Patent ID: 7120251

Claim:
A data player for reading contents 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; and contents decoding means for decoding the encrypted contents by using the decoding key; wherein the decoding key is obtained by the key obtaining means and stored in the key holding means, wherein the encrypted contents read from the digital medium is decoded with the decoding key by the contents decoding means to play the contents, wherein the playback state obtaining means obtains the playback state of the digital medium, and wherein the decoding key stored in the key holding means is discarded when it is confirmed that the playback state of the digital medium has changed.