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/module.h>
  13 #include <linux/init.h>
  14 #include <linux/slab.h>
  15 #include <linux/random.h>
  16 #include <linux/skbuff.h>
  17 #include <asm/string.h>
  18
  19 #include <net/ieee80211.h>
  20
  21 #include <linux/crypto.h>
  22 #include <asm/scatterlist.h>
  23 #include <linux/crc32.h>
  24
  25 MODULE_AUTHOR("Jouni Malinen");
  26 MODULE_DESCRIPTION("Host AP crypt: WEP");
  27 MODULE_LICENSE("GPL");
  28
  29 struct prism2_wep_data {
  30         u32 iv;
  31 #define WEP_KEY_LEN 13
  32         u8 key[WEP_KEY_LEN + 1];
  33         u8 key_len;
  34         u8 key_idx;
  35         struct crypto_tfm *tfm;
  36 };
  37
  38 static void *prism2_wep_init(int keyidx)
  39 {
  40         struct prism2_wep_data *priv;
  41
  42         priv = kmalloc(sizeof(*priv), GFP_ATOMIC);
  43         if (priv == NULL)
  44                 goto fail;
  45         memset(priv, 0, sizeof(*priv));
  46         priv->key_idx = keyidx;
  47
  48         priv->tfm = crypto_alloc_tfm("arc4", 0);
  49         if (priv->tfm == NULL) {
  50                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  51                        "crypto API arc4\n");
  52                 goto fail;
  53         }
  54
  55         /* start WEP IV from a random value */
  56         get_random_bytes(&priv->iv, 4);
  57
  58         return priv;
  59
  60       fail:
  61         if (priv) {
  62                 if (priv->tfm)
  63                         crypto_free_tfm(priv->tfm);
  64                 kfree(priv);
  65         }
  66         return NULL;
  67 }
  68
  69 static void prism2_wep_deinit(void *priv)
  70 {
  71         struct prism2_wep_data *_priv = priv;
  72         if (_priv && _priv->tfm)
  73                 crypto_free_tfm(_priv->tfm);
  74         kfree(priv);
  75 }
  76
  77 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  78 static int prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,
  79                                u8 *key, int keylen, void *priv)
  80 {
  81         struct prism2_wep_data *wep = priv;
  82         u32 klen, len;
  83         u8 *pos;
  84
  85         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  86                 return -1;
  87
  88         len = skb->len - hdr_len;
  89         pos = skb_push(skb, 4);
  90         memmove(pos, pos + 4, hdr_len);
  91         pos += hdr_len;
  92
  93         klen = 3 + wep->key_len;
  94
  95         wep->iv++;
  96
  97         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
  98          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
  99          * can be used to speedup attacks, so avoid using them. */
 100         if ((wep->iv & 0xff00) == 0xff00) {
 101                 u8 B = (wep->iv >> 16) & 0xff;
 102                 if (B >= 3 && B < klen)
 103                         wep->iv += 0x0100;
 104         }
 105
 106         /* Prepend 24-bit IV to RC4 key and TX frame */
 107         *pos++ = (wep->iv >> 16) & 0xff;
 108         *pos++ = (wep->iv >> 8) & 0xff;
 109         *pos++ = wep->iv & 0xff;
 110         *pos++ = wep->key_idx << 6;
 111
 112         return 0;
 113 }
 114
 115 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 116  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 117  * so the payload length increases with 8 bytes.
 118  *
 119  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 120  */
 121 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 122 {
 123         struct prism2_wep_data *wep = priv;
 124         u32 crc, klen, len;
 125         u8 *pos, *icv;
 126         struct scatterlist sg;
 127         u8 key[WEP_KEY_LEN + 3];
 128
 129         /* other checks are in prism2_wep_build_iv */
 130         if (skb_tailroom(skb) < 4)
 131                 return -1;
 132
 133         /* add the IV to the frame */
 134         if (prism2_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 135                 return -1;
 136
 137         /* Copy the IV into the first 3 bytes of the key */
 138         memcpy(key, skb->data + hdr_len, 3);
 139
 140         /* Copy rest of the WEP key (the secret part) */
 141         memcpy(key + 3, wep->key, wep->key_len);
 142
 143         len = skb->len - hdr_len - 4;
 144         pos = skb->data + hdr_len + 4;
 145         klen = 3 + wep->key_len;
 146
 147         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 148         crc = ~crc32_le(~0, pos, len);
 149         icv = skb_put(skb, 4);
 150         icv[0] = crc;
 151         icv[1] = crc >> 8;
 152         icv[2] = crc >> 16;
 153         icv[3] = crc >> 24;
 154
 155         crypto_cipher_setkey(wep->tfm, key, klen);
 156         sg.page = virt_to_page(pos);
 157         sg.offset = offset_in_page(pos);
 158         sg.length = len + 4;
 159         crypto_cipher_encrypt(wep->tfm, &sg, &sg, len + 4);
 160
 161         return 0;
 162 }
 163
 164 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 165  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 166  * ICV (4 bytes). len includes both IV and ICV.
