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Researchers Simplify Quantum Cryptography
Stony Stevenson writes "Quantum cryptography, the most secure method of transmitting data, has taken a step closer to mainstream viability with a technique that simplifies the distribution of keys. Researchers at NIST claim that the new 'quantum key distribution' method minimizes the required number of detectors, the most costly components in quantum crypto. Four single-photon detectors are usually required (these cost $20K to $50K each) to send and decode cryptography keys. In the new method, the researchers designed an optical component that reduces the required number of detectors to two. (The article mentions that in later refinements to the published work, they have reduced the requirement to one detector.) The researchers concede that their minimum-detector arrangement cuts transmission rates but point out that the system still works at broadband speeds."
Either this post is first or it isn't. I won't know until I press submit.
Women are like electronics: you don't know how damaged they are until you try to turn them on.
Is there anywhere in the world actually using this sort of technology? Is it used in the military at all?
It is impossible to crack because there is no way to decode it without the right key. Algorithms like RSA or DES can be brute forced with enough horse power, for instance, when the quantum computer is invented it could make short work of them. Quantum cryptology will be the only defense.
The big deal is that the cracking time for non-quantum algorithms reduces to O(n) for length n keys. OTOH, for quantum encryption, the cracking time minimum threshold is O(n^n) for length n keys. Hyperbolically, the linear analog is also true in that with quantum decryption, it is possible to crack non-quantum algorithms in O(n) time (again for length n keys), but quantum algorithms require O(n^n) to decrypt. Note that without the correct key, the quantum algorithm requires O(n^n) regardless of whether the cracker is employing spherical numerical analysis techniques or advanced quantum distribution array matrices.
The fact of the matter is that quantum encryption provides much greater security than standard algorithmic encryption.
With this simplification, thousands of cats are saved from having to deliver code keys.
I think you've misunderstood something. "Quantum encryption" is something of a misnomer. It's actually a physical process that can be used by Alice and Bob to establish a commonly shared secret that is random (and unknown to even Alice and Bob before the process starts). This secret is then typically used as a one-time pad.
________
Entranced by anime since late summer 2001 and loving it ^_^
Every time I hear about Alice and Bob, I now think of this
Quantum cryptography is supposed to provide secrecy by detecting eavesdroppers, since other parties observing your conversation should disturb some physical properties that you can subsequently measure.
The sexy part is that if there is a third party who tries to eavesdrop, the attempt will both fail and can be detected by the two communicating parties, and that the security of quantum cryptography has nothing to do with the lack of ability to factor large numbers, but is instead based on physical principles (quantum mechanics). Of course, the sensitivity to eavesdropping means that the system is probably vulnerable to a denial of service attack, depending on how the two communicating parties relate to eavesdropping.
Otherwise, you are perfectly correct. Many cryptographers, including Bruce Schneier, believe that quantum cryptography is a solution to the wrong problem. Nowadays, most probably, the least secure part of your communication system isn't in your key distribution scheme, but is somewhere else --- like in social engineering, or the computer systems which deal with the decrypted cleartext.
Here's something I've never understood. Alice prepares a one-time pad and sends it along using this quantum dealie. Eve intercepts it. Now supposedly this thing changes every time someone observes it, but could Eve just generate a new one based on the data she acquired? Alice created one 'from scratch', why can't Eve?
Describing the rate as "Broadband Speeds" is about as useful as describing the performance of a supercar as "roadworthy" (there's your car analogy).
For reference, in Australia not only does the incumbent Telco consider 256/64kbps to be broadband, but they also describe it as "Fast".
Presumably because the one-time pad is your decryption key. Encryption wouldn't be especially useful if you could just put in a password (not "the" password, but "a" password) and unlock the secrets, would it?
That's my best guess, I've never really understood the theory either. It IS quantum physics, after all.
How are sites slashdotted when nobody reads TFAs?
yeah, so it's completely random and comes out of nowhere. But a gigantic equation based on an exact millisecond on the computer's clock might as well have come from nowhere too cuz nobody can record or measure that. But the next couple replies actually make sense (almost) about how it prevents eavesdropping. I still don't buy the completely made up, cat in a box, quantum flux until someone "measures it" even though measures it doesn't make sense in the tradition sense and is unproven in the absolute molecular sense but I'll just take their word for it and assume it means it can only be decrypted once or something. In that case I guess a test packet could be sent first and if it arrives unencrypted, someone else decrypted it first and they can stop transmission. But wait, it would have to contain a previously agreed upon message to be able to tell if it was encrypted or not so the man in the middle could fake it. I'm no quantum physicist but there's a way to beat everything.
