linux/net/wireless/lib80211_crypt_wep.c
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   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
  28MODULE_AUTHOR("Jouni Malinen");
  29MODULE_DESCRIPTION("lib80211 crypt: WEP");
  30MODULE_LICENSE("GPL");
  31
  32struct 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
  42static 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                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                priv->rx_tfm = NULL;
  60                goto fail;
  61        }
  62        /* start WEP IV from a random value */
  63        get_random_bytes(&priv->iv, 4);
  64
  65        return priv;
  66
  67      fail:
  68        if (priv) {
  69                if (priv->tx_tfm)
  70                        crypto_free_blkcipher(priv->tx_tfm);
  71                if (priv->rx_tfm)
  72                        crypto_free_blkcipher(priv->rx_tfm);
  73                kfree(priv);
  74        }
  75        return NULL;
  76}
  77
  78static void lib80211_wep_deinit(void *priv)
  79{
  80        struct lib80211_wep_data *_priv = priv;
  81        if (_priv) {
  82                if (_priv->tx_tfm)
  83                        crypto_free_blkcipher(_priv->tx_tfm);
  84                if (_priv->rx_tfm)
  85                        crypto_free_blkcipher(_priv->rx_tfm);
  86        }
  87        kfree(priv);
  88}
  89
  90/* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  91static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  92                               u8 *key, int keylen, void *priv)
  93{
  94        struct lib80211_wep_data *wep = priv;
  95        u32 klen;
  96        u8 *pos;
  97
  98        if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  99                return -1;
 100
 101        pos = skb_push(skb, 4);
 102        memmove(pos, pos + 4, hdr_len);
 103        pos += hdr_len;
 104
 105        klen = 3 + wep->key_len;
 106
 107        wep->iv++;
 108
 109        /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
 110         * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
 111         * can be used to speedup attacks, so avoid using them. */
 112        if ((wep->iv & 0xff00) == 0xff00) {
 113                u8 B = (wep->iv >> 16) & 0xff;
 114                if (B >= 3 && B < klen)
 115                        wep->iv += 0x0100;
 116        }
 117
 118        /* Prepend 24-bit IV to RC4 key and TX frame */
 119        *pos++ = (wep->iv >> 16) & 0xff;
 120        *pos++ = (wep->iv >> 8) & 0xff;
 121        *pos++ = wep->iv & 0xff;
 122        *pos++ = wep->key_idx << 6;
 123
 124        return 0;
 125}
 126
 127/* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 128 * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 129 * so the payload length increases with 8 bytes.
 130 *
 131 * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 132 */
 133static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 134{
 135        struct lib80211_wep_data *wep = priv;
 136        struct blkcipher_desc desc = { .tfm = wep->tx_tfm };
 137        u32 crc, klen, len;
 138        u8 *pos, *icv;
 139        struct scatterlist sg;
 140        u8 key[WEP_KEY_LEN + 3];
 141
 142        /* other checks are in lib80211_wep_build_iv */
 143        if (skb_tailroom(skb) < 4)
 144                return -1;
 145
 146        /* add the IV to the frame */
 147        if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 148                return -1;
 149
 150        /* Copy the IV into the first 3 bytes of the key */
 151        skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 152
 153        /* Copy rest of the WEP key (the secret part) */
 154        memcpy(key + 3, wep->key, wep->key_len);
 155
 156        len = skb->len - hdr_len - 4;
 157        pos = skb->data + hdr_len + 4;
 158        klen = 3 + wep->key_len;
 159
 160        /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 161        crc = ~crc32_le(~0, pos, len);
 162        icv = skb_put(skb, 4);
 163        icv[0] = crc;
 164        icv[1] = crc >> 8;
 165        icv[2] = crc >> 16;
 166        icv[3] = crc >> 24;
 167
 168        crypto_blkcipher_setkey(wep->tx_tfm, key, klen);
 169        sg_init_one(&sg, pos, len + 4);
 170        return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);
 171}
 172
 173/* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 174 * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 175 * ICV (4 bytes). len includes both IV and ICV.
