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Single Photons Bounced Off Orbiting Satellite
KentuckyFC writes "If we're ever going to benefit from the perfect security of quantum communication, we're going to need ways of transmitting entangled photons around the globe and certainly further than the current record of 144km through the atmosphere. Anton Zeilinger at the University of Vienna and colleagues have taken an important step towards this by bouncing individual photons off the Ajisai geodetic satellite (essentially a space-based disco ball) which is orbiting at 1400km. The group says the experiment is an important proof of principle for satellite-based quantum communications."
Not to mention photons are like words: you shouldn't use those you don't understand. Is it a wave or is it matter? Huh, Mr. Smarty Pants? Oh, what's that you say? A boson followed by a long explanation, how utterly predictable! Ha, you would say that. No. I want answers and I wanted them back when the church would persecute you for publishing them!
We need something smaller. Go back to the lab, anything larger than a Planck Length is unacceptable. And only 1400km? So help me god, if you can't express the distance it travels in double up arrow notation or tetration, I don't want to hear about it. Come on people, this is real science, not some religious mumbo jumbo (6,000 years? Is that the absolute limit of your imagination!?)
My work here is dung.
There's no place like localhost
This is just an elaborate game of pong, isn't it...
I record my sleeptalking
From my understanding it does serve a practical purpose in that intercepting the message changes it. Thus while you can't stop people from tapping into your message, you do have instant feedback about when that happens.
I am Slashdot. Are you Slashdot as well?
Real security improvements. There is no proof that there is not a trivial way to factorise multiples of large prime numbers, which is the basis of most current encryption standards. There are alternatives, but again there is no proof that these cannot be cracked quickly.
;-)
Even though it is unlikely that someone will have a mathematical breakthrough that would allow your PDA to break 2kb keys, we know that a lot (maybe all) of these algorithms could be cracked with a quantum computer. It is possible that the US NSA already has such a computer, maybe together with Russia, China and Bill Gates
Quantum encryption is proven to be uncrackable without showing that someone is listening. With a preamble of two-way communications you can have a connection that is proven to be absolutely secure, and no breakthrough in mathematics or technology will break it.
People are still puzzling over how the world's largest rave got started. It seems that once a light show started from what appeared to be a giant disco ball in space people everywhere got out their glow sticks, drugs and pacifiers and started dancing.
You are using English. Please learn the difference between loose and lose; they're, there, and their; your and you're.
Breaking quantum cryptography is not hard, it is impossible. The security is guaranteed by the laws of physics. Unless quantum mechanics is flat out wrong, it can never be broken, period. And saying quantum mechanics could be wrong is like saying gravity could be wrong.
About quantum computing, it's actually closer to providing new computational powers than you might think. In terms of a powerful, programmable computer that can factor large numbers, we are a long way off. But in terms of being able to simulate certain quantum systems that current supercomputers cannot, we are fairly close.
Intercepting (and breaking) quantum crypto is very much so possible. If Charlie intercepts Bob's fotons on their way to Alice, and Charlie can transmit the very same fotons he just recieved, he can intercept the message succesfully without Alice or Bob ever noticing (perhaps a lag because Charlie has to do some work before he transmits). What Charlie cannot do is old style wiretapping: every foton is a carier of one bit and reading it causes the bit to flip and thus Alice knowing the line is tapped. Reading the foton, throwing that foton away and sending another foton with precisely the same orientation/spin as the foton he recieved to Alice will be undetectably. Never mind that in practice not now and probably not you can have 1 foton = 1 bit, but you'll need a group of fotons = 1 bit. And when there's a group, there's room to play for a wiretapper.
I refer you to the no cloning theorem. And you are correct, that in practice there is a probability that there can be more than one photon per bit sent. However, there are ways of correcting for this such as privacy amplification. The guys who are doing this stuff are smart. They know what they're doing. Physicists don't throw around terms like "provably secure" lightly.
The German Enigma machine from WWII was fairly uncrackable, even for the decoders at Betchley Park, but the German operators got lazy, and weren't following proper procedures, which allowed Turning et. al. to get a toehold into the crack.
