Quantum Cryptography Broken, and Fixed

schliz writes in with research out of Sweden in which researchers showed that, looking at a quantum cryptographic system as a whole, it was possible for an eavesdropper to extract some information about the QC key, thus reducing the security of the overall system. The team then proposed a cheap and simple fix for the problem. "The advanced technology was thought to be unbreakable due to laws of quantum mechanics that state that quantum mechanical objects cannot be observed or manipulated without being disturbed. But a research team at Linköping University in Sweden claim that it is possible for an eavesdropper to [get around the limitations] without being discovered. In a research paper, published in the international engineering journal IEEE Transactions on Information Theory (abstract), the researchers propose a change in the quantum cryptography process that they expect will restore the security of the technology."

Comments

So is the cat dead?

[EmbeddedJanitor]

Quantum stuff is so illogical to us mortals that you'd expect attempting to break it would just make it stronger.

Re:So is the cat dead?

[Tackhead]

> Quantum stuff is so illogical to us mortals that you'd expect attempting to break it would just make it stronger.

Which is precisely what happened.

In a research paper, published in the international engineering journal IEEE Transactions on Information Theory (abstract), the researchers propose a change in the quantum cryptography process that they expect will restore the security of the technology.

By being sufficiently precise about the nature of the insecurity, they changed the probability of its being insecure!

Furthermore, now that we know it's secure again (that is, we've proven it to be secure, effectively computing the probability of insecurity to be precisely zero), we no longer know anything about the nature of the system's security holes again!

That was all supposed to be a lead-up to a Heisenberg Uncertainty Principle joke, but it's actually a pretty good description of how computer security works in even the non-quantum world. The more secure you think your system is, the more likely it is you'll get 0wn3d in some completely unexpected way. The known unknowns aren't the ones you've gotta worry about, and nailing them down doesn't do anything about the unknown unknowns, other than to collapse the joke's waveform into something resembling a Don Rumsfeld speech.

In anything other than a Slashdot quantum crypto discussion, that sort of whiplash-inducing change of joke subjects would be highly improbable. As it stands, I'm going to shift gears a third time and hand it off to Douglas Adams.

Zaphod: Tackhead, is this sort of thing going to happen every time you post using the Infinite Improbability joke drive?
Tackhead: Very probably, I'm afraid.

Re:So is the cat dead?

[NotQuiteReal]

You can increase the complexity by using a tri-state cat.

It can be either alive or dead or both alive and dead.

We call these three states alive, dead and zombie.

There, I hope that sheds some photons on the matter.

Re:So is the cat dead?

[tzanger]

I thought a tri-state cat would be alive, dead and high-impedance.

Re:So is the cat dead?

[bh_doc]

*sigh* Dude, the whole point of the bi-state cat is that both alive and dead is exactly the state the cat ends up in. It's a superposition until you measure it. That's why it's so bizarre. Schrodinger's cat is a zombie.

I know the solution

[jollyreaper]

They were connecting the computers via cat-5 cable. Everyone knows you're supposed to use Schrödinger's cat-5 cable in that sort of application.

There is no such thing as absolute security

[Anonymous Coward]

If data is stored, with the intent and purpose of actually being retrievable at some time in the future, and a mechanism exists to access said data, then it is not absolutely secure because it has been designed to be retrieved.
As long as there is even one access method there exists the opportunity to expoloit it somehow.

That wacky quantum cryptography

[Anonymous Coward]

It was actually broken AND fixed at the SAME TIME!

Re:That wacky quantum cryptography

[mrbluze]

It was actually broken AND fixed at the SAME TIME! Kind of like a Windows Update.

Re:Wah?

[mrbluze]

The advanced technology was thought to be unbreakable due to laws of quantum mechanics that state that quantum mechanical objects cannot be observed or manipulated without being disturbed.

Well the worst thing about an encrypted stream is that you trust it, not really knowing if someone is listening half way down the line. If you get a hint that it's being listened to, you can start sending garbage (or misinformation) down the line so as to confuse the hell out of the eavesdropper, whilst taking up alternative methods of communication or something.

This makes me wonder if cryptography needs to become cleverer. I mean, depending on the type of data you're sending, might there be a role in padding encrypted streams with 'honeypot' data, like random bits of vaguely interesting crap that the expected listener might want to be interested in. Sort of a live equivalent of Truecrypt's plausible deniability.

What do people think about that?

Article is a dupe...

[The Master Control P]

Just like the last time, the laws of quantum physics still work and it is still impossible to observe a quantum system without altering it. The researchers found that the classical authentication protocols that prevent man-in-the-middle attacks were insufficient.

The End of The Science of Cryptography

[Whiteox]

There was an interesting book on cryptography which I loaned to a friend, that surmised that the law of cryptography which state that every code can be broken is now defunct due to quantum cryptography.
This in effect means that the science of cryptography has met its end in terms of development.
Like the game of checkers, there are no more moves to make.
At the time of publication (2002?), the longest distance an encrypted quantum message sent and received was approximately 50kms and considered to be impossible to break.

No, not really

[Moraelin]

No, not really. QC only works over dedicated, point-to-point fibre optic lines.

Do you understand that one crucial aspect? If I want to talk to you completely securely, with quantum handshake, and able to detect eavesdroppers, I would need one uninterrupted strand of fibre from Germany to wherever you are. Screw 50kms, we're talking potentially tens of thousands of kilometres.

Or a chain of routers along the way that we both trust blindly to not be compromised, because each breaks that quantum handshake, and each is a point where someone could eavesdrop. You can't tunnel QC over such a hop, so it's a bit like having SSL only from your computer to your ISP, then have it decrypted there and re-encrypted to the next hop, and so on.

It's also pretty much against the whole idea of a network like the Internet. Since again, it needs dedicated uninterrupted point-to-point connections, not a loose mesh of routing machines. (You _could_ transmit the rest over the internet once you negotiated a key over QC, but: 1. you still need a dedicated connection for that handshake, and 2. you still need normal cryptography for the actual transmission then.)

For two John Does like us it's already pretty infeasible to go QC all the way.

Even for someone like the US Army:

1. Good luck having an all-QC connection from Washington to Baghdad. Even in 50 km segments, you need a lot of basically routers every 50 km on the ocean floor, each of them being a potential eavesdropping point. So if you ditch normal cryptography, you'd need to do... what? Park a couple of submarines near each of them to make damn sure the Russkies and Chinese don't tamper with them? Have permanent manned bases on the ocean floor every 50 km, with a company of soldiers watching each router, and watching each other so none of them can be a double agent and tamper with it?

2. And what do you do if someone drops a depth charge on one of those? You sure you don't want some regular crypto as backup?

3. That still doesn't help your communication to your airplanes, tanks, cruise missiles, etc, there. You can't tie a cable from each of them to Washington.

Etc.

So basically... well, let me put it mildly: I don't know what book you've read, or by what author, but I'd bet it wasn't written by someone who knows much about cryptography. It sounds more like the kind of predictions made by self-styled "pundits" like Cringely or Dvorak. Or, of course, any other of the many like them.

Re:Wah?

[catprog]

The thing is you can only accurately read about 50% of the photons.

When Eve reads the message changes to 50% correct, 50% incorrect.

When Bob gets the photons his 50% will consist of 25% correct and 25% incorrect ones. (assuming true randomness)

When Alice and Bob compare there keys they will see the discrepancy.

Then the 1 and 0 are XORs with the message and then the result is sent.

http://en.wikipedia.org/wiki/Quantum_cryptography#Polarized_photons_-_Charles_H._Bennett_and_Gilles_Brassard_.281984.29