The "thermonuclear device," so named by Mr. Assange's lawyer, is believed to refer to a mysterious 1.4 GB file labeled "insurance" that was uploaded onto the WikiLeaks website in late July, just after the website published 77,000 Afghan war documents.
The file, believed to include the more than 251,000 US State Department cables obtained by WikiLeaks, is seen as an insurance policy for the embattled WikiLeaks in case of potential attacks on its founder or its website before the full trove is made available to the public.
“... this is, I think, what they believe to be a thermonuclear device effectively in the electronic age,” Mr. Assange’s lawyer, Mark Stephens, said Sunday during an interview on the BBC’s Andrew Marr Show.
The encrypted file has since been downloaded by tens of thousands of supporters, according to The Sunday Times, though the 256-digit code believed to unlock it has not yet been released. The Times added that the cache was suspected to include unredacted documents on BP and the US-run Guantánamo Bay detention facility.
Assange appeared to refer to the file on Dec. 3 during a Q&A with the public on the Guardian’s website, but characterized it only as including the State Department cables.
“The Cable Gate archive has been spread, along with significant material from the US and other countries to over 100,000 people in encrypted form," he said in the online forum. "If something happens to us, the key parts will be released automatically. Further, the Cable Gate archives is in the hands of multiple news organizations.”
"Cable Gate" is the title of WikiLeaks' largest leak yet, though fewer than 1,000 of the more than 251,000 cables have been released to the public since the leak began on Nov. 28.
The latest release of cables has brought increased pressure on Assange from the US and Swedish governments, culminating this morning with his arrest at a London police station on accusations of rape, unlawful coercion, and sexual molestation in Sweden.
Will WikiLeaks now release the key to open the insurance file? Not yet. The Associated Press reports that a WikiLeaks spokesman said the file will be "used only if 'grave matters' take place involving WikiLeaks staff."
An unbreakable code
Could someone crack the encryption code and review or even publish the file on their own? Unlikely. Nigel Smart, professor of cryptology at Bristol University, told The Sunday Times that even powerful military computers would be unable to crack the encryption. “This isn’t something that can be broken with a modern computer. You need the key to open it,” he said.
The US Department of Defense is reportedly aware of the "insurance" file but has been unable to establish its contents. If anyone can crack the code, it would be the US National Security Agency, according to James Bamford, who has written two books on the NSA.
"This is the kind of thing that they are geared for, since this is the type of thing a terrorist organization might have – a website that has damaging information on it,” Mr. Bamford told the Associated Press in August soon after the insurance file appeared. “They would want to break into it, see what's there and then try to destroy it."
"It's either 1.4 Gig of embarrassing secret documents, or 1.4 Gig of random data bluffing. There's no way to know."