During those 20 years, the Reagan military buildup came and went, the Soviet Union fell and the Cold War ended, and a bevy of new military enemies emerged. Electronic communications exploded through faxes, cellphones, the Internet, etc. Cryptography came out of the shadows to become an essential technology of the networked world. And computing power increased ten thousand-fold.

Also during those 20 years, the NSA gradually opened its doors to the outside world. Its mission -- to eavesdrop on all foreign communications of interest to the United States -- remained constant throughout, but the agency that used to call itself "No Such Agency" and "Never Say Anything" started appearing in public, talking to the press and making itself known. And probably more than anyone else, James Bamford helped pry those doors open.

"Body of Secrets" is one fascinating book. It's a secret history of U.S. foreign policy from the perspective of signals intelligence, beginning with the Cold War and continuing through the year 2000. And it's chock-full of juicy stuff: secret Cold War missions over the Soviet Union, government coverups of military debacles, eavesdropping on our friends and enemies. Stuff you have trouble imagining a civilian being able to research and publish.

Bamford has two weapons: the tenacity needed to exploit the Freedom of Information Act and the patience to wade through mounds of public papers in archives around the country. They have both served him well.

In 1979, while researching "The Puzzle Palace," Bamford wanted information on an NSA operation called Shamrock: an illegal program to read all international telegrams sent out of the U.S. The NSA would not respond to any queries, but he heard of a 1975 investigation by the Department of Justice. One FOIA request and nine months later, he received an impressive (and incriminating) 300-page document summarizing the program. On his next visit to the unhelpful public relations offices at the NSA, he showed people there the document. They freaked, and tried desperately to get it back.

The NSA waited for 1981 and a new president, and started applying pressure on Bamford. The Department of Justice claimed that the document was "accidentally" declassified and should be returned. (At the time, the law specifically stated that once something was declassified, it could not be reclassified, which the Reagan administration later changed.) A few tense meetings and threatening letters followed, but Bamford held firm. Shamrock was described fully in "The Puzzle Palace."

William Friedman founded America's first peacetime code-breaking agency -- the Black Chamber -- shortly before World War II and is considered the father of the NSA. After he retired he had a falling out with the NSA. He stopped trusting the agency, and it started regarding him as a security risk. At his death, he left his papers to the Virginia Military Institute and not with the NSA. Even so, NSA officials drove down to VMI, examined everything and persuaded the archivist to lock up a bunch of the documents in a vault at the institute. Also during his "Puzzle Palace" research, Bamford went to VMI to read Friedman's papers, noticed the omissions and convinced the archivist to release those papers. He also found former NSA director Marshall Carter's papers there; the NSA didn't even know about them. When the NSA tried to have Bamford prosecuted after the publication of "The Puzzle Palace," these papers were what the NSA considered to be government secrets.

Maya Angelou reads from "The Heart of a Woman"