Position-Based Quantum Cryptography Proved Secure 45
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."
Exciting news (Score:3, Informative)
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 [arxiv.org] 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 [arxiv.org] 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.