> 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.
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