Automatic Dependent Surveillance-Broadcast (ADS-B) is a widely used secondary surveillance radar standard for aviation and is a significant component in ensuring air traffic safety. Unfortunately, it has been demonstrated that ADS-B has security flaws. This paper addresses some of these issues by proposing a method and system architecture for verification of received signal authenticity on ADS-B In enabled aircraft. The method is based on physical layer signal analysis, i.e. estimation of signal source range and direction-of-arrival. Proposed system architecture includes a directional slotted antenna system and multi-channel receiver on ADS-B In side, but requires no change to existing ADS-B protocol. The proposed techniques provide security against message injection attacks, such as spoofing, and partial security against jamming. We assess estimation of error bounds and performance of the proposed techniques in simulated use-case scenarios.