Insider Threat - Web services are growing demand with fundamental advancements and have given more space to researchers for improving security of all real world applications. Accessing and get authenticated in many applications on web services, user discloses their password and other privacy data to the server for authentication purposes. These shared information should be maintained by the server with high security, otherwise it can be used for illegal purposes for any authentication breach. Protecting the applications from various attacks is more important. Comparing the security threats, insider attacks are most challenging to identify due to the fact that they use the authentication of legitimate users and their privileges to access the application and may cause serious threat to the application. Insider attacks has been studied in previous researchers with different security measures, however there is no much strong work proposed. Various security protocols were proposed for defending insider attackers. The proposed work focused on insider attack protection through Elgamal cryptography technique. The proposed work is much effective on insider attacks and also defends against various attacks. The proposed protocol is better than existing works. The key computation cost and communication cost is relatively low in this proposed work. The proposed work authenticates the application by parallel process of two way authentication mechanism through Elgamal algorithm.