Messages in this thread | | | Subject | Re: PATCH - ext2fs privacy (i.e. secure deletion) patch | From | Albert Cahalan <> | Date | 07 Feb 2004 04:55:59 -0500 |
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Hans Reiser writes:
> There is an extensive literature on how you can recover > deleted files from media that has been erased a dozen > times,
I doubt this is true in any way that matters.
Unless you get REALLY lucky with bad sector substitution and you know the secret vendor-specific drive commands to fetch bad sectors, you'll need the physical hardware.
no hardware ---> no data recovery
Given that you do have the physical hardware, how are you going to read it? You'll need some equipment that will cost you many millions of dollars. So this isn't going to be anybody but the CIA, NSA, or non-US equivelent. They won't bother very often; even a "black" budget is limited. Are you so sure you're worth it?
Does the "extensive literature" cover drives made in the last year? (decade?) These days, manufacturers are using extremely thin layers of surface material over an inert substrate. Magnetic domains flip in an all-or-nothing fashion; the old recovery methods rely on finding some buried domains that didn't flip. With the layers getting damn thin, I doubt any will exist. There just won't be any residual signal from previous writes, and so the recovery methods have nothing to work with.
> but breaking encryption is harder. It is more > secure to not put the data on disk unencrypted at all > is my point.....
This leads to one method of implementing the secure deletion flag. At boot, generate a random key for the log file. At file creation, generate a random key for the file body and inode. (these are internal to the filesystem) When you want to destroy something, wipe the key. Remember to flush and regenerate the log file.
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