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Swedish Researchers Break 'Unbreakable' Quantum Cryptography (eurekalert.org) 101

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.
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Swedish Researchers Break 'Unbreakable' Quantum Cryptography

• It just shows that... (Score:1)

It just shows that nothing is unbreakable or at least, it tends to prove it.

• Re:It just shows that... (Score:5, Insightful)

on Saturday December 19, 2015 @07:50AM (#51149475)

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)."

• Re: (Score:2)

There is theoretically unbreakable crypto and crypto that is provably hard enough to break as to be unbreakable practically for a long, long time. The quantum-snake-oil "encryption" is neither. First, it has the requirement that some physical models are absolute truth. That would be a first in physics, so far there were always inaccuracies, and circumstances where the theoretical models failed. And second, it relies on a physical, analog implementation being perfect. That is uisually not possible to achieve

• Re: (Score:2)

Aside from the one-time pad, there is no crypto that is provably hard to break.

All practical decryption is in NP, in that we can verify the correctness of the decryption in polynomial time. Therefore, the most we can say about crypto algorithms is that they may be (but, AIUI, are not provably) NP-complete. This means that they may be efficiently solvable. It seems unlikely, but we can't prove it otherwise. Alternately, we might find other ways to crack a given cipher. Again, it seems unlikely, but

• Re: (Score:2)

You are very, very wrong on this. With a good key-schedule and a maximum message size used per key, even the Enigma is provable "hard to break", or rather impossible to break. It requires random keys and something like a maximum of 4k characters encrypted per key (if I remember the numbers right).

Your NP argument completely misses the point in several regards: First, for practical attacks, P is not "efficient". Second, what makes you think you can verify the correctness of decryption in the first place? Tha

• Re: (Score:2)

True, there is a minimum text length to break ciphers, based on what is known of the cipher and the amount of redundancy in the language. (I don't think you'd have any real difficulty reading that last sentence with vowels omitted, for example, which means the vowels primarily provide redundancy.) A break requires a certain minimum of text.

As far as recognizing plaintext, this is automatic in cases with known plaintext or forced plaintext, and cipher experts want them to resist these attacks as well.

• quantum crypto is not "unbreakable" (Score:1)

by Anonymous Coward

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.

• Re:quantum crypto is not "unbreakable" (Score:5, Informative)

on Friday December 18, 2015 @06:45PM (#51146769) Homepage

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.

• Re: (Score:2)

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.

Unless physical reality turns out to not quite follow the theoretical models precisely. So far that has always been the case.

• Re: (Score:2)

They don't mean blind in the sense of giving the detector so many photons that it is blinded but rather by cleverly adding a small number of extra photons they can make the detectors think everything is ok.
• Re: (Score:2)

We actually do blind the detector by flooding it with photons.
• Re:quantum crypto is not "unbreakable" (Score:4, Informative)

on Friday December 18, 2015 @07:32PM (#51147023)
Blinding detectors is kind of a tell-tale sign that something is wrong and parties should stop transmitting.

FTA: "An intuitive countermeasure to our attack is to add a power monitor to the analysis station that detects if the incoming light is too bright. If such an anomaly is detected, Alice and/or Bob are alerted and discard the relevant measurement outcomes. This modified Franson interferometer would not be vulnerable to the specific attack as described so far; however, it does not solve the postselection loophole, which is the actual issue at hand. "
• Re: (Score:2)

Someone read TFA? Pinch me ;)
• Submitter has no clue what QC is. (Score:3, Insightful)

on Friday December 18, 2015 @06:51PM (#51146787) Homepage

"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."

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.

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.

Third, quantum key exchange is a protocol, not a cipher. It relies on quantum mechanics features to tell Alice or Bob the just receive key is compromised or not since it is not possible for a man in the middle to observe the key without being noticed. That is the idea behind this mechanism. Once keys are securely exchanged between both parties, a classically encrypted communication can take place between both parties.

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. 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. I don't really see where the problem is here since it is easy to determine the exchange can no longer be trusted due to high luminosity.

And finally, it seems to me this is old news.

• Re:Submitter has no clue what QC is. (Score:5, Informative)

on Friday December 18, 2015 @07:23PM (#51146951) Homepage
Paper author here.

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!

• Re: (Score:2)

You didn't break any encryption here. Sorry to said so, but you still persist with this nonsense. The quantum key distribution is not encrypting anything, it transmits in clear the keys and the quantum effect is what tell you if the keys were compromised or not by someone looking at them. That's it and that's all. Whatever the keys are, one-time pad or anything else, the encryption will proceed thru another communication channel with classical encryption.

