Conjugal secrets. (quantum cryptography) (Science and Technology)

Economist (US), The, April, 1989

Conjugal secrets

WERNER HEISENBERG, the discoverer of the uncertainty principle in quantum mechanics, is an unlikely ally for James Bond. But spies, and others with a penchant for secrecy, need all the help they can get. The only code that can never be broken is one whose "key" is at least as long as the message itself, and used only once. Even these "one-time pad" codes have a drawback: both the sender and the receiver need to know the key, so it can be filched when it is passed between them.

Where dirty tricks, computer power and mathematical ingenuity have failed, the laws of physics can help. According to the uncertainty principle, there are limits--in theory, not just in practice--to the knowledge one can have about the states of sub-atomic...

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