[dm-crypt] Use of GCM mode with dm-crypt

Arno Wagner arno at wagner.name
Wed Apr 27 15:43:23 CEST 2011

On Wed, Apr 27, 2011 at 11:41:01AM +0200, Milan Broz wrote:
> On 04/27/2011 10:40 AM, Samantha Adams wrote:
> Basically it would be new encryption DM target (it can share code
> but the mapping here is different).
> The crucial question where do you want to store authentication tag...
> If there is some standard way, perhaphs it can be done.
> But isn't better to provide these integrity services to filesystem
> on top of dmcrypt? (so fs can allocate blocks storing integrity info)

In my view, integrity check, just as compression (and the filesystem
itself) all belong on top of encryption. For the other two, this is
obvious. For the integrity check, what is the FS layer to do if it
fails? If you have error correction or redundancy in the FS, then
it can do something, but on crypto-layer you can just propagate the
error and handling would be done elsewhere. Also note that the 
problem of storing the tags.checksums goes away on the FS layer,
as one of the primary tasks of a FS is storing metadata.

Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name 
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