A YANG Data Model for a Truststore
draft-ietf-netconf-trust-anchors-15

Document Type Active Internet-Draft (netconf WG)
Author Kent Watsen 
Last updated 2021-05-18
Replaces draft-kwatsen-netconf-trust-anchors
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NETCONF Working Group                                          K. Watsen
Internet-Draft                                           Watsen Networks
Intended status: Standards Track                             18 May 2021
Expires: 19 November 2021

                   A YANG Data Model for a Truststore
                  draft-ietf-netconf-trust-anchors-15

Abstract

   This document defines a YANG module for configuring bags of
   certificates and bags of public keys that can be referenced by other
   data models for trust.  Notifications are sent when certificates are
   about to expire.

Editorial Note (To be removed by RFC Editor)

   This draft contains placeholder values that need to be replaced with
   finalized values at the time of publication.  This note summarizes
   all of the substitutions that are needed.  No other RFC Editor
   instructions are specified elsewhere in this document.

   Artwork in this document contains shorthand references to drafts in
   progress.  Please apply the following replacements:

   *  "AAAA" --> the assigned RFC value for draft-ietf-netconf-crypto-
      types

   *  "BBBB" --> the assigned RFC value for this draft

   Artwork in this document contains placeholder values for the date of
   publication of this draft.  Please apply the following replacement:

   *  "2021-05-18" --> the publication date of this draft

   The following Appendix section is to be removed prior to publication:

   *  Appendix A.  Change Log

Status of This Memo

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

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   This Internet-Draft will expire on 19 November 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Relation to other RFCs  . . . . . . . . . . . . . . . . .   3
     1.2.  Specification Language  . . . . . . . . . . . . . . . . .   5
     1.3.  Adherence to the NMDA . . . . . . . . . . . . . . . . . .   5
   2.  The "ietf-truststore" Module  . . . . . . . . . . . . . . . .   5
     2.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   6
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  12
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  21
   3.  Support for Built-in Trust Anchors  . . . . . . . . . . . . .  29
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
     4.1.  Security of Data at Rest  . . . . . . . . . . . . . . . .  32
     4.2.  Unconstrained Public Key Usage  . . . . . . . . . . . . .  32
     4.3.  The "ietf-truststore" YANG Module . . . . . . . . . . . .  32
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
     5.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  33
     5.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  33
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  33
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  34
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  36

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     A.1.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.2.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.3.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.4.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.5.  04 to 05  . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.6.  05 to 06  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.7.  06 to 07  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.8.  07 to 08  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.9.  08 to 09  . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.10. 09 to 10  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.11. 10 to 11  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.12. 11 to 12  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.13. 12 to 13  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.14. 13 to 14  . . . . . . . . . . . . . . . . . . . . . . . .  38
     A.15. 14 to 15  . . . . . . . . . . . . . . . . . . . . . . . .  38
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  39
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   This document defines a YANG 1.1 [RFC7950] module having the
   following characteristics:

      Provide a central truststore for storing raw public keys and/or
      certificates.

      Provide support for storing named bags of raw public keys and/or
      named bags of certificates.

      Provide types that can be used to reference raw public keys or
      certificates stored in the central truststore.

      Provide groupings that enable raw public keys and certificates to
      be configured locally or as references truststore instances.

      Enable the truststore to be instantiated in other data models, in
      addition to or in lieu of the central trusttore instance.

1.1.  Relation to other RFCs

   This document presents one or more YANG modules [RFC7950] that are
   part of a collection of RFCs that work together to, ultimately,
   enable the configuration of the clients and servers of both the
   NETCONF [RFC6241] and RESTCONF [RFC8040] protocols.

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   The modules have been defined in a modular fashion to enable their
   use by other efforts, some of which are known to be in progress at
   the time of this writing, with many more expected to be defined in
   time.

   The normative dependency relationship between the various RFCs in the
   collection is presented in the below diagram.  The labels in the
   diagram represent the primary purpose provided by each RFC.
   Hyperlinks to each RFC are provided below the diagram.

