Re: [RFC 2/4] Add rsa support

["Jan Lübbe" <jlu@pengutronix.de>]

On Mo, 2015-03-16 at 11:27 +0100, Jean-Christophe PLAGNIOL-VILLARD
wrote:
> On 11:00 Mon 16 Mar     , Jan Lübbe wrote:
> > On Fr, 2015-03-13 at 16:49 +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > > you just need to have a unique ID on the HW and then use a x509 object
> > > to store it. then signed it with you CA. As only validated keys can be
> > > used, you can easly give a generated key for a specific HW.
> > > And this key will be valid only for this HW.
> > 
> > Yes, this sounds useful. So you'd have a board-specific way to check the
> > unique ID constraint in an intermediate cert against the HW ID?
> yes more or less but but at the key itself as you will have to upload the
> key to the board. And the key will only be accepted to be stored as it will
> be valid and have the HW ID.

OK. Sounds good to me.

> And for the record remember if you want to use module in secured boot mode
> for the kernel you will have to use x509 certificate anyway.
> 
> So why not to use the same principal.
> 
> u-boot way is not what is doing today on the market for authentication
> format. Today it's x509 or PGP.
> 
> So I do prefer to stay as standard as possible, this does not mean we can not
> support the FTD stuff. But IMHO it's not the right way.

x509 only defines the certificate format, not how it is used to sign
kernel, initramfs and device tree.

The kernel defines its own format based on ELF and store the signature
inside. That can't be reused directly for the kernel itself, initramfs
or DTB. UEFI has again its own format.

We don't want to sign kernel, initramfs and DTB individually, as this
would allow an attacker to mix-and-match these to trigger a
vulnerability. So we need to have some format which supports signing a
given configuration consisting of specific kernel, initramfs and DTB.

FIT handles this requirement. It also supports having multiple
configurations (each signed) referencing for example the same kernel
+initramfs but different DTBs for a set of similar boards.

What is the image format you intend to use with x509 certs?

Regards,
Jan
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