Wireless networking researchers have proposed a way to jam wireless signals without power.
In a paper distributed through ArXiv, a group of boffins from universities in Australia, China, Singapore, and South Korea describe a technique that uses intelligent reflecting surface (IRS) technology, an emerging wireless signal optimization scheme, to interfere with signals instead of enhancing them.
IRS is related to software-defined radio, using software to control how materials redirect radio-frequency (RF) signals. Just as acoustical engineering is used to improve sound reflections in movie theaters and concert halls, IRS aims to improve RF signal behavior in various environments, but via software-controlled surfaces rather than fixed architectural elements.
An IRS-enabled element like a wall would include a controller that communicates with tunable chips that can programmatically alter the signal-scattering characteristics of the surface to target signals. It differs from amplify-and-forward signal relay because it relies on passive techniques to control beam steering, without a power component and active circuits that handle re-transmission.
Turning the good into bad
The attack described can jam a wireless communications system by changing how signals reflect and can do so without leaving an energy footprint, the researchers explain, making it difficult to detect and prevent.
"The reason is that in our proposed scheme, the magnitudes of reflectioncoefficients and phase shifts of all passive reflecting elements can be carefully designed such that the total received signals at the legitimate receiver from the direct and reflecting links can be added destructively, which can significantly reduce the received power and thus diminish the SINR at the LR," the radio boffins state.
In simulated results, they show that their proposed IRS-based jammer can reduce signal power by up to 99 per cent, and in some scenarios outperforms conventional active signal jamming.
Don't panic, yet
In an email to The Register, Sergi Abadal, director of research for N3Cat at VISORSURF and a postdoctoral researcher at Universitat Politècnica de Catalunya (UPC), said, "Research in IRS has been exploding lately, with lots of proposals. Most of them are theoretical and simulation-based, with a few experimental prototypes as notable exceptions."
Having looked briefly at the paper, he stressed that it's theoretical and the results need to be taken with caution until there's experimental validation. But he allowed that the technique described seems plausible.
"Many works have proposed using IRS to help with wireless communications (increasing coverage, signal strength, reducing interference, and so on)," said Abadal. "In general, the way of increasing the signal strength is to make all the reflections to reach the receiver in a way that can be 'coherently combined' (their phases are aligned and their power adds up)."
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"Therefore, theoretically, nothing prevents you from using similar techniques to make the reflections reach the receiver in a way that are 'destructively combined' (their phases are opposite and they interfere with each other)," he explained.
To interfere with signals in this manner, Abadal said you'd need to know the position of the transmitter and the intended receiver, which could be obtained by interacting with an access point or base station – which might be difficult if done illegitimately – or by inferring the positions from signals captured in the environment.
This technique, if developed into something more than a theoretical attack, should be applicable against current wireless systems.
"If the conditions are right – the IRS exists and is capable of inferring the position of the transmitter and of the receiver it wants to jam – then it could be possible in current wireless systems," Abadal said.
The paper, IRS-based Wireless Jamming Attacks: When Jammers can Attack without Power, is co-authored by Bin Lyu, Dinh Thai Hoang, Shimin Gong, Dusit Niyato, and Dong In Kim. ®