back to article Location-based quantum crypto now possible, boffins say

Researchers say they have devised a foolproof way to encrypt messages that can be unlocked only by a recipient physically located in a specific place, solving a problem that has vexed cryptographers for years. The technique for position-based quantum cryptography is scheduled to be presented at the 2010 IEEE Symposium on …


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  1. I didn't do IT.

    Electron Pairing, anyone?

    What happened with the wild claims that Electron pairing would circumvent the need to transmit messages over ANY network whatsoever?

    Two electrons, paired, would provide the ability to "flip" one and the other would automatically flip in sympathetic order. While the data rate may be less than a T1, it would be impossible to intercept and would be completely undetectible in its "transmission".

    Not only that, there was quite the speculation that it would happen instantaneously - no matter the distance (thereby circumventing light speed restrictions on data transfer).

    What happened to all of this?

    1. Gary F

      Pair 8 to sent 1 byte at a time

      I remember that. I also saw the Christmas Lecture on quantum mechanics that demonstrated this, although very crudely. It's still a theory I think so please allow 20 years for a real device to appear.

    2. D.B.


      "Not only that, there was quite the speculation that it would happen instantaneously - no matter the distance (thereby circumventing light speed restrictions on data transfer)."

      This line says to me you've probably got something wrong. Or the claims were indeed wild.

      Are you sure you're not thinking of quantum entanglement of photon pairs, as a method of generating secure keys? If so then we can't circumvent the speed of light - the photons still have to be exchanged. And once exchanged we cannot "flip" them to send a message. Rather they can be used to generate a random shared key, which can then be used to send our real message (again, at less than the speed of light). The attraction is that it is impossible* for a third party to intercept the key when it is being transmitted without our noticing.

      *under certain assumptions which may not be true in the real world

    3. Ru

      Re: Electron Pairing, anyone?

      > Not only that, there was quite the speculation that it would happen instantaneously - no matter the distance (thereby circumventing light speed restrictions on data transfer).

      You can't send useful information faster than the speed of light. Reality doesn't appear to work like that. Perhaps you're thinking of quantum superdense coding which allows you to significantly increase the bandwidth available from more mundane communication channels, but you still can't send a message any faster than the speed of light.

      The two halves of the electron pair (or indeed any other quantum bit carrying medium) must be *together* when entangled, so you have to send one half of the pair away with the person you're communicating with.

      They can then perform some operation on it, and send it back to you. The trick is that the quantum state can hold more bits of quantum information than it can of classic information, thus increasing the bandwidth of the channel. Furthermore, interception of the bit in transit gives no useful information at all, because both halves of the state are required for useful decoding.

      You're still having to send 2 bits out and 2 bits back for a total of, say, 4 bits of useful information exchange, but compared to one-time pads and the like, superdense coding is much higher bandwidth (which would only send 2 bits of useful information in this case).

      > What happened to all of this?

      Was never possible. General relativity puts serious limits on the number of awesome sci-fi toys and tools that can exist in reality.

      Stopping quantum decoherence and related issues is why we don't have commercial quantum computers and communication lines... its pretty tricky stuff. Easier than fusion though, I reckon, so maybe its only 20 years off? :o)

      > TL; DR

      GBT physics class. No FTL communications for you, ever.

    4. Anonymous Coward
      Anonymous Coward

      @Electron Pairing, anyone?

      I seem to recall there was a story (mabe here on the reg) a while back that someone had proved by experiment that instantaneous quantum entanglement can occur.

      something about doing it over a few KM of distance. I was a bit sceptical as it was just the one story and I would assume that the fact that someone had proved Einstien wrong would have attracted more attention than just one small story.

      Anyone know what came of this?

      1. D.B.

        hmm again

        Nothing about quantum entanglement proves einstein wrong.

