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    SubjectRe: Wanted: Secure-delete utility for Linux
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    Kev <klmitch@MIT.EDU> said:
    > Horst von Brand <vonbrand@sleipnir.valparaiso.cl> said:
    > > Write a tiny program for the task, something like:
    > [snip]
    > > x =3D time(NULL);

    > This is already insecure; you can do better by reading 4 bytes from
    > /dev/{u,}random as appropriate.

    Makes a lot of sense. Iff it is Linux...

    > Also, I would probably use a
    > cryptographic hash function instead...

    I understood that a cryptographically strong hash wasn't needed here. You
    are just trying to overwrite the data to be wiped with (pseudo)random bytes
    to make recovery more difficult, and the objection to using /dev/urandom
    (cryptographically strong hash) was that it is too slow. I don't know
    anything about the technology to be used for this "recovery", but what was
    discussed here was using an electron microscope to read off the previous
    contents of the platter bit by bit. Sounds horribly expensive to me, if
    your data is important enough to warrant protection against _that_ kind of
    reading, you'll be more than willing to sandblast the magnetic covering off
    the disk and melt the whole down afterwards.

    If your objection stands, you could reseed the sequence each, say, 200
    iterations, and just use the high byte each time.
    --
    Horst von Brand vonbrand@sleipnir.valparaiso.cl
    Casilla 9G, Viña del Mar, Chile +56 32 672616

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