src/net/80211/wep.c

   1 /*
   2  * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 #include <gpxe/net80211.h>
  22 #include <gpxe/sec80211.h>
  23 #include <gpxe/crypto.h>
  24 #include <gpxe/arc4.h>
  25 #include <gpxe/crc32.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <errno.h>
  29
  30 /** @file
  31  *
  32  * The WEP wireless encryption method (insecure!)
  33  *
  34  * The data field in a WEP-encrypted packet contains a 3-byte
  35  * initialisation vector, one-byte Key ID field (only the bottom two
  36  * bits are ever used), encrypted data, and a 4-byte encrypted CRC of
  37  * the plaintext data, called the ICV. To decrypt it, the IV is
  38  * prepended to the shared key and the data stream (including ICV) is
  39  * run through the ARC4 stream cipher; if the ICV matches a CRC32
  40  * calculated on the plaintext, the packet is valid.
  41  *
  42  * For efficiency and code-size reasons, this file assumes it is
  43  * running on a little-endian machine.
  44  */
  45
  46 /** Length of WEP initialisation vector */
  47 #define WEP_IV_LEN      3
  48
  49 /** Length of WEP key ID byte */
  50 #define WEP_KID_LEN     1
  51
  52 /** Length of WEP ICV checksum */
  53 #define WEP_ICV_LEN     4
  54
  55 /** Maximum length of WEP key */
  56 #define WEP_MAX_KEY     16
  57
  58 /** Amount of data placed before the encrypted bytes */
  59 #define WEP_HEADER_LEN  4
  60
  61 /** Amount of data placed after the encrypted bytes */
  62 #define WEP_TRAILER_LEN 4
  63
  64 /** Total WEP overhead bytes */
  65 #define WEP_OVERHEAD    8
  66
  67 /** Context for WEP encryption and decryption */
  68 struct wep_ctx
  69 {
  70         /** Encoded WEP key
  71          *
  72          * The actual key bytes are stored beginning at offset 3, to
  73          * leave room for easily inserting the IV before a particular
  74          * operation.
  75          */
  76         u8 key[WEP_IV_LEN + WEP_MAX_KEY];
  77
  78         /** Length of WEP key (not including IV bytes) */
  79         int keylen;
  80
  81         /** ARC4 context */
  82         struct arc4_ctx arc4;
  83 };
  84
  85 /**
  86  * Initialize WEP algorithm
  87  *
  88  * @v crypto    802.11 cryptographic algorithm
  89  * @v key       WEP key to use
  90  * @v keylen    Length of WEP key
  91  * @v rsc       Initial receive sequence counter (unused)
  92  * @ret rc      Return status code
  93  *
  94  * Standard key lengths are 5 and 13 bytes; 16-byte keys are
  95  * occasionally supported as an extension to the standard.
  96  */
  97 static int wep_init ( struct net80211_crypto *crypto, const void *key,
  98                       int keylen, const void *rsc __unused )
  99 {
 100         struct wep_ctx *ctx = crypto->priv;
 101
 102         ctx->keylen = ( keylen > WEP_MAX_KEY ? WEP_MAX_KEY : keylen );
 103         memcpy ( ctx->key + WEP_IV_LEN, key, ctx->keylen );
 104
 105         return 0;
 106 }
 107
 108 /**
 109  * Encrypt packet using WEP
 110  *
 111  * @v crypto    802.11 cryptographic algorithm
 112  * @v iob       I/O buffer of plaintext packet
 113  * @ret eiob    Newly allocated I/O buffer for encrypted packet, or NULL
 114  *
 115  * If memory allocation fails, @c NULL is returned.
