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Re: [dm-devel] my encryption

Am Mo, den 13.10.2003 schrieb Joe Thornber um 14:23:

> > Maybe, i'm not a cryptoanalyser, but GBDE does this, and i think they
> > do it for a reason. The idea is that you can attack the encryption if
> > you have "known plaintext", and a filesystem stores known meta data
> > at a known location.
> y, I can see that making a difference for some encryption schemes.
> Perhaps we should think about putting that in.

Knowing things about the underlying structure of the filesystem or
encryption scheme makes it easier for attacks. You've simply got a lot
of data to analyse and if you know in which order it's put on the disk
it makes this a lot easier.

GBDE also changes the encryption key every nth sector. The IV (the
additional "per-sector-perturbation data") isn't predictible either.
Some keys are spread all over the volume in special sectors so that you
first have to know how to decode these before you can begin making
assumptions about the actual encrypted data. Because you don't know
where these sectors are without having the master key it makes the kind
of attacks stated above nearly impossible.

Christophe Saout <christophe saout de>
Please avoid sending me Word or PowerPoint attachments.
See http://www.fsf.org/philosophy/no-word-attachments.html

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