Beads and glue defeat forgers. (Technology).

Eye-catching holograms on credit cards thwart would-be forgers. Using light to enhance security in a new way, researchers at the Massachusetts Institute of Technology (MIT) have devised a cheap, translucent material to be embedded in credit cards, identity cards, and other possessions. Built-in windows made of the material would endow items with unique identifiers that are almost impossible to tamper with or copy, says co-inventor Ravikanth S. Pappu, now at the company ThingMagic in Cambridge, Mass. He and his colleagues describe the new security tags in the Sept. 20 Science.

The MIT team made the tags by randomly mixing microscopic glass spheres into transparent epoxy and then hardening the glue into wafers about the size of Chiclets. A laser beam passing through a tag produces a speckle pattern, which then is used to calculate an identification number.

One reason the tags are so robust against duplication, says Pappu, is that slightly altering the laser beam's angle totally changes the resulting speckles. Consequently, a single tag can generate about 10 billion unique identifiers. A security system might check any number of those to confirm an item's authenticity. To flawlessly forge the tag, someone would have to make so perfect a copy that it would recreate all those patterns--a nearly impossible feat.