In recent years extensive research is going on for the development of applications which convert physical devices into smart devices. Industry 4.0 adopt the technologies under Cyber Physical Systems (CPS) for the development of such types of smart devices. Increase in the use of such type of smart devices without any security mechanism causes an open invitation for cyber attackers to perform cyber-attacks on such devices. Even current security algorithms are not efficiently work due to some constraints of smart devices. The goal of this research paper is to provide effective solution against different cyber-attacks on CPS applications. This paper proposed session key-based security mechanism which is used for the prevention of cyber-attacks and authentication of cyber devices.