Air gapping

Air gapping is a security measure that involves physically isolating a computer or network to prevent it from connecting directly or wirelessly to other systems that can connect to the Internet. Air gapping is used to protect many types of critical systems, including those that support the stock market, the military, the government and industrial power industries.

To prevent unauthorized data extrusion through electromagnetic or electronic exploits, there must be a specified amount of space between the air-gapped system and outside walls and between its wires and the wires for other technical equipment. In the United States, the U.S. National Security Agency TEMPEST project provides best practices for using air gaps as a security measure.

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 such measures may 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.

As of this writing, the Defense Advanced Research Projects Agency (DARPA) is awarding grants for prototype hardware and software designs that will keep sensitive data physically isolated. The grants are made possible under the Guaranteed Architecture for Physical Security (GAPS) program.

Enhancing air-gapped security measures

The problem with physical separation as a security technique is that, as complexity increases in some system or network to be isolated, so does the likelihood that some unknown or unauthorized external connection will arise.

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.

The software-defined perimeter (SDP) framework is another tool network engineers can use to create a type of "virtual air gapping" through policy enforcement. SDP requires external endpoints that want to access internal infrastructure to comply with authentication policies and ensures that only authenticated systems can see internal IP addresses.