Towards 'unbreakable' message exchange

Aug 03, 2012
Towards 'unbreakable' message exchange

Single particles of light, also known as photons, have been produced and implemented into a quantum key distribution (QKD) link, paving the way for unbreakable communication networks.

The results of the experiment, undertaken by a close collaboration of researchers based in Wuerzburg, Munich and Stuttgart, have been published today in .

The single were produced using two devices made of semiconductor nanostructures that emitted a photon each time they were excited by an . The two devices were made up of different so they emitted photons with different colours.

QKD is not a new phenomenon and has been in commercial use for several years; one of its first uses was to encode the national election ballot results in Switzerland in 2007. The techniques currently being used on a commercial scale rely on lasers to create the source of photons; however, researchers hope to further increase the efficiency of QKD by returning to the original concept of using single photons for generating a secure key.

One of the project coordinators, Dr Sven Hoefling, said: "The nature of light emitted by lasers is very different from light emitted by single . Whereas the emission events in lasers occur completely random in time, an ideal single photon source emits exactly one photon upon a trigger event, which in our case is an electrical pulse.

"The random nature of emission events from strongly attenuated lasers sometimes results in the emission of two photons very close to each other. Such multiple photon events can be utilized by an eavesdropper to extract information.

"Single photon sources, such as the ones used in our study, are predestined for use in the systems using protocols."

QKD is a process that enables two parties, 'Alice' and 'Bob', to share a secret key that can then be used to protect data they want to send to each other. The is made up of a stream of photons that 'spin' in different directions – vertically, horizontally or diagonally – according to the sender's preferences.

The laws of physics state that it is not possible to measure the state, or 'spin', of a particle like a photon without altering it, so if 'Eve' attempted to intercept the key that was sent between 'Alice' and 'Bob', it would become instantly noticeable.

In their experiment, the single photons were produced with high efficiency, then made into a key and successfully transmitted from the sender to the receiver across 40 cm of free space in the laboratory.

The researchers are aware that to make this experiment more practical and commercially viable, it needs to be scaled up so that quantum keys can be sent over larger distances. To do this, quantum repeater stations need to be incorporated into the network to 'amplify' the message.

"Meanwhile, quantum keys have been sent over 500 metres of free space on top of the roofs in the centre of Munich, Germany. Several projects have also been funded to develop this technology further," continued Hoefling.

Explore further: Physicists discuss quantum pigeonhole principle

More information: "Quantum key distribution using quantum dot–single photon emitting diodes in the red and near infrared spectral range" Tobias Heindel et al 2012 New J. Phys. 14 083001, iopscience.iop.org/1367-2630/14/8/083001/article

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packrat
1 / 5 (1) Aug 04, 2012
How can you have a repeater if anything done to the photons changes them and makes the message unreadable?

daywalk3r
1 / 5 (4) Aug 05, 2012
How can you have a repeater if anything done to the photons changes them and makes the message unreadable?
The "repeater" absorbs the former photon and re-emitts a new one.

What worries me more though.. Why is Eve being put in the role of a man? (in the middle) xD

This however still isn't even close to providing 100% "unbreakable" data exchange. It just shifts the focus of "Eve" from a cheapo man-in-the-middle key/data interception role, to a more sophisticated weak-point exploiting one.

And the weak-points in this case becomming exactly those repeater stations and/or any photon-electron interfaces along the data path.

In the end, Eve is probably going to get the keys directly from Alice or Bob anyway, without them even knowing about it..
Bewia
not rated yet Aug 05, 2012
..quantum key distribution (QKD) link, paving the way for unbreakable communication networks...
There is a possibility that an unauthorized person can extract the key without being discovered, by simultaneously manipulating both the quantum-mechanical and the regular communication needed in quantum cryptography.
'Unbreakable' Quantum Cryptography Broken
antialias_physorg
1 / 5 (1) Aug 05, 2012
And the weak-points in this case becomming exactly those repeater stations and/or any photon-electron interfaces along the data path.

As with any previous scheme the point here is not that Eve cannot get the key. She can. The point of quntum data transmission is not encryption but is that you NOTICE that Eve is there and stop the transmission.

Before now Eve could flood the receiver (because many photons were needed due to losses and the inability to create single photons) to the point that she was undetectable. With a single photon source that is no longer possible.
daywalk3r
1 / 5 (3) Aug 05, 2012
And the weak-points in this case becomming exactly those repeater stations and/or any photon-electron interfaces along the data path.
As with any previous scheme the point here is not that Eve cannot get the key. She can. The point of quntum data transmission is not encryption but is that you NOTICE that Eve is there and stop the transmission.

And that's exactly the reason why I listed repeater stations or any photon-electron convertors/interfaces as becomming the new weakest points, where Eve could still TAP into the data stream while remaining undetected (duh).

And, the core point of (secure) quantum data transmission might not be encryption, but it quite evidently is part of the article, as it's QKD all over..

:-)
antialias_physorg
not rated yet Aug 06, 2012
where Eve could still TAP into the data stream while remaining undetected (duh).

If she taps into it the photon is gone. It is a quantum of energy. You cannot take less than one quantum of energy out ofthe system. This would be immediately noticeable by the other side (since that quantum isn't being received)

And, the core point of (secure) quantum data transmission might not be encryption, but it quite evidently is part of the article, as it's QKD all over..

Notice the K in QKD. It stands for 'key'. The key is transmitted in clear. After you have transmitted the key (securely) you can use it on a regular channel for the transmission of the actual data. The quantum channel is not used for that (its way too slow).
daywalk3r
1 / 5 (3) Aug 06, 2012
If she taps into it the photon is gone. It is a quantum of energy.
What part of "photon-electron interface" and/or "repeater station" you do not understand? Tell and if time allows, I might try to explain.

Though the next part might clear it up for you a bit..

Notice the K in QKD. It stands for 'key'. ...
Playing mr. Obvious now? :-/

The key is transmitted in clear.
Of course it is, and all I was trying to say is, that as long as there is stuff like the proposed repeater stations and various photon-electron interfaces along its transmission PATH (which in the scope of this article is pretty much the case), then it will still be possible for Eve to obtain the key WITHOUT having to "touch" a single photon from the pure-quantum sections of the transmission line.

With the only condition of being in the right place at the right time (tapping a conductor at the time of key exchange) - and until we are talking about a pure-photon system, this is possible.

Get it now?