Due to their special characteristics, vehicle-based ad hoc networks (VANET) are susceptible to a number of security issues. Particularly when many vehicles are present within the RSU’s coverage area, existing authentication methods struggle to ensure that the roadside unit (RSU) rapidly authenticates each vehicle’s signature. A novel agent-based message verification method is consequently proposed. The proxy vehicle analyses the messages sent by other vehicles and sends the results of its analysis to the neighbouring RSU. The RSU verifies the output results from the proxy vehicle to reduce computational overhead. The proposed method has been shown to satisfy the message authentication security requirements under the discrete logarithm issue for the elliptic curve. Additionally, simulation results show that the suggested authentication method requires 76% less time to validate 3,000 messages than the conventional authentication method and can more effectively meet the VANET’s requirements for message authentication.