Internet-Draft YANG-CHARRA for TPMs July 2024
Birkholz, et al. Expires 30 January 2025 [Page]
Workgroup:
RATS Working Group
Internet-Draft:
draft-ietf-rats-yang-tpm-charra-23
Published:
Intended Status:
Standards Track
Expires:
Authors:
H. Birkholz
Fraunhofer SIT
M. Eckel
Fraunhofer SIT
S. Bhandari
ThoughtSpot
E. Voit
Cisco
B. Sulzen
Cisco
L. Xia
Huawei
T. Laffey
HPE
G. Fedorkow
Juniper

A YANG Data Model for Challenge-Response-based Remote Attestation Procedures using TPMs

Abstract

This document defines YANG Remote Procedure Calls (RPCs) and a few configuration nodes required to retrieve attestation evidence about integrity measurements from a device, following the operational context defined in TPM-based Network Device Remote Integrity Verification. Complementary measurement logs are also provided by the YANG RPCs, originating from one or more roots of trust for measurement (RTMs). The module defined requires at least one TPM 1.2 or TPM 2.0 as well as a corresponding TPM Software Stack (TSS), or equivalent hardware implementations that include the protected capabilities as provided by TPMs as well as a corresponding software stack, included in the device components of the composite device the YANG server is running on.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on 30 January 2025.

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Table of Contents

1. Introduction

This document is based on the general terminology defined in the [RFC9334] and uses the operational context defined in [I-D.ietf-rats-tpm-based-network-device-attest] as well as the interaction model and information elements defined in [I-D.ietf-rats-reference-interaction-models]. The currently supported hardware security modules (HSMs) are the Trusted Platform Modules (TPMs) [TPM1.2] and [TPM2.0] as specified by the Trusted Computing Group (TCG). One TPM, or multiple TPMs in the case of a Composite Device, are required in order to use the YANG module defined in this document. Each TPM is used as a root of trust for storage (RTS) in order to store system security measurement Evidence. And each TPM is used as a root of trust for reporting (RTR) in order to retrieve attestation Evidence. This is done by using a YANG RPC to request a quote which exposes a rolling hash of the security measurements held internally within the TPM.

Specific terms imported from [RFC9334] and used in this document include: Attester, Composite Device, Evidence.

Specific terms imported from [TPM2.0-Key] and used in this document include: Endorsement Key (EK), Initial Attestation Key (IAK), Attestation Identity Key (AIK), Local Attestation Key (LAK).

1.1. Requirements notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. The YANG Module for Basic Remote Attestation Procedures

One or more TPMs MUST be embedded in a Composite Device that provides attestation Evidence via the YANG module defined in this document. The ietf-tpm-remote-attestation YANG module enables a composite device to take on the role of an Attester, in accordance with the Remote Attestation Procedures (RATS) architecture [RFC9334], and the corresponding challenge-response interaction model defined in the [I-D.ietf-rats-reference-interaction-models] document. A fresh nonce with an appropriate amount of entropy [NIST-915121] MUST be supplied by the YANG client in order to enable a proof-of-freshness with respect to the attestation Evidence provided by the Attester running the YANG datastore. Further, this nonce is used to prevent replay attacks. The method for communicating the relationship of each individual TPM to specific measured component within the Composite Device is out of the scope of this document.

2.1. YANG Modules

In this section the several YANG modules are defined.

2.1.1. 'ietf-tpm-remote-attestation'

This YANG module imports modules from [RFC6991] with prefix 'yang', [RFC8348] with prefix 'hw', [I-D.ietf-netconf-keystore] with prefix 'ks', and 'ietf-tcg-algs.yang' Section 2.1.2.3 with prefix 'taa'. Additionally, references are made to [RFC8032], [RFC8017], [RFC6933], [TPM1.2-Commands], [TPM2.0-Arch], [TPM2.0-Structures], [TPM2.0-Key], [TPM1.2-Structures], [bios-log], [BIOS-Log-Event-Type], as well as Appendix A and Appendix B.

2.1.1.1. Features

This module supports the following features:

  • 'mtpm': Indicates that multiple TPMs on the device can support remote attestation. For example, this feature could be used in cases where multiple line cards are present, each with its own TPM.
  • 'bios': Indicates that the device supports the retrieval of BIOS/UEFI event logs. [bios-log]
  • 'ima': Indicates that the device supports the retrieval of event logs from the Linux Integrity Measurement Architecture (IMA, see Appendix A).
  • 'netequip_boot': Indicates that the device supports the retrieval of netequip boot event logs. See Appendix A and Appendix B.
2.1.1.2. Identities

This module supports the following types of attestation event logs: 'bios', 'ima', and 'netequip_boot'.

2.1.1.3. Remote Procedure Calls (RPCs)

In the following, RPCs for both TPM 1.2 and TPM 2.0 attestation procedures are defined.

2.1.1.3.1. 'tpm12-challenge-response-attestation'

This RPC allows a Verifier to request signed TPM PCRs (TPM Quote operation) from a TPM 1.2 compliant cryptoprocessor. Where the feature 'mtpm' is active, and one or more 'certificate-name' is not provided, all TPM 1.2 compliant cryptoprocessors will respond. A YANG tree diagram of this RPC is as follows:

+---x tpm12-challenge-response-attestation {taa:tpm12}?
  +---w input
  |  +---w tpm12-attestation-challenge
  |     +---w pcr-index*          pcr
  |     +---w nonce-value         binary
  |     +---w certificate-name*   certificate-name-ref
  |             {tpm:mtpm}?
  +--ro output
     +--ro tpm12-attestation-response* []
        +--ro certificate-name    certificate-name-ref
        +--ro up-time?            uint32
        +--ro TPM_QUOTE2?         binary
2.1.1.3.2. 'tpm20-challenge-response-attestation'

This RPC allows a Verifier to request signed TPM PCRs (TPM Quote operation) from a TPM 2.0 compliant cryptoprocessor. Where the feature 'mtpm' is active, and one or more 'certificate-name' is not provided, all TPM 2.0 compliant cryptoprocessors will respond. A YANG tree diagram of this RPC is as follows:

+---x tpm20-challenge-response-attestation {taa:tpm20}?
   +---w input
   |  +---w tpm20-attestation-challenge
   |     +---w nonce-value            binary
   |     +---w tpm20-pcr-selection* []
   |     |  +---w tpm20-hash-algo?   identityref
   |     |  +---w pcr-index*         pcr
   |     +---w certificate-name*      certificate-name-ref
   |             {tpm:mtpm}?
   +--ro output
      +--ro tpm20-attestation-response* []
         +--ro certificate-name       certificate-name-ref
         +--ro TPMS_QUOTE_INFO        binary
         +--ro quote-signature?       binary
         +--ro up-time?               uint32
         +--ro unsigned-pcr-values* []
            +--ro tpm20-hash-algo?   identityref
            +--ro pcr-values* [pcr-index]
               +--ro pcr-index    pcr
               +--ro pcr-value?   binary

An example of an RPC challenge requesting PCRs 0-7 from a SHA-256 bank could look like the following:

<rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <tpm20-attestation-challenge
      xmlns="urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation">
    <certificate-name>
      (identifier of a TPM signature key with which the Attester is
      supposed to sign the attestation data)
    </certificate-name>
    <nonce>
      0xe041307208d9f78f5b1bbecd19e2d152ad49de2fc5a7d8dbf769f6b8ffdeab9
    </nonce>
    <tpm20-pcr-selection>
      <tpm20-hash-algo
          xmlns="urn:ietf:params:xml:ns:yang:ietf-tcg-algs">
        TPM_ALG_SHA256
      </tpm20-hash-algo>
      <pcr-index>0</pcr-index>
      <pcr-index>1</pcr-index>
      <pcr-index>2</pcr-index>
      <pcr-index>3</pcr-index>
      <pcr-index>4</pcr-index>
      <pcr-index>5</pcr-index>
      <pcr-index>6</pcr-index>
      <pcr-index>7</pcr-index>
    </tpm20-pcr-selection>
  </tpm20-attestation-challenge>
</rpc>

A successful response could be formatted as follows:

<rpc-reply message-id="101"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <tpm20-attestation-response
      xmlns="urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation">
    <certificate-name
        xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore">
      (instance of Certificate name in the Keystore)
    </certificate-name>
    <attestation-data>
      (raw attestation data, i.e., the TPM quote; this includes,
      among other information, a composite digest of requested PCRs,
      the nonce, and TPM 2.0 clock information.)
    </attestation-data>
    <quote-signature>
      (signature over attestation-data using the TPM key
      identified by sig-key-id)
    </quote-signature>
  </tpm20-attestation-response>
</rpc-reply>
2.1.1.4. 'log-retrieval'

This RPC allows a Verifier to acquire the Evidence which was extended into specific TPM PCRs. A YANG tree diagram of this RPC is as follows:

