length_after_encode

# File activesupport/lib/active_support/message_encryptor.rb, line 320
      def length_after_encode(length_before_encode)
        if @url_safe
          (4 * length_before_encode / 3.0).ceil # length without padding
        else
          4 * (length_before_encode / 3.0).ceil # length with padding
        end
      end