Abstract: The invention provides a vehicle security device with an electronic use-authorization coding arrangement for preventing unauthorized access to the vehicle. The vehicle security device utilizes digital signature algorithm for encrypting and transmitting authorization and synchronization information, so that the storage of secret information is essential only at the key unit in order to transmit authorization and/or synchronizing information from the key unit to the vehicle unit in a way which is very effectively protected against falsification. Thus, reading out vehicle unit information does not permit unauthorized manufacture of a copied key.

Abstract: The invention provides a vehicle security device utilizing a rapid encryption method which operates on the basis of a "one-way function" and which requires storage in the vehicle of at most one item of secret coded information in a single piece of equipment, out of any desired number of pieces of equipment involved in vehicle security. In all such pieces of equipment only the one-way function values corresponding to inverse images stored in a key unit need to be present, the reading out of the said one-way function values making unauthorized manufacture of a copied key impossible. Security against interception and storage of information transmitted at the key end in order to produce copied keys is ensured by including an item of random information, transmitted at the vehicle end, in this authentication information.

Abstract: The invention provides a vehicle security device with an electronic use-authorization coding arrangement for identifying authorized access to the vehicle. The vehicle security device utilizes an encryption method which operates on the basis of a one-way function, so that it is only absolutely necessary to store secret code information at the key end, specifically in the form of different inverse images of a one-way function. Only the one-way function values corresponding to these inverse images need be present at the vehicle end, a reading-out of which does not permit unauthorized manufacture of a copied key because of the virtual irreversibility of the one-way function.