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

[Laurence Lundblade <[e-mail]>]

> On Jun 5, 2022, at 12:34 PM, Michael Richardson <[e-mail]> wrote:
> 
> 
> 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.

Yes, of course malware will lie. Any successful attack on the system can result in forged claims. This is true of each and every claim.

There are two paths from the Endorser to the Verifier. One is direct and the other is via the Attester. Both are subject to attack. There’s no reason to assume one path is more secure than the other, though one might be in practice.

The one through the Attester is needed to bind the claims to a transaction being carried out ($$, admission to the network, access to data).


> 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.

Yes, Evidence is not trusted until Verified. This is true of every claim.

The UEID claim has the same security characteristics as the security-level claim or even the contents of a PCR.

They are all contingent on the Attester Manufacturer building the Attester correctly and they are all subject to the same attacks.

How is security-level different?


> 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.

An Endorsement always means believe at least one claim in Evidence. It has to work like that. You agree with that, right?

If one, why not all? What’s the distinction?

LL