Re: mac share/freeware app for overwriting unused hd space?

[Ray Arachelian <sunder@escape.com>]

On Thu, 27 Jul 1995, Timothy C. May wrote:

> At 2:27 PM 7/27/95, j. ercole wrote:
> >Can anyone point me towards a program that's freeware or shareware that
> >will overwrite all the unused i.e., "trashed" space on my hard drive(s)?  I
> >sincerely apologise if this is a faq.  I know norton's will do it but I
> >don't presently have that installed on my machine.  Thanks oodles,

Something could be written to just write a bunch of random garbage to a 
file until the volume runs out of free space, then overwrite that file 
several times before deleting it.  I think this is what MacTools's 
Trashback - EraseFreeSpace option does.  I used to do this for DOS 
machines with a batch file:

Type this is at the DOS prompt (for those who use DOS):
COPY CON FILLDRIVE.BAT

@ECHO OFF
@DIR >>KILLME.TXT
@TYPE KILLME.TXT >>KILLME.TXT
@FILLDRIVE.BAT   (hit RETURN ON THIS LINE AND THEN HOLD CONTROL AND HIT Z,
                  and RETURN again.)

Just run this until you see hard drive full errors.  This creates an 
exponentially increasing file called "KILLME.TXT" by copying that file to 
itself on each pass.  First pass the file is the size of the directory, 
the second pass, it's 3 times the size, the third pass 7 times, the 
fourth pass, it's 15 times, etc.

When your finnally run out of space, hit CONTROL-BREAK and then delete 
the KILLME.TXT file to release the free space.

Basically, no matter who I work for, I write a batch file that zaps the 
SecureDevice file on the root directory, then runs this thing, so if I 
have to leave the place in a hurry I can erase my personal files without 
much hassle and little danger of having them compromised.  (I also have a 
few other neat tools to let me know if someone has been snooping on my 
machine at work, but I won't disclose those :-)

Do this a few times and everything is cool.  Off the top of my head, the 
unix equivalent would be:

ls -l >>killme.txt
cat killme.txt >>killme.txt
filldrive

But be careful not to run this when other folks are on, or if you're not 
the sysadmin as you'll overrun your quota very quickly.  (The above 
wasn't tested, and I'm not sure if under unix you can append a file to 
itself, etc. so #include <stdwarnings_n_disclaimers.h>

> At the most serious level of attack (the "threat model"), such as the FBI
> labs in Quantico or the NSA, there are reports that specialized disk drive
> heads are used to recover earlier signals that are not erased even with N
> active overwrite steps (apparently the head jitter in most drives means
> that each write cycle is slightly different, even on the same disk region,
> and a slight "shadow" or "ghost" of previous writes can sometimes be
> extracted).

In this day and age drives are getting smaller and smaller while the 
capacity increases. This means the tracks are smaller and the data spill 
caused by the jitter is smaller and smaller tending towards almost 
useless.   I really think our TLA friends are having a harder 
time at this than usual.  But suffice to say I still do a wipe three or 
four times anyway.  i.e. It's easy to do something like this on a 5.25" 
full height 40MB MFM drive, but on a 4GB 3.5" LPS drive, much, much harder.

(I guess though, I must be paranoid though as I did buy a nice big bulk 
eraser built for floppies. <evil grin>)

> --Tim May, who hopes this will not reignite the thread about how to use
> thermite to permanently erase disk drives

Ditto.


=================================================================93=======
 + ^ + |  Ray Arachelian | Amerika: The land of the Freeh. | \-_    _-/  |
  \|/  |sunder@escape.com| Where day by day, yet another   |  \  --  /   |
<--+-->|                 | Constitutional right vanishes.  |6 _\-  -/_  6|
  /|\  |    Just Say     |                                 |----\  /---- | 
 + v + | "No" to the NSA!| Jail the censor, not the author!|     \/      |
=======/---------------------------------------------------------VI------/
      /  I watched and weeped as the Exon bill passed, knowing that yet /
     / another freedom vanished before my eyes.  How soon before we see/
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