Say I am at my office. I am now trying to talk to my friend with a LUI instant message application.

I have a blanket covered over my keyboard, just like Snowden, probably good enough to hide my password. However, there are two problems:

Firstly, someone might replace my keyboard with a one that look visually similar but have a slightly different sound produced for each key I pressed, so a nearby sound interceptor can intercept the keys I entered.

Secondly, my friend's and my messages are shown on the screen with totally no protection. An inexpensive camera would suffice to capture all the messages. I was thinking about implementing an encryption algorithm, communicating over my computer and me, but I think either it is too insecure or it is too complicated for my mind to handle, e.g., I cannot compute even plain RSA in my head.

How can I mitigate the sound and visual attacks?

Edit 1

I understand that there is no "perfect security". I hope to reduce the risk instead of eliminating them.

For problem 1, I am currently only targeting acoustic attacks. It is taken under the assumption that even if the keyboard is bugged, only acoustic attacks will be carried out.

  • There is no such thing as perfect security. The existence of function necessarily implies the existence of some risk. That said, these threats are primarily threats to the physical environment. To mitigate them, improve your physical security and access management. – Xander Jan 15 '16 at 19:24
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    Your keyboard already makes different sounds for different keys. There are well-documented attacks based on this. Also, if they can replace your keyboard, they can install a special one that stores data and does other bad stuff. There is no security without physical security. – Neil Smithline Jan 15 '16 at 19:27
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    How would implementing an encryption algorithm stop a camera from capturing what's displayed on the screen? – NotMe Jan 15 '16 at 20:06
  • Block the camera with instructables.com/id/Laptop-Compubody-Sock and have a white-noise generator drowning out the keyboard clicks. – TessellatingHeckler Jan 15 '16 at 20:40
  • And don't forget about leaking keyboard strokes through the power outlet of your computer - cnet.com/news/sniffing-keystrokes-via-laser-and-keyboard-power – Neil Smithline Jan 15 '16 at 22:45

Mitigation for attacks leveraging the environment (planting external microphones, or cameras) must be based in additional security measures to protect the environment. Physical security, in other words.

This can take several forms, including isolating the computing environment. (A keyboard in a low-walled cubical, for instance leaks acoustic information into a far larger and harder to control environment than a keyboard in a locked, insulated office. Better personnel access control would be another measure you might take, to limit the ability of an attacker to place a device in the environment in the first place.

The old saying is, you can't protect the data on your computer against an attacker who already owns your machine. A corollary then, is that you can't protect the optical and auditory data emitted by your computer into the environment from an attacker who owns the environment.


How can I mitigate the sound and visual attacks?

How far are you prepared to go?

Video: There are several methods to either "scramble" a LCD video image so that special glasses are required to see it again, or narrow the angle of vision of a LCD screen so that it is only visible by the person sitting exactly in front. The narrower the focusing, the most uncomfortable the performance, since you need to keep your eyes inside a specific volume of space or the video image will appear to fade to black. Passive polarizing glasses are easily defeated by a polarizing filter on the spy camera, and "active" glasses are clunky and, well, if you're putting a hardware gizmo on your nose, you might as well go for gold and use a "private cinema" visor that would directly enclose your eyes and bypass the monitor altogether.

Audio: since the blanket on keyboard setup is already bound to mark you as Snowden-level paranoid, you could just as well set up a keyboard typing soundtrack to muddy the waters for eavesdroppers. You could even go full Matrix and use a virtual keyboard from your VR visor: while conceivable, decoding what you're typing from the small twitches of your fingers donning virtual reality gloves would be a nice mess for any attacker.

Other possibilities include laser keyboards (which cannot be blanketed, unfortunately, and are quite video vulnerable) and silent keyboards.

However, if it's possible to install a microphone and camera on the premises, then it's also equally possible to either attempt Van Eck phreaking of the keyboard signals, plug a hardware keylogger on the cable, or straightaway hide a transmitter inside the keyboard (this would be usually done by first purchasing an identical keyboard, then installing the transmitter inside, then swapping the keyboards. You might want to supplement yours with an easily overlooked, yet recognizable scratch in an unobtrusive place).

So, I'd go with securing the place first.


The Snowden blanket involves covering the screen and keyboard of your system. Not the keyboard alone.
To mitigate the audio attack, you will need to record the sound each keystroke on the 'bugged' keyboard makes and play a randomised version of this audio through a speaker while you are using the keyboard. For precision you may need to use db meters and perform frequency analysis to make sure the sound is as close as possible to the actual keyboard.
The only issue is, if the attacker has gone this far to steal your keystrokes, he/she most likely would use Van Eck phreaking as per @Isemi's post.

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