December 8, 2020 feature
Nanoelectromechanical tags for tamper-proof product identification and authentication
Researchers in cybersecurity aim to realize truly unclonable identification and authentication tags to defend global systems from ever-increasing counterfeit attacks. In a new report now published on Nature: Microsystems & Nanoengineering, Sushant Rassay and a team of researchers in electrical and computer engineering at the University of Florida, U.S., demonstrated nanoscale tags to explore an electromechanical spectral signature as a fingerprint based on the inherent randomness of the fabrication process. The ultraminiature size and transparent constituents of the nanoelectromechanical (NEMS) tags provided substantial immunity to physical tampering and cloning efforts. The NEMS can typically convert forms of mechanical and vibrational energy from the environment into electric power by developing reliable power sources for ultralow power wireless electronic devices. The team also developed adaptive algorithms to digitally translate the spectral signature into binary fingerprints. The experiments highlighted the potential of clandestine (stealthy) NEMS to secure identification and authentication across a range of products and consumer goods.
Developing technologies to fight counterfeit trade
The emergence of counterfeit trade can significantly impact the global economic system, while escalating to impose broad social damage and pose international security threats as a source of white-collar crime. Counterfeit trade is conventionally fought using physical tags to identify, authenticate, and track genuine items by generating digital fingerprints or watermarks. The effectiveness of a physical tag can be defined by its applicability to diverse goods ranging from edibles to electronics, its perseverance to cloning alongside the associated cost of production. Researchers have developed a variety of general-purpose physical tag technologies, including quick response (QR) patterns, universal product code (UPC) and radiofrequency identification (RFID) tags. However, such techniques are limited and therefore pose security risks. Scientists had therefore recently developed nanoscale physical unclonable functions or nanophysical unclonable functions (PUFs) to identify substantial limits of identification and authentication tags. In this study, Rassay et al. presented a radically different approach using nanoelectromechanical systems (NEMS) to realize stealthy physical tags. The constructs maintained substantial immunity to tampering and cloning with generic applicability across a range of products.
The NEMS tags showed an electromechanical spectral signature composed of a large set of high-quality-factor (Q) resonance peaks. In general, the Q-factor describes the properties of an oscillator or resonator and the nature of the stored energy of the resonator, where a higher Q indicates that oscillations disperse slowly to cause a lower rate of energy loss relative to the stored energy of the resonator. These physical characteristics coupled to their ultraminiature size and transparent constituents ensured the immunity of NEMS tags towards physical tampering and cloning efforts. The cost-effective tags can be used in cluttered environments with large background noise and interference. To create the NEMS tags, Rassay et al. sandwiched a thin piezoelectric film between two metallic layers and enhanced the tag by choosing transparent materials to form constituent layers, then implemented the tags on a glass substrate to evaluate their transparency. The constituents provided a large electromechanical coupling coefficient to allow excitation of the mechanical resonance modes with miniscule magnetic powers. The team ultimately patterned the NEMS tag and observed the product using scanning electron microscopy (SEM) to highlight its optical transparency.
Principle-of-action and digital translation
During the development of the NEMS tags, the scientists delved into the properties of the electromechanical spectral signature to facilitate identification. The team designed the lateral geometry of the NEMS tags to create a large set of high-Q mechanical resonance modes across a small frequency range of interest (80-90 MHz). Based on the varying characteristics of the corresponding peaks to the resonance modes, Rassay et al. assigned a binary string to the NEMS tags.
The random nature of the material distribution allowed them to create visually identical NEMS tags with unique digital fingerprints that were only reflected in their spectral signature, and therefore nearly impossible to reverse engineer. The random and intrinsic uncertainties of the label constituents were desirable as it provided two distinct security benefits; first, it allowed the team to create unique identifiers or fingerprints for each of the batch-fabricated devices. Second, the material-based intrinsic randomness was advantageous to protect the information during its manufacture, thereby preventing counterfeit products. The translation procedure contained wireless interrogation and digital translation components, where the team implemented a series of elaborate steps to generate a unique binary string designated to each NEMS tag.
Characterizing the NEMS tag
To measure the spectral signature tags, Rassay et al. used near-field wireless interrogation across the frequency span of 80 to 90 MHz. To accomplish this, they positioned an intelligent character recognition (ICR) magnetic near-field microprobe with a coil radius of 50 µm for wireless interrogation through magnetic coupling. The team positioned the microprobe at a sub-2-mm vertical distance from the label, connected to a network analyzer to measure the reflection response across the frequency spectrum. The team then compared the spectral signatures of four NEMS labels, which they randomly picked from the array. For example, the 31-bit string assigned to the spectral signature fingerprints highlighted the entropy of the clandestine NEMS technology. As proof of concept, the team quantified the entropy under different temperature ranges for ten NEMS tags with identical designs using the interdevice Hamming distance (a metric to compare two binary data strings) to measure the uniqueness of the binary strings corresponding to the spectral signatures.
Outlook of the anti-counterfeiting stealth technology
In this way, Sushant Rassay and colleagues showed a new physical tag technology to identify and authenticate the use of the electromechanical spectral signatures of clandestine nanoelectromechanical (NEMS) tags. The ultraminiature device provided an optically transparent and visually undetectable indirect method for information storage. They engineered the spectral signature of the NEMS tag to have a large number of high-Q mechanical resonance peaks. The team obtained distinct fingerprints for the NEMS tags due to intrinsic variations of the material properties and extrinsic variations of the fabrication process. The scientists also developed a translation algorithm to designate a binary string to the spectral signature of each tag. The resulting large entropy and robustness of the NEMS tags highlighted the potential of the technology to identify and authenticate products.
Yansong Gao et al. Emerging Physical Unclonable Functions With Nanotechnology, IEEE Access (2016). DOI: 10.1109/ACCESS.2015.2503432
Riikka Arppe et al. Physical unclonable functions generated through chemical methods for anti-counterfeiting, Nature Reviews Chemistry (2017). DOI: 10.1038/s41570-017-0031
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