Re: FileCopy overwrites the existing file

So I can't just say "I don't believe it is possible" or better take Anton's approach:
"My software works: prove me that I'm wrong".

Could you please provide a quotation in order to back up the above
statement - otherwise, this is just libel....


By selling the software and ensuring your customers the
data is really destroyed and not to be recovered (or at least by giving
very high probability of that, like 99.9999%), you put your reputation
with your words.

It would be unwise to guarantee anything. More on this below:

I would really like to have such confidence,
overwriting large file is quite expensive and if I had to do it, say 5
times instead of once it will take 5 times as long.
Btw, I've seen a software that allows a user to overwrite the sectors up
to 100 hundred times!

And still there is no 100% guarantee....

The problem is that the disk may have "bad sectors" that are not
accessible to the software, so that you have no chance to access them.
Before they became "bad", these sectors were usable, so that they may
have some data left over, and specially tuned hardware should not have
a problem retrieving it. In other words, data that you have overwritten
in location X may have a copy of it left in inaccessible location Y,
and there is not that much that you can do about it.

I think this is the main reason why US Department of Defence disposes
of top-secret data only by incinerating the disk...

Anton Bassov



Grzegorz Wróbel wrote:
Uwe Sieber wrote:
In 2003 the german computer magazine c't charged some recovery firms
(Ibas, Ontrack and Vogon) to restore a text file that had been
overwritten once with zeros.

None of the firms had been able to restore a single byte.

Were the companies instructed what kind of recovery is requested? Ie
that the data had been overwritten with zeros once and we need what was
before that? If not the company naturally recovered the last value ie
zeros. I wouldn't assume such recovery is a regular offer.

Recovery firms are very successful restoring data from crashed, burned,
watered harddisks but restoring overwritten data seems be left to
agencies which make the impossible possible... I don't belive that it's
possible on a modern harddisk.


I would like to believe it as well. As a author of data destroying
software it is *you* who should guarantee that the erased data is not
recoverable, not vice versa. So I can't just say "I don't believe it is
possible" or better take Anton's approach: "My software works: prove me
that I'm wrong". By selling the software and ensuring your customers the
data is really destroyed and not to be recovered (or at least by giving
very high probability of that, like 99.9999%), you put your reputation
with your words. I would really like to have such confidence,
overwriting large file is quite expensive and if I had to do it, say 5
times instead of once it will take 5 times as long.
Btw, I've seen a software that allows a user to overwrite the sectors up
to 100 hundred times! My first impression was that the authors were
victims of paranoia. I don't think like that anymore, though they
certainly exaggerated a bit.

--
Grzegorz Wróbel
http://www.4neurons.com/
677265676F727940346E6575726F6E732E636F6D

.

Relevant Pages

  • bugtraq@planetcobalt.net
    ... "Overwriting Hard Drive Data: The Great Wiping Controversy". ... modern ePRML drives. ... of a few regarding data recovery after a file has been 'zeroed' and ...
    (Security-Basics)
  • Re: Inquiry:How to totally wipe out the entire hard drive
    ... Overwriting with zeros once is not at all secure. ... that doesn't work on modern drives, and admitted that only one random write ... would likely be more than enough to prevent recovery. ...
    (Debian-User)
  • Re: what happens to deleted files
    ... It has never been done, not even by Dr. Gutmann himself, and he is the one who first advanced the theory that it might be possible to recover data from overwritten drives. ... The best that Dr. Gutmann could do with MFM was to show that there "might" be a possibility that some bits of data might be recoverable, he was never able to recover actual files and he has never been able to publicly demonstrate that he actually could recovery files on zero written drives, and nobody else either ever could. ... The reason that the US government or any other entities who work with very sensitive data might melt or destroy drives instead of securely overwriting them is not because of the possibility of data recovery on these drives, it is because of the possibility of user or software errors when doing the wiping. ... There is one area which can be of real concern with regards to wiped drives and where actual "bits" of data recovery could be made, cluster tips. ...
    (microsoft.public.windowsxp.help_and_support)
  • Re: Deleted file retrieval
    ... types of recovery, Software & Hardware. ... that does what's called a "Zero Fill" - Writes Zeros to all areas ... completely overwritten numerous times, ... unretrievable by overwriting it's data with another file of equal or ...
    (microsoft.public.windowsxp.general)
  • Re: FileCopy overwrites the existing file
    ... None of the firms had been able to restore a single byte. ... Ie that the data had been overwritten with zeros once and we need what was before that? ... I wouldn't assume such recovery is a regular offer. ... I would really like to have such confidence, overwriting large file is quite expensive and if I had to do it, say 5 times instead of once it will take 5 times as long. ...
    (microsoft.public.win32.programmer.kernel)