(also radio telegram)
TEMPEST shielding definition
The acronym TEMPEST stands for Transient Electromagnetic Pulse Emanating Surveillance Technology. TEMPEST shielding is both the act and the material that stops electromagnetic emanations from transferring to equipment and reaching sensitive information. It usually involves using specialized materials and techniques to encase electronic equipment and cables in a Faraday cage. TEMPEST was a project by the US government dedicated to studying computers and other electronic equipment and their sensitivity and security in terms of spying and sharing data from the electromagnetic resonance they emit.
Types of TEMPEST signals
- RED baseband signals. A type of conducted emission that can be added to electrical conductors linked to circuits inside the equipment. The RED signal is more likely to transmit if there is a higher frequency or data rate. The signal can transmit through conductors connected to circuits that process the RED signal. Another way to transmit it is through the air by inductive coupling, which means the signal can “jump“ from one device to another.
- Modulated spurious carriers. It occurs when another RED data signal modulates a carrier signal. The carrier signal is usually an unwanted signal that already exists in the equipment or is created intentionally. The modulated signal can spread into the air and other outside conductors, which causes electromagnetic interference.
- Impulsive emanations. Electronic devices that process digital signals often produce impulsive emanations, especially when they go from one digital state to another very quickly. Because this change is fast, it creates short bursts of electromagnetic energy, which transfers through external conductors or the air and can possibly cause interference with other devices.