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Here is a good introductory article on QC (quatum cryptography) entitled What is Quantum Cryptography I ran across recently.  For those of you who have never heard of QC, its going to be commonplace in our lives before too long, replacing the popular public key cryptography system we use today, and certainly change how we, as developers, deal with encrypted data.  QC is something I follow with interest, and have been for about 2 years now, although the ideas of QC have been around for much longer.  Below are a few short explanations from 2 good QC sites, and one recently published news article that explain QC.

Here is the QC definition from qubit.org

While classical cryptography employs various mathematical techniques to restrict eavesdroppers from learning the contents of encrypted messages, in quantum mechanics the information is protected by the laws of physics. In classical cryptography an absolute security of information cannot be guaranteed. The Heisenberg uncertainty principle and quantum entanglement can be exploited in a system of secure communication, often referred to as "quantum cryptography". Quantum cryptography provides means for two parties to exchange a enciphering key over a private channel with complete security of communication.

Here is a paragraph from a great site for information, including many published papers (not all in English though) at http://www.quantenkryptographie.at/

Quantum cryptography is a superior technology which overcomes limitations and drawbacks of classical cryptographic schemes by utilizing quantum physical effects.  The appeal of quantum cryptography is that its security is based on the laws of nature. In contrast to existing classical schemes of Key Distribution, Quantum Key Distribution does not invoke the transport of the key, since it is created at the sender and receiver site immediately. Furthermore, the key is created from a completely random sequence, which is in general an extremely diffcult task in classical schemes. Finally, eavesdropping is easily detected due to the fragile nature of the qubits invoked for the quantum key distribution.

Here is a quote from an article published a few weeks ago titled “ Single photons distributed for quantum cryptography “, where a Japanese telephone company successfully demonstrated QC in a photonic network of optical fibers – http://www.ferret.com.au/articles/e6/0c030ee6.asp

Quantum cryptography is seen as the next generation cryptographic system to replace the public-key protocol for protecting data. It utilises the property that the quantum state is very delicate to the external environment, and is destroyed when an eavesdropper observes it. Since the secret key encoded in the quantum state, single photon, cannot be identically replicated, the receiver can easily detect if the secret key had been stolen.