GPS, Danger In Space, and Robby the Robot

I wanted to start off this week with a great piece of research and journalism by Stephen Murdock.

Al Williams wrote it up, Spy Tech, the GPS numbers station.

If you don't know number stations during the Cold War and I guess on into the present, they were radio stations broadcasting strings of apparently random numbers spoken out.

And, you know, they're quote mysterious, but I think we all know what's going on.

I think it is a secret coded transmission by probably US military in a lot of cases.

The radio stations are broadcasting without a call sign on bands where they should be.

So whoever's doing it has got quite some nerve.

And I think people of radio direction find it, the number stations, and they almost always end up at US military bases.

Or in Russia somewhere.

So open secret, and I think that's what's cool about them in a way, is that it's broadcasting an open secret for everyone to hear, but presumably the encryption is so strong that only the intended recipient can figure out what's going on.

And the number stations are all very careful to control their format, groups of five numbers and the same number of them every time, and so they're kind of trying to hide the metadata there.

This all becomes relevant when talking about this GPS number station.

Stephen Murdock here points out that there are 22 bytes, 178 bits in subframe 4, page 17 of the standard GPS satellite signal that is, quote, special messages with specific contents at the discretion of operating command.

Impressive.

And if that doesn't scream secret spy stuff to you, I don't know what does.

So every GPS satellite has been transmitting these codes.

Every receiver can read them.

The standard for reading them is also open.

So in that sense, it's exactly analogous to the number stations.

It's specified to be text only.

although it's most certainly not text.

And Stephen does a great statistical analysis on this, and it's absolutely not any possible text encoding.

It looks like random bits by and large.

And so he does distribution compression tests and stuff.

But he does find some regularities.