13 May 2004

Censored words unmasked: US intelligence exposed as student decodes Iraq memo

Armed with little more than an electronic dictionary and text-analysis software, Claire Whelan, a graduate student in computer science at Dublin City University in Ireland, has managed to decrypt words that had been blotted out from declassified documents to protect intelligence sources.

She and one of her PhD supervisors, David Naccache, a cryptographer with Gemplus, which manufactures banking and security cards, tackled two high-profile documents. One was a memo to US President George Bush that had been declassified in April for an inquiry into the 11 September 2001 terrorist attacks. The other was a US Department of Defense memo about who helped Iraq to 'militarize' civilian Hughes helicopters.

It all started when Naccache saw the Bush memo on television over Easter. "I was bored, and I was looking for challenges for Claire to solve. She's a wild problem solver, so I thought that with this one I'd get peace for a week," Naccache says. Whelan produced a solution in slightly less than that.

Demasking blotted out words was easy, Naccache told Nature. "Optical recognition easily identified the font type - in this case Arial - and its size," he says. "Knowing this, you can estimate the size of the word behind the blot. Then you just take every word in the dictionary and calculate whether or not, in that font, it is the right size to fit in the space, plus or minus 3 pixels.

About 16 ways round this technique spring to mind immediately. All the same, we'll hear the usual chorus that this technique justifies ever greater sececy in the War on Terror. The WoT is fast becoming a war on checks and balances as anything else.

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