The risk of illegal information access, notably in money transactions, requires more and more advanced cryptographic techniques against criminals and the occasional mischevious teenager.
Quantum cryptography has been regarded as 100-percent protection against attacks on sensitive data traffic but a research team at Linköping University in Sweden has found a hole in even this advanced technology.
When an encrypted message needs to be sent over a computer network, the most difficult problem is how the key should be transmitted. One way is to literally send it by courier (which has its own security risks) or, if it's in your budget, attached to the wrist of James Bond. But the most common way is a "public key," like https:// for online banking and security functions in Web browsers.
A public key is regarded as secure, since enormous calculations are required to break the long strings of data bits - some 2,000 - that make up the key.
Quantum cryptography is considered absolutely secure but very few people use it. It requires special hardware, such as a type of laser that emits polarized light particles (photons) via optic fiber or through the air and some companies and banks in Austria are testing such a system, and trials are even underway with satellite-TV transmission.
In quantum cryptography, security is guaranteed by the laws of quantum mechanics. Quantum-mechanical objects have the peculiar property that they cannot be measured or manipulated without being disturbed. If somebody tries to copy a quantum-cryptographic key in transit, it will make extra 'noise.' An eavesdropper can cause problems, but not extract usable information.
Jan-Åke Larsson, associate professor of applied mathematics at Linköping University, working with his student Jörgen Cederlöf, has shown that not even quantum cryptography is 100-percent secure. There is a theoretical possibility that an unauthorized person can extract the key without being discovered, by simultaneously manipulating both the quantum-mechanical and the regular communication needed in quantum cryptography.
"The concern involves authentication, intended to secure that the message arriving is the same as the one that was sent. We have scrutinized the system as a whole and found that authentication does not work as intended. The security of the current technology is not sufficient," says Jan-Åke Larsson.
In the IEEE Transactions on Information Theory article, the authors propose a change that solves the problem.
"We weren't expecting to find a problem in quantum cryptography, of course, but it is a really complicated system. With our alteration, quantum cryptography will be a secure technology," says Jan-Åke Larsson.
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