Trusted Path Routing

Internet-Draft	trust-path	August 2023
Voit, et al.	Expires 29 February 2024	[Page]

Abstract

There are end-users who believe encryption technologies like IPSec alone are insufficient to protect the confidentiality of their highly sensitive traffic flows. These end-users want their flows to traverse devices which have been freshly appraised and verified for trustworthiness. This specification describes Trusted Path Routing. Trusted Path Routing protects sensitive flows as they transit a network by forwarding traffic to/from sensitive subnets across network devices recently appraised as trustworthy.¶

4. End-to-end Solution

4.1. Network Topology Assembly

To be included in a Trusted Topology, Stamped Passports are shared between Attested Devices (such as routers) as part of link layer authentication. Upon receiving and appraising the Stamped Passport during the link layer authentication phase, the Relying Party Attested Device decides if this link should be added as an active adjacency for a particular Trusted Topology. In Figure 1 below, this might be done by applying an Appraisal Policy for Attestation Results. The policy within each device might specify the evalutation of a 'hardware' claim as defined in [attestation-results], Section 2.3.4. With the appraisal, an Attesting Device be most recently appraised with the 'hardware' Trustworthiness Claim in the 'affirming' range. If Attested Device has been appraised outside that range, it would not become part of the Trustworthy Topology.¶

When enough links have been successfully added, the Trusted Topology will support edge-to-edge forwarding as routing protocols flood the adjacency information across the network domain.¶

               .------------.                .----------.
               | Attested   |                | Edge     |
 .----------.  | Device 'x' |                | Attested |
 | Attested |  |            |                | Device   |
 | Device   |  |            |                |          |
 |          |  |        trust>---------------<no_trust  |
 |  no_trust>--<trust       |  .----------.  |          |---Sensitive
 |          |  '------------'  |     trust>==<trust     |   Subnet
 |     trust>==================<trust     |  |          |
 '----------'                  |          |  '----------'
                               | Attested |
                               | Device   |
                               '----------'

Figure 1: Trusted Path Topology Assembly

As the process described above repeats over time across the set of links within a network domain, Trusted Topologies can be extended and maintained. Traffic to and from Sensitive Subnets is then identified at the edges of the network domain and passed into this Trusted Topology. Traffic exchanged with Sensitive Subnets can then be forwarded across that Trusted Topology from all edges of the network domain. After the initial Trusted Topology establishment, new and existing devices will continue to provide incremental Stamped Passports. As each link is added/removed from the Trusted Topology, the topology will adjust itself accordingly.¶

Ultimately from an operator and users point of view, the delivered network will be more secure and therefore the service provided more valuable. As network operators attach great importance to the innate security of links, also delivering security for transited network and networking devices will also prove valuable.¶

4.2. Attestation Information Flows

Critical to the establishment and maintenance of a Trusted Topology is the Stamped Passport. A Stamped Passport is comprised of Evidence from both an Attester and a Verifier. A Stamped Passport is a valid type of AR-augmented evidence as described in [attestation-results].¶

Stamped Passports are exchanged between adjacent network devices over a link layer protocols like 802.1x or MACSEC. As both sides of a link may need might need to appraise the other, independent Stamped Passports will often be transmitted from either side of the link. Additionally, as link layer protocols will continuously re-authenticate the link, this allows for fresh Stamped Passports to be constantly appraised by either side of the connection.¶

Each Stamped Passport will include the most recent Verifier provided Attestation Results, as well as the most recent TPM Quote for that Attester. Upon receiving this information as part of link layer authentication, the Relying Party Router appraises the results and decides if this link should be added to a Trusted Topology.¶

Figure 2 describes this flow of information using the time definitions described in [RATS-Arch], and the information flows defined in Section 7 of [RATS-Interactions]. This figure is also a valid embodiment of the "Interaction Model" described within [attestation-results]. (Note that the Relying Party must also be an Attested Device in order to attract Sensitive Subnet traffic which may flow from the Attester.)¶

