A passage covered with black ink in a document recently diffused by
the White House was reconstituted. The method could be applied to
considerable declassified files. I "was bored" in front of
television, the weekend of Easter, "when the memo of the CIA with
George Bush was diffused", remembers David Naccache, specialist in the
coding of the data of the French company Gemplus. "I telephoned at
once Claire Whelan, a colleague of Dublin City University, from which
I direct the thesis, to propose to him to attack the censored
passages". Mission accomplished, or almost. The "memo" in question,
addressed on August 6, 2001 by the CIA to president Bush and entitled
"Ben Laden determined to strike in the USA", had been just
declassified by the White House. This one wanted to prove that the
precision of the warnings of the services of information was not
sufficient to make it possible to the president to prevent the attacks
of September 11. But five passages specifying the sources of the
collected information had been covered with black ink. For the
cryptologist David Naccache, these illegible fragments were as many
red rags. The result of its efforts - "conduits on a purely deprived
basis", specifies it, concerned not to imply its employer in his
initiative - was presented Tuesday May 4 at the time of the conference
Eurocrypt 2004 which joined together until May 6 with Interlaken, in
Switzerland, the gotha of world cryptography. "the demonstration was
extremely impressive", judge Jean-Jacques Quisquater (university of
Leuwen-the-New), specialist in the field, which greets this company of
"reverse engineering of censured document". David Naccache and his
pupil indeed succeeded in discovering one of the censured words. The
term "Egyptian" seems the only possible one to them. They want to
polish their method before returning their verdict on a longer
passage, in order not to discredit it. And they straightforwardly
threw the towel for a completely isolated word, for lack of sufficient
indices. Technology employed does not have, at first sight, anything
revolutionist. The two researchers initially "rectified" the text,
deformed at the time of its digitalization - the slope was only of
0,52°. They then used a software of character recognition to
determine the police force of the text which fixes the number of signs
per unit of length. The simple recourse to an English dictionary then
makes it possible to draw up a list of possible words. "1 530
corresponded", indicates David Naccache. But the "an" preceding the
word mystery implied that this one necessarily started with a vowel,
which made it possible to bring back the list to 346 words. In
French, an index provided by articles like "un" or "une", in the same
way, would have made it possible to tighten research. The selection
was also facilitated by the fact that the bill of character, Arial, is
"proportional", i.e. the "width" of the letters varies. The space
occupied by an I differs from that taken by W, which can give
additional indices, compared to the police forces known as
"monospace", like the Mail, often used, where all the letters are
worth. "Among" the surviving "words, five or six could make
direction, but only Egyptian corresponded to the context", indicates
the cryptologist. This last stage raises more human intelligence than
of the geometry of the text. To choose among Ukrainian, univited,
unofficial, incursive, Egyptian, indebted and Ugandan, the two
researchers were based on their good direction, Uganda and the Ukraine
seeming too far away from the theatre of the operations to be
retained, for example. No doubt the analysis of the "memo" of the CIA
reveals only one "an open secret", recognizes David Naccache. But the
method systematizes research. In another "memo", it revealed that
civil helicopters militarized by the Iraqis had been bought in Korea
South And nothing is opposed to the automated application of this
technique to the whole of the déclassifiés documents, in which it
could put at the day "of the isolated words, even of the groups of two
or three words". Opinion with the critics... Herve Morin
reference
http://www.lemonde.fr/web/article/0,1-0@2-3244,36-364008,0.html |
