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