  .------------------.
  | Attester         |
  |                  |
  | (Attested Device |
  |   / Router)      |                           .------------------.
  |  .-------------. |                           | Relying Party    |
  |  | TPM based   | |                           |   / Verifier B   |
  |  | Attesting   | |           .----------.    |                  |
  |  | Environment | |           | Verifier |    | (Attested Device |
  |  '-------------' |           |     A    |    |   / Router)      |
  '------------------'           '----------'    '------------------'
        time(VG)                       |                 |
          |<------nonce--------------time(NS)            |
          |                            |                 |
 time(EG)(1)------Evidence------------>|                 |
          |                          time(RG)            |
          |<------Attestation Results-(2)                |
          ~                            ~                 ~
        time(VG')?                     |                 |
          ~                            ~                 ~
          |<------nonce---------------------------------(3)time(NS')
          |                            |                 |
time(EG')(4)------Stamped Passport---------------------->|
          |                            |   time(RG',RA')(5)
                                                        (6)
                                                         ~
                                                      time(RX')

Figure 2: Trusted Path Timing

To summarize Figure 2 above, Evidence about a specific Attester is generated. Some subset of this evidence will be in the form of PCR quotes which are signed by a TPM that exists as the Attester's Attesting Environment. This Evidence will be delibered to and appraised by Verifier A. Verifier A will then appraise the Attester and give it a Trustworthiness Vector. This Trustworthiness Vector is then signed by Verifier A and be returned as Attestation Results to the Attester. Later, when a request comes in from a Relying Party, the Attester assembles and returns a Stamped Passport. The Stamped Passport contains all the information necessary for Verifier B to appraise the most recent Trustworthiness Vector of the Attester. Based on the Verifier B appraisal, the link will be included or not in a Trusted Topology maintained on the Relying Party.¶

More details on the mechanisms used in the construction, verification, and transmitting of the Stamped Passport are listed below. These numbers match to both the numbered steps of Figure 2 and numbered steps described in Section 3 of [attestation-results]:¶

4.2.1. Step 1

Evidence about and Attester is generated. A portion of this Evidence will include a PCR quote signed by a TPM private LDevID key that exists within the Attester's TPM based Attesting Environment. The Attester sends a signed TPM Quote which includes PCR measurements to Verifier A at time(EG).¶

There are two alternatives for Verifier A to acquire this signed Evidence:¶

Subscription to the <attestation> stream defined in [stream-subscription]. Note: this method is recommended as it will minimize the interval between when a PCR change is made in a TPM, and when the PCR change appraisal is incorporated within a subsequent Stamped Passport.¶
Periodic polling of RPC <tpm20-challenge-response-attestation> or the RPC <tpm12-challenge-response-attestation> which are defined in [RATS-YANG].¶

4.2.2. Step 2

Verifier A appraises the Evidence from Step 1. A portion of this appraisal process will follow the appraisal process flow described below. This appraisal process MUST be able to set at least the following set of Trustworthiness Claims from [attestation-results]: 'hardware', 'instance-identity', and 'executables'. The establishment of a Trustworthiness Vector uses the following Figure 3 logic on the Verifier:¶

Start: TPM Quote Received, log received, or appraisal timer expired
       for the the Attesting network device.

Appraisal 0: set Trustworthiness Vector = Null

Appraisal 1: Is there sufficient fresh signed evidence to appraise?
  (yes) - No Action
  (no) -  Goto End

Appraisal 2: Appraise Hardware Integrity PCRs
   if (hardware NOT "0") - push onto vector
   if (hardware NOT affirming or warning), go to End

Appraisal 3: Appraise Attesting Environment identity
   if (instance-identity <> "0") - push onto vector

Appraisal 4: Appraise executable loaded and filesystem integrity
   if (executables NOT "0") - push onto vector
   if (executables NOT affirming or warning), go to End

Appraisal 5: Appraise all remaining Trustworthiness Claims
        Independently and set as appropriate.

