The StegFS FAQ

$Id: FAQ.txt,v 1.1 2000/01/16 14:09:35 admcd Exp $

* What is StegFS?

StegFS is a Steganographic File System. That is an 'Information Hiding'
File System. The presence of files stored in it can be plausibly
denied.


* Why should I use StegFS?

StegFS encrypts files stored in its hidden levels. In this it performs
the same purpose as a cryptographic file system such as CFS, TCFS,
etc.  However, StegFS also offers steganography. Allows you to use
several levels of hidden files. If someone demands that you give them
your keys, you can reveal the contents of some levels whilst plausibly
denying that any further levels are used. An attacker cannot identify
the existence of any further levels, even if they look at the disk
directly.


* So StegFS is better than a cryptographic file system such as CFS,
TCFS, etc?

Well, yes and no.
The information hiding comes at a price. To ensure the security we
have to allow data in the file system to be accidently overwritten. To
avoid losing files we, therefore, write several copies of each file
block and inode so that, if some are overwritten, others can hopefully
be recovered. This replication obviously requires more disk space for
a given file. There is also a performance penalty due to the need to
write several copies of everything. There is also the risk that all
copies of a given block will be overwritten, in which case its
contents are lost.

If you don't think you need the plausible deniability aspect, then
don't use a steganographic file system, use a cryptographic file
system instead. You will get better performance, waste less disk space
and stand less chance of files being destroyed.


* I've forgotten my passphrase, can you get my files back for me?

No. I suggest you just try all 2^128 possible keys.


* I work for the Inland Revenue. Prof. X has shown me the chemical
  formulae and rock 'n' roll .mp3's in his stegfs file system. I think
  there are also some tax related records there (about non-reported but
  taxable income from his world-wide sell out lecturing tour). Can you
  show me how to prove that these further hidden level exists?

No. I suggest you just try all 2^128 possible keys.