In this article, we propose an efficient lattice-based ring signature scheme for message authentication in vehicular ad-hoc networks (VANETs). It provides unconditional identity privacy preservation, message authentication, and location privacy for the sender vehicle. The authentication of messages is extremely vital as it gives motivation for vehicles to accept, act, and further transmit messages to other vehicles in the network as well as remain a member of the network. Any unauthorized vehicle cannot transmit fraud messages into the network if messages are authenticated. The public key cryptography-based methods are more relevant for message authentication because of their easy key management and local derivation of keys. However, they add complexity to the whole network and require significant storage and computational power. Also, the predictable mobility characteristics of vehicles moving on the road make them vulnerable to tracking. This requires an additional mechanism to preserve location privacy. The proposed scheme provides unconditional identity privacy and location privacy. It is more efficient than the existing ring signature schemes in case of signature generation and verification process. Theoretical analysis and experimental results show that the proposed scheme provides security and unconditional privacy to vehicles in VANETs.