End

Figure 3: Verifier A Appraisal Flow

After the appraisal and generation of the Trustworthiness Vector, the following are assembled as the set of Attestation Results from this particular appraisal cycle:¶

(2.1) the Public Attestation Key which was used to validate the TPM Quote of Step 1. This is encoded by <public-key>, <public-key-format>, and <public-key-algorithm-type>.¶

(2.2) the appraised Trustworthiness Vector of the Attester as calculated in Figure 3 ¶

(2.3) the PCR state information from the TPM Quote of (1) plus the time information associated with the TPM Quote of (1). Specifically if the Attester has a TPM2, then the values of the TPM PCRs are included (i.e., <TPM2B_DIGEST>, <tpm20-hash-algo>, and <pcr-index>), as are the timing counters from the TPM (i.e., <clock>, <reset-counter>, <restart-counter>, and <safe>). Likewise if the Attester has a TPM1.2, the TPM PCR values of the <pcr-index> and <pcr-value> are included. Timing information comes from the Verifier itself via the <timestamp> object.¶

(2.4) a Verifier A signature across (2.1) though (2.3). This signature is encoded by <verifier-signature>, <verifier-key-algorithm-type>, and <verifier-signature-key-name>.¶

Immediately subsequent to each Verifier appraisal cycle of an Attester, these Attestation Results MUST be pushed to the Attesting Router. This is done via a daatstore write to the following YANG model on the Attester. A YANG tree showing the relevant YANG objects is below. The YANG model describing each of these objects is described later in the document. Note however that although the YANG model shows the specific objects which are needed, the specific set of objects needs to be encoded in CDDL. This makes the payload going over TLS more efficient. Look for this encoding in a new version of the draft which is pending.¶

module: ietf-trustworthiness-claims
  +--rw attestation-results!
     +--rw (tpm-specification-version)?
        +--:(tpm20-attestation-results-cddl) {taa:tpm20}?
        |  +--rw tpm20-attestation-results-cddl
        |     +--rw trustworthiness-vector
        |     |  +--rw hardware?            hardware
        |     |  +--rw instance-identity?   instance-identity
        |     |  +--rw executables?         executables
        |     |  +--rw configuration?       configuration
        |     +--rw tpm20-pcr-selection* [tpm20-hash-algo]
        |     |  +--rw tpm20-hash-algo    identityref
        |     |  +--rw pcr-index*         tpm:pcr
        |     +--rw TPM2B_DIGEST                         binary
        |     +--rw clock                                uint64
        |     +--rw reset-counter                        uint32
        |     +--rw restart-counter                      uint32
        |     +--rw safe                                 boolean
        |     +--rw attester-certificate-name
        |     |       tpm:certificate-name-ref
        |     +--rw appraisal-timestamp
        |     |       yang:date-and-time
        |     +--rw verifier-algorithm-type              identityref
        |     +--rw verifier-signature                   binary
        |     +--rw verifier-certificate-keystore-ref
        |             tpm:certificate-name-ref
        +--:(tpm12-attestation-results-cddl) {taa:tpm12}?
           +--rw tpm12-attestation-results-cddl
              +--rw trustworthiness-vector
              |  +--rw hardware?            hardware
              |  +--rw instance-identity?   instance-identity
              |  +--rw executables?         executables
              |  +--rw configuration?       configuration
              +--rw pcr-index*                           pcr
              +--rw tpm12-pcr-value*                     binary
              +--rw tpm12-hash-algo                      identityref
              +--rw TPM12-quote-timestamp
              |       yang:date-and-time
              +--rw attester-certificate-name
              |       tpm:certificate-name-ref
              +--rw appraisal-timestamp
              |       yang:date-and-time
              +--rw verifier-algorithm-type              identityref
              +--rw verifier-signature                   binary
              +--rw verifier-certificate-keystore-ref
                      tpm:certificate-name-ref

Figure 4: Attestation Results Tree

4.2.3. Step 3

At time(NS') some form of time-based freshness (such as a nonce or Epoch Handle [RATS-Interactions]) will be generated in a way which makes it available to the Relying Party. Soon after time(NS'), a Relying Party will make a Link Layer authentication request to an Attester via a either [MACSEC] or [IEEE-802.1X]. This connection request MUST expect the return of [RFC3748] credentials from the Attester.¶

4.2.4. Step 4

Upon receipt of the Link Layer request from Step 3, a Stamped Passport is generated and sent to the Relying Party. The Stamped Passport MUST include the following:¶

(4.1) The Attestation Results from Step 2¶

(4.2) New signed, verifiably fresh PCR measurements based on a TPM quote at time(EG') which incorporates the freshness information known by the Relying Party from Step 3. If it is a nonce, the freshness information will have been delivered as part of the link layer connection request in Steps 3.¶

Stamped Passports contain following objects, defined in this document via YANG. A subsequent draft will convert the objects below into CDDL format so that the objects can efficiently be passed over EAP.¶

