Re: partially encrypted filesystem

[Jörn Engel]

On Thu, 4 December 2003 07:20:21 -0800, Linus Torvalds wrote:
> On Thu, 4 Dec 2003, Jörn Engel wrote:
> >
> > Isn't that a problem already handled by all compressing filesystems?
> > Or did I miss something really stupid?
> 
> Yes, compression and encryption are really the same thing from a fs
> implementation standpoint - they just have different goals. So yes, any
> compressed filesystem will largely have all the same issues.
> 
> And compression isn't very easy to tack on later either.

So - as sick as it sounds - jffs2 may actually be the fs of choice
when doing encryption, even though working on a hard drive and not
flash.  Cool. :)

> Encryption does have a few extra problems, simply because of the intent.
> In a compressed filesystem it is ok to say "this information tends to be
> small and hard to compress, so let's not" (for example, metadata). While
> in an encrypted filesystem you shouldn't skip the "hard" pieces..

Depends on how much security you really care about.  If you really
don't mind the pain involved, some metadata should explicitly *not* be
encrypted, to avoid known plaintext attacks.  To a serious attacker,
this could be a death stroke for ext[23] over cryptoloop, actually.

In real life, though, the humans are usually the weakest link, so this
doesn't matter anyway.

> (Encrypted filesystems also have the key management issues, further
> complicating the thing, but that complication tends to be at a higher
> level).

Trivial, as long as you can live with a single key for the whole
filesystem.  If that is not acceptable, there may even be problems in
the vfs already.

Jörn

-- 
Data dominates. If you've chosen the right data structures and organized
things well, the algorithms will almost always be self-evident. Data
structures, not algorithms, are central to programming.
-- Rob Pike
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