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Author Topic: Old "secure delete" commands on newer file systems  (Read 2048 times)

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Offline AmigaManceTopic starter

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Old "secure delete" commands on newer file systems
« on: January 07, 2009, 05:52:59 PM »
Hi.
 While browsing on Aminet i stumbled on some commands which are able to delete files in a way that they can not be recovered later on. Some of the packages i found:
Erase.lha
SecureDel42_1.lha
Wipe10.lha
SDelete.lha

 My concern is that these commands are old and i can't tell if they are OFS/FFS specific like DiskSalv for example. This could put my partition in danger.
 Thus, i would like to know if anyone have used them on SFS or PFS partitions.
A1200 PPC user.
 

Offline Tenacious

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Re: Old "secure delete" commands on newer file systems
« Reply #1 on: January 07, 2009, 07:12:45 PM »
IIRC, some of these programs use a strategy of writing some nonsensical data pattern to all the disk locations occupied by the undesirable file.  Then those locations are tagged as available to be used/overwritten in the future.

I'm no expert, but, this method would seem to be safe for any file system.

If you find more info, keep us updated.
 

Offline Thomas

Re: Old "secure delete" commands on newer file systems
« Reply #2 on: January 07, 2009, 09:15:23 PM »
Quote
I'm no expert, but, this method would seem to be safe for any file system.


Yes, it's safe for any file system but it's also different for each file system. There is no way for an application program to find out the blocks which are occupied by a file without knowing the file system. Actually, depending on the file system implementation, data does not need to be organized in blocks at all.

So no, as long as the documentation does not state that a program works with PFS or SFS, it does not do so.

It might even be the case that a program which works on OFS does not work on FFS. Or even worse, such old programs might assume that they work on OFS while actually they corrupt the FFS.

Bye,
Thomas


Offline Zac67

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Re: Old "secure delete" commands on newer file systems
« Reply #3 on: January 07, 2009, 09:36:15 PM »
Depending on how exactly the tools try to accomplish their task, they might work, might not work or might even damage the FS.

The latter will happen if they access the disk on block level without noticing that the FS in use is not understood by them.
As long as they depend on using the file level to erase the data it'll be safe at least.

When the FS makes no attempt to save a file from being inadvertently overwritten/destroyed it will also work - I'm not aware of any Amiga FS being able to do so, but I haven't used ProFS or SFS yet. Obviously the FS in question would come with tools allowing you to recover overwritten data, otherwise it's very unlikely that such a feature exists.

(The file level works by opening the file for modification, overwriting the contents with arbitrary data or certain bit patterns, possibly several times and finally deleting the file. A file system with overwrite protection creates a backup during this process, i.e. stores the new data in a previously empty area of the disk while keeping the old data in the background. E.g. Novell Netware does this in some scenarios.)
 

Offline itix

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Re: Old "secure delete" commands on newer file systems
« Reply #4 on: January 07, 2009, 10:09:17 PM »
They are probably safe. At least Erase is but result is not guaranteed if you are using filesystem caches or data is written to different location. Anyway:

Quote

 Q. How does Erase 'erase' a file?

 A. When erasing a file the following steps are taken:
    1. The files protection flags are set to RWED
    2. The files comment is cleared
    3. The ownership information (if using mufs) is cleared
    4. The file creation date is cleared
    5. The file is overwritten 'TIMES' times with data (data is actually
       different each time, ascii codes TIMES..0)
    6. The file size is set to 0
    7. The file is deleted as normal

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