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 *tfm;
  37 };
  38
  39 static void *prism2_wep_init(int keyidx)
  40 {
  41         struct prism2_wep_data *priv;
  42
  43         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  44         if (priv == NULL)
  45                 goto fail;
  46         priv->key_idx = keyidx;
  47
  48         priv->tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  49         if (IS_ERR(priv->tfm)) {
  50                 printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "
  51                        "crypto API arc4\n");
  52                 priv->tfm = NULL;
  53                 goto fail;
  54         }
  55
  56         /* start WEP IV from a random value */
  57         get_random_bytes(&priv->iv, 4);
  58
  59         return priv;
  60
  61       fail:
  62         if (priv) {
  63                 if (priv->tfm)
  64                         crypto_free_blkcipher(priv->tfm);
  65                 kfree(priv);
  66         }
  67         return NULL;
  68 }
  69
  70 static void prism2_wep_deinit(void *priv)
  71 {
  72         struct prism2_wep_data *_priv = priv;
  73         if (_priv && _priv->tfm)
  74                 crypto_free_blkcipher(_priv->tfm);
  75         kfree(priv);
  76 }
  77
  78 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  79 static int prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,
  80                                u8 *key, int keylen, void *priv)
  81 {
  82         struct prism2_wep_data *wep = priv;
  83         u32 klen, len;
  84         u8 *pos;
  85
  86         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  87                 return -1;
  88
  89         len = skb->len - hdr_len;
  90         pos = skb_push(skb, 4);
  91         memmove(pos, pos + 4, hdr_len);
  92         pos += hdr_len;
  93
  94         klen = 3 + wep->key_len;
  95
  96         wep->iv++;
  97
  98         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
  99          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 100          * can be used to speedup attacks, so avoid using them. */
 101         if ((wep->iv & 0xff00) == 0xff00) {
 102                 u8 B = (wep->iv >> 16) & 0xff;
 103                 if (B >= 3 && B < klen)
 104                         wep->iv += 0x0100;
 105         }
 106
 107         /* Prepend 24-bit IV to RC4 key and TX frame */
 108         *pos++ = (wep->iv >> 16) & 0xff;
 109         *pos++ = (wep->iv >> 8) & 0xff;
 110         *pos++ = wep->iv & 0xff;
 111         *pos++ = wep->key_idx << 6;
 112
 113         return 0;
 114 }
 115
 116 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 117  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 118  * so the payload length increases with 8 bytes.
 119  *
 120  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 121  */
 122 static int prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 123 {
 124         struct prism2_wep_data *wep = priv;
 125         struct blkcipher_desc desc = { .tfm = wep->tfm };
 126         u32 crc, klen, len;
 127         u8 *pos, *icv;
 128         struct scatterlist sg;
 129         u8 key[WEP_KEY_LEN + 3];
 130
 131         /* other checks are in prism2_wep_build_iv */
 132         if (skb_tailroom(skb) < 4)
 133                 return -1;
 134
 135         /* add the IV to the frame */
 136         if (prism2_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 137                 return -1;
 138
 139         /* Copy the IV into the first 3 bytes of the key */
 140         memcpy(key, skb->data + hdr_len, 3);
 141
 142         /* Copy rest of the WEP key (the secret part) */
 143         memcpy(key + 3, wep->key, wep->key_len);
 144
 145         len = skb->len - hdr_len - 4;
 146         pos = skb->data + hdr_len + 4;
 147         klen = 3 + wep->key_len;
 148
 149         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 150         crc = ~crc32_le(~0, pos, len);
 151         icv = skb_put(skb, 4);
 152         icv[0] = crc;
 153         icv[1] = crc >> 8;
 154         icv[2] = crc >> 16;
 155         icv[3] = crc >> 24;
 156
 157         crypto_blkcipher_setkey(wep->tfm, key, klen);
 158         sg.page = virt_to_page(pos);
 159         sg.offset = offset_in_page(pos);
 160         sg.length = len + 4;
 161         return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
 162 }
 163
 164 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 165  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 166  * ICV (4 bytes). len includes both IV and ICV.
