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    SubjectRe: Unswappable memory needed is user space
    On Tue, 8 Dec 1998, Zow Terry Brugger wrote:

    > > I'm making a crypto program (under french law).
    > > It crypts a file and then totally erase the uncrypted by filling it with
    > > zero.
    > >
    > Don't know about the non-swap mem, but what you're doing here is another
    > problem. Just writting zeros to the disk won't prevent the file from still
    > being read off the disk by some very syphisicated techniques (done by looking
    > at the magnetic fields on the platter in a clean box). Instead, you want to
    > write over the file at least three times with random bits. This too may be
    > insufficient if ext2 (or whatever other underlying fs) relocates the file when
    > you go to write over it (hence, the origional is in one place, marked as free
    > space, and your random data is in another). Anyone know more about this?
    > >
    > > christophe leroy
    > >
    > -"Zow"

    generally, something like overwrite with zeros, then with ones, then
    repeat 3 times. Overwrite randomly a few times, then with zeros again.
    Shouldn't be trouble with ext2, as long as you don't unlink the file befor
    destroying it. As for non-swapping, someone said it wouldn't protect
    against an untrusted root. This is almost true. Root _could_ dump the
    memory out at just the right moment, but this would be pretty hard..... (I

    / David Feuer \
    | |
    | |

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