    +---x log-retrieval
       +---w input
       |  +---w log-type        identityref
       |  +---w log-selector* []
       |     +---w name*                      string
       |     +---w (index-type)?
       |     |  +--:(last-entry)
       |     |  |  +---w last-entry-value?    binary
       |     |  +--:(index)
       |     |  |  +---w last-index-number?   uint64
       |     |  +--:(timestamp)
       |     |     +---w timestamp?           yang:date-and-time
       |     +---w log-entry-quantity?        uint16
       +--ro output
          +--ro system-event-logs
             +--ro node-data* []
                +--ro name?         string
                +--ro up-time?      uint32
                +--ro log-result
                   +--ro (attested_event_log_type)
                      +--:(bios) {bios}?
                      |  +--ro bios-event-logs
                      |     +--ro bios-event-entry* [event-number]
                      |        +--ro event-number    uint32
                      |        +--ro event-type?     uint32
                      |        +--ro pcr-index?      pcr
                      |        +--ro digest-list* []
                      |        |  +--ro hash-algo?   identityref
                      |        |  +--ro digest*      binary
                      |        +--ro event-size?     uint32
                      |        +--ro event-data*     binary
                      +--:(ima) {ima}?
                      |  +--ro ima-event-logs
                      |     +--ro ima-event-entry* [event-number]
                      |        +--ro event-number               uint64
                      |        +--ro ima-template?              string
                      |        +--ro filename-hint?             string
                      |        +--ro filedata-hash?             binary
                      |        +--ro filedata-hash-algorithm?   string
                      |        +--ro template-hash-algorithm?   string
                      |        +--ro template-hash?             binary
                      |        +--ro pcr-index?                 pcr
                      |        +--ro signature?                 binary
                      +--:(netequip_boot) {netequip_boot}?
                         +--ro boot-event-logs
                            +--ro boot-event-entry* [event-number]
                               +--ro event-number               uint64
                               +--ro ima-template?              string
                               +--ro filename-hint?             string
                               +--ro filedata-hash?             binary
                               +--ro filedata-hash-algorithm?   string
                               +--ro template-hash-algorithm?   string
                               +--ro template-hash?             binary
                               +--ro pcr-index?                 pcr
                               +--ro signature?                 binary
2.1.1.5. Data Nodes

This section provides a high level description of the data nodes containing the configuration and operational objects with the YANG model. For more details, please see the YANG model itself in Figure 1.

Container 'rats-support-structures':

This houses the set of information relating to remote attestation for a device. This includes specific device TPM(s), the compute nodes (such as line cards) on which the TPM(s) reside, and the algorithms supported across the platform.

Container 'tpms':

Provides configuration and operational details for each supported TPM, including the tpm-firmware-version, PCRs which may be quoted, certificates which are associated with that TPM, and the current operational status. Of note are the certificates which are associated with that TPM. As a certificate is associated with a particular TPM attestation key, knowledge of the certificate allows a specific TPM to be identified.

+--rw tpms
   +--rw tpm* [name]
      +--rw name                string
      +--ro hardware-based      boolean
      +--ro physical-index?     int32 {hw:entity-mib}?
      +--ro path?               string
      +--ro compute-node        compute-node-ref {tpm:mtpm}?
      +--ro manufacturer?       string
      +--rw firmware-version    identityref
      +--rw tpm12-hash-algo?    identityref {taa:tpm12}?
      +--rw tpm12-pcrs*         pcr
      +--rw tpm20-pcr-bank* [tpm20-hash-algo]  {taa:tpm20}?
      |  +--rw tpm20-hash-algo    identityref
      |  +--rw pcr-index*         tpm:pcr
      +--ro status              enumeration
      +--rw certificates
         +--rw certificate* [name]
            +--rw name            string
            +--rw keystore-ref?   leafref {ks:asymmetric-keys}?
            +--rw type?           enumeration

container 'attester-supported-algos' - Identifies which TCG hash algorithms are available for use on the Attesting platform. An operator will use this information to limit algorithms available for use by RPCs to just a desired set from the universe of all allowed hash algorithms by the TCG.

     +--rw attester-supported-algos
        +--rw tpm12-asymmetric-signing*   identityref {taa:tpm12}?
        +--rw tpm12-hash*                 identityref {taa:tpm12}?
        +--rw tpm20-asymmetric-signing*   identityref {taa:tpm20}?
        +--rw tpm20-hash*                 identityref {taa:tpm20}?

container 'compute-nodes' - When there is more than one TPM supported, this container maintains the set of information related to the compute node associated with a specific TPM. This allows each specific TPM to identify to which 'compute-node' it belongs.

     +--rw compute-nodes {tpm:mtpm}?
        +--ro compute-node* [node-id]
           +--ro node-id                string
           +--ro node-physical-index?   int32 {hw:entity-mib}?
           +--ro node-name?             string
           +--ro node-location?         string
2.1.1.6. YANG Module 
<CODE BEGINS> file "[email protected]"
module ietf-tpm-remote-attestation {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation";
  prefix tpm;

  import ietf-yang-types {
    prefix yang;
  }
  import ietf-hardware {
    prefix hw;
  }
  import ietf-keystore {
    prefix ks;
  }
  import ietf-tcg-algs {
    prefix taa;
  }

  organization
    "IETF RATS (Remote ATtestation procedureS) Working Group";
  contact
    "WG Web  : <https://datatracker.ietf.org/wg/rats/>
     WG List : <mailto:[email protected]>
     Author  : Eric Voit <[email protected]>
     Author  : Henk Birkholz <[email protected]>
     Author  : Michael Eckel <[email protected]>
     Author  : Shwetha Bhandari <[email protected]>
     Author  : Bill Sulzen <[email protected]>
     Author  : Liang Xia (Frank) <[email protected]>
     Author  : Tom Laffey <[email protected]>
     Author  : Guy Fedorkow <[email protected]>";
  description
    "A YANG module to enable a TPM 1.2 and TPM 2.0 based
     remote attestation procedure using a challenge-response
     interaction model and the TPM 1.2 and TPM 2.0 Quote
     primitive operations.

     Copyright (c) 2022 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 Revised 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
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
     itself for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
     NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
     'MAY', and 'OPTIONAL' in this document are to be interpreted as
     described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.";

  revision 2022-05-17 {
    description
      "Initial version";
    reference
      "RFC XXXX: A YANG Data Model for Challenge-Response-based Remote
       Attestation Procedures using TPMs";
  }

  /*****************/
  /*   Features    */
  /*****************/

  feature mtpm {
    description
      "The device supports the remote attestation of multiple
       TPM based cryptoprocessors.";
  }

  feature bios {
    description
      "The device supports the bios logs.";
    reference
      "bios-log:
       https://trustedcomputinggroup.org/wp-content/uploads/
       PC-ClientSpecific_Platform_Profile_for_TPM_2p0_Systems_v51.pdf
       Section 9.4.5.2";
  }

  feature ima {
    description
      "The device supports Integrity Measurement Architecture logs.
       Many variants of IMA logs exist in the deployment.  Each encodes
       the log entry contents as the specific measurements which get
       hashed into a PCRs as Evidence.  See the reference below for
       one example of such an encoding.";
    reference
      "ima-log:
       https://www.trustedcomputinggroup.org/wp-content/uploads/
       TCG_IWG_CEL_v1_r0p41_pub.pdf  Section 5.1.6";
  }

  feature netequip_boot {
    description
      "The device supports the netequip_boot logs.";
    reference
      "netequip-boot-log:
       RFC XXXX  Appendix B";
  }

  /*****************/
  /*   Typedefs    */
  /*****************/

  typedef pcr {
    type uint8 {
      range "0..31";
    }
    description
      "Valid index number for a PCR.  A {{TPM2.0}} compliant PCR index
       extends from 0-31.  At this time a typical TPM would have no
       more than 32 PCRS.";
  }

  typedef compute-node-ref {
    type leafref {
      path "/tpm:rats-support-structures/tpm:compute-nodes"
         + "/tpm:compute-node/tpm:node-id";
    }
    description
      "This type is used to reference a hardware node.  Note that an
       implementer might include an alternative leafref pointing to a
       different YANG module node specifying hardware structures.";
  }

  typedef certificate-name-ref {
    type leafref {
      path "/tpm:rats-support-structures/tpm:tpms/tpm:tpm"
         + "/tpm:certificates/tpm:certificate/tpm:name";
    }
    description
      "A type which allows identification of a TPM based certificate.";
  }

  /******************/
  /*   Identities   */
  /******************/

  identity attested_event_log_type {
    description
      "Base identity allowing categorization of the reasons why an
       attested measurement has been taken on an Attester.";
  }

  identity ima {
    base attested_event_log_type;
    description
      "An event type recorded in IMA.";
  }

  identity bios {
    base attested_event_log_type;
    description
      "An event type associated with BIOS/UEFI.";
  }

  identity netequip_boot {
    base attested_event_log_type;
    description
      "An event type associated with Network Equipment Boot.";
  }

  /*****************/
  /*   Groupings   */
  /*****************/

  grouping tpm20-hash-algo {
    description
      "The cryptographic algorithm used to hash the TPM2 PCRs.  This
       must be from the list of platform supported options.";
    leaf tpm20-hash-algo {
      type identityref {
        base taa:hash;
      }
      must '. = /tpm:rats-support-structures'
         + '/tpm:attester-supported-algos/tpm:tpm20-hash' {
        error-message "This platform does not support tpm20-hash-algo";
      }
      description
        "The hash scheme that is used to hash a TPM2.0 PCR. This
         must be one of those supported by a platform.
         Where this object does not appear, the default value of
         'taa:TPM_ALG_SHA256' will apply.";
    }
  }

  grouping tpm12-hash-algo {
    description
      "The cryptographic algorithm used to hash the TPM1.2 PCRs.";
    leaf tpm12-hash-algo {
      type identityref {
        base taa:hash;
      }
      must '. = /tpm:rats-support-structures'
         + '/tpm:attester-supported-algos/tpm:tpm12-hash' {
        error-message "This platform does not support tpm12-hash-algo";
      }
      description
        "The hash scheme that is used to hash a TPM1.2 PCR. This
         MUST be one of those supported by a platform.
         Where this object does not appear, the default value of
         'taa:TPM_ALG_SHA1' will apply.";
    }
  }

  grouping nonce {
    description
      "A random number intended to guarantee freshness and for use
       as part of a replay-detection mechanism.";
    leaf nonce-value {
      type binary;
      mandatory true;
      description
        "A cryptographically generated random number which should
         not be predictable prior to its issuance from a random
         number generation function. The random number MUST be
         derived from an entropy source external to the Attester.