Worst, it seems you do not understand at all why one-

• Re: (Score:2)

It's hard to argue about QKD without understanding how it works. Your starting point about QKD transmitting keys in the clear is wrong, as the information does not even exist in the quantum channel. Alice's and Bob's measurement operations are what create the secret key. That key is then used in a one-time pad. Also, OTP is exactly what we use after finishing a QKD session. The key requirements you talk about is exactly what makes OTP 100% secure.
• Re: (Score:2)

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.

I don't understand this. Sending a one-time pad key is equivalent to sending the plaintext, as far as information transfer goes. (Otherwise, it isn't a real one-time pad.) The only advantage of the 1TP is that we can send the pad when we can get a secure communications channel, and then send messages at arbitrary times over insecure channels. If y

• Re: (Score:2)

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.

I don't understand this. Sending a one-time pad key is equivalent to sending the plaintext, as far as information transfer goes. (Otherwise, it isn't a real one-time pad.) The only advantage of the 1TP is that we can send the pad when we can get a secure communications channel, and then send messages at arbitrary times over insecure channels. If you have a reliable and persistent secure channel, why bother with the 1TP key?

Excellent question! QKD is just what it means, key distribution. There is actually no transmission between sender and receiver, instead it randomly establishes a secret, shared key at Alice's and Bob's place. Therefore, to do transmission, you use OTP to perform encryption.

• Re: (Score:2)

Thank you. That was a good explanation.

• Re: (Score:3)

If the light beam is too strong, it clearly no longer depicted the quantum characteristics needed to secure the key exchange. I don't really see where the problem is here since it is easy to determine the exchange can no longer be trusted due to high luminosity.

The paper addresses this.
• Why are people always picking on Alice and Bob? (Score:5, Funny)

on Friday December 18, 2015 @06:54PM (#51146795)
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.
• Re: (Score:1)

Ted and Carol are looking for them...

• Re: (Score:2)

Alice should go back to that restaurant.

• Re: (Score:3)

One time they even had a threesome with a man-in-the-middle.

• Re: (Score:2)

What Bob doesn't know is that Bruce Schneier is having torrid affairs with Alice and Eve.

• Poor Alice and Bob (Score:2)

When will they figure we are all plying games with them, and they believe they are talking in secret about secrets, secretly.

• Too bad Comey doesn't read slashdot (Score:3)

on Friday December 18, 2015 @07:22PM (#51146939)

Too bad FBI director James Comey doesn't read /. He'd see how insecure even the most thuoght to be secure secure things - like backdoors - are and perhaps lose the impulse to make things even less secure and start moving in the other direction.

You know, it's possible that somewhere in the FBI there's one highly capable James Corney who is right now mopping floors in the basement because every time he and James Comey were evaluated by their superiors, personnel mixed up their reviews, owing to an unfortunate choice of fonts on the review forms.

• The real question is... (Score:2)

... allows them to extract the secret information sent between Alice and Bob.

... who the hell are Alice and Bob and why are they always sending secret information in these types of stories. Someone should report them.

See something, say something people ! - geesh.

• Interesting for some nations (Score:2)

A few nations do not have a lot of hardened mil only networks. They have to use public telco networks passing into a lot of other nations domestic infrastructure thanks to competition policy and trade deals.
The way around having to use very public, foreign owned networks and satellites sourced from many different providers for gov and mil communications was often thought to be emerging quantum cryptography.
Australia is spending huge amounts of time, funding and effort to try and keep the idea of national
• Déjà vu (Score:2)

This has a strong smell of déjà vu. Something is secure within a domain of application. Attacker push the system outside of domain of application.

I am almost certain I did read something similar several years ago with quantum crypto and blinded receptor

• I knew it... (Score:2)

I just knew Alice was up to something with Bob.

That fucking skank whore...

• No method of quantum encryption is truly secure (Score:1)

"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."

No method of quantum encryption is truly secure. The problem with these methods of quantum encryption is that they take too narrow a view of quantum physics and do not deal with the potential for attackers also using quantum techniques. If your quantum system has more energy and the right configuration it should be possible to break virtually any qua

• Me & Alice (Score:2)

I can't speak for Alice, but I'm getting sick and tired of having to do half of the encryption in the world. Most of the time it's just Lorem Ipsum anyway. I do this by moving rocks around in a desert, you know. It's not fun.

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