of black marked certificates keeping the families of black marks smaller helps keep the detection thresholds lower and therefore enables faster detection under large scale attacks a large number of simultaneous attackers temporal separation may become difficult as subsequent black marked certificates are likely to correspond to different attackers spatial separation may still be feasible this embodiment provides a solution to the u201c one affects many u201d problem by which an attacker affects all other vehicles that share the certificate used during the attack in that all are considered candidate attackers and have to go through a re keying procedure according to this solution a number of geographic areas are defined and the search for an attacker is concentrated in the geographic area where certificate misuse was first detected the search slowly expands in coverage until the attacker is identified assuming that the effect due to a vehicle driving across different areas is negligible in several practical scenarios this method turns the u201c one affects many u201d effect into a u201c one affects none u201d effect the embodiment can be implemented as a refinement to a basic combinatorial scheme the goal of this embodiment is to create a novel technique that solves the following u201c one affects many u201d problem assume that an attacker uses one anonymous key and its associated certificate to send malicious messages upon discovery of malicious activity in these messages this certificate is revoked and added to the certificate revocation list as a consequence since several other vehicles share the same certificate these vehicles are affected in that they are considered candidate attackers and have to go through a re keying procedure by.