encrypted file system issues (was Re: PGP "master keys")

[Perry E. Metzger]

"Travis H." <solinym at gmail.com> writes:
> Does anyone have any experience with disk or filesystem encryption,
> especially with regard to unclean shutdowns and power failures? Normal
> file systems are designed to fail in ways that are easy to
> clean up with fsck, but when you start to throw encryption into the
> mix, it seems like you can easily end up with something unrecoverable.

Not if you design it correctly. Disk encryption systems like CGD work
on the block level, and do not propagate CBC operations across blocks,
so if the atomic disk block write assumption is correct (and almost
all modern file systems operate on that assumption), you have no more
real risk of corruption than you would in any other application. The
only real risk points come in if you're doing a re-key of the entire
disk or some similar operation in which care must be taken with the
design or you could leave yourself in an unknown state.

> Even without encryption I've seen apparent bugs in ext2fs on SMP
> machines that lead to sectors of nulls placed in files that were being
> written around the time the system crashed.

Bugs happen in everything.

Perry

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