Watch what you type

Power sockets can be used to eavesdrop on what people type on a computer.

Putting this story into words, Frank VK2FJL.

"Security researchers found that poor shielding on some keyboard cables means useful data can be leaked about each character typed.

By analysing the information leaking onto power circuits, the researchers could see what a target was typing.

It has been demonstrated to work at a distance of up to 15m, but refinement may mean it could work over much longer distances.

The research focused on the cables used to connect PS/2 keyboards to desktop PCs. The researchers pointed out that, the six wires inside a PS/2 cable are typically "close to each other and poorly shielded".

This means that information travelling along the data wire, when a key is pressed, leaks onto the earth wire in the same cable. The earth wire, via the PC's power unit, ultimately connects to the plug in the power socket, and from there information leaks out onto the circuit supplying electricity to a room.

Even better, said the researchers, data travels along PS/2 cables one bit at a time and uses a clock speed far lower than any other PC component. Both these qualities make it easy to pick out voltage changes caused by key presses.

A digital oscilloscope was used to gather data about voltage changes on a power line and filters were used to remove those caused by anything other than the keyboard".

Frank, VK2FJL

Wireless Institute of Australia