Google's Super Secret Search Algorithm: SELECT @search_results FROM internet WHERE @search_results = 'good'
What speeds are they calling broadband? 200Kbps?
It's a summertime Northern Hemisphere and a wintertime Southern Hemisphere. Slice the world the other way and its daytime in one hemisphere and nighttime in the other. And its always dark down here in my parents' basement.
You also failed to mention that it is impossible to eavesdrop on the communication of the keys. This is probably the most important part because it can make one time pad encryption useful on computer networks. Without quantum cryptography, your one time pad is only as safe as how you send it (RSA encryption, chaos encryption, snail mail). Additionally, quantum cryptography can't be reverse engineered to find the algorithm for your one time pad.
This is all nice, but it is going to be tricky to implement it in the future. How do you send a photon from one computer to another a long distance away without using repeaters or branches? It will be a little tricky. Would this require a fiber optic connection between every computer that wants to communicate with quantum encryption? Or can you adjust the medium so that photons are transmitted and branched undisturbed?
There is only one cryptography scheme with proven secrecy, and that is the one time pad. Even if you assume no errors occur in its implementation, no physicist can guarantee there will never be discovered a way to eavesdrop on transmissions that use Quantum Cryptography. In contrast with the one time pad a Mathematician can more or less prove, at least to the extent you can prove anything at all, that eavesdropping is only possible if the implementation is flawed.
In practice none of this is relevant since the hassles associated with correctly implementing either QC or a OTP are sufficiently large that for most applications they are both inferior to public key cryptography and symmetric ciphers. There are some exceptions, but the only way you could possibly justify describing quantum cryptography as "the most secure way to transmit data" would be by ignoring so many aspects of information security that it will have no relevance to practical applications.
The reason Eve can't just generate a new pad is because there are two methods of generating a photon and two methods of measuring a photon. Each method of generating a photon has a matched way of measuring it. If you use the matched measurement method you correctly get the bit Alice sent. If you use the incorrect method you get a random 0 or 1 no matter what bit Alice sent. Eve (and Bob too) has no way of telling which method Alice used. In quantum key distribution, after sending the photons, Alice would contact Bob over a different channel. They would tell which method they used, and if they used matching methods keep that bit. If they used different methods they would throw out the bit. If Eve regenerated the bits, she could not have used the same methods as Alice since she doesnt know which methods were used. So Alice and Bob's keys won't match up which will result in any information passed between them to be undecodable and they will know someone eavesdropped.
Quantum Key Distribution is, in its most naive form, still vulnerable to man in the middle attacks. It makes it a little more difficult because you must be able to intercept information on two different channels (the quantum channel and the classical electronic channel), but it is still doable. (There are, however, cryptographic methods of detecting man in the middle attacks, but thats a subject for another time).
The laws of probability forbid it!
I'm all for R&D into pure science, and I'm not bagging the concept of quantum cryptography, but why does this need to be a commercial product?
Is there really anyone out there paranoid enough to need/want this besides various three-letter agencies? Maybe this is proveably secure, we think, but what is more likely - Someone finds a loophole in the very weird world of quantum mechanics that makes quantum cryptography as we know it obsolite, or someone figures out a way to find prime factors of obsenely large numbers in a reasonable time.
This article is about how it may be possible have a quantum crypto setup with a bandwidth of maybe 1024kbps by spending only $20k-$50k on one component to the system. I bet there is a lot of other components.
Compare this with a basic commodity PC, which can could encrypt 1024kbps using AES with ridiculous ease.
This is how I understand it: In normal cryptography, you have to worry about "the man in the middle" intercepting the message and then cracking it at their leisure. In quantum crypto, "the man in the middle" can't do this. They need the keys beforehand to even record the message. And another thing is, they can't just eavesdrop passively, they must do actual "man in the middle", ie. intercept the message and re-send it in real time.
Somebody correct me if I'm badly mistaken...
