Stego file system (Was: Inaccurate study)u

[Julian Assange]

>  I haven't read the paper terribly thoroughly yet, but surely another
> way of doing this is simply to hide one or more encrypted filesystems
> in the free block list of a standard filesystem ? (and another inside
> that if you want another level).
> 
>  Given some known plaintext, there's the standard attack of searching
> through the space of possible filesystems until you get to one which
> gives valid information, but I don't think that's likely to be 
> practical.

It's actually far more complicated than this. Don't forget that
magnetic drives record far, far more than you want them too. i.e
previous over-written "layers" of information (which can be got at
with stm techniques), relative magnetic domain leakage into unused
areas, relative field strength surface areas, and chemical changes
in the recording surface in response to magnetic changes (writes)
can all be used to show that "other" areas of the drive have been
used.

It's a bit unfortunate Ross didn't address this issues in the second
half of his paper (which was otherwise pretty good). Marutukku uses
a block-swaping/re-encrypting algorithm to prevent these kind of
magneto-statistical attacks, but the issue is so complex to deal
with *efficiently*, that I'm unable to prove Marutukku's effectiveness
against such an attack.  It maybe possible that a decent STM jocky
can say things like "there have been n writes to the portion of
disk representing this part of the cryptographically deniable
file-system in the last y seconds" leading to an observation like:
"we are 67% confident that the magnetic media in question recently
contained data not revealed by the divulged key(s)" -- not confident
enough for beyond a reasonable doubt, but perhaps confident enough
for continued beatings.

Cheers,
Julian.