PHP5 numeric string encryption and decryption code_PHP tutorial

/* ----------------------------------------------------------------------------
* 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 less than 8 digits in length
*/
    private $match = "111111";

    /**
* Compare the 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;
    }
}
?>