Laser finds surfaces have built-in DNA

The surfaces of most paper documents, plastic cards and cardboard packages contain unique 'fingerprints' that could be used to combat fraud, according to physicists in the UK.

The fingerprint is contained in microscopic imperfections on the surface and can be read by a portable laser scanner.

The results could eliminate the need for expensive security measures -- such holograms, chips and special inks -- on passports, identity cards and pharmaceutical packaging.

Russell Cowburn and co-workers at Imperial College, London, Durham University and the University of Sheffield used a "laser speckle" to examine the structure of different surfaces.

The technique is already routine to measure surface roughness in metal and paper and for visualizing blood in vivo. They scanned a focused laser beam over a sheet of white paper and used photodetectors to record the intensity of the light reflected from four different angles.

The physicists then quantified how much random fluctuations on the paper differed from the mean value (the zero positional shift) and converting values into 1s and 0s to obtain the 'fingerprint' code.

They obtained different codes for different sheets from the same pack and achieved similar results for plastic credit and identity cards and cardboard packaging.

A sheet of paper could be identified even after screwing up into a ball, submerged inwater, baked at 180°C, scribbled on with ballpoint and marker pens, and scrubbed with abrasives.

Cowburn says "This is a system so secure that not even the inventors would be able to crack it, since there is no known manufacturing process for copying surface imperfections at the necessary level of precision."

The probability of two pieces of paper sharing the same fingerprint is less than 1 in 1027 and for smoother surfaces, such as plastic cards and cardboard, 1 in 1020. And each fingerprint only takes up between 200-500 bytes of storage space in a database.

"It's as if documents and packaging have their own unique DNA," said Cowburn

Source:http://optics.org/articles/news