php5 download php5 numeric string encryption and decryption code

/* ----------------------------------------------------------------------------
* Script Name: encrypt.php
* Creation Date: 2008-4-7 10:36
* Last Modified: 2008-4-12 16:00
* Author: meyu
* Copyright (c) 2007
* Purpose: 数字字符串简易加解密
* ----------------------------------------------------------------------------*/
class Encryption {
    /**
    * The final ciphertext code can be set to any non-repeating 10-digit English characters a-zA-Z
 */
    private $replacement = 'urskydMeIV';
    /**
   * The first bit of the added ciphertext can be set to a 1-digit integer other than 0, that is, 1-9
 */
    private $prefix = "8";
    /**
      * Public key, a positive integer with a length less than 8 digits
    */
    private $match = "111111";
    /**
    * Compare array after conversion
    */
    private $replaceenc;
    private $replacedec;
    function __construct() {
        for($i =0; $i < 10; $i++) {
            $this->replaceenc['/'.$i.'/'] = $this->replacement{$i};
            $this->replacedec['/'.$this->replacement{$i}.'/'] = $i;
        }
    }
    public function encrypt($str) {
        return preg_replace(
            array_keys($this->replaceenc),
            $this->replaceenc,
            $this->mynotin(preg_replace("/(.)(.)/", "${2}${1}", $str))
        );
    }
    public function decrypt($str) {
        return preg_replace("/(.)(.)/", "${2}${1}",
            $this->mynotout(preg_replace(array_keys($this->replacedec),$this->replacedec,$str))
        );
    }
    private function mynotin($str) {
        $str_out = "";
        $i = 0;
        while(isset($str{7*$i})) {
            $str_out .= (($this->prefix.substr($str, $i*7, 7))+0)^$this->match;
            $i++;
        }
        return $str_out;
    }
    private function mynotout($str) {
        $str_out = "";
        $i = 0;
        while(isset($str{8*$i})) {
            $str_out .= substr((substr($str, $i*8, 8)+0)^$this->match, 1);
            $i++;
        }
        return $str_out;
    }
}
?>

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