Electromagnetic Interference and the Faraday Cage

In an earlier post I talked about electromagnetic radiation sort of as an aside to a discussion of PC heat as a covert communication channel. Here I’d like to talk a little about what electromagnetic radiation is how to block it and how it can be used destructively. Before I do, I’d like to reiterate a disclaimer I’ve made before: Products or websites mentioned or linked to in this article or others by me do not imply endorsement by me or by Learning Tree International in any way. These sites and products are used as examples only. Neither I nor Learning Tree International receive any consideration or compensation as a result of such mention.

All electronic devices emit electromagnetic radiation or waves. That is, they are all mini transmitters. PCs are shielded to prevent that radiation from going out too far. This shielding is called a Faraday Cage. You’ve probably experienced a mobile phone placed near speakers emitting (intentionally) it’s signal and that signal being received by the speakers and making an annoying noise. That’s the electromagnetic radiation interfering with the speakers. We call that EMI for electromagnetic interference. Not all electromagnetic radiation is “interference”. Mobile phones, microwave ovens, television satellites and other sources emit electromagnetic radiation intentionally. The sun emits electromagnetic radiation, too.

EMI can be significant. Older computers were especially an issue and the US Federal Communication came up with standards for devices used in homes and different ones used in businesses.

Some cables (STP – the cable, not the engine additive — for example) are shielded to prevent the interference from devices such as PCs and mobile phones from interfering with communication through that cable.

STP Cable
Hurzelchen at the German language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

While most of us are concerned with unwanted noise on cables or from PCs, EMI can be quite significant and dangerous. During nuclear testing in the Pacific during the Cold War, Hawaii suffered the impact of an electromagnetic pulse or EMP. That pulse was a high amount of energy in a short time. The pulse was received on power cables – much like the mobile phone transmissions are received on nearby speaker cables – and damaged street lights and other electronic devices. That threat is significant. An article on forbes.com noted that “[A] single missile with a warhead that actually doesn’t have to be all that large, has the potential to take out the U.S. power grid, destroy our electronics networks, and create an existential crisis like nothing the world has ever witnessed.” That is pretty serious. The article also describes methods for protection from such an attack, but you and I probably won’t be able to do much for our own hardware.

Of course, smaller EMP weapons with less scope and power have been developed. They range in size from ones mounted on a Humvee to briefcase-sized weapons. These don’t use nuclear weapons, either. They use plain old electricity.

In Learning Tree’s System and Network Security Introduction we talk about using a Faraday Cage for an entire room or building to prevent eavesdropping in communication in that building or room. In a future post I’ll talk about RFID “tap and pay” cards and RFID passports and how to protect them from being remotely accessed. (Hint: it involves a Faraday Cage.)

To your safe computing,
John McDermott

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