New research by several UK institutions, including Imperial College London in collaboration with Durham University and the University of Sheffield, may offer a ubiquitous, inexpensive way to secure documents based on microscopic surface imperfections.
Naturally occurring randomness in the physical properties of materials provides a means of ascribing a unique "fingerprint" to that material, which can be probed easily using the optical phenomenon of laser speckle. James Buchanan from Imperial College London and his research team examined the fine structure of different surfaces using the diffuse scattering of a focused laser. Speckle, which can hinder other optical techniques used in homeland security applications, is commonly used for determining surface roughness, identifying small deformations on metal, and visualizing blood flow in the medical industry.
A scanning electron micrograph of the surface of normal office paper shows a complex pattern of fibers, even when the paper is handled roughly. The fibers form the fingerprint for paper documents. Photo courtesy
Del Atkinson, Durham University.
By focusing a laser beam across a sheet of standard white paper and continuously recording the reflected intensity from four different angles using photodetectors, the team was able to differentiate the random fluctuations from different types of paper. Similar results were also obtained between other types of material, including plastic credit cards and identity cards. They found that even after the object had been handled roughly, recognition was good. For paper this included screwing it into a tight ball, submerging it in water, scorching the surface, scribbling over the scanned area with ink, and scrubbing it with an abrasive cleaning pad. Comparing the amplitude of the cross correlation peak, it was possible to determine the probability of two objects sharing indistinguishable fingerprints. For the two different types of paper, the correlation was 10-72.
An atomic force micrograph of the surface of a plastic ID card is shown here. The slight undulations to the surface form the fingerprint for plastic items. Photo courtesy Gang Xiong, Durham University
With the 200-500 bytes of storage space that each fingerprint provides and the ability to use a low-cost portable laser scanner, researchers hope that this technique will provide a new approach to authentication and tracking, offering a complementary method for existing fraud protection techniques. Indeed, the group has already spun out a company, Ingenia Technology Ltd. (London), to commercialize their findings. Regarding the method's ability to differentiate between different types of paper, Russell Cowburn, group leader and co-author, explains, "We obtain a unique signature for every note; the paper type is largely irrelevant. We can uniquely differentiate every single dollar bill from every other dollar bill. It works equally well on dollars, euros, and pounds."
Here, a schematic shows how the technology would be used. A focused laser is scanned over the surface of the item to be identified. The sensor records an imprint in the reflected laser light of the underlying naturally-occurring irregularities on the surface (paper fibers in this case, shown in the inset) and converts this into a serial code. Photo courtesy Ingenia Technology LTD.
The range of applications for this technique is considered to be vast, including preventing grey-market trafficking of tobacco and pharmaceuticals. More directly, the technique can be used as an adjunct to other security technologies for securing passports, visas, and birth certificates. Because it works well with bank notes, the technique could facilitate the removal of counterfeit notes from circulation and enable shops to check the authenticity of notes at the point of sale. As for ease of use, Cowburn says, "We've done extensive tests on both the sensitivity of positioning of the item and also the usability of the system by unskilled personnel."
Dennis Treece from the Massachusetts Port Authority said he anticipates greater use of the technology in the identification of forged passports and very high-end historic documents, which could be registered and stored in a database and used by agencies such as police investigators, museums, and auction houses. The cost, installation, maintenance, and training for the readers, however, was highlighted as an important part that needs to be quantified before developing a market for this technology. "The technology can be an effective tool for high-stakes forgery detection and ought to be encouraged if it works as advertised," Treece says.