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.

a bit more info

[plasticquart]

A few things to note:

British-government-owned company involved: QinetiQ

Article from The Economist: "Free-space" optics
'"Free-space" optics requires no fibre' (oh, how I love that British English)

Quantum secure key exchange paper: here

Re:a bit more info

[whatisthatvelvet]

This article from the Economist is a good read:

>From The Economist print edition
"Free-space" optics requires no fibre. That may be an advantage

FIBRE optics revolutionised communication by abolishing the law that light can travel only in a straight line. From that point on, light signals could be treated in the same way as electrical ones, and bent round corners. Some people, however, are never satisfied. And these dissatisfied engineers are trying to turn the clock back by developing systems that use "free-space" optics-in other words sending information from place to place by shining laser beams through the air.

Free-space optics has three advantages. It is easy to install. It can handle a technology known as wavelength division multiplexing (WDM) without, as it were, blinking. And it seems suited to a new-and allegedly uncrackable-encryption technique called quantum key distribution.

Speed of installation comes from not having to dig up the road to lay conduits. Free-space optics may thus be an answer to the difficulty of providing broadband connections to customers' homes and offices-the so-called "last mile". Free-space links that operate at speeds of up to 20 gigabits a second-as good as fibre-have now been demonstrated. They can be installed in hours rather than the weeks or months normally needed for broadband access. And if they can be put into place quickly, they can be upgraded quickly, too.

That matters in the context of WDM, a technique that allows a single optical path to carry thousands of parallel channels, as long as each is encoded in a slightly different colour. Upgrading a fibre network for WDM is hard. First, individual fibres are each compatible with only a few WDM schemes. The exact chemical composition of a fibre's glass determines how transparent it is to different frequencies, and also its tendency to disperse those frequencies even when it is transparent. Both restrictions reduce the number of channels that can be carried. Moreover, even if a particular fibre can be used with a particular scheme, the light sources, amplifiers, switches and associated paraphernalia usually cannot. Amplifiers, for instance, will not boost all colours equally, so special devices are necessary to compensate.

Free-space optics suffers from none of these problems. Air is transparent to a wide range of frequencies and has few dispersive tendencies (at least, when the weather is good). And with the associated kit clustered together in base stations, upgrades are easy to carry out.

The third advantage-for quantum key distribution-is more speculative. The technique exploits the arcana of quantum mechanics to let two computers swap a cryptographic key (and thus the means to decode a message) with perfect security.

Quantum key distribution has been demonstrated successfully in fibres, but it suffers from one major drawback: it requires a dedicated link, and so cannot be implemented in a network. However, two experiments carried out in the past few weeks have shown that it works with free-space optics. First, researchers at QinetiQ, a British-government-owned company, and Ludwig Maximilian University, in Munich, Germany, exchanged keys between two alpine mountain-tops more than 23km apart, though they did so at night, when sunlight could not confuse the signal. Then, another group of researchers, from Los Alamos National Laboratory in New Mexico, announced that they had performed a 10km key exchange in broad daylight.

These two groups are working towards military applications in which the key is exchanged from the ground to a satellite. But both recognise that the technology might be exploited commercially, and are part of a European Union collaboration called QuComm that is encouraging this.

Free-space optics would have the odd drawback, such as flocks of birds, showers of snowflakes or banks of fog interrupting the beams. But message-encoding systems are already set up to cope with lost data. Many customers might be willing to put up with a 99.999% available service that could be installed straight away, rather than waiting indefinitely for the 100% availability of fibre.

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:Hypothetically

[Des Herriott]

I recommend reading The Code Book (Simon Singh) if you want to understand how quantum cryptography works.

But basically - no, what you suggest does not happen. You don't use a quantum channel (i.e. single photon stream) to send the message itself, you use it to agree a key, which is used as a one-time pad. The encrypted message could be sent over any channel - because it's encrypted with a one-time pad, it's absolutely secure on the wire. Remember the problem with one-time pads is key distribution, not decryption - if (and only if) you can securely distribute the key, one-time pads are pretty much perfect.

The key agreement protocol includes safeguards to avoid eavesdropping too - quantum physics means you can't reliably sample the stream of photons without changing it, and the protocol includes consistency-checking - if everything doesn't match up, the key-exchange is scrapped.

So basically, quantum cryptography is really just a very clever way of sharing a one-time pad key.

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.

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

[RayBender]

An important additional point that is getting missied is this: if anyone intercepts the message it is immediately obvious to the intended recipient. In effect, by intercepting the signal the snooper corrupts the signal, so the intended recipient will not get an intelligble message. So this is even better than a one-time pad...

Of course, if there is something we don't yet know about quantum mech then perhaps it's not perfectly safe. Also, actually achieving 100% secure communication requires care in implementing the design - you can't put too many photons out there or some of them can be intercepted without tipping off the recipient.