Subject: [Rats] draft-voit-rats-trusted-path-routing (was RE: Composite Evidence)

From: "Eric Voit (evoit)" <[email-masked]>
Date: Thu, 27 Feb 2020 16:58:32 +0000

Reviving this old thread, I have posted:

https://datatracker.ietf.org/doc/draft-voit-rats-trusted-path-routing/

This draft provides some thinking on previous questions raised on this thread:

*	includes a use case which can benefit from Composite Evidence (i.e., sending 
networking flows only across successfully attested routers),
*	describes how an attesting device might assemble a passport which contains 
Composite Evidence, and
*	includes a proposal for how a Verifier might subscribe to a stream of 
Evidence.

Hopefully this can help provide some network transport context to the 
draft-ietf-rats-architecture discussions.

Thanks,
Eric

From: Eric Voit, January 22, 2020 7:04 PM

Henk,         Dave,

Michael,    Ned,

I promised you a definition for Composite Evidence.  You can see my proposed 
definition directly the text below, but I am not willing yet to place it in a 
Pull Request. I thought an email thread might be helpful first.

Anyway my strawman definition for Composite Evidence is:  Evidence which 
includes multiple sub-elements of evidence, more than one of which can be 
computationally verified to have been generated by a specific Attester 
Subcomponent or Verifier.

I built this definition considering the passport model, which looks like it 
will often needs to use composite evidence.  As an example of why I believe 
this, see the use case below.

    .--------------.

    |  Verifier A  |

    '--------------'

        ^     [2]

        |     Verifier A signed Attestation Results @time(x) (

    evidence(  |  determination, hash(TpmQuote@time(x)))

    TpmQuote   |

    @time(x))  |

       [1]     V

     .-------------.                           .---------------.

     |  Attester   |<------nonce @time(y)---[3]|  Verifier B   |

     |    .-----.  |                           |       /       |

     |    | Tpm |  |[4]-composite evidence ( ->| Relying Party |

     |    '-----'  |      TpmQuote@time(y),    '---------------'

     '-------------'      TpmQuote@time(x),

                          Verifier A signed Attestation Results @time(x) )

In the example above, evidence at time x is generated and signed within a TPM. 
This would *not* be composite evidence.   This evidence would be evaluated by 
Verifier A, signed, and returned as Attestation Results to the Attester.   A 
subsequent request from a Relying Party at time y could pull three 
independently signed elements of evidence from the Attester.  These three 
would comprise the composite evidence which when taken together would allow 
Verifier B / Relying Party to evaluate the current trustworthiness of the 
Attester.

Does this definition meet your needs?

Thanks,

Eric