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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.


    Cheers,
    Dick Johnson
    ***** FILE SYSTEM MODIFIED *****
    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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