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/*

 * Host AP crypt: host-based WEP encryption implementation for Host AP driver

 *

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

 *

 * 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/ieee80211.h>

#include <linux/crypto.h>

#include <linux/crc32.h>

MODULE_AUTHOR("Jouni Malinen");

MODULE_DESCRIPTION("Host AP crypt: WEP");

MODULE_LICENSE("GPL");

struct prism2_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 *prism2_wep_init(int keyidx)

{

        struct prism2_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)) {

                printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "

                       "crypto API arc4\n");

                priv->tx_tfm = NULL;

                goto fail;

        }

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

        if (IS_ERR(priv->rx_tfm)) {

                printk(KERN_DEBUG "ieee80211_crypt_wep: could not allocate "

                       "crypto API arc4\n");

                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 prism2_wep_deinit(void *priv)

{

        struct prism2_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 prism2_wep_build_iv(struct sk_buff *skb, int hdr_len,

                               u8 *key, int keylen, void *priv)

{

        struct prism2_wep_data *wep = priv;

        u32 klen, len;

        u8 *pos;

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

                return -1;

        len = skb->len - hdr_len;

        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 prism2_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)

{

        struct prism2_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 prism2_wep_build_iv */

        if (skb_tailroom(skb) < 4)

                return -1;

        /* add the IV to the frame */

        if (prism2_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 prism2_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)

{

        struct prism2_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 prism2_wep_set_key(void *key, int len, u8 * seq, void *priv)

{

        struct prism2_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 prism2_wep_get_key(void *key, int len, u8 * seq, void *priv)

{

        struct prism2_wep_data *wep = priv;

        if (len < wep->key_len)

                return -1;

        memcpy(key, wep->key, wep->key_len);

        return wep->key_len;

}

static char *prism2_wep_print_stats(char *p, void *priv)

{

        struct prism2_wep_data *wep = priv;

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

        return p;

}

static struct ieee80211_crypto_ops ieee80211_crypt_wep = {

        .name = "WEP",

        .init = prism2_wep_init,

        .deinit = prism2_wep_deinit,

        .build_iv = prism2_wep_build_iv,

        .encrypt_mpdu = prism2_wep_encrypt,

        .decrypt_mpdu = prism2_wep_decrypt,

        .encrypt_msdu = NULL,

        .decrypt_msdu = NULL,

        .set_key = prism2_wep_set_key,

        .get_key = prism2_wep_get_key,

        .print_stats = prism2_wep_print_stats,

        .extra_mpdu_prefix_len = 4,     /* IV */

        .extra_mpdu_postfix_len = 4,    /* ICV */

        .owner = THIS_MODULE,

};

static int __init ieee80211_crypto_wep_init(void)

{

        return ieee80211_register_crypto_ops(&ieee80211_crypt_wep);

}

static void __exit ieee80211_crypto_wep_exit(void)

{

        ieee80211_unregister_crypto_ops(&ieee80211_crypt_wep);

}

module_init(ieee80211_crypto_wep_init);

module_exit(ieee80211_crypto_wep_exit);