TEMPEST

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TEMPEST pertains to technical security countermeasures, standards, and instrumentation that prevent or minimise the exploitation of vulnerable data communications equipment by technical surveillance or eavesdropping.

Beware the microchip.

Any device with a microchip generates an electromagnetic field, often called a "compromising emanation" by security experts. With the proper surveillance equipment, these emanations can be intercepted and the signal reconstructed and analysed. Unprotected equipment can, in fact, emit a signal into the air like a radio station—and nobody wants to risk his or her job and a whole lot more by broadcasting national security or trade secrets to the wrong people.

Some of the most vulnerable devices are speakerphones, printers, fax machines, scanners, external disc drives, and other high-speed, high-bandwidth peripherals. If the snoop is using a high-quality interception device, your equipment's signals can be acquired up to several hundred feet away.

Arguably one of the most vulnerable pieces of equipment is an analogue VGA monitor. If a spy were to introduce a Trojan into your system, he or she could monitor and store key presses and passwords used during the day. When the system's not in use at night, the spy could pulse the VGA screen with grayscale images that have a strong signal at particular frequencies. VGA uses single-ended signaling that has a high common-mode emission level not protected by cable shielding, and it's possible to monitor these signals outside the secure zone using a radio receiver. Even without a Trojan, a sophisticated receiver located nearby picks up and views what's on the VGA monitor.

What TEMPEST is and isn't.

It should come as no surprise that the federal government became concerned about signal leakage. In fact, its interest goes back to the days of World War I when the Army was trying to exploit weaknesses of enemy combat phones and radio transmitters. Since then, the scope of the government's interests has broadened beyond battlefield equipment. In the last 40 years, the National Security Agency (NSA) has taken several industry measurement standards and greatly beefed them up. These enhanced criteria are commonly referred to as the TEMPEST standards (although the NSA also calls them EMSEC standards, short for "emissions security").

TEMPEST disciplines involve designing circuits to minimise emanations and the application of appropriate shielding, grounding, and bonding.