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    TEMPEST stands for Transient Electromagnetic Pulse Surveillance

    Computers and other electronic equipment release interference to their
    surrounding environment. You may observe this by placing two video
    monitors close together. The pictures will behave erratically until you
    space them apart.

    What is important for an observer is the emission of digital pulses (zeroes and ones)
    as these are used in computers and data communications. The channel for this radiation
    is in two arrangements, radiated emissions and conducted emissions.
    Radiated emissions are assembled when components in electrical devices
    form to act as antennas. Conducted emissions are formed when radiation
    is conducted along cables and wires.

    Although most of the time these RF emissions are simply annoyances, they
    can sometimes be very helpful. Suppose we wanted to see what project a
    target is working on. We could sit in a van outside her office and use
    sensitive electronic equipment to attempt to pick up and decipher the
    radiated emissions from her video monitor. These emissions normally
    exist at around 55-245 MHz and can be picked up as far as one kilometer

    A monitoring device can distinguish between different sources emitting
    RF radiation because the sources emanating the radiation are made up of
    dissimilar elements and this coupled with other factors varies the
    emitted frequency. For example different electronic components in VDUs,
    different manufacturing processes involved in reproducing the VDUs,
    different line syncs, etc… By synchronizing our raster with the
    targets raster we can passively draw the observed screen in real-time.
    This technology can be acquired by anyone, not just government agencies.

    The target could shield the emissions from her equipment or use
    equipment that does not generate strong emissions. However, TEMPEST
    equipment is not legal for civilian use in the United States.

    TEMPEST is the US Government program for evaluation and endorsement of
    electronic equipment that is safe from eavesdropping. TEMPEST
    certification refers to the equipment having passed a testing phase and
    agreeing to emanations rules specified in the government document NACSIM
    5100A (Classified). This document sets forth the emanation levels that
    the US Government believes equipment can give off without compromising
    the information it is processing.

    For more information concerning TEMPEST, visit The Complete, Unofficial TEMPEST Information Page.

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