        Imagine for a moment that you and I start out standing side by side in the middle of a very long road. A trustworthy third person gives us an envelope each, and tells us that both envelopes contain the same randomly generated message. We then set off walking in opposite directions away from each other along the road. At a pre-arranged time we stop, open our envelopes, and read the message contained within. 'Instantaneously' I know exactly what message you are reading, no matter how far apart we are. But no information has travelled faster than light. In particular, the fact we are both instantly reading the same message does not let me instantly communicate any new information to you that was not originally in that message (e.g. anything interesting I've passed as I walked down the road). We can't even choose what the message in the envelope says - the trustworthy third person always does that, and it's always random.

        This scenario corresponds very very roughly to a 'latent variable' model of quantum entanglement. Bell's theorem says that such models cannot explain all the predictions of quantum mechanic, but they're still pretty useful as an approximate way to visualise situations like this.

        (Any people who actually study this stuff want to point out the mistakes I've made above? I'm always intersted to hear them :D )

    5. Daniel B.

      Action at a spooky distance

      If I remember, this is the "Einstein-(something)-Paradox" and is referred to in the Xenosaga game. It is based in the fact that entangled particles would always have an opposite spin with the same speed & such; measuring one of the particles would give you automatically the measure of the other particle, even if it is light-years away. Theoretically, altering the spin on particle 1 would alter the spin on particle 2 *instantaneously*, so that it could work as an FTL comms link.

      Of course, this is all theoretical.

  2. Anonymous Coward
    Anonymous Coward

    Oops I bumped the computer

    Oops I bumped the computer.

    There may be stuff related to electron pairing happening at the LHC, but I'm pretty sure that the ansible tech is still quite some way off.

    1. Charles Manning

      Well it moved anyway...

      The earth surface + computer is revolving the centre of the Earth at approx 300 metres/second.

      The Earh moves around the sun at approx 9500km/sec

      And the sun is moving through space at ???

      So what's the chance of you ever being in the right place to decrypt the data?

      This sounds like a very cool way to siphon up DARPA funding without ever being stuck in the position that you can be proved wrong.

  3. This post has been deleted by its author

  4. Paul 129

    Lab stuff

    "The main technique for such a protocol is known as distance bounding"

    Im sure im missing something, but if it means an evesdropper just needs to match the cable length....

    Mines the one with the large reel of fibre

  5. Nick Kew

    Time-based too?

    I once encrypted a message that could only be read on April 1st.

    1. Gannon (J.) Dick

      Wow, Synchronicity

      I once encrypted a message, but I forgot what it was now.

  6. Mystic Megabyte


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    * 9XDxm7D5xn

    * vCB8djoLn7

    * vrDQpfnnhg

    * hpzU66Pasg

    * 5ui6QCzFxX

    * nsopgGRQJB

    * tXwJSo32pT

    * SOn1blupNw

    1. Lionel Baden
      Thumb Up


      i just woke up the wife laughing !!! thanks !!

  7. Lou Gosselin

    Don't get it.

    "The task of verifying a recipient's location involves sending the quantum equivalent of bits using a protocol that requires the receiver to respond to random challenges. The so-called no-cloning principle of quantum mechanics makes impossible for people elsewhere to provide the correct answer."

    I'm obviously missing a key piece of info. What's to prevent someone responding to the random challenges from a physically different location?

    The quantum bits, as I understand it, cannot be intercepted without modification by a man in the middle. However, by itself (without traditional authentication keys), a man in the middle is still possible when the impostor pretends to be both end points such that each end point is security connected to the impostor. The impostor can act as a relay, while snooping the traffic.

    I guess we'll find out when this is presented, but it sounds like the claims in this article are a little off base.

    1. Ken Hagan Gold badge

      Re: Don't get it

      I skimmed the PDF and I think the article should have mentioned response times. The idea seems to be that the round-trip time for responding to a challenge has a lower limit dependent on the distance between the parties. I didn't see any discussion of whether you then need to build up a "web" of trusted parties to "triangulate" with, but it might be there (or in one of the referenced papers).

      The claim, then, is that you can then couple this property with the "no undetected tampering" property of quantum messages to produce a tamper-proof triangulation of the location of the other party.

