First, the computers scan for particular telephone numbers or exchanges; just as White House telephones begin with area code 202 and exchange 456, phones used by foreign governments have distinctive patterns.
Next, for communications sent in code, NSA's code-breakers, or cryptanalysts, put the computers to work. If the code is unfamiliar, they may have to mount a "brute force attack," trying every possible combination of the numeric "key" that can unlock the text.
The number of possible keys for one common encryption system is about 70,000,000,000,000,000, or 70 quadrillion. A personal computer might be able to check 100,000 keys per second - but would still take 22,652 years to exhaust the possibilities. NSA's supercomputers probably can break the code in seconds, cryptography experts say.
Once decoded, written communications such as diplomatic cables or commercial faxes can be scanned by the computers for keywords, flagging messages for analysts to review. Keyword lists, in dozens of languages, might include the name of a firm suspected of supplying chemical weapons components, the number of a drug cartel's Swiss bank account or simply the word "nuclear."
Voice communications are trickier. Because pronunciation varies so greatly, only in the last few years have computers begun to recognize keywords with reasonable accuracy. But NSA is in the forefront of such work, and is sponsoring research at Johns Hopkins University and elsewhere to create software that can recognize a language, transcribe speech and perhaps even summarize what is said.
Meanwhile, NSA has spent millions to program computers to recognize individual voices, switching on tape recorders when a targeted individual comes on the line. Such equipment was provided by NSA to the Colombians and used during the hunt for drug lord Pablo Escobar, who was shot to death by security forces in December 1993.
Rapid automated sorting of intercepts is becoming steadily more crucial as NSA labors to keep pace with the communications explosion, NSA Director McConnell, a 52-year-old vice admiral, told a seminar on military intelligence last summer.
All the books and periodicals in the Library of Congress, Admiral McConnell said, contain about 1 quadrillion bits of information. The information transmitted over one satellite channel could fill the Library of Congress in about nine months. But a single strand of fiber-optic cable can carry enough information to fill the Library of Congress in just three weeks.
"With the technology that's on the drawing boards now, we will fill up the Library of Congress about every three hours," Admiral McConnell said. "That's the kind of volume we're having to deal with in a global context."
Even as the intercepts flowing into Fort Meade have reached flood tide, NSA has been plucking from the gigabits of data a changing mix of intelligence. Commerce replaces communism: The Soviet air force has been supplanted by the European aircraft consortium Airbus. But the eavesdropping goes on.
Louis W. Tordella, the courtly mathematician who virtually ran NSA for many years as deputy director, says U.S. officials facing challenges abroad inevitably will turn to NSA.
"I think it's fair to say that the demands on the agency approach infinity," he says. "Everybody wants to know everything about everything."
In this series
Today: NSA eavesdrops on allied presidents, military strongmen, drug dealers and trade negotiators.
Tuesday: Maryland's largest employer is one of America's strangest workplaces.
Thursday: NSA has a secret within a secret: eavesdroppers undercover abroad.
Dec. 10: Scores of countries thought their coded messages were secure. Was NSA reading over their shoulders?
Dec. 12: Trolling for foreign secrets, NSA routinely picks up Americans' overseas calls. And it's legal.
Dec. 14: The next war may be fought with computers. NSA is getting ready.
A reprint of the NSA series will be available for $3.95. To order, call SunSource at (410) 332-6800.