Scientists create a novel hydrogel for unclonable security tags

Encryption technologies are vital in today’s digital landscape to protect sensitive information from hackers and prevent fraud. While cutting-edge encryption has been developed for data, sophisticated protection for physical objects such as high-value products, access cards and documents has lagged behind until now.

Scientists have now developed a new hydrogel that acts as an unclonable physical tag. The work is published in the journal Advanced Materials.

Physical items are easily copied or faked because their built-in security tags are often weak or simple to clone. To solve this security gap, a team of researchers from China first mixed two chemicals together: polypyrrole, which conducts electricity; and polystyrene sulfonate, a flexible polymer. The result was a soft, conductive, jelly-like substance.

While this gel was setting, the team zapped it with an electrical field in a process called regional assembly cross-linking (RAC). This forced the ingredients inside the gel to rearrange into an irregular network of conductive and non-conductive regions, creating a kind of chaotic maze of electrical paths.

This maze is one-of-a-kind and serves as the gel’s unclonable security tag. When anyone sends an electric signal into the gel, it has to navigate the random internal maze. Because the maze contains billions of random electrical points that all affect the signal differently, the signal that comes out the other end is a unique electrical signature. According to the researchers, this method creates over ten million billion possible signatures (codes).

Testing the technology

To test their innovation, the scientists sent the same electrical challenge signal (set of electrical pulses) into the gel 1,000 times, and it produced the same secret electrical signature every time. This means the gel’s unique “fingerprint” is reliable and stable. The team also made another gel under identical conditions to simulate what a hacker would do and found that the output codes were significantly different. This confirmed that the internal structure of the gel is impossible to replicate, making a tag unclonable. Even sophisticated AI models like Transformers couldn’t crack the gel.

“The RAC-Gel thus maintains strong resistance to machine-learning-based attacks, even under high levels of model optimization,” wrote the researchers in their paper.

By creating so many complex, unpredictable codes, the study authors believe the effort to crack the gel would be too expensive to be worthwhile, stating, “Elevating the cost of decryption beyond the value of the protected information represents one of the most effective approaches to encryption.”

The researchers didn’t just create the gel; they also built a functional prototype tag by integrating the gel onto a flexible plastic film with electrodes. Future plans include developing flexible security chips for products, enhancing the gel’s complexity and scaling up production.

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