An authentication apparatus for a non-real-time IPTV system decrypts a first encrypted value included in a contents request message received from a device using a preset session key, and then verifies the validity of the contents request message. If the verification results of the contents request message are valid, the authentication apparatus encrypts a variation between timestamps of the authentication apparatus and the device using the session key, and then generates a second encrypted value. After verification information by which the device is capable of verifying the authentication apparatus has been generated using the second encrypted value, the authentication apparatus sends verification information, together with contents corresponding to the contents request message, to the device.