/*

   * lib80211 crypt: host-based WEP encryption implementation for lib80211

   *

   * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>

   * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>

   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation. See README and COPYING for
   * more details.
   */

  #include <linux/err.h>

  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/slab.h>
  #include <linux/random.h>

  #include <linux/scatterlist.h>

  #include <linux/skbuff.h>

  #include <linux/mm.h>

  #include <asm/string.h>

  #include <net/lib80211.h>

  #include <linux/crypto.h>

  #include <linux/crc32.h>
  
  MODULE_AUTHOR("Jouni Malinen");

  MODULE_DESCRIPTION("lib80211 crypt: WEP");

  MODULE_LICENSE("GPL");

  struct lib80211_wep_data {

  	u32 iv;
  #define WEP_KEY_LEN 13
  	u8 key[WEP_KEY_LEN + 1];
  	u8 key_len;
  	u8 key_idx;

  	struct crypto_blkcipher *tx_tfm;
  	struct crypto_blkcipher *rx_tfm;

  };

  static void *lib80211_wep_init(int keyidx)

  {

  	struct lib80211_wep_data *priv;

  	priv = kzalloc(sizeof(*priv), GFP_ATOMIC);

  	if (priv == NULL)
  		goto fail;

  	priv->key_idx = keyidx;

  	priv->tx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  	if (IS_ERR(priv->tx_tfm)) {

  		priv->tx_tfm = NULL;

  		goto fail;
  	}

  	priv->rx_tfm = crypto_alloc_blkcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
  	if (IS_ERR(priv->rx_tfm)) {

  		priv->rx_tfm = NULL;

  		goto fail;
  	}

  	/* start WEP IV from a random value */
  	get_random_bytes(&priv->iv, 4);
  
  	return priv;

        fail:

  	if (priv) {

  		if (priv->tx_tfm)

  			crypto_free_blkcipher(priv->tx_tfm);

  		if (priv->rx_tfm)

  			crypto_free_blkcipher(priv->rx_tfm);

  		kfree(priv);
  	}
  	return NULL;
  }

  static void lib80211_wep_deinit(void *priv)

  {

  	struct lib80211_wep_data *_priv = priv;

  	if (_priv) {
  		if (_priv->tx_tfm)

  			crypto_free_blkcipher(_priv->tx_tfm);

  		if (_priv->rx_tfm)

  			crypto_free_blkcipher(_priv->rx_tfm);

  	}

  	kfree(priv);
  }

  /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */

  static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,

  			       u8 *key, int keylen, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  	u32 klen;

  	u8 *pos;

  	if (skb_headroom(skb) < 4 || skb->len < hdr_len)

  		return -1;

  	pos = skb_push(skb, 4);
  	memmove(pos, pos + 4, hdr_len);
  	pos += hdr_len;
  
  	klen = 3 + wep->key_len;
  
  	wep->iv++;
  
  	/* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
  	 * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
  	 * can be used to speedup attacks, so avoid using them. */
  	if ((wep->iv & 0xff00) == 0xff00) {
  		u8 B = (wep->iv >> 16) & 0xff;
  		if (B >= 3 && B < klen)
  			wep->iv += 0x0100;
  	}
  
  	/* Prepend 24-bit IV to RC4 key and TX frame */

  	*pos++ = (wep->iv >> 16) & 0xff;
  	*pos++ = (wep->iv >> 8) & 0xff;
  	*pos++ = wep->iv & 0xff;

  	*pos++ = wep->key_idx << 6;

  	return 0;
  }
  
  /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
   * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
   * so the payload length increases with 8 bytes.
   *
   * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
   */

  static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  	struct blkcipher_desc desc = { .tfm = wep->tx_tfm };

  	u32 crc, klen, len;
  	u8 *pos, *icv;
  	struct scatterlist sg;
  	u8 key[WEP_KEY_LEN + 3];

  	/* other checks are in lib80211_wep_build_iv */

  	if (skb_tailroom(skb) < 4)
  		return -1;

  	/* add the IV to the frame */

  	if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))

  		return -1;

  	/* Copy the IV into the first 3 bytes of the key */

  	skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);

  	/* Copy rest of the WEP key (the secret part) */
  	memcpy(key + 3, wep->key, wep->key_len);

  	len = skb->len - hdr_len - 4;
  	pos = skb->data + hdr_len + 4;
  	klen = 3 + wep->key_len;

