What is TEMPEST? Electromagnetic Leakage and Emission Security

The heart of the problem: unintentional emissions

Every operating electronic circuit — monitor, keyboard, network cable, printer — radiates an electromagnetic trace of the signal it processes. An eavesdropper with the right equipment can reconstruct the original data from these traces: the screen image, the keys pressed, the traffic on the line.

In NATO/US literature this risk area goes by the code name TEMPEST. Wim van Eck's 1985 feat of reconstructing a monitor's image from a distance with ordinary equipment is the classic demonstration that brought the subject to the public; today's attack surface is far wider.

Standards and levels

NATO manages emission security through the three equipment levels of the SDIP-27 standard (Level A/B/C) and a zoning approach that defines a facility's environmental risk: how close an eavesdropper can get determines which level is required.

Certified TEMPEST equipment is expensive, so in most organizations the practical architecture is mixed: a shielded room for critical operations (architectural shielding), standard equipment inside, and filtering at the line and power entries.

Layers of protection

• Architectural shielding: lining the room surfaces with 80-100+ dB class materials (A300-HEMP, A190, HNG100)
• Distance and zoning: moving critical equipment away from the façade, the car park and neighbouring areas
• Cabling: shielded/fibre lines, correct grounding, line filters
• Equipment choice: certified hardware at the most critical end
• Verification: IEEE 299-based acceptance measurements and periodic checks

Frequently Asked Questions

Is TEMPEST only a concern for government agencies?

No. R&D centres, financial institutions, law firms and organizations preparing competitive examinations — anyone whose intellectual property passes through a screen and keyboard is subject to the same physics.

From how many metres can I be eavesdropped on?

It depends on the device, the ambient noise and the eavesdropper's equipment; the literature includes demonstrations over tens of metres, and under favourable conditions hundreds. A security plan is built around the 'worst-case' distance.

Doesn't software encryption close this risk?

No — the leakage occurs while the data is still on the screen or keyboard, that is, before it is encrypted. TEMPEST is the complement of cryptography, not its alternative.