Vehicle navigation system with a protected storage medium

A navigation or multimedia system is provided in which it is checked whether a user is authorized to use files, such as road map data. For this purpose, the navigation system has means for checking authorized use of files on the mass storage medium on which the files are stored. The files are stored in particular in encrypted form. According to a method according to the invention for unlocking usage rights to a file, it is provided that the user initially inputs a first and a second encrypted code (PIN or ACW) into the navigation system. These codes are converted into vectors. With the device identifier ID of the navigation system and the first encrypted code PIN, a key k is first calculated. With the key k and the second encrypted code ACW, an access authorization identifier AC is calculated, which is compared with the access authorization identifiers of the files stored on the storage medium. If these identifiers match, the associated file is decrypted and released for use by the navigation system.