Quantum, Paranoid And Secrets...

In a world of secrets, it pays to be paranoid. From ancient Rome to the modern age, most classical schemes for cryptography have relied on the 'decoding' step involving some problem that is hard to solve – but hard, rather than impossible. That has left cryptographic schemes, including those in wide use today, vulnerable to clever people or advances in technology.

Daddie...line 18 on page 5 is just sooo wrong!

Quantum cryptography, by contrast, offers security protected by the laws of physics. The technique provides a way for two parties to share a secret key – a random sequence of 1s and 0s – which can then be used to scramble a message. The security comes from quantum laws providing a built-in way to detect eavesdropping attempts. When the key is transmitted, using photons, say, any interception of the signal changes it in a way the legitimate parties can detect. Insecure keys can then be discarded.
But a "malicious manipulator" might have the ability to control the setup or influence the communicating parties' choice of settings in transmitting the key. The manipulation could even be something enshrined in fundamental physics – a limit on the amount of free will that humans can exercise.
It's a huge challenge to face, but the researchers believe quantum cryptography can still sometimes triumph. Ekert and his colleagues have worked out how to calculate, given the degree of manipulation, how much genuine 'randomness' remains in the key. This offers a measure of how much of the key has been left untouched and will, in turn, determine how much of the key can be guaranteed secret... (physorg.com)
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