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!"

Comments

Speed of sound versus ping times

[Chiasmus_]

It seems to me that the speed of sonar through water is a physical certainty; that's why we can accurately use it to detect the distance from an object.

Internet traffic is another matter. If I tried to use a ping time to measure the geographic distance to another server, I'd be about as scientific as the Slashdot poll.

Am I wrong, or could internet latency give or take 100 ms or so from a ping, rendering the encrypted message readable by.. no one?

Oh yes you CAN intercept it along the way

[PD]

Theoretically, at least.

In astronomy, the coolest research is in adaptive optics (do a Google search and you will be reading in fascination all day). Here it is in a nutshell, step by step:

1) The earth's atmosphere is turbulent. That turbulence causes the images of stars to dance around in telescopes, making the image all fuzzy. This is what causes the stars to twinkle when you look at them. Avoiding this problem is the big reason why the Hubble Space Telescope gets such amazing photos when it is much smaller than the largest telescopes on the Earth.
2) How to fix this problem without launching telescopes into space? Adaptive optics, of course. If you can flex a telescope mirror into exactly the right shape, you can compensate exactly for the distortion that turbulence introduces into the image, removing the majority of the noise from the signal. Suddenly the image becomes almost perfectly clear and steady, not fuzzy.
3) We know that stars look like points of light, even through the largest telescopes. When we receive a fuzzy image, a very fast computer figures out what shape a mirror would have to be to focus that fuzzy image back into a single point of light. That star is called a reference star. Any interesting objects close to that star are also therefore made clear.
4) Commands are sent to mechanical actuators on the back of a mirror that deform it to the correct shape to focus the reference star. This happens very quickly, so the resulting image is steady and sharp, despite all the turbulence in the atmosphere. Neat trick.

OK, so that's how it works.
You can do the same thing to submarines too, if you know what they sound like. The submarine's sound becomes the "reference star" in this case. When you receive the garbled signal, you might be able to correct it based on the sub's sound. If you apply that correction to the message as well, you might be able to hear the message.

This has a lot of problems, so practically it wouldn't work. For example, the easiest way to defeat the intercept is to change the noise that your sub makes, maybe with a random noisemaker. But that makes your sub less quiet. Also, the person trying to make the intercept would have to be listening to the sub before the message is sent, because once the message is sending, that would make the sub a random noise and you couldn't focus the sound. And, since the turbulence conditions change (I don't know how fast), over time your ability to focus the sound into a message would steadily degrade. The sending submarine would only have to figure out how fast the sea conditions are changing, and only start sending the good parts of the message after you've lost your ability to focus the sound.