Single-Photon LED: Key To Uncrackable Encryption? 228
nut writes: "The BBC are carrying this story of new type of LED so precise that it can emit just one photon of light each time it is switched on. It has been developed by scientists from Toshiba Research Limited and the University of Cambridge. It is described in the journal Science, although I can find no mention of it on their website. One of the applications of this is supposedly uncrackable encryption, due to the law of indeterminacy. This application is described fully in 'The Code Book', by Simon Singh, although the method was only theoretical at the time the book was first published."
But it may still be hackable (Score:0, Interesting)
- The line can still be hacked, because it is possible to put a TEE into the circuit, just as long as STDOUT looks like STDIN.
- It may be possible to hack elsewhere, al la Magic Lanten.
- It would be very succeptable to stray photons, including those made by quantum effects...
Or am I wrong....Superconducting Fibreoptics (Score:2, Interesting)
Man in the middle (Score:2, Interesting)
It prevents people from reading the message then passing it on, but not from reading then generating an identical one. Admittedly this is a problem with all mediums, but quantum mechanics aren't the final solution yet.
mick
clearing up some confusion (Score:2, Interesting)
Me and my friend have previous shared a secret key, which is a random string of bits, of length 10. Now I wish to send my friend a message, a bitstring which is also of length 10. I take each bit from the key, and add it to the corresponding bit of the plaintext, modulo 2 (think XOR), to generate my ciphertext. e.g. if our key is 1010010101111010 and my plaintext is 1011110110101010, then my ciphertext is 0001100011010000. The key is then destroyed (for high security, it's stored on magnetic tape, then physically burned once used), never to be used again.
Now, let's say you have intercepted a message from me to my friend. The message is 1100101010000100. The only things you know about the secret key used before are: (1) it has never been used before; (2) it as a random (and uniformly distributed) smattering of 1's and 0's. Now tell me: what was the original message?
Unless public-key cryptography, it is not prone to "key attacks" (since you have no public key to work with). Unlike other symmetric-key (aka secret-key) cryptosystems, you have no frequency analysis or algorithmic analysis to work with. So long as you don't know any of the bits of the key, it is literally uncrackable, and has been for the past 80 years.
So, then the question is, how do you and your friend decide on a key? It's not easy. The best way, so far, is to physically go to your friend's house, make sure no one else is around, generate a random bistring, copy it onto two tapes (your friend keeps one; you take the other home), and keep it safe until it's time to use it.
What quantum cryptography does is lets you send a key to your friend over a long distance. But, do to quantum mechanics, you and your friend will be alerted if someone has intercepted it.
Nothing's really changed substantially here. It's the same uncrackable cipher that's been uncrackable for the past 80 years. The only difference is that now you can generate keys with your friend over a long distance, without having to drive to his house.
Re:Uncrackable encryption HOWTO (Score:3, Interesting)
Uncrackable encryption is nothing new; the problem is produicng the large sequences of random data (one time pads) and distributing them securely.
As the old saying goes, "if you have a secure way to distribute the key (pad), why not use it to distribute the message..?"
Cheers,
Tim
Re:law of indeterminacy?? (Score:4, Interesting)
Look up "Schrodinger's Cat" at everything2 or google. Prepare to have your head explode. It sounds like the physacists have been reading too much zen.
There are a few ways I like to explain it:
Q: does a tree falling in the forest make any sound if nobody's there to hear it?
A: The tree doesn't fall in the forest, but also doesn't not-fall in the forest if nobody's there to hear it.
It's almost as if God is lazy and doesn't figure out what's going on all over the universe until someone checks to see what happened. Most of the time, there's enough watching going on that things happen normally. However, if you set up experiments to be isoled and unobservable enough, strange things happen and you can catch God being lazy.
In the world of quantum, thing can be in a state of quantum superposition. Schrodinger made up a little story to explain the idea. Suppose you are about to keep things from disturbing a cat in a sealed box. And suppose you were able to isolate the Cat from observation. And suppose that you were to place a radioactive source in the box and a time and some poison, such that if the radioactive source underwent decay within a certain ammount of time, the poison would be released, killing the cat. Forget for the moment that we can only achieve this kind of isolation on very small scales.
