Colin Plumb wrote on 1998-12-08 20:18 UTC:
> I've always wanted to set up some secret-sharing filesystem where
> you have to download multiple "shares" to reconstruct the data.
> But other combinations of those exact same shares give other data.
>
> E.g. file1 XOR file2 is smut1.jpg
> file3 XOR file4 is smut2.jpg
> ... etc.
>
> However, file(2*n) XOR file(2*n+1) is... interesting.
This is actually close to the basis for one of the two constructions for
a plausible deniability file system, as it is described in the "The
Steganographic File System" paper by Anderson/Needham/Shamir in D.
Aucsmith, Information Hiding, Lecture Notes on Computer Science 1525,
Springer-Verlag, 1998, ISBN 3-540-65386-4. You need some additional
logic though to perform not only reads but also writes to the file
system in a plausible deniable way; see the paper for some ideas on how
to do this efficiently.
BTW, one of the more interesting of our current undergraduate final year
projects is to build a variant of this into Linux e2fs.
Markus
--
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org, WWW: <http://www.cl.cam.ac.uk/~mgk25/>