 167  *
 168  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 169  * failure. If frame is OK, IV and ICV will be removed.
 170  */
 171 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 172 {
 173         struct prism2_wep_data *wep = priv;
 174         u32 crc, klen, plen;
 175         u8 key[WEP_KEY_LEN + 3];
 176         u8 keyidx, *pos, icv[4];
 177         struct scatterlist sg;
 178
 179         if (skb->len < hdr_len + 8)
 180                 return -1;
 181
 182         pos = skb->data + hdr_len;
 183         key[0] = *pos++;
 184         key[1] = *pos++;
 185         key[2] = *pos++;
 186         keyidx = *pos++ >> 6;
 187         if (keyidx != wep->key_idx)
 188                 return -1;
 189
 190         klen = 3 + wep->key_len;
 191
 192         /* Copy rest of the WEP key (the secret part) */
 193         memcpy(key + 3, wep->key, wep->key_len);
 194
 195         /* Apply RC4 to data and compute CRC32 over decrypted data */
 196         plen = skb->len - hdr_len - 8;
 197
 198         crypto_cipher_setkey(wep->tfm, key, klen);
 199         sg.page = virt_to_page(pos);
 200         sg.offset = offset_in_page(pos);
 201         sg.length = plen + 4;
 202         crypto_cipher_decrypt(wep->tfm, &sg, &sg, plen + 4);
 203
 204         crc = ~crc32_le(~0, pos, plen);
 205         icv[0] = crc;
 206         icv[1] = crc >> 8;
 207         icv[2] = crc >> 16;
 208         icv[3] = crc >> 24;
 209         if (memcmp(icv, pos + plen, 4) != 0) {
 210                 /* ICV mismatch - drop frame */
 211                 return -2;
 212         }
 213
 214         /* Remove IV and ICV */
 215         memmove(skb->data + 4, skb->data, hdr_len);
 216         skb_pull(skb, 4);
 217         skb_trim(skb, skb->len - 4);
 218
 219         return 0;
 220 }
 221
 222 static int prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)
 223 {
 224         struct prism2_wep_data *wep = priv;
 225
 226         if (len < 0 || len > WEP_KEY_LEN)
 227                 return -1;
 228
 229         memcpy(wep->key, key, len);
 230         wep->key_len = len;
 231
 232         return 0;
 233 }
 234
 235 static int prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)
 236 {
 237         struct prism2_wep_data *wep = priv;
 238
 239         if (len < wep->key_len)
 240                 return -1;
 241
 242         memcpy(key, wep->key, wep->key_len);
 243
 244         return wep->key_len;
 245 }
 246
 247 static char *prism2_wep_print_stats(char *p, void *priv)
 248 {
 249         struct prism2_wep_data *wep = priv;
 250         p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 251         return p;
 252 }
 253
 254 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
 255         .name = "WEP",
 256         .init = prism2_wep_init,
 257         .deinit = prism2_wep_deinit,
 258         .build_iv = prism2_wep_build_iv,
 259         .encrypt_mpdu = prism2_wep_encrypt,
 260         .decrypt_mpdu = prism2_wep_decrypt,
 261         .encrypt_msdu = NULL,
 262         .decrypt_msdu = NULL,
 263         .set_key = prism2_wep_set_key,
 264         .get_key = prism2_wep_get_key,
 265         .print_stats = prism2_wep_print_stats,
 266         .extra_mpdu_prefix_len = 4,     /* IV */
 267         .extra_mpdu_postfix_len = 4,    /* ICV */
 268         .owner = THIS_MODULE,
 269 };
 270
 271 static int __init ieee80211_crypto_wep_init(void)
 272 {
 273         return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
 274 }
 275
 276 static void __exit ieee80211_crypto_wep_exit(void)
 277 {
 278         ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
 279 }
 280
 281 module_init(ieee80211_crypto_wep_init);
 282 module_exit(ieee80211_crypto_wep_exit);