net/ieee80211/ieee80211_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 <net/ieee80211.h>
  22
  23
  24 #include <linux/crypto.h>
  25 #include <asm/scatterlist.h>
  26 #include <linux/crc32.h>
  27
  28 MODULE_AUTHOR("Jouni Malinen");
  29 MODULE_DESCRIPTION("Host AP crypt: WEP");
  30 MODULE_LICENSE("GPL");
  31
  32
  33 struct prism2_wep_data {
  34         u32 iv;
  35 #define WEP_KEY_LEN 13
  36         u8 key[WEP_KEY_LEN + 1];
  37         u8 key_len;
  38         u8 key_idx;
  39         struct crypto_tfm *tfm;
  40 };
  41
  42
  43 static void * prism2_wep_init(int keyidx)
  44 {
  45         struct prism2_wep_data *priv;
  46
  47         priv = kmalloc(sizeof(*priv), GFP_ATOMIC);
  48         if (priv == NULL)
  49                 goto fail;
  50         memset(priv, 0, sizeof(*priv));
  51         priv->key_idx = keyidx;
  52
  53         priv->tfm = crypto_alloc_tfm("arc4", 0);
  54         if (priv->tfm == NULL) {
  55                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  56                        "crypto API arc4\n");
  57                 goto fail;
  58         }
  59
  60         /* start WEP IV from a random value */
  61         get_random_bytes(&priv->iv, 4);
  62
  63         return priv;
  64
  65 fail:
  66         if (priv) {
  67                 if (priv->tfm)
  68                         crypto_free_tfm(priv->tfm);
  69                 kfree(priv);
  70         }
  71         return NULL;
  72 }
  73
  74
  75 static void prism2_wep_deinit(void *priv)
  76 {
  77         struct prism2_wep_data *_priv = priv;
  78         if (_priv && _priv->tfm)
  79                 crypto_free_tfm(_priv->tfm);
  80         kfree(priv);
  81 }
  82
  83
  84 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
  85  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
  86  * so the payload length increases with 8 bytes.
  87  *
  88  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
  89  */
  90 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
  91 {
  92         struct prism2_wep_data *wep = priv;
  93         u32 crc, klen, len;
  94         u8 key[WEP_KEY_LEN + 3];
  95         u8 *pos, *icv;
  96         struct scatterlist sg;
  97
  98         if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
  99             skb->len < hdr_len)
 100                 return -1;
 101
 102         len = skb->len - hdr_len;
 103         pos = skb_push(skb, 4);
 104         memmove(pos, pos + 4, hdr_len);
 105         pos += hdr_len;
 106
 107         klen = 3 + wep->key_len;
 108
 109         wep->iv++;
 110
 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)
 117                         wep->iv += 0x0100;
 118         }
 119
 120         /* Prepend 24-bit IV to RC4 key and TX frame */
 121         *pos++ = key[0] = (wep->iv >> 16) & 0xff;
 122         *pos++ = key[1] = (wep->iv >> 8) & 0xff;
 123         *pos++ = key[2] = wep->iv & 0xff;
 124         *pos++ = wep->key_idx << 6;
 125
 126         /* Copy rest of the WEP key (the secret part) */
 127         memcpy(key + 3, wep->key, wep->key_len);
 128
 129         /* Append little-endian CRC32 and encrypt it to produce ICV */
 130         crc = ~crc32_le(~0, pos, len);
 131         icv = skb_put(skb, 4);
 132         icv[0] = crc;
 133         icv[1] = crc >> 8;
 134         icv[2] = crc >> 16;
 135         icv[3] = crc >> 24;
 136
 137         crypto_cipher_setkey(wep->tfm, key, klen);
 138         sg.page = virt_to_page(pos);
 139         sg.offset = offset_in_page(pos);
 140         sg.length = len + 4;
 141         crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
 142
 143         return 0;
 144 }
 145
 146
 147 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 148  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 149  * ICV (4 bytes). len includes both IV and ICV.
 150  *
 151  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 152  * failure. If frame is OK, IV and ICV will be removed.
