One of the fastest growing industries in America is autonomous vehicle technology. The main motivation is to decrease the number of accidents each year. This leads to the challenge presented in this paper, preventing the spoofing of signals coming into autonomous vehicles. The increased complexity of these vehicles creates more vulnerabilities for attackers to take advantage of. Authentication of vehicular ad hoc networks is one method to help stop the potential hacking of autonomous vehicles. We propose a two-factor authentication for GPS signals by synchronizing with Stratum-1 clocks and digital signatures to prevent man-in-the-middle attacks. The experiment uses a computer to simulate a GPS signal that is sent to a Raspberry Pi 3 along with a timestamp and hashed key using RSA-1024. The Raspberry Pi 3 represents the vehicle. The method presented will prevent GPS spoofing attacks that are using modified or corrupted messages, an impersonation attack, or a roadside unit replication attack.