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SFILL(1) General Commands Manual SFILL(1)

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 thieves, law enforcement or other threats. The wipe algorithm 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 finished.

COMMANDLINE OPTIONS

fast (and insecure mode): no /dev/urandom, no synchronize mode.
wipe only free inode space, not free disk space
wipe only free disk space, not free inode space
lessens the security. Only two passes are written: one mode with 0xff and a final mode with random values.
-l for a second time lessons the security even more: only one random pass is written.
verbose mode
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

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 ...
Beware of NFS. You can't ensure you really completely wiped your data from the remote disks. (especially because of caching)
Raid Systems use stripped disks and have got large caches. It's hard to wipe them.
Some of your data might have a copy in your swapspace. sswap is available for this task.
The size of files with fat32 filesystems is limited to 4 GB; sfill can fail to smash the complete filesystem if the free space is bigger than this limit, because this command creates the biggest possible anonymous file and securely erases its content.

To work around this limitation, the recommended package libgsecuredelete0 can be installed, and one can call the script /usr/libexec/libgsecuredelete0/gsd-sfill-helper which creates as many anonymous files as the filesystem can bare, and then smashes them all.

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)