The widespread use of tolling requires provisions for users of vehicles roaming through many different toll domains. For autonomous toll systems one party (the toll service provider) provides the metering for the other parties, the toll domain's toll chargers. The toll service provider uses onboard equipment (OBE) installed in the vehicle to calculate the toll and draws up the toll declarations for toll chargers. In practice such a scheme will work only if the toll charger can check the trustworthiness of the declaration while on the other hand the privacy of the user should be respected as well.
The secure monitoring concept described in this paper provides this trust and privacy. OBE data can be checked on the spot and for toll declarations it can be checked whether the declaration account corresponds with unobtrusive observations of the vehicle in the toll domain. The concept is based on well known cryptographic techniques. For the OBE this requires the use of a trusted element (e.g. smart card) but does not impose any further security requirements on the onboard equipment. Therefore, secure monitoring may lead also to less expensive onboard equipment.