/*
 * Host AP crypt: host-based WEP encryption implementation for Host AP driver
 *
 * Copyright (c) 2002-2004, Jouni Malinen <jkmaline@cc.hut.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 <crypto/skcipher.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#include "rtllib.h"

#include <linux/scatterlist.h>
#include <linux/crc32.h>

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_skcipher *tx_tfm;
        struct crypto_skcipher *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_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(priv->tx_tfm)) {
                pr_debug("rtllib_crypt_wep: could not allocate crypto API arc4\n");
                priv->tx_tfm = NULL;
                goto fail;
        }
        priv->rx_tfm = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(priv->rx_tfm)) {
                pr_debug("rtllib_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) {
                crypto_free_skcipher(priv->tx_tfm);
                crypto_free_skcipher(priv->rx_tfm);
                kfree(priv);
        }
        return NULL;
}


static void prism2_wep_deinit(void *priv)
{
        struct prism2_wep_data *_priv = priv;

        if (_priv) {
                crypto_free_skcipher(_priv->tx_tfm);
                crypto_free_skcipher(_priv->rx_tfm);
        }
        kfree(priv);
}

/* 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;
        u32 klen, len;
        u8 key[WEP_KEY_LEN + 3];
        u8 *pos;
        struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb +
                                    MAX_DEV_ADDR_SIZE);
        u32 crc;
        u8 *icv;
        struct scatterlist sg;
        int err;

        if (skb_headroom(skb) < 4 || skb_tailroom(skb) < 4 ||
            skb->len < hdr_len){
                pr_err("Error!!! headroom=%d tailroom=%d skblen=%d hdr_len=%d\n",
                       skb_headroom(skb), skb_tailroom(skb), 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++ = key[0] = (wep->iv >> 16) & 0xff;
        *pos++ = key[1] = (wep->iv >> 8) & 0xff;
        *pos++ = key[2] = wep->iv & 0xff;
        *pos++ = wep->key_idx << 6;

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

        if (!tcb_desc->bHwSec) {
                SKCIPHER_REQUEST_ON_STACK(req, wep->tx_tfm);

                /* Append little-endian CRC32 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;

                sg_init_one(&sg, pos, len+4);
                crypto_skcipher_setkey(wep->tx_tfm, key, klen);
                skcipher_request_set_tfm(req, wep->tx_tfm);
                skcipher_request_set_callback(req, 0, NULL, NULL);
                skcipher_request_set_crypt(req, &sg, &sg, len + 4, NULL);
                err = crypto_skcipher_encrypt(req);
                skcipher_request_zero(req);
                return err;
        }

        return 0;
}


/* Perform WEP decryption on given struct 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;
        u32  klen, plen;
        u8 key[WEP_KEY_LEN + 3];
        u8 keyidx, *pos;
        struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb +
                                    MAX_DEV_ADDR_SIZE);
        u32 crc;
        u8 icv[4];
        struct scatterlist sg;
        int err;

        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;

        if (!tcb_desc->bHwSec) {
                SKCIPHER_REQUEST_ON_STACK(req, wep->rx_tfm);

                sg_init_one(&sg, pos, plen+4);
                crypto_skcipher_setkey(wep->rx_tfm, key, klen);
                skcipher_request_set_tfm(req, wep->rx_tfm);
                skcipher_request_set_callback(req, 0, NULL, NULL);
                skcipher_request_set_crypt(req, &sg, &sg, plen + 4, NULL);
                err = crypto_skcipher_decrypt(req);
                skcipher_request_zero(req);
                if (err)
                        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 void prism2_wep_print_stats(struct seq_file *m, void *priv)
{
        struct prism2_wep_data *wep = priv;

        seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
}

static struct lib80211_crypto_ops rtllib_crypt_wep = {
        .name                   = "R-WEP",
        .init                   = prism2_wep_init,
        .deinit                 = prism2_wep_deinit,
        .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 rtllib_crypto_wep_init(void)
{
        return lib80211_register_crypto_ops(&rtllib_crypt_wep);
}


static void __exit rtllib_crypto_wep_exit(void)
{
        lib80211_unregister_crypto_ops(&rtllib_crypt_wep);
}

module_init(rtllib_crypto_wep_init);
module_exit(rtllib_crypto_wep_exit);

MODULE_LICENSE("GPL");