Draft: draft-ietf-rats-reference-interaction-models

Commentary: ( leaving in two refs that are now DAA , but will becoming -daa later ) , refactoring of remaining loose ends , removed the changelog
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This document describes interaction models for remote attestation
procedures (RATS).  Three conveying mechanisms - Challenge/Response,
Uni-Directional, and Streaming Remote Attestation - are illustrated
and defined.  Analogously, a general overview about the information
elements typically used by corresponding conveyance protocols are
highlighted.  Privacy preserving conveyance of Evidence via Direct
Anonymous Attestation is elaborated on in the context of the
Attester, Endorser, and Verifier role.
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This document describes interaction models for remote attestation
procedures (RATS).  Three conveying mechanisms - Challenge/Response,
Uni-Directional, and Streaming Remote Attestation - are illustrated
and defined.  Analogously, a general overview about the information
elements typically used by corresponding conveyance protocols are
highlighted.
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prevent inconsistencies in descriptions of interaction models in
other documents (due to text cloning and evolution over time),
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illustrate the application of Direct Anonymous Attestation (DAA)
for the defined set of reference models.
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other documents (due to text cloning and evolution over time), and to
set of characteristics captured here in this document and variants of
these interaction models used in other specifications or solutions.
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Furthermore, any processes and duties that go beyond carrying out
remote attestation procedures are out-of-scope.  For instance, using
the results of a remote attestation that are created by the Verifier,
e.g., how to trigger remediation actions or recovery processes, as
well as such remediation actions and recovery processes themselves,
are also out-of-scope.
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Furthermore, any processes and duties that go beyond carrying out
remote attestation procedures are out-of-scope.
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For instance, using the results of a remote attestation procedure
that are created by the Verifier, e.g., how to triggering remediation
actions or recovery processes, as well as such remediation actions
and recovery processes themselves, are also out-of-scope.
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DAA DAA is a signature scheme used in RATS that allows preservation
of the privacy of users that are associated with an Attester (e.g.
its owner).  Essentially, DAA can be seen as a group signature scheme
with the feature that given a DAA signature no-one can find out who
the signer is, i.e., the anonymity is not revocable.  To be able to
sign anonymously an Attester has to obtain a credential from a DAA
Issuer.  The DAA Issuer uses a private/public key pair to generate a
credential for an Attester and makes the public key (in the form of a
public key certificate) available to the verifier in order to enable
them to validate the DAA signature obtained as part of the Evidence.
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In order to support these DAA signatures, the DAA Issuer MUST
associate a single key pair with each group of Attesters and use the
same key pair when creating the credentials for all of the Attesters
in this group.  The DAA Issuer's public key certificate used by a
group of Attesters replaces the individual Attester Identity
documents during authenticity validation as a part of the appraisal
of Evidence conducted by a Verifier.  This is in contrast to
intuition that there has to be a unique Attester Identity per device.
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This document extends the duties of the Endorser role as defined by
the RATS architecture with respect to the provision of these Attester
Identity documents to Attesters.  The existing duties of the Endorser
role and the duties of a DAA Issuer are quite similar as illustrated
in the following subsections.
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The associated private keys are used by the DAA Issuer to provide
an Attester with a credential that it can use to convince the
Verifier that its Evidence is valid.  To keep their anonymity the
Attester randomizes this credential each time that it is used.
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The Verifier can use the DAA Issuer's public key certificate,
together with the randomized credential from the Attester, to
confirm that the Evidence comes from a valid Attester.
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A credential is conveyed from an Endorser to an Attester in
combination with the conveyance of the public key certificates
from Endorser to Verifier.
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The zero-knowledge proofs required cannot be created by an Attester
alone - like the Endorsements of RoTs - and have to be created by a
trustable third entity - like an Endorser.  Due to that semantic
overlap, the Endorser role is augmented via the definition of DAA
duties as defined below.  This augmentation enables the Endorser to
convey trustable third party statements both to Verifier roles and
Attester roles.
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An Attester Identity MAY be a unique identity, it MAY be included
in a zero-knowledge proof (ZKP), or it MAY be part of a group
signature, or it MAY be a randomized DAA credential.
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In order to provide proofs of authenticity, Attestation Evidence
SHOULD be cryptographically associated with an identity document
(e.g., a PKIX certificate or trusted key material, or a randomized
DAA credential respectively), or SHOULD include a correct,
unambiguous, and stable reference to an accessible identity
document.
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An Attester Identity MAY be a unique identity, it MAY be included
in a zero-knowledge proof (ZKP), or it MAY be part of a group
signature, or it MAY be a randomised DAA credential DAA.
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In order to provide proofs of authenticity, Attestation Evidence
SHOULD be cryptographically associated with an identity document
(e.g. an PKIX certificate or trusted key material, or a randomised
DAA credential DAA), or SHOULD include a correct and unambiguous
and stable reference to an accessible identity document.
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In DAA, the Attester's identity is not revealed to the verifier.
The Attester is issued with a credential by the Endorser that is
randomised and then used to anonymously confirm the validity of
their evidence.  The evidence is verified using the Endorser's
public key.
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The Attester is issued with a credential by the Endorser that is
randomised and then used to anonymously confirm the validity of their
evidence.  The evidence is verified using the Endorser's public key.
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In DAA, Authentication Secret IDs are represented by the Endorser
(DAA issuer)'s public key that MUST be used to create DAA
credentials for the corresponding Authentication Secrets used to
protect Evidence.
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In DAA, an Authentication Secret ID does not identify a unique
Attesting Environment but associated with a group of Attesting
Environments.  This is because an Attesting Environment should not
be distinguishable and the DAA credential which represents the
Attesting Environment is randomised each time it used.
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Revised the relabeling of "claims" with "assertion" in
alignment with the RATS Architecture I-D.
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Text revisions based on changes in I-D.ietf-rats-architecture
and comments provided on rats@ietf.org.