New chip masks unencrypted wireless messages


image: Princeton researchers have developed a method to thwart eavesdropping by integrating security into the physical nature of wireless transmissions. The signal is clear to the intended recipient but noise to others.
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Credit: Illustration by Ella Maru Studio / Princeton University

Emerging 5G wireless systems are designed to support high-bandwidth, low-latency networks connecting everything from autonomous robots to self-driving cars. But these large and complex communication networks could also pose new security challenges.

Encryption methods now used to secure communications from prying eyes can be difficult to scale to such high-speed, ultra-low latency systems for 5G and beyond. Indeed, the very nature of encryption requires an exchange of information between the sender and the recipient to encrypt and decrypt a message. This exchange makes the link vulnerable to attacks; it also requires computation that increases latency. Latency, the time between sending instructions over a network and arriving data, is a key metric for tasks such as autonomous driving and industrial automation. For networks that support latency-critical systems, such as self-driving cars, robots, and other cyber-physical systems, minimizing response time is critical.

Seeking to fill this security gap, researchers at Princeton University have developed a methodology that integrates security into the physical nature of the signal. In a report published on November 22 in Electronic Nature, the researchers describe how they developed a new millimeter-wave wireless microchip that enables secure wireless transmissions to prevent interception without reducing the latency, efficiency, and speed of the 5G network. According to the principal investigator Kaushik Sengupta, the technique is expected to make it very difficult to listen to such high frequency wireless transmissions, even with multiple malicious actors in collusion.

“We are in a new era of wireless – the networks of the future are going to be increasingly complex while serving a wide range of different applications that require very different functionality,” said Sengupta. “Think of low-power smart sensors in your home or industry, high-bandwidth augmented reality or virtual reality, and self-driving cars. To serve this and serve that well, we need to think about security holistically and at all levels. “

Instead of relying on encryption, Princeton’s method shapes the transmission itself to outsmart any spies. To explain this, it helps to imagine wireless transmissions as they emerge from an antenna array. With a single antenna, radio waves radiate from the antenna as one wave. When there are multiple antennas operating in a network, these waves interfere with each other like waves of water in a pond. Interference increases the size of some peaks and troughs and smooths others.

An antenna array is able to use this interference to direct a transmission along a defined path. But next to the main transmission there are secondary paths. These secondary paths are weaker than the primary transmission, but in a typical system, they contain exactly the same signal as the primary path. By exploiting these paths, potential spies can compromise transmission.

Sengupta’s team realized that they could outsmart prying eyes by making the signal appear at the prying eyes’ location almost like noise. They do this by hashing the message at random and assigning different parts of the message to subsets of antennas in the network. The researchers were able to coordinate the transmission so that only a receiver in the right direction could put the signal together in the correct order. Everywhere else, choppy signals arrive in a way that resembles noise.

Sengupta compared the technique to cutting a piece of music in a concert hall.

“Imagine in a concert hall, playing Beethoven’s Symphony No. 9, each instrument, instead of playing all the notes in the piece, decides to play notes chosen at random. They play these notes at the right time and remain silent between them, so that every note of the original piece is played by at least one instrument. As the sound waves carrying these notes from all the instruments pass through the room, at a certain point, they can be made to arrive precisely in the right way. The listener sitting there would enjoy the original piece as if nothing had changed. Everyone would hear a cacophony of missing notes arriving at random times, almost like noise. This is, in principle, the secret sauce behind transmission security, made possible by precise spatial and temporal modulation of these high frequency electromagnetic fields.

If a spy attempted to intercept the message by interfering with the main transmission, it would cause transmission problems and would be detectable by the intended user. While it’s theoretically possible that multiple spies could work together to collect the noise-like signals and attempt to reassemble them into a coherent transmission, Sengupta said the number of receivers needed to do so would be “extraordinarily large.”

“We have shown for the first time that it is possible to assemble multiple noise-like signatures in the original signal by getting along with prying people applying AI, but it is very difficult. And we also showed techniques how the transmitter can trick them. It’s a cat and mouse game.

Edward Knightly, a professor at Rice University who was not involved in the research, said Sengupta’s work was “an important step” in securing future networks.

“He showed experimentally, for the first time, how to defeat even a sophisticated opponent using machine learning data collected from multiple synchronized vantage points,” he said.

The team has created the entire end-to-end system in a silicon chip that is fabricated by standard silicon foundry processing.

Sengupta said it would also be possible to use encryption with the new system for additional security. “You can always encrypt on top of it, but you can reduce the encryption load with an extra layer of security,” he said. “It’s a complementary approach.

Secure space-time modulated millimeter wave wireless links that resist distributed eavesdropping attacks was published on November 22 in Nature Electronics. In addition to Sengupta, the authors include Suresh Venkatesh, post-doctoral researcher and Xuyang Lu, graduate student at Princeton University and Bingjun Tang, visiting researcher at Princeton University. The project was supported in part by the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office, the DURIP Grant, and the Defense Advanced Research Projects Agency.

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