 153  */
 154 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 155 {
 156         struct prism2_wep_data *wep = priv;
 157         u32 crc, klen, plen;
 158         u8 key[WEP_KEY_LEN + 3];
 159         u8 keyidx, *pos, icv[4];
 160         struct scatterlist sg;
 161
 162         if (skb->len < hdr_len + 8)
 163                 return -1;
 164
 165         pos = skb->data + hdr_len;
 166         key[0] = *pos++;
 167         key[1] = *pos++;
 168         key[2] = *pos++;
 169         keyidx = *pos++ >> 6;
 170         if (keyidx != wep->key_idx)
 171                 return -1;
 172
 173         klen = 3 + wep->key_len;
 174
 175         /* Copy rest of the WEP key (the secret part) */
 176         memcpy(key + 3, wep->key, wep->key_len);
 177
 178         /* Apply RC4 to data and compute CRC32 over decrypted data */
 179         plen = skb->len - hdr_len - 8;
 180
 181         crypto_cipher_setkey(wep->tfm, key, klen);
 182         sg.page = virt_to_page(pos);
 183         sg.offset = offset_in_page(pos);
 184         sg.length = plen + 4;
 185         crypto_cipher_decrypt(wep->tfm, &sg, &sg, plen + 4);
 186
 187         crc = ~crc32_le(~0, pos, plen);
 188         icv[0] = crc;
 189         icv[1] = crc >> 8;
 190         icv[2] = crc >> 16;
 191         icv[3] = crc >> 24;
 192         if (memcmp(icv, pos + plen, 4) != 0) {
 193                 /* ICV mismatch - drop frame */
 194                 return -2;
 195         }
 196
 197         /* Remove IV and ICV */
 198         memmove(skb->data + 4, skb->data, hdr_len);
 199         skb_pull(skb, 4);
 200         skb_trim(skb, skb->len - 4);
 201
 202         return 0;
 203 }
 204
 205
 206 static int prism2_wep_set_key(void *key, int len, u8 *seq, void *priv)
 207 {
 208         struct prism2_wep_data *wep = priv;
 209
 210         if (len < 0 || len > WEP_KEY_LEN)
 211                 return -1;
 212
 213         memcpy(wep->key, key, len);
 214         wep->key_len = len;
 215
 216         return 0;
 217 }
 218
 219
 220 static int prism2_wep_get_key(void *key, int len, u8 *seq, void *priv)
 221 {
 222         struct prism2_wep_data *wep = priv;
 223
 224         if (len < wep->key_len)
 225                 return -1;
 226
 227         memcpy(key, wep->key, wep->key_len);
 228
 229         return wep->key_len;
 230 }
 231
 232
 233 static char * prism2_wep_print_stats(char *p, void *priv)
 234 {
 235         struct prism2_wep_data *wep = priv;
 236         p += sprintf(p, "key[%d] alg=WEP len=%d\n",
 237                      wep->key_idx, wep->key_len);
 238         return p;
 239 }
 240
 241
 242 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
 243         .name                   = "WEP",
 244         .init                   = prism2_wep_init,
 245         .deinit                 = prism2_wep_deinit,
 246         .encrypt_mpdu           = prism2_wep_encrypt,
 247         .decrypt_mpdu           = prism2_wep_decrypt,
 248         .encrypt_msdu           = NULL,
 249         .decrypt_msdu           = NULL,
 250         .set_key                = prism2_wep_set_key,
 251         .get_key                = prism2_wep_get_key,
 252         .print_stats            = prism2_wep_print_stats,
 253         .extra_prefix_len       = 4, /* IV */
 254         .extra_postfix_len      = 4, /* ICV */
 255         .owner                  = THIS_MODULE,
 256 };
 257
 258
 259 static int __init ieee80211_crypto_wep_init(void)
 260 {
 261         return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
 262 }
 263
 264
 265 static void __exit ieee80211_crypto_wep_exit(void)
 266 {
 267         ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
 268 }
 269
 270
 271 module_init(ieee80211_crypto_wep_init);
 272 module_exit(ieee80211_crypto_wep_exit);