Air gapping is a security measure that involves isolating a computer or network and preventing it from establishing an external connection. For example, an air gapped computer is one that is physically segregated and incapable of connecting wirelessly or physically with other computers or network devices.
Air-gapped networks are used to protect many types of critical systems, including those that support the stock market, the military, the government and industrial power industries. The U.S. National Security Agency TEMPEST project provides recommendations for using air gapping as a security measure. To prevent unauthorized data extrusion through electromagnetic or electronic exploits, there is often a specified amount of space between the air gapped system and outside walls and between its wires and the wires for other technical equipment. For a system with extremely sensitive data, a Faraday cage can be used to prevent electromagnetic radiation (EMR) escaping from the air-gapped equipment.
Although these measures seem extreme, van Eck phreaking can be used to intercept data such as key strokes or screen images from demodulated EMR waves, using special equipment from some distance away. Other proof-of-concept (POC) attacks for air gapped systems have shown that electromagnetic emanations from infected sound cards on isolated computers can be exploited and continuous wave irradiation can be used to reflect and gather information from isolated screens, keyboards and other computer components.
Perhaps the most important way to protect a computing device or network from an air gap attack is through end user security awareness training. The infamous Stuxnet worm, which was designed to attack air gapped industrial control systems, is thought to have been introduced by infected thumb drives found by employees or obtained as free giveaways.
Editor's note: The software-defined perimeter (SDP) framework is sometimes referred to as a method of virtual air gapping. SDP requires authentication of all external endpoints attempting to access internal infrastructure and ensures that only authenticated systems can see internal IP addresses.