Re: [Rats] Composite Evidence

Michael Richardson <> Fri, 24 January 2020 18:19 UTC

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From: Michael Richardson <>
To: "Smith\, Ned" <>
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Date: Fri, 24 Jan 2020 13:19:36 -0500
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Subject: Re: [Rats] Composite Evidence
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Smith, Ned <> wrote:
    mcr> [%] I think you are saying that rather than documenting that we
    mcr> forward a union of evidence and attestation results, that we
    mcr> document that will create a kind of evidence, which includes attestation results?

    Ned> Maybe. It really is a case of multiplexing several conversations
    Ned> over the same conveyance mechanism, but otherwise conversations
    Ned> could be de-multiplexed (without creating unnecessary
    Ned> cross-dependencies). For example in both Passport and BK-Check
    Ned> topology models, a message is simply relayed. The endpoints are
    Ned> still the way they're defined in the Roles Arch diagram.

yes, I agree, we could send a list of evidence and a list of attestion
results from components.  I don't really know what the list of potential
*verification* protocols is.
(I know that I want to include it in RFC8366/BRSKI voucher-requests, once
that is an RFC)

I don't think this communication can ever be via certificate, while the final
attestation results could be placed inside a certificate.

    Ned> Email may not be the best way to try to illustrate but here goes. I
    Ned> assert that Eric's diagram can be recast into two graphs where graph
    Ned> (a) is the sub-component attester (A1), the local verifier (V1) and
    Ned> a relying party (RP). The second graph (b) consists of the top level
    Ned> Attester (A2), a remote verifier (V2) and the same relying party
    Ned> (RP).

    Ned> Looks something like:
    Ned> (a) A1 --- E1 ---> V1 --- AR1 ---> RP;
    Ned> (b) A2 --- E2 ---> V2 --- AR2 ---> RP.

I agree this is a reasonable diagram.

    Ned> If it makes sense to define "routing claims" that assert that A2
    Ned> intended to piggy back AR1 with E2 then that should imply that if E2
    Ned> = (c1) and c2 = routing claim then E2' = (c1, c2). The conveyance
    Ned> still carries (AR1, E2') , but possibly the c2 claim names AR1 as
    Ned> the piggy i.e. = "AR1".

Are you saying that the fact that (b) is relayed via E1 is important, and
should be communicated by having E1 sign the transaction as well?

    Mcr> It could be that there are competitive or regulatory reasons why the Lead
    Mcr> Attester does not wish to reveal the types of the line cards attached.
    Mcr> Consider an automobile (or passenger rail car, or human-rated Rocket) that
    Mcr> needs to attest that it has four good tires (which passed their 20,000km
    Mcr> inspection), but which does not wish to reveal which manufacturer provided
    Mcr> those tires.  Passing on evidence directly would be a problem.

    Ned> [nms] Privacy is an important consideration. If Evidence is privacy
    Ned> sensitive, then it can be encrypted. The routing claims don't
    Ned> require transparent Evidence to name them. Could compute a hash of E
    Ned> or AR or if endpoints have security associations, then E and AR can
    Ned> be encrypted and a digest of ciphertext becomes its name for the
    Ned> purpose of routing claims (see my response above).


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