The One Time Pad is provably unbreakable, but the British were able to decypher Soviet OTPs, because they had reused the pads after a year, thinking no-one would go back that far. One of our Admirals did the same thing, but there's no evidence he got caught.
The obvious back door to a quantum crypto machine would be the operator, or some part of the process before the plaintext is encrypted. Just because physics says that the process is unbreakable, doesn't mean the machine can't malfunction, and the malfunction may not be detectable by the operator. i.e. perhaps the machine can detect any malfunction, but the indicator light that tells the operator is broken.
Even though OTP is provably secure, the military proceeds and ends each message with gibberish, to throw off attempts at decoding.
All ideas^H^H^H^H^Hprocesses in this post are Patent Pending. (as well as the process of patenting all postings)
"You need the photons to be "entangled". That means effectively in their own little world, not intereacting with the universe in any way."
What are you smoking? Where did you get that definition of entanglement?
Read up on the topic.
Pay special attention to the "faster than light discussion" parts to see why they need to send the photon.
) Human Kind Vs Human Creation
) It'd be interesting to see how many humans would survive to serve us.
Oh great...
I can't wait until someone at the RIAA figures out how to protect music with quantum DRM. You get to listen to a song ONCE, then it doesn't exist anymore.
They will charge PER listening.
- For the complete works of Shakespeare: cat
Hi,
I am a theoretical particle physicist, and I understand what you are trying to say, and I understand what the replies are saying as well.
You are correct that the 'basic' quantum cryptography that is taught can be hacked. This is just because a simplified version is used in books, because it's confusing enough.
Others who point out the no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization (for example). Basically the way it work is like this:
Alice picks one of four polarizations at random, out of vertically polarised (0 degrees, say), horizontally polarised 90 degrees), or polarised at 45 degrees, or at -45 degrees.
Bob then picks, at random, whether to measure the polarization horizontally/vertically or to rotate his polariser 45 degrees and measure at 45 degrees or at -45 degrees.
If Bob chooses the 'wrong' direction, he'll get a random result. If he chooses the 'right' direction, then he'll get the correct result. After this is done, Alice tells Bob how she sent it, and Bob can discard all the measurements in which he chose the wrong direction to measure in. If Bob tells Alice the same results that Alice sent, then they know there was no interference.
There is no way to measure the 'true' polarization of the light that Alice sent, because you have to have your polariser either measuring horizontal/vertical, or measuring at 45/-45. You can't have it do both. So noone can monitor and then reemit a photon with the same polarization.
Others have created quantum crypto systems that take the possibility of cloning into account, http://w3.antd.nist.gov/pubs/Mink-SPIE-One-Time-Pad-6244_22.pdf
'basic' quantum cryptography that is taught can be hacked This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve). I haven't heard of a way to do this without falling back onto more conventional cryptographic techniques such as RSA signatures - at least when doing quantum crypto over fiber. Maybe sending photons through the atmosphere means you can actually just see if somebody is acting as a man-in-the-middle.The satellite is covered with retroreflectors, aka corner cubes. It is a property of three perpendicular planes that any light is returned along its incident path. Reflectors are used on bikes and cars, and highway signs (and high-gain front projection screens).
http://www.af.ca/halifax/sciences/gim/LAGEOS-NASA.jpg
The sphere, LAGEOS, is covered with corner cubes. For scale, I think it's about 60cm in diameter. To send a single photon up and receive it is amazingly accurate, and lucky. Divergence of a laser results in many orders of magnitude loss of signal over those distances. I believe we know the orbits of these inert satellites to better than 5cm, at least we did two decades ago when I worked on TLRS and MOBLAS station stuff at Goddard. We would send 200 ps pulses (Nd:YAG laser) and then gather the returns in a telescope - sometimes of only several photons out of the entire pulse - which were then used to calculate time-if-flight and determine the exact location on earth. This was done to track motion of the tectonic plates.
Is it just my observation, or are there way too many stupid people in the world?