A Simple Printed and Laminated Metasurface, Costing Cents, Opens 6G Comms to Eavesdropping Attacks

A team of researchers at Rice University and Brown University has found a way to eavesdrop on 6G wireless signals even before the technology is broadly deployed — by building a tunable metasurface in five minutes for well under a dollar using just standard paper, a cheap printer, a foil transfer sheet, and a laminator.

"Awareness of a future threat is the first step to counter that threat," says co-author Edward Knightly, the Sheafor-Lindsay Professor of Electrical and Computer Engineering at Rice, of the team's decision to focus on next-generation 6G technologies. "The frequencies that are vulnerable to this attack aren’t in use yet, but they are coming and we need to be prepared."

The attack, dubbed "Metasurface-in-the-Middle," works by redirecting a portion of a focused 150GHz transmission beam using a customized metasurface built for just cents in materials. "Next-generation wireless will use high frequencies and pencil beams to support wide-band applications like virtual reality and autonomous vehicles," explains Knightly of the legitimacy of the team's focus on tight-beam transmissions.

"[These] openings and orientations are very specifically done to get the signal to diffract in the exact direction Eve wants,” first author Zhambyl Shaikhanov explains of the metasurface's mesh-like design, referring to the cryptography world's usual name for an attacker attempting to eavesdrop on a communication between subjects Alice and Bob.

“After she designs the metasurface, she prints it on a regular laser printer, and then she uses a hot stamping technique that's used in crafting. She places a metal foil on the printed paper, feeds it through a laminator and the heat and pressure create a bond between the metal and the toner."

That metasurface can then be placed between Alice and Bob to redirect enough of the signal for eavesdropping to take place — and in a much more subtle way than standing between the two in-person with a bunch of radio equipment. The redirection can even take place through other surfaces, allowing the metasurface to be hidden inside a thin book or a stack of papers.

"People have been quoted saying millimeter-wave [mmWave] frequencies are 'covert' and 'highly confidential' and that they 'provide security,'" Shaikhanov warns. "The thinking is, 'If you have a super narrow beam, nobody can eavesdrop on the signal because they would have to physically get between the transmitter and the receiver.' What we’ve shown is that Eve doesn’t have to be obtrusive to mount this attack."

The team's work is to be presented at the Association for Computing Machinery's WiSec 2022 conference, and has been published in the proceedings under open-access terms.