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/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/skbuff.h>
  18 #include <asm/string.h>
  19
  20 #include <net/ieee80211.h>
  21
  22 #include <linux/crypto.h>
  23 #include <asm/scatterlist.h>
  24 #include <linux/crc32.h>
  25
  26 MODULE_AUTHOR("Jouni Malinen");
  27 MODULE_DESCRIPTION("Host AP crypt: WEP");
  28 MODULE_LICENSE("GPL");
  29
  30 struct prism2_wep_data {
  31         u32 iv;
  32 #define WEP_KEY_LEN 13
  33         u8 key[WEP_KEY_LEN + 1];
  34         u8 key_len;
  35         u8 key_idx;
  36         struct crypto_blkcipher *tx_tfm;
  37         struct crypto_blkcipher *rx_tfm;
  38 };
  39
  40 static void *prism2_wep_init(int keyidx)
  41 {
  42         struct prism2_wep_data *priv;
  43
  44         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  45         if (priv == NULL)
  46                 goto fail;
  47         priv->key_idx = keyidx;
  48
  49         priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  50         if (IS_ERR(priv->tx_tfm)) {
  51                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  52                        "crypto API arc4\n");
  53                 priv->tx_tfm = NULL;
  54                 goto fail;
  55         }
  56
  57         priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  58         if (IS_ERR(priv->rx_tfm)) {
  59                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  60                        "crypto API arc4\n");
  61                 priv->rx_tfm = NULL;
  62                 goto fail;
  63         }
  64         /* start WEP IV from a random value */
  65         get_random_bytes(&priv->iv, 4);
  66
  67         return priv;
  68
  69       fail:
  70         if (priv) {
  71                 if (priv->tx_tfm)
  72                         crypto_free_blkcipher(priv->tx_tfm);
  73                 if (priv->rx_tfm)
  74                         crypto_free_blkcipher(priv->rx_tfm);
  75                 kfree(priv);
  76         }
  77         return NULL;
  78 }
  79
  80 static void prism2_wep_deinit(void *priv)
  81 {
  82         struct prism2_wep_data *_priv = priv;
  83         if (_priv) {
  84                 if (_priv->tx_tfm)
  85                         crypto_free_blkcipher(_priv->tx_tfm);
  86                 if (_priv->rx_tfm)
  87                         crypto_free_blkcipher(_priv->rx_tfm);
  88         }
  89         kfree(priv);
  90 }
  91
  92 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  93 static int prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,
  94                                u8 *key, int keylen, void *priv)
  95 {
  96         struct prism2_wep_data *wep = priv;
  97         u32 klen, len;
  98         u8 *pos;
  99
 100         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
 101                 return -1;
 102
 103         len = skb->len - hdr_len;
 104         pos = skb_push(skb, 4);
 105         memmove(pos, pos + 4, hdr_len);
 106         pos += hdr_len;
 107
 108         klen = 3 + wep->key_len;
 109
 110         wep->iv++;
 111
 112         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 113          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 114          * can be used to speedup attacks, so avoid using them. */
 115         if ((wep->iv & 0xff00) == 0xff00) {
 116                 u8 B = (wep->iv >> 16) & 0xff;
 117                 if (B >= 3 && B < klen)
 118                         wep->iv += 0x0100;
 119         }
 120
 121         /* Prepend 24-bit IV to RC4 key and TX frame */
 122         *pos++ = (wep->iv >> 16) & 0xff;
 123         *pos++ = (wep->iv >> 8) & 0xff;
 124         *pos++ = wep->iv & 0xff;
 125         *pos++ = wep->key_idx << 6;
 126
 127         return 0;
 128 }
 129
 130 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 131  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 132  * so the payload length increases with 8 bytes.
 133  *
 134  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 135  */
 136 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 137 {
 138         struct prism2_wep_data *wep = priv;
 139         struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
 140         u32 crc, klen, len;
 141         u8 *pos, *icv;
 142         struct scatterlist sg;
 143         u8 key[WEP_KEY_LEN + 3];
 144
 145         /* other checks are in prism2_wep_build_iv */
 146         if (skb_tailroom(skb) < 4)
 147                 return -1;
 148
 149         /* add the IV to the frame */
 150         if (prism2_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 151                 return -1;
 152
 153         /* Copy the IV into the first 3 bytes of the key */
 154         memcpy(key, skb->data + hdr_len, 3);
 155
 156         /* Copy rest of the WEP key (the secret part) */
 157         memcpy(key + 3, wep->key, wep->key_len);
 158
 159         len = skb->len - hdr_len - 4;
 160         pos = skb->data + hdr_len + 4;
 161         klen = 3 + wep->key_len;
 162
 163         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 164         crc = ~crc32_le(~0, pos, len);
 165         icv = skb_put(skb, 4);
 166         icv[0] = crc;
 167         icv[1] = crc >> 8;
 168         icv[2] = crc >> 16;
 169         icv[3] = crc >> 24;
 170
 171         crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
 172         sg.page = virt_to_page(pos);
 173         sg.offset = offset_in_page(pos);
 174         sg.length = 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 prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 186 {
 187         struct prism2_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.page = virt_to_page(pos);
 215         sg.offset = offset_in_page(pos);
 216         sg.length = plen + 4;
 217         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 218                 return -7;
 219
 220         crc = ~crc32_le(~0, pos, plen);
 221         icv[0] = crc;
 222         icv[1] = crc >> 8;
 223         icv[2] = crc >> 16;
 224         icv[3] = crc >> 24;
 225         if (memcmp(icv, pos + plen, 4) != 0) {
 226                 /* ICV mismatch - drop frame */
 227                 return -2;
 228         }
 229
 230         /* Remove IV and ICV */
 231         memmove(skb->data + 4, skb->data, hdr_len);
 232         skb_pull(skb, 4);
 233         skb_trim(skb, skb->len - 4);
 234
 235         return 0;
 236 }
 237
 238 static int prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)
 239 {
 240         struct prism2_wep_data *wep = priv;
 241
 242         if (len < 0 || len > WEP_KEY_LEN)
 243                 return -1;
 244
 245         memcpy(wep->key, key, len);
 246         wep->key_len = len;
 247
 248         return 0;
 249 }
 250
 251 static int prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)
 252 {
 253         struct prism2_wep_data *wep = priv;
 254
 255         if (len < wep->key_len)
 256                 return -1;
 257
 258         memcpy(key, wep->key, wep->key_len);
 259
 260         return wep->key_len;
 261 }
 262
 263 static char *prism2_wep_print_stats(char *p, void *priv)
 264 {
 265         struct prism2_wep_data *wep = priv;
 266         p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 267         return p;
 268 }
 269
 270 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
 271         .name = "WEP",
 272         .init = prism2_wep_init,
 273         .deinit = prism2_wep_deinit,
 274         .build_iv = prism2_wep_build_iv,
 275         .encrypt_mpdu = prism2_wep_encrypt,
 276         .decrypt_mpdu = prism2_wep_decrypt,
 277         .encrypt_msdu = NULL,
 278         .decrypt_msdu = NULL,
 279         .set_key = prism2_wep_set_key,
 280         .get_key = prism2_wep_get_key,
 281         .print_stats = prism2_wep_print_stats,
 282         .extra_mpdu_prefix_len = 4,     /* IV */
 283         .extra_mpdu_postfix_len = 4,    /* ICV */
 284         .owner = THIS_MODULE,
 285 };
 286
 287 static int __init ieee80211_crypto_wep_init(void)
 288 {
 289         return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
 290 }
 291
 292 static void __exit ieee80211_crypto_wep_exit(void)
 293 {
 294         ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
 295 }
 296
 297 module_init(ieee80211_crypto_wep_init);
 298 module_exit(ieee80211_crypto_wep_exit);