Vehicle-mounted device for automatic charge receipt system

Abstract

A vehicle-mounted device for an automatic charge receipt system capable of being designed, manufactured and installed while an encrypting/decrypting algorithm and/or encrypting/decrypting keys remain hidden. Included is an arrangement for discrimination (i.e., identification) of a vehicle-mounted device or user each time a utilization charge is determined/settled, wherein an initial portion of communications concerning discrimination is conducted without encrypting/decrypting, and remaining portions of communications are conducted with encrypting/decrypting so as to protect an integrity and security of the automatic charge receipt system. Confindential components/information, e.g., the encrypting/decrypting algorithm and/or keys, and components directly handling such information are arranged within a tamper-/access-resistant unit (preferably as a sealed integrated circuit package) in the vehicle-mounted device. Since an encryptor and a decryptor directly read the encrypting/decrypting key without such key being detectable outside of the sealed unit, it is not necessary for components outside the sealed unit to receive and/or handle the aforesaid encrypting/decrypting key or their contents. Accordingly such key remains hidden (i.e., inaccessable) within the sealed unit. The arrangement can further include an authentication protocol such as a 3-way authentication protocol, a 2-way.times.2 authentication protocol and a Fiat-Shimir authentication protocol.