Messages in this thread | | | Subject | Re: Wanted: Secure-delete utility for Linux | Date | Wed, 23 Dec 1998 23:48:24 -0400 | From | Horst von Brand <> |
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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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