In a digital content protection system for legally transmitting encrypted digital content from a transmitting device to a receiving device, unique device identifiers for devices are registered to a specific server in advance. The server also stores in advance information relating to an authentication method usable by each device, associating the information relating to an authentication method with the unique device identifiers. The transmitting device determines whether an identifier unique to the second device is stored on the server. When stored, the transmitting device determines that the receiving device is legal and determines from the server the appropriate authentication procedure. When the transmitting device has the determined procedure, the transmitting device uses this procedure to verify the authenticity of the receiving device. When the transmitting device does not have the determined procedure, the transmitting device acquires the authentication procedure from a source external to the transmitting device and then uses the acquired procedure to validate the receiving device.