Patent ID: 8583912
Filing Date: 2013-11-12
Classification: H04L

Abstract:
1. A client terminal comprising: a cipher session establishing section configured to establish a cipher session use connection between said client terminal as a source client terminal and a relay server by transmitting/receiving a cipher session establishment message between said source client terminal and said relay server, and to notify header information contained in a cipher session header to said relay server; a shared key managing section configured to hold a client shared key with a destination client terminal; a data enciphering section configured to perform an encipherment of a data from an application by using said client shared key, and a Message Authentication Code (MAC) calculation of said data, by using said client shared key and to output the performing result as an encrypted client cipher data and at least partially encrypted cipher session header; a message producing section configured to insert said encrypted client cipher data into a cipher data field and the at least partially encrypted cipher session header into the non-cipher data field to produce a data communication message including the cipher data field in which said client cipher data is inserted and the non-cipher data field in which said at least partially encrypted cipher session header containing said header information is inserted, wherein said message producing section produces the data communication message with a terminal ID of the destination client terminal, the terminal ID being in a format readable by said relay server without decoding the encrypted cipher data field of the data communication message; and a transmitting section configured to transmit said data communication message destined to said destination client terminal to said relay server by using said cipher session use connection, wherein the client terminal is connected to the relay server via a firewall, the firewall being set to allow two-directional communication using the cipher session established with the relay server for the source client terminal to transmit and the destination client terminal to receive the data by the relayed data communication message, the firewall monitoring the cipher session establishment message to confirm a completion of transmitting/receiving the cipher session establishment message, whether the data communication message is transmitted/received between the terminals on established cipher session connections, and whether the data communication message follows a defined format in order to determine whether to block the data communication message.