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Date: Thu, 20 Mar 2014 09:23:14 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140320082314.GD28673@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] Adding dmcrypt to QEMU block drivers
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To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, =?iso-8859-1?Q?Beno=EEt?= Canet <benoit@irqsave.net>, "Hamilton,
	Peter A." <Peter.Hamilton@jhuapl.edu>, Markus Armbruster <armbru@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "Coffman,
	Joel M." <Joel.Coffman@jhuapl.edu>

On Tue, Mar 18, 2014 at 01:30:44PM +0000, Daniel P. Berrange wrote:
> On Tue, Mar 18, 2014 at 02:08:19PM +0100, Stefan Hajnoczi wrote:
> > On Mon, Mar 17, 2014 at 08:48:08PM -0400, Hamilton, Peter A. wrote:
> > I guess the filter would be deployed below the image format:
> > qcow2 -> luks -> file
> 
> I could see it being either above or below the image format at
> mgmt app's choice. Having it above the image format means only
> the payload is encrypted, so you can still query the basic
> metadata (like logic disk size, backing files) without decrypting,
> which is a nice aspect of the way qcow2 encryption historically
> worked. I could see though that people might want even the header
> encrypted to prevent anyone seeing anything about the image format
> without keys.

The difference is that if you encrypt just the payload then dmcrypt
compatibility is much less useful since the data is now intermingled
with image format metadata.

But I agree in some cases it may be the right thing to do.