Apart from 'asking' WikiLeaks not to post any more classified documents, the U.S. will attempt a three-pronged attack - from the White House, the Pentagon and the NSA - to plug the WikiLeak.

An online whistle-blower’s threat to release more classified Pentagon and State Department documents is raising hard questions of what the U.S. government can or would do, legally, technically or even militarily to stop it.

Constrained by the massive reach of the Internet, sophisticated encryption software and the domestic legal system, the answer seems to be - Not much.

If the U.S. government believes that the classified documents that WikiLeaks is preparing to disclose will threaten national security or put lives at risk, however, cyber and legal experts say the options could expand to include cyber strikes to take down the WikiLeaks web site and destroy its files or covert operations to steal or disable the files.

It all sounds, at times, like a spy movie, where the possibilities extend as far as the imagination can reach. But, most outsiders agree that reality is likely to be far less dramatic.

At the centre of the drama is the posting last week of a massive 1.4 gigabyte mystery file named “Insurance” on the WikiLeaks website.

The “Insurance” file is encrypted, nearly impossible to open until WikiLeaks provides the passwords. But experts suggest that if anyone can crack it, it would be the secretive National Security Agency.

That file, coupled with WikiLeaks’ release of more than 77,000 secret military documents last month, prompted the Pentagon to “demand” that the web site’s editor-in-chief, Julian Assange, cancel any new document dumps and pull back the Afghan war data he already posted.

WikiLeaks slammed the demand as an obnoxious threat, and Pentagon spokesman Geoff Morrell declined to detail what, if any, actions the Defense Department may be ready to take.

Few people involved in the case, for the Pentagon and other agencies, would talk openly about what the Pentagon or America’s clandestine NSA could or would do to stop the expected document dump. It is not even clear whether U.S. officials know what WikiLeaks has.

State Department spokesman P.J. Crowley answered it this way- “Do we believe that WikiLeaks has additional cables? We do. Do we believe that those cables are classified? We do. And are they State Department cables? Yes.”

Officials say the data may also include up to 15,000 military documents related to the Afghan war that were not made public in the initial release.

Daniel Schmitt, a WikiLeaks spokesman in Berlin, said Saturday the new batch of classified documents the website is preparing to release will contribute to the public’s understanding of the war.

“Hopefully with this understanding, public scrutiny will then influence governments to develop better politics,” he told The Associated Press.

Mr. Schmitt denied that the disclosure of the documents is a threat to U.S. security interests.

Assuming the documents contain highly sensitive information that, if made public, might threaten national security, the United States must weigh a number of options, experts say.

First, from a legal standpoint, there probably is little the U.S. government can do to stop WikiLeaks from posting the files.

It is against federal law knowingly and wilfully to disclose or transmit classified information. Mr. Assange, an Australian who has no permanent address and travels frequently, is not a U.S. citizen.

Since Mr. Assange is a foreign national living in a foreign country, it is not clear that U.S. law would apply, said Marc Zwillinger, a Washington, D.C., lawyer and former federal cyber crimes prosecutor. He said prosecutors would have to figure out what crime to charge Mr. Assange with, and then face the daunting task of trying to indict him or persuade other authorities to extradite him.

It would be equally difficult, Mr. Zwillinger said, to use an injunction effectively to prevent users from getting access to the data.

“Could the U.S. get an injunction to force U.S. Internet providers to block traffic to and from WikiLeaks such that people couldn’t access the website?” Mr. Zwillinger said. “It’s an irrelevant question. There would be thousands of paths to get to it. So it wouldn’t really stop people from getting to the site. They would be pushing the legal envelope without any real benefit.”

Legal questions aside, the encrypted file conjures visions of secret codebreakers hunched over their laptops, tearing open secret, protected files in seconds with a few keystrokes.

Reality is not that simple, particularly if, as the file name suggests, the documents are encrypted. It appears WikiLeaks used state-of-the-art software requiring a sophisticated electronic sequence of numbers, called a 256 bit key, to open them.

The main way to break such an encrypted file is by what is called a “brute force attack”, which means trying every possible key, or password, said Herbert Lin, a senior computer science and cryptology expert at the National Research Council of the National Academy of Sciences.

Unlike a regular six or eight character password that most people use every day, a 256 bit key would equal a 40-50 character password, he said.

If, said Mr. Lin, it takes 0.1 nanosecond to test one possible key, and you used 100 billion computers to test the possible number variations, “it would take this massive array of computers 10 to the 56 power seconds - the number 1, followed by 56 zeros” to plow through all the possibilities.

How long is that?

“The age of the universe is 10 to the 17th power seconds,” said Lin. “We will wait a long time for the U.S. government or anyone else to decrypt that file by brute force.”

Could the NSA, which is known for its supercomputing and massive electronic eavesdropping abilities abroad, crack such an impregnable code?

It depends on how much time and effort they want to put into it, said James Bamford, who has written two books on the NSA.

The NSA has the largest collection of supercomputers in the world. And officials have known for some time that WikiLeaks has classified files in its possession.

The agency, he speculated, has probably been looking for a vulnerability or gap in the code, or a back door into the commercial encryption program protecting the file.

At the more extreme end, the NSA, the Pentagon and other U.S. government agencies, to include the newly created Cyber Command, probably have reviewed options for using a cyber attack against the website, which could disrupt networks, files, electricity and so on.

“This is the kind of thing that they are geared for,” said Mr. Bamford, “since this is the type of thing a terrorist organization might have - a website that has damaging information on it. They would want to break into it, see what’s there and then try to destroy it.”

The vast nature of the Internet, however, makes it essentially impossible to stop something, or take it down, once it has gone out over multiple servers.

In the end, U.S. officials will have to weigh whether a more aggressive response is worth the public outrage it probably would bring. Most experts predict that, despite the uproar, the government probably will do little other than bluster, and the documents will come out anyway.

“Once you start messing with Internet, taking things down, and going to the maximum extent to hide everything from coming out, it doesn’t necessarily serve your purpose,” said Mr. Bamford. “It makes the story bigger than it would have been had the documents been released in the first place.”

He and others pointed to the Pentagon Papers saga in 1971, when The New York Times published a top-secret Pentagon study of the history of U.S. involvement in Vietnam.

“It wasn’t Pentagon papers that took down Richard Nixon,” said Mr. Bamford. “It was his attempt to stop the papers that brought him down.”

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