You are comparing apples with oranges. The bit your mathematician can "prove" is only part of the problem quantum encryption aims to solve. Ie quantum encryption also includes key exchange (and in fact typically uses a one time pad for the data transfer).
You can't simply ignore the key exchange problems on the mathematicians side.
Perhaps the laws of physics that are supposed to protect quantum encryption will turn out to be false but based on our current understanding there is no better way to do it.
How is your mathemetician going to distribute his one time pad?
Boffoonery - downloadable Comedy Benefit for Bletchley Park
You do realize that QC is just a method of securly distributing a one-time-pad between two endpoints, right? They don't use the photons to send the message data, that gets XORed later and sent via normal channels. So if everyone is wrong about quantum mechanics translates directly to "the OTP implementation is flawed". While OTPs are hard to implement (Where did I put that onionpaper again?) the whole point of developing QC is to get to the point someday where it IS practical/hasslefree to distribute the "pad". Ever faster and over longer distances.
"You saved 1968." - Ms. Valerie Pringle to the crew of Apollo 8
Plus with quantum encryption you can utilize lunar wainshafts to feed the unilatral phase dectractors and Karnot-Graham meters.
...
The laws of probability forbid it!
I was with you up until about there. It occurs to me that there are any number of mathematical terms that could be combined at random to induce the same effect in me, and I wonder if this is true of all the people who modded you up.
I think i'm just gonna take your word for it.
DRM: Terminator crops for your mind!
For a really really good look at security, try to track down the earliest black+white TV series of Mission Impossible - (almost no gadgets, lots of neat social engineering).
Andy
It's not so hard, let me explain:
spherical numerical analysis techniques: That is standard maths; If you need to compute something involving for instance a cow, you start with "Assume a spherical cow with radius R".
advanced quantum distribution array matrices: That just your normal quantum distribution array matrices but with the new icons and toolbar.
Whoa boy, you are right about that.
DRM: Terminator crops for your mind!
Google it...
or check this: http://it.slashdot.org/article.pl?sid=06/12/13/1458238&from=rss
"Knowing everything doesn't help..."
From what I understand, quantum computing will basically allow the equivalent of massively parallel computation, so you can find the key that solves the message easily. In RSA, it means that it could factor the large prime numbers that make up the public key, and mathematically generate the private key from those.
It is pitch black. You are likely to be eaten by a grue.
"Conventional" encryption algorithms can be brute forced even without the correct key - it will just take a really long time. As I understand it, the point of quantum cryptography is that it is completely impossible to break, because the transmission would be scrambled the moment someone tries to tap the connection.
Don't expect the above to be completely correct, though - I'm hardly a cryptography expert (which doesn't stop me from putting a reference in my sig).
Tomato wedge sperm darts that are Republican.
Actually... This could have been the first post, not the first post, or both. And even though you had pressed submit, you probably wouldn't be able to find out anyway.
Fact: Everything I say is fiction.
Here's something I've never understood. Alice prepares a one-time pad and sends it along using this quantum dealie. Eve intercepts it. Now supposedly this thing changes every time someone observes it, but could Eve just generate a new one based on the data she acquired? Alice created one 'from scratch', why can't Eve?
... Again, hopefully you remember from your school days that, if you send that polarized light though a second filter at an angle to the first, a proportion of the light gets through (cos^2 theta). But, QM says that you cannot predict which photons will make it through the second filter, it's entirely probabilistic.
,|-> to transmit her bit and Bob used or |V>. She can retransmit that value but, if Alice sent |+> or |-> instead then she'll have corrupted the bit. If she measures or |-> but if Alice sent |H> or |V> then she'll corrupt that bit instead. Infact, on average, regardless of which measurement she makes, she'll end up corrupting 1/2 of the values that Alice and Bob have "successfully" exchanged.
Lookup quantum cloning and the "no cloning theorem".
But basically (and this is a naive implementation that won't actually work), Alice transmits to Bob using linearly polarized photons. Now, if you remember from your school days, if you shine a light though a polarization filter and then through another filter at the same angle, all the light that gets through the first filter gets through the second filter as well.
So, let Alice transmit a horizontally polarized photon |H> if she wants to send a 1 and |V> if she wants to send a 0.
Bob uses a horizontally polarized filter = 1 (the photon gets through and he detects it, = 0. The photon gets stopped and he doesn't detect it.
