[9465] in cryptography@c2.net mail archive
Re: "Pirate Utopia," FEED, February 20, 2001
daemon@ATHENA.MIT.EDU (Ray Dillinger)
Mon Sep 24 15:28:50 2001
Date: Mon, 24 Sep 2001 11:44:51 -0700 (PDT)
From: Ray Dillinger <bear@sonic.net>
To: Nomen Nescio <nobody@dizum.com>
Cc: cryptography@wasabisystems.com
In-Reply-To: <98ba5a909156be25b0ffc9bacbed7e44@dizum.com>
Message-ID: <Pine.LNX.4.21.0109241138120.6890-100000@bolt.sonic.net>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
On Mon, 24 Sep 2001, Nomen Nescio wrote:
>The Stegdetect paper proceeded to further analyze the 20000+ images by
>looking for passwords that would produce meaningful messages from the
>hypothesized hidden content, via dictionary attack. No valid passwords
>were found, and the authors concluded therefore that these were all
>false positives. This does not seem to be a fully supported conclusion.
Actually, dictionary attacks reveal about sixty percent of passwords,
so for every six passwords you find on a dictionary attack, you can
infer ten actual stegotexts times the ratio between your analyzed and
discovered (possibly-false) positives.
While he has analyzed only two percent of his sample, that's a sufficient
number that if even even a tenth of one percent of his positives were
real he'd have discovered at least a few passwords.
The paper is solid statistical methods; lack of any dictionary-yeilding
passwords in that big a sample is very strong evidence that the sample
is overwhelmingly made up of false positives.
Bear
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