As commerce rushes online, the ability to send private messages over public communications networks has become vitally important. The most secure means of encryption is for both the sender and the recipient of a message to use the same long string of random digits-known as a key-as the basis for encoding and decoding. But such a key must be exchanged, and whether the hand-off takes place via telephone, armored guard or carrier pigeon, there is always a risk of interception.

Well, almost always. Years ago, physicists came up with an approach called "quantum cryptography" that relies upon the bizarre laws of quantum mechanics to definitively shut out snoops and transmit key data in absolute security. IBM physicist Charles Bennett and his colleagues built the first working laboratory prototype in 1989. Now, researchers at IBM Almaden Research Center in San Jose, Calif., have built a device out of off-the-shelf telecommunications components that they say will soon move quantum cryptography out of the physics lab and into the real world.