Embodiments of the present invention disclose a network system. The system includes user equipment, a network authentication device, and a service authentication device. The service authentication device is configured to obtain reference information and generate a second shared key with reference to the reference information and a first shared key, where the first shared key is a shared key pre-configured between the user equipment and the service authentication device; the user equipment is configured to obtain the reference information and generate the second shared key with reference to the reference information and the first shared key; the service authentication device is configured to send the second shared key to the network authentication device; and the network authentication device is configured to receive the second shared key, where the second shared key is used by the user equipment and the network authentication device to generate a target shared key.