lkml.org 
[lkml]   [1998]   [Dec]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Wanted: Secure-delete utility for Linux
Date
From
Dave Cinege wrote:
> Shail Bains wrote:
> >
> > Linux equivalent of WipeFile: srm (Secure ReMove) at
> > metalab.unc.edu/pub/Linux/system/filesystems/srm.lsm
> >
> > Dunno of an equivalent for WipeDisk, though...
>
> dd if=/dev/zero of=/dev/hdX : >
>
> To be really sure I think that should be followed by /dev/urandom
> then zero again.
>
> AFAIK DoD military grade wiping is zero->random->zero->random->zero.

Personally I'd say that you should write random values a few times in
a row.

In your case, you're overwriting a zero bit with a zero in 50% of the
"write random data" passes. On a 1G disk, that means that after three
"write random data" passes (interleaved with write zeroes or not),
about 128 Mb worth of bits has simply been overwritten with "0" once.

Not good.

Thinking about it, I guess that "fixed pattern" overwriting is better.
Even better would be to do:

write random pattern.
write inverse of the previous random pattern.
write non-random pattern.
write inverse of previous pattern.

repeat (preferably: twice).

Note that you really should use a real random pattern. Not a pseudo
random one. Recovering a bit that has been overwritten a few times is
MUCH harder if you don't know the intermediate values.


"Drive savers" (expensive company doing data recovery (*) ) told me they
couldn't even read through data that was overwritten once. "Only the
guys in the black suits have that kind of technology".


Regards,

Roger.

Commercial plug:
(*) Call me first if you have a problem: BitWizard will recover
exactly the same amount of data as DriveSavers in most cases.

--
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
* Never blow in a cat's ear because if you do, usually after three or *
* four times, they will bite your lips! And they don't let go for at *
* least a minute. -- Lisa Coburn, age 9

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:46    [W:0.655 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site