235
 236         return wep->key_len;
 237 }
 238
 239
 240 static char * prism2_wep_print_stats(char *p, void *priv)
 241 {
 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);
 245         return p;
 246 }
 247
 248
 249 static struct hostap_crypto_ops hostap_crypt_wep = {
 250         .name                   = "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 */
 262 };
 263
 264
 265 static int __init hostap_crypto_wep_init(void)
 266 {
 267         if (hostap_register_crypto_ops(&hostap_crypt_wep) < 0)
 268                 return -1;
 269
 270         return 0;
 271 }
 272
 273
 274 static void __exit hostap_crypto_wep_exit(void)
 275 {
 276         hostap_unregister_crypto_ops(&hostap_crypt_wep);
 277 }
 278
 279
 280 module_init(hostap_crypto_wep_init);
 281 module_exit(hostap_crypto_wep_exit);