  8. Anonymous Coward


    you could still plant a bug at either end,

    listen in with a laser mic,

    because it could use insecure lines, you could tell them "it's encrypted honest" after disabling the computers and installing a permanently green LED,

    send round a Russian estate agent to see if anyone's interested in buying a flat (actually that probably wouldn't work),

    get the motherboard built in China,

    send one of the computer operators a PDF,

    or download the transcripts from wikileaks.

  9. DT

    it's late, but

    @I didn't do IT.

    possibly you're confusing entangled electrons with entangled photons.

    @Lou Gosselin

    "I'm obviously missing a key piece of info"

    The key piece of information was in the piece "no cloning" as well as the linked PDF.

    The imposter can't act as a relay without breaking the laws of physics -collapsing waveforms and all that. Due to Q.E. the sender would be able to tell the message had been read.

    "it sounds like the claims in this article are a little off base"?

    Seriously... first you concede a lack of understanding, then you cast aspersions on the claims?!!

    Welcome to the future where "everyone is entitled to an equal opinion"! It's visible on a daily basis within the New Scientist comments sections... high school grads attempting to pick holes in PHD research (or rather a journalist's summary of it!) Why can't people just say "I don't know enough about this subject to make any kind of value judgement".

    1. Lou Gosselin

      Re: it's late, but

      I'm not sure if you've thought about this sufficiently. You wrongly assume that I just dismissed the quantum entanglement.

      The claim I'm doubting is that the device will only work from a specific location.

      If this were true, even the owner shouldn't be able to fake the location any more than a thief. However, what would stop someone from moving the crypto device, possibly putting a fake in it's place, then acting as a relay between the fake and original locations?

      Obviously latencies can change, but as long as the device is moved closer to the other party and/or uses a more direct network, then artificial latency can be introduced to match the original. Even just a 5ms jitter can mean a 1000 mile discrepancy by the speed of light. To get 1 mile accuracy, the jitter has to be constrained to 0.005ms. So switched networks are clearly ruled out.

      Even on complete circuit networks, there's still the problem that public networks are rarely "line of sight", the thief could almost certainly find a shorter path than the original. The resulting slack means that he can change locations without this being detected.

    2. Henrik Madsenh

      common mistake

      "possibly you're confusing entangled electrons with entangled photons."

      Yes, I do that all the time...

  10. Anonymous Coward
    Thumb Up

    How wide is the range?

    I mean if it's just literally "the receiving computer has to be on the right side of this desk" then it's just about useable. If it's "breathe heavily on the computer and you've moved it out of range" then its' almost useless.

    Couldn't you do a "budget" version using NMEA strings? Use 2 or 3 strings as a key- making regular brute-forcing a pain. Maybe have another layer of encryption over that to make sure that someone couldn't just be literally in the right place at the right time. Then have the decrypting station equipped with GPS and get it to brute-force the NMEA encryption using the known parts of the string, coupled with a lookup table populated with the values of all lats/longs/alts/etc of the surrounding area?

    Stick to a set format and it'd become very easy to brute force- if you knew what you were looking for and where the message was intended to be received.

    Quantum location encryption sounds great, though!

    1. Jimmahh

      It's worse than that... they've moved Jim =P

      Hell, if the allowed area is small enough continental drift starts to become a problem with long distance calls ;-)

      That'd be interesting to try and have to explain to a room full of generals suddenly looking a blank screen mid-sentence if you forgot to take it into account...

  11. amanfromMars 1 Silver badge

    The Speed of Thought Instantly Smashes Light Speed Limitation to Travel to Smithereens

    "While the research solves an important problem, it's unlikely to see practical applications anytime soon, crypto and security expert Bruce Schneier said.

    “Don't expect this in a product anytime soon,” he blogged. “Quantum cryptography is mostly theoretical and almost entirely laboratory-only. But as research, it's great stuff.”"

