The expense and breadth of American spy operations have always been a closely guarded secret, never made public.

But a report from the Washington Post last week, based on information provided by former NSA contractor Edward Snowden, reveals that the so-called "black budget" is nearly $53 billion — and it has grown tremendously in the days since 9/11. In the 178-page summary obtained by the Post are an outline of the technology, ongoing operations, and successes and failures of the U.S. intelligence community.

"The United States has made a considerable investment in the intelligence community since the terror attacks of 9/11, a time which includes wars in Iraq and Afghanistan, the Arab Spring, the proliferation of weapons of mass destruction technology, and asymmetric threats in such areas as cyber-warfare," Director of National Intelligence James R. Clapper said in a statement to the Washington Post.

The Post withheld some information obtained from Snowden after U.S. officials shared concerns about potentially exposing sources or causing harm to U.S.

The current cost of U.S. intelligence operations rival that of their former peak during the Cold War, which is estimated to be the equivalent of $71 billion dollars at today's values. The cost has risen to accommodate an increasingly complicated world, Clapper wrote in response to the Post.

"Never before has the IC (intelligence community) been called upon to master such complexity and so many issues in such a resource-constrained environment," he wrote.

Some critics have pointed out that because the burden of funding intelligence operations requires a significant contribution of taxpayer dollars, the allocation of the money should be made transparent — a proposal Snowden advocates.

Though much of the government is undergoing a belt-tightening brought on by sequestration, the 2013 black budget is just 2.4 percent below that of 2012. A close aid to the president said he's unsure how likely that number is to continue dropping.

"Even if you grant the good intentions and the good will of the present people conducting these programs, once you grant government power, government doesn't give that power up," said Lee Hamilton, a member of the president's Homeland Security Advisory Council. "What you have to be alert to here is not just abuse of power in the present time, but abuse of power in perpetuity."

Snowden's budget leak includes a case against cutting the intelligence budget and projects intelligence spending to remain stagnant through 2017.

U.S. officials have justified the spending by its apparent success in preventing another serious terrorist attack on the U.S., like 9/11. However, recent terrorist attacks from American citizens, including the bombing of the Boston Marathon in April, remain the most difficult activity for intelligence agents to track.