UBAPV2G: a unique batch authentication protocol for vehicle-to-grid communications. “Vehicle-to-grid” (V2G) power will be a new green energy scheme in which electric or plug-in hybrid vehicles communicate with the smart grid to sell demand response services by either delivering electricity into the grid or by throttling their charging rate. Due to high vehicular speed, sporadic connection, limited communication range, and large volume of data that need to be transmitted, V2G communications have the crucial requirements of fast authentication and encryption/decryption. This paper proposes a unique batch authentication protocol UBAPV2G that takes into account the characteristics of vehicle communication. The performance analysis shows that UBAPV2G can achieve less authentication delay, less computational cost, and less communication traffic, and security analysis shows that UBAPV2G is strong enough to defend against security attacks. The experimental results also demonstrate that UBAPV2G can achieve less authentication delay for large number of packets. Thus, UBAPV2G protocol is suitable for the stringent requirement of real time V2G communications.