Re: [Rats] Endorsement ID and verification key (was Processing Endorsements and Evidence into Results)

[Thomas Fossati <[e-mail]>]

Hi Laurence,

On 07/04/2020, 20:12, "Laurence Lundblade" <[e-mail]> wrote:
> On one extreme is a separate endorsement for every device ("micro
> endorsement"?), which is what I think Thomas and ARM PSA are tending
> towards. The other extreme is one endorsement for a product line
> (macro endorsement"?), say a product line of TPMs. Then it's more
> like the data sheet for the product.
>
> Then there's different ways to fan this out to the different key /
> signing schemes (per-device key, group key, ECDAA, X.509). For example
> a macro-endorsement could include the root of an X.509 hierarchy and
> the individual devices (or groups of devices) would have individual
> keys that chain up.  With a micro-endorsement the per-device public
> key could be per endorsement.

One tiny clarification.  While it's true that the current PSA
attestation format gravitates towards micro-endorsements, that is not a
necessary outcome of the underlying security architecture.  The baseline
requirement is for a raw public key, but nothing prevents it being a
certified key instead.

There is both already shipped and in-progress work that would help
moving in the direction, specifically:
- have the attestation key associated with a profiled [1] and compressed
  [2] cert;
- have EAT / PSA tokens carry cert material instead of just key
  identifiers [3].

cheers!

[1] RFC7925
[2] draft-mattsson-tls-cbor-cert-compress
[3] draft-ietf-cose-x509

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