So far, so good but... Eve does exactly what you suggested and measures the photon and then regenerates it - so Bob doesn't see any difference.
Now it starts getting clever
So as well as using |H>,|V> to transmit 1 and 0, Alice also uses |+>,|-> where these are 45 degree polarizations. Alice uses one or the other completely at random.
Bob, when he measures at his end also choses whether to measure the horizontal polarization = Alice and Bob use the same polarization angle so Bob detects the photon
= Alice and Bob use crossed polarization filters so Bob doesn't detect the photon
= Alice and Bob's filters are at 45 degrees so Bob may or may not detect a photon
= ditto
= ditto
= ditto
= Alice and Bob use the same polarization angle so Bob detects the photon
= Alice and Bob use crossed polarization filters so Bob doesn't detect the photon
Once Alice and Bob have done this, Bob tells Alice which measurement he's done (over a classical channel, they don't care who might eavesdrop.) If Alice and Bob have used the same basis - i.e. Alice used |H>,|V> to transmit her bit and Bob used
Now Eve can get really clever. Instead of measuring the photon, she can clone it and then measure her clone. Now it turns out that there is a limit to how good her cloning machine can be so, although it won't corrupt half of the bits that Alice and Bob transmit, it will corrupt at least 1/6.
(Actually, in the naive scheme outlined above I think Eve can do:
a|H> + b|V> => a|HH> + b|VV>, store her photon, wait for Bob to measure, eavesdrop the message from Bob to Alice and then make the same measurement on her stored photon. But this only works because the only possible values for a,b in the naive scheme are (0,1), (1,0), (1/sqrt2,1/sqrt2), (1/sqrt2, -1/sqrt2) but I'm right on the limits of my understanding of QM and entangled photons now so I could be completely wrong)
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
Grrr. < needed :-(
... Again, hopefully you remember from your school days that, if you send that polarized light though a second filter at an angle to the first, a proportion of the light gets through (cos^2 theta). But, QM says that you cannot predict which photons will make it through the second filter, it's entirely probabilistic.
Here's something I've never understood. Alice prepares a one-time pad and sends it along using this quantum dealie. Eve intercepts it. Now supposedly this thing changes every time someone observes it, but could Eve just generate a new one based on the data she acquired? Alice created one 'from scratch', why can't Eve?
Lookup quantum cloning and the "no cloning theorem".
But basically (and this is a naive implementation that won't actually work), Alice transmits to Bob using linearly polarized photons. Now, if you remember from your school days, if you shine a light though a polarization filter and then through another filter at the same angle, all the light that gets through the first filter gets through the second filter as well.
So, let Alice transmit a horizontally polarized photon |H> if she wants to send a 1 and |V> if she wants to send a 0.
Bob uses a horizontally polarized filter <H| to measure Alice's photon. <H|H> = 1 (the photon gets through and he detects it, <H|V> = 0. The photon gets stopped and he doesn't detect it.
So far, so good but... Eve does exactly what you suggested and measures the photon and then regenerates it - so Bob doesn't see any difference.
Now it starts getting clever
So as well as using |H>,|V> to transmit 1 and 0, Alice also uses |+>,|-> where these are 45 degree polarizations. Alice uses one or the other completely at random.
Bob, when he measures at his end also choses whether to measure the horizontal polarization <H| or diagonal polarization <+| completely at random. There are eight cases:
<H|H> = Alice and Bob use the same polarization angle so Bob detects the photon
<H|V> = Alice and Bob use crossed polarization filters so Bob doesn't detect the photon
<H|+> = Alice and Bob's filters are at 45 degrees so Bob may or may not detect a photon
<H|-> = ditto
<+|H> = ditto
<+|V> = ditto
<+|+> = Alice and Bob use the same polarization angle so Bob detects the photon
<+|-> = Alice and Bob use crossed polarization filters so Bob doesn't detect the photon
Once Alice and Bob have done this, Bob tells Alice which measurement he's done (over a classical channel, they don't care who might eavesdrop.) If Alice and Bob have used the same basis - i.e. Alice used |H>,|V> to transmit her bit and Bob used <H| to measure it or Alice used |+>,|-> to transmit her bit and Bob used <+| to measure it then Alice says "correct" and Bob knows what bit Alice sent. If Bob used the wrong measurement then Alice says "incorrect" and they both throw that bit away.
