public function decryptData( $encryptedData, $iv, &$data )
{
   if (strlen($this->sessionKey) != 24) {
      return ErrorCode::$IllegalAesKey;
   }
   $aesKey=base64_decode($this->sessionKey);

       
   if (strlen($iv) != 24) {
      return ErrorCode::$IllegalIv;
   }
   $aesIV=base64_decode($iv);

   $aesCipher=base64_decode($encryptedData);

   $result=openssl_decrypt( $aesCipher, "AES-128-CBC", $aesKey, 1, $aesIV);

   $dataObj=json_decode( $result );
   if( $dataObj  == NULL )
   {
      return ErrorCode::$IllegalBuffer;
   }
   if( $dataObj->watermark->appid != $this->appid )
   {
      return ErrorCode::$IllegalBuffer;
   }
   $data = $result;
   return $data;
}