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Encryption Security Science

Single-Photon LED: Key To Uncrackable Encryption? 228

Posted by timothy
from the morse-code-writ-small dept.
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."
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Single-Photon LED: Key To Uncrackable Encryption?

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  • by Anonymous Coward on Thursday December 13, 2001 @06:19PM (#2701696)
    The article is unfortunately a little light on details. The application of these devices seems to be for sharing key material for an OTP. Seems that it could be considerably more practical than the quantum entanglement of particles methods previously discussed.
  • by mbessey (304651) on Thursday December 13, 2001 @06:21PM (#2701708) Homepage Journal
    The line can't be tapped, because if you intercept the photons, you can't re-create the signal. Read an article on Quatum Cryptography.

  • by pryan (169593) on Thursday December 13, 2001 @06:28PM (#2701747) Homepage
    I've been following this technology with great interest. There seems to be a fundamental problem: it is point to point. Its applications will be fairly limited.

    It seems to me, at least in terms of networks, that this would really be used to secure lines between networks, clusters, or individual computers. But on today's public Internet, this isn't really an issue. Of course, I would rather use this technology than to not have lines protected with quantum indeterminism.

    Most security people are more concerned about platform security than link security. If this technology can be used to reinforce something used for platform security, then boo yeah! Otherwise, this is cool, but I'm not going to get a heart condition over it.

    The only platform benefit I see is reducing the need to perform expensive computations to encrypt and decrypt data. Let the link take care of that and thus increase performance. Of course, how many nodes on the Internet only want to talk to their nearest neighbor? And how many routers and such are between them and their nearest neighbor? It might not even be possible to secure the link between a node and its nearest neighbor in most cases.

    I doubt this technology will impact current Internet infrastructure all that much. We'll see.
  • Abstract (Score:3, Informative)

    by Aetrix (258562) on Thursday December 13, 2001 @06:32PM (#2701777) Homepage

    Here's the Science Magazine Abstract


    Electrically Driven Single Photon Source
    Zhiliang Yuan 1, Beata E. Kardynal 1, R. Mark Stevenson 1, Andrew J. Shields 1,Charlene J. Lobo 2, Ken Cooper 2, Neil S. Beattie 3, David A. Ritchie 2, Michael Pepper 3
    1 Toshiba Research Europe Limited, Cambridge Research Laboratory, 260 Cambridge Science Park, Milton Road, Cambridge, CB4 0WE, UK.
    2 Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, UK.
    3 Toshiba Research Europe Limited, Cambridge Research Laboratory, 260 Cambridge Science Park, Milton Road, Cambridge, CB4 0WE, UK; Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, UK.

    Electroluminescence from a single quantum dot within the intrinsic region of a p-i-n junction is demonstrated to act as an electrically driven single photon source. At low injection currents the dot electroluminescence spectrum reveals a single sharp line due to exciton recombination, while another line due to the biexciton emerges at higher current. The second order correlation function of the diode displays anti-bunching under a DC drive current. Single photon emission is stimulated using sub-nanosecond voltage pulses. These results suggest that semiconductor technology can be used to mass-produce a single photon source for applications in quantum information technology.

    -----End Abstract-----

    If anyone has access to Science Online ( you can download the PDF reprint at this link: here [].

  • NOT Uncrackable (Score:5, Informative)

    by MikeyNg (88437) <mikeyng@gmai l . com> on Thursday December 13, 2001 @06:37PM (#2701794) Homepage

    The application refers to its use in quantum cryptography. It doesn't render the encryption process uncrackable, but makes it able to detect that someone is eavesdropping and/or has broken the encryption. With current methods, you can't tell if someone has broken your key and read your message. Using quantum cryptography, you can tell when someone has read your message.

    (It all goes along the lines of you can't observe something without changing it. If someone along the way intercepts the message and observes it, they will change the message and you can detect THAT on the other end.)

  • by Anonymous Coward on Thursday December 13, 2001 @06:49PM (#2701847)
    1. 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.

    Actually, if the predictions of quantum mechanics are correct, this is not possible.

    The way that this works is not intuitive at all, so don't worry if you don't understand it. Einstein, Podalsky, and Rosen published a famous paper showing that quantum mechanics necessarily leads to these kind of effects.

