As the number of recorded transactions in today’s automotive world runs second only to point of sale transactions in the food industry, full automation of the process of funds exchange between a vehicle and its surroundings is an inevitable development. Possible applications are in fueling, parking, use of toll roads, etc. Public key cryptography techniques offer scientifically recognized solutions to the unique, practical problems associated with transaction authentication procedures using the open communication channel between a vehicle and an unprotected ground terminal, with an unprecedented degree of security and convenient implementation. No valuable secrets embedded in costly security modules are kept at the terminals. Playback of recorded taped communications or attempts at rehashing messages would be useless, and will not assist illicit falsification or forging of subsequent transactions. To prevent the unauthorized use of the crediting facility of a vehicle, an integral part of this facility is to be carried by the driver when the vehicle is not in operation. This can be integrated into existing electronic ignition keys. A public key cryptographic module installed in a vehicle can also be used for theft prevention by enhancing both ignition security and remote controlled door locking/unlocking mechanisms. The same device can be used for authenticating smartcard-based prepayment systems for parking or toll-road usage. This methodology could become standard on production models.