Ultrasecure Quantum Communications Over Thin Air

SlashDotIDOne writes "Well, given a hundred years at university and a few extra titles to my name, I'd be comfortable trying to summarize the article so don't take what I say at face value. Apparently British and German researchers have found a way to use quantum crypto through the air, thus allowing it to be used to communicate with satellites, etc. A very secure form since you know whether a message was intercepted, rather hard to tamper with ;). Courtesy India times and Google's new news service."

Comments

Re:Ok..

[richie2000]

Works now. *phew* For a while there, I almost believed that someone actually wanted to read the article before posting. We have normality.

Karmawhoring:

Super-secret codes head for space AFP [ WEDNESDAY, OCTOBER 02, 2002 11:36:33 PM ]
PARIS: Quantum cryptography, a technique of producing secret messages that are reputedly uncrackable, may soon be used by orbiting communications satellites thanks to experiments by British and German researchers.

The traditional weakness of sending encoded messages is eavesdropping. Quantum cryptography gets around this by sending an encoded message and, separately, a key to decode it, which are transmitted in pulses of individual light particles called photons.

By the nature of quantum mechanics, if a single photon is intercepted en route, that changes the state of the information package as it arrives at the other end.

That is a telltale for the legitimate recipient that his message has been tampered with -- the same as if someone received a letter that had been clumsily opened and then resealed, leaving traces of glue and fingerprints on the envelope.

The problem with quantum codes, though, has been how to send messages over long distances.

Data is of course already sent by laser light down fibre-optic networks. But this technique is unsuitable for quantum cryptography, for the laser signal has to be boosted every 10 kilometers (six miles), which causes the quantum state of the key to be rearranged.

Researchers from QinetiQ, the commercial arm of the British military research agency, and from Munich's Ludwig-Maximilian University say they have now demonstrated that it is possible to send a quantum-encoded message through the air.

Reporting in Thursday's issue of Nature, the British science weekly, they say they successfully transmitted packages across 23.4 kilometers (14.62 miles) between mountains in the German Alps.

A laser transmitter was set up at the top of the 2,950-metre (9,587-feet) Zugspitze, and sent out pulses to a receiver, a 25-centimetre (10-inch) shop-bought telescope, positioned on line of sight on another peak, the 2,244-metre (7,293) Westlichekarwendespitze.

With some adjustments to amplify the signal, it should be possible to send keys to satellites in near-Earth orbit, at an altitude of 500-1,000 kilometers (310-620 miles), the scientists say.

"This marks a step towards... a global key-distribution system," the authors say.

Quantum codes have obvious uses for military and government communications.

The big question, though, is whether they should be allowed to enter the commercial domain, where they could be used by organised crime and terrorism to thwart eavesdropping by police.

Au contraire. Americans found the way in '98...

[Peter T Ermit]

...here, quickly improved it to 0.5 and 1 km, and then 10 km. Don't quite know why Nature thought this particular paper was so revolutionary -- wake me when they get to about 300 km, the minimal bounce-off-satellite trip.

BBC Link

[Izeickl]

The BBC has a more laymans view of things here

Re:Secure?

[AndrewHowe]

You don't use this method to send your secret message, you use it to send a random one time pad. If it is intercepted, you just send a new one. You keep doing this until your recipient gets one that was not intercepted. Then you encrypt your secret message with this (now known to be secret) one time pad and Bob's Alice's uncle.
The one problem I see with this is that Eve (the eavesdropper) can effectively DoS Alice and Bob's communication, by intercepting everything, thus stopping them from ever agreeing on a private key.

Re:"The Code Book" mentioned this several years ag

[ajs]

Even photons must create some gravity. It would be possible to detect them if the detector was sensitive enougth.

You miss the point. The information is not encoded by modulating the frequency or the amplitude of the photons, it's done by manipulating quantum variables that are sensitive to observation. So, when you snoop the data, you change it, and the stream becomes corrupt. Personally, I just don't see how this beats symetric key cryptography where you can communicate the public portion in the clear (e.g. encode it into public transmissions or send out six couriers with the same info, since you don't care if one of them is intercepted).

Re:"The Code Book" mentioned this several years ag

[Rich0]

Symmetric key cryptography is sensitive to brute-force and possibly cryptanalysis - especially if the key is recycled. You also need couriers. If you are going to use couriers - have them at least carry CD-ROMs full of one-time pad data - that isn't any less practical to achieve.

The adavantage of quantum crypto is that it gets rid of the couriers. What if the attacker intercepts all six couriers - possibly by bribing them all. It just takes one more factor out of the equation. Also - the transmission is not susceptible to cryptanalysis or brute force, assuming your key data is truly random. The actual transmission is encrypted by one-time pad - the only way to crack it is to have the key.

And you are right - the basis of quantum physics is that you CANNOT measure the photon properties using any technique at all without altering them. If there is a clever way around this it would mean that the laws of physics as we understand them are quite wrong. Not that this is impossible, but quantum theory has been tested quite thoroughly. There is always that one experiment that could shoot it all down - but nobody has found it yet.

Re:Any details at all would have been nice

[Jobe_br]

This doesn't matter. What's being transmitted here is not the message, its the one-time cipher pads used to encrypt/decrypt the message. The gov't./military already uses one-time pads - but, they're disseminated on physical media, requiring delivery and disposal by physical, trusted personnel. So, this is about transmitting that one-time cipher pad, not about transmitting the actual messages. The messages, once encoded with the one-time cipher pad that is to be used for that particular transmission (pre-determined by the gov't./military) will be transmitted in the clear over current transmission media (public/private networks, transcontinental/oceanic fiber, military/communications satellites, etc.) The "messsage", encrypted with the one-time cipher that this new transmission medium disseminated, is unbreakable by untrusted parties, because of the one-time pad being used, not because of the transmission type being used.

The one article I read about this talks about the satellite communications that were being intercepted in Europe from NATO troops in the Balkans. This new quantum crypto transmission method for one-time pads has nothing to do with that - THAT was about the military not having enough encrypted satellite channels for the amount of data that they were needed to transfer. This wouldn't change that in one bit. This only affects the legwork currently needed to disseminate one-time pads to all necessary parties. The one-time pad systems are already being used, this would just make the process a bit less resource intensive and available to more parties (not just the ones that have reliable access to diplomatic couriers). Maybe that would change the situation above, because more people could take advantage of the one-time pad system, but I doubt it. This seemed more of a limitation of the satellite bandwidth than anything else.

Cheers!

Re:"The Code Book" mentioned this several years ag

[theCoder]

No, quantum cryptography ensures that only the intended receiver received the message. Anyone snooping the message would be detected by the receiver (it's complicated to explain, but it has to do with the rotation of the light wave (remember that photons are both particle and wave)). So, you don't send data over a quantum link, you send your temporary key. When both sides have the key (and know that no one else could have sniffed it), they can use regular channels to send the data encrypted with that key.