php5数字型字符串加解密代码

<?php
/* ----------------------------------------------------------------------------

• 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 {
/**

• 最终的密文代码，可设为任意不重复的10位英文字符a-zA-Z
  */
  private $replacement = 'urskydMeIV';

/**   
 * 增加的密文第一位，可设为1位除0以外的整数，即 1-9   
 */   
private $prefix = "8";   

/**   
 * 公钥,长度小于8位的正整数   
 */   
private $match = "111111";   

/**   
 * 转换后对照数组   
 */   
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;   
}   

}
?>