         Note that a nonce sent into a TPM will typically be 160 or 256
         binary digits long.  (This is 20 or 32 bytes.) So if fewer
         binary digits are sent, this nonce object will be padded
         with leading zeros within Quotes returned from the TPM.
         Additionally if more bytes are sent, the nonce will be trimmed
         to the most significant binary digits.";
    }
  }

  grouping tpm12-pcr-selection {
    description
      "A Verifier can request one or more PCR values using its
       individually created Attestation Key Certificate (AC).
       The corresponding selection filter is represented in this
       grouping.";
    leaf-list pcr-index {
      type pcr;
      description
        "The numbers/indexes of the PCRs. In addition, any selection
         of PCRs MUST verify that the set of PCRs requested are a
         subset the set of PCRs exposed by in the leaf-list
         /tpm:rats-support-structures
         /tpm:tpms/tpm:tpm[name=current()]/tpm:tpm12-pcrs";
    }
  }

  grouping tpm20-pcr-selection {
    description
      "A Verifier can acquire one or more PCR values, which are hashed
       together in a TPM2B_DIGEST coming from the TPM2.  The selection
       list of desired PCRs and the Hash Algorithm is represented in
       this grouping.";
    list tpm20-pcr-selection {
      unique "tpm20-hash-algo";
      description
        "Specifies the list of PCRs and Hash Algorithms that can be
         returned within a TPM2B_DIGEST.";
      reference
        "TPM2.0-Structures:
         https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.9.7";
      uses tpm20-hash-algo;
      leaf-list pcr-index {
        type pcr;
        description
          "The numbers of the PCRs that which are being tracked
           with a hash based on the tpm20-hash-algo.  In addition,
           any selection of PCRs MUST verify that the set of PCRs
           requested are a subset the set of PCR indexes selected
           are available for that specific TPM.";
      }
    }
  }

  grouping certificate-name-ref {
    description
      "Identifies a certificate in a keystore.";
    leaf certificate-name {
      type certificate-name-ref;
      mandatory true;
      description
        "Identifies a certificate in a keystore.";
    }
  }

  grouping tpm-name {
    description
      "A unique TPM on a device.";
    leaf name {
      type string;
      description
        "Unique system generated name for a TPM on a device.";
    }
  }

  grouping node-uptime {
    description
      "Uptime in seconds of the node.";
    leaf up-time {
      type uint32;
      description
        "Uptime in seconds of this node reporting its data";
    }
  }

  grouping tpm12-attestation {
    description
      "Contains an instance of TPM1.2 style signed cryptoprocessor
       measurements.  It is supplemented by unsigned Attester
       information.";
    uses node-uptime;
    leaf pcr-data {
      type binary;
      description
        "The value created and signed for the quote (type TPM_PCR_INFO_SHORT),
         i.e., the 'pcrData' part of a TPM1.2 Quote2 operation result.";
      reference
        "TPM1.2-Commands:
         TPM1.2 commands rev116 July 2007, Section 16.5
         https://trustedcomputinggroup.org/wp-content/uploads
         /TPM-Main-Part-3-Commands_v1.2_rev116_01032011.pdf";
    }
    leaf version-info {
      type binary;
      description
        "The version info (type TPM_CAP_VERSION_INFO),
         i.e., the 'versionInfo' part of a TPM1.2 Quote2 operation result.";
      reference
        "TPM1.2-Commands:
         TPM1.2 commands rev116 July 2007, Section 16.5
         https://trustedcomputinggroup.org/wp-content/uploads
         /TPM-Main-Part-3-Commands_v1.2_rev116_01032011.pdf";
    }
    leaf sig {
      type binary;
      description
        "The signed data blob, i.e., the signature
         i.e., the 'sig' part of a TPM1.2 Quote2 operation result.";
      reference
        "TPM1.2-Commands:
         TPM1.2 commands rev116 July 2007, Section 16.5
         https://trustedcomputinggroup.org/wp-content/uploads
         /TPM-Main-Part-3-Commands_v1.2_rev116_01032011.pdf";
    }
  }

  grouping tpm20-attestation {
    description
      "Contains an instance of TPM2 style signed cryptoprocessor
       measurements.  It is supplemented by unsigned Attester
       information.";
    leaf quote-data {
      type binary;
      mandatory true;
      description
        "A hash of the latest PCR values (and the hash algorithm used)
         which have been returned from an Attester for the selected PCRs
         and Hash Algorithms.";
      reference
        "TPM2.0-Structures:
         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;
      description
        "Quote signature returned by TPM Quote.  The signature was
         generated using the key associated with the
         certificate 'name'.";
      reference
        "TPM2.0-Structures:
         https://www.trustedcomputinggroup.org/wp-content/uploads/
         TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 11.2.1";
    }
    uses node-uptime;
    list unsigned-pcr-values {
      description
        "PCR values in each PCR bank. This might appear redundant with
         the TPM2B_DIGEST, but that digest is calculated across multiple
         PCRs.  Having to verify across multiple PCRs does not
         necessarily make it easy for a Verifier to appraise just the
         minimum set of PCR information which has changed since the last
         received TPM2B_DIGEST.  Put another way, why should a Verifier
         reconstruct the proper value of all PCR Quotes when only a
         single PCR has changed?
         To help this happen, if the Attester does know specific PCR
         values, the Attester can provide these individual values via
         'unsigned-pcr-values'.   By comparing this information to
         what has previously been validated, it is possible for a
         Verifier to confirm the Attester's signature while eliminating

         significant processing.  Note that there should never be a
         result where an unsigned PCR value differs from what may be
         reconstructed from the within the PCR quote and the event logs.
         If there is a difference, a signed result which has been
         verified from retrieved logs is considered definitive.";
      uses tpm20-hash-algo;
      list pcr-values {
        key "pcr-index";
        description
          "List of one PCR bank.";
        leaf pcr-index {
          type pcr;
          description
            "PCR index number.";
        }
        leaf pcr-value {
          type binary;
          description
            "PCR value.";
          reference
            "TPM2.0-Structures:
             https://www.trustedcomputinggroup.org/wp-content/uploads/
             TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.9.7";
        }
      }
    }
  }

  grouping log-identifier {
    description
      "Identifier for type of log to be retrieved.";
    leaf log-type {
      type identityref {
        base attested_event_log_type;
      }
      mandatory true;
      description
        "The corresponding measurement log type identity.";
    }
  }

  grouping boot-event-log {
    description
      "Defines a specific instance of an event log entry
       and corresponding to the information used to
       extend the PCR";
    leaf event-number {
      type uint32;
      description
        "Unique event number of this event which monotonically
         increases within a given event log.  The maximum event
         number should not be reached, nor is wrapping back to
         an earlier number supported.";
    }
    leaf event-type {
      type uint32;
      description
        "BIOS Log Event Type:
         https://trustedcomputinggroup.org/wp-content/uploads/
         TCG_PCClient_PFP_r1p05_v23_pub.pdf  Section 10.4.1";
    }
    leaf pcr-index {
      type pcr;
      description
        "Defines the PCR index that this event extended";
    }
    list digest-list {
      description
        "Hash of event data";
      leaf hash-algo {
        type identityref {
          base taa:hash;
        }
        description
          "The hash scheme that is used to compress the event data in
           each of the leaf-list digest items.";
      }
      leaf-list digest {
        type binary;
        description
          "The hash of the event data using the algorithm of the
           'hash-algo' against 'event data'.";
      }
    }
    leaf event-size {
      type uint32;
      description
        "Size of the event data";
    }
    leaf-list event-data {
      type binary;
      description
        "The event data.  This is a binary structure
         of size 'event-size'. For more on what
         might be recorded within this object
         see [bios-log] Section 9 which details
         viable events which might be recorded.";
    }
  }

