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 <j@w1.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/err.h>
  13 #include <linux/module.h>
  14 #include <linux/init.h>
  15 #include <linux/slab.h>
  16 #include <linux/random.h>
  17 #include <linux/scatterlist.h>
  18 #include <linux/skbuff.h>
  19 #include <linux/mm.h>
  20 #include <asm/string.h>
  21
  22 #include <net/ieee80211.h>
  23
  24 #include <linux/crypto.h>
  25 #include <linux/crc32.h>
  26
  27 MODULE_AUTHOR("Jouni Malinen");
  28 MODULE_DESCRIPTION("Host AP crypt: WEP");
  29 MODULE_LICENSE("GPL");
  30
  31 struct prism2_wep_data {
  32         u32 iv;
  33 #define WEP_KEY_LEN 13
  34         u8 key[WEP_KEY_LEN + 1];
  35         u8 key_len;
  36         u8 key_idx;
  37         struct crypto_blkcipher *tx_tfm;
  38         struct crypto_blkcipher *rx_tfm;
  39 };
  40
  41 static void *prism2_wep_init(int keyidx)
  42 {
  43         struct prism2_wep_data *priv;
  44
  45         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  46         if (priv == NULL)
  47                 goto fail;
  48         priv->key_idx = keyidx;
  49
  50         priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  51         if (IS_ERR(priv->tx_tfm)) {
  52                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  53                        "crypto API arc4\n");
  54                 priv->tx_tfm = NULL;
  55                 goto fail;
  56         }
  57
  58         priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  59         if (IS_ERR(priv->rx_tfm)) {
  60                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  61                        "crypto API arc4\n");
  62                 priv->rx_tfm = NULL;
  63                 goto fail;
  64         }
  65         /* start WEP IV from a random value */
  66         get_random_bytes(&priv->iv, 4);
  67
  68         return priv;
  69
  70       fail:
  71         if (priv) {
  72                 if (priv->tx_tfm)
  73                         crypto_free_blkcipher(priv->tx_tfm);
  74                 if (priv->rx_tfm)
  75                         crypto_free_blkcipher(priv->rx_tfm);
  76                 kfree(priv);
  77         }
  78         return NULL;
  79 }
  80
  81 static void prism2_wep_deinit(void *priv)
  82 {
  83         struct prism2_wep_data *_priv = priv;
  84         if (_priv) {
  85                 if (_priv->tx_tfm)
  86                         crypto_free_blkcipher(_priv->tx_tfm);
  87                 if (_priv->rx_tfm)
  88                         crypto_free_blkcipher(_priv->rx_tfm);
  89         }
  90         kfree(priv);
  91 }
  92
  93 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  94 static int prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,
  95                                u8 *key, int keylen, void *priv)
  96 {
  97         struct prism2_wep_data *wep = priv;
  98         u32 klen, len;
  99         u8 *pos;
 100
 101         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
 102                 return -1;
 103
 104         len = skb->len - hdr_len;
 105         pos = skb_push(skb, 4);
 106         memmove(pos, pos + 4, hdr_len);
 107         pos += hdr_len;
 108
 109         klen = 3 + wep->key_len;
 110
 111         wep->iv++;
 112
 113         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 114          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 115          * can be used to speedup attacks, so avoid using them. */
 116         if ((wep->iv & 0xff00) == 0xff00) {
 117                 u8 B = (wep->iv >> 16) & 0xff;
 118                 if (B >= 3 && B < klen)
 119                         wep->iv += 0x0100;
 120         }
 121
 122         /* Prepend 24-bit IV to RC4 key and TX frame */
 123         *pos++ = (wep->iv >> 16) & 0xff;
 124         *pos++ = (wep->iv >> 8) & 0xff;
 125         *pos++ = wep->iv & 0xff;
 126         *pos++ = wep->key_idx << 6;
 127
 128         return 0;
 129 }
 130
 131 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 132  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 133  * so the payload length increases with 8 bytes.
