"That's some serious wiping you're doing. I suspect that it must take a fierce amount of time to complete."
Yes, it might be a bit overkill for the average user to overwrite the free space 35 times (and it takes a lot of time do it's work). I based the code on the paper Secure Deletion of Data from Magnetic and Solid-State Memory by Peter Gutmann.

"An alternative approach would be to securely wipe the contents of sensitive files before deleting them. This will be much, much faster."
srm and wipe does just that, but that's the problem: they only wipe files, leaving your "deleted" temporary files etc in the open.

"I read it, you might scribble garbage on a large section of the free space of the disk and still manage to avoid overwriting an area where sensitive information lies waiting to be recovered."
Yes, i haven't added the code to overwrite the slack space for example, but i will (someday:).

"The US Department of Defense ..."
The whole Rainbow-series (including the Orange Book) is really good which I would recommend to anybody. However I don't really trust a 7 layer overwrite.

Changes to be made:
* Add 6 layer overwrite (0x49,0x24,0x92,0x6D,0xB6,0xDB)
* Add DoD standard (7 layer overwrite)
* Add 8 layer random owerwrite
* Better "interface"