"New Scientist " is a TWO PAGE layout for a magazine article.

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Quantum Confidential

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Want to beat the hackers once and for all? As Simon Singh finds out, the enigmatic quantumm world is about to make your secrets safe as houses.

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Bryan Cannon

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It could happen in a few months or a few years. But sooner or later, a mathematician could make a discovery that jeopardized international security, threatens the future of Internet commerce, and imperils the privacy of e-mails. Today's codes and ciphers are good, to be sure. But it is probably only a matter of time before they become useless.

With the coming of the information age, we rely ever more heavily on cryptography to protect us from snoopers, cybercrooks and Big Brother. Some of today's most secure codes exploit the fact that while it is easy to multiply two prime numbers together, it is almost impossible to start with the answer and work out which two primes were used to create it. But the day a mathematical genius discovers a short cut for finding the hidden prime numbers, these codes will crumble.

What everyone is looking for is a new form of code, one that is truly unbreakable. That's where the quantum world comes in. Exploiting the strange uncertainties of quantum physics can give you a code that nobody - no matter how clever - will ever be able to crack.

That's the theory. The trouble comes when you try putting it into practice. When quantum particles interact with the large-scale world they tend to lose the delicate information they contain. This makes it fiendishly difficult to use them to send information over any sensible distance. Difficult, but not impossible. In the past few years, researchers have succeeded in sending quantum-encrypted messages tens of kilometers down optical fibres. Now the challenge is to find a way to send quantum-encrypted information through the air. This will open the way to fully secure global communications, beamed up to an orbiting satellite and forwarded to any place on Earth. It's a phenomenal technical problem, but this year researchers at the Los Alamos National Laboratory in New Mexico achieved a breakthrough that looks set to transform the way we keep our secrets.

Cryptographers often describe code scenarios in terms of a trio of characters called Alice, Bob, and Eve. While Alice is trying to send a sensitive message to Bob, Eve is trying to eavesdrop. To keep her message secret, Alice has to encrypt it, and for this she can use a cipher known as a "one-time pad". Cryptographers have known about the on-time pad technique for decades and it is logically uncrackable. The encryption requires three separate stages. First, Alice transforms her message into a series of 1s and 0s. Second, Alice creates a key - a random series of 1s and 0s that is as long as the message. Third, Alice adds each element of the key to the corresponding element of the message, to create an encrypted text also made up of 1s and 0s; the only unusual adding rule is that 1 + 1 = 0. Finally, Alice sends the encrypted text to Bob.

This type of code is impossible to crack because each element of Alice's key is random. Even if Eve were to use computational brute force to try every possible key, she's find that many of them made some sort of sense, and wouldn't know how to choose between the alternatives. Bob, on the other hand, has a copy of the key, and can decipher they message by simply subtracting the key from the encrypted text.

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New Scientist

www.newscientist.com

2 october 1999

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