<?php
// +----------------------------------------------------------------------
// | TOPThink [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2011 http://topthink.com All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: liu21st <liu21st@gmail.com>
// +----------------------------------------------------------------------
// $Id$
namespace Think;
class Crypt {

    /**
     * 加密字符串
     * @access static
     * @param string $str 字符串
     * @param string $key 加密key
     * @return string
     */
    static public function encrypt($data,$key,$expire=0){
        $key    =   md5($key);
        $data   =   base64_encode($data);
        $x=0;
        $len = strlen($data);
        $l = strlen($key);
        $char =  '';
        for ($i=0;$i< $len;$i++) {
            if ($x== $l) $x=0;
            $char   .=substr($key,$x,1);
            $x++;
        }
        $str    =   sprintf('%010d', $expire ? $expire + time():0);
        for ($i=0;$i< $len;$i++) {
            $str    .=chr(ord(substr($data,$i,1))+(ord(substr($char,$i,1)))%256);
        }
        return str_replace('=', '',base64_encode($str));
    }

    /**
     * 解密字符串
     * @access static
     * @param string $str 字符串
     * @param string $key 加密key
     * @return string
     */
    static public function decrypt($data,$key){
        $key    =   md5($key);
        $x=0;
        $data   =   base64_decode($data);
        $expire =   substr($data,0,10);
        $data   =   substr($data,10);
        if($expire>0 && $expire<time()) {
            return '';
        }
        $len = strlen($data);
        $l = strlen($key);    
        $char =     $str = '';
        for ($i=0;$i< $len;$i++) {
            if ($x== $l) $x=0;
            $char   .=substr($key,$x,1);
            $x++;
        }
        for ($i=0;$i< $len;$i++) {
            if (ord(substr($data,$i,1))<ord(substr($char,$i,1))) {
                $str    .=chr((ord(substr($data,$i,1))+256)-ord(substr($char,$i,1)));
            }else{
                $str    .=chr(ord(substr($data,$i,1))-ord(substr($char,$i,1)));
            }
        }
        return base64_decode($str);
    }
}