Position-Based Quantum Cryptography Proved Secure

KentuckyFC writes "Physicists have developed a new kind of quantum cryptography that uses position measurements to guarantee the security of a message. The technique is based on triangulation. Alice uses several transmitters to send messages to Bob who returns them immediately at the speed of light. If the return arrives within a certain time period, Alice can be certain that Bob is where he says he is. Physicists proved a few years ago that when the messages are purely classical this method is not secure because Eve can use any number of receivers to work out where Bob is and then use this information to trick Alice. However, the same physicists have now proved that the quantum version of the same position-based scheme is perfectly secure, essentially because Eve cannot easily measure the value of any qubits in the message. Alice and Bob go on to use the qubits to exchange a cryptographic key, a one-time pad, that they use to encrypt a message. The beauty of the technique is that a message encrypted in this way can be read only by somebody at a specific location, something that governments, banks, and the military, not to mention everybody else, may find useful."

Comments

nonlocal results and human weak links

[drDugan]

The position based exchange, of individual qubits, as describing in TFA is for key exchange, leading to a one-time pad . The interesting thing is that once the one time pad is securely created and delivered, the locality is then longer restricted, the " can then be used to send a perfectly secure message" from TFA can then be anywhere.

But from a security point of view, this is nice, but a major part of security holes don't come from technology, they come from personnel and the ability to trick people. Unless you completely restrict the physical location of the people, information encrypted this "perfect" technology still falls prey to human foibles. As stated in TFA " theoretical security is not the same as practical security"

Re:nonlocal results and human weak links

[blair1q]

If you look at WWII and the Cold War, cryptography was tremendously important.

It was even more important in WWI. The Germans had submarine warfare, and there was no sonar, making subs pretty much invincible. Germany also had a strong surface fleet. They succeeded in driving the Allied fleet out of the North Sea. They could have owned the entire ocean, cut off all trade and resupply of the Allies, taken Europe and then Britain, and then by degrees the rest of the world.*

But the British had captured a German codebook and were using it to track subs and ships, made easier by the German practice of daily radio communications (admiralties being groups of control freaks with politically motivated bosses, they tended to be clingy that way.) They still considered the North Sea dangerous, but were able to maintain a blockade by patrolling the Channel and the North Atlantic.

* - It's likely they wouldn't have had to "take" the U.S.; we at the time were isolationist and neutral, and in fact had welcomed a German submarine as heroes when she ran under the British blockade to get supplies from us. They used their biggest sub and gutted it for the trip, but the effectiveness was minimal so they never tried it again. The point is, if the British hadn't had control of the ocean, the Germans could have been trading with the world's prime source of natural resources all along while they were knocking down one nation after another, and America would have fed Germany right up until the moment Germany turned on America. Instead, the Germans got desperate, started attacking civilian vessels, sunk the Lusitania, disgusted us all, and put America on the side of the Allies, though it would be some time before we did more than supply them.

Re:nonlocal results and human weak links

[Bakkster]

I think we are getting to the point of over-emphasizing that fact, as if cryptography were unimportant. OK, this might not show up in Outlook Express. But there really ARE important applications for secure wireless transmissions, and there really ARE extremely professional and well-funded researchers on the "other side" who will use every algorithmic trick in the book to crack them. If you look at WWII and the Cold War, cryptography was tremendously important. Even the cryptographic attacks on "everyday" technologies like WiFi and ATMs available to the average script kiddie are quite impressive. So I wouldn't be too blase about cryptography not being the weak link.

The best part is that both weaknesses were used to break the Enigma cipher. They first exploited weaknesses in the cipher itself (letters couldn't be encrypted to themselves) and then weaknesses in the operators (the lazy Nazi would frequently choose Der Fuhrer's birthday for his cipher).

Hmm...

[fuzzyfuzzyfungus]

Could the work that has been done in "slowing" light be used to interfere with this?(or, more practically, since the speed of light varies based on the medium, would you need a completely accurate characterization of the contents of the light paths that the signal travelled over for your certainty to be valid?

On the plus side, this will finally provide a way for Bob to prove to Alice's satisfaction that he isn't with Eve, and Alice will be able to demonstrate the same about Mallory. Bliss through superior quantum physics!

general relativity destroys the security

[rubycodez]

this only works in a perfectly flat space-time, if unknown or changing (known or caused by hostile party) curvatures are present the whole thing falls apart

Eve's always been a trouble maker.

[fahrbot-bot]

Eve can use any number of receivers to work out where Bob is and then use this information to trick Alice.

I'm concerned that this Eve character keeps causing trouble. First for Adam, now Alice and Bob.

No, *not* proved secure.

[Daffy Duck]

From TFA:

"Unfortunately we do not have a security proof, and we leave it as an open problem to find an attack or prove its security," they say.

So how did the summary conclude "proved secure" from that?

Exciting news

[Vadim Makarov]

There are two things about this publication that make it remarkable.

1. This is a new useful information processing primitive that is only possible to do quantum, not in any classical information processing (the paper cites impossibility proof in classical domain). There's just a handful such quantum primitives known today (e.g., QKD, Shor's algorithm), so discovering one more is a great deal.

2. It is practically implementable with today's quantum crypto hardware. In fact, I expect any lab that has a working free-space QKD system can be working on an experimental demonstration of location-restricted QKD right now. It may just take some software rewriting and a couple extra wi-fi links to assemble a full 2D-location QKD scheme.

To be fair I must mention that the location primitive has been published two months ago by R. Malaney from Australia. However, his version was more difficult to implement (although also doable with today's experimental techniques), and notably it lacked QKD functionality. Now with this publication the scheme is complete and is even supplied with a security proof. My applauds to the authors.