sys/netproto/802_11/wlan_wep/ieee80211_crypto_wep.c

   1 /*
   2  * Copyright (c) 2002-2005 Sam Leffler, Errno Consulting
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. The name of the author may not be used to endorse or promote products
  14  *    derived from this software without specific prior written permission.
  15  *
  16  * Alternatively, this software may be distributed under the terms of the
  17  * GNU General Public License ("GPL") version 2 as published by the Free
  18  * Software Foundation.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  21  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  22  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  23  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  24  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  25  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  26  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  27  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  28  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  29  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  *
  31  * $FreeBSD: src/sys/net80211/ieee80211_crypto_wep.c,v 1.7.2.1 2005/12/22 19:02:08 sam Exp $
  32  * $DragonFly: src/sys/netproto/802_11/wlan_wep/ieee80211_crypto_wep.c,v 1.3 2006/11/28 14:44:03 sephe Exp $
  33  */
  34
  35 /*
  36  * IEEE 802.11 WEP crypto support.
  37  */
  38 #include <sys/param.h>
  39 #include <sys/systm.h>
  40 #include <sys/mbuf.h>
  41 #include <sys/malloc.h>
  42 #include <sys/kernel.h>
  43 #include <sys/module.h>
  44 #include <sys/endian.h>
  45
  46 #include <sys/socket.h>
  47
  48 #include <net/if.h>
  49 #include <net/if_arp.h>
  50 #include <net/if_media.h>
  51 #include <net/ethernet.h>
  52
  53 #include <netproto/802_11/ieee80211_var.h>
  54
  55 static  void *wep_attach(struct ieee80211com *, struct ieee80211_key *);
  56 static  void wep_detach(struct ieee80211_key *);
  57 static  int wep_setkey(struct ieee80211_key *);
  58 static  int wep_encap(struct ieee80211_key *, struct mbuf *, uint8_t keyid);
  59 static  int wep_decap(struct ieee80211_key *, struct mbuf *, int hdrlen);
  60 static  int wep_enmic(struct ieee80211_key *, struct mbuf *, int);
  61 static  int wep_demic(struct ieee80211_key *, struct mbuf *, int);
  62
  63 static const struct ieee80211_cipher wep = {
  64         .ic_name        = "WEP",
  65         .ic_cipher      = IEEE80211_CIPHER_WEP,
  66         .ic_header      = IEEE80211_WEP_IVLEN + IEEE80211_WEP_KIDLEN,
  67         .ic_trailer     = IEEE80211_WEP_CRCLEN,
  68         .ic_miclen      = 0,
  69         .ic_attach      = wep_attach,
  70         .ic_detach      = wep_detach,
  71         .ic_setkey      = wep_setkey,
  72         .ic_encap       = wep_encap,
  73         .ic_decap       = wep_decap,
  74         .ic_enmic       = wep_enmic,
  75         .ic_demic       = wep_demic,
  76 };
  77
  78 static  int wep_encrypt(struct ieee80211_key *, struct mbuf *, int hdrlen);
  79 static  int wep_decrypt(struct ieee80211_key *, struct mbuf *, int hdrlen);
  80
  81 struct wep_ctx {
  82         struct ieee80211com *wc_ic;     /* for diagnostics */
  83         uint32_t        wc_iv;          /* initial vector for crypto */
  84 };
  85
  86 /* number of references from net80211 layer */
  87 static  int nrefs = 0;
  88
  89 static void *
  90 wep_attach(struct ieee80211com *ic, struct ieee80211_key *k)
  91 {
  92         struct wep_ctx *ctx;
  93
  94         ctx = kmalloc(sizeof(struct wep_ctx), M_DEVBUF, M_NOWAIT | M_ZERO);
  95         if (ctx == NULL) {
  96                 ic->ic_stats.is_crypto_nomem++;
  97                 return NULL;
  98         }
  99
 100         ctx->wc_ic = ic;
 101         get_random_bytes(&ctx->wc_iv, sizeof(ctx->wc_iv));
 102         nrefs++;                        /* NB: we assume caller locking */
 103         return ctx;
 104 }
 105
 106 static void
 107 wep_detach(struct ieee80211_key *k)
 108 {
 109         struct wep_ctx *ctx = k->wk_private;
 110
 111         FREE(ctx, M_DEVBUF);
 112         KASSERT(nrefs > 0, ("imbalanced attach/detach"));
 113         nrefs--;                        /* NB: we assume caller locking */
 114 }
 115
 116 static int
 117 wep_setkey(struct ieee80211_key *k)
 118 {
 119         return k->wk_keylen >= 40/NBBY;
 120 }
 121
 122 /*
 123  * Add privacy headers appropriate for the specified key.
