Twente University, the Netherlands, PhD student Bas Goorden proposes a new method of validating a credit card:
A card can be equipped with a wafer-thin layer of dry, white paint containing millions and millions of nanoparticles. If you shoot a light particle into the paint layer, it will bounce around between the nanoparticles like a ball in a pinball machine, until it escapes. If a bank generates photons with a complex and unique pattern of bright spots (the ‘question’), the photons that escape from the nanoparticles show a new unique pattern of bright spots (the ‘answer’), which can then be checked. The bank will only approve the transaction if the pattern of bright spots provided as an answer is correct."