net/wireless/lib80211_crypt_wep.c

   1 /*
   2  * lib80211 crypt: host-based WEP encryption implementation for lib80211
   3  *
   4  * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
   5  * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation. See README and COPYING for
  10  * more details.
  11  */
  12
  13 #include <linux/err.h>
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/slab.h>
  17 #include <linux/random.h>
  18 #include <linux/scatterlist.h>
  19 #include <linux/skbuff.h>
  20 #include <linux/mm.h>
  21 #include <asm/string.h>
  22
  23 #include <net/lib80211.h>
  24
  25 #include <linux/crypto.h>
  26 #include <linux/crc32.h>
  27
  28 MODULE_AUTHOR("Jouni Malinen");
  29 MODULE_DESCRIPTION("lib80211 crypt: WEP");
  30 MODULE_LICENSE("GPL");
  31
  32 struct lib80211_wep_data {
  33         u32 iv;
  34 #define WEP_KEY_LEN 13
  35         u8 key[WEP_KEY_LEN + 1];
  36         u8 key_len;
  37         u8 key_idx;
  38         struct crypto_blkcipher *tx_tfm;
  39         struct crypto_blkcipher *rx_tfm;
  40 };
  41
  42 static void *lib80211_wep_init(int keyidx)
  43 {
  44         struct lib80211_wep_data *priv;
  45
  46         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  47         if (priv == NULL)
  48                 goto fail;
  49         priv->key_idx = keyidx;
  50
  51         priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  52         if (IS_ERR(priv->tx_tfm)) {
  53                 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate "
  54                        "crypto API arc4\n");
  55                 priv->tx_tfm = NULL;
  56                 goto fail;
  57         }
  58
  59         priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  60         if (IS_ERR(priv->rx_tfm)) {
  61                 printk(KERN_DEBUG "lib80211_crypt_wep: could not allocate "
  62                        "crypto API arc4\n");
  63                 priv->rx_tfm = NULL;
  64                 goto fail;
  65         }
  66         /* start WEP IV from a random value */
  67         get_random_bytes(&priv->iv, 4);
  68
  69         return priv;
  70
  71       fail:
  72         if (priv) {
  73                 if (priv->tx_tfm)
  74                         crypto_free_blkcipher(priv->tx_tfm);
  75                 if (priv->rx_tfm)
  76                         crypto_free_blkcipher(priv->rx_tfm);
  77                 kfree(priv);
  78         }
  79         return NULL;
  80 }
  81
  82 static void lib80211_wep_deinit(void *priv)
  83 {
  84         struct lib80211_wep_data *_priv = priv;
  85         if (_priv) {
  86                 if (_priv->tx_tfm)
  87                         crypto_free_blkcipher(_priv->tx_tfm);
  88                 if (_priv->rx_tfm)
  89                         crypto_free_blkcipher(_priv->rx_tfm);
  90         }
  91         kfree(priv);
  92 }
  93
  94 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  95 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  96                                u8 *key, int keylen, void *priv)
  97 {
  98         struct lib80211_wep_data *wep = priv;
  99         u32 klen, len;
 100         u8 *pos;
 101
 102         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
 103                 return -1;
 104
 105         len = skb->len - hdr_len;
 106         pos = skb_push(skb, 4);
 107         memmove(pos, pos + 4, hdr_len);
 108         pos += hdr_len;
 109
 110         klen = 3 + wep->key_len;
 111
 112         wep->iv++;
 113
 114         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 115          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 116          * can be used to speedup attacks, so avoid using them. */
 117         if ((wep->iv & 0xff00) == 0xff00) {
 118                 u8 B = (wep->iv >> 16) & 0xff;
 119                 if (B >= 3 && B < klen)
 120                         wep->iv += 0x0100;
 121         }
 122
 123         /* Prepend 24-bit IV to RC4 key and TX frame */
 124         *pos++ = (wep->iv >> 16) & 0xff;
 125         *pos++ = (wep->iv >> 8) & 0xff;
 126         *pos++ = wep->iv & 0xff;
 127         *pos++ = wep->key_idx << 6;
 128
 129         return 0;
 130 }
 131
 132 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 133  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 134  * so the payload length increases with 8 bytes.
