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Filename : RC4.php
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<?php

/**
 * PHPExcel_Reader_Excel5_RC4
 *
 * Copyright (c) 2006 - 2015 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * @category   PHPExcel
 * @package    PHPExcel_Reader_Excel5
 * @copyright  Copyright (c) 2006 - 2015 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt    LGPL
 * @version    ##VERSION##, ##DATE##
 */
class PHPExcel_Reader_Excel5_RC4
{
    // Context
    protected $s = array();
    protected $i = 0;
    protected $j = 0;

    /**
     * RC4 stream decryption/encryption constrcutor
     *
     * @param string $key Encryption key/passphrase
     */
    public function __construct($key)
    {
        $len = strlen($key);

        for ($this->i = 0; $this->i < 256; $this->i++) {
            $this->s[$this->i] = $this->i;
        }

        $this->j = 0;
        for ($this->i = 0; $this->i < 256; $this->i++) {
            $this->j = ($this->j + $this->s[$this->i] + ord($key[$this->i % $len])) % 256;
            $t = $this->s[$this->i];
            $this->s[$this->i] = $this->s[$this->j];
            $this->s[$this->j] = $t;
        }
        $this->i = $this->j = 0;
    }

    /**
     * Symmetric decryption/encryption function
     *
     * @param string $data Data to encrypt/decrypt
     *
     * @return string
     */
    public function RC4($data)
    {
        $len = strlen($data);
        for ($c = 0; $c < $len; $c++) {
            $this->i = ($this->i + 1) % 256;
            $this->j = ($this->j + $this->s[$this->i]) % 256;
            $t = $this->s[$this->i];
            $this->s[$this->i] = $this->s[$this->j];
            $this->s[$this->j] = $t;

            $t = ($this->s[$this->i] + $this->s[$this->j]) % 256;

            $data[$c] = chr(ord($data[$c]) ^ $this->s[$t]);
        }
        return $data;
    }
}