 124  */
 125 static int
 126 wep_encap(struct ieee80211_key *k, struct mbuf *m, uint8_t keyid)
 127 {
 128         struct wep_ctx *ctx = k->wk_private;
 129         struct ieee80211com *ic = ctx->wc_ic;
 130         uint32_t iv;
 131         uint8_t *ivp;
 132         int hdrlen;
 133
 134         hdrlen = ieee80211_hdrspace(ic, mtod(m, void *));
 135
 136         /*
 137          * Copy down 802.11 header and add the IV + KeyID.
 138          */
 139         M_PREPEND(m, wep.ic_header, MB_DONTWAIT);
 140         if (m == NULL)
 141                 return 0;
 142         ivp = mtod(m, uint8_t *);
 143         ovbcopy(ivp + wep.ic_header, ivp, hdrlen);
 144         ivp += hdrlen;
 145
 146         /*
 147          * XXX
 148          * IV must not duplicate during the lifetime of the key.
 149          * But no mechanism to renew keys is defined in IEEE 802.11
 150          * for WEP.  And the IV may be duplicated at other stations
 151          * because the session key itself is shared.  So we use a
 152          * pseudo random IV for now, though it is not the right way.
 153          *
 154          * NB: Rather than use a strictly random IV we select a
 155          * random one to start and then increment the value for
 156          * each frame.  This is an explicit tradeoff between
 157          * overhead and security.  Given the basic insecurity of
 158          * WEP this seems worthwhile.
 159          */
 160
 161         /*
 162          * Skip 'bad' IVs from Fluhrer/Mantin/Shamir:
 163          * (B, 255, N) with 3 <= B < 16 and 0 <= N <= 255
 164          */
 165         iv = ctx->wc_iv;
 166         if ((iv & 0xff00) == 0xff00) {
 167                 int B = (iv & 0xff0000) >> 16;
 168                 if (3 <= B && B < 16)
 169                         iv += 0x0100;
 170         }
 171         ctx->wc_iv = iv + 1;
 172
 173         /*
 174          * NB: Preserve byte order of IV for packet
 175          *     sniffers; it doesn't matter otherwise.
 176          */
 177 #if _BYTE_ORDER == _BIG_ENDIAN
 178         ivp[0] = iv >> 0;
 179         ivp[1] = iv >> 8;
 180         ivp[2] = iv >> 16;
 181 #else
 182         ivp[2] = iv >> 0;
 183         ivp[1] = iv >> 8;
 184         ivp[0] = iv >> 16;
 185 #endif
 186         ivp[3] = keyid;
 187
 188         /*
 189          * Finally, do software encrypt if neeed.
 190          */
 191         if ((k->wk_flags & IEEE80211_KEY_SWCRYPT) &&
 192             !wep_encrypt(k, m, hdrlen))
 193                 return 0;
 194
 195         return 1;
 196 }
 197
 198 /*
 199  * Add MIC to the frame as needed.
 200  */
 201 static int
 202 wep_enmic(struct ieee80211_key *k, struct mbuf *m, int force)
 203 {
 204         return 1;
 205 }
 206
 207 /*
 208  * Validate and strip privacy headers (and trailer) for a
 209  * received frame.  If necessary, decrypt the frame using
 210  * the specified key.
 211  */
 212 static int
 213 wep_decap(struct ieee80211_key *k, struct mbuf *m, int hdrlen)
 214 {
 215         struct wep_ctx *ctx = k->wk_private;
 216         struct ieee80211_frame *wh;
 217
 218         wh = mtod(m, struct ieee80211_frame *);
 219
 220         /*
 221          * Check if the device handled the decrypt in hardware.
 222          * If so we just strip the header; otherwise we need to
 223          * handle the decrypt in software.
 224          */
 225         if ((k->wk_flags & IEEE80211_KEY_SWCRYPT) &&
 226             !wep_decrypt(k, m, hdrlen)) {
 227                 IEEE80211_DPRINTF(ctx->wc_ic, IEEE80211_MSG_CRYPTO,
 228                     "[%6D] WEP ICV mismatch on decrypt\n",
 229                     wh->i_addr2, ":");
 230                 ctx->wc_ic->ic_stats.is_rx_wepfail++;
 231                 return 0;
 232         }
 233
 234         /*
 235          * Copy up 802.11 header and strip crypto bits.
 236          */
 237         ovbcopy(mtod(m, void *), mtod(m, uint8_t *) + wep.ic_header, hdrlen);
 238         m_adj(m, wep.ic_header);
 239         m_adj(m, -wep.ic_trailer);
 240
 241         return 1;
 242 }
 243
 244 /*
 245  * Verify and strip MIC from the frame.
