A number of years ago, MIT researchers invented a cryptographic ID tag that’s repeatedly smaller and significantly cheaper than the normal radio frequency tags (RFIDs) often attached to products to confirm their authenticity.

This tiny tag, which offers greater security than RFIDs, uses terahertz waves, that are smaller and have much higher frequencies than radio waves. But this terahertz tag had a serious security flaw with traditional RFIDs: A counterfeiter could peel the tag off a real item and reattach it to a counterfeit, the authentication system none the wiser.

Researchers have now overcome this vulnerability by utilizing terahertz waves to develop a tamper-proof ID tag that also offers the benefits of being small, low cost and secure.

They mix microscopic metal particles into the adhesive that sticks the label to an object, then use terahertz waves to detect the unique pattern these particles form on the thing’s surface. “Similar to a fingerprint, this random adhesive pattern is used to authenticate the item,” explains Eunseok Lee, a doctoral student in electrical engineering and computer science (EECS) and lead writer of a paper on the anti-tampering label.

“These metal particles are essentially like mirrors for terahertz waves. If I spread a series of mirror pieces on a surface after which shine light on them, I get a special reflected pattern depending on the orientation, size and position of those mirrors. But in the event you peel off the chip and put it back on, you destroy this pattern,” adds Ruonan Han, an associate professor at EECS who leads the Terahertz Integrated Electronics Group within the Research Laboratory of Electronics.

The researchers made a light-powered anti-tampering tag that’s about 4 square millimeters in size. They also demonstrated a machine learning model that helps detect tampering by identifying similar fingerprints from adhesive patterns with greater than 99 percent accuracy.

Because the terahertz tag is so low cost to supply, it may very well be implemented across an enormous supply chain. And due to its small size, the tag could be attached to items which might be too small for traditional RFIDs, reminiscent of certain medical devices.

The paper, presented on the IEEE Solid State Circuits Conference, is a collaboration between Hans Group and the Energy-Efficient Circuits and Systems Group of Anantha P. Chandrakasan, MIT’s chief innovation and strategy officer and dean of the MIT School of Engineering, and the Vannevar Bush Professor of EECS. Co-authors include EECS graduates Xibi Chen, Maitryi Ashok and Jaeyeon Won.

Prevent manipulation

This research project was partially inspired by Han’s favorite automotive wash. The company taped an RFID tag to its windshield to authenticate its membership on the automotive wash. For added security, the label was fabricated from fragile paper, so it will be destroyed if a dishonest customer tried to peel it off and fasten it to a different windshield.

But that is not a very reliable method to prevent tampering. For example, someone could use an answer to dissolve the adhesive and safely remove the delicate label.

Instead of authenticating the label, a greater security solution is to authenticate the item itself, says Han. To achieve this, the researchers targeted the adhesive on the interface between the label and the surface of the item.

Your anti-tamper label incorporates a series of tiny slits that allow terahertz waves to go through the label and strike microscopic metal particles which were mixed into the adhesive.

Terahertz waves are sufficiently small to detect the particles, while larger radio waves wouldn’t be sensitive enough to detect them. Additionally, by utilizing terahertz waves with a wavelength of 1 millimeter, the researchers were in a position to create a chip that doesn’t require a bigger antenna outside the chip.

After terahertz waves go through the label and strike the surface of the thing, they’re reflected or backscattered to a receiver for authentication. How these waves are backscattered relies on the distribution of the metal particles that reflect them.

The researchers placed multiple slits on the chip to permit waves to hit different points on the thing’s surface, allowing them to capture more information in regards to the random distribution of the particles.

“These reactions can’t be duplicated so long as the adhesive interface is destroyed by a counterfeiter,” says Han.

A provider first reads the tamper-proof label once it’s attached to an item after which stores this data within the cloud for later use for verification.

AI for authentication

But when it got here time to check the anti-tamper label, Lee encountered an issue: It was very difficult and time-consuming to take precise measurements to find out whether two adhesive patterns matched.

He contacted a friend on the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) and together they tackled the issue using AI. They trained a machine learning model that might compare adhesive patterns and calculate their similarity with greater than 99 percent accuracy.

“One drawback is that we only had a limited data sample for this demonstration. However, we could improve the neural network in the longer term if a lot of these tags were deployed in a supply chain, which might give us many more data samples,” says Lee.

The authentication system can also be limited by the proven fact that terahertz waves have a high loss in transmission, so the sensor must only be about 4 centimeters away from the tag to get an accurate reading. For an application reminiscent of barcode scanning, this distance wouldn’t be an issue, but for some potential applications, reminiscent of an automatic highway toll booth, it will be too short. In addition, the angle between the sensor and the tag have to be lower than 10 degrees, otherwise the terahertz signal shall be affected an excessive amount of.

They plan to handle these limitations in future work and hope to encourage other researchers to be more optimistic about what could be achieved with terahertz waves, despite the numerous technical challenges, Han says.

“One thing we really need to point out here is that the applying of the terahertz spectrum can extend far beyond broadband wireless. In this case, you should utilize terahertz for ID, security and authentication. There are quite a lot of options on the market,” he adds.

This work is supported partly by the US National Science Foundation and the Korea Foundation for Advanced Studies.

This article was originally published at news.mit.edu