  grouping bios-event-log {
    description
      "Measurement log created by the BIOS/UEFI.";
    list bios-event-entry {
      key "event-number";
      description
        "Ordered list of TCG described event log
         that extended the PCRs in the order they
         were logged";
      uses boot-event-log;
    }
  }

  grouping ima-event {
    description
      "Defines a hash log extend event for IMA measurements";
    reference
      "ima-log:
       https://www.trustedcomputinggroup.org/wp-content/uploads/
       TCG_IWG_CEL_v1_r0p41_pub.pdf  Section 4.3";
    leaf event-number {
      type uint64;
      description
        "Unique event number of this event which monotonically
         increases.  The maximum event number should not be
         reached, nor is wrapping back to an earlier number
         supported.";
    }
    leaf ima-template {
      type string;
      description
        "Name of the template used for event logs
         for e.g. ima, ima-ng, ima-sig";
    }
    leaf filename-hint {
      type string;
      description
        "File name (including the path) that was measured.";
    }
    leaf filedata-hash {
      type binary;
      description
        "Hash of filedata as updated based upon the
         filedata-hash-algorithm";
    }
    leaf filedata-hash-algorithm {
      type string;
      description
        "Algorithm used for filedata-hash";
    }
    leaf template-hash-algorithm {
      type string;
      description
        "Algorithm used for template-hash";
    }
    leaf template-hash {
      type binary;
      description
        "hash(filedata-hash, filename-hint)";
    }
    leaf pcr-index {
      type pcr;
      description
        "Defines the PCR index that this event extended";
    }
    leaf signature {
      type binary;
      description
        "Digital file signature which provides a
         fingerprint for the file being measured.";
    }
  }

  grouping ima-event-log {
    description
      "Measurement log created by IMA.";
    list ima-event-entry {
      key "event-number";
      description
        "Ordered list of ima event logs by event-number";
      uses ima-event;
    }
  }

  grouping network-equipment-boot-event-log {
    description
      "Measurement log created by Network Equipment Boot. The Network
       Equipment Boot format is identical to the IMA format. In
       contrast to the IMA log, the Network Equipment Boot log
       includes every measurable event from an Attester, including
       the boot stages of BIOS, Bootloader, etc. In essence, the scope
       of events represented in this format combines the scope of BIOS
       events and IMA events.";
    list boot-event-entry {
      key "event-number";
      description
        "Ordered list of Network Equipment Boot event logs
         by event-number, using the IMA event format.";
      uses ima-event;
    }
  }

  grouping event-logs {
    description
      "A selector for the log and its type.";
    choice attested_event_log_type {
      mandatory true;
      description
        "Event log type determines the event logs content.";
      case bios {
        if-feature "bios";
        description
          "BIOS/UEFI event logs";
        container bios-event-logs {
          description
            "BIOS/UEFI event logs";
          uses bios-event-log;
        }
      }
      case ima {
        if-feature "ima";
        description
          "IMA event logs.";
        container ima-event-logs {
          description
            "IMA event logs.";
          uses ima-event-log;
        }
      }
      case netequip_boot {
        if-feature "netequip_boot";
        description
          "Network Equipment Boot event logs";
        container boot-event-logs {
          description
            "Network equipment boot event logs.";
          uses network-equipment-boot-event-log;
        }
      }
    }
  }

  /**********************/
  /*   RPC operations   */
  /**********************/

  rpc tpm12-challenge-response-attestation {
    if-feature "taa:tpm12";
    description
      "This RPC accepts the input for TSS TPM 1.2 commands made to the
       attesting device.";
    input {
      container tpm12-attestation-challenge {
        description
          "This container includes every information element defined
           in the reference challenge-response interaction model for
           remote attestation. Corresponding values are based on
           TPM 1.2 structure definitions";
        uses tpm12-pcr-selection;
        uses nonce;
        leaf-list certificate-name {
          if-feature "tpm:mtpm";
          type certificate-name-ref;
          must "/tpm:rats-support-structures/tpm:tpms"
             + "/tpm:tpm[tpm:firmware-version='taa:tpm12']"
             + "/tpm:certificates/"
             + "/tpm:certificate[name=current()]" {
            error-message "Not an available TPM1.2 AIK certificate.";
          }
          description
            "When populated, the RPC will only get a Quote for the
             TPMs associated with these certificate(s).";
        }
      }
    }
    output {
      list tpm12-attestation-response {
        unique "certificate-name";
        description
          "The binary output of TPM 1.2 TPM_Quote/TPM_Quote2, including
           the PCR selection and other associated attestation evidence
           metadata";
        uses certificate-name-ref {
          description
            "Certificate associated with this tpm12-attestation.";
        }
        uses tpm12-attestation;
      }
    }
  }

  rpc tpm20-challenge-response-attestation {
    if-feature "taa:tpm20";
    description
      "This RPC accepts the input for TSS TPM 2.0 commands of the
       managed device. ComponentIndex from the hardware manager YANG
       module is used to refer to dedicated TPM in composite devices,
       e.g. smart NICs, is not covered.";
    input {
      container tpm20-attestation-challenge {
        description
          "This container includes every information element defined
           in the reference challenge-response interaction model for
           remote attestation. Corresponding values are based on
           TPM 2.0 structure definitions";
        uses nonce;
        uses tpm20-pcr-selection;
        leaf-list certificate-name {
          if-feature "tpm:mtpm";
          type certificate-name-ref;
          must "/tpm:rats-support-structures/tpm:tpms"
             + "/tpm:tpm[tpm:firmware-version='taa:tpm20']"
             + "/tpm:certificates/"
             + "/tpm:certificate[name=current()]" {
            error-message "Not an available TPM2.0 AIK certificate.";
          }
          description
            "When populated, the RPC will only get a Quote for the
             TPMs associated with the certificates.";
        }
      }
    }
    output {
      list tpm20-attestation-response {
        unique "certificate-name";
        description
          "The binary output of TPM2_Quote from one TPM of the
           node which identified by node-id. An TPMS_ATTEST structure
           including a length, encapsulated in a signature";
        uses certificate-name-ref {
          description
            "Certificate associated with this tpm20-attestation.";
        }
        uses tpm20-attestation;
      }
    }
  }

  rpc log-retrieval {
    description
      "Logs Entries are either identified via indices or via providing
       the last line received. The number of lines returned can be
       limited. The type of log is a choice that can be augmented.";
    input {
      uses log-identifier;
      list log-selector {
        description
          "Only log entries which meet all the selection criteria
           provided are to be returned by the RPC output.";
        leaf-list name {
          type string;
          description
            "Name of one or more unique TPMs on a device.  If this
             object exists, a selection should pull only the objects
             related to these TPM(s).  If it does not exist, all
             qualifying TPMs that are 'hardware-based' equals true
             on the device are selected. When this selection
             criteria is provided, it will be considered as a logical
             AND with any other selection criteria provided.";
        }
        choice index-type {
          description
            "Last log entry received, log index number, or timestamp.";
          case last-entry {
            description
              "The last entry of the log already retrieved.";
            leaf last-entry-value {
              type binary;
              description
                "Content of a log event which matches 1:1 with a
                 unique event record contained within the log.  Log
                 entries after this will be passed to the
                 requester.  Note: if log entry values are not unique,
                 this MUST return an error.";
            }
          }
          case index {
            description
              "Numeric index of the last log entry retrieved, or
               zero.";
            leaf last-index-number {
              type uint64;
              description
                "The last numeric index number of a log entry.
                 Zero means to start at the beginning of the log.
                 Entries after this will be passed to the
                 requester.";
            }
          }
          case timestamp {
            leaf timestamp {
              type yang:date-and-time;
              description
                "Timestamp from which to start the extraction.  The
                 next log entry after this timestamp is to
                 be sent.";
            }
            description
              "Timestamp from which to start the extraction.";
          }
        }
        leaf log-entry-quantity {
          type uint16;
          description
            "The number of log entries to be returned. If omitted, it
             means all of them.";
        }
      }
    }
    output {
      container system-event-logs {
        description
          "The requested data of the measurement event logs";
        list node-data {
          unique "name";
          description
            "Event logs of a node in a distributed system
             identified by the node name";
          uses tpm-name;
          uses node-uptime;
          container log-result {
            description
              "The requested entries of the corresponding log.";
            uses event-logs;
          }
        }
      }
    }
  }

