A navigation unit having a data decryption algorithm is connected to a data storage and reading unit having a storage medium storing map data, the data storage and reading unit having a nonalterable access number, and the navigation unit connects to a broadcast radio receiver. The navigation unit receives, through the broadcast radio receiver, broadcast radio signals having encrypted information. The navigation unit reads the nonalterable access number, processes the number through a hash algorithm, and compares the processed access number to another access number to decrypt the encrypted information.