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