    Their goal was actually to show that quantum mechanics was unacceptable as a physical theory because they did not believe nature could possibly behave this way. But as far as we can tell, nature really does work in these mysterious ways.
  • More accurately (Score:2, Informative)

    by parc (25467) on Thursday December 13, 2001 @06:57PM (#2701876)
    More accurately, Quantum encryption IS OTP. The quantum part comes in when you generated the pad.
  • Re:NOT Uncrackable (Score:5, Informative)

    by MWright (88261) on Thursday December 13, 2001 @07:03PM (#2701920)
    It is uncrackable.

    It does detect if someone is eavesdropping, but it detects it as the key is generated, not when you send the message. Your post implies that you send the message, and can detect if anyone eavesdrops... this is not the case. Two parties use these quantum effects to generate random numbers... they can detect if someone is eavesdropping on this; if someone is, they don't have to use that key (even if someone does try to eavesdrop, it won't work, by the way). Once they have this key, they can use it in One-Time-Pad encryption, which is also uncrackable (see a text on information theory for an explanation about why OTPs are uncrackable).
  • Re:NOT Uncrackable (Score:2, Informative)

    by MWright (88261) on Thursday December 13, 2001 @07:06PM (#2701934)
    Quantum computing and quantum encryption are two different things. Quantum encryption technically would not even need a computer at all... as long as you have some way of transmitting and receiving photons, and some way to detect them, etc., pen and paper would be enough (though very impractical!)
  • no (Score:2, Informative)

    by Anonymous Coward on Thursday December 13, 2001 @07:12PM (#2701963)
    No one ever said DES is uncrackable. No one (intelligente) has said, nor will ever say, that the new AES is uncrackable. No one (intelligent) has said, nor will ever say, that public-key cryptography is uncrackable. They will say the computations to crack them are "intractable", but not impossible.

    The one-time pad (Vernam cipher), however, is uncrackable. It has been used very heavily since it was first introduced (1917) and, beyond being arguably the simplest automated cipher ever devised, is still being proven to be completely 100% uncrackable. Unfortunately, since the key lengths are at least as long as the message, and the keys can only be used once, exchanging keys can be a bit burdensome. Quantum cryptography is basically concerned with ways of exchanging pads securely. If our current understanding of the Heisenburg principle is correct, then current quantum cryptography (in combination with OTP's) is 100% uncrackable.

    The failures of previous ciphers, especially public-key ones, is due to underestimating the difficulty (or "intractability") of certain computational tasks, but no one would have ever claimed that they were COMPLETELY secure, just secure ENOUGH. The Vernam cipher does not rely on computation (beyond addition mod 2), and is completely uncrackable.

  • Re:Glowing (Score:2, Informative)

    by QuMa (19440) on Thursday December 13, 2001 @07:33PM (#2702024)
    Actually, under the right circumstances the human eye can detect a single photon. However, due to the preprocessing done by the brain this signal doesn't actually reach any conscious part of your brain (for lack of better terms). But you don't need that many photon's, 10 or 20 should be perfectly detectable [] under the right circumstances.
  • Re:Man in the middle (Score:2, Informative)

    by zuvembi (30889) <I_charge_100USD_ ...> on Thursday December 13, 2001 @07:51PM (#2702129) Homepage
    Actually that is incorrect.

    You'll have to look for a description of it, but it is in fact in impossible to eavesdrop and then resend the information. There is a very good description in "The Code Book" by Simon Singh. I'm not sure where else you would look.
  • Re:NOT Uncrackable (Score:3, Informative)

    by MikeyNg (88437) <mikeyng@gmai l . com> on Thursday December 13, 2001 @08:32PM (#2702316) Homepage

    OK, that makes sense. Take my karma down a couple of notches for being incorrect. At least I *sound* like I know what I'm talking about. :)

    I was just incorrect on the implementation of how you'd use something like this. I can see how using this to generate and "send" OTPs makes it uncrackable. My bad.

  • by pc486 (86611) on Thursday December 13, 2001 @09:31PM (#2702529) Homepage
    "The Code Book", at least the british version, does describe that this unbreakable quantum encryption actually had several sucessful attempts befor this special LED appeared. I believe it was sucessfully done though the air at up to one mile. I would quote but since I'm moving the book is packed up. If you don't own the book, go buy it. It's a very good read.
  • by Mr_Icon (124425) on Thursday December 13, 2001 @09:48PM (#2702599) Homepage

    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."