If an Attester includes a TPM2, these YANG objects are:¶

    +---n tpm20-stamped-passport
       +--ro attestation-results
       |  +--ro trustworthiness-vector
       |  |  +--ro hardware?            hardware
       |  |  +--ro instance-identity?   instance-identity
       |  |  +--ro executables?         executables
       |  |  +--ro configuration?       configuration
       |  +--ro tpm20-pcr-selection* [tpm20-hash-algo]
       |  |  +--ro tpm20-hash-algo    identityref
       |  |  +--ro pcr-index*         tpm:pcr
       |  +--ro TPM2B_DIGEST                         binary
       |  +--ro clock                                uint64
       |  +--ro reset-counter                        uint32
       |  +--ro restart-counter                      uint32
       |  +--ro safe                                 boolean
       |  +--ro attester-certificate-name
       |  |       tpm:certificate-name-ref
       |  +--ro appraisal-timestamp
       |  |       yang:date-and-time
       |  +--ro verifier-algorithm-type              identityref
       |  +--ro verifier-signature                   binary
       |  +--ro verifier-certificate-keystore-ref
       |          tpm:certificate-name-ref
       +--ro tpm20-quote
          +--ro TPMS_QUOTE_INFO    binary
          +--ro quote-signature    binary

Figure 5: YANG Tree for a TPM2 Stamped Passport

Note that where a TPM2.0 is used, the PCR numbers and hash algorithms quoted in Step 1 MUST match the PCR numbers and hash algorithms quoted in this step.¶

And if the Attester is a TPM1.2, the YANG object are:¶

    +---n tpm12-stamped-passport
       +--ro attestation-results
       |  +--ro trustworthiness-vector
       |  |  +--ro hardware?            hardware
       |  |  +--ro instance-identity?   instance-identity
       |  |  +--ro executables?         executables
       |  |  +--ro configuration?       configuration
       |  +--ro pcr-index*                           pcr
       |  +--ro tpm12-pcr-value*                     binary
       |  +--ro tpm12-hash-algo                      identityref
       |  +--ro TPM12-quote-timestamp
       |  |       yang:date-and-time
       |  +--ro attester-certificate-name
       |  |       tpm:certificate-name-ref
       |  +--ro appraisal-timestamp
       |  |       yang:date-and-time
       |  +--ro verifier-algorithm-type              identityref
       |  +--ro verifier-signature                   binary
       |  +--ro verifier-certificate-keystore-ref
       |          tpm:certificate-name-ref
       +--ro tpm12-quote
          +--ro TPM_QUOTE2?   binary

Figure 6: YANG Tree for a TPM1.2 Stamped Passport

With either of these passport formats, if the TPM quote is verifiably fresh, then the state of the Attester can be appraised by a network peer.¶

Note that with [MACSEC] or [IEEE-802.1X], Step 3 plus Step 4 will repeat periodically independently of any subsequent iteration Steps 1 and Step 2. This allows for periodic reauthentication of the link layer in a way not bound to the updating of Verifier A's Attestation Results.¶

4.2.5. Step 5

Upon receipt of the Stamped Passport generated in Step 4, the Relying Party appraises this Stamped Passport as per its Appraisal Policy for Attestation Results. The result of this application will determine how the Stamped Passport will impact adjacencies within a Trusted Topology. The decision process is as follows:¶

(5.1) Verify that (4.2) includes the freshness context from Step 3.¶

(5.2) Use a local certificate to validate the signature (4.1).¶

(5.3) Verify that the hash from (4.2) matches (4.1)¶

(5.4) Use the identity of (2.1) to validate the signature of (4.2).¶

(5.5) Failure of any steps (5.1) through (5.4) means the link does not meet minimum validation criteria, therefore appraise the link as having a null Verifier B Trustworthiness Vector. Jump to Step 6.¶

