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Wiping Files

Posted on 2000-05-13
Medium Priority
Last Modified: 2010-05-02
i have a  program called undelete and i am trying to make a program that can wipe files and when i wipe them i can't undelete them with this program.
other people do it and i don't know why i can't get the file back, what is a better program to use for undeleting because some people say they can undelete the file simply if it had been over written 3 times and i don't understand how or with what program.
Question by:adam8
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Expert Comment

ID: 2807567
The solution is simple:

My answer is not quite complete, but it's easy to figure out - overwrite the file ten times, replacing every character with "¤". This'll be easy to modify (increase CONST_OVERWRITES for more security). If this doesn't work, then tell me.

Open "File To Overwrite" for input as #1
    Temp = lof(1)
close #1
for Overwrites = 1 to 10
    Open "File To Overwrite" for output as #1
        do while len(Buffer) < Temp
            Buffer = Buffer & "¤"
        print #1,Buffer
    close #1

The official solution to the overwrite problem is as follows:

(adapted from National Computer Security Center "A guide to understanding data....")

Overwriting is a process by which unclassified data are written to storage locations that previously held sensitive data... To purge the storage media, the DoD requires overwriting with a pattern, then with its complement, and finally with another pattern; e.g., overwrite first with 0011 0101, followed by 1100 1010, then 100 0111. The number of times an overwrite must be accomplished depends on the storage media, sometimes on its sensitivity... In any case, a purge is not complete until a final overwrite is made using unclassified data."

Author Comment

ID: 2807975
not what i was really looking for.
what program can people use to get data that has been overwritten.
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 2808034
In fact this is not normal software, because you need very special hardware.

Normal software (including OS) is telling you what the hardware controller is telling you.
This special undelete software/hardware combination however use much more sophisticated methods to check what data had been on the disk. Even overwritten or deleted files can may be restored.
I do not know the name of these, and i think you won't get that in normal shop.
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Expert Comment

ID: 2808391
I believe that if you overwrite the file 8x it's impossible to restore the data, even if you are using technology from the US Army.

What you need to remember when you are dealing with files in a OS like Windows you are actually dealing with a buffer in memory, and you will have to make sure the data is saved to disk after you have changed the data. Otherwhise, in the worst scenario, you are just saving over the data in the internal buffer 8x times and just saving over the data on the physical disk once. You need to flush the buffer to disk after every save. The solution to this could be to use the Reset statement instead of the Close statement, because Reset will flush the buffer, but I can not guarantee this is true.

Maybe this is the problem with your program, that it overwrites the buffer 8x but only saves to the physical disk once. This way it's easy to 'undelete' the file.

Author Comment

ID: 2810055
the thing is that vin want to make a wiping program but if i cant test its strength with a undelete program it might be a bad program

Author Comment

ID: 2810058
the thing is that want want to make a wiping program but if i cant test its strength with a undelete program it might be a bad program
LVL 28

Accepted Solution

Ark earned 80 total points
ID: 2810172
Try tiramisu
When I got win_chih last year, this program only can help me to recover data. Then, this year, one of mine the fellow worker has taken by error my hard disk (removable) and has formatted it with low level format and change partitions. This isn't a big problem, but then hi tried to install NT system on it for four(!) times, every time using low level formatting before installation. Tiramisu recover me 98% of data.


Author Comment

ID: 2816534
i will look for it

Author Comment

ID: 2854946
Comment accepted as answer
LVL 28

Expert Comment

ID: 2857109
Hello, adam8
Thanks for points. Does your app wipe files so tiramutsu can not restore them?
BTW, if you need new free version of tiramisu, take a look at http://www.simnet.is/xit/FOSI/  (or http://fosi.da.ru - through redirector)

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