New unclonable authentication system proposed by researchers

A team of European researchers have proposed a new type of authentication system that works in the same way as butterfly and peacock wings, and which can't be cloned or copied.

The cross-disciplinary collaboration between the Universities of Luxembourg, Ljubljana and Vienna say the new anti-counterfeiting method produces unique reflecting patterns and is a new type of Physical Unclonable Function (PUF), which the researchers say has "enormous potential" in authentication.

PUFs respond in a unique way to different physical inputs, such as scattering light in unpredictable directions, sparkling with variable colours when illuminated or starting up in random states when switched on. PUFs are generally found in microchips, ensuring that the silicon components come from an authorised factory.

Taking this on board, the researchers have explored the concept of the more rare optical PUFs, which generate a response to light input that can be captured by a camera in order to authenticate the item of value that the PUF is attached to.

This new type of PUF that the researchers propose, published in the journal Scientific Reports, is based on the peculiar optics of spheres of cholesteric liquid crystals. The self-assembled periodic structure of these liquid crystals means the spheres reflect specific colours in the same way as butterfly and peacock wings.

A detailed analysis of the optics of a number of such spheres revealed that the spheres communicate with each other by light in unexpected ways, creating unique colourful patterns that can be tuned dynamically by changing the way the spheres are illuminated.

"Because different types of liquid crystal spheres can be arranged randomly in a token, generating patterns that are equally random, it is impossible to copy the token and its related set of patterns, rendering it highly attractive as a PUF to authenticate people or objects," the researchers say. "Any attempt at tampering with the arrangement will likely ruin the structure." And any attempt to transfer the PUF to a copy would carry evidence of the tampering.

A stochastic arrangement alongside other random factors "can additionally be introduced to increase the inherent entropy and to render each arrangement unclonable and capable of generating a unique, and we hypothesise, unpredictable optical pattern," the researchers say.

In today's globalised and connected world, the ability to authenticate objects and people has become a security-critical business at many levels; personal, societal, and national, the researchers say, adding that current authentication strategies are not bulletproof.

"From this point of view, an attractive solution would be to have unclonable non-biometric physical tokens. For being commercially appealing, the production costs of such unique tokens need to be low. These features lead to the concept of PUFs."

The researchers believe such optical PUFs could be used to trace artwork, jewellery, documents and medications. They could also be applied as temporary tattoos or printed onto clothes and used as a proof of identity.

More research is however required before these PUFs can be realistically exploited, the researchers add.

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