Patent ID: 11146550

Abstract:
A system for determining whether spoofing occurs at an activating communication line under the condition that a connection by three-way handshake can be established between activating and activated communication lines regardless of the spoofing. Authentication units are arranged above communication terminal devices respectively. While a three-way handshake is executed once between the communication terminal devices, a three-way handshake is executed twice between the associated communication lines. One communication line activates the other communication line, and when a connection by a first three-way handshake is established between the communication lines, the connection is disconnected. Thereafter, it is determined at the activating communication line whether a SYN(2) is sent from the activated communication line at a predetermined timing, while it is determined at the activated communication line whether a SYN+ACK(2) as a response to the SYN(2) is reached or not from the activating communication line, thereby the communication lines are mutually authenticated.