 246  */
 247 static int
 248 wep_demic(struct ieee80211_key *k, struct mbuf *skb, int force)
 249 {
 250         return 1;
 251 }
 252
 253 static const uint32_t crc32_table[256] = {
 254         0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
 255         0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
 256         0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
 257         0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
 258         0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
 259         0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
 260         0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
 261         0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
 262         0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
 263         0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
 264         0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
 265         0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
 266         0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
 267         0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
 268         0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
 269         0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
 270         0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
 271         0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
 272         0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
 273         0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
 274         0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
 275         0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
 276         0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
 277         0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
 278         0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
 279         0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
 280         0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
 281         0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
 282         0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
 283         0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
 284         0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
 285         0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
 286         0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
 287         0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
 288         0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
 289         0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
 290         0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
 291         0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
 292         0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
 293         0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
 294         0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
 295         0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
 296         0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
 297         0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
 298         0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
 299         0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
 300         0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
 301         0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
 302         0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
 303         0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
 304         0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
 305         0x2d02ef8dL
 306 };
 307
 308 static int
 309 wep_encrypt(struct ieee80211_key *key, struct mbuf *m0, int hdrlen)
 310 {
 311 #define S_SWAP(a,b) do { uint8_t t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
 312         struct wep_ctx *ctx = key->wk_private;
 313         struct mbuf *m = m0;
 314         uint8_t rc4key[IEEE80211_WEP_IVLEN + IEEE80211_KEYBUF_SIZE];
 315         uint8_t icv[IEEE80211_WEP_CRCLEN];
 316         uint32_t i, j, k, crc;
 317         size_t buflen, data_len;
 318         uint8_t S[256];
 319         uint8_t *pos;
 320         u_int off, keylen;
 321
 322         ctx->wc_ic->ic_stats.is_crypto_wep++;
 323
 324         /* NB: this assumes the header was pulled up */
 325         memcpy(rc4key, mtod(m, uint8_t *) + hdrlen, IEEE80211_WEP_IVLEN);
 326         memcpy(rc4key + IEEE80211_WEP_IVLEN, key->wk_key, key->wk_keylen);
 327
 328         /* Setup RC4 state */
 329         for (i = 0; i < 256; i++)
 330                 S[i] = i;
 331         j = 0;
 332         keylen = key->wk_keylen + IEEE80211_WEP_IVLEN;
 333         for (i = 0; i < 256; i++) {
 334                 j = (j + S[i] + rc4key[i % keylen]) & 0xff;
 335                 S_SWAP(i, j);
 336         }
 337
 338         off = hdrlen + wep.ic_header;
 339         data_len = m->m_pkthdr.len - off;
 340
 341         /* Compute CRC32 over unencrypted data and apply RC4 to data */
 342         crc = ~0;
 343         i = j = 0;
 344         pos = mtod(m, uint8_t *) + off;
 345         buflen = m->m_len - off;
 346         for (;;) {
 347                 if (buflen > data_len)
 348                         buflen = data_len;
 349                 data_len -= buflen;
 350                 for (k = 0; k < buflen; k++) {
 351                         crc = crc32_table[(crc ^ *pos) & 0xff] ^ (crc >> 8);
 352                         i = (i + 1) & 0xff;
 353                         j = (j + S[i]) & 0xff;
 354                         S_SWAP(i, j);
 355                         *pos++ ^= S[(S[i] + S[j]) & 0xff];
 356                 }
 357                 if (m->m_next == NULL) {
 358                         if (data_len != 0) {            /* out of data */
