full-disclosure - Re: Possible issues with encrypted Linux filesystems?

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Date: Tue, 14 Dec 2010 09:11:12 -0500
From: Jeffrey Walton <noloader@...il.com>
To: Steve Pinkham <steve.pinkham@...il.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Possible issues with encrypted Linux
	filesystems?

On Mon, Dec 13, 2010 at 11:53 AM, Steve Pinkham <steve.pinkham@...il.com> wrote:
>> I'm now worried that if an attacker knows, or "guesses" that you are
>> using, say, CentOS Linux 5.5, (or at least some mutation of Red Hat),
>> he might use this knowledge of "known artefacts" to his advantage, by
>> starting out from the data he knows "must be there", and looking for
>> it's "patterns". I don't know... This may be a longshot, wishful
>> thinking or both, but somehow it feels to me like it's a lot easier
>> to break a code when you already know exactly what the decrypted data
>> is, and what it looks like.
>
> These sorts of attacks were the design criteria for modern disk
> encryption modes.
>
> http://en.wikipedia.org/wiki/Disk_encryption_theory
>
> XTS is the current best mode for FDE.
NIST chooses algorithms which are not patented or if patented,
publicly available and royalty free. So the algorithm might not be the
best per se - but a selection will not [usually] be encumbered.

An example of "patented, but publicly available" is the Digital
Signature Algorithm (DSA) which is one of three algorithms specified
in the Digital Signature Standard. Kravitz holds a patent on DSA, but
Schnorr claims he holds an earlier patent and Kravitz's patent is
invalid.

As an example of "side stepping a patent", NIST approved two
authenticated encryption modes: CCM and GCM. The modes are two pass,
meaning one pass for the encryption, and one pass for the
authentication. Single pass algorithms are available, but they are
patented. So NIST choose two pass algorithms.

Jeff

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