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A team of researchers at the Ben-Gurion University of the Negev have successfully demonstrated that information from an air-gapped computer can be stolen using only a simple cellphone that can connect to a GSM network.

The “gap” in air gap refers to the lack of a physical or wireless connection to the internet which, in theory, should make the computer more secure. In a world where more and more things are built to be connected to the internet, air gap computers are frequently used to keep highly sensitive, valuable information secure from prying eyes.

According to Yuval Elovici, head of the University’s Cyber Security Research Center, the air gap exploit works because of the fundamental way that computers put out low levels of electromagnetic radiation.

Cell phones, Elovici explains, are extremely good at intercepting the kinds of signals that computers emit even when they’re not actually touching the internet. His team’s findings are particularly noteworthy because of the kind of phones that can be used to before the exploit.

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Typically, the kinds of environments that use air-gapped computers make a point of keeping smartphones away from any information that needs to be contained. This particular method of capturing data, however, can be accomplished with the kind of simple feature phone that many people working high-security environments are required to use.

The amount of data that can be captured through the phone hack is small, but it’s enough to give someone the ability to scrape passwords and encryption keys within minutes. The exploit requires that both the computer being attacked and the phone used to do the attacking have GSMem, a customized piece of malware, installed and running, meaning that the hack isn’t exactly easy to pull off.

In its paper describing the mechanics of breaking the air gap, the research team is careful to point out that other applications of this exploit are possible and potentially more threatening. By using a more powerful data receiver a person could, the team found, intercept larger amounts of data from an air-gapped computer without needing to be physically close to it.

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"When using a dedicated, yet affordable hardware receiver, the effective distance reached over 30 meters," the paper explains.