 359                                 IEEE80211_DPRINTF(ctx->wc_ic,
 360                                     IEEE80211_MSG_CRYPTO,
 361                                     "[%6D] out of data for WEP "
 362                                     "(data_len %zu)\n",
 363                                     mtod(m0, struct ieee80211_frame *)->i_addr2,
 364                                     ":", data_len);
 365                                 return 0;
 366                         }
 367                         break;
 368                 }
 369                 m = m->m_next;
 370                 pos = mtod(m, uint8_t *);
 371                 buflen = m->m_len;
 372         }
 373         crc = ~crc;
 374
 375         /* Append little-endian CRC32 and encrypt it to produce ICV */
 376         icv[0] = crc;
 377         icv[1] = crc >> 8;
 378         icv[2] = crc >> 16;
 379         icv[3] = crc >> 24;
 380         for (k = 0; k < IEEE80211_WEP_CRCLEN; k++) {
 381                 i = (i + 1) & 0xff;
 382                 j = (j + S[i]) & 0xff;
 383                 S_SWAP(i, j);
 384                 icv[k] ^= S[(S[i] + S[j]) & 0xff];
 385         }
 386         return ieee80211_mbuf_append(m0, IEEE80211_WEP_CRCLEN, icv);
 387 #undef S_SWAP
 388 }
 389
 390 static int
 391 wep_decrypt(struct ieee80211_key *key, struct mbuf *m0, int hdrlen)
 392 {
 393 #define S_SWAP(a,b) do { uint8_t t = S[a]; S[a] = S[b]; S[b] = t; } while(0)
 394         struct wep_ctx *ctx = key->wk_private;
 395         struct mbuf *m = m0;
 396         uint8_t rc4key[IEEE80211_WEP_IVLEN + IEEE80211_KEYBUF_SIZE];
 397         uint8_t icv[IEEE80211_WEP_CRCLEN];
 398         uint32_t i, j, k, crc;
 399         size_t buflen, data_len;
 400         uint8_t S[256];
 401         uint8_t *pos;
 402         u_int off, keylen;
 403
 404         ctx->wc_ic->ic_stats.is_crypto_wep++;
 405
 406         /* NB: this assumes the header was pulled up */
 407         memcpy(rc4key, mtod(m, uint8_t *) + hdrlen, IEEE80211_WEP_IVLEN);
 408         memcpy(rc4key + IEEE80211_WEP_IVLEN, key->wk_key, key->wk_keylen);
 409
 410         /* Setup RC4 state */
 411         for (i = 0; i < 256; i++)
 412                 S[i] = i;
 413         j = 0;
 414         keylen = key->wk_keylen + IEEE80211_WEP_IVLEN;
 415         for (i = 0; i < 256; i++) {
 416                 j = (j + S[i] + rc4key[i % keylen]) & 0xff;
 417                 S_SWAP(i, j);
 418         }
 419
 420         off = hdrlen + wep.ic_header;
 421         data_len = m->m_pkthdr.len - (off + wep.ic_trailer),
 422
 423         /* Compute CRC32 over unencrypted data and apply RC4 to data */
 424         crc = ~0;
 425         i = j = 0;
 426         pos = mtod(m, uint8_t *) + off;
 427         buflen = m->m_len - off;
 428         for (;;) {
 429                 if (buflen > data_len)
 430                         buflen = data_len;
 431                 data_len -= buflen;
 432                 for (k = 0; k < buflen; k++) {
 433                         i = (i + 1) & 0xff;
 434                         j = (j + S[i]) & 0xff;
 435                         S_SWAP(i, j);
 436                         *pos ^= S[(S[i] + S[j]) & 0xff];
 437                         crc = crc32_table[(crc ^ *pos) & 0xff] ^ (crc >> 8);
 438                         pos++;
 439                 }
 440                 m = m->m_next;
 441                 if (m == NULL) {
 442                         if (data_len != 0) {            /* out of data */
 443                                 IEEE80211_DPRINTF(ctx->wc_ic,
 444                                     IEEE80211_MSG_CRYPTO,
 445                                     "[%s] out of data for WEP "
 446                                     "(data_len %zu)\n",
 447                                     mtod(m0, struct ieee80211_frame *)->i_addr2,
 448                                     ":", data_len);
 449                                 return 0;
 450                         }
 451                         break;
 452                 }
 453                 pos = mtod(m, uint8_t *);
 454                 buflen = m->m_len;
 455         }
 456         crc = ~crc;
 457
 458         /* Encrypt little-endian CRC32 and verify that it matches with
 459          * received ICV */
 460         icv[0] = crc;
 461         icv[1] = crc >> 8;
 462         icv[2] = crc >> 16;
 463         icv[3] = crc >> 24;
 464         for (k = 0; k < IEEE80211_WEP_CRCLEN; k++) {
 465                 i = (i + 1) & 0xff;
 466                 j = (j + S[i]) & 0xff;
 467                 S_SWAP(i, j);
 468                 /* XXX assumes ICV is contiguous in mbuf */
 469                 if ((icv[k] ^ S[(S[i] + S[j]) & 0xff]) != *pos++) {
 470                         /* ICV mismatch - drop frame */
 471                         return 0;
 472                 }
 473         }
 474         return 1;
 475 #undef S_SWAP
 476 }
 477
 478 /*
 479  * Module glue.
 480  */
 481 static int
 482 wep_modevent(module_t mod, int type, void *unused)
 483 {
 484         switch (type) {
 485         case MOD_LOAD:
 486                 ieee80211_crypto_register(&wep);
 487                 return 0;
 488         case MOD_UNLOAD:
 489                 if (nrefs) {
 490                         printf("wlan_wep: still in use (%u dynamic refs)\n",
 491                                 nrefs);
 492                         return EBUSY;
 493                 }
 494                 ieee80211_crypto_unregister(&wep);
 495                 return 0;
 496         }
 497         return EINVAL;
 498 }
 499
 500 static moduledata_t wep_mod = {
 501         "wlan_wep",
 502         wep_modevent,
 503         0
 504 };
 505 DECLARE_MODULE(wlan_wep, wep_mod, SI_SUB_DRIVERS, SI_ORDER_FIRST);
 506 MODULE_VERSION(wlan_wep, 1);
 507 MODULE_DEPEND(wlan_wep, wlan, 1, 1, 1);