Re: [RFC V4 PATCH 00/15] Signature verification of hibernatesnapshot

[Pavel Machek]

On Wed 2013-09-25 15:16:54, James Bottomley wrote:
> On Wed, 2013-09-25 at 17:25 -0400, Alan Stern wrote:
> > On Wed, 25 Sep 2013, David Howells wrote:
> > 
> > > I have pushed some keyrings patches that will likely affect this to:
> > > 
> > > 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=keys-devel
> > > 
> > > I intend to ask James to pull these into his next branch.  If he's happy to do
> > > so, I can look at pulling at least your asymmetric keys patch on top of them.
> > 
> > This suggests a point that I raised at the Linux Plumbers conference:
> > 
> > Why are asymmetric keys used for verifying the hibernation image?  It
> > seems that a symmetric key would work just as well.  And it would be a
> > lot quicker to generate, because it wouldn't need any high-precision
> > integer computations.
> 
> The reason is the desire to validate that the previous kernel created
> something which it passed on to the current kernel (in this case, the
> hibernation image) untampered with.  To do that, something must be
> passed to the prior kernel that can be validated but *not* recreated by
> the current kernel.

I don't get this. Why is it important that current kernel can't
recreate the signature?

Current kernel is not considered malicious (if it were, you have worse
problems).

								Pavel

PS: And yes, it would be nice to have
Documentation/power/swsusp-uefi.txt (or something) explaining the
design.

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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