On Fri, 22 Dec 2000, Matthew Mondor wrote:

> The best cryptography software I used does create different lenght results
> each time the same block is encrypted, if there exists such encryption
> systems that can be used for filesystems the size would vary but could be
> estimated

It will always be possible to create an equally powerful cryptosystem
without random cyphertext expansion.

Known cyphertext expansion is much more applicable for a filesystem -
divide the disk into clusters, and store (say) 8 blocks of data in a
10-block cluster.

Basically, you pad your 8 blocks of data up to 10 blocks by shoving in
some random data, then encrypt the lot with a non-expanding cypher. The
extra random data places a barrier to known or chosen plaintext attacks.

ABS

-- 
                               Alaric B. Snell
 http://www.alaric-snell.com/  http://RFC.net/  http://www.warhead.org.uk/
   Any sufficiently advanced technology can be emulated in software