A system performs mutual authentication between a controller and a first device, creates a group key, shares the group key, and sets the first device as a reference device. The system performs mutual authentication between the controller and a second device, and shares the group key with the second device. Thereafter, the system, performs mutual authentication between the controller and the first device, updates the group key, and shares the updated group key between the controller and the first device. At a group key update timing when the group key is updated, the system performs mutual authentication between the controller and the second device, and shares the updated group key with the second device.