So, on average, for each two bits that Alice tries to send to Bob, one will be thrown away and the other will be a good value.
Now Eve tries to eavesdrop. If she measures <H| then she'll detect |H> or |V>. She can retransmit that value but, if Alice sent |+> or |-> instead then she'll have corrupted the bit. If she measures <+| instead then she can retransmit |+> or |-> but if Alice sent |H> or |V> then she'll corrupt that bit instead. Infact, on average, regardless of which measurement she makes, she'll end up corrupting 1/2 of the values that Alice and Bob have "successfully" exchanged.
Now Eve can get really clever. Instead of measuring the photon, she can clone it and then measure her clone. Now it turns out that there is a limit to how good her cloning machine can be so, although it won't corrupt half of the bits that Alice and Bob transmit, it will corrupt at least 1/6.
(Actually, in the naive scheme outlined above
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
You don't transmit the message using QC, you transmit a OTP. So if Eve does intercept it then all she gets is a bunch of random bits, Alice and Bob detect the interception, throw the OTP away and start again.
The best that Eve can do is a DOS attack.
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
That's a relief. I was worried there for a while.
FAQs are evil.
There is an even bigger problem with quantum ''encryption'': The pysical models are only ever exact to some degree. It is quite possible that some minor, not yet discoverd, effect exists that completely breaks security. If you really want to be secure, definitely stick to the stuff we understand.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
The fact of the matter is that quantum encryption provides much greater security than standard algorithmic encryption.
In your dreams. No quantum computer exists that can break encryption used today by a very, very large margin. It seems doubtful whether researchers can get beyond a few bits at all, let alone scale up to a few thousands. Presently this is all hype to get research money. There have been much more similar things that failed and only very few that deliverd on their claims.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
... for making the comment I was about to make. :)
I see someone didn't read the instructions and looked at the light while posting.
Get a web developer
The one-time pad requires a shared-secret key in order to be able to encode and decode encrypted messages. Sharing the key securely becomes a huge logistical problem.
Quantum cryptography promises, through quantum theory, that anyone trying to skim data from a secure channel ultimately corrupts it. So by measuring the noise level in the channel you can detect an eavesdropper.
A typical Quantum cryptography scheme requires two channels. One of the channels is a classical channel, like the internet, which is used to exchange the encrypted message. The other is a low noise quantum channel, which is capable of exchanging some kind of physical entity with information about the key encoded in its configuration. An example of such a physical entity would be a collection of polarized photons.
The rough idea is that you exchange the key over the quantum channel. If while doing that your "noise level" rises beyond a certain threshold, you abort the transmission. Otherwise the key to your OTP is now shared and you transmit your encrypted message over the classical channel.
I didn't miss your point, science isn't provably true and quantum mechanics may someday turn out to be wrong, exposing a loophole which allows for eavesdropping. But quantum cryptography isn't as much of a cryptography scheme as it is a transmission vehicle.
Still, if you want to find a flaw with quantum cryptography, you don't have to look very hard. Quantum cryptography assumes that your man in middle just wants to read data out of the channel without breaking the link. It is easily defeated if someone can make themselves into a relay.
i.e. Quantum cryptography is defeated if an eavesdropper cuts both the quantum and classical channels and inserts herself into the middle:
Sender ===>>=== Attacker ===>>== Receiver
where she pretends to be the receiver to the sender and rebroadcasts the message as if she were the sender to the receiver.
...quantum cryptography now requires 30% less cats and 46% fewer radioactive isotopes.
Random Thoughts From A Diseased Mind (Not For Dummies)
The reason governments throw money at it is because whoever can build the first working one would theoretically have the keys to the kingdom. If a working quantum computer existed (and worked as theorized) suddenly secure communication over the internet would be a liability, thats assuming if one ever gets built (and works) and the public knows about it.
You left out the new 'quantum bar'. It's really cool because when you click the little star, it creates a quantum super state where the address is simultaneously bookmarked and not bookmarked. A lot of people have been complaining about all the extra clutter, but that's just because they are observing the results.
Well, that's how the Federation does it anyway.
Please stand clear of the doors, por favor mantenganse alejado de las puertas
Maybe.
Uniform density!
