We present a chat system based on Windows Communication Foundation (WCF) and Windows Presentation Foundation (WPF) with emphasis on security aspects of WCF. As the name indicates, WCF lays down the foundation for the communication between server and client, while WPF is a graphical user interface system in .NET. Through the chat system, we explore the security measures implemented in X.509, which include the contracts, endpoints and the usage of the service. This is then presented by developing an application which implements the WCF security aspects in a client-server architecture and effectively handles the security. WCF provide a very rich and easy configurable environment to implement security. The client and server will communicate by using xml messages. WCF provides two mechanisms for transfer security which is transport security and message security. We will make use of these security mechanism provided by the WCF in our application. One common use of the WCF is to provide a way to distribute and collect data and information to and from multiple clients at the same time, with no hassle in the user experience on the client side. The four core security features that WCF addresses are Authentication, Authorization, Confidentiality, Integrity and auditing. WCF supports a variety of authentication options including user name, Windows, and certificate authentication which will be studied in detail.