Vehicular ad hoc networks (VANETs) provide opportunities to exchange traffic information among vehicles allowing drivers to not only adjust their routes but also prevent possible collisions. Due to the criticality of exchanged information, message authentication which will not expose the privacy of vehicles is required. The majority of current authentication schemes for VANETs depend primarily on public-key cryptography which brings extra overhead in terms of delay and requires infrastructure support for certificate verification. Symmetric-key based techniques can be more efficient, but they introduce significant key maintenance overheads. Herein, by considering the natural group behavior of vehicle communications, we propose an efficient and lightweight symmetric-key based authentication scheme for VANETs based on group communication. Expanding the protocol's flexibility, we also propose an extension which integrates certain benefits of asymmetric-key techniques. We analyze the security properties of our proposed schemes to show there applicability when there is little to no infrastructure support. In addition, the proposed protocol was implemented and tested with real-world vehicle data. Simulation results confirmed the efficiency in terms of delay with respect to other proposed techniques.