  /**************************************/
  /*   Config & Oper accessible nodes   */
  /**************************************/

  container rats-support-structures {
    description
      "The datastore definition enabling verifiers or relying
       parties to discover the information necessary to use the
       remote attestation RPCs appropriately.";
    container compute-nodes {
      if-feature "tpm:mtpm";
      description
        "Holds the set of device subsystems/components in this
         composite device that support TPM operations.";
      list compute-node {
        key "node-id";
        unique "node-name";
        config false;
        min-elements 2;
        description
          "A component within this composite device which
           supports TPM operations.";
        leaf node-id {
          type string;
          description
            "ID of the compute node, such as Board Serial Number.";
        }
        leaf node-physical-index {
          if-feature "hw:entity-mib";
          type int32 {
            range "1..2147483647";
          }
          config false;
          description
            "The entPhysicalIndex for the compute node.";
          reference
            "RFC 6933: Entity MIB (Version 4) - entPhysicalIndex";
        }
        leaf node-name {
          type string;
          description
            "Name of the compute node.";
        }
        leaf node-location {
          type string;
          description
            "Location of the compute node, such as slot number.";
        }
      }
    }
    container tpms {
      description
        "Holds the set of TPMs within an Attester.";
      list tpm {
        key "name";
        unique "path";
        description
          "A list of TPMs in this composite device that RATS
           can be conducted with.";
        uses tpm-name;
        leaf hardware-based {
          type boolean;
          config false;
          mandatory true;
          description
            "System generated indication of whether this is a
             hardware based TPM.";
        }
        leaf physical-index {
          if-feature "hw:entity-mib";
          type int32 {
            range "1..2147483647";
          }
          config false;
          description
            "The entPhysicalIndex for the TPM.";
          reference
            "RFC 6933: Entity MIB (Version 4) - entPhysicalIndex";
        }
        leaf path {
          type string;
          config false;
          description
            "Device path to a unique TPM on a device.  This can change
             across reboots.";
        }
        leaf compute-node {
          if-feature "tpm:mtpm";
          type compute-node-ref;
          config false;
          mandatory true;
          description
            "Indicates the compute node measured by this TPM.";
        }
        leaf manufacturer {
          type string;
          config false;
          description
            "TPM manufacturer name.";
        }
        leaf firmware-version {
          type identityref {
            base taa:cryptoprocessor;
          }
          mandatory true;
          description
            "Identifies the cryptoprocessor API set supported.  This
             is automatically configured by the device and should not
             be changed.";
        }
        uses tpm12-hash-algo {
          when "derived-from-or-self(firmware-version, 'taa:tpm12')";
          if-feature "taa:tpm12";
          refine "tpm12-hash-algo" {
            description
              "The hash algorithm overwrites the default used for PCRs
               on this TPM1.2 compliant cryptoprocessor.";
          }
        }
        leaf-list tpm12-pcrs {
          when
            "derived-from-or-self(../firmware-version, 'taa:tpm12')";
          if-feature "taa:tpm12";
          type pcr;
          description
            "The PCRs which may be extracted from this TPM1.2
             compliant cryptoprocessor.";
        }
        list tpm20-pcr-bank {
          when
            "derived-from-or-self(../firmware-version, 'taa:tpm20')";
          if-feature "taa:tpm20";
          key "tpm20-hash-algo";
          description
            "Specifies the list of PCRs that may be extracted for
             a specific Hash Algorithm on this TPM2 compliant
             cryptoprocessor.  A bank is a set of PCRs which are
             extended using a particular hash algorithm.";
          reference
            "TPM2.0-Structures:
             https://www.trustedcomputinggroup.org/wp-content/uploads/
             TPM-Rev-2.0-Part-2-Structures-01.38.pdf  Section 10.9.7";
          leaf tpm20-hash-algo {
            type identityref {
              base taa:hash;
            }
            must '/tpm:rats-support-structures'
               + '/tpm:attester-supported-algos'
               + '/tpm:tpm20-hash' {
              error-message "This platform does not support tpm20-hash-algo";
            }
            description
              "The hash scheme actively being used to hash a
               one or more TPM2.0 PCRs.";
          }
          leaf-list pcr-index {
            type tpm:pcr;
            description
              "Defines what TPM2 PCRs are available to be extracted.";
          }
        }
        leaf status {
          type enumeration {
            enum operational {
              value 0;
              description
                "The TPM currently is running normally and
                 is ready to accept and process TPM quotes.";
              reference
                "TPM2.0-Arch:
                 https://trustedcomputinggroup.org/wp-content/uploads/
                 TCG_TPM2_r1p59_Part1_Architecture_pub.pdf
                 Section 12";
            }
            enum non-operational {
              value 1;
              description
                "TPM is in a state such as startup or shutdown which
                 precludes the processing of TPM quotes.";
            }
          }
          config false;
          mandatory true;
          description
            "TPM chip self-test status.";
        }
        container certificates {
          description
            "The TPM's certificates, including EK certificates
             and Attestation Key certificates.";
          list certificate {
            key "name";
            description
              "Three types of certificates can be accessed via
               this statement, including Initial Attestation
               Key Certificate, Local Attestation Key Certificate or
               Endorsement Key Certificate.";
            leaf name {
              type string;
              description
                "An arbitrary name uniquely identifying a certificate
                 associated within key within a TPM.";
            }
            leaf keystore-ref {
              if-feature "ks:central-keystore-supported";
              if-feature "ks:asymmetric-keys";
              type leafref {
                path "/ks:keystore/ks:asymmetric-keys/ks:asymmetric-key"
                   + "/ks:name";
              }
              description
                "A reference to a specific certificate of an
                 asymmetric key in the Keystore.";
            }
            leaf type {
              type enumeration {
                enum endorsement-certificate {
                  value 0;
                  description
                    "Endorsement Key (EK) Certificate type.";
                  reference
                    "TPM2.0-Key:
                     https://trustedcomputinggroup.org/wp-content/
                     uploads/TPM-2p0-Keys-for-Device-Identity-
                     and-Attestation_v1_r12_pub10082021.pdf
                     Section 3.11";
                }
                enum initial-attestation-certificate {
                  value 1;
                  description
                    "Initial Attestation key (IAK) Certificate type.";
                  reference
                    "TPM2.0-Key:
                     https://trustedcomputinggroup.org/wp-content/
                     uploads/TPM-2p0-Keys-for-Device-Identity-
                     and-Attestation_v1_r12_pub10082021.pdf
                     Section 3.2";
                }
                enum local-attestation-certificate {
                  value 2;
                  description
                    "Local Attestation Key (LAK) Certificate type.";
                  reference
                    "TPM2.0-Key:
                     https://trustedcomputinggroup.org/wp-content/
                     uploads/TPM-2p0-Keys-for-Device-Identity-
                     and-Attestation_v1_r12_pub10082021.pdf
                     Section 3.2";
                }
              }
              description
                "Function supported by this certificate from within the
                 TPM.";
            }
          }
        }
      }
    }
    container attester-supported-algos {
      description
        "Identifies which TPM algorithms are available for use on an
         attesting platform.";
      leaf-list tpm12-asymmetric-signing {
        when "../../tpm:tpms"
           + "/tpm:tpm[tpm:firmware-version='taa:tpm12']";
        if-feature "taa:tpm12";
        type identityref {
          base taa:asymmetric;
        }
        description
          "Platform Supported TPM12 asymmetric algorithms.";
      }
      leaf-list tpm12-hash {
        when "../../tpm:tpms"
           + "/tpm:tpm[tpm:firmware-version='taa:tpm12']";
        if-feature "taa:tpm12";
        type identityref {
          base taa:hash;
        }
        description
          "Platform supported TPM12 hash algorithms.";
      }
      leaf-list tpm20-asymmetric-signing {
        when "../../tpm:tpms"
           + "/tpm:tpm[tpm:firmware-version='taa:tpm20']";
        if-feature "taa:tpm20";
        type identityref {
          base taa:asymmetric;
        }
        description
          "Platform Supported TPM20 asymmetric algorithms.";
      }
      leaf-list tpm20-hash {
        when "../../tpm:tpms"
           + "/tpm:tpm[tpm:firmware-version='taa:tpm20']";
        if-feature "taa:tpm20";
        type identityref {
          base taa:hash;
        }
        description
          "Platform supported TPM20 hash algorithms.";
      }
    }
  }
}
<CODE ENDS>
Figure 1

2.1.2. 'ietf-tcg-algs'

This document has encoded the TCG Algorithm definitions of [TCG-Algos], revision 1.32. By including this full table as a separate YANG file within this document, it is possible for other YANG models to leverage the contents of this model. Specific references to [RFC2104], [RFC8017], [ISO-IEC-9797-1], [ISO-IEC-9797-2], [ISO-IEC-10116], [ISO-IEC-10118-3], [ISO-IEC-14888-3], [ISO-IEC-15946-1], [ISO-IEC-18033-3], [IEEE-Std-1363-2000], [IEEE-Std-1363a-2004], [NIST-PUB-FIPS-202], [NIST-SP800-38C], [NIST-SP800-38D], [NIST-SP800-38F], [NIST-SP800-56A], [NIST-SP800-108], [bios-log], as well as Appendix A and Appendix B exist within the YANG Model.

2.1.2.1. Features

There are two types of features supported: 'TPM12' and 'TPM20'. Support for either of these features indicates that a cryptoprocessor supporting the corresponding type of TCG TPM API is present on an Attester. Most commonly, only one type of cryptoprocessor will be available on an Attester.

