A stealthy way to gain access to a phone or tablet uses electromagnetic signals to swipe and tap on a touchscreen left on a table. Devices capable of carrying out such an attack could be used to force someone鈥檚 device to download malware or to send money to the attacker.
Two different research groups independently came up with similar approaches to achieve the attack. Both rely on placing a single device that contains an antenna for sending signals and a phone locator on the underside of a table. Once a touchscreen device, such as a phone or tablet, is placed on the table, the phone locator infers its position and orientation. The antenna then transmits electromagnetic signals that mimic the electric field disturbances caused by physical human touch.
One version, called Invisible Finger, was created by at the University of Florida and colleagues. It convinced both iOS and Android devices to recognise the electromagnetic touches, although the placement of those touches was more accurate on iOS devices than on Android devices. The team presented the at security conference Black Hat in Las Vegas in August.
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at Zhejiang University in China and colleagues called their version GhostTouch. It worked with multiple Android devices but failed on certain OPPO phone models and the iPhone 7 Plus. The researchers presented their at the USENIX Security Symposium in Boston, Massachusetts, in August.
In both cases, the attackers would need to do some sneaky shoulder surfing or social engineering to obtain the password to unlock the device. Once in, they could use the electromagnetic signals to access messaging apps, download malware and even authorise a request for money through a payment app. If they knew the device鈥檚 phone number but not the password, they would still be able to call it and surreptitiously answer the call to start eavesdropping.
One significant barrier for carrying out the attack in both approaches is that the strength of the electromagnetic signal requires the target device to be very close to the antenna 鈥� within 20 millimetres for Invisible Finger and 40 millimetres for GhostTouch. The target device must also be lying face down.
This means that such an attack is unlikely to be used for simply scamming someone, but could be used by a well-resourced espionage operation. 鈥淲e believe regular users do not need to worry too much about this type of attack,鈥� says Shan. 鈥淲e would be more worried about activists, journalists or other high-value targets.鈥�
