A playback method using a playback device that plays a system stream file is provided. The playback device includes an individual decryption key that is owned individually by each of playback devices, and a common decryption key that is owned in common by a plurality of playback devices. The system stream file includes a first system stream file configured to be played back using both the individual decryption key and the common decryption key, and a second system stream file configured to be played back using only the common decryption key among the individual decryption key and the common decryption key. The method includes identifying whether the system stream file to be playback is the first system stream file or the second system stream file, in accordance with a file extension of the system stream file, and selecting a decryption process of the system stream file.