National Geographic : 2012 Mar
NEXT The dot system works in pairs; seven strains squared equals 49 possible characters. That's enough to represent the alphabet, numbers zero to nine, and a few basic symbols. Ironically, the main drawback is what makes the system so secure: It doesn't use technology. "It's time-consuming to work with toothpicks and vials of bacteria," says Walt. He hopes printable messages will one day be possible, perhaps to deter pharmaceutical tampering and counterfeiting---a case of germs protecting medicine. ---Johnna Rizzo • Spies have a new tool for encoding secret texts: bacteria. NOTE TO 007: There's a new way to send covert communiqués. Dubbed SPAM (steganography by printed arrays of microbes), this living invisible ink was created by a team of scientists at Tufts University in response to an encryption challenge from the Defense Advanced Research Projects Agency. The result: Cold War subterfuge reimagined as a safe, playful spin on germ warfare. Encoders use a dropper or toothpick to arrange tiny circular colonies of E. coli on a thin sheet of paper, choosing among seven innocuous strains genetically altered to fluoresce a different color once a chemical is added. When the secret text reaches the right recipient, it's "opened" by pressing it onto a petri dish, where the colonies grow. Adding the chemical cipher---the Tufts scientists used ampi- cillin---reveals the dot matrix to the naked eye. For more security, the bacteria can be modified to lose color capability after a set time---an automatic self-destruct mode that lead researcher David Walt likens to Mission: Impossible. This cryptic message was created with just an eyedropper and strains of harmless, fluorescing E. coli.