                                  crypto-types
                                    ^      ^
                                   /        \
                                  /          \
                         truststore         keystore
                          ^     ^             ^  ^
                          |     +---------+   |  |
                          |               |   |  |
                          |      +------------+  |
   tcp-client-server      |     /         |      |
      ^    ^        ssh-client-server     |      |
      |    |           ^            tls-client-server
      |    |           |              ^     ^        http-client-server
      |    |           |              |     |                 ^
      |    |           |        +-----+     +---------+       |
      |    |           |        |                     |       |
      |    +-----------|--------|--------------+      |       |
      |                |        |              |      |       |
      +-----------+    |        |              |      |       |
                  |    |        |              |      |       |
                  |    |        |              |      |       |
               netconf-client-server       restconf-client-server

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   +=======================+===========================================+
   |Label in Diagram       | Originating RFC                           |
   +=======================+===========================================+
   |crypto-types           | [I-D.ietf-netconf-crypto-types]           |
   +-----------------------+-------------------------------------------+
   |truststore             | [I-D.ietf-netconf-trust-anchors]          |
   +-----------------------+-------------------------------------------+
   |keystore               | [I-D.ietf-netconf-keystore]               |
   +-----------------------+-------------------------------------------+
   |tcp-client-server      | [I-D.ietf-netconf-tcp-client-server]      |
   +-----------------------+-------------------------------------------+
   |ssh-client-server      | [I-D.ietf-netconf-ssh-client-server]      |
   +-----------------------+-------------------------------------------+
   |tls-client-server      | [I-D.ietf-netconf-tls-client-server]      |
   +-----------------------+-------------------------------------------+
   |http-client-server     | [I-D.ietf-netconf-http-client-server]     |
   +-----------------------+-------------------------------------------+
   |netconf-client-server  | [I-D.ietf-netconf-netconf-client-server]  |
   +-----------------------+-------------------------------------------+
   |restconf-client-server | [I-D.ietf-netconf-restconf-client-server] |
   +-----------------------+-------------------------------------------+

                       Table 1: Label to RFC Mapping

1.2.  Specification Language

   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.

1.3.  Adherence to the NMDA

   This document is compliant with the Network Management Datastore
   Architecture (NMDA) [RFC8342].  For instance, trust anchors installed
   during manufacturing (e.g., for trusted well-known services), are
   expected to appear in <operational> (see Section 3).

2.  The "ietf-truststore" Module

   This section defines a YANG 1.1 [RFC7950] module that defines a
   "truststore" and groupings supporting downstream modules to reference
   the truststore or have locally-defined definitions.

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   This section defines a YANG 1.1 [RFC7950] module called "ietf-
   truststore".  A high-level overview of the module is provided in
   Section 2.1.  Examples illustrating the module's use are provided in
   Examples (Section 2.2).  The YANG module itself is defined in
   Section 2.3.

2.1.  Data Model Overview

   This section provides an overview of the "ietf-truststore" module in
   terms of its features, typedefs, groupings, and protocol-accessible
   nodes.

2.1.1.  Features

   The following diagram lists all the "feature" statements defined in
   the "ietf-truststore" module:

   Features:
     +-- central-truststore-supported
     +-- local-definitions-supported
     +-- certificates
     +-- public-keys

      |  The diagram above uses syntax that is similar to but not
      |  defined in [RFC8340].

2.1.2.  Typedefs

   The following diagram lists the "typedef" statements defined in the
   "ietf-truststore" module:

   Typedefs:
     leafref
       +-- certificate-bag-ref
       +-- certificate-ref
       +-- public-key-bag-ref
       +-- public-key-ref

      |  The diagram above uses syntax that is similar to but not
      |  defined in [RFC8340].

   Comments:

   *  All of the typedefs defined in the "ietf-truststore" module extend
      the base "leafref" type defined in [RFC7950].

   *  The leafrefs refer to certificates, public keys, and bags in the
      central truststore, when this module is implemented.

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   *  These typedefs are provided as an aid to downstream modules that
      import the "ietf-truststore" module.

