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from the new-toys-are-all-made-in-china dept.
China has launched a satellite that will beam entangled photons to base stations on Earth:
China has successfully launched the world's first quantum-enabled satellite, state media said. It was carried on a rocket which blasted off from the Jiuquan Satellite Launch Centre in China's north west early on Tuesday. The satellite is named after the ancient Chinese scientist and philosopher Micius. The project tests a technology that could one day offer digital communication that is "hack-proof". But even if it succeeds, it is a long way off that goal, and there is some mind-bending physics to get past first.
The satellite will create pairs of so-called entangled photons - tiny sub-atomic particles of light whose properties are dependent on each other - beaming one half of each pair down to base stations in China and Austria. This special kind of laser has several curious properties, one of which is known as "the observer effect" - its quantum state cannot be observed without changing it. So, if the satellite were to encode an encryption key in that quantum state, any interception would be obvious. It would also change the key, making it useless.
(Score: 0) by Anonymous Coward on Wednesday August 17 2016, @02:25PM
I'm not a physicist but... (you know good stuff is coming now)
If a photon is both a particle and a wave, the latter behaving (conceptually) as waves of water
If I 'beam down' a photon
Doesn't that mean that the wave will cover a huge area on earth?
Now If observation of the wave 'collapses' the wave-function and basically makes the encryptors go "hnnggg... someone else is watching this, this is not secure" (basically the equivalence - if I understand correctly - of flipping a bit in a blob of encrypted data making the algorithm go "I can't decrypt this, something's wrong")
Wouldn't I be able to do a DoS this communication by just watching the wave anywhere on earth where the wave would hit?
Inquiring minds would like to know...
(Score: 2) by wonkey_monkey on Wednesday August 17 2016, @03:36PM
Doesn't that mean that the wave will cover a huge area on earth?
Nope. It'll be tightly focused. Has to be.
If it wasn't, for some reason, and you were able to detect a photon at some remote site, that wouldn't have been one of the ones that would end up being used in the encryption key anyway, as it woudn't have been received at the receiving station.
systemd is Roko's Basilisk
(Score: 2) by Capt. Obvious on Wednesday August 17 2016, @06:04PM
A single photon is both a wave and a particle. However, the spotlight from a flashlight is not a single photon/single wave. It is made up of tons of photons. In fact, one of the big concerns in this system is that multiple photons are sent for any given bit. Each photon can only be "read" once and cannot be reproduced (oversimplification, reproduction is accurate 50% of the time). But if you send 2 photons with the same bit, and I intercept one of them, then I can read that one and you cannot detect it.
You can DOS this communication by taking a similar laser, pointing it at the receiver, and turning it on.
(Score: 2) by maxwell demon on Thursday August 18 2016, @10:11AM
I am a physicist, so let me explain.
First: Yes, a wave spreads, but the spread can be controlled to a good extent. For example, a laser pointer emits a wave, yet if you pointed a laser pointer to the moon, you'd get a spot of merely 40 meters diameter. A satellite is much closer than the moon, so it should certainly be possible to limit the spread basically to the receiver.
Second: It is not really accurate to say that the photon is both a particle and a wave. Rather some of its properties are as we would expect particles to behave, and others are as we would expect waves to behave. But a photon is neither a particle nor a wave; it just shows behaviour we know of those. In particular, the wave-like behaviour only describes the probability of finding it at some place. So a photon you've found outside the receiver would not have found inside the receiver anyway, and therefore would anyway have been lost for key generation. So you cannot do a DoS attack that way. You could, of course, do a DoS attack by going in between the satellite and the receiver, but then it would probably be easier to just send your own photons to the receivers so that the entangled photons from the satellite no longer can reliably be detected.
Third: In typical quantum cryptography protocols, the photons don't transport the encrypted message, they are just used to generate a one-time pad that is then used to classically encrypt the message. One-time pads are provably secure (indeed, they are the only cryptographic method that is proven to be so), and all the quantum stuff does is to ensure that the pad is truly random, and that nobody but the sender and the recipient have the one-time pad.
The Tao of math: The numbers you can count are not the real numbers.