2.1.2.2. Identities

There are three types of identities in this model:

  1. Cryptographic functions supported by a TPM algorithm; these include: 'asymmetric', 'symmetric', 'hash', 'signing', 'anonymous_signing', 'encryption_mode', 'method', and 'object_type'. The definitions of each of these are in Table 2 of [TCG-Algos].
  2. API specifications for TPM types: 'tpm12' and 'tpm20'
  3. Specific algorithm types: Each algorithm type defines what cryptographic functions may be supported, and on which type of API specification. It is not required that an implementation of a specific TPM will support all algorithm types. The contents of each specific algorithm mirrors what is in Table 3 of [TCG-Algos].
2.1.2.3. YANG Module 
<CODE BEGINS> file "[email protected]"
module ietf-tcg-algs {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-tcg-algs";
  prefix taa;

  organization
    "IETF RATS (Remote ATtestation procedureS) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/rats/>
     WG List:  <mailto:[email protected]>
     Author:   Eric Voit <mailto:[email protected]>";
  description
    "This module defines identities for asymmetric algorithms.

     Copyright (c) 2022 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 Revised
     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
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
     for full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.";

  revision 2022-03-23 {
    description
      "Initial version";
    reference
      "RFC XXXX: A YANG Data Model for Challenge-Response-based Remote
       Attestation Procedures using TPMs";
  }

  /*****************/
  /*   Features    */
  /*****************/

  feature tpm12 {
    description
      "This feature indicates algorithm support for the TPM 1.2 API
       as per Section 4.8 of TPM1.2-Structures:
       TPM Main Part 2 TPM Structures
       https://trustedcomputinggroup.org/wp-content/uploads/TPM-
       Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf";
  }

  feature tpm20 {
    description
      "This feature indicates algorithm support for the TPM 2.0 API
       as per Section 11.4 of Trusted Platform Module Library
       Part 1: Architecture. See TPM2.0-Arch:
       https://trustedcomputinggroup.org/wp-content/uploads/
       TCG_TPM2_r1p59_Part1_Architecture_pub.pdf";
  }

  /*****************/
  /*  Identities   */
  /*****************/

  identity asymmetric {
    description
      "A TCG recognized asymmetric algorithm with a public and
       private key.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2,
       https://trustedcomputinggroup.org/resource/
       tcg-algorithm-registry/TCG-_Algorithm_Registry_r1p32_pub";
  }

  identity symmetric {
    description
      "A TCG recognized symmetric algorithm with only a private key.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity hash {
    description
      "A TCG recognized hash algorithm that compresses input data to
       a digest value or indicates a method that uses a hash.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity signing {
    description
      "A TCG recognized signing algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity anonymous_signing {
    description
      "A TCG recognized anonymous signing algorithm.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity encryption_mode {
    description
      "A TCG recognized encryption mode.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity method {
    description
      "A TCG recognized method such as a mask generation function.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity object_type {
    description
      "A TCG recognized object type.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 2";
  }

  identity cryptoprocessor {
    description
      "Base identity identifying a crytoprocessor.";
  }

  identity tpm12 {
    if-feature "tpm12";
    base cryptoprocessor;
    description
      "Supportable by a TPM1.2.";
    reference
      "TPM1.2-Structures:
       https://trustedcomputinggroup.org/wp-content/uploads/
       TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf
       TPM_ALGORITHM_ID values, Section 4.8";
  }

  identity tpm20 {
    if-feature "tpm20";
    base cryptoprocessor;
    description
      "Supportable by a TPM2.";
    reference
      "TPM2.0-Structures:
       https://trustedcomputinggroup.org/wp-content/uploads/
       TPM-Rev-2.0-Part-2-Structures-01.38.pdf";
  }

  identity TPM_ALG_RSA {
    if-feature "tpm12 or tpm20";
    base tpm12;
    base tpm20;
    base asymmetric;
    base object_type;
    description
      "RSA algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8017. ALG_ID: 0x0001";
  }

  identity TPM_ALG_TDES {
    if-feature "tpm12";
    base tpm12;
    base symmetric;
    description
      "Block cipher with various key sizes (Triple Data Encryption
       Algorithm, commonly called Triple Data Encryption Standard)
       Note: was banned in TPM1.2 v94";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 18033-3. ALG_ID: 0x0003";
  }

  identity TPM_ALG_SHA1 {
    if-feature "tpm12 or tpm20";
    base hash;
    base tpm12;
    base tpm20;
    description
      "SHA1 algorithm - Deprecated due to insufficient cryptographic
       protection.  However, it is still useful for hash algorithms
       where protection is not required.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10118-3. ALG_ID: 0x0004";
  }

  identity TPM_ALG_HMAC {
    if-feature "tpm12 or tpm20";
    base tpm12;
    base tpm20;
    base hash;
    base signing;
    description
      "Hash Message Authentication Code (HMAC) algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3,
       ISO/IEC 9797-2 and RFC2104. ALG_ID: 0x0005";
  }

  identity TPM_ALG_AES {
    if-feature "tpm12";
    base tpm12;
    base symmetric;
    description
      "The AES algorithm with various key sizes";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3,
       ISO/IEC 18033-3. ALG_ID: 0x0006";
  }

  identity TPM_ALG_MGF1 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    base method;
    description
      "hash-based mask-generation function";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3,
       IEEE Std 1363-2000 and IEEE Std 1363a-2004.
       ALG_ID: 0x0007";
  }

  identity TPM_ALG_KEYEDHASH {
    if-feature "tpm20";
    base tpm20;
    base hash;
    base object_type;
    description
      "An encryption or signing algorithm using a keyed hash.  These
       may use XOR for encryption or an HMAC for signing and may
       also refer to a data object that is neither signing nor
       encrypting.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3,
       ALG_ID: 0x0008";
  }

  identity TPM_ALG_XOR {
    if-feature "tpm12 or tpm20";
    base tpm12;
    base tpm20;
    base hash;
    base symmetric;
    description
      "The XOR encryption algorithm.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3.
       ALG_ID: 0x000A";
  }

  identity TPM_ALG_SHA256 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SHA 256 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10118-3. ALG_ID: 0x000B";
  }

  identity TPM_ALG_SHA384 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SHA 384 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10118-3. ALG_ID: 0x000C";
  }

  identity TPM_ALG_SHA512 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SHA 512 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10118-3. ALG_ID: 0x000D";
  }

  identity TPM_ALG_NULL {
    if-feature "tpm20";
    base tpm20;
    description
      "NULL algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3.
       ALG_ID: 0x0010";
  }

  identity TPM_ALG_SM3_256 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SM3 hash algorithm.";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10118-3:2018. ALG_ID: 0x0012";
  }

  identity TPM_ALG_SM4 {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    description
      "SM4 symmetric block cipher";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3.
       ALG_ID: 0x0013";
  }

  identity TPM_ALG_RSASSA {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    description
      "RFC 8017 Signature algorithm defined in section 8.2
       (RSASSAPKCS1-v1_5)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8017.  ALG_ID: 0x0014";
  }

  identity TPM_ALG_RSAES {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base encryption_mode;
    description
      "RFC 8017 Signature algorithm defined in section 7.2
       (RSAES-PKCS1-v1_5)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8017. ALG_ID: 0x0015";
  }

  identity TPM_ALG_RSAPSS {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    description
      "Padding algorithm defined in section 8.1 (RSASSA PSS)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8017. ALG_ID: 0x0016";
  }

  identity TPM_ALG_OAEP {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base encryption_mode;
    description
      "Padding algorithm defined in section 7.1 (RSASSA OAEP)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8017. ALG_ID: 0x0017";
  }

  identity TPM_ALG_ECDSA {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    description
      "Signature algorithm using elliptic curve cryptography (ECC)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 14888-3. ALG_ID: 0x0018";
  }

  identity TPM_ALG_ECDH {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base method;
    description
      "Secret sharing using ECC";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-56A. ALG_ID: 0x0019";
  }

  identity TPM_ALG_ECDAA {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    base anonymous_signing;
    description
      "Elliptic-curve based anonymous signing scheme";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       TCG TPM 2.0 library specification. ALG_ID: 0x001A";
  }

  identity TPM_ALG_SM2 {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    base encryption_mode;
    base method;
    description
      "SM2 - depending on context, either an elliptic-curve based,
       signature algorithm, an encryption scheme, or a key exchange
       protocol";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3.
       ALG_ID: 0x001B";
  }

  identity TPM_ALG_ECSCHNORR {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    description
      "Elliptic-curve based Schnorr signature";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3.
       ALG_ID: 0x001C";
  }

  identity TPM_ALG_ECMQV {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base method;
    description
      "Two-phase elliptic-curve key";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-56A. ALG_ID: 0x001D";
  }

  identity TPM_ALG_KDF1_SP800_56A {
    if-feature "tpm20";
    base tpm20;
    base hash;
    base method;
    description
      "Concatenation key derivation function";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-56A  (approved alternative1) section 5.8.1.
       ALG_ID: 0x0020";
  }

  identity TPM_ALG_KDF2 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    base method;
    description
      "Key derivation function";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       IEEE 1363a-2004 KDF2 section 13.2. ALG_ID: 0x0021";
  }

  identity TPM_ALG_KDF1_SP800_108 {
    base TPM_ALG_KDF2;
    description
      "A key derivation method";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-108 - Section 5.1 KDF. ALG_ID: 0x0022";
  }

  identity TPM_ALG_ECC {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base object_type;
    description
      "Prime field ECC";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 15946-1. ALG_ID: 0x0023";
  }

