Re: [Qemu-devel] QCOW2 cryptography and secure key handling

[Daniel P. Berrange]

On Tue, Jul 23, 2013 at 05:22:47PM +0200, Stefan Hajnoczi wrote:
> On Tue, Jul 23, 2013 at 04:40:34PM +0200, Benoît Canet wrote:
> > > More generally, QCow2's current encryption support is woefully inadequate
> > > from a design POV. If we wanted better encryption built-in to QEMU it is
> > > best to just deprecate the current encryption support and define a new
> > > qcow2 extension based around something like the LUKS data format. Using
> > > the LUKS data format precisely would be good from a data portability
> > > POV, since then you can easily switch your images between LUKS encrypted
> > > block device & qcow2-with-luks image file, without needing to re-encrypt
> > > the data.
> > 
> > I read the LUKS specification and undestood enough part of it to understand 
> > the
> > potentials benefits (stronger encryption key, multiple user keys, 
> > possibility to
> > change users keys).
> > 
> > Kevin & Stefan: What do you think about implementing LUKS in QCOW2 ?
> 
> Using standard or proven approachs in crypto is a good thing.  I haven't
> looked at qcow2 encryption in the past because fairly few people
> actually use it.
> 
> One use-case I have heard about is qcow2 files over NFS.  The network
> and the storage system should not see guest data.  Only the host and the
> VM should see the data.

Yep, that is the core usecase. You are securing the system such that
only the VM host administrator/processes can compromise the data. It
is protected against malicious storage and/or network administrators.

> A big win with LUKS is that you can change the passphrase without
> re-encrypting the data.

Other benefits of LUKs are

 - Strong encryption key, even if the passphrase itself is weak
 - Support for multiple passphrases
 - Support for arbitrary different encryption algorithms / settings
 - Ability to detect whether the passphrase is correct or not rather
   than just decrypting to produce garbage

Regards,
Daniel
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