What is TEMPEST?

Propagation of TEMPEST Signals

There are four basic means by which compromising emanations may be propagated. These are:

1. Electromagnetic Radiation - This electromagnetic field generated by RED signals can be either detected outside the Secure Space or coupled onto BLACK lines connected to or located near, the equipment that exit the secure space.
2. Line Conduction – In this case, CE is conducted as signal/noise on the external or interface lines. The external lines include signal lines, control and indicator lines, and AC and DC powerlines, nonelectric wires/cables, conduits, ducts, etc.
3. Modulation of an intended signal – Here, the carrier is an intended signal being transmitted. However, it is amplified or angle-modulated by the basic RED data signal or a signal related to the basic RED data signal. It is then radiated into space or coupled into the equipment’s external conductors.
4. Acoustics – Other sources of CE exist where mechanical operations occur, and sound is produced. Keyboards, printers, relays - these produce sound and consequently can be sources of compromise.

RED/BLACK Telecommunication Systems

Standard RED/BLACK handling criteria define physical separation guidelines to decrease the probability that electromagnetic emissions from RED devices might couple to BLACK systems.

1. The RED/BLACK concept is the basis for the development of secure facility criteria, discussed in detail throughout our TEMPEST blog series. The RED/BLACK concept dictates that electrical and electronic circuits, components, equipment, systems, etc., which handle national security plain language information in an electrical signal form (RED) be separated from those handling encrypted or unclassified information (BLACK).
2. RED/BLACK guidelines have been developed to detail the procedures required for proper equipment and system shielding, separation, grounding, and filtering to minimize TEMPEST signals.

Equipment Design:

TEMPEST security issues are best prevented by meticulous design consideration at each stage of the equipment or system development. Although it is nearly impossible to completely prevent the generation of such compromising emanations, the following objectives guide best practice for TEMPEST system design:

1. Minimize amplitude and frequency spectrum for all compromising emanations
2. Prevent RED signals from coupling to BLACK lines or circuits
3. Prevent emanations from escaping from the equipment through conducted, radiated, and acoustic means

Consideration for TEMPEST Equipment/Facility Design

When designing a Tempest equipment/facility or retrofitting commercial equipment, some or all the following techniques can be helpful:

1. Preventive Measures - Identify RED signals and circuits. This identification serves as a basis for all preventive/containment methods which may follow.
2. Functions and Format Selections - RED data handling schemes or input/output techniques.
3. Signal Power Levels - The signal operating levels of all RED data circuits and stages should be as low as possible to minimize propagation of compromising emanations.
4. Signal Spectrum Limits - The objective is to limit the spectra of RED data signals to contain their energies within the RED environment.
5. Circuit Arrangement and Layout - Prevention of coupling RED signal processing circuits onto BLACK circuits by separating those to minimizing interelement and inter-circuit RED signal paths.
6. Return Path Layout – Excessive return path lengths and impedances between various points of the return paths for power and signal currents can result in unintentional inter-circuit signal coupling and spurious signal generation. Common return paths for RED and BLACK return currents must be avoided.
7. Stage Decoupling - Without adequate decoupling, currents and voltages representing compromising emanations can be propagated from an originating element through the equipment power supply via power leads.
8. Shielding - Shielding separates two regions so that, in passing from one to the other, an electric/ magnetic field is attenuated by reflection and absorption losses. Shielding can be accomplished with conductor and/or cable shields, conduit, gaskets, magnetic foils, screens, and shielded enclosures.
9. Filtering - A filter functions by allowing certain frequencies to pass while attenuating all others. The filters used for compromising emanation containment usually are low-pass interference reduction types. They are used on signal lines (analog or digital), control lines, and powerlines. To perform effectively, they must be selected with care to ensure correct pass and stop bands, attenuation levels, and input-output impedance. In some instances, special designs are required. The filters must be located and installed at the point of power/control/signal entry and exit to the RED equipment / secure shielded compartment (SCIF). Adherence to established installation guidelines and is critical. High input-output isolation for both conducted and radiated signals must be created.
10. Isolation – Circuit isolation is achieved through the use of transformers, feedback amplifiers, or optical couplers. In some applications, these can be more effective than an EMI filter.

Partner with Astrodyne TDI

Astrodyne TDI is an industry leader in the design and manufacturing of EMI Filters for a variety of applications including TEMPEST systems. With over 60 years in the power industry, a staff of highly experienced professionals, and a global reach, we specialize in creating valuable solutions to meet our client's unique needs. Our team can help you select the best EMI filter and power solution and guide you through the design or retrofit process of a TEMPEST facility. Contact Astrodyne TDI today to learn more about how we can assist you with your TEMPEST needs.