This morning I’m sitting outside on the deck, as the sun comes up over the mountains, cup of coffee in hand. Living at 6000 ft is a high.
Being your typical girl my thoughts turn to sound waves and the principles of Van Eck phreaking.The concept is simple: using radio waves to literally see the screen of another computer user’s CRT.
Here’s a brief explanation from WikiPedia so it’s fairly crap:
Information that drives the video display takes the form of high frequency electrical signals. These oscillating electric currents create electromagnetic radiation in the RF range. These radio emissions are correlated to the video image being displayed, so in theory they can be used to recover the displayed image.My brain was having a problem comprehending the exact mechanisms for this.
So I decided to call Stephen Hawking.
“Steve! It’s Rachael. Get your lazy bragging wheel-chair bound ass out of bed.”
All I can hear on the other end of the phone is a bunch of flopping and thudding.
Jesus. It’s not as if the guy needs his damned beauty sleep. What does he do all day but sit on his ass?
After a moment I hear “Rachael? What time is it? 6:30 in the morning?”
Except I hear it in that stupid machine voice with all the annoying clicks from that damned box he uses.
For all I know he’s pissed but really who cares. It’s not like he’s got a fucking hike scheduled this afternoon.
I explain my questions about the Van Eck phreaking theory. Sometimes Steve is sorta slow up the uptake so I use really little words.
Before I’m halfway through he starts whining about the last time he was over at my house; he’s still holding a grudge after I filled those ten Diet Coke Bottles with Menthos, attached them to the back of his wheelchair, and sent him blasting off into traffic on South Virginia Street.
It’s not as if an accident is going to incapacitate him. Hell he’s already a crip. Jesus dude get over it.
Anyway, after he gets his shit together and back on track I ask why a computer, which is not a radio last time I checked, is emitting radio signals.
Stephen explains that it’s all a consequence of computers being binary (everything is run on transitions from zero to one and back again).
Computer bits are achieved by regulating back and forth from 0 volts (representing binary 0) to 5 volts (representing binary 1). This manifests as a square wave. Grab an old physics textbook off the shelf if you don’t remember what one of these looks like. I’ll wait.
Okay? Well, it seems that in reality these square waves are not ‘perfect’. In other words they don’t have the nice sharp angles and flat lines shown in books. So now take that goddamned textbook and throw it against the wall. I’ll wait.
Actually the waves have interference in them, even though they jump from 0 to 5 with rapidity. So the square wave actually has lots of really tiny peaks and valleys (smaller waves in the larger square wave) and the lines are not literally flat, straight or exact at all. They look like a kindergartner drew them. Or Stephen.
The little tiny peak and valley waves are called ‘ringing’.This ‘ringing’ between the actual binary numbers resonate within the circuitry of the computer. Since it’s bouncing around looking for a value it emits electromagnetic waves.
“So Steve what you’re saying is that this resonating turns every wire and metal cable in the computer into a kind of radio transmitter? That whenever the computer is on it’s sending out radio wave emissions?”
“Yes” click click. It sounds like the bastard is gargling with fucking tacks.
I asked The Gimp-Meister how a person determined which emissions represented the signals from the screen hardware and screen buffer. After all if every ringing is being emitted that’s a hell of a lot of information and most of it has got to be just noise.
Steve said that there are very few predictable signals but one of them is the ticks of the CRT monitor reading horizontal and vertical retrace intervals. Note: that last refers to the way a CRT scans the screen to retrieve information from the screen buffer. Go look it up yourself. I can’t do everything. Sheesh.
The bottom line is that by isolating the radio signal pattern from the CRT a person could literally see, on their own computer CRT, what was on the desktop of someone else.
Oh god I’d better not tell Tinfoil Hat Guy Web Client about this. Aiiiii.
Now you have to realize that this conversation took for-fucking-ever what with Steve whacking on his voice keyboard and me constantly saying “What? What? I can’t understand you Dude. Can’t you enunciate for goddsake?!”
The point is that I now have a better understanding of Van Eck phreaking.
Sadly, being just a girl, I’m not certain that my sophomoric explanation can impart this idea to you. Hopefully it can.
It’s pretty damned cool.Too bad my curiosity doesn’t pay the bills. Stephen probably would have offered to let me stay with him a while except he’s broke right now.
Something about buying a new wheelchair after crashing his into a parked car on South Virginia Street.
Steve. Lighten up. Have a Coke and a smile.
Tale Spinnin’ [LP Vinyl]
By: Weather Report
Release date: 1975