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China Launches World's First Quantum Communications Satellite (theverge.com)
hackingbear quotes a report from The Verge: China's quantum network could soon span two continents, thanks to a satellite launched earlier today. Launched at 1:40pm ET, the Quantum Science Satellite is designed to distribute quantum-encrypted keys between relay stations in China and Europe. When working as planned, the result could enable unprecedented levels of security between parties on different continents. China's new satellite would put that same fiber-based quantum communication system to work over the air, utilizing high-speed coherent lasers to connect with base stations on two different continents. The experimental satellite's payload also includes controllers and emitters related to quantum entanglement. The satellite will be the first device of its kind if the quantum equipment works as planned. According to the Wall Street Journal, the project was first proposed to the European Space Agency in 2001 but was unable to gain funding.
The military application is there if the quantum technology is protecting secret communication to a level that makes it impossible for anyone external to view it.
I wonder if they have been able to also implement a way to detect if someone listens to the signal using entanglement. It would be quite the deal if it was possible to detect that on a wireless signal.
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
Here's a human readable primer on it:
http://www.techrepublic.com/blog/it-security/how-quantum-cryptography-works-and-by-the-way-its-breakable/
I've marked the backchannel of extra filtering information with a **** below. You will see this in all Quantum signal experiments. An extra channel of information used to fixup the result. Think about it for a second, you're exchanging KEYS not information, and the KEY exchange itself requires an exchange of a backchannel in a secure way!
How it works for light:
Alice uses a light source to create a photon.
The photon is sent through a polarizer and randomly given one of four possible polarization and bit designations — Vertical (One bit), Horizontal (Zero bit), 45 degree right (One bit), or 45 degree left (Zero bit).
The photon travels to Bob's location.
Bob has two beamsplitters — a diagonal and vertical/horizontal - and two photon detectors.
Bob randomly chooses one of the two beamsplitters and checks the photon detectors.
The process is repeated until the entire key has been transmitted to Bob.
****Bob then tells Alice in sequence which beamsplitter he used.
Alice compares this information with the sequence of polarizers she used to send the key.
Alice tells Bob where in the sequence of sent photons he used the right beamsplitter.
Now both Alice and Bob have a sequence of bits (sifted key) they both know.
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The assumption is that the attacker cannot see the key exchange message without affecting it by more than a statistical error.
However real world attacks mean you can read the photon and send a similar polarized photon to Bob. In the Swedish attack on this, they sent LOTS of photons, some of which were bound to have the correct polarization, in effect they overwhelmed the detector which has no way of knowing if photons are at both slits because Bob only checks one slit. But an easier attack is to attack the back channel of info. Since Alice keeps sending till she thinks Bob has the full key, an attacker can force her to keep sending till *he* has the key from his choice of photons by intercepting Bobs message back and adding his own mistakes to it.
In the real world fiber optics have repeaters (electrical signal boosters) and QC key exchange does not work.
In the real world fiber optics lose photons, and you cannot send individual photons and reliably receive it at the other end.
Here (the space satellites) it likely also has no purpose, they could not ensure the single 'photon' is sent and received, it would be lost in the atmosphere, so there will be extra fixup signals. You could attack that extra-fixup too in a real world system, as well as the back channel. e.g. man in balloon intercepts the signal and sends a fake signal. He can't generate a real fake signal fast enough, so he generates his own. Did he guess right? No? Send the missing-bit signal and try again. Those sorts of attacks will likely be possible with their real world implementation.