(5.6) Compare the time(EG) TPM state to the time(EG') TPM state¶

If TPM2.0¶
1. If the <TPM2B_DIGEST>, <reset-counter>, <restart-counter> and <safe> are equal between the Attestation Results and the TPM Quote at time(EG') then Relying Party can accept (2.1) as the link's Trustworthiness Vector. Jump to Step 6.¶
2. If the <reset-counter>, <restart-counter> and <safe> are equal between the Attestation Results and the TPM Quote at time(EG'), and the <clock> object from time(EG') has not incremented by an unacceptable number of seconds since the Attestation Result, then Relying Party can accept (2.1) as the link's Trustworthiness Vector. Jump to Step 6.)¶
3. Assign the link a null Trustworthiness Vector.¶
If TPM1.2¶
1. If the <pcr-index>'s and <tpm12-pcr-value>'s are equal between the Attestation Results and the TPM Quote at time(EG'), then Relying Party can accept (2.1) as the link's Trustworthiness Vector. Jump to step (6).¶
2. If the time hasn't incremented an unacceptable number of seconds from the Attestation Results <timestamp> and the system clock of the Relying Party, then Relying Party can accept (2.1) as the link's Trustworthiness Vector. Jump to step 6.)¶
3. Assign the link a null Trustworthiness Vector.¶

(5.7) Assemble the Verifier B Trustworthiness Vector¶

Copy Verifier A Trustworthiness Vector to Verifier B Trustworthiness Vector¶
Prune any Trustworthiness Claims the Relying Party doesn't accept from this Verifier.¶

4.2.6. Step 6

After the Trustworthiness Vector has been validated or reset, based on the link's Trustworthiness Vector, the Relying Party adjusts the link affinity of the corresponding ISIS [I-D.ietf-lsr-flex-algo] topology. ISIS will then replicate the link state across the IGP domain. Traffic will then avoid links which do not have a qualifying Trustworthiness Vector.¶

5. YANG Module

This YANG module imports modules from [RATS-YANG], [crypto-types] and [RFC6021].¶

<CODE BEGINS> ietf-trustworthiness-claims@2021-11-03.yang
module ietf-trustworthiness-claims {
  yang-version 1.1;
  namespace
   "urn:ietf:params:xml:ns:yang:ietf-trustworthiness-claims";
  prefix tc;

  import ietf-yang-types {
    prefix yang;
  }
  import ietf-tcg-algs {
    prefix taa;
    reference
      "draft-ietf-rats-yang-tpm-charra";
  }
  import ietf-tpm-remote-attestation {
    prefix tpm;
    reference
      "draft-ietf-rats-yang-tpm-charra";
  }

  organization "IETF";
  contact
    "WG Web:   <http://tools.ietf.org/wg/rats/>
     WG List:  <mailto:rats@ietf.org>

     Editor:   Eric Voit
               <mailto:evoit@cisco.com>";

  description
    "This module contains conceptual YANG specifications for
    subscribing to attestation streams being generated from TPM chips.

    Copyright (c) 2020 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, is permitted pursuant to, and subject to the license
    terms contained in, the Simplified BSD License set forth in
    Section 4.c of the IETF Trust's Legal Provisions Relating to IETF
    Documents (https://trustee.ietf.org/license-info).

    This version of this YANG module is part of RFC XXXX; see the RFC
    itself for full legal notices.";

  revision 2021-11-03 {
    description
      "Initial version.";
    reference
      "draft-voit-rats-trustworthy-path-routing";
  }


  /*
   * TYPEDEF
   */

  typedef trustworthiness-claim {
    type int8;
    description
      "A Verifier asserted value designed to enable a common
      understanding of a Verifier trustworthiness appraisal.  The
      value assignments for this 8 bit signed integer will follow
      these guidelines:

      Affirming: The Verifier affirms the Attester support for this
      aspect of trustworthiness
        - Values 2 to 31: A standards enumerated reason for affirming.
        - Values -2 to -32: A non-standard reason for affirming.

      Warning: The Verifier warns about this aspect of trustworthiness.
        - Values 32 to 63: A standards enumerated reason for the
          warning.
        - Values -33 to -64: A non-standard reason for the warning.

      Contraindicated: The Verifier asserts the Attester is explicitly
      untrustworthy in regard to this aspect.
        - Values 64 to 127: A standards enumerated reason for the
          contraindication.
        - Values -65 to -128: A non-standard reason for the
          contraindication.

