我如何用更长的密码来加密该字符串？

Question

我必须用更长的密码来加密一个字符串。我不确定该怎么做。

@IBAction func btnAdd(_ sender: Any) {
    let alertController = UIAlertController(title: "Add Category", message: "", preferredStyle: .alert)

    let saveAction = UIAlertAction(title: "Add", style: .default, handler: { alert -> Void in
        let firstTextField = alertController.textFields![0] as UITextField
        self.categories.add(firstTextField.text!)
        self.tblCatetgory.reloadData()
    })
    let cancelAction = UIAlertAction(title: "Cancel", style: .default, handler: {
        (action : UIAlertAction!) -> Void in })
    alertController.addTextField { (textField : UITextField!) -> Void in
        textField.placeholder = "Enter Category!!!"
    }

    alertController.addAction(saveAction)
    alertController.addAction(cancelAction)

    self.present(alertController, animated: true, completion: nil)
}