  identity TPM_ALG_SYMCIPHER {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base object_type;
    description
      "Object type for a symmetric block cipher";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       TCG TPM 2.0 library specification. ALG_ID: 0x0025";
  }

  identity TPM_ALG_CAMELLIA {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    description
      "The Camellia algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 18033-3. ALG_ID: 0x0026";
  }

  identity TPM_ALG_SHA3_256 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "ISO/IEC 10118-3 - the SHA 256 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST PUB FIPS 202. ALG_ID: 0x0027";
  }

  identity TPM_ALG_SHA3_384 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SHA 384 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST PUB FIPS 202. ALG_ID: 0x0028";
  }

  identity TPM_ALG_SHA3_512 {
    if-feature "tpm20";
    base tpm20;
    base hash;
    description
      "The SHA 512 algorithm";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST PUB FIPS 202. ALG_ID: 0x0029";
  }

  identity TPM_ALG_CMAC {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    description
      "block Cipher-based Message Authentication Code (CMAC)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 9797-1:2011 Algorithm 5. ALG_ID: 0x003F";
  }

  identity TPM_ALG_CTR {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base encryption_mode;
    description
      "Counter mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10116. ALG_ID: 0x0040";
  }

  identity TPM_ALG_OFB {
    base tpm20;
    base symmetric;
    base encryption_mode;
    description
      "Output Feedback mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10116. ALG_ID: 0x0041";
  }

  identity TPM_ALG_CBC {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base encryption_mode;
    description
      "Cipher Block Chaining mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10116. ALG_ID: 0x0042";
  }

  identity TPM_ALG_CFB {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base encryption_mode;
    description
      "Cipher Feedback mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10116. ALG_ID: 0x0043";
  }

  identity TPM_ALG_ECB {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base encryption_mode;
    description
      "Electronic Codebook mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       ISO/IEC 10116. ALG_ID: 0x0044";
  }

  identity TPM_ALG_CCM {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    base encryption_mode;
    description
      "Counter with Cipher Block Chaining-Message Authentication
       Code (CCM)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-38C. ALG_ID: 0x0050";
  }

  identity TPM_ALG_GCM {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    base encryption_mode;
    description
      "Galois/Counter Mode (GCM)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-38D. ALG_ID: 0x0051";
  }

  identity TPM_ALG_KW {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    base encryption_mode;
    description
      "AES Key Wrap (KW)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-38F. ALG_ID: 0x0052";
  }

  identity TPM_ALG_KWP {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    base encryption_mode;
    description
      "AES Key Wrap with Padding (KWP)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-38F. ALG_ID: 0x0053";
  }

  identity TPM_ALG_EAX {
    if-feature "tpm20";
    base tpm20;
    base symmetric;
    base signing;
    base encryption_mode;
    description
      "Authenticated-Encryption Mode";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       NIST SP800-38F. ALG_ID: 0x0054";
  }

  identity TPM_ALG_EDDSA {
    if-feature "tpm20";
    base tpm20;
    base asymmetric;
    base signing;
    description
      "Edwards-curve Digital Signature Algorithm (PureEdDSA)";
    reference
      "TCG-Algos:TCG Algorithm Registry Rev1.32  Table 3 and
       RFC 8032. ALG_ID: 0x0060";
  }
}
<CODE ENDS>

Note that not all cryptographic functions are required for use by ietf-tpm-remote-attestation.yang. However, the full definition of Table 3 of [TCG-Algos] will allow use by additional YANG specifications.

3. IANA Considerations

This document registers the following namespace URIs in the [xml-registry] as per [RFC3688]:

URI:

urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation

Registrant Contact:

The IESG.

XML:

N/A; the requested URI is an XML namespace.

URI:

urn:ietf:params:xml:ns:yang:ietf-tcg-algs

Registrant Contact:

The IESG.

XML:

N/A; the requested URI is an XML namespace.

This document registers the following YANG modules in the registry [yang-parameters] as per Section 14 of [RFC6020]:

Name:

ietf-tpm-remote-attestation

Namespace:

urn:ietf:params:xml:ns:yang:ietf-tpm-remote-attestation

Prefix:

tpm

Reference:

draft-ietf-rats-yang-tpm-charra (RFC form)

Name:

ietf-tcg-algs

Namespace:

urn:ietf:params:xml:ns:yang:ietf-tcg-algs

Prefix:

taa

Reference:

draft-ietf-rats-yang-tpm-charra (RFC form)

4. Security Considerations

The YANG module ietf-tpm-remote-attestation.yang specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].

There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes as well as their sensitivity/vulnerability:

Container '/rats-support-structures/attester-supported-algos':

'tpm12-asymmetric-signing', 'tpm12-hash', 'tpm20-asymmetric-signing', and 'tpm20-hash'. All could be populated with algorithms that are not supported by the underlying physical TPM installed by the equipment vendor. A vendor should restrict the ability to configure unsupported algorithms.

Container: '/rats-support-structures/tpms':

'name': Although shown as 'rw', it is system generated. Therefore, it should not be possible for an operator to add or remove a TPM from the configuration.

'tpm20-pcr-bank': It is possible to configure PCRs for extraction which are not being extended by system software. This could unnecessarily use TPM resources.

'certificates': It is possible to provision a certificate which does not correspond to an Attestation Identity Key (AIK) within the TPM 1.2, or an Attestation Key (AK) within the TPM 2.0 respectively. In such a case, calls to an RPC requesting this specific certificate could result in either no response or a response for an unexpected TPM.

RPC 'tpm12-challenge-response-attestation':

The receiver of the RPC response must verify that the certificate is for an active AIK, i.e., the certificate has been confirmed by a third party as being able to support Attestation on the targeted TPM 1.2.

RPC 'tpm20-challenge-response-attestation':

The receiver of the RPC response must verify that the certificate is for an active AK, i.e., the private key confirmation of the quote signature within the RPC response has been confirmed by a third party to belong to an entity legitimately able to perform Attestation on the targeted TPM 2.0.

RPC 'log-retrieval':

Requesting a large volume of logs from the Attester could require significant system resources and create a denial of service.

Information collected through the RPCs above could reveal that specific versions of software and configurations of endpoints that could identify vulnerabilities on those systems. Therefore, RPCs should be protected by NACM [RFC8341] with a default setting of deny-all to limit the extraction of attestation data by only authorized Verifiers.

For the YANG module ietf-tcg-algs.yang, please use care when selecting specific algorithms. The introductory section of [TCG-Algos] highlights that some algorithms should be considered legacy, and recommends implementers and adopters diligently evaluate available information such as governmental, industrial, and academic research before selecting an algorithm for use.

