Slashdot Mirror
Optical Cryptography
chill writes: "In Cryptonomicon, Neil Stephenson wrote about Bell Labs' research into using static, or chaotic signals to mask communications. A message would be generated, then the signal masked in noise. Someone on the other end would subtract out the noise to get the signal. Works great if both ends have the exact same noise. Now, Jia-ming Liu, professor of electrical engineering at UCLA, is giving a presentation on doing essentially the same thing using OC-48 (2.5 Gbps) optical circuits. The presentation will be at the upcoming Optical Fiber Communications Conference and Exhibit. There is an article covering this and some other nice advances in optical over in Wired."
If you're interested in how they syncronize the noisy lasers, here is a shortcut to the non-linear faq... a bit of easy evening reading for your enjoyment.
Great... now the RIAA/MPAA will be breathing down our necks for bypassing "noise-based-encryption" protection schemes every time we shield an audio or network cable...
The encryption in cryptonomicon was a one time pad. The pad was implemented as a record, but the concept was the same. The fact that the conversation could only last as long as the record and each record was only used once is indicative.
But then, perhaps the lasers could be considered an infinite one-time pad? Of course, if anyone else is listening to the synchronisation codes, couldn't they themselves end up with a synched laser too?
As a form of encryption, this doesn't appear (to me) to be incredibly useful to the average person. It doesn't secure the communication, only the physical connection between the two points. However, it would work for keeping snooping foreign governments from listening in on international traffic on submarine cables. Or nasty pirates from splicing themselves into the cable TV network...
This form of chaotic synchronizing communication works by a dynamical systems property. It seems like magic but it is not really.
It relies on the effect of chaotic synchronization. That sort of amazing fact that even though you can have a dynamical system that is continuously unstable in 'some degrees of freedom' making up the chaotic system the combination system of transmitter and receiver can still be stable in the 'transverse' direciton to the synchronization manifold.
All communication systems work by synchronization whether implicitly or explicitly. Here you will explicitly have chaotic oscillators as both transmitters and receivers. Yes, radio is like this too, you have a linear oscillator in the transmitting tower and an oscillator in your RF circuit in your receiver and their electric fields will synchronize the receiver's oscillator to the transmitter.
The trick is how to add in modulation and demodulation that does not destabilize the system and still permit reconstruction of the transmitted information.
All chaotic systems essentially have some sort of nonlinear feedback. The trick that seems to work very frequently with optical dynamics is to mix in some of the transmitted signal coming over the channel with the self-regenerated system at the receiver. In previous work with fiber optic ring laser it really was literally mixing optical signals, in the thing I did it was mixing in electro-optic electrical feedback signals; more like mixing intensities.
It turns out that a fairly generic form of dynamics often seems to work.
I worked on this project from a theoretical modeling level with Jia-Ming Liu's group at UCLA.
(We're at UCSD not UCLA).
I'm not sure what this new work is about but in the version that I did there was no significant role for the dynamics or properties of the fiber optics in the creation of the chaos or the demodulation.
It will a very significant amount of engineering to make this fully practical and find all the good properties but that's true for every advance.
How does one hide messages in reandom noise, though? Would it work to LZ-compress them, to make them appear random?
LZ+Huffman (i.e. deflate, the core of gzip and pkzip) works, but you get more compression in a Burrows-Wheeler based scheme such as bzip2. More compression => more entropy per coded symbol => more resistance to known plaintext attacks.
Will I retire or break 10K?