      None: The Verifier makes no assertions about this Trustworthiness
      Claim.  The following values are reserved with the following
      meanings across all instances of trustworthiness-claim.
        - Value 0: Note: this should always be always treated
          equivalently by the Relying Party as no claim being made.
          I.e., the RP's Appraisal Policy for Attestation Results
          SHOULD NOT make any distinction between a Trustworthiness
          Claim with enumeration '0', and no Trustworthiness Claim
          being provided.
        - Value 1: The Evidence received contains unexpected elements
          which the Verifier is unable to parse.  An example might be
          that the wrong type of Evidence has been delivered.
        - Value -1: An unexpected error occurred during the Verifier's
          appraisal processing. Note: while no claim is being made, the
          Relying Party MAY make a distinction between a
          Trustworthiness Claim with enumeration '-1', and no
          Trustworthiness Claim being provided.";
  }

  typedef hardware {
    type trustworthiness-claim;
    description
      "A Verifier has appraised any Attester hardware and firmware
      which are able to expose fingerprints of their identity and
      running code.

      The following are specific reserved values of hardware and
      the meanings of these reserved values:

      0: No assertion

      1: The Verifer cannot parse unexpected Evidence

      -1:Verifier malfunction

      2: An Attester has passed its hardware and/or firmware
         verifications needed to demonstrate that these are
         genuine/supported.

      32:An Attester contains only genuine/supported hardware and/or
         firmware, but there are known security vulnerabilities.

      96:Attester hardware and/or firmware is recognized, but its
         trustworthiness is contraindicated.

      97:A Verifier does not recognize an Attester's hardware or
         firmware, but it should be recognized.";
  }

  typedef instance-identity {
    type trustworthiness-claim;
    description
      "A Verifier has appraised an Attesting Environment's unique
      identity based upon private key signed Evidence which can be
      correlated to a unique instantiated instance of the Attester.
      (Note: this Trustworthiness Claim should only be generated if
      the Verifier actually expects to recognize the unique identity
      of the Attester.)

      The following are specific reserved values of instance-identity
      and the meanings of these reserved values:

      0: No assertion

      1: The Verifer cannot parse unexpected Evidence

      -1:Verifier malfunction

      2: The Attesting Environment is recognized, and the associated
         instance of the Attester is not known to be compromised.

      96:The Attesting Environment is recognized, and but its unique
         private key indicates a device which is not trustworthy.

      97:The Attesting Environment is not recognized; however the
         Verifier believes it should be.";
  }

  typedef executables {
    type trustworthiness-claim;
    description
      "A Verifier has appraised and evaluated relevant runtime files,
      scripts, and/or other objects which have been loaded into the
      Target environment's memory.

      The following are specific reserved values of executables and
      the meanings of these reserved values:

      0: No assertion

      1: The Verifer cannot parse unexpected Evidence

      -1:Verifier malfunction

      2: Only a recognized genuine set of approved executables,
         scripts, files, and/or objects have been loaded during
         and after the boot process.

      3: Only a recognized genuine set of approved executables have
         been loaded during the boot process.

      32:Only a recognized genuine set of executables, scripts, files,
         and/or objects have been loaded.  However the Verifier cannot
         vouch for a subset of these due to known bugs or other known
         vulnerabilities.

      33:Runtime memory includes executables, scripts, files, and/or
         objects which are not recognized.

      96:Runtime memory includes executables, scripts, files, and/or
         object which are contraindicated.

      99:Cryptographic validation of the Evidence has failed.";
  }

  typedef configuration {
    type trustworthiness-claim;
    description
      "A Verifier has appraised an Attester's configuration, and is
      able to make conclusions regarding the exposure of known
      vulnerabilities.

      The following are specific reserved values of configuration and
      the meanings of these reserved values:

      0: No assertion

      1: The Verifer cannot parse unexpected Evidence

      -1:Verifier malfunction

      2: The configuration is a known and approved config

      3: The configuration includes or exposes no known vulnerabilities

      32:The configuration includes or exposes known vulnerabilities

      64:The configuration is unsupportable as it exposes unacceptable
         security vulnerabilities.";
  }


