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Move Over, Quantum Cryptography: Classical Physics Can Be Unbreakable Too
MrSeb writes "Researchers from Texas A&M University claim to have pioneered unbreakable cryptography based on the laws of thermodynamics; classical physics, rather than quantum. In theory, quantum crypto (based on the laws of quantum mechanics) can guarantee the complete secrecy of transmitted messages: To spy upon a quantum-encrypted message would irrevocably change the content of the message, thus making the messages unbreakable. In practice, though, while the communication of the quantum-encrypted messages is secure, the machines on either end of the link can never be guaranteed to be flawless. According to Laszlo Kish and his team from Texas A&M, however, there is a way to build a completely secure end-to-end system — but instead of using quantum mechanics, you have to use classical physics: the second law of thermodynamics, to be exact. Kish's system is made up of a wire (the communication channel), and two resistors on each end (one representing binary 0, the other binary 1). Attached to the wire is a power source that has been treated with Johnson-Nyquist noise (thermal noise). Johnson noise is often the basis for creating random numbers with computer hardware."
Johnson noise.
Give me Classic Slashdot or give me death!
I want to know if the Laszlo in this story also has an underground room where he prepares and sends in entries to the publishers clearing house sweepstakes. And who's dorm room closet does he come out of?
Is it just my observation, or are there way too many stupid people in the world?
Unbreakable encryption that can be decrypted is much harder.
"Have you ever thought about just turning off the TV, sitting down with your kids, and hitting them?"
The problem with using the second law of thermodynamics for this is that it is a statistical observation, not a natural law.
I remember when this was posted on Slashdot 7 years ago.
Is it a coincidence that Johnson-Nyquist noise sounds exactly like an accordion and bagpipe duo playing La Marseillaise?
Claude Shannon proved in the 1940's that the Vernam cipher with a key the same size as the message, aka one time pad, has perfect security. The USA built the world first digital audio system during WWII in order to give such perfect security to voice communications between Roosevelt and Churchill, among others.
This approach assumes that only Alice and Bob know the current and voltage of the power source. This can be brute forced until a tangible message is found. Next...
The basic idea of the key exchange is a variant of an older key exchange idea. The very basic idea involves Alice and Bob having a wire that goes between them. Each of the two has two resistors one with very low resistance and one with high resistance. To gain a series of random bits, Alice and Bob both randomly choose a resistor and connect it to the wire and then measure the resistance through the whole system. If they both used the high or both used the low resistance resistors they throw out those exchanges. Whenever they have one medium and one high, they will both know which one had a low and which one had a high because they'll know their own. But Eve the evil eavesdropper even if she has a connection into the line won't be able to get this just from knowing the total resistance. In some weak respects this resembles a physical analog of the Diffie-Hellman http://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange. The process being proposed here though, a Kish key exchange http://en.wikipedia.org/wiki/Kish_cypher does some clever stuff with the thermodynamics end to deal with man-in-the-middle and other related attacks.
He said "Johnson".. and then he said "thermal".. that was cool..
Through obscurity
Throw in a buch of gobble-de-gook and only know which bit is meaningful, that's the answer.
A feeling of having made the same mistake before: Deja Foobar
I don't know about y'all, but I like my cats dead when I open the box.
It's a far stretch to call thermodynamics "classical physics": it was the first physics to include probabilities (which is not classical), and as such it is a precursor of quantum physics.
As someone pointed out, this was on Slashdot 7 years ago. Here's the referenced paper.
The idea is simple. At both ends of the wire, random data modulated with content is being emitted. At any point on the wire, you see the sum of two random sources. But each end knows their own random data, and can subtract it out.
To break the system, you need two taps on the wire, some distance apart. Now you get to see the sums of the signals from each end, but with different time shifts between them due to propagation delay. With that data, you can separate out what's coming from each end. This allows recovering the original signals.
"No new encryption system is worth looking at unless it comes from someone who has already broken a very hard one." - Friedman.
Use messengers. I think this is an old idea. As far as quantum security, I will wait for quantum computers. Unbreakable come on. Anything can be hacked eventually.
This isn't b3ta, you know.
Given the variety of additional factors, such as path loss, crosstalk, temperature differences, difference in cable materials, etc., etc., the system is limited to only particular environments. It would never work on a standard telephone line to a house for example.
Back to the drawing board.
In the household we obey the laws of thermodynamics! -Homer Simpson
...encryption. If "spying" on the contents would permanently alter the contents, thus it "unbreakable", wouldn't also reading the contents do so, (making them unreadable)?
... does not exist. Anyone promising complete security is either a naive idiot or a lier.
