An apparatus for a television includes storage areas for storing a key and authentication information, a communication unit to transmit and receive information from a server supplying protected content, and a controller to control output of the protected content from the server based on an authentication procedure. This procedure includes encrypting the stored authentication information with the key, transmitting the encrypted authentication information to the server, and then outputting the protected content received from the server for display after transmission of the encrypted authentication information if determined to be valid.