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SAN ANTONIO, Texas -- When it's time to make sure that communications from and to the aircraft of the president of the United States are safe from eavesdropping, who do you call? The Air Force's 346th Test Squadron.

Part of the 688th Cyberspace Wing, which itself is part of the 24th Air Force, based at Lackland Air Force base here, the 346th is tasked with making sure that electronic emissions aboard all the service's aircraft are secure. Even Air Force One.

As part of CNET Road Trip 2014, I've come to Lackland, located in this south-central Texas city of 1.3 million, to see just how the Air Force "hardens" its aircraft from unwanted eavesdropping. Though I came to hear technicians talk about their efforts on board any number of the service's planes, I wasn't expecting to hear about their recent work to secure communications on Air Force One.

"Talk about" is a relative term, as the technicians who were part of the Air Force One hardening team couldn't reveal much more than that they had evaluated the president's plane. Yet just knowing that their work includes such a crucial aircraft put what they do for the Air Force in a very clear perspective.

According to Col. Dean Clothier, the vice commander of the 688th Cyberspace Wing, the work of the 346th Test Squadron is just one element of his organization's broader work to ensure that vulnerabilities in the service's essential systems -- from physical infrastructure to water and power systems to radios and other communications equipment aboard airplanes -- are secure. Defending the cyber components of all Air Force infrastructure is the task of the 24th Air Force, and often that means trying to attack their own systems. "We look for vulnerabilities for cybersystems to be breached," Clothier said.

On the flightline

When someone tells you they're taking you out to see the biggest plane that the Air Force flies, you start to wonder how huge it will be when you're standing in front of it. And that's just what happened during my visit to Lackland: Driven to the flightline for a briefing on how the Air Force tackles unsecure emissions aboard a Lockheed C-5 Galaxy, I found myself staring up at a whale of a plane.

Measuring 248 feet long and 65 feet high, with a wingspan of 223 feet, this is an airplane that feels every bit as big as the football field it would span. Its mammoth cargo bay can easily hold six Greyhound buses, I'm told, though I have to imagine the number is much higher.

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Still, despite the incredible size of this workhorse cargo plane, the work done by the 346th Test Squadron to secure the C-5's emissions is not much different than what it does with other aircraft. Though he wouldn't spell out the specific vulnerabilities his unit battles every day, citing security concerns, Lt. Col Brendan Casey, the commander of the 346th, talked generally about the work.

The job, Casey explained, is about making certain that when an Air Force plane is new, upgraded, or has new communications equipment installed, those systems are evaluated to be sure they're safe from eavesdropping, and that any electronic signals are protected. "The goal," Casey said, "is that the [signals do] not emanate far enough to be captured."

Casey's team flies to air logistics centers throughout the Air Force's global operations, traveling with its own RV, a white, nondescript vehicle with US government plates known as a mobile assessment vehicle. Inside, technicians run tests of equipment on board the planes for any problems that need addressing.

It works like this: Technicians from the 346th turn on a plane's systems, one by one, and using a special antenna measure what data can be collected from the aircraft and from how far away. The worry is that a bad actor could set up shop somewhere in proximity to an Air Force plane and pull in electronic signals, looking for some vulnerability to exploit, or information to steal. For example, a decision maker aboard a plane may be discussing how many troops are involved in a mission or where a mission is supposed to take place. This is not information the military wants leaked.

As each system is evaluated, Casey's team reports the results up the chain of command so decision makers can determine whether a plane is ready for the fleet. "The good thing," Casey said of what he calls EMSEC, or emissions security, "is that we've been doing this for so long that very few [unsafe] emissions" are usually found.

One of the biggest risks, according to Maj. Anil Hariharan, director of operations for the 346th Test Squadron, is what he called "crosstalk," where a signal from one communications system is captured and accidentally broadcast by another that's less secure. That means the technicians have to test every single radio, or anything that can transmit aboard Air Force planes. That can be time-consuming. All told, Hariharan said, there can be between 137 and 200 systems on an Air Force aircraft.

The ghostly E

To demonstrate how all of this works, the 346th team has set up an insecure laptop on board the C-5 that has a big E on its screen made up of up bunch of other letters. They want to show me how, in the mobile assessment vehicle, parked 20 feet or so away from the raised nose of the giant plane, they can eavesdrop on the laptop's signal.

Sure enough, inside the van, as two technicians fiddle with settings on their assessment equipment -- oscilloscopes, spectrum analyzers, audio and signal generators, and fiber-optics transmitters -- the E suddenly appears. Though it's ghostly, and doesn't seem to reveal the full extent of the image that's visible on the laptop, it's clear that they've caught some of the signal.

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That's exactly what they're looking for, Casey explained. Emissions could couple onto another cable, or high-frequency radio signals may be vulnerable. Unshielded cables sitting next to each other could be a problem. And even small power sources like a laptop could be transmitting over high-frequency signals, Casey said.

What are the solutions? Every situation is different, but in the case of the laptop with the E on it, there are a number of possibilities. For starters, use of the laptop could be restricted to certain areas of the plane. Or its cables could be changed or shielded. But just as likely is that crews might be restricted from using laptops at all, or to using hardened laptops, Casey said. Or use of laptops and radios at the same time may be prohibited.

For Casey's team, this is nonstop work, throughout the Air Force's vast network of facilities. And it's clear they take their work seriously, no matter what plane they're assessing. But in case anyone doubted the work was crucial, one technician told me, having to make sure Air Force One was properly hardened showed that their efforts are "a very important mission."

Keep an eye out for more behind-the-scenes stories and photo galleries as I travel throughout Texas, Oklahoma, Arkansas, Tennessee, and Kansas during this year's Road Trip. I'll seek out most interesting technology, military, aviation, architecture, and other destinations our country has to offer. From U.S. Air Force basic training to NASA's Johnson Space Center and FedEx's massive package-sorting hub, and much more, Road Trip 2014 will take you along with me.