2.1.3.  Groupings

   The "ietf-truststore" module defines the following "grouping"
   statements:

   *  local-or-truststore-certs-grouping
   *  local-or-truststore-public-keys-grouping
   *  truststore-grouping

   Each of these groupings are presented in the following subsections.

2.1.3.1.  The "local-or-truststore-certs-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "local-or-
   truststore-certs-grouping" grouping:

     grouping local-or-truststore-certs-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- certificate* [name]
          |        +-- name?                            string
          |        +---u ct:trust-anchor-cert-grouping
          +--:(truststore) {central-truststore-supported,certificates}?
             +-- truststore-reference?   ts:certificate-bag-ref

   Comments:

   *  The "local-or-truststore-certs-grouping" grouping is provided
      soley as convenience to downstream modules that wish to offer an
      option whether a bag of certificates can be defined locally or as
      a reference to a bag in the truststore.

   *  A "choice" statement is used to expose the various options.  Each
      option is enabled by a "feature" statement.  Additional "case"
      statements MAY be augmented in if, e.g., there is a need to
      reference a bag in an alternate location.

   *  For the "local-definition" option, the "certificate" node uses the
      "trust-anchor-cert-grouping" grouping discussed in Section 2.1.4.7
      of [I-D.ietf-netconf-crypto-types].

   *  For the "truststore" option, the "truststore-reference" is an
      instance of the "certificate-bag-ref" discussed in Section 2.1.2.

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2.1.3.2.  The "local-or-truststore-public-keys-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "local-or-
   truststore-public-keys-grouping" grouping:

     grouping local-or-truststore-public-keys-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- public-key* [name]
          |        +-- name?                     string
          |        +---u ct:public-key-grouping
          +--:(truststore) {central-truststore-supported,public-keys}?
             +-- truststore-reference?   ts:public-key-bag-ref

   Comments:

   *  The "local-or-truststore-public-keys-grouping" grouping is
      provided soley as convenience to downstream modules that wish to
      offer an option whether a bag of public keys can be defined
      locally or as a reference to a bag in the truststore.

   *  A "choice" statement is used to expose the various options.  Each
      option is enabled by a "feature" statement.  Additional "case"
      statements MAY be augmented in if, e.g., there is a need to
      reference a bag in an alternate location.

   *  For the "local-definition" option, the "public-key" node uses the
      "public-key-grouping" grouping discussed in Section 2.1.4.4 of
      [I-D.ietf-netconf-crypto-types].

   *  For the "truststore" option, the "truststore-reference" is an
      instance of the "certificate-bag-ref" discussed in Section 2.1.2.

2.1.3.3.  The "truststore-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "truststore-
   grouping" grouping:

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     grouping truststore-grouping
       +-- certificate-bags {certificates}?
       |  +-- certificate-bag* [name]
       |     +-- name?          string
       |     +-- description?   string
       |     +-- certificate* [name]
       |        +-- name?                            string
       |        +---u ct:trust-anchor-cert-grouping
       +-- public-key-bags {public-keys}?
          +-- public-key-bag* [name]
             +-- name?          string
             +-- description?   string
             +-- public-key* [name]
                +-- name?                     string
                +---u ct:public-key-grouping

   Comments:

   *  The "truststore-grouping" grouping defines a truststore instance
      as being composed of certificates and/or public keys, both of
      which are enabled by "feature" statements.  The structure
      supporting certificates and public keys is essentially the same,
      having an outer list of "bags" containing in inner list of objects
      (certificates or public keys).  The bags enable trust anchors
      serving a common purpose to be grouped and referenced together.

   *  For certificates, each certificate is defined by the "trust-
      anchor-cert-grouping" grouping Section 2.1.4.7 of
      [I-D.ietf-netconf-crypto-types].  Thus the "cert-data" node is a
      CMS structure that can be composed of a chain of one or more
      certificates.  Additionally, the "certificate-expiration"
      notification enables the server to alert clients when certificates
      are nearing or have already expired.

