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MEC Endorsements #174

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Dec 6, 2023
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MEC Endorsements #174

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78df184
the MEC part of
henkbirkholz Dec 1, 2023
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q
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1ddc942
added condition-triple-record.cddl
henkbirkholz Dec 1, 2023
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Update cddl/triples-map.cddl
nedmsmith Dec 5, 2023
7dfefbc
fixed some lint
henkbirkholz Dec 6, 2023
f553dd3
addressing https://github.com/ietf-rats-wg/draft-ietf-rats-corim/pull…
henkbirkholz Dec 6, 2023
c261262
added condition-triple-record.cddl to frags
henkbirkholz Dec 6, 2023
12d4d91
tweaks
thomas-fossati Dec 6, 2023
ce64489
transplant
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6d01bbc
Andy's fix
thomas-fossati Dec 6, 2023
afcdc90
Add naming consistency
yogeshbdeshpande Dec 6, 2023
1fdbe84
Add reference to the MEC triple
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df72b52
Update cddl/triples-map.cddl
henkbirkholz Dec 6, 2023
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Update cddl/mec-endorsement-triple-record.cddl
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c3fd39d
align naming
thomas-fossati Dec 6, 2023
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Update draft-ietf-rats-corim.md
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issue tracking
thomas-fossati Dec 6, 2023
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1 change: 1 addition & 0 deletions cddl/corim-frags.mk
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Expand Up @@ -14,6 +14,7 @@ COMID_FRAGS += coswid-triple-record.cddl
COMID_FRAGS += crypto-key-type-choice.cddl
COMID_FRAGS += domain-dependency-triple-record.cddl
COMID_FRAGS += domain-membership-triple-record.cddl
COMID_FRAGS += mec-endorsement-triple-record.cddl
COMID_FRAGS += domain-type-choice.cddl
COMID_FRAGS += endorsed-triple-record.cddl
COMID_FRAGS += entity-map.cddl
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4 changes: 4 additions & 0 deletions cddl/mec-endorsement-triple-record.cddl
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@@ -0,0 +1,4 @@
multi-env-conditional-endorsement-triple-record = [
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conds: [ + stateful-environment-record ]
endorsements: [ + endorsed-triple-record ]
]
2 changes: 2 additions & 0 deletions cddl/triples-map.cddl
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Expand Up @@ -17,5 +17,7 @@ triples-map = non-empty<{
[ + conditional-endorsement-series-triple-record ]
? &(conditional-endorsement-triples: 9) =>
[ + conditional-endorsement-triple-record ]
? &(mec-endorsement-triples: 10) =>
[ + multi-env-conditional-endorsement-triple-record ]
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* $$triples-map-extension
}>
28 changes: 27 additions & 1 deletion draft-ietf-rats-corim.md
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Expand Up @@ -99,7 +99,7 @@ informative:
seriesinfo: Version 1.0, Revision 0.19
date: July 2020
target: https://trustedcomputinggroup.org/wp-content/uploads/DICE-Layering-Architecture-r19_pub.pdf
IANA.concise-software-identifier: coswid-reg
IANA.coswid: coswid-reg
SPDM:
title: Security Protocol and Data Model (SPDM)
author:
Expand Down Expand Up @@ -1186,6 +1186,32 @@ Evidence.
{::include cddl/domain-membership-triple-record.cddl}
~~~



#### Multi-Environment Conditional (MEC) Endorsements Triple {#sec-comid-triple-mec-endorsements}
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The semantics of the Multi-Environment Conditional (MEC) Endorsements Triple is as follows:

> "IF accepted state matches the `cond` value, THEN `env` is associated with the endorsed value(s) `ends`."
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~~~ cddl
{::include cddl/mec-endorsement-triple-record.cddl}
~~~

A `multi-env-conditional-endorsement-triple-record` has the following parameters:

* `conds`: all target environments, along with a specific state, that need to match `state-triples` entries in the ACS for the endorsement(s) to apply
* `endorsements`: endorsements that are added to the ACS `state-triples` if all `conds` match.

The order in which MEC Endorsement triples are evaluated is important: different sorting may produce different end-results in the computed ACS.

Therefore, the set of applicable MEC Endorsement triple MUST be topologically sorted based on the criterion that a MEC Endorsement triple is evaluated before another if its Target Environment and Endorsement pair is found in any of the stateful environments of the second triple.
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I have a feeling that there might be some edge cases where a verifier needs the ability to use a more complex algorithm than topological sorting.
Would it be better to make this a SHOULD?

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there must be no ambiguity in the processing rules.
If there are cases where topo-sorting is not the unique criterion (or a completely different criterion is used) we need to describe the steps clearly.


Notes:

* In order to give the expected result, the condition must describe the expected context completely.
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This note makes me think about a lot of different questions:

  • Is there a case where other conditions might partly describe the expected context?
  • What problems occur if the CoRIM author chooses to only partly describe the context?
  • Why is this triple different from other triples, for example conditional-endorsement-triple-record?

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This note makes me think about a lot of different questions:

  • Is there a case where other conditions might partly describe the expected context?
  • What problems occur if the CoRIM author chooses to only partly describe the context?
  • Why is this triple different from other triples, for example conditional-endorsement-triple-record?
    Agree 100% on your last point, we need to make edits to optimise and only put forward one triple, instead of these two which are effectively singular and plural instances of doing the same thing!

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This note makes me think about a lot of different questions:

  • Is there a case where other conditions might partly describe the expected context?

hmm, what kind of implicit matching are you thinking of?

  • What problems occur if the CoRIM author chooses to only partly describe the context?

You'd get false positives.

  • Why is this triple different from other triples, for example, conditional-endorsement-triple-record?

This is a superset of conditional-endorsement-triple-record. As such, it makes the other redundant, at a small increase in the serialisation cost.

The "series" one is a bit of a different beast: it does some sort of short-circuited OR, so in terms of condition-matching rules it's substantially different.

* The scope of a single MEC triple encompasses an arbitrary amount of environments across all layers in an Attester.
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The implication of a scope that covers all grouping / appraisal contexts is the EMT expressions must have some aspect that is globally unique (at least within the expected scope). EMT scope should be described as part of the EMT construction and not as a footnote to a particular triple construction.

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The implication of a scope that covers all grouping / appraisal contexts is the EMT expressions must have some aspect that is globally unique (at least within the expected scope). EMT scope should be described as part of the EMT construction and not as a footnote to a particular triple construction.

See Issue #176

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Suggested change
* The scope of a single MEC triple encompasses an arbitrary amount of environments across all layers in an Attester.
* A single MEC triple can be used to make an endorsement conditional on multiple environments across layers or in different modules.


#### CoMID-CoSWID Linking Triple {#sec-comid-triple-coswid}

A CoSWID triple relates reference measurements contained in one or more CoSWIDs
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