Approved for Release by NSA on 9-27-2007, FOIA Case # 51633
TEMPEST: A Signal Problem
The story of the discovery of various compromising radiations from communications and Comsec equipment.
In 1962, an officer assigned to a very small intelligence detachment in Japan was performing the routine duty of inspecting the area around his little cryptocenter. As required, he was examining a zone 200 ft. in a radius to see if there was any "clandestine technical surveillance." Across the street, perhaps a hundred feet away, was a hospital controlled by the Japanese government. He sauntered past a kind of carport jutting out from one side of the building and, up under the eaves, noticed a peculiar thing—a carefully concealed dipole antenna, horizontally polarized, with wires leading through the solid cinderblock wall to which the carport abutted. He moseyed back to his headquarters, then quickly notified the counter-intelligence people and fired off a report of this "find" to Army Security Agency, who, in turn, notified NSA. He was directed to examine this antenna in detail and perhaps recover it, but although the counter-intelligence folks had attempted to keep the carport under surveillance that night, the antenna had mysteriously disappeared when they checked the next day. Up on the roof of the hospital was a forest of Yagi's, TV antennae, all pointing towards Tokyo in the normal fashion, except one. That one was aimed right at the U.S. cryptocenter.
You may recall the highly publicized flap which occured in 1964 when more than 40 microphones were discovered in the U.S. embassy in Moscow. Most people were concerned about all the conversations that may have been overheard and the resultant compromise of our diplomatic plans and intelligence activities associated with the embassy. We were concerned with something else: What could those microphones do to the cryptomachines used there? And what were the unpublicized gadgets also found with microphones for? Why was there a large metal grid carefully buried in the cement of the ceiling over the Department of State communications area? A grid with a wire leading off somewhere. And what was the purpose of the wire that terminated in a very fine mesh of smaller hair-like wires? And, while we were at it, how did these finds relate to other mysterious finds and reports from behind the Curtain—reports dating clear back to 1953?
Why, way back in 1954, when the Soviets published a rather comprehensive set of standards for the suppression of radio frequency interference, were those standards much more stringent for their teletypewriters and other communications equipment than for such things as diathermy machines, industrial motors, and the like, even though the teletypewriters were much quieter in the first place?
Behind these events and questions lies a long history beginning with the discovery of a possible threat, the slow recognition of a large number of variations of that threat, and, lumbering along a few months or a few years afterwards, a set of countermeasures to reduce or eliminate each new weakness that has been revealed.
The Problem Defined
To state the general nature of the problem in brief: Any time a machine is used to process classified information electrically, the various switches, contacts, relays, and other components in that machine may emit radio frequency or acoustic energy. These emissions, like tiny radio broadcasts, may radiate through free space for considerable distances—a half mile or more in some cases.