 134  *
 135  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 136  */
 137 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 138 {
 139         struct prism2_wep_data *wep = priv;
 140         struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
 141         u32 crc, klen, len;
 142         u8 *pos, *icv;
 143         struct scatterlist sg;
 144         u8 key[WEP_KEY_LEN + 3];
 145
 146         /* other checks are in prism2_wep_build_iv */
 147         if (skb_tailroom(skb) < 4)
 148                 return -1;
 149
 150         /* add the IV to the frame */
 151         if (prism2_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 152                 return -1;
 153
 154         /* Copy the IV into the first 3 bytes of the key */
 155         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 156
 157         /* Copy rest of the WEP key (the secret part) */
 158         memcpy(key + 3, wep->key, wep->key_len);
 159
 160         len = skb->len - hdr_len - 4;
 161         pos = skb->data + hdr_len + 4;
 162         klen = 3 + wep->key_len;
 163
 164         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 165         crc = ~crc32_le(~0, pos, len);
 166         icv = skb_put(skb, 4);
 167         icv[0] = crc;
 168         icv[1] = crc >> 8;
 169         icv[2] = crc >> 16;
 170         icv[3] = crc >> 24;
 171
 172         crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
 173         sg_init_one(&sg, pos, len + 4);
 174         return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
 175 }
 176
 177 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 178  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 179  * ICV (4 bytes). len includes both IV and ICV.
 180  *
 181  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 182  * failure. If frame is OK, IV and ICV will be removed.
 183  */
 184 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 185 {
 186         struct prism2_wep_data *wep = priv;
 187         struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
 188         u32 crc, klen, plen;
 189         u8 key[WEP_KEY_LEN + 3];
 190         u8 keyidx, *pos, icv[4];
 191         struct scatterlist sg;
 192
 193         if (skb->len < hdr_len + 8)
 194                 return -1;
 195
 196         pos = skb->data + hdr_len;
 197         key[0] = *pos++;
 198         key[1] = *pos++;
 199         key[2] = *pos++;
 200         keyidx = *pos++ >> 6;
 201         if (keyidx != wep->key_idx)
 202                 return -1;
 203
 204         klen = 3 + wep->key_len;
 205
 206         /* Copy rest of the WEP key (the secret part) */
 207         memcpy(key + 3, wep->key, wep->key_len);
 208
 209         /* Apply RC4 to data and compute CRC32 over decrypted data */
 210         plen = skb->len - hdr_len - 8;
 211
 212         crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
 213         sg_init_one(&sg, pos, plen + 4);
 214         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 215                 return -7;
 216
 217         crc = ~crc32_le(~0, pos, plen);
 218         icv[0] = crc;
 219         icv[1] = crc >> 8;
 220         icv[2] = crc >> 16;
 221         icv[3] = crc >> 24;
 222         if (memcmp(icv, pos + plen, 4) != 0) {
 223                 /* ICV mismatch - drop frame */
 224                 return -2;
 225         }
 226
 227         /* Remove IV and ICV */
 228         memmove(skb->data + 4, skb->data, hdr_len);
 229         skb_pull(skb, 4);
 230         skb_trim(skb, skb->len - 4);
 231
 232         return 0;
 233 }
 234
 235 static int prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)
 236 {
 237         struct prism2_wep_data *wep = priv;
 238
 239         if (len < 0 || len > WEP_KEY_LEN)
 240                 return -1;
 241
 242         memcpy(wep->key, key, len);
 243         wep->key_len = len;
 244
 245         return 0;
 246 }
 247
 248 static int prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)
 249 {
 250         struct prism2_wep_data *wep = priv;
 251
 252         if (len < wep->key_len)
 253                 return -1;
 254
 255         memcpy(key, wep->key, wep->key_len);
 256
 257         return wep->key_len;
 258 }
 259
 260 static char *prism2_wep_print_stats(char *p, void *priv)
 261 {
 262         struct prism2_wep_data *wep = priv;
 263         p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 264         return p;
 265 }
 266
 267 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
 268         .name = "WEP",
 269         .init = prism2_wep_init,
 270         .deinit = prism2_wep_deinit,
 271         .build_iv = prism2_wep_build_iv,
 272         .encrypt_mpdu = prism2_wep_encrypt,
 273         .decrypt_mpdu = prism2_wep_decrypt,
 274         .encrypt_msdu = NULL,
 275         .decrypt_msdu = NULL,
 276         .set_key = prism2_wep_set_key,
 277         .get_key = prism2_wep_get_key,
 278         .print_stats = prism2_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 ieee80211_crypto_wep_init(void)
 285 {
 286         return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
 287 }
 288
 289 static void __exit ieee80211_crypto_wep_exit(void)
 290 {
 291         ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
 292 }
 293
 294 module_init(ieee80211_crypto_wep_init);
 295 module_exit(ieee80211_crypto_wep_exit);