A system and method for assigning certificates and reducing the size of the certificate revocation lists in a PKI based architecture for a vehicle wireless communications system that includes separating a country, or other area, into geographic regions and assigning region-specific certificates to the vehicles. Therefore, a vehicle need only process certificates and certificate revocation lists for the particular region that it is traveling in. Vehicles can be assigned multiple certificates corresponding to more than one region in the vehicles vicinity as advance preparation for possible travel or transmission into nearby regions. Further, the expiration time of certificates assigned to vehicles corresponding to a given geographic region can be tailored to be inversely proportional to the distance from a registered home region of the vehicle. A scalable design for a back-end certifying authority with region-based certificates can also be provided.