  /*
   * GROUPINGS
   */

  grouping trustworthiness-vector {
    description
      "Allows the inclusion of a Trustworthiness Vector into
      other constructs.";
    container trustworthiness-vector {
      description
        "One or more Trustworthiness Claims assigned which expose the
        Verifiers evaluation of the Evidence associated with the
        AIK which signed as associated TPM Quote.";
      leaf hardware {
        type hardware;
        description
          "An 8 bit signed integter encoded per the typedef.";
      }
      leaf instance-identity {
        type instance-identity;
        description
          "An 8 bit signed integter encoded per the typedef.";
      }
      leaf executables {
        type executables;
        description
          "An 8 bit signed integter encoded per the typedef.";
      }
      leaf configuration {
        type configuration;
        description
          "An 8 bit signed integter encoded per the typedef.";
      }
    }
  }

  grouping verifier-evidence {
    description
      "Evidence generated by the Verifier.";
    leaf appraisal-timestamp {
      type yang:date-and-time;
      mandatory true;
      description
        "The timestamp of the Verifier's appraisal.  This can be used
        by a Relying Party to determine the freshness of the
        attestation results.";
    }
    leaf verifier-algorithm-type {
      type identityref {
        base taa:asymmetric;
      }
      mandatory true;
      description
        "Platform asymmetric algorithm used in the Verifier signature
        process.";
    }
    leaf verifier-signature {
      type binary;
      mandatory true;
      description
        "Signature of the Verifier across all the current objects in
        the attestation-results container except for 'verifier-
        signature' and 'verifier-certificate-keystore-ref'.
        This assumes CDDL encoding of the objects in the current
        order of this YANG model.";
    }
    leaf verifier-certificate-keystore-ref {
      type tpm:certificate-name-ref;
      mandatory true;
      description
        "A reference to a specific certificate to an asymmetric key
        in the Keystore for the Verifier which can be used to validate
        the 'verifier-signature'. Note that the
        'name' reference must be globally unique so that it can be
        read by the Relying Party in a way which identifies a
        specific Verifier.";
    }
  }

  grouping tpm20-cddl-attestation-results {
    description
      "Elements combined into a CDDL representation for TPM2.0.";
    uses trustworthiness-vector;
    list tpm20-pcr-selection {
      key "tpm20-hash-algo";
      description
        "Specifies the list of PCRs and Hash Algorithms used by the
        Verifier.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.9.7";
      uses tpm:tpm20-hash-algo;
      leaf-list pcr-index {
        type tpm:pcr;
        description
          "The numbers of the PCRs associated with the TPM2B_DIGEST.";
      }
    }
    leaf TPM2B_DIGEST {
      mandatory true;
      type binary;
      description
        "A hash of the latest PCR values (and the hash algorithm used)
        which have been returned from a Verifier for the selected PCRs
        identified within TPML_PCR_SELECTION.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
        TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.12.1";
    }
    leaf clock {
      mandatory true;
      type uint64;
      description
        "Clock is a monotonically increasing counter that advances
         whenever power is applied to a TPM2. The value of Clock is
         incremented each millisecond.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.11.2";
    }
    leaf reset-counter {
      mandatory true;
      type uint32;
      description
        "This counter increments on each TPM Reset.  The most common
        TPM Reset would be due to a hardware power cycle.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.11.3";
    }
    leaf restart-counter {
      mandatory true;
      type uint32;
      description
        "This counter shall increment by one for each TPM Restart or
        TPM Resume. The restartCount shall be reset to zero on a TPM
        Reset.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.11.4";
    }
    leaf safe {
      mandatory true;
      type boolean;
      description
        "This parameter is set to YES when the value reported in Clock
        is guaranteed to be unique for the current Owner. It is set to
        NO when the value of Clock may have been reported in a previous
        attestation or access.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
        TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.11.5";
    }
    leaf attester-certificate-name {
      mandatory true;
      description
        "The Attester is associated with these results.";
      type tpm:certificate-name-ref;
    }
    uses verifier-evidence;
  }

  grouping tpm12-cddl-attestation-results {
    description
      "Elements combined into a CDDL representation for TPM1.2.";
    uses trustworthiness-vector;
    uses tpm:tpm12-pcr-selection;
    leaf-list tpm12-pcr-value {
      type binary;
      description
        "The list of TPM_PCRVALUEs from each PCR selected in sequence
        of tpm12-pcr-selection.";
      reference
        "https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf
         Section 10.9.7";
    }
    uses tpm:tpm12-hash-algo {
      refine "tpm12-hash-algo" {
        mandatory true;
      }
    }
    leaf TPM12-quote-timestamp {
      type yang:date-and-time;
      mandatory true;
      description
        "The timestamp for when the indicator of freshness (such as a
        nonce) was generated.  This is the indicator of freshness
        which was used in the generation of the TPM1.2 quote.  This
        timestamp can be used by a Relying Party to determine the
        freshness of the attestation results.";
    }
    leaf attester-certificate-name {
      mandatory true;
      description
        "The Attester is associated with these results.";
      type tpm:certificate-name-ref;
    }
    uses verifier-evidence;
  }

