Current encryption strategies are based on the assumed complexity of various mathematical problems computer can solve. A message is properly encrypted if a hacker would need a lot of time and resources to decrypt it. But as computers become more and more powerful the encrypted messages become easier to crack. Moreover, the mathematical problems cryptography is based upon sometimes prove to be less complex than previously thought.

Quantum cryptography is something completely different. It's not based on assumed complexity of mathematical problems; it is based on physical principles - more specifically, on Heisenberg's incertitude principle. This principle states that when one measures some quantum property one, by necessity, influences some other quantum property. The quantum world is in such a way that there are no such things as completely independent properties.

The basic idea is that when a hacker tries to observe what you transmit to somebody else he/she will change the transmitted message. Therefore, if communication was based on this fundamental aspect of the quantum world no hacker could hack in without being detected.

"Quantum cryptography is trying to make all transmissions secure, so this could be very useful for online banking, for example," says Professor Hoi-Kwong Lo, an expert in physics and electrical and computer engineering at University of Toronto's Centre for Quantum Information and Quantum Control and the senior author of a new study about the technique. "The idea can be implemented now, because we actually did the experiment with a commercial device."

The study describes the first experimental proof of a quantum decoy technique to encrypt data over fiber optic cable. The encrypted message is carried by laser light through fiber optic cables. The technique varies the intensity of photons and introduces photonic "decoys", which were transmitted over a 15-kilometre telecommunication fiber. After the signals are sent, a second broadcast tells the receiving computer which photons carried the message and which were decoys. If a hacker tries to "eavesdrop" on the data stream to figure out the encryption key, the mere act of eavesdropping changes the decoys - a clear sign to the receiving computer that the data has been tampered with.