5. References

5.1. Normative References

[bios-log]
"TCG PC Client Platform Firmware Profile Specification, Section 9.4.5.2", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/PC-ClientSpecific_Platform_Profile_for_TPM_2p0_Systems_v51.pdf>.
[BIOS-Log-Event-Type]
"TCG PC Client Platform Firmware Profile Specification", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf>.
[cel]
"Canonical Event Log Format, Section 4.3", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_IWG_CEL_v1_r0p41_pub.pdf>.
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore and Keystore Operations", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-35, , <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-keystore-35>.
[I-D.ietf-rats-tpm-based-network-device-attest]
Fedorkow, G., Voit, E., and J. Fitzgerald-McKay, "TPM-based Network Device Remote Integrity Verification", Work in Progress, Internet-Draft, draft-ietf-rats-tpm-based-network-device-attest-14, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-tpm-based-network-device-attest-14>.
[IEEE-Std-1363-2000]
"IEEE 1363-2000 - IEEE Standard Specifications for Public-Key Cryptography", n.d., <https://standards.ieee.org/standard/1363-2000.html>.
[IEEE-Std-1363a-2004]
"1363a-2004 - IEEE Standard Specifications for Public-Key Cryptography - Amendment 1: Additional Techniques", n.d., <https://ieeexplore.ieee.org/document/1335427>.
[ISO-IEC-10116]
"ISO/IEC 10116:2017 - Information technology", n.d., <https://www.iso.org/standard/64575.html>.
[ISO-IEC-10118-3]
"Dedicated hash-functions - ISO/IEC 10118-3:2018", n.d., <https://www.iso.org/standard/67116.html>.
[ISO-IEC-14888-3]
"ISO/IEC 14888-3:2018 - Digital signatures with appendix", n.d., <https://www.iso.org/standard/76382.html>.
[ISO-IEC-15946-1]
"ISO/IEC 15946-1:2016 - Information technology", n.d., <https://www.iso.org/standard/65480.html>.
[ISO-IEC-18033-3]
"ISO/IEC 18033-3:2010 - Encryption algorithms", n.d., <https://www.iso.org/standard/54531.html>.
[ISO-IEC-9797-1]
"Message Authentication Codes (MACs) - ISO/IEC 9797-1:2011", n.d., <https://www.iso.org/standard/50375.html>.
[ISO-IEC-9797-2]
"Message Authentication Codes (MACs) - ISO/IEC 9797-2:2011", n.d., <https://www.iso.org/standard/51618.html>.
[NIST-PUB-FIPS-202]
"SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions", n.d., <https://csrc.nist.gov/publications/detail/fips/202/final>.
[NIST-SP800-108]
"Recommendation for Key Derivation Using Pseudorandom Functions", n.d., <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-108.pdf>.
[NIST-SP800-38C]
"Recommendation for Block Cipher Modes of Operation: the CCM Mode for Authentication and Confidentiality", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38c/final>.
[NIST-SP800-38D]
"Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38d/final>.
[NIST-SP800-38F]
"Recommendation for Block Cipher Modes of Operation: Methods for Key Wrapping", n.d., <https://csrc.nist.gov/publications/detail/sp/800-38f/final>.
[NIST-SP800-56A]
"Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", n.d., <https://csrc.nist.gov/publications/detail/sp/800-56a/rev-3/final>.
[RFC2104]
Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, , <https://doi.org/10.17487/RFC2104>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://doi.org/10.17487/RFC2119>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://doi.org/10.17487/RFC3688>.
[RFC6020]
Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://doi.org/10.17487/RFC6020>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://doi.org/10.17487/RFC6241>.
[RFC6242]
Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://doi.org/10.17487/RFC6242>.
[RFC6933]
Bierman, A., Romascanu, D., Quittek, J., and M. Chandramouli, "Entity MIB (Version 4)", RFC 6933, DOI 10.17487/RFC6933, , <https://doi.org/10.17487/RFC6933>.
[RFC6991]
Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://doi.org/10.17487/RFC6991>.
[RFC8017]
Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, , <https://doi.org/10.17487/RFC8017>.
[RFC8032]
Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, , <https://doi.org/10.17487/RFC8032>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://doi.org/10.17487/RFC8040>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://doi.org/10.17487/RFC8174>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://doi.org/10.17487/RFC8341>.
[RFC8348]
Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A YANG Data Model for Hardware Management", RFC 8348, DOI 10.17487/RFC8348, , <https://doi.org/10.17487/RFC8348>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://doi.org/10.17487/RFC8446>.
[RFC9334]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, , <https://doi.org/10.17487/RFC9334>.
[TCG-Algos]
"TCG Algorithm Registry", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG-_Algorithm_Registry_r1p32_pub.pdf>.
[TPM1.2]
TCG, "TPM 1.2 Main Specification", , <https://trustedcomputinggroup.org/resource/tpm-main-specification/>.
[TPM1.2-Commands]
"TPM Main Part 3 Commands", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Main-Part-3-Commands_v1.2_rev116_01032011.pdf>.
[TPM1.2-Structures]
"TPM Main Part 2 TPM Structures", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Main-Part-2-TPM-Structures_v1.2_rev116_01032011.pdf>.
[TPM2.0]
TCG, "TPM 2.0 Library Specification", , <https://trustedcomputinggroup.org/resource/tpm-library-specification/>.
[TPM2.0-Arch]
"Trusted Platform Module Library - Part 1: Architecture", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TCG_TPM2_r1p59_Part1_Architecture_pub.pdf>.
[TPM2.0-Key]
TCG, "TPM 2.0 Keys for Device Identity and Attestation, Rev12", , <https://trustedcomputinggroup.org/wp-content/uploads/TPM-2p0-Keys-for-Device-Identity-and-Attestation_v1_r12_pub10082021.pdf>.
[TPM2.0-Structures]
"Trusted Platform Module Library - Part 2: Structures", n.d., <https://trustedcomputinggroup.org/wp-content/uploads/TPM-Rev-2.0-Part-2-Structures-01.38.pdf>.
[UEFI-Secure-Boot]
"Unified Extensible Firmware Interface (UEFI) Specification Version 2.9 (March 2021), Section 32.1 (Secure Boot)", n.d., <https://uefi.org/sites/default/files/resources/UEFI_Spec_2_9_2021_03_18.pdf>.

5.2. Informative References

[I-D.ietf-rats-reference-interaction-models]
Birkholz, H., Eckel, M., Pan, W., and E. Voit, "Reference Interaction Models for Remote Attestation Procedures", Work in Progress, Internet-Draft, draft-ietf-rats-reference-interaction-models-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-reference-interaction-models-11>.
[IMA-Kernel-Source]
"Linux Integrity Measurement Architecture (IMA): Kernel Sourcecode", n.d., <https://github.com/torvalds/linux/blob/df0cc57e057f18e44dac8e6c18aba47ab53202f9/security/integrity/ima/>.
[NIST-915121]
"True Randomness Can't be Left to Chance: Why entropy is important for information security", n.d., <https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=915121>.
[xml-registry]
"IETF XML Registry", n.d., <https://www.iana.org/assignments/xml-registry/xml-registry.xhtml>.
[yang-parameters]
"YANG Parameters", n.d., <https://www.iana.org/assignments/yang-parameters/yang-parameters.xhtml>.

Appendix A. Integrity Measurement Architecture (IMA)

IMA extends the principles of Measured Boot [TPM2.0-Arch] and Secure Boot [UEFI-Secure-Boot] to the Linux operating system, applying it to operating system applications and files. IMA has been part of the Linux integrity subsystem of the Linux kernel since 2009 (kernel version 2.6.30). The IMA mechanism represented by the YANG module in this specification is rooted in the kernel version 5.16 [IMA-Kernel-Source]. IMA enables the protection of system integrity by collecting (commonly referred to as measuring) and storing measurements (called Claims in the context of IETF RATS) of files before execution so that these measurements can be used later, at system runtime, in remote attestation procedures. IMA acts in support of the appraisal of Evidence (which includes measurement Claims) by leveraging Reference Values stored in extended file attributes.

In support of the appraisal of Evidence, IMA maintains an ordered list (with no duplicates) of measurements in kernel-space, the Stored Measurement Log (SML), for all files that have been measured before execution since the operating system was started. Although IMA can be used without a TPM, it is typically used in conjunction with a TPM to anchor the integrity of the SML in a hardware-protected secure storage location, i.e., Platform Configuration Registers (PCRs) provided by TPMs. IMA provides the SML in both binary and ASCII representations in the Linux security file system securityfs (/sys/kernel/security/ima/).

IMA templates define the format of the SML, i.e., which fields are included in a log record. Examples are file path, file hash, user ID, group ID, file signature, and extended file attributes. IMA comes with a set of predefined template formats and also allows a custom format, i.e., a format consisting of template fields supported by IMA. Template usage is typically determined by boot arguments passed to the kernel. Alternatively, the format can also be hard-coded into custom kernels. IMA templates and fields are extensible in the kernel source code. As a result, more template fields can be added in the future.

IMA policies define which files are measured using the IMA policy language. Built-in policies can be passed as boot arguments to the kernel. Custom IMA policies can be defined once during runtime or be hard-coded into a custom kernel. If no policy is defined, no measurements are taken and IMA is effectively disabled.

A comprehensive description of the content fields in native Linux IMA TLV format can be found in Table 16 of the Canonical Event Log (CEL) specification [cel]. The CEL specification also illustrates the use of templates to enable extended or customized IMA TLV formats in Section 5.1.6.

Appendix B. IMA for Network Equipment Boot Logs

Network equipment can generally implement similar IMA-protected functions to generate measurements (Claims) about the boot process of a device and enable corresponding remote attestation. Network Equipment Boot Logs combine the measurement and logging of boot components and operating system components (executables and files) into a single log file in a format identical to the IMA format. Note that the format used for logging measurement of boot components in this scheme differs from the boot logging strategy described elsewhere in this document.

During the boot process of the network device, i.e., from BIOS to the end of the operating system and user-space, all files executed can be measured and logged in the order of their execution. When the Verifier initiates a remote attestation process (e.g., challenge-response remote attestation as defined in this document), the network equipment takes on the role of an Attester and can convey to the Verifier Claims that comprise the measurement log as well as the corresponding PCR values (Evidence) of a TPM.

The Verifier can appraise the integrity (compliance with the Reference Values) of each executed file by comparing its measured value with the Reference Value. Based on the execution order, the Verifier can compute a PCR Reference Value (by replaying the log) and compare it to the Measurement Log Claims obtained in conjunction with the PCR Evidence to assess their trustworthiness with respect to an intended operational state.

Network equipment usually executes multiple components in parallel. This holds not only during the operating system loading phase, but also even during the BIOS boot phase. With this measurement log mechanism, network equipment can take on the role of an Attester, proving to the Verifier the trustworthiness of its boot process. Using the measurement log, Verifiers can precisely identify mismatching log entries to infer potentially tampered components.

This mechanism also supports scenarios that modify files on the Attester that are subsequently executed during the boot phase (e.g., updating/patching) by simply updating the appropriate Reference Values in Reference Integrity Manifests that inform Verifiers about how an Attester is composed.

Authors' Addresses

Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Michael Eckel
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Shwetha Bhandari
ThoughtSpot
Eric Voit
Cisco Systems
Bill Sulzen
Cisco Systems
Liang Xia (Frank)
Huawei Technologies
101 Software Avenue, Yuhuatai District
Nanjing
Jiangsu, 210012
China
Tom Laffey
Hewlett Packard Enterprise
Guy C. Fedorkow
Juniper Networks
10 Technology Park Drive
Westford