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SubjectRe: Secure deletion
On Thu, 23 Jul 1998, Alexander Kjeldaas wrote:

> On Thu, Jul 23, 1998 at 09:14:44AM -0400, Richard B. Johnson wrote:
> >
> > If you don't need 'instantaneous' security, i.e., you can clean up
> > your disk(s) once a day, just make a program that writes a file,
> > filled with "SECURITY ", until the disk partition is full.
> > Close the file, sync the file-system, then delete the file.
> >
> This probably won't work for a block that has been reused in another
> file, but where the whole block hasn't been overwritten by the new
> file. Let's say I have a 100k file, delete it and create 100 1-byte
> files which occupies the blocks from the 100k file (blocksize 1k).
> Then there will be 1023 bytes in each block which are allocated, but
> with unknown state. Whether they are overwritten by 0s or not written
> at all is unspecified.

There are always things that "won't work". If your disks are "cleaned"
each night, you will find a high probability that the unwritten data
will contain the security pattern. In fact, since I started using this
technique (two years), I have never seen any unwritten data that
didn't contain (1) The rest of the sector-buffer, (2) The words
"SECURITY" with 8 trailing blanks.

Dick Johnson
Penguin : Linux version 2.1.108 on an i586 machine (66.15 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.

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