   *  For public keys, each public key is defined by the "public-key-
      grouping" grouping Section 2.1.4.4 of
      [I-D.ietf-netconf-crypto-types].  Thus the "public-key" node can
      be one of any number of structures specified by the "public-key-
      format" identity node.

2.1.4.  Protocol-accessible Nodes

   The following tree diagram [RFC8340] lists all the protocol-
   accessible nodes defined in the "ietf-truststore" module, without
   expanding the "grouping" statements:

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   module: ietf-truststore
     +--rw truststore
        +---u truststore-grouping

     grouping local-or-truststore-certs-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- certificate* [name]
          |        +-- name?                            string
          |        +---u ct:trust-anchor-cert-grouping
          +--:(truststore) {central-truststore-supported,certificates}?
             +-- truststore-reference?   ts:certificate-bag-ref
     grouping local-or-truststore-public-keys-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- public-key* [name]
          |        +-- name?                     string
          |        +---u ct:public-key-grouping
          +--:(truststore) {central-truststore-supported,public-keys}?
             +-- truststore-reference?   ts:public-key-bag-ref
     grouping truststore-grouping
       +-- certificate-bags {certificates}?
       |  +-- certificate-bag* [name]
       |     +-- name?          string
       |     +-- description?   string
       |     +-- certificate* [name]
       |        +-- name?                            string
       |        +---u ct:trust-anchor-cert-grouping
       +-- public-key-bags {public-keys}?
          +-- public-key-bag* [name]
             +-- name?          string
             +-- description?   string
             +-- public-key* [name]
                +-- name?                     string
                +---u ct:public-key-grouping

   The following tree diagram [RFC8340] lists all the protocol-
   accessible nodes defined in the "ietf-truststore" module, with all
   "grouping" statements expanded, enabling the truststore's full
   structure to be seen:

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   module: ietf-truststore
     +--rw truststore
        +--rw certificate-bags {certificates}?
        |  +--rw certificate-bag* [name]
        |     +--rw name           string
        |     +--rw description?   string
        |     +--rw certificate* [name]
        |        +--rw name                      string
        |        +--rw cert-data                 trust-anchor-cert-cms
        |        +---n certificate-expiration
        |                {certificate-expiration-notification}?
        |           +-- expiration-date    yang:date-and-time
        +--rw public-key-bags {public-keys}?
           +--rw public-key-bag* [name]
              +--rw name           string
              +--rw description?   string
              +--rw public-key* [name]
                 +--rw name                 string
                 +--rw public-key-format    identityref
                 +--rw public-key           binary

     grouping local-or-truststore-certs-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- certificate* [name]
          |        +-- name?                     string
          |        +-- cert-data                 trust-anchor-cert-cms
          |        +---n certificate-expiration
          |                {certificate-expiration-notification}?
          |           +-- expiration-date    yang:date-and-time
          +--:(truststore) {central-truststore-supported,certificates}?
             +-- truststore-reference?   ts:certificate-bag-ref
     grouping local-or-truststore-public-keys-grouping
       +-- (local-or-truststore)
          +--:(local) {local-definitions-supported}?
          |  +-- local-definition
          |     +-- public-key* [name]
          |        +-- name?                string
          |        +-- public-key-format    identityref
          |        +-- public-key           binary
          +--:(truststore) {central-truststore-supported,public-keys}?
             +-- truststore-reference?   ts:public-key-bag-ref
     grouping truststore-grouping
       +-- certificate-bags {certificates}?
       |  +-- certificate-bag* [name]
       |     +-- name?          string
       |     +-- description?   string

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       |     +-- certificate* [name]
       |        +-- name?                     string
       |        +-- cert-data                 trust-anchor-cert-cms
       |        +---n certificate-expiration
       |                {certificate-expiration-notification}?
       |           +-- expiration-date    yang:date-and-time
       +-- public-key-bags {public-keys}?
          +-- public-key-bag* [name]
             +-- name?          string
             +-- description?   string
             +-- public-key* [name]
                +-- name?                string
                +-- public-key-format    identityref
                +-- public-key           binary

   Comments:

   *  Protocol-accessible nodes are those nodes that are accessible when
      the module is "implemented", as described in Section 5.6.5 of
      [RFC7950].