 135  *
 136  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 137  */
 138 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 139 {
 140         struct lib80211_wep_data *wep = priv;
 141         struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
 142         u32 crc, klen, len;
 143         u8 *pos, *icv;
 144         struct scatterlist sg;
 145         u8 key[WEP_KEY_LEN + 3];
 146
 147         /* other checks are in lib80211_wep_build_iv */
 148         if (skb_tailroom(skb) < 4)
 149                 return -1;
 150
 151         /* add the IV to the frame */
 152         if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 153                 return -1;
 154
 155         /* Copy the IV into the first 3 bytes of the key */
 156         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 157
 158         /* Copy rest of the WEP key (the secret part) */
 159         memcpy(key + 3, wep->key, wep->key_len);
 160
 161         len = skb->len - hdr_len - 4;
 162         pos = skb->data + hdr_len + 4;
 163         klen = 3 + wep->key_len;
 164
 165         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 166         crc = ~crc32_le(~0, pos, len);
 167         icv = skb_put(skb, 4);
 168         icv[0] = crc;
 169         icv[1] = crc >> 8;
 170         icv[2] = crc >> 16;
 171         icv[3] = crc >> 24;
 172
 173         crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
 174         sg_init_one(&sg, pos, len + 4);
 175         return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
 176 }
 177
 178 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 179  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 180  * ICV (4 bytes). len includes both IV and ICV.
 181  *
 182  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 183  * failure. If frame is OK, IV and ICV will be removed.
 184  */
 185 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 186 {
 187         struct lib80211_wep_data *wep = priv;
 188         struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
 189         u32 crc, klen, plen;
 190         u8 key[WEP_KEY_LEN + 3];
 191         u8 keyidx, *pos, icv[4];
 192         struct scatterlist sg;
 193
 194         if (skb->len < hdr_len + 8)
 195                 return -1;
 196
 197         pos = skb->data + hdr_len;
 198         key[0] = *pos++;
 199         key[1] = *pos++;
 200         key[2] = *pos++;
 201         keyidx = *pos++ >> 6;
 202         if (keyidx != wep->key_idx)
 203                 return -1;
 204
 205         klen = 3 + wep->key_len;
 206
 207         /* Copy rest of the WEP key (the secret part) */
 208         memcpy(key + 3, wep->key, wep->key_len);
 209
 210         /* Apply RC4 to data and compute CRC32 over decrypted data */
 211         plen = skb->len - hdr_len - 8;
 212
 213         crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
 214         sg_init_one(&sg, pos, plen + 4);
 215         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 216                 return -7;
 217
 218         crc = ~crc32_le(~0, pos, plen);
 219         icv[0] = crc;
 220         icv[1] = crc >> 8;
 221         icv[2] = crc >> 16;
 222         icv[3] = crc >> 24;
 223         if (memcmp(icv, pos + plen, 4) != 0) {
 224                 /* ICV mismatch - drop frame */
 225                 return -2;
 226         }
 227
 228         /* Remove IV and ICV */
 229         memmove(skb->data + 4, skb->data, hdr_len);
 230         skb_pull(skb, 4);
 231         skb_trim(skb, skb->len - 4);
 232
 233         return 0;
 234 }
 235
 236 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 237 {
 238         struct lib80211_wep_data *wep = priv;
 239
 240         if (len < 0 || len > WEP_KEY_LEN)
 241                 return -1;
 242
 243         memcpy(wep->key, key, len);
 244         wep->key_len = len;
 245
 246         return 0;
 247 }
 248
 249 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 250 {
 251         struct lib80211_wep_data *wep = priv;
 252
 253         if (len < wep->key_len)
 254                 return -1;
 255
 256         memcpy(key, wep->key, wep->key_len);
 257
 258         return wep->key_len;
 259 }
 260
 261 static char *lib80211_wep_print_stats(char *p, void *priv)
 262 {
 263         struct lib80211_wep_data *wep = priv;
 264         p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 265         return p;
 266 }
 267
 268 static struct lib80211_crypto_ops lib80211_crypt_wep = {
 269         .name = "WEP",
 270         .init = lib80211_wep_init,
 271         .deinit = lib80211_wep_deinit,
 272         .encrypt_mpdu = lib80211_wep_encrypt,
 273         .decrypt_mpdu = lib80211_wep_decrypt,
 274         .encrypt_msdu = NULL,
 275         .decrypt_msdu = NULL,
 276         .set_key = lib80211_wep_set_key,
 277         .get_key = lib80211_wep_get_key,
 278         .print_stats = lib80211_wep_print_stats,
 279         .extra_mpdu_prefix_len = 4,     /* IV */
 280         .extra_mpdu_postfix_len = 4,    /* ICV */
 281         .owner = THIS_MODULE,
 282 };
 283
 284 static int __init lib80211_crypto_wep_init(void)
 285 {
 286         return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 287 }
 288
 289 static void __exit lib80211_crypto_wep_exit(void)
 290 {
 291         lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 292 }
 293
 294 module_init(lib80211_crypto_wep_init);
 295 module_exit(lib80211_crypto_wep_exit);