Abstract: A more secure TCP/IP protocol stack is provided having an enhanced transport layer. Encryption and decryption logic is arranged on the transmission side and on the reception side for processing a payload of a transport layer protocol, such as TCP or UDP. By employing this enhanced transport layer, a cryptograph process communication can be realized by dissolving various kinds of restrictions which a conventional IPsec or SSL possesses without affecting upper layer processing, and, at the same time, maintaining compatibility with the IP layer.