From the article:
"The idea is straightforward. Alice wants to send Bob a message via an ordinary wire. At each end of the wire, there are two different resistors that correspond to a 0 or 1. Alice encodes her message by connecting these two resistors to the wire in the required sequence. Bob, on the other hand, connects his resistors to the wire at random. The crucial part of this set up is that the actual current and voltage through the wire is random, ideally Johnson noise. The essential features of this noise are determined by the combination of resistors at each end. This noise is public--anybody can see or measure it. Now here's the clever bit. Bob knows which resistor he connected to the wire and so can work out which resistor Alice must have connected."
This can be broken through long term monitoring by a radio receiver. In cryptography terms, it is akin to a one-time pad. Because there is a finite number of resistors at both ends, checking all combinations is feasible.
A ridiculouos idea, if you're an electrical engineer, for many reasons:
(1) The noise on the wire, for reasonable values of resistors and bandwidth, is down in the low microvolts. If the cable is unshielded, it's going to pick up several microvolts of radio signals per foot. Even if it's really well shielded, we're still talking microvolts per kilometer.
(2) Eve can put a probe signal on the wire, it just has to be random noise. Alice and Bob have no way of proving that a small spike of random noise, only half a standard deviation above the average, isn't perfectly fine Johnson noise coming from the other end. Eve knows the amplitude of the noise she is putting on the wire, so she can subtract that amount, and the difference reveals the values of the resistors.
(3) For any moderately long wire, in the kilometer range, there is a time delay, allowing Eve to inject short bursts of noise and get the resistor info from each end coming back, spread out in time.
(4) Bell Labs proposed this idea, the part about injecting noise inn from both ends, back around 1955.
First and foremost is that there has to be TWO conductors unless we are dealing with static voltages. You can use one wire and the ground as the second conductor, but there is going to be significant resistance in any kind of useable length. This means that there are at least two places for someone to be making measurements to figure out the necessary information.
Second, this method has a limited number of logical states (LL, LH, HL, HH) that encode two bits of data which will be clearly observable on the wire. Of the four states you will see three unique wire states (Low, med, high) with only one not disclosing the state of both ends. Once you established these states by observing the wire, you can easily determine two of the four states. Thus by simple voltage measurements you have already decoded half of the information you need. What's left is to simply observe the direction of the current and that will tell you what end of the wire has low or high resistance.
I don't think thermal noise really matters here because for this to be a practical system you will have to pick voltage sources that have enough signal to noise so you can detect them at the both ends of the wire. They may look like random noise, and even be random noise, but in order for there to be a delectable result at either end of the wire means there is a measurable value. Further, in order to detect highs and lows, each end of the system will have to KNOW what voltage is being applied, or how could they know the voltage/current to look for?
I suppose you could improve your security by increasing the number of resisters, but if this worked for two, it is sure to work for more than two values, just with more emphasis on the current measurements being required.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
Every time something involving quantum mechanics come up, the comments are along the lines of "wow, amazing, too bad I will never understand." Since this system uses classical thermodynamics, all the comments are more like "classical mechanics? oh yeah I learnt that in high school. Nah, this system can't work, its obvious". It's pretty obvious that whatever the merits of this system, it rests on some pretty subtle and advanced physics, not the sort of thing an average person or even an undergrad physics major, could debunk.
Starting my PhD in quantum cryptography in August and this is of course a very interesting idea.
Quantum hacker.
and say that if you get to the messenger, all encryption becomes futile anyway, i'm a bad person, right
"In practice, though, while the communication of the quantum-encrypted messages is secure, the machines on either end of the link can never be guaranteed to be flawless." Actually, in practice, this isn't true. The communication of qbits currently requires the sending of multiple particles that have been operated on in the same way to overcome the problem of particles interacting with the universe and getting into a "dirty" state. Because of this, certain kinds of man-in-the-middle attacks are possible against quantum cryptographic methods, at least as currently practiced. The quote from the summary makes much more sense if we s/practice/theory/.
They discovered, upon opening th box, that Dr Schrodinger had killed the cat with a hammer.
Innocent people shouldn't be forced to pay for inferior software development.
--"Code Complete" Microsoft Press
Many "laws" in physics and chemistry are merely useful approximations or things that are usually but not always true. Take Ohm's Law, in a real world material current is not perfectly linearly dependant on potential, you get interesting curves instead, and some materials even have inverse relationship. Besides, the "laws" of physics are man-made attempts to model the behaviour of reality, and might be refined or replaced at a future date with something more useful or more accurate. Good scientists are more than happy to point this out, it is after all a big incentive to improve man's knowledge and abilities.