<p>A key memory medium stores a medium identifier, a medium inherent key based on the medium identifier, an encrypted user key of a user key based on the medium inherent key, and an encrypted contents key of a contents key based on the user key. A contents memory medium stores an encrypted contents software of the contents software based on the contents key. A start-up software of the contents software is executed. The medium inherent key is generated using the medium identifier. The user key is derived from the encrypted user key using the medium inherent key. The contents key is derived from the encrypted contents key using the user key. The contents software is derived from the encrypted contents using the contents key.</p>