Now, according to quatum mechanics, the cat's state of being alive or dead is entangled with the state of decay of the radioactive source. The really wierd thing is that the way things work in the quantum world, the radioactive source has both decayed and not decayed. It's a quantum supoerposition. Due to the entanglement, this means that the cat is both dead and not dead at the same time. Only when you observe the contents of the box does the superposition collapse into a definate state. So, as soon as you open the box and look at the cat it has either been hungry for the past hour or dead for the past hour. One second earlier, it has actually been both hungry and dead. It's really goofy. Supposedly Schrodinger later wished he had picked a better story, but now we're stuck with Schrodinger's demented story of a quantum entangled cat.
This is really how things work in the world of quantum... kinda.
The way Feignman (sp?) describes this phenomenon in his book "QED" is through a variation on the classic double slit experiment. In the double slit experiment, you have a monochromatic light source (all of the photons have the same wavelength), and a barrier with two slits in it. Due to the wave properties of all particles*, including photons, the "light waves" go through the split, and come out the other side as two sets of waves that create an interference pattern. In come places the waves line up and create double-bright spots, and other places the waves are 180 degrees out of phase and absolutely no light arrives. Suppose you were to try this experiment with single photon emitter instead of the continous light source, and throw in a way to make sure the photon goes through one of the two slits and is directed toward your photodetector. Obviously the photon goes through one slit or the other, not both. Unfortunately, in this case the obvious is wrong. If you put a photodetector at a point where the photons comming from the two slits cancel eachother out, you find that the single photon somehow goes through both slits simultaneously and cancels itself out! This is strange to say the least. Suppose then you decide to investigate further by taking a detector that will detect if a single particle has passed through it, but not block the single particle. Such detectors supposedly exist. You find that half the time the photon goes through the slit you're watching and half the time it goes through the other slit, bit it always arrives at the far detector. So, ths photon never arrives if you don't check which slit it went though, but if you check which slit it went though, it always arrives. The photon acts diferently when you watch it! I think the example makes more sense if it's described with an electron, since electrons can be attracted to the detector. Feignman may have actually used an electron is his example. It's been a few years since I read QED.
The standard way to interperet this whole thing is that the particle is in a superposition of going left and going right unless you force it to be in one state or the other by measuring it.
The whole crypto aspect comes in when you devise schemes where there are two ways of measuring something. If you measure in one way, you get the right answer, if you measure in the other way, you get complete garbage. The most practical way to do this is with the polarization of a single photon. If you send a photon in a calcite crystal, it takes one path if it's polarized along the crystal grain, and another path is it's polarised perpendicular ot the crystal grain. If the photon comes in polarized 45 degrees to the crystal grain, it has a 50% chance of comming out in either spot. You put a detector at each spot and see which way the photon came out in order to detect polarity. You use this to do secure key exchange in the following way: the sender randomly picks to send each photon polarized in one of four orientations (vertically, hozontally, and two ways diagonally.) For each photon, the reciever randomly decides to orient his detector rectilinearly or diagonally. After measuring each photon, the reciever tells the sender which of the two detector orientations he used. The sender then tells the reciever which of the two detector orientations should have been used. The correct orientation reads the polarization correctly, the wrong orientation is 45 degrees to the photon's polarization and spits out complete garbage. Since you can's split a photon, you need to measure it one way or the other, not both. After the sender and reciever have talked about the detector orientations, they know which bits were received correctly and use those bits as an encryption key (probably in something like a one-time pad). Note that an attacher can bug the line and observe the photons, but in doing so his calcite crystal ends up aligning the polrization of the photon to be consistant with the measurement. An attacker needs to keep transmitting bits to the reciever, but half the time he's reading garbage bits and re-transmitting garbage bits. The sender and reciever will notice when 25% of their key bits are incorrect and know that they're being snooped on.
* I had to calculate the wavelength of a flying golfball once (thank you MIT freshman physics). The wavelength of any particle is a constant times one over the momentum of the particle. A golf ball has a hell of a lot smaller wavelength than any observed photon, due to the extremely small ammount of momentum carried by any routinely occuring photon seen on Earth.
Detecting a single photon using FET (Score:2, Interesting)
Andrew Shields and others released a paper [cam.ac.uk] last year on possible use of normal FET technology in conjunction with a layer of "nanometer-sized quantum dots" for the detection of a single photon. I'm not sure that the method he demonstrates there could be adapted to commercial scale crypto, but it certainly seems to be a possibility.
I'm no expert, and Shields' comments on problems of attenuation in fiber transmitters may render the unique selling point of quantum crypto (that snooping can be detected) moot, but it still looks very promising for such a young idea.