Chapter XII: Quantum Keys
Back some hundreds of years ago, messages were often sent with an official seal. To do this you would heat a stick of sealing wax until a blob melted off the end onto the outside of your message. You would then stamp the blob with your seal, which would leave your characteristic mark embossed in the now hardened sealing wax. Anyone wishing to secretly read the message would probably have to break the seal -- and this would likely be detectable.
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Theoretically, you could make an exact copy of the message and the seal and seal it all up so the intended recipient couldn't tell the message had been intercepted. But what if there were a way to send a message in such a way that it was absolutely impossible to tell if the message had been intercepted? Quantum Key Distribution (QKD) uses quantum mechanics to guarantee secure communication. It enables two parties to produce a shared random secret key known only to them -- which can then be used to encrypt and decrypt messages.
In the world of the very small, at the level of electrons, things behave differently. You can't "see" an electron like you can see a billiard ball. Seeing involves light, which we know to be composed of minute particles called photons. When a photon hits a billiard ball it has a negligible effect, but when a photon hits an electron it knocks it off course (just like a billiard ball would if it hit another billiard ball). This field, known as Quantum Mechanics, was discovered by an ingenious physicist named Werner Heisenberg in 1927.
By using a feature of quantum mechanics know as Quantum Entanglement, a communication system can be implemented that detects eavesdropping. A key can be produced that is guaranteed to be secure. If the key is intercepted the communication is aborted and a new key has to be generated and sent. Once both parties have a key known only to them they can exchange message using any number of traditional methods.
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In June 2017 in a landmark study, a team of Chinese scientists using an experimental satellite tested quantum entanglement over unprecedented distances, beaming entangled pairs of photons to three ground stations across China -- each separated by more than 1,200 kilometers. The test verifies a mysterious and long-held tenet of quantum theory, and firmly establishes China as the front-runner in a burgeoning “quantum space race” to create a secure, quantum-based global communications network -- that is, a potentially unhackable “quantum internet” that would be of immense geopolitical importance.
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The Chinese always had a reputation for being inscrutable. Now it seems that will soon be absolutely inscrutable.