WHEN Acredit card company asked the MIT Media Lab to develop a technique to produce card identifiers that, unlike magnetic stripes, would be extremely difficult to forge, graduate student Ravikanth Pappu devised a cheap and simple solution. He embeds hundreds of glass beads into dime- size epoxy tokens. When a laser shines on a token, its beads scatter the light in a unique pattern that can be digitally stored as a fingerprint or “key.” Retailers could use readers to check patterns against keys in a secure database. Pappu says there is no known technology that can counterfeit the tokens or their keys. Now a principal at ThingMagic in Cam- bridge, MA, which is developing “embedded intelligence” as well as radio frequency identification technologies, Pappu says credit card companies are calling, interested in building tokens into their cards. The technique could also be used for tamper-resistant packaging, or to create identifiers for computer chips. According to Neil Gershenfeld, Pappu’s MIT advisor, cryptographers are often very critical of new ideas, but they have “welcomed this new approach.”