- An Irish graduate student has uncovered words blacked-out
of declassified US military documents using nothing more than a dictionary
and text analysis software.
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- Claire Whelan, a computer science student at Dublin City
University was given the problems by her PhD supervisor as a diversion.
David Naccache, a cryptographer with Gemplus, challenged her to discover
the words missing from two documents: one was a memo to George Bush, and
another concerned military modifications to civilian helicopters.
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- The process is quite straightforward, and according to
Naccache, Whelan's success proves that merely blotting words out of declassified
documents will not keep the contents secret.
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- The first task is to identify the font, and font size
the missing word was written in. Once that is done, the dictionary search
begins for words that fit the space, plus or minus three pixels, Naccache
explained.
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- This process yielded 1,530 possibilities for word blanked
out of a sentence in the Bush memo. Then, the text anaysis routine checks
for words that would make sense in English. The sentence was: "An
Egyptian Islamic Jihad (EIJ) operative told an XXXXXXXX service at the
same time that Bin Ladin was planning to exploit the operative's access
to the US to mount a terrorist strike." Just 346 words remained on
the list at this stage.
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- The next stage is to involve the brain of the researcher.
This eliminated all but seven words: Ugandan, Ukrainian, Egyptian, uninvited,
incursive, indebted and unofficial. Naccache plumped for Egyptian, in this
case.
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- Whelan subjected the helicopter memo to the same scrutiny,
and the results suggested South Korea was the most likely anonymous supplier
of helicopter knowledge to Iraq.
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- Although the technique is no good for tackling larger
sections of text, it does show that officials need to be more careful with
their sensitive documents. Naccache argues that the most important conclusion
of this work "is that censoring text by blotting out words and re-scanning
is not a secure practice".
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- According to the original report in Nature, intelligence
experts may consider changing procedures.
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- http://www.theregister.co.uk/2004/05/13/student_unlocks_military_secrets/
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