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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."
Karmawhoring:
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Excellent book for lay-people and crypto-beginners: Review Here
;)
This has been a working theory for years (and the book suggests it had been done across a distance of several hundred meters back then!)
I hate it when people say "wow, we have an unbreakable code now". We find out new things and rubbish old theories about the universe and it's properties all the time, we may have violated the second law of thermodynamics, what's to say this is "unbreakable" - it's only secure so far
Johns: Well, how does it look now? Riddick: Looks clear.
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.
Whether they should be allowed?? Whether they're allowed or not has little bearing on what would happen. You look at the US's export restrictions for crypto, asking people outside the US to download the inferior version, they haven't exactly worked wonders have they?
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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.
Who said that this is the big question? This is not the "big question"; it has already been determined that "terrorists" did not and generally dont use crypto for communication, so thats just a lame excuse to keep the tools crippled (see A5).
Organized crime? just because an infinitessimal number of "organized criminals" (just where the hell are the disorganized criminals? [yes yes, GAOL]) might use crypto to secure thier telephones doesnt mean that the vast majority of people should be denied access, or given access only to cripple ware.
But you know this.
These agenda setting questions are pure bad journalism, plain and simple, and simple minded.
ATH0 Bitcoin: 1DnwFLXczVZV8kLJbMYoheUrpqHesjxrSi
Basically, if you can bug the users keystrokes when they type in their password for the crypto system, then that system is toast- similarly if they have a physical token- if you steal that token.
Or you bribe/blackmail the guy; or you use "lead pipe" cryptanalysis- you hit the guy over the head until he tells you his password.
This system looks good; but don't assume that its going to be 100% secure. In the real world it can't be, unless there's no people in the loop, not even designing the system.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"First, I'd like to point out that quantum computation and quantum encryption are two almost completely separate concepts. Quantum encryption is based on the fact that quantum states cannot be measured without altering. The most common example is the polarization of a photon, but it will work for any quantum state, so long as there exist, effectively, two unique states that can transmit the data.
Quantum computation, however, is much more complex and much more interesting. Quantum computers are based on the concept of quantum entanglement, the ability of a quantum state to exist in a superposition of all of its mutually exclusive states: It's a 1 and a 0. However, this is not as easy to use as one might think. While it's true that if you have n quantum logic gates you have the ability to input 2^n data values simultaneously (as opposed to only 1 piece of data if you have n digital logic gates), this is not going to be the end of classical computing for a few reasons. First, quantum computers have to be perfectly reversible. That means for every output there's an input and vice versa. And there has to be no way of knowing the initial states of the data. You don't process data, you process probabilities in a quantum computer; if you know exactly what any one value is throughout the computation, you can find out all of the values: the superposition ends and you're stuck with a useless chunk of machinery. This means YOU CAN ONLY GET ONE RESULT FROM ANY QUANTUM COMPUTATION, THE END RESULT. You can't see what the data in the middle is or the computer becomes useless. (Landauer's principle makes heat loss data loss. When your processor gets hot, it's losing data. If the same thing happened to a quantum computer, it wouldn't be quantum anymore.) Decoherence is what happens when you randomly lose data to the environment by design, not by choice, and the superposition ends. This is bad for Q.C. Oh, and quantum computers can only do *some* things faster, like prime factorization and discrete logarithms. Not multiplication or addition. Plus, the circuits that would do basic arithmetic would be bigger and slower than what you've currently got.
So what does this all mean? It means that quantum computers are going to provide some advantages (real quick big number factorization), and some disadvantages (that whole RSA standard). The most realistic initial use of quantum computers will be as add-ons to existing super-computers to resolve certain types of NP-Complete headaches that regular math can't simplify yet. At best they will someday be an add-on to your PC; but they will never replace the digital computer.~
If you want more info, check out http://www.qubit.org, it's got some decent tutorials.
Anyone got a link to the Nature article itself?
:)
From the guff written here, it all seems implausible. Encoding a message in single photons is fine, but I find it hard to believe that you can transmit a stream of photons several miles through the atmosphere without a single one of them being absorbed or scattered (which would look the same as interception). It's just light, after all.
I wish I could remember any physics. Then I could say something about the possibility of "amplifying" a signal in which the symbols are single photons. But I can't, so I won't even try.
Plus, even taking the above on trust, it doesn't sound too hard to disrupt (with, say, a mirror).
Corrections and extra technical info most welcome!
These sigs are more interesting tha
I remember reading once that Philip K Dick (writer of Blade Runner, Minority Report) went mad at the end of his life, one of the reasons being that he was convinced that there were zillions of alien transmissions going through the air which were screwing with his mind.
Perhaps he was right. Perhaps taking lots of hard drugs allows you to tune in to alien quantum communications. Sounds like some experimenting needs to be done...
From the article:
"Gift a Washing Machine & get Pearl Set Free @ INR 8590"
They obviously don't know that Perl is FREE for most systems.
Follow me
from the article (yes I read it)
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.
If we don't let the public use this, everyone we don't want to have it will get it eventually. There wont be a user base to be framiliar with to help the government in finding the weaknesses. It is the same with cryptography software. Those who want it really bad can write their own or violate an EULA. The law abiding public is shut off from protecting their own things when terrorists and organized crime still can.
Help I'm a rock.
...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.
The BBC has a more laymans view of things here
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Ultrasecure Quantum Communications Over Thin Air
But how thin does my air have to be? I mean, I try to keep my air in shape but it certainly isn't as thin as it used to be. Perhaps if I move to Tibet.
Well at least the communications are ultrasecure - I find that secure just isn't enough.
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.
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).
One time pads are ABSOLUTELY unbreakable...
Erm, no they're not. If you get hold of the decrypting pad you can break it, not that much different than stealing a pgp key and passphrase really.
He who defends everything, defends nothing. -- Fredrick The Great
Does anyone else think it would be a great addition to Slashdot's stories if they would include a link to the google news search under every headline? I don't think it would be that hard to automate, but it sure would open the door for us users to see a lot of different articles per issue discussed.
~ now you know
Assuming someone doesn't steal the key and you did it correctly, then yes.
But if you didn't do it correctly, or your pad choices aren't truly random, or someone knows some of the plaintext, or half a dozen other things, then a one time pad can be broken with a lot of guesswork.
- Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life.
Second, they talk about boosting the signal to achieve the ability to transmit to satalites. This would be at the detriment of the security of the key as the greater the signal strength, the more photons it carries, the easier it is to split off a portion of the beam to be read. This of course is still not in any way easy as statistical analysis of the strength of the signal can reveal that it is being split.
Third, the fact that the signals are being bounced of a satilite autmoatically invalidates the security. If it is relayed, the key is stored in non-quantum states which invalidates it's security. The article sais that the signal on fiber optics has to be boosted every 6 miles. That is also garbage. Boosting the signal again invalidates the security. I don't know anywhere that quantum keys are used through signal boosters.
This experiment is notable though. The farthest a quantum key has been transmitted was 32ish km (I believe in germany), over a single fiber-optic cable. This is the first transmission of a quantum key over a signifigant length through atmosphere.
I do security
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.
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.
"Save the whales, feed the hungry, free the mallocs" -- author unknown