Greg Miller, a Pulitzer Prize-winning national security correspondent for The Washington Post, is the author of “The Apprentice: Trump, Russia and the Subversion of American Democracy.”

It has been more than six years since Edward Snowden landed at Sheremetyevo Airport in Moscow for what he expected to be a tense but temporary wait for a connecting flight on his way to asylum in Ecuador. Instead, he was stranded at the airport for 40 days in a futile search for safe passage beyond the reach of the U.S. government. When he finally left the terminal, it was as a pawn in a U.S.-Russia standoff, and he was confronting life as a permanent resident of Moscow.

“Exile,” he writes in his new memoir, “is an endless layover.”

The espionage abuses that Snowden exposed before he became a fugitive in 2013 — most notably the U.S. government’s mass collection of unsuspecting Americans’ phone records — look no less alarming in hindsight. But after the public reckoning he provoked came a wave of technology-driven crises: Russia’s election interference in 2016, the racist manifestos that surfaced after mass shootings, the broader descent into dysfunctional public discourse.

It’s hard to look at Snowden now and not see him as a figure from a bygone era, sounding warnings about grave dangers to privacy and liberty to a public that proceeded blithely to surrender reams of personal data to Facebook and other platforms.

Snowden’s book, “Permanent Record,” is an exploration of his disenchantment with a digital universe that, early in his life, he saw as a source of liberation, even salvation. He traces his rapid path from a tech-obsessed teen to positions of tremendous access at powerful U.S. spy agencies, culminating in his decision to expose the sweeping and invasive surveillance networks that the CIA and National Security Agency had erected in the aftermath of 9/11.

Snowden demonstrates a knack for explaining in lucid and compelling language the inner workings of these systems and the menace he came to believe they posed.

But the consuming concern for personal privacy that he says compelled his leak works against him as the author of a memoir. He revealed some of the U.S. government’s most closely guarded intelligence programs, but he withholds from readers any truly revealing material about his own life. As a result, “Permanent Record” is a book that mostly skims the surface of Snowden’s relatively familiar life story. It becomes more energetic when he expounds on the architecture of sprawling computer systems that hoover up our personal data and the perils they pose to humanity.

No matter where you are physically, “you are also elsewhere,” he writes in one of the book’s most evocative sections. “The records of a life lived in Geneva dwell in the Beltway. . . . The videos of a funeral in Varanasi are up on Apple’s iCloud,” he laments. “Our data wanders endlessly.”

Snowden doesn’t point to any single moment when he crossed from conscience-wracked employee to — depending on your perspective — determined turncoat or whistleblower. It was a transformation that took place gradually.

While Snowden is not completely forthcoming in his account of one of the most serious security breaches in U.S. history, he provides glimpses of his tradecraft. While working in 2012 at an NSA facility called the Tunnel, under a pineapple field in Hawaii, Snowden used his access as a systems administrator to begin assembling a library of documents on the agency’s most far-reaching surveillance programs. Night by night, he probed the corners of the agency’s network and copied the files to a micro SD card, the size of a fingernail, that he smuggled past security guards in the “pried-off square of a Rubik’s cube” that he carried everywhere.

His ability to solve the Rubik’s puzzle in seconds dazzled colleagues. He gave cubes as gifts to those he was seeking to dupe and gave them tips on how to solve them. “The more that people got used to them, the less they’d ever want a closer look at mine,” he reasoned.

He spent entire shifts filling up the data cards, then took them home and offloaded their contents onto an encrypted hard drive that he didn’t even bother to hide; it sat on his desk in plain view of anyone who might enter.

After assembling his collection of files, he began reaching out tentatively to journalists. Some of the most gripping passages in the book center on his forays around Oahu in a car loaded with a laptop and technical equipment. He would pilfer wireless signals from resorts and libraries to send encrypted messages to journalists, including the documentarian Laura Poitras and the columnist Glenn Greenwald. In these communications, he used the pseudonym “Verax,” speaker of truth, as a counterpoint to the adopted moniker of WikiLeaks founder Julian Assange: “Mendax,” speaker of lies. Throughout the book, Snowden distinguishes his leak — in particular his decision to turn over his trove to journalists who engaged in discussions with the government — from the unfiltered dumps that have become WikiLeaks’ signature.

As he progressed with the plot, he became increasingly paranoid. “I kept imagining a team of FBI agents lying in wait for me,” he writes. But that team never materialized, and by 2013 Snowden was planning his endgame. That spring, he emptied his bank accounts and shoved the cash into a steel box for the girlfriend he was about to abandon. He told his employer — at that time he was working on contract to the NSA — that he needed to take an emergency medical leave. Then he disappeared, paying cash for an airline ticket to Hong Kong.

The outcome will be familiar to anyone who tracked the explosive stories that began running that May in the Guardian and The Washington Post, articles revealing that the NSA had collected a massive stockpile of data on millions of Americans and was exploiting secret relationships with tech powers including Microsoft and Google.

The revelations triggered what President Barack Obama grudgingly called an overdue “national conversation” about the country’s surveillance powers. In time, U.S. spy agencies were forced to retreat from operations that had stretched if not exceeded constitutional limits. The reports also showed the extent to which U.S. officials had for years misled the public about spy agencies’ domestic capabilities.

For many who had been in charge of these programs, it was particularly galling that this had been engineered by a 29-year-old contractor. To some, that Snowden had acted unilaterally out of some sense of patriotic obligation bordered on megalomania. Those critics will find hints in Snowden’s book of such grandiosity. Snowden berates himself for supporting the Iraq War, as if he somehow helped steer the country into that conflict. He proudly recounts episodes when he infuriated CIA bosses; refers to himself as a spy, when colleagues probably considered him support staff; and agonizes, sometimes out of proportion, over his role in erecting or maintaining the surveillance systems he exposed.

Snowden was also widely suspected by U.S. intelligence officials of being an asset of Chinese or Russian intelligence, based on little more than the fact that he ended up seeking refuge in Hong Kong and Moscow. Snowden insists in the book that he never shared a single file with another government. Before leaving Hong Kong, he writes, he “wiped my four laptops completely clean and destroyed the cryptographic key,” which meant he could no longer access any of the documents.

In the latter section of the book, he describes a gripping scene when Russian officials — presumably from the Federal Security Service, the successor to the KGB — whisk him into a room where they pressure him to cooperate. Snowden says he cut them off. “If you want to search my bag, it’s right here,” he said. “But I promise you, there’s nothing in it that can help you.”

Weeks later, Russian authorities finally issued him a temporary visa for a stay that has now dragged on for six years. One of this book’s greatest flaws is that it gives us almost no meaningful insight into that life of perpetual exile.

Snowden describes how he was joined in Russia by his American girlfriend, Lindsay Mills, and offers their marriage two years ago as a happy ending.

But what is that existence really like? Does he have regrets? To what extent has he pursued a possible return to the United States? And most important, how has he adapted to life in a nation known for the sort of repressive surveillance that he feared was encroaching on his own country?

The speaker of truth doesn’t answer.

Permanent Record

By Edward Snowden

Metropolitan. 339 pp. $30