Friday, September 15, 2006

A Softer World, E-mail Spying and Signal to Noise Ratio

Have you ever lied about your age, income or political affiliation on a survey just because you don't think anyone really needed to know that much about you?

Have you ever said "no, thanks" to a pollster because you worry that polls make people think there's nothing they can do to affect the outcome of an election?

Have you ever contributed to the failure of a top-level corporate plan that was devised with no rank-and-file input?

These thoughts all came to mind after I saw today's edition of A Softer World, one of my favorite web comics, created by Emily Horne and Joey Comeau:

text: i FREEDOM FIGHTER BOMBING love you whether you reply JIHAD or not
if my GODLESS WESTERN PRESIDENT letters are flagged
our love will outlive us in their SUBWAY SARIN GAS computers

The comic also made me wonder about whether there really is a vast NSA email database, and if so, what we could do about it. But first, a little about signal-to-noise ratio.

Once upon a time, before I started working for a small independent government watchdog, I worked for a small defense contracting firm as an electronic intelligence analyst. One of my jobs was to calculate the effectiveness of a radar system. Most people have a rough understanding of how a radar system works: a beam of electromagnetic radiation (ie, light, but at a higher frequency that we can't see) is shined at your car. Some of it bounces back at the radar detector. The speed of the car shifts the frequency of the light a little bit, and the radar receiver figures out from this shift just how fast you were going.

But while you're driving down the lane, there are lots of things going on around you that might also be reflecting the radar beam back to the detector. This creates noise, which is basically as everything else that the receiver picks up that isn't reflected directly back from your vehicle. If the ratio of the signal strength to noise strength is high enough, then the detector is reliable enough to identify transgressors.


If you have no problem with the radar, then you can just drive the speed limit. But suppose you wanted to avoid having your speed detected, what could you do? One way would be to use a radar detector, which can alert to when the radar's on you. This is called a "passive countermeasure." The problem is, it might already be too late; if you see the radar then the radar sees you.

What you really want is to decrease the effectiveness of the radar by lowering its signal to noise ratio. You could start with your car. Most cars behave like mirrors to a radar beam: big blocks of metal that shine a lot of the energy directly back at the detector. If you had a lot of money you might be able to design a vehicle using difficult-to-detect composite materials like the Air Force uses, making sure your car's innards (like the radiator) are properly designed as well. This might be somewhat expensive, and your unique vehicle would soon be covered in the local media, making your attempts at stealth rather moot.

Another passive countermeasure would be to get a scrambler that mangles the radar signal and reflects it back with confusing information. The problem here is that acting alone you can't really return enough power to reliably confuse a well-designed receiver.

You could send out your own signal to try to jam the receiver; this is called an "active countermeasure." The problem here is that you don't necessarily know all the details of how the receiver works, so you'd have to put out a lot of power, and the receiver might be able to detect what you're doing (which is probably illegal).

Going it alone is clearly not the answer.

But what if you managed to get a lot of other people to, even those driving below the speed limit, to jam just a little bit, each one using a little power but in different frequencies, or scrambling a little bit, or modifying their cars just a little bit? All together, you might be able to increase the noise level enough to make the radar unreliable.

What does any of this have to do with NSA spying on our email?

This brings me back to today's edition of A Softer World. I'm no expert, but it's possible that the NSA software that scans email is looking for certain words and phrases (the signal) against the background noise of millions of "uninteresting" emails. What, I wonder, would happen if those triggers became so common that they no longer worked to identify the signal, but instead became part of the noise?

There's a danger of course if nobody goes along with you. After all, what do you think would happen to the first few people who started sending out emails with "Jihad meeting, bring your own anthrax" as the subject line. And of course, I'd rather see constitutional protections for our privacy, and at the very least, some kind of law banning warrantless domestic surveillance (what, we already have one of those?). Still, I can daydream about living in a society where the masses rise up and flood the net with emails titled "I'm mad as BUSH SUCKS hell, and I'm not going to take it TERRORISM PLANS anymore!"

Disclaimer: this message is for enterainment purposes only and is not intended to undermine or compromise any legal antiterrorism activity


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