Re: [dm-crypt] Efficacy of xts over 1TB

[Arno Wagner <arno@wagner.name>]

On Sat, Aug 21, 2010 at 10:45:35PM +0200, Christoph Anton Mitterer wrote:
> Hi.
> 
> 
> But this goes IMO more in the plausible denyability direction, doesn't
> it?

I think not even that. The attacker already know you likely have
encrypted data or a lot of randomness. But then you have been
changing that in a typical pattern for filesystem access.

The data leakage is real, but very, very low in volume and will
not matter in almost all situations IMO, and therefore nobody
will bother attacking that. Now if you store and process
highly sensitive data in the exabyte-range, it might be a
minor concern (an attacker could plant a document and later
detect ot has been added to the encrypted device), but even
there effort is extreme. 

This is an example of an academic attack. Interesting, and
show a real limit of the employed encryption method, but
irrelevant for the real world.

> An attacker would still be not able to read what was written.
> And for most applications it should be extremely difficult or even
> impossible to make any conclusions,.. because of fragmentation... etc.
> pp.

I agree.

> Another issue is of course when you have corrupted programs in the
> system.... but then you're screwed anyway,... and there are usually much
> easier to implement hidden channels.... (but this argument shouldn't
> count as I always say myself ;) ).

Indeed. Just use a sequence of secors, and change or not them 
in a pattern.

Arno
-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
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