Re: [Rats] Function of an endorsement relative to evidence

[Michael Richardson <[e-mail]>]

Laurence Lundblade <[e-mail]> wrote:
    > Assuming for the sake or argument here that the Attester Manufacturer
    > and Endorser are the same, it goes like this. The
    > Endorser/AttesterManufacturer only puts private keys into devices that
    > it knows are built correctly. They won’t lie. They’ll protect their
    > keys. They produce correct claims. This really is the fundamental work
    > of the Endorser/AttesterManufacturer above all else.

I'm with until you say, "They won't lie", as it's totally irrelevant.

Of course malware will lie.  That's the whole point of this process.
If they keys are protected, then the claims the malware generates will not
validate.   But, it will try, based upon some private key extracted out
of some other device that was subject to some silicon level attack.


A piece of Evidence, saying, "I'm security-level FOO", signed by ME, is
completely meaningless.
Only after the Verifier has looked up the public key can it have any meaning.
You know this, you've said exactly this multiple times.

But, only at that point, the "security-level" (or any other integer based
big/little comparison of stuff) comes out of the Endorsement.   It's just
wasted bits to put it anywhere else.

So, it is *NEVER* useful as Evidence.  EVER.

    > The Endorsement can mean “believe all the Evidence from this
    > Attester”. (It might always not be all the Evidence, but it will always
    > be some of the Evidence).

That's a really bizarre thing to put in an Endorsement.

    > By this it is entirely reasonable for security-level to be transmitted
    > either as an Endorsement or in Evidence.

No, it's not.

    > I think there is also room for security-level in Evidence in composite
    > device attestation. One Attester may have a good way to evaluate the
    > security-level of a subsystem, perhaps a subsystem that varies from
    > device to device.

I don't even believe this is useful.

--
Michael Richardson <[e-mail]>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide