Patent ID: 8819418

Claim:
A communication system comprising: a certificate authority configured to perform authentication; a roadside device configured to be provided at a roadside; a plurality of vehicle-mounted terminals each having a certificate; a first server configured to collect position information about the vehicle-mounted terminals; and a second server configured to manage information about the roadside device and vehicle-mounted terminals whose certificate is invalidated, wherein the communication system is configured to transmit and receive information between the roadside device and the vehicle-mounted terminals and between the vehicle-mounted terminals, wherein the vehicle-mounted terminals are each configured to transmit its own position information to the first server, wherein the certificate authority is configured to: acquire appearance information about vehicle-mounted terminals whose likelihood of appearing is greater than a predetermined threshold, the certificate authority acquires the appearance information according to place and time from the first server; allow the second server to verify the validity of a certificate of a vehicle-mounted terminal that is acquired from the first server; generate a first list of vehicle-mounted terminals having valid certificates and a second list of vehicle-mounted terminals having invalid certificates according to place and time based on a verification result; and transmit the first list and the second list to the roadside device and the vehicle-mounted terminals; and wherein the roadside device and the vehicle-mounted terminals are configured to verify a certificate using the received first and second lists.