[Pkg-cryptsetup-devel] LVM on encrypted device?

Jonas Meurer jonas at freesources.org
Thu Feb 2 21:26:21 UTC 2006

On 02/02/2006 Hadmut Danisch wrote:
> Yup. The RAID record could reveal information, such as the name, when
> last mounted, and things like that. It could further be systematically
> modified by an attacker. 
> If you put encryption on RAID, then all raid disks must have the same
> encryption key. Maybe not wanted. 
> When removing one RAID disk (e.g. because of failure) an attacker
> could compare the disk with the other disk and see how many sectors
> have been changed meanwhile. Could even try a replay attack by copying
> sectors back to the other disk. 
> I admit these conditions are rather rare and may occur seldomly. This
> was just an example. Putting LVM on encryption would be significantly
> more important.

accepted, it would be useful to support that.

> > correct, current debian cryptsetup packages don't support lvm over
> > cryptsetup. is this often used?
> No, because it's not supported. The chicken-and-egg problem. 

i meant in general, not in the debian world.

> > yes, maybe running cryptdisks twice would be the best. but how to check
> > whether a device is a physical one or not? i'm not sure about how to
> > realize that.
> Maybe just check whether the device entry exists? 
> /dev/hda3 exists at the first run, 
> /dev/mapper/example does not, but at the second run.

that would be the easiest way. and it even would solve another problem:
if a removable device is not available, it's simply not mentioned. that
makes encrypted removable devices even more secure.
only if /etc/fstab has an entry for the fs on the removable media, boot
process breaks.

> Or just treat /dev/mapper differently?

no, i don't like that idea, as people could also use /dev/vg_name/*, and
maybe not only lvm suffers from that problem (i don't know for example
about evms etc.).

i like the idea, that cryptdisks checks for the existance of the source
device before running cryptsetup over it. and running cryptdisks twice
in the boot process shouldn't be too hard.


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