For example, if each CD or other medium from a particular source (e.g., Microsoft) has a serial number, that serial number may be encrypted (e.g., with a private key of a public key/private key system) and stored in the RFID IC. When the playback device reads the RFID IC, it retrieves this encrypted serial number and decrypts this number (e.g., with the source's public key) to obtain the unencrypt