Low EMI/TEMPEST Computer System

Covers the modification of a standard PC computer to reduce the radiated electromagnetic interference (EMI) and reduce the exposure to Van Eck/TEMPEST style remote data monitoring.

Hardening Your Computing Assets  (86k PDF)

van Eck-style Radiation Interception Experiments

Keyboard Notes

  1. Super Shield spray paint the internal keyboard plastic sections, two layers.
    • Helps prevent RF radiation from escaping the keyboard's plastic case.

  2. 0.01 µF RF bypass capacitors (surface mount) across keyboard cable's incoming Vcc and Ground wires.  Capacitors also across the 3 LED's cathode & anode.
    • Bypasses high frequency (VHF) radiation to ground.  LEDs can rectify low frequency radiation into higher frequencies, which can make monitoring easier.

  3. Copper foil shield over keyboard controller IC.
  4. Copper tape around exposed keyboard control lines.
  5. Shorten internal keyboard wires.
    • Help prevent controller IC clock and data information from escaping.

  6. Eliminate chassis ground screw.  Solder keyboard cable chassis ground directly to copper foil.
    • Short, direct soldered grounds have lower inductance and are more effective and higher frequencies.

  7. Maintain seperate data and chassis grounds.
    • Keep the noisy grounds from effecting one another.

  8. Remove all manufacture name and/or serial numbers.
  9. Super Glue any screws holding the keyboard together.  JB Weld or potting compound may be even better.
    • Helps prevent any tampering or replacement.

  10. Add external ferrite bead over the keyboard control cable.
  11. If possible, cut the keyboard cable to the minimum required length.  If not possible, roll the excess cable in a loop.  Be sure the cable is shielded.
    • Helps to prevent the keyboard cable from becoming an antenna.  "Looping" cable turns it into an inductor, preventing radiation.

  12. Disable the +5 VDC power line for the keyboard connector (computer internal) and use hidden batteries to power your keyboard.
    • To defeat inline key stroke recorders which use the keyboard power line.

Don't use wireless (RF or IR) keyboards.  Replace the keyboard cable with a fiber optic link and replace the keyboard key "switches" with opto-electronic or CCD pickup devices.  The distinct noise each key gives off can also be used to interpret which key was pressed.  You can practice this by listening to someone else type, use the distinct spacebar sound to compile a list of the length of each word typed.

Mouse Notes

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