  /*
   * NOTIFICATIONS
   */

  notification tpm20-stamped-passport {
    description
      "The augmentation of the most recent Attestation Results
      delivered from a Verifier with a TPM2.0 Quote.";
    container attestation-results {
      description
        "The latest Verifier delivered Attestation Results.";
      uses tpm20-cddl-attestation-results;
    }
    container tpm20-quote {
      description
        "The TPM2.0 quote delivered in response to a connectivity
        request.";
      leaf TPMS_QUOTE_INFO {
        type binary;
        mandatory true;
        description
          "A hash of the latest PCR values (and the hash algorithm
           used) which have been returned from a Verifier for the
           selected PCRs and Hash Algorithms.";
        reference
          "https://www.trustedcomputinggroup.org/wp-content/uploads/
           TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.12.1";
      }
      leaf quote-signature {
        type binary;
        mandatory true;
        description
          "Quote signature returned by TPM Quote.  The signature was
           generated using the key associated with the
           certificate 'name'.";
        reference
          "https://www.trustedcomputinggroup.org/wp-content/uploads/
           TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 11.2.1";
      }
    }
  }

  notification tpm12-stamped-passport {
    description
      "The augmentation of the most recent Attestation Results
      delivered from a Verifier with a TPM1.2 Quote.";
    container attestation-results {
      description
        "The latest Verifier delivered Attestation Results.";
      uses tpm12-cddl-attestation-results;
    }
    container tpm12-quote {
      description
        "The TPM1.2 quote delivered in response to a connectivity
        request.";
      leaf TPM_QUOTE2 {
        type binary;
        description
          "Result of a TPM1.2 Quote2 operation. This includes PCRs,
           signatures, locality, the provided nonce and other data which
           can be further parsed to appraise the Attester.";
        reference
          "TPM1.2 commands rev116 July 2007, Section 16.5";
      }
    }
  }

  /*
   * DATA NODES
   */

  container attestation-results {
    presence
      "Indicates that Verifier has appraised the security posture of
      the Attester, and returned the results within this container.";
    description
      "Retains the most recent Attestation Results for this Attester.
      It must only be written by a Verfier which is to be trusted by a
      Relying Party.";

    choice tpm-specification-version {
      description
        "Identifies the cryptoprocessor API set which drove the
        Attestation Results.";
      case tpm20-attestation-results-cddl {
        if-feature "taa:tpm20";
        description
          "Attestation Results which are returned from the
           evaluation of Evidence which includes a TPM2 quote.";
        container tpm20-attestation-results-cddl {
          description
            "Attestation Results which are returned from the
             evaluation of Evidence which includes a TPM2 quote.";
          uses tpm20-cddl-attestation-results;
        }
      }
      case tpm12-attestation-results-cddl {
        if-feature "taa:tpm12";
        description
          "Attestation Results which are returned from the
           evaluation of Evidence which includes a TPM1.2 quote.";
        container tpm12-attestation-results-cddl {
          description
            "Attestation Results which are returned from the
             evaluation of Evidence which includes a TPM1.2 quote.";
          uses tpm12-cddl-attestation-results;
        }
      }
    }
  }
}
<CODE ENDS>

Trusted Path Routing

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction

2. Terminology

2.1. Terms

2.2. Requirements Notation

3. Implementation Prerequisites

4. End-to-end Solution

4.1. Network Topology Assembly

4.2. Attestation Information Flows

4.2.1. Step 1

4.2.2. Step 2

4.2.3. Step 3

4.2.4. Step 4

4.2.5. Step 5

4.2.6. Step 6

5. YANG Module

6. Security Considerations

7. References

7.1. Normative References

7.2. Informative References

Appendix A. Acknowledgements

Appendix B. Change Log

Appendix C. Open Questions

Authors' Addresses