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Holographic Sonar Cryptography
Atomic Snarl writes: "New Scientist.com has this story on how to encrypt a underwater sonar message using multiple sound path timing.
By detecting and adapting for the current variations on underwater sound channels,
the transmitted message can be received intelligibly only at a single point.
This holographic approach suggests a method of web encryption using multiple
hop paths and ping times to create a message which can only be decoded when
received at a specific target node!"
Even if you could eliminate the problems with the latency, the asymmetric routing that exists in the internet will kill this technique. This communication technique depends on the forward and the reverse path being identical - something which is not true when asymmetric routing is used.
There is no such thing as luck. Luck is nothing but an absence of bad luck.
A much more detailed (7 pages) article on time-reversed acoustics appeared in the November 1999 issue of Scientific American.
I pasted the summary below, but here's a link to the summary just to make it official.
Time-Reversed Acoustics
Mathias Fink
Record sound waves, then replay them in reverse from a speaker array, and the waves will naturally travel back to the original sound source as if time had been running backward. That process can be used to destroy kidney stones, locate defects in materials and communicate with submarines.
I thought it was so cool that I wrote a program to simulate the effect. It simulates 1 or more waves emitted by 1 or more sources, and records the waves at 1 or more "microphones". It then treats the "microphones" as "speakers" and plays back the time reversal of the recording. At first the screen is filled with chatoic expanding circles, but after a while the expanding (and fading) circles combine to create a CONTRACTING and STRENGTHENING circle!
I wrote it for my own curiosity, and the code is "dirty". If there's some real intrest here I could dig it out and clean it up a bit.
- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
The sonar conditions vary considerably through time. There are inversion layers and tunnels that are formed due to the differences in the index of refraction for the audio signals.
In optical holography, you are recording the interference patterns resulting from a reference beam and reflected light. When you shine a laser of the right wavelength through or off the hologram, the interference patterns are "replayed" thus reproducing the image.
Little if any information can be gleamed from a single intererence pattern.
In the case of sonar, you are recording audio interference patterns. However, unlike in an optical holographic environment, the conditions change drastically under water depending upon weather condition and seasonal (or even geophysical (i.e earthquakes and volcanos) variations.
In a controlled scenario as described in the article, it works because the replay occurs in a very short time period and the interference patterns may not change much. Without an initial reference signal, it may be very hard to get a good mapping of the sonar environment.
As for the security, I wonder if you recorded the signal eminating from a single transducer at short range if you could actually receive the message at a spot other than intended.
RD