    Uhm... I believe this is wrong. The book was issued in 1999, and it contains this sentence in chapter 8:

    In 1995, researchers at the University of Geneva succeeded in implementing quantum cryptography in an optic fiber that stretched 23 km from Geneva to the town of Nyon.

    Moreover, one paragraph further we see:

    More recently, a group of scientists at Los Alamos National Laboratory in New Mexico has once again begun to experiment with quantum cryptography in the air. Their ultimate aim is to create a quantum cryptographic system that can operate via satellites. If this could be achieved, it would enable absolutely secure global communication. So far the Los Alamos group has succeeded in transmitting a quantum key through air over a distance of 1 km.

    One of us is wrong -- either I'm reading this from an edited version of "the Code Book", although nowhere does it say "second edition", or the original poster needs to re-check his facts.

  • by hephro (166117) on Friday December 14, 2001 @04:24AM (#2703390) Homepage
    The experiments you cite were proofs of concept. In particular, they could not guarantee that their light source would only emit one photon at a time and hence they had very bad security (if the light source emits two photons, you can capture one and let the other go; the two photons are correlated and you can essentially use the stolen photon to break the protocol.)

  • by aqu4fiend (528775) <> on Friday December 14, 2001 @01:21PM (#2705247)
    You've made a couple of mistakes in your post. Although it's really cool to learn about Schrodinger's cat in freshman physics, once you get into the math of it, it's not quite as it seems. When physicists started examining quantum behaviour, they started with a certain frame of reference. Two very basic concepts in this frame of reference are the particle, and the wave. Light had been "proven" to be a wave phenomenon many years earlier by refraction experiments. However, all attempts to detect the medium through which it moved were in vain (see esp. Michelson & Morley). Einstein's work on the photoelectric effect (which earned him his Nobel Prize) "proved" that light was a particle phenomenon - light was composed of photons. The sometimes-particle-sometimes-wave nature of light is referred to as particle wave duality. Duality was also observed in other seemingly self-contradictory experiments (e.g. the oft-quoted double slit experiment).

    In introductory physics, this is where they tell you that light is a particle and a wave, then about Schrodingers Cat, and about Heisenberg uncertainty (the more exactly you know the position of a particle, the less exactly you know its momentum, and analogous relationships with wavelength, etc).

    Wow!, say all the young physics students. The world is inherently unknowable! Take /that/, determinists!

    Sadly, the young physics students do not understand. The paradoxes "explained" by the above arise from the fact that a photon is /not/ a particle. It is also /not/ a wave. It's something else. But it's really useful to describe as a particle - sometimes. Other times, it's useful to describe it as a wave. We have reams and reams of equations and theorems to deal with particles and waves, so when we can model a photon as one of them, life is easy. However, since both the wave model and the particle model are inherently wrong, if you set up an experiment properly, you can produce what seems to be a paradox. Heisenberg uncertainty merely describes the breakdown of the two models mathematically. Schrodinger's Cat is an /analogy/ only - it describes a phenomenon that only applies to things like photons and electrons.

    Interestingly, once you measure a particle/wave, you change it - since it is impossible to measure something without interacting with it. The first explanation most people hear is that when you measure a photon as a particle, there's something about a waveform collapsing, and it "becomes" a particle. This is easy to understand, but is, unfortunately, pure rubbish. If you measure it as a particle, you will get some results that are consistent with it being a particle, and you will change something about it. That's all.

    So to get to the encryption (although I'm sure this is already (-oo, offtopic)) here's how it works: find a particle that will change in some way measurable if snooped on. Have the sender and receiver each come up with a random sequence (polarizations). Using your photons, find the common choices in the random number streams. Now - if the photon is snooped on, (measured too early) you can tell. Even if you don't notice the snooping, unless the snooper picked the same sequence of common choices, (s)he's left with nothing. And that's the end of my post.

"Hey Ivan, check your six." -- Sidewinder missile jacket patch, showing a Sidewinder driving up the tail of a Russian Su-27