Recently, a new technique will replace conventional radar systems and be deployed as part of the next generation air transportation systems. Unlike in traditional radar systems where aircraft only respond to interrogations by ground stations. In the ADS-B system, aircraft continuously obtain their positions based on some satellite positioning techniques (e.g., GPS) and periodically broadcast their positions as well as some other information such as the current velocity to ground stations and other aircraft. Recently, flight tracker Web sites based on the mashup of ADS-B data have gained popularity, providing Web users with a visual overview of air-traffic around the world. Each aircraft equipped with an ADS-B device keeps broadcasting plaintext messages to other aircraft and the ground station controllers once or twice per second. The lack of security measures in ADS-B systems makes it susceptible to different attacks. Among the various security issues, we investigate the integrity and authenticity of ADS-B messages. In this project we demonstrate that attacks range from passive attacks (evasdropping) to active attacks(message jamming ,replying of injection) .This prompts the idea to bring RSA algorithm and HMAC to generate signature in which we can overcome and predict the attack and can ensure the integrity of message.