SRM(1)SRM(1)NAMEsrm - secure remove (secure_deletion toolkit)
SYNOPSISsrm [-d] [-f] [-l] [-l] [-r] [-v] [-z] files
DESCRIPTIONsrm is designed to delete data 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 srm goes like this:
* 1 pass with 0xff
* 5 random passes. /dev/urandom is used for a secure RNG if avail‐
able.
* 27 passes with special values defined by Peter Gutmann.
* 5 random passes. /dev/urandom is used for a secure RNG if avail‐
able.
* Rename the file to a random value
* Truncate the file
As an additional measure of security, the file is opened in O_SYNC mode
and after each pass an fsync() call is done. srm writes 32k blocks for
the purpose of speed, filling buffers of disk caches to force them to
flush and overwriting old data which belonged to the file.
COMMANDLINE OPTIONS-d ignore the two special dot files . and .. on the commandline.
(so you can execute it like "srm -d .* *")
-f fast (and insecure mode): no /dev/urandom, no synchronize mode.
-l lessens the security. Only two passes are written: one mode with
0xff and a final mode random values.
-l-l for a second time lessons the security even more: only one
random pass is written.
-r recursive mode, deletes all subdirectories.
-v verbose mode
-z wipes the last write with zeros instead of random data
LIMITATIONS
NFS Beware of NFS. You can't ensure you really completely wiped your
data from the remote disks.
Raid Raid Systems use stripped disks and have got large caches. It's
hard to wipe them.
swap, /tmp, etc.
Some of your data might have a temporary (deleted) copy some‐
where on the disk. You should use sfill which comes with the
secure_deletion package to ensure to wipe also the free
diskspace. However, If already a small file aquired a block with
your precious data, no tool known to me can help you here. For a
secure deletion of the swap space sswap is available.
BUGS
No bugs. There was never a bug in the secure_deletion package (in con‐
trast 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
srm 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 MER‐
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.
SEE ALSO
sfill (1), sswap (1), smem (1)
SRM(1)
