thinkphp微信开发（消息加密解密）php7出错解决办法

原来程序一直使用thinkphp官方的WeChat包，在使用php5.6时，消息发送正常，升级成php7.2后，发送不了消息。一番排查发现php7.2不在支持 MCrypt 加解密，PHP手册在7.1迁移页面给出了替代方案,就是用OpenSSL取代MCrypt。

只需用以下代码替换原WechatCrypt.class.php 文件响应 方法即可，前提是服务器要开通openssl模块

 /**
     * 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){
    	try {
    		//获得16位随机字符串，填充到明文之前
    		$random = self::getRandomStr(16);
    		$text = $random . pack("N", strlen($text)) . $text . $this->appId;
    		$iv = substr($this->cyptKey, 0, 16);
    		$text = self::PKCS7Encode($text, 32);
    		$encrypted = openssl_encrypt($text, 'AES-256-CBC', substr($this->cyptKey, 0, 32), OPENSSL_ZERO_PADDING, $iv);
    		return $encrypted;
    	} catch (Exception $e) {
    		throw new \Exception("aes 加密失败");
    	}
    }

    /**
     * 对密文进行解密
     * @param  string $encrypt 密文
     * @return string          明文
     */
    public function decrypt($encrypt){
    	try {
    		$iv = substr($this->cyptKey, 0, 16);
    		$decrypt = openssl_decrypt($encrypt, 'AES-256-CBC', substr($this->cyptKey, 0, 32), OPENSSL_ZERO_PADDING, $iv);
    	} catch (Exception $e) {
    		 throw new \Exception("解密失败");
    	}
    	
    	$decrypt = self::PKCS7Decode($decrypt, 32);
    	if (strlen($decrypt) < 16) {
    		throw new \Exception("非法密文字符串！");
    	}
    	$content = substr($decrypt, 16, strlen($decrypt));
    	$len_list = unpack("N", substr($content, 0, 4));
    	$xml_len = $len_list[1];
    	$xml_content = substr($content, 4, $xml_len);
    	$from_appid = substr($content, $xml_len + 4);
    	//验证APP_ID
    	if($from_appid !== $this->appId){
    		throw new \Exception("非法APP_ID！");
    	}
    	return $xml_content;
    }