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.

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