Security is a big concern for data networks users. Data encryption considered to be one of the best solutions for security issues. There are some standard encryption algorithms that used to encrypt transferred data using encryption keys. DES, 3DES, and AES are common encryption algorithms used in TCP/IP networks. Virtual Private Networking (VPN) is the one of the best security mechanisms that used encrypted virtual tunnels .In this paper the effect of encryption delay on TCP based applications is discussed. Simulation is a major part of this paper.