Patent ID: 7577251

Claim:
A data player for reading contents encrypted by a contents key and the contents key encrypted by a decoding key, from a digital medium, and playing the encrypted contents by using the decoding key which is stored in a key storage unit, said data player comprising: key obtaining means for performing mutual authentication with the key storage unit to obtain the decoding key stored in the key storage unit; key holding means for holding the decoding key; playback state obtaining means for monitoring the playback state of the digital medium; encrypted contents key decoding means for decoding the encrypted contents key by using the decoding key to obtain the contents key; and encrypted contents decoding means for decoding the encrypted contents by using the contents key; wherein the decoding key is obtained by the key obtaining means and stored in the key holding unit, the encrypted contents key read from the digital medium is decoded with the decoding key by the contents key decoding means to obtain the contents key, the encrypted contents read from the digital medium is decoded by using the contents key to play the contents, and the decoding key stored in the key holding means is discarded according to the playback state of the digital media which is obtained by the playback state obtaining means.