Where's the car, Mr. BadAnalogyGuy?
how is babby formed?
So, rather than just eavesdropping the message from Bob to Alice, she would actually need to destructively intercept it and change it.
People are mixing up two different things here - quantum transmission, the one you can't read unnoticed, and encryption/decryption using quantum computers and algorithms.
The first one has been demonstrated, and works over limited distances.
The second is an "advanced concept", right next to fusion reactors.
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
Who cares? I want to know if it will run Duke Nukem Forever!
hmmm.... that sounds a lot like coolwebsearch...
Article Summary states "Four single-photon detectors are usually required (these cost $20K to $50K each)"
sounds expensive.
except, the real article states: "Bob uses four single-photon detectors, costing approximately $5,000-$20,000 each."
still pretty expensive, but it sounds like you could have a working one of these for only 10k in detectors!
Actually, breaking quantum cryptography should be fairly simply. All you have to do is break the laws of quantum mechanics. A good lawyer should be enough to accomplish this feat.
Actually, the message telling which bits were send and/or measured at a 45% angle is only exchanged after Bob has measured the quantum bits. So, even can't just store them, measure them and re-inject them after the fact.
So, rather than just eavesdropping the message from Bob to Alice, she would actually need to destructively intercept it and change it.
Eve isn't intercepting the bits. She's creating a pair of correlated photons without actually making any measurement. She sends one on to Bob and stores the other for measuring later.
a|H> + b|V> => a|HH> + b|VV>. I'm pretty sure this transformation is allowed for all values of a and b. Note that she is NOT cloning (a|H> + b|V>)(a|H> + b|V>) which would be prohibited.
Having said that, I think my quick thoughts were incorrect. I was assuming
|HH> = k|++> + k|--> when I think it should have been 1/2|++> + 1/2|+-> + 1/2|-+> + 1/2|-->
(k=1/sqrt2) now that I think about it properly.
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
Also you can control/change the path of the photon using electro-optical controls without changing it's state (or at least without changing the part of the state that carries the information), though this would likely be more difficult/expensive to implement on a wide scale.
Nonsense. Quantum encryption, when properly implemented, cannot be cracked. Period. If you have a perfectly good and fast quantum computer, you still could not crack quantum encryption. RSA can be broken using Shor's algorithm, but that is O(log(n)^3), not O(n). And if you don't have a quantum computer lying around, then it's a lot worse than that.
Parent shouldn't be modded informative, just about everything he said was wrong.
That's roughly correct, however the caveat to QC is that the end result must be some sort of amalgamation of all the "parallel" runs. I.e. you can't have all your parallel runs produce different outputs, and look at each output independently.
It ties in with superposition. You can know some sort of "final answer" by processing superposition states, but you can't know intermediate answers (or the results of each individual "parallel run") without collapsing the superposition-solution into a single intermediate answer. So, basically, you'll randomly get *one* of all the possible intermediate answers.
That still didn't come out as clear as I'd hoped. QC is tricky stuff.
If by "conventional" you include the one-time pad, properly used, then quantum cryptography is possible to crack. The issue is that the one-time pad is relatively difficult to use properly.
One of the canonical examples of the power of quantum cryptography, BB84, is basically just a secure way to negotiate between two parties a one-time pad (thus the process called quantum key distribution, QKD). If there is someone listening in as the negotiation takes place, quantum mechanics means that (1) they often get useless information and (2) they often disturb the transmission in a way that can be detected (with exponentially increasing probability).
I'm less familiar with newer quantum crypto strategies (if I've overlooked something, please point me to it), but from my understanding it pretty much boils down to this. Basically, if you can brute-force crack a random string (which is what the result of a one-time pad should produce, arguably), you can crack quantum crypto. But then, if you're cracking random strings you can probably find whatever you like in them.
I was just discussing entanglement swapping with my supervisor the other day, actually. Neat concept. Roughly, person A has two entangled photons, A1 and A2. Person B has similar, B1 and B2. They both send their 1 photons to C. C entangles A1 and B1 and because of this, A2 and B2 are now entangled. This can then be used to generate a bit of a key.
We were actually discussing it in the context of producing entanglement between ions (good for storage/memory) and photons (good for transmission), since in the real-world it's unlikely actual repeaters will receive photons from both parties at the same time so that the entanglement can be swapped.