Re: SVSM Attestation and vTPM specification additions - v0.60

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2023-01-10 at 15:32 -0600, Tom Lendacky wrote:
[...]
> My thoughts were to again use GUIDs to identify the key and key-type 
> present, i.e. EK RSA-2048 or EK EC (NIST-P256), etc:
> 
>         16-byte data GUID (e.g. EK EC (NIST-P256))
>         4-byte data length
>         data
> 
>         16-byte data GUID (e.g. SRK EC (NIST-P256))
>         4-byte data length
>         data

I really wouldn't use GUIDS because the TPM structures should all be
self describing.  The structure we're thinking of packing into the
attestation report to be hashed with the nonce is the TPMT_PUBLIC of
the EK.  The algorithm, attributes, policy and name hash which are in
the public area should define the exact template that was used to
construct the public key.  Note that there are about 2^70 possible
combinations, which is why I don't think you want a GUID for each one
...

James