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Swedish Researchers Break 'Unbreakable' Quantum Cryptography (eurekalert.org)
New submitter etnoy writes: Quantum key distribution is supposed to be a perfectly secure method for encrypting information. Even with access to an infinitely fast computer, an attacker cannot eavesdrop on the encrypted channel since it is protected by the laws of quantum mechanics. In recent years, several research groups have developed a new method for quantum key distribution, called "device independence." This is a simple yet effective way to detect intrusion. Now, a group of Swedish researchers question the security of some of these device-independent protocols. They show that it is possible to break the security by faking a violation of the famous Bell inequality. By sending strong pulses of light, they blind the photodetectors at the receiving stations which in turn allows them to extract the secret information sent between Alice and Bob.
The point of quantum crypto is to be able to detect whether someone is eavesdropping on you. Blinding detectors is kind of a tell-tale sign that something is wrong and parties should stop transmitting.
Paper author here. You can try detecting my specific attack, but it won't help. Sooner or later I'll find a way around your countermeasure and break it again. What we actually show in the paper is that the security proof is flawed. Fix the security proof and I won't ever be able to break it.
Quantum hacker.
Why are people always picking on Alice and Bob? All they want to do is live in peace, but they're thrown into black holes, sucked into whirlpools, and subjected to all sorts of unimaginable things.
Submitter has no clue what QC is.
Oh, sorry. I confess I know nothing about quantum cryptography, I just happened to break it.
First of all, quantum key distribution is not a method for encrypting information. As its name judiciously indicates, it is a method to securely exchange encryption keys. This is not the same thing at all.
Semantics. QKD is a way of obtaining a secure key which we then use to perform one-time pad encryption. In other words, we use it for encrypting information.
Second, the speed of the attacker's computer has no role in this attack and quantum key distribution has never claimed a code is unbreakable since there is no code to break here.
It's a layman's definition of the concept of information-theoretic security (ITS). Normal crypto is secure under certain hardness assumptions (i.e. hard to factor integers, hard to do discrete logarithms). If you give the attacker an infinitely fast computer, all those crypto methods will be broken. QKD on the other hand remains secure.
Of course, if you are blinding the receiver, it may be possible to tamper with the key, however, the blinded party should notice it has been blinded.
This is a very good question and there is a very good answer (one I even answer in the paper itself!) You can surely detect my attack by using an optical power meter, but eventually I'll figure out a way around this as well. What our paper really shows is that there is a missing link in the security proof. Fix the proof and you'll be safe forever.
The whole thing rests on very low luminosity photons exchange. If the light beam is too strong, it clearly no longer depicted the quantum characteristics needed to secure the key exchange.
Which makes our attack even juicier. We don't even need to use quantum phenomena to break the security of the QKD device, we just good ol' classical pulses of light.
And finally, it seems to me this is old news.
Please tell me more!
Quantum hacker.
No, it shows that this method of key distribution might be borked, nothing more.
Short logic lesson, your reasoning is indistinguishable in form from: 3 is prime, therefore all numbers are prime.
Or more bluntly: (Ex) P(x) --> (Ax) P(x)
is falsifiable in first-order logic. In English, this is "if there exists some x such that P(x), then for all x it is the case that P(x)."