Running a voltage through a wire generates an RF field. This is the principle that allows antennas to work. Unfortunately the same principle applies to all voltage- carrying conductors. With the correct receiver these RF fields can be exploited to eavesdrop on computer data.
In 1985 PTT researcher Wim Van Eck wrote the paper that defined 'EMSEC' (Emissions Security) as it is known today. TEMPEST is the name for the U.S. Government's program to classify and reduce the emissions exploited by a Van Eck monitoring system, not the name for the monitoring system itself.
Because TEMPEST is a passive monitoring technique, detecting TEMPEST monitoring is impossible. It is possible however to determine how vulnerable a computer is to TEMPEST monitoring by measuring the amount of ELF radiation it emits. This can be acomplished via the use of a field-strength meter or magnometer.
* Shielding: Shielded equipment is available for purchase (prices are exhorbitant), or may be improvised. Improvised shielding is possible with either EMI shielding products (such as EMI tape, EMI shielding panels, or even EMI paint), or a system to absorb the radation (a good reference for improvised TEMPEST countermeasures is TEMPEST in a Teapot). Monitors are the biggest EMI 'pump' in any computer system. Replacing CRTs with LCD or plasma displays will cut the emmitted EMR significantly.
* Jamming: Jamming TEMPEST might be a possibility. Generating digital noise from 55-245 MHz should theoretically overwhelm TEMPEST receivers.
* TEMPEST Viewers: Newer versions of PGP offer an option to view text in a window that claims to make TEMPEST monitoring more difficult by reducing the RF radiated.
* Despite sporadic updates, Joel M maintains an excellent and absolutely comprehensive
site on TEMPEST technology. <
* US Army Engineer Corps TEMPEST/EMP Hardening Manuals:
Emmissions monitoring is expensive and complicated. There are cheaper and simpler ways to siphon data off remote computers. Several remote administration programs exist that will output the contents of a computer monitor to a remote screen. The BO Peep Back Orifice 2000 plugin allows realtime monitoring of target computer screens. Port monitors are available for Windows systems that will monitor and log all serial and parallel port activity.
EMSEC shielding will have no effect on the above eavesdropping methods. They can be countered using counter trojan techniques.
Telecommunications Electronics Material Protected From Emanating Spurious Transmissions?
Transient ElectroMagnetic Pulse Emanation Standard?
Transient Electromagnetic Pulse Surveillance Technology?
Transient Emanations Protected From Emanating Spurious Transmissions?
Transient Electromagnetic Pulse Emanation Standard?
Telecommunications EMission Security STandards?
Whether TEMPEST is an accronym or not is a subject of some debate, as no official declaration has even been made about it's meaning