 167  *
 168  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 169  * failure. If frame is OK, IV and ICV will be removed.
 170  */
 171 static int prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 172 {
 173         struct prism2_wep_data *wep = priv;
 174         struct blkcipher_desc desc = { .tfm = wep->tfm };
 175         u32 crc, klen, plen;
 176         u8 key[WEP_KEY_LEN + 3];
 177         u8 keyidx, *pos, icv[4];
 178         struct scatterlist sg;
 179
 180         if (skb->len < hdr_len + 8)
 181                 return -1;
 182
 183         pos = skb->data + hdr_len;
 184         key[0] = *pos++;
 185         key[1] = *pos++;
 186         key[2] = *pos++;
 187         keyidx = *pos++ >> 6;
 188         if (keyidx != wep->key_idx)
 189                 return -1;
 190
 191         klen = 3 + wep->key_len;
 192
 193         /* Copy rest of the WEP key (the secret part) */
 194         memcpy(key + 3, wep->key, wep->key_len);
 195
 196         /* Apply RC4 to data and compute CRC32 over decrypted data */
 197         plen = skb->len - hdr_len - 8;
 198
 199         crypto_blkcipher_setkey(wep->tfm, key, klen);
 200         sg.page = virt_to_page(pos);
 201         sg.offset = offset_in_page(pos);
 202         sg.length = plen + 4;
 203         if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 204                 return -7;
 205
 206         crc = ~crc32_le(~0, pos, plen);
 207         icv[0] = crc;
 208         icv[1] = crc >> 8;
 209         icv[2] = crc >> 16;
 210         icv[3] = crc >> 24;
 211         if (memcmp(icv, pos + plen, 4) != 0) {
 212                 /* ICV mismatch - drop frame */
 213                 return -2;
 214         }
 215
 216         /* Remove IV and ICV */
 217         memmove(skb->data + 4, skb->data, hdr_len);
 218         skb_pull(skb, 4);
 219         skb_trim(skb, skb->len - 4);
 220
 221         return 0;
 222 }
 223
 224 static int prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)
 225 {
 226         struct prism2_wep_data *wep = priv;
 227
 228         if (len < 0 || len > WEP_KEY_LEN)
 229                 return -1;
 230
 231         memcpy(wep->key, key, len);
 232         wep->key_len = len;
 233
 234         return 0;
 235 }
 236
 237 static int prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)
 238 {
 239         struct prism2_wep_data *wep = priv;
 240
 241         if (len < wep->key_len)
 242                 return -1;
 243
 244         memcpy(key, wep->key, wep->key_len);
 245
 246         return wep->key_len;
 247 }
 248
 249 static char *prism2_wep_print_stats(char *p, void *priv)
 250 {
 251         struct prism2_wep_data *wep = priv;
 252         p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 253         return p;
 254 }
 255
 256 static struct ieee80211_crypto_ops ieee80211_crypt_wep = {
 257         .name = "WEP",
 258         .init = prism2_wep_init,
 259         .deinit = prism2_wep_deinit,
 260         .build_iv = prism2_wep_build_iv,
 261         .encrypt_mpdu = prism2_wep_encrypt,
 262         .decrypt_mpdu = prism2_wep_decrypt,
 263         .encrypt_msdu = NULL,
 264         .decrypt_msdu = NULL,
 265         .set_key = prism2_wep_set_key,
 266         .get_key = prism2_wep_get_key,
 267         .print_stats = prism2_wep_print_stats,
 268         .extra_mpdu_prefix_len = 4,     /* IV */
 269         .extra_mpdu_postfix_len = 4,    /* ICV */
 270         .owner = THIS_MODULE,
 271 };
 272
 273 static int __init ieee80211_crypto_wep_init(void)
 274 {
 275         return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);
 276 }
 277
 278 static void __exit ieee80211_crypto_wep_exit(void)
 279 {
 280         ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);
 281 }
 282
 283 module_init(ieee80211_crypto_wep_init);
 284 module_exit(ieee80211_crypto_wep_exit);