  	/* Append little-endian CRC32 over only the data and encrypt it to produce ICV */

  	crc = ~crc32_le(~0, pos, len);
  	icv = skb_put(skb, 4);
  	icv[0] = crc;
  	icv[1] = crc >> 8;
  	icv[2] = crc >> 16;
  	icv[3] = crc >> 24;

  	crypto_blkcipher_setkey(wep->tx_tfm, key, klen);

  	sg_init_one(&sg, pos, len + 4);

  	return crypto_blkcipher_encrypt(&desc, &sg, &sg, len + 4);

  }

  /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
   * the frame: IV (4 bytes), encrypted payload (including SNAP header),
   * ICV (4 bytes). len includes both IV and ICV.
   *
   * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
   * failure. If frame is OK, IV and ICV will be removed.
   */

  static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  	struct blkcipher_desc desc = { .tfm = wep->rx_tfm };

  	u32 crc, klen, plen;
  	u8 key[WEP_KEY_LEN + 3];
  	u8 keyidx, *pos, icv[4];
  	struct scatterlist sg;
  
  	if (skb->len < hdr_len + 8)
  		return -1;
  
  	pos = skb->data + hdr_len;
  	key[0] = *pos++;
  	key[1] = *pos++;
  	key[2] = *pos++;
  	keyidx = *pos++ >> 6;
  	if (keyidx != wep->key_idx)
  		return -1;
  
  	klen = 3 + wep->key_len;
  
  	/* Copy rest of the WEP key (the secret part) */
  	memcpy(key + 3, wep->key, wep->key_len);
  
  	/* Apply RC4 to data and compute CRC32 over decrypted data */
  	plen = skb->len - hdr_len - 8;

  	crypto_blkcipher_setkey(wep->rx_tfm, key, klen);

  	sg_init_one(&sg, pos, plen + 4);

  	if (crypto_blkcipher_decrypt(&desc, &sg, &sg, plen + 4))
  		return -7;

  
  	crc = ~crc32_le(~0, pos, plen);
  	icv[0] = crc;
  	icv[1] = crc >> 8;
  	icv[2] = crc >> 16;
  	icv[3] = crc >> 24;
  	if (memcmp(icv, pos + plen, 4) != 0) {
  		/* ICV mismatch - drop frame */
  		return -2;
  	}
  
  	/* Remove IV and ICV */
  	memmove(skb->data + 4, skb->data, hdr_len);
  	skb_pull(skb, 4);
  	skb_trim(skb, skb->len - 4);
  
  	return 0;
  }

  static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  
  	if (len < 0 || len > WEP_KEY_LEN)
  		return -1;
  
  	memcpy(wep->key, key, len);
  	wep->key_len = len;
  
  	return 0;
  }

  static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  
  	if (len < wep->key_len)
  		return -1;
  
  	memcpy(key, wep->key, wep->key_len);
  
  	return wep->key_len;
  }

  static char *lib80211_wep_print_stats(char *p, void *priv)

  {

  	struct lib80211_wep_data *wep = priv;

  	p += sprintf(p, "key[%d] alg=WEP len=%d
  ", wep->key_idx, wep->key_len);

  	return p;
  }

  static struct lib80211_crypto_ops lib80211_crypt_wep = {

  	.name = "WEP",

  	.init = lib80211_wep_init,
  	.deinit = lib80211_wep_deinit,

  	.encrypt_mpdu = lib80211_wep_encrypt,
  	.decrypt_mpdu = lib80211_wep_decrypt,

  	.encrypt_msdu = NULL,
  	.decrypt_msdu = NULL,

  	.set_key = lib80211_wep_set_key,
  	.get_key = lib80211_wep_get_key,
  	.print_stats = lib80211_wep_print_stats,

  	.extra_mpdu_prefix_len = 4,	/* IV */
  	.extra_mpdu_postfix_len = 4,	/* ICV */

  	.owner = THIS_MODULE,

  };

  static int __init lib80211_crypto_wep_init(void)

  {

  	return lib80211_register_crypto_ops(&lib80211_crypt_wep);

  }

  static void __exit lib80211_crypto_wep_exit(void)

  {

  	lib80211_unregister_crypto_ops(&lib80211_crypt_wep);

  }

  module_init(lib80211_crypto_wep_init);
  module_exit(lib80211_crypto_wep_exit);