A TEMPEST in a ... wall outlet?

[unixronin]

Bruce Schneier points to a paper on keyboard sniffing by detecting crosstalk between poorly shielded keyboard cables and power lines.  He also observes that the NSA has known about this principle for decades.

What I want to know is, why haven’t we switched to optical interconnect cables yet?  Component-stereo CD changers have had digital-optical outputs for over ten years now, and the home audio industry is hardly known for leading the field in interconnect technology.  Mice, keyboards — heck, ALL HIDs — monitors, external disks, even powered computer speakers:  they could all easily use optical-fiber data connections.  Many devices would still need power, of course, but the low levels of power required by devices that don’t already have their own separate power supply could be carried on a braid layer around the fiber.  Most speeds of what we’re still calling Ethernet can already run over fiber.  There’s no technical reason why we should be using copper cables any more for anything except supplying power — and copper is becoming expensive enough that it was actually cost-effective for thieves to steal 45km of undersea Internet cable from the seabed off Korea in order to sell it as scrap.  Even telephony devices run over copper only because telephones have historically been line-powered devices and the installed base is too huge to easily change.

Make sure computer cases are properly shielded and power supplies back-filtered to prevent feeding RFI back into their own power lines, and we could probably virtually eliminate RFI emissions from computers except for the display — and as a bonus, it would reduce their susceptibility to RFI and crosstalk.  (Even with magnetically-shielded computer speakers, I’ve had crosstalk issues when a monitor cable passes a few inches too close to a powerful speaker.)

Reason says it ought to be possible to RFI-shield flat-panel displays too.  (Perhaps a transparent conductive coating on one of the face layers?)

Comments

[montieth.livejournal.com]

This is somewhat NOT new. You know how the military always refers to wired communications as 'secure' from intercept. Those were not the case during WWI. Early morse type fuller phones used dual or single wires for transmission/reception. Single wire worked using earth return. The problem was that the Germans figured out they could use some not so fancy gear to more or less eavesdrop on fullerphone (http://home.planet.nl/~meuls003/fullerphone/fullerphone.html) conversations which were using earth return/ground spikes.

Basically, where they can get noticeable differences in voltages from your ground leg, they're going to be able to intercept. Power and Ground voltage filtering would help this greatly. I wonder if a capacitor attached to your ground lead would dampen the square waves that the keyboards send. Where the grounds aren't easy to get to, one could have a problem. But even a house has external faucets and outlets where one could run a tap line to.

I guess filtering the ground (you can't isolate it) at the power connection would help too.

[mrmeval.livejournal.com]

I've never heard the military say that wired is secure. It is in fact printed on every telephone on a military base that it is subject to be monitored and they don't mean only by them. Every briefing I took when getting a security clearance said the same thing.

On a tempest rated computer everything is shielded or filtered. The power had a large filter section for the AC before it's fed to the supply. The vents used honeycomb shields. If data had to be sent from the computer to somewhere else it either got hand carried on a disk or the computer was hooked by shielded cable to an encryption device that would encrypt it and send it safely on it's way.

The cases have extra space for all the filters. Any part of it that opened to the outside had an RF gasket.

The concept of red/black is that red is unencrypted and had to be in a shielded and protected machine/area, black is encrypted and can go wherever you want.

[montieth.livejournal.com]

Tactically secure under field conditions. Ie a radio will be easily DF'd and intercepted if it's regular voice. Basically a LOT of field manuals state to use wired commo lines.