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