Shielded Enclosure / Faraday Cage Guide

A properly built shielded enclosure (SE) / Faraday cage is a great physical layer control when you're using a hardened laptop for signing or accessing high-value crypto.

A shielded enclosure is probably not needed if you can keep people about 80 meters away from your PC or laptop. Even at 20 meters, you are generally pretty safe. However, highly professional entities (governments) have the ability to eavesdrop from much farther away, so if you are a high-value target, an SE is a good idea.

Why use a shielded enclosure with a hardened laptop or PC

  • Blocks RF eavesdropping & injection. Prevents attackers from capturing electromagnetic emissions from the laptop or from injecting radio-frequency commands or attacks (e.g., remote keyloggers, malicious implants using RF).
  • Reduces malware/remote access risk during air-gapped operations. Even if the laptop is otherwise exposed, the SE helps keep wireless/over-the-air attack vectors closed while you sign or access keys.
  • Prevents unintended beaconing. Stops the device from broadcasting or receiving Bluetooth/Wi-Fi/GNSS/NFC signals while sensitive operations occur.

High-level construction pointers

  1. Rigid conductive shell. Use continuous conductive material: copper sheet or heavy gauge aluminium, or an electrically conductive mesh with very small openings. For portable SEs conductive fabric (silver/copper cloth) over a frame also works for many purposes.
  2. Seam integrity. All seams must be electrically continuous: overlapping seams, conductive tape, or conductive gasketing. Gaps are where RF leaks. Use EMI/RFI shielding tape or compression gaskets at doors/hinges.
  3. Door/access. A hinged door or removable panel for inserting/removing the laptop. The door must compress a conductive gasket for full perimeter contact.
  4. Optical interface. Use optical fibre feedthrough. This forces air-gapped communication and maintains RF isolation.
  5. Power considerations. Battery operation (no external power connections crossing the shield) is safest. If external power is needed, use proper power line filters.

Grounding

Proper grounding is crucial for RF effectiveness.
  • Single-point ground. Connect the SE to building/mains ground at ONE point only to avoid ground loops that can create RF ingress paths.
  • Low impedance path. Use heavy gauge wire or copper braiding for the ground connection. Minimize length and inductance.
  • Test continuity. A proper building ground rod will probably need to be installed. It must be tested with a megger to meet proper specs for a shielded enclosure.
Bottom line: A properly constructed shielded enclosure adds significant electromagnetic isolation to hardened laptop operations. The key is continuous conductivity, proper grounding, and maintaining seam integrity.