Our department’s Professor Young Min Song, in collaboration with Professor Hyeon‑Ho Jeong’s research team at GIST School of EECS, has developed a replication‑impossible security authentication technology based on nature‑inspired nanophotonic structures.
This technology can be easily embedded into physical products such as ID cards or QR codes and, being visually indistinguishable from existing items, provides strong tamper‑proof protection without compromising design. It holds broad potential for applications requiring genuine‑product authentication, including premium consumer goods, pharmaceuticals, and electronics.
Until now, anti‑tampering measures like QR codes and barcodes have been limited by their ease of replication and the difficulty of assigning truly unique identifiers to each item. A recently spotlighted solution is the physically unclonable function (PUF)*, which leverages the natural randomness arising during manufacturing to grant each device a unique physical signature, thereby enhancing security and authentication reliability.
However, existing PUF technologies, while achieving randomness and uniqueness, have struggled with color consistency control and are easily identified (and thus attacked) from the outside. * Physically Unclonable Function (PUF): A technique that uses physical variations formed during the manufacturing process to generate a unique authentication key. Because these variations are inherently random and unclonable, even if the authentication data is stolen, constructing the exact hardware for authentication is effectively impossible.
In response, the research team turned its attention to the unique phenomenon of structural color* observed in natural organisms. For example, the wings of butterflies, feathers of birds, and leaves of seaweed all contain nanoscale microstructures arranged in a form of quasiorder*—a pattern that is neither completely ordered nor entirely random. These structures appear to exhibit uniform coloration to the naked eye, but internally contain subtle randomness that enables survival functions such as camouflage, communication, and predator evasion.
* Quasi‑order: A structural arrangement that is neither fully ordered nor fully disordered. In nature, nano‑scale elements are arranged in a pattern that blends order with randomness—found, for example, in butterfly wings, seaweed leaves, and bird feathers—producing uniform color at a macroscopic scale while embedding unique optical features.
* Structural Color: Color produced not by pigments but by nano‑meter‑scale structures that interact with light, commonly seen in living organisms. Classic examples include the iridescent wings of butterflies and the feathers of peacocks.
The researchers drew inspiration from these natural phenomena. They deposited a thin dielectric layer of HfO₂ onto a metallic mirror and then used electrostatic self‑assembly to arrange gold nanoparticles (tens of nanometers in size) into a quasi‑ordered plasmonic metasurface*. Visually, this nanostructure exhibits a uniform reflection color; under a high‑magnification optical microscope, however, each region reveals a distinct random scattering pattern—an “optical fingerprint*”—that is impossible to replicate. * Plasmonic Metasurface: An ultrathin optical structure comprising precisely arranged metallic nano‑elements that exploit surface plasmon resonance to locally enhance electromagnetic fields, enabling far more compact and precise light–matter interaction than conventional optics. * Optical Fingerprint: A unique pattern of reflection, scattering, and interference produced when light interacts with a micro‑ or nano‑scale structure. Because these patterns arise from random structural variations that cannot be exactly duplicated, they serve as a practically unclonable security feature.
The team confirmed that leveraging these nano‑scale stochastic patterns enhances PUF performance compared to conventional approaches.
In a hypothetical hacking scenario where an attacker attempts to recreate the device, the time required to decrypt the optical fingerprint would exceed the age of the Earth, rendering replication virtually impossible. Through demonstration experiments on pharmaceuticals, semiconductors, and QR codes, the researchers validated the technology’s practical industrial applicability.
Analysis of over 500 generated PUF keys showed an average bit‑value distribution of 0.501, which is remarkably close to the ideal balance of 0.5, and an average inter‑key Hamming distance of 0.494, demonstrating high uniqueness and reliability. Additionally, the scattering patterns remained stable under various environmental stresses, including high temperature, high humidity, and friction, confirming excellent durability.
Professor Young Min Song emphasized, “Whereas conventional security labels can be deformed by even minor damage, our technology secures both structural stability and unclonability. In particular, by separating visible color information from the invisible unique‑key information, it offers a new paradigm in security authentication.”
Professor Hyeon‑Ho Jeong added, “By reproducing structures in which order and disorder coexist in nature through nanotechnology, we have created optical information that appears identical externally yet is fundamentally unclonable. This technology can serve as a powerful anti‑counterfeiting measure across diverse fields, from premium consumer goods to pharmaceutical authentication and even national security.”
This work, guided by Professor Young Min Song (KAIST School of Electrical Engineering) and Professor Hyeon‑Ho Jeong (GIST School of EECS), and carried out by Gyurin Kim, Doeun Kim, JuHyeong Lee, Juhwan Kim, and Se‑Yeon Heo, was supported by the Ministry of Science and ICT and the National Research Foundation’s Early‑Career Research Program, the Regional Innovation Mega Project in R&D Special Zones, and the GIST‑MIT AI International Collaboration Project.
The results were published online on July 8, 2025, in the international journal Nature Communications.
* Paper title: Quasi‑ordered plasmonic metasurfaces with unclonable stochastic scattering for secure authentication
