Network system interface for controlling confidential information

A network system including a first site and a second site connected to each other via an open network and a closed network, wherein

• the first site includes
• a first computer,
• a second computer,
• a first interface connecting the first computer and the second computer to each other, and
• an encryption/decryption unit connected to the second computer, and
• the second site includes
• a third computer,
• a fourth computer,
• a second interface connecting the third computer and the fourth computer to each other, and
• a decryption/encryption unit connected to the fourth computer,
• the first computer and the third computer belong to the open network,
• the second computer and the fourth computer belong to the closed network,
• the first interface performs control so that format information of first confidential information passes through the first interface but the first confidential information does not pass through the first interface between the first computer and the second computer,
• the second interface performs control so that format information of second confidential information passes through the second interface but the second confidential information does not pass through the second interface between the third computer and the fourth computer,
• the encryption/decryption unit and the decryption/encryption unit are connected to a wide area network, and form a virtually closed network using encryption in the wide area network,
• for the open network, the first site and the second site are connected to each other via the wide area network,
• for the closed network, the first site and the second site are connected to each other via the virtually closed network,
• the encryption/decryption unit and the decryption/encryption unit each include a dedicated circuit through which the first and second confidential information is passed without being passed through either of the first and second interfaces.