    I take it with that statement, Bruce, that you do speak for BT, which has all ITs Future Processing Information and Artificial Intelligence, Quantum Encrypted..... for Provision of Cyber Security to All Random Right Royal and Regularly Irregular Rogue Exe User .... Vigilant and Venerable and Virulent Independent Non State Actors ...... Masters and Mistresses of the Virtual Domain with their Alternate IT Reality Fields ......... Media Concoctions ...... Bigger Pictures.

    A New MasterPiece Big Picture would provide infinite new trails and tales of its novel source provision, and fed from the Kernel Base direct into Processing Heads for Enrichment, quickly eliminates Base Frailties and re-energises Prime Core Stock with SMART Natural Trickledown to what would then Create an Elevated Base Supply Level with Smart Leadership, Top Down Virtual Machine Supplied, Administered and Maintained with Mentoring and Monitoring to Highly Accommodating Space Protocols in Command and Control Projects into IntelAIgent Community Enterprises.

    There's a lot going on, out there ..... take care, with your dare ware, if it is buggered up scareware, with infected deep codes/dodgy binary numbers ...... for they can deliver the Phanton Ghost of your Dreams and a Nightmare of a Trip to ..... well, Helter Skelter land is a modest enough cloak in which One can Surmise. .......

  12. Rob O'Connor

    But but but...

    What happens if, say, the attacker is on the floor above the intended recipient? You mention geographic location but not necessary in 3 dimensions. What's the granularity of the method of determing position?

  13. TeeCee Gold badge

    'ang on a minute

    Surely if you know where the sender is and that they're stationary you can't decrypt their message without killing their cat?

    Or something like that, it's all quantum you know.

  14. Anonymous Coward
    Anonymous Coward

    "I don't know enough about this subject"

    I don't know enough about this particular subject to make any kind of value judgement yet.

    But I know enough to be mildly amused when I see a Microsoft employee's name on a paper about security, and location-based stuff.

    "Windows Genuine Advantage has determined that you have moved this system since you last updated your licence records. Please contact Microsoft to update your records again (and have your credit card details to hand)."

  15. Anonymous Coward

    Location based.

    Theoretically, will it still work in the UAE or Saudi?

  16. Anonymous Coward
    Anonymous Coward

    My first thought

    was the article a couple of hours earlier entitled "Hack uses Google Street View data to stalk its victims" “This is geo location gone terrible”.

  17. Kubla Cant

    Yeah but no but

    Key distribution may be a problem with static recipients such as embassies and HQs, but the real problem, Shirley, is distributing keys to mobile units like forward command posts and spies.

    I don't know what I'm talking about and I can't be bothered to read the PDF, but does this mean you have to know exactly where the recipient is before you can send an encrypted message? Or is the key created when the link is established, in which case it sounds like it would be vulnerable to spoofing.

  18. Wize

    Locations can be faked.

    GPS systems have been proven to be susceptible to attacks letting them think they are else where, so could fake a location from that.

    If we are talking connection across the internet, then the guy next door, with a box delaying transmission (delaying data packets) could pretend to be the other party, eg your bank, and steal your login then tell his mate who is next door to the bank with a similar setup to empty your account.

    Or have they got something more magical?

  19. trottel

    Location based?

    ...on a spinning planet in a traveling, spinning solar system, in a traveling, spinning galaxy... yeah, right. Makes sense to me. *Distance* based maybe...

  20. Anonymous Coward

    Inferring the location

    OK. Maybe you can't decrypt the message (if you're say, the enemy) but I wonder how much brain-bending maths is required to work out the precise location of both parties of the intercepted quantum message? If you can infer these locations then they can be destroyed physically and fairly instantly. This would mean that it doesn't MATTER what the message contains as long as the recipient and the sender are destroyed in the process (nullyfying the immediate usefullness of the information whcih can also be decoded later at your leisure just in case it's got anything interesting in it).

    I would advise anyone against relying on the uncrackableness of their communication systems, especially in wartime - remember Enigma...

    Grenade cos it's war-stuff

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