[ISN] Student uncovers US military secrets
isn at c4i.org
Mon May 17 04:45:09 EDT 2004
By Lucy Sherriff
13th May 2004
An Irish graduate student has uncovered words blacked-out of
declassified US military documents using nothing more than a
dictionary and text analysis software.
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.
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.
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
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.
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.
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.
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".
According to the original report in Nature
(http://www.nature.com/nature), intelligence experts may consider
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