Re: partially encrypted filesystem

From: Jörn Engel
Date: Thu Dec 04 2003 - 12:31:15 EST

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.


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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