<?php

// +----------------------------------------------------------------------

// | ThinkPHP [ WE CAN DO IT JUST THINK IT ]

// +----------------------------------------------------------------------

// | Copyright (c) 2006-2015 http://thinkphp.cn All rights reserved.

// +----------------------------------------------------------------------

// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )

// +----------------------------------------------------------------------

// | Author: 麦当苗儿 <zuojiazi.cn@gmail.com> <http://www.zjzit.cn>

// +----------------------------------------------------------------------



namespace Com;



class WechatCrypt{

    /**

     * 加密KEY

     * @var string

     */

    private $cyptKey = '';



    /**

     * 公众平台APPID

     * @var string

     */

    private $appId = '';



    /**

     * 构造方法，初始化加密KEY

     * @param string $key   加密KEY

     * @param string $appid 微信APP_KEY

     */

    public function __construct($key, $appid){

        if($key && $appid){

            $this->appId   = $appid;

            $this->cyptKey = base64_decode($key . '=');

        } else {

            throw new \Exception('缺少参数 APP_ID 和加密KEY!');

        }

    }



    /**

     * 对明文进行加密

     * @param  string $text  需要加密的字符串

     * @return string        密文字符串

     */

    public function encrypt($text){

        //填充到明文之前的随机字符

        $random = self::getRandomStr(16);



        //网络字节序

        $size = pack("N", strlen($text));



        //生成被加密字符串

        $text = $random . $size . $text . $this->appId;



        //打开加密算法模块

        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');



        //使用PKCS7对明文进行补位

        $text = self::PKCS7Encode($text, mcrypt_enc_get_key_size($td));



        //初始化加密算法模块

        mcrypt_generic_init($td, $this->cyptKey, substr($this->cyptKey, 0, 16));



        //执行加密

        $encrypt = mcrypt_generic($td, $text);

        

        //关闭加密算法模块

        mcrypt_generic_deinit($td);

        mcrypt_module_close($td);



        //输出密文

        return base64_encode($encrypt);

    }



    /**

     * 对密文进行解密

     * @param  string $encrypt 密文

     * @return string          明文

     */

    public function decrypt($encrypt){

        //BASE64解码

        $encrypt = base64_decode($encrypt);



        //打开加密算法模块

        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');



        //初始化加密算法模块

        mcrypt_generic_init($td, $this->cyptKey, substr($this->cyptKey, 0, 16));



        //执行解密

        $decrypt = mdecrypt_generic($td, $encrypt);

        

        //去除PKCS7补位

        $decrypt = self::PKCS7Decode($decrypt, mcrypt_enc_get_key_size($td));



        //关闭加密算法模块

        mcrypt_generic_deinit($td);

        mcrypt_module_close($td);



        if(strlen($decrypt) < 16){

            throw new \Exception("非法密文字符串！");

        }



        //去除随机字符串

        $decrypt = substr($decrypt, 16);



        //获取网络字节序

        $size = unpack("N", substr($decrypt, 0, 4));

        $size = $size[1];



        //APP_ID

        $appid = substr($decrypt, $size + 4);



        //验证APP_ID

        if($appid !== $this->appId){

            throw new \Exception("非法APP_ID！");

        }

        

        //明文内容

        $text = substr($decrypt, 4, $size);



        return $text;

    }



    /**

     * PKCS7填充字符

     * @param string  $text 被填充字符

     * @param integer $size Block长度

     */

    private static function PKCS7Encode($text, $size){

        //字符串长度

        $str_size = strlen($text);



        //填充长度

        $pad_size = $size - ($str_size % $size);

        $pad_size = $pad_size ? : $size;

        

        //填充的字符

        $pad_chr = chr($pad_size);



        //执行填充

        $text = str_pad($text, $str_size + $pad_size, $pad_chr, STR_PAD_RIGHT);



        return $text;

    }



    /**

     * 删除PKCS7填充的字符

     * @param string  $text 已填充的字符

     * @param integer $size Block长度

     */

    private static function PKCS7Decode($text, $size){

        //获取补位字符

        $pad_str = ord(substr($text, -1));



        if ($pad_str < 1 || $pad_str > $size) {

            return '';

        } else {

            return substr($text, 0, strlen($text) - $pad_str);

        }

    }



    /**

     * 生成指定长度的字符串

     * @param  integer $len 字符串长度

     * @return string       生成的字符串

     */

    private static function getRandomStr($len){

        static $pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";



        $str = '';

        $max = strlen($pol) - 1;

        for ($i = 0; $i < $len; $i++) {

            $str .= $pol[mt_rand(0, $max)];

        }



        return $str;

    }

}