Vehicle security device with electronic use authorization coding

Vehicle security device having an electronic use-authorization coding arrangement comprising:

• a user-end key unit for receiving an item of random information, and for subsequently transmitting an item of user code information which is dependent thereon;
• a vehicle-end apparatus for transmitting said item of random information, for subsequently receiving a transmitted item of user code information, and for determining an item of actual authorization information which is dependent on the item of user code information;
• and
• means for comparing said item of actual authorization information with an item of desired authorization information present at the vehicle unit, and for generating an item of use-enabling information based on a result of said comparing, wherein:
• successively transmitted items of user code information contain changing inverse images calculated by means of a one-way function, which inverse images are logic linked in coded form to the item of random information;
• the vehicle end apparatus includes means for extracting inverse image information from an item of received user code information;
• the desired authorization information is in each case a one-way function value of the inverse image contained in an associated item of user code information;
• and
• determination of the actual authorization information from the received user code information includes the formation of a one-way function value of the inverse image contained in the received user code information.