Air Gap

Noun · Verb · Security & Infosec

Definitions

  1. Air Gap is a security measure where a computer or network is physically isolated from unsecured networks, including the internet, to prevent unauthorized access or data exfiltration. Air-gapped systems have no wired or wireless connections to external networks, making remote cyberattacks extremely difficult. They are used to protect the most sensitive environments: military command systems, nuclear facility controls, classified government networks, financial transaction processing, and critical infrastructure like power grids. Despite their strong isolation, air-gapped systems are not impervious. Notable attacks like Stuxnet demonstrated that malware can bridge air gaps through infected USB drives. Other exotic attack vectors include acoustic signals, electromagnetic emissions, heat variations, and even blinking hard drive LEDs. Maintaining a true air gap requires strict physical security, controlled media transfer protocols, and constant vigilance against social engineering.

    In plain English: Keeping a computer completely disconnected from the internet and all other networks — the ultimate 'unplug it' security strategy.

  2. As a verb, to air-gap a system means to deliberately isolate it from all network connections. Also used metaphorically for any strict separation between systems or teams that should not share data.

    Example: 'We air-gapped the payment processing environment from the general corporate network after the audit findings.'

    Source: verb form

Etymology

1970s
Military and intelligence agencies develop physically isolated networks for classified data, calling the separation an 'air gap'
2010
Stuxnet demonstrates that even air-gapped systems can be compromised — the worm jumped via infected USB drives to Iranian centrifuges
2013
Edward Snowden revelations show NSA techniques for bridging air gaps using radio signals and acoustic channels

Origin Story

The Gap That Keeps Secrets Safe

An air gap is a security measure that physically isolates a computer or network from unsecured networks, including the internet. The term borrows from electrical engineering, where an air gap is a literal space of air between two conductors that prevents current from flowing between them. In computing, air-gapped systems have no wired or wireless connections to external networks. The concept dates back to the earliest days of classified computing. Military and intelligence agencies have used physical isolation to protect sensitive systems since the Cold War era. The U.S. Department of Defense's classified networks (SIPRNet and JWICS) are air-gapped from the public internet. The importance of air gaps gained public attention through several dramatic breaches. The Stuxnet worm, discovered in 2010, was specifically designed to cross air gaps via USB drives to sabotage Iranian nuclear centrifuges. This demonstrated that even physically isolated systems are not invulnerable. Researchers have since demonstrated exotic attacks that can exfiltrate data from air-gapped machines using electromagnetic emissions, acoustic signals from CPU fans, blinking LEDs, and even heat fluctuations between adjacent computers. Despite these theoretical vulnerabilities, air gaps remain a cornerstone of security for nuclear facilities, financial trading systems, and classified military networks.

Context: Military/intelligence computing, Cold War era

Fun fact: Researchers at Ben-Gurion University have demonstrated over a dozen methods to breach air gaps, including one called 'AirHopper' that uses a computer's monitor cable as a makeshift FM radio transmitter to send data to a nearby phone.

Related Terms