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."

Seems like a waste of noise...

[b0r0din]

Maybe I'm completely off here, but if you're using noise interference, wouldn't that be sort of wasting bandwidth? This is a cool technology, I wonder if there would be a way to mask a signal and at the same time run multiple signals, so you could essentially split the information through a long pipe (like the laser) using the chaotic noise, and each would be able to be filtered out (at some sort of router) and sent to various places accordingly. Seems it would be much more efficient to carry information that way.

How is this different from

[Anonymous Coward]

a One Time Pad?

OTP: person a adds agreed upon random noise to the plaintext. person b subtracts the same random noise from the cyphertext.

This: person a adds agreed upon random noise to the singal. person b subtracts the same random noise from the encrypted signal.

Seems the only difference is what level of the stack you apply the OTP.

Security through obscurity

[BillShatner]

This just looks like another way to hide a needle in a haystack. I believe there would be a couple ways to get around this:

The voice module for some of the high end (25+ CD) Pioneer CD changers is able to hear your voice even if the music is blasting. It does this by taking the music that's playing and mixing it into the microphone preamp 180 degrees out of phase, cancelling out most of the music. This isn't perfect, but I've seen it work, and I'm sure it can be adapted to do the same thing here. In fact, any imperfections may even help, due to the fact that you can (probably) tune it and pick up the real signal out of the mess.

Brute force. How random is this random noise? If you can create a similar noise generator, all you have to do is filter out 80% of the crap, and you'll be able to grab the signal. It's like picking out the flashlight from a group of strobes. It's a PITA, but once you cover most of the strobes, you can see the flashlight.

Re:No chaotic communication is *not* a one time pa

[metacell]

That is very interesting, mbkennel.

So you mean there is a chaotic system A at the sender's end, and another chaotic system B at the receiver's end, of the same type?

And that they would diverge if left to themselves, but are continously synchronized with each other, so both A and B generate approximately the same signal (the same "sequence of encryption keys", if this had been digital encryption).

And that an eavesdropper, with his own chaotic system C, cannot synchronize it with A and B?

Use BWT instead of LZ for even more diffusion

[yerricde]

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 [redhat.com]. More compression => more entropy per coded symbol => more resistance to known plaintext attacks.

Nulls.

[TheSHAD0W]

This technique is actually very old, though it wasn't used bit by bit. You're inserting null terms into the cypher stream. Prior to modern cryptological methods nulls were fairly popular, but the technique has fallen into disuse because of its increasing the message size, and because 1:1 stream cyphers are SO much more convenient. Besides, the new cryptosystems are unbreakable, right? Right?

Even having a small multiple of nulls to significant elements increases the complexity of calculation exponentially. For example, a 1:1 proportion of null bits in 512-bit blocks. The result is a 1024-bit blocked key stream. You can't do any sort of intelligent analysis of the stream unless you can figure out which bits are significant, and there are 2^512 possible permutations of significant and garbage bits for each block.

Pointless, actually...

[nweaver]

One of the classic mistakes is creating your own cryptographic algorithm when perfectly good ones will suffice.

AES/Rijndael is FAST in hardware, a $10 FPGA can do counter mode encryption, fully key agile, at 1.3 Gbps. Why create an algorithm dependant on chaotic laser behavior when you know that you can get cheap encryption which is secure in available hardware.

Chaotic crypto crackable, OTPs not

[billstewart]

Most of the chaotic cryptosystems people have tried to design have been crackable, and cracked. Perhaps there's something about this one that's different, but just because something's relatively hard to predict doesn't make it impossible for people who are far better at math than I am.

By contrast, a theoretical one-time pad is theoretically provably uncrackable - if you really do have uncorrelated random bits for your pad, and you really only use them once, it's perfectly secure, and even knowing N-1 bits of a message tells you nothing about the other bit. In practice, source of random numbers aren't always perfect, and sometimes people cheat and reuse pads - the NSA's "Venona" crack of Soviet crypto primarily succeeded due to rampant reuse of pads by sloppy crypto users, though I think they also found some non-randomness in the pads that they could exploit a bit. But this optical system guarantees that if you know the initial conditions, you can use the first N-1 bits of a message to predict the next one, and sometimes you may be able to deduce those initial conditions closely enough to crack the system.