 116  */
 117 static struct io_buffer * wep_encrypt ( struct net80211_crypto *crypto,
 118                                         struct io_buffer *iob )
 119 {
 120         struct wep_ctx *ctx = crypto->priv;
 121         struct io_buffer *eiob;
 122         struct ieee80211_frame *hdr;
 123         const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
 124         int datalen = iob_len ( iob ) - hdrlen;
 125         int newlen = hdrlen + datalen + WEP_OVERHEAD;
 126         u32 iv, icv;
 127
 128         eiob = alloc_iob ( newlen );
 129         if ( ! eiob )
 130                 return NULL;
 131
 132         memcpy ( iob_put ( eiob, hdrlen ), iob->data, hdrlen );
 133         hdr = eiob->data;
 134         hdr->fc |= IEEE80211_FC_PROTECTED;
 135
 136         /* Calculate IV, put it in the header (with key ID byte = 0), and
 137            set it up at the start of the encryption key. */
 138         iv = random() & 0xffffff; /* IV in bottom 3 bytes, top byte = KID = 0 */
 139         memcpy ( iob_put ( eiob, WEP_HEADER_LEN ), &iv, WEP_HEADER_LEN );
 140         memcpy ( ctx->key, &iv, WEP_IV_LEN );
 141
 142         /* Encrypt the data using RC4 */
 143         cipher_setkey ( &arc4_algorithm, &ctx->arc4, ctx->key,
 144                         ctx->keylen + WEP_IV_LEN );
 145         cipher_encrypt ( &arc4_algorithm, &ctx->arc4, iob->data + hdrlen,
 146                          iob_put ( eiob, datalen ), datalen );
 147
 148         /* Add ICV */
 149         icv = ~crc32_le ( ~0, iob->data + hdrlen, datalen );
 150         cipher_encrypt ( &arc4_algorithm, &ctx->arc4, &icv,
 151                          iob_put ( eiob, WEP_ICV_LEN ), WEP_ICV_LEN );
 152
 153         return eiob;
 154 }
 155
 156 /**
 157  * Decrypt packet using WEP
 158  *
 159  * @v crypto    802.11 cryptographic algorithm
 160  * @v eiob      I/O buffer of encrypted packet
 161  * @ret iob     Newly allocated I/O buffer for plaintext packet, or NULL
 162  *
 163  * If a consistency check for the decryption fails (usually indicating
 164  * an invalid key), @c NULL is returned.
 165  */
 166 static struct io_buffer * wep_decrypt ( struct net80211_crypto *crypto,
 167                                         struct io_buffer *eiob )
 168 {
 169         struct wep_ctx *ctx = crypto->priv;
 170         struct io_buffer *iob;
 171         struct ieee80211_frame *hdr;
 172         const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
 173         int datalen = iob_len ( eiob ) - hdrlen - WEP_OVERHEAD;
 174         int newlen = hdrlen + datalen;
 175         u32 iv, icv, crc;
 176
 177         iob = alloc_iob ( newlen );
 178         if ( ! iob )
 179                 return NULL;
 180
 181         memcpy ( iob_put ( iob, hdrlen ), eiob->data, hdrlen );
 182         hdr = iob->data;
 183         hdr->fc &= ~IEEE80211_FC_PROTECTED;
 184
 185         /* Strip off IV and use it to initialize cryptosystem */
 186         memcpy ( &iv, eiob->data + hdrlen, 4 );
 187         iv &= 0xffffff;         /* ignore key ID byte */
 188         memcpy ( ctx->key, &iv, WEP_IV_LEN );
 189
 190         /* Decrypt the data using RC4 */
 191         cipher_setkey ( &arc4_algorithm, &ctx->arc4, ctx->key,
 192                         ctx->keylen + WEP_IV_LEN );
 193         cipher_decrypt ( &arc4_algorithm, &ctx->arc4, eiob->data + hdrlen +
 194                          WEP_HEADER_LEN, iob_put ( iob, datalen ), datalen );
 195
 196         /* Strip off ICV and verify it */
 197         cipher_decrypt ( &arc4_algorithm, &ctx->arc4, eiob->data + hdrlen +
 198                          WEP_HEADER_LEN + datalen, &icv, WEP_ICV_LEN );
 199         crc = ~crc32_le ( ~0, iob->data + hdrlen, datalen );
 200         if ( crc != icv ) {
 201                 DBGC ( crypto, "WEP %p CRC mismatch: expect %08x, get %08x\n",
 202                        crypto, icv, crc );
 203                 free_iob ( iob );
 204                 return NULL;
 205         }
 206         return iob;
 207 }
 208
 209 /** WEP cryptosystem for 802.11 */
 210 struct net80211_crypto wep_crypto __net80211_crypto = {
 211         .algorithm = NET80211_CRYPT_WEP,
 212         .init = wep_init,
 213         .encrypt = wep_encrypt,
 214         .decrypt = wep_decrypt,
 215         .priv_len = sizeof ( struct wep_ctx ),
 216 };
 217
 218 /**
 219  * Initialize trivial 802.11 security handshaker
 220  *
 221  * @v dev       802.11 device
 222  * @v ctx       Security handshaker
 223  *
 224  * This simply fetches a WEP key from netX/key, and if it exists,
 225  * installs WEP cryptography on the 802.11 device. No real handshaking
 226  * is performed.
