Totally Secure Non-Quantum Communications?

An anonymous reader writes "TEES is reporting that Dr Laszlo Kish, an associate professor at Texas A&M, has proposed a 'classical, not quantum, encryption scheme that relies on classical physical properties -- current and voltage. He said his scheme is absolutely secure, fast, robust, inexpensive and maintenance-free and relies on simultaneous encrypting of information by both the sender and the receiver.' The scheme uses properties similar to Johnson noise along with Kirchoff's Law to provide what he hopes to be an easier method of secure communications. Arxiv also has the full text [PDF Warning] of the paper."

Comments

How this works and why it will fail

[goombah99]

I'll confess my understanding of this is sketchy at this point. But as I read it the concept is this one has a wire connecting two resistors. The Johnson noise in the wire is determined jointly by the resistors. Both sides, sender and receiver are changing the resistance values simultaneously with the sender putting in the message and the receiver putting in random crap which gets added to the signal. A person monitoring the voltage in the middle can't tell what fraction of the noise came from which side. Therefore the message can't be extracted. Clever. Oddly it's a lot like the bell's theorem experiment in QM where both sides are changing their filters.

What seems to be the flaw in this is that he assumes that the attacker must inject current unidirectionally to determine which resistance is at which end. Perhaps another means exists, courtesy of the speed of light.

Namely if you monitor the voltage at two points along the wire then you can distinguish between a wave proapgating from left to right and right to left. So you can now determine what fraction of the noise is coming from the left and what is coming from the right. Even if the noise level made his hard to do, there's also the moment of the resistor switch to capture. Each time the resistor is changed, even if it were perfectly synchronous, the left side's noise will reach the left tap sooner he the right tap.

This last effect could possibly be masked by injecting large amounts of noise into the system during the switch. (but of course this would also mask any current injection by the attacker as well). But the former effect of the noise signals propagation might still be detectable.