[28792] in bugtraq
Re: Preventing exploitation with rebasing
daemon@ATHENA.MIT.EDU (Crispin Cowan)
Wed Feb 5 18:05:22 2003
Message-ID: <3E406D7B.9020308@wirex.com>
Date: Tue, 04 Feb 2003 17:48:43 -0800
From: Crispin Cowan <crispin@wirex.com>
MIME-Version: 1.0
To: Alan DeKok <aland@freeradius.org>
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Alan DeKok wrote:
>Brian Hatch <bugtraq@ifokr.org> wrote:
>
>
>>People keep saying "but it won't stop everything", and that's true.
>>
>>
> Exactly. Even DES isn't "perfectly" secure, (i.e. unbreakable). It
>*obfuscates* the data, but does not *secure* it. The benefit of DES
>is that it has a provable level of obfuscation.
>
> This takes the security versus obscurity argument from the realm of
>personal opinion to one of quantitative statements. We should have a
>similar goal for this discussion.
>
With one other critical factor: Systems that can be *properly*
criticized for being "security through obscurity" have the property that
the "obscurity" factor is fixed at software release time, or earlier.
Thus the attacker need only crack the key once, and then own thousands
of copies.
Systematic diversity (as explored by me
<http://wirex.com/%7Ecrispin/crackerpatch.pdf>, Forrest et al, proposed
in Bugtraq yesterday by Huang, and here in this thread) is qualitatively
different in that the "key" (the degree of rebasing offset) can be
chosen at runtime. If it is chosen with sufficient entropy, then it is
as effective as a similar amount of entropy in your favorite crypto
system. More, because with crypto the attacker can grind on your
ciphertext off line, but with systematic diversity, the attacker has to
grind on your machine, which you tend to notice sooner or later :-)
Crispin
--
Crispin Cowan, Ph.D.
Chief Scientist, WireX http://wirex.com/~crispin/
Security Hardened Linux Distribution: http://immunix.org
Available for purchase: http://wirex.com/Products/Immunix/purchase.html
Just say ".Nyet"
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