NAME¶
sfill - secure free disk and inode space wiper (secure_deletion toolkit)
SYNOPSIS¶
sfill [-f] [-i] [-I] [-l] [-l] [-v] [-z] directory/mountpoint
DESCRIPTION¶
sfill is designed to delete data which lies on available diskspace on
mediums in a secure manner which can not be recovered by thiefs, law
enforcement or other threats. The wipe algorythm is based on the paper
"Secure Deletion of Data from Magnetic and Solid-State Memory"
presented at the 6th Usenix Security Symposium by Peter Gutmann, one of the
leading civilian cryptographers.
The
secure data deletion process of sfill goes like this:
- *
- 1 pass with 0xff
- *
- 5 random passes. /dev/urandom is used for a secure RNG if
available.
- *
- 27 passes with special values defined by Peter
Gutmann.
- *
- 5 random passes. /dev/urandom is used for a secure RNG if
available.
afterwards as many temporary files as possible are generated to wipe the free
inode space. After no more temporary files can be created, they are removed
and sfill is finnished.
COMMANDLINE OPTIONS¶
- -f
- fast (and insecure mode): no /dev/urandom, no synchronize
mode.
- -i
- wipe only free inode space, not free disk space
- -I
- wipe only free disk space, not free inode space
- -l
- lessens the security. Only two passes are written: one mode
with 0xff and a final mode with random values.
- -l
- -l for a second time lessons the security even more: only
one random pass is written.
- -v
- verbose mode
- -z
- wipes the last write with zeros instead of random data
directory/mountpoint this is the location of the file created in your
filesystem. It should lie on the partition you want to write.
LIMITATIONS¶
- FILESYSTEM INTELLIGENCE
- Most filesystems (ext2, ffs, etc.) have several features
included to enhance performance, which will result in that sfill might not
receive all available free space. Sad but true. Nothing can be done about
that ...
- NFS
- Beware of NFS. You can't ensure you really completely wiped
your data from the remote disks. (especially because of caching)
- Raid
- Raid Systems use stripped disks and have got large caches.
It's hard to wipe them.
- swap
- Some of your data might have a copy in your swapspace.
sswap is available for this task.
BUGS¶
No bugs. There was never a bug in the secure_deletion package (in contrast to my
other tools, whew, good luck ;-) Send me any that you find. Patches are nice
too :)
AUTHOR¶
van Hauser / THC
<vh@thc.org>
DISTRIBUTION¶
The newest version of the
secure_deletion package can be obtained from
http://www.thc.org
sfill and the
secure_deletion package is (C) 1997-2003 by van
Hauser / THC (vh@thc.org)
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; Version 2.
This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE. See the GNU General Public License for more details.
SEE ALSO¶
srm (1),
sswap (1),
sdmem (1)