 227  */
 228 static int trivial_init ( struct net80211_device *dev )
 229 {
 230         u8 key[WEP_MAX_KEY];    /* support up to 128-bit keys */
 231         int len;
 232         int rc;
 233
 234         if ( dev->associating &&
 235              dev->associating->crypto == NET80211_CRYPT_NONE )
 236                 return 0;       /* no crypto? OK. */
 237
 238         len = fetch_setting ( netdev_settings ( dev->netdev ),
 239                               &net80211_key_setting, key, WEP_MAX_KEY );
 240
 241         if ( len <= 0 ) {
 242                 DBGC ( dev, "802.11 %p cannot do WEP without a key\n", dev );
 243                 return -EACCES;
 244         }
 245
 246         /* Full 128-bit keys are a nonstandard extension, but they're
 247            utterly trivial to support, so we do. */
 248         if ( len != 5 && len != 13 && len != 16 ) {
 249                 DBGC ( dev, "802.11 %p invalid WEP key length %d\n",
 250                        dev, len );
 251                 return -EINVAL;
 252         }
 253
 254         DBGC ( dev, "802.11 %p installing %d-bit WEP\n", dev, len * 8 );
 255
 256         rc = sec80211_install ( &dev->crypto, NET80211_CRYPT_WEP, key, len,
 257                                 NULL );
 258         if ( rc < 0 )
 259                 return rc;
 260
 261         return 0;
 262 }
 263
 264 /**
 265  * Check for key change on trivial 802.11 security handshaker
 266  *
 267  * @v dev       802.11 device
 268  * @v ctx       Security handshaker
 269  */
 270 static int trivial_change_key ( struct net80211_device *dev )
 271 {
 272         u8 key[WEP_MAX_KEY];
 273         int len;
 274         int change = 0;
 275
 276         /* If going from WEP to clear, or something else to WEP, reassociate. */
 277         if ( ! dev->crypto || ( dev->crypto->init != wep_init ) )
 278                 change ^= 1;
 279
 280         len = fetch_setting ( netdev_settings ( dev->netdev ),
 281                               &net80211_key_setting, key, WEP_MAX_KEY );
 282         if ( len <= 0 )
 283                 change ^= 1;
 284
 285         /* Changing crypto type => return nonzero to reassociate. */
 286         if ( change )
 287                 return -EINVAL;
 288
 289         /* Going from no crypto to still no crypto => nothing to do. */
 290         if ( len <= 0 )
 291                 return 0;
 292
 293         /* Otherwise, reinitialise WEP with new key. */
 294         return wep_init ( dev->crypto, key, len, NULL );
 295 }
 296
 297 /** Trivial 802.11 security handshaker */
 298 struct net80211_handshaker trivial_handshaker __net80211_handshaker = {
 299         .protocol = NET80211_SECPROT_NONE,
 300         .init = trivial_init,
 301         .change_key = trivial_change_key,
 302         .priv_len = 0,
 303 };