 176 *
 177 * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 178 * failure. If frame is OK, IV and ICV will be removed.
 179 */
 180static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 181{
 182        struct lib80211_wep_data *wep = priv;
 183        struct blkcipher_desc desc = { .tfm = wep->rx_tfm };
 184        u32 crc, klen, plen;
 185        u8 key[WEP_KEY_LEN + 3];
 186        u8 keyidx, *pos, icv[4];
 187        struct scatterlist sg;
 188
 189        if (skb->len < hdr_len + 8)
 190                return -1;
 191
 192        pos = skb->data + hdr_len;
 193        key[0] = *pos++;
 194        key[1] = *pos++;
 195        key[2] = *pos++;
 196        keyidx = *pos++ >> 6;
 197        if (keyidx != wep->key_idx)
 198                return -1;
 199
 200        klen = 3 + wep->key_len;
 201
 202        /* Copy rest of the WEP key (the secret part) */
 203        memcpy(key + 3, wep->key, wep->key_len);
 204
 205        /* Apply RC4 to data and compute CRC32 over decrypted data */
 206        plen = skb->len - hdr_len - 8;
 207
 208        crypto_blkcipher_setkey(wep->rx_tfm, key, klen);
 209        sg_init_one(&sg, pos, plen + 4);
 210        if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
 211                return -7;
 212
 213        crc = ~crc32_le(~0, pos, plen);
 214        icv[0] = crc;
 215        icv[1] = crc >> 8;
 216        icv[2] = crc >> 16;
 217        icv[3] = crc >> 24;
 218        if (memcmp(icv, pos + plen, 4) != 0) {
 219                /* ICV mismatch - drop frame */
 220                return -2;
 221        }
 222
 223        /* Remove IV and ICV */
 224        memmove(skb->data + 4, skb->data, hdr_len);
 225        skb_pull(skb, 4);
 226        skb_trim(skb, skb->len - 4);
 227
 228        return 0;
 229}
 230
 231static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 232{
 233        struct lib80211_wep_data *wep = priv;
 234
 235        if (len < 0 || len > WEP_KEY_LEN)
 236                return -1;
 237
 238        memcpy(wep->key, key, len);
 239        wep->key_len = len;
 240
 241        return 0;
 242}
 243
 244static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 245{
 246        struct lib80211_wep_data *wep = priv;
 247
 248        if (len < wep->key_len)
 249                return -1;
 250
 251        memcpy(key, wep->key, wep->key_len);
 252
 253        return wep->key_len;
 254}
 255
 256static char *lib80211_wep_print_stats(char *p, void *priv)
 257{
 258        struct lib80211_wep_data *wep = priv;
 259        p += sprintf(p, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 260        return p;
 261}
 262
 263static struct lib80211_crypto_ops lib80211_crypt_wep = {
 264        .name = "WEP",
 265        .init = lib80211_wep_init,
 266        .deinit = lib80211_wep_deinit,
 267        .encrypt_mpdu = lib80211_wep_encrypt,
 268        .decrypt_mpdu = lib80211_wep_decrypt,
 269        .encrypt_msdu = NULL,
 270        .decrypt_msdu = NULL,
 271        .set_key = lib80211_wep_set_key,
 272        .get_key = lib80211_wep_get_key,
 273        .print_stats = lib80211_wep_print_stats,
 274        .extra_mpdu_prefix_len = 4,     /* IV */
 275        .extra_mpdu_postfix_len = 4,    /* ICV */
 276        .owner = THIS_MODULE,
 277};
 278
 279static int __init lib80211_crypto_wep_init(void)
 280{
 281        return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 282}
 283
 284static void __exit lib80211_crypto_wep_exit(void)
 285{
 286        lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 287}
 288
 289module_init(lib80211_crypto_wep_init);
 290module_exit(lib80211_crypto_wep_exit);
 291
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