   *  The protcol-accessible nodes for the "ietf-truststore" module are
      an instance of the "truststore-grouping" grouping discussed in
      Section 2.1.3.3.

   *  The reason for why the "truststore-grouping" exists separate from
      the protocol-accessible nodes definition is to enable instances of
      the truststore to be instantiated in other locations, as may be
      needed or desired by some modules.

2.2.  Example Usage

   The examples in this section are encoded using XML, such as might be
   the case when using the NETCONF protocol.  Other encodings MAY be
   used, such as JSON when using the RESTCONF protocol.

2.2.1.  A Truststore Instance

   This section presents an example illustrating trust anchors in
   <intended>, as per Section 2.1.4.  Please see Section 3 for an
   example illustrating built-in values in <operational>.

   The example contained in this section defines eight bags of trust
   anchors.  There are four certificate-based bags and four public key
   based bags.  The following diagram provides an overview of the
   contents in the example:

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   Certificate Bags
     +-- Trust anchor certs for authenticating a set of remote servers
     +-- End entity certs for authenticating a set of remote servers
     +-- Trust anchor certs for authenticating a set of remote clients
     +-- End entity certs for authenticating a set of remote clients

   Public Key Bags
     +-- SSH keys to authenticate a set of remote SSH server
     +-- SSH keys to authenticate a set of remote SSH clients
     +-- Raw public keys to authenticate a set of remote SSH server
     +-- Raw public keys to authenticate a set of remote SSH clients

   Following is the full example:

   <truststore
     xmlns="urn:ietf:params:xml:ns:yang:ietf-truststore"
     xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">

     <!-- A bag of Certificate Bags -->
     <certificate-bags>

       <!-- Trust Anchor Certs for Authenticating Servers -->
       <certificate-bag>
         <name>trusted-server-ca-certs</name>
         <description>
           Trust anchors (i.e. CA certs) used to authenticate server
           certificates.  A server certificate is authenticated if its
           end-entity certificate has a chain of trust to one of these
           certificates.
         </description>
         <certificate>
           <name>Server Cert Issuer #1</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>Server Cert Issuer #2</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

       <!-- End Entity Certs for Authenticating Servers -->
       <certificate-bag>
         <name>trusted-server-ee-certs</name>
         <description>
           Specific end-entity certificates used to authenticate server
           certificates.  A server certificate is authenticated if its
           end-entity certificate is an exact match to one of these
           certificates.

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         </description>
         <certificate>
           <name>My Application #1</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>My Application #2</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

       <!-- Trust Anchor Certs for Authenticating Clients -->
       <certificate-bag>
         <name>trusted-client-ca-certs</name>
         <description>
           Trust anchors (i.e. CA certs) used to authenticate client
           certificates.  A client certificate is authenticated if its
           end-entity certificate has a chain of trust to one of these
           certificates.
         </description>
         <certificate>
           <name>Client Identity Issuer #1</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>Client Identity Issuer #2</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

       <!-- End Entity Certs for Authenticating Clients -->
       <certificate-bag>
         <name>trusted-client-ee-certs</name>
         <description>
           Specific end-entity certificates used to authenticate client
           certificates.  A client certificate is authenticated if its
           end-entity certificate is an exact match to one of these
           certificates.
         </description>
         <certificate>
           <name>George Jetson</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>Fred Flintstone</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

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     </certificate-bags>

     <!-- A List of Public Key Bags -->
     <public-key-bags>

       <!-- Public Keys for Authenticating SSH Servers -->
       <public-key-bag>
         <name>trusted-ssh-public-keys</name>
         <description>
           Specific SSH public keys used to authenticate SSH server
           public keys.  An SSH server public key is authenticated if
           its public key is an exact match to one of these public keys.

           This list of SSH public keys is analogous to OpenSSH's
           "/etc/ssh/ssh_known_hosts" file.
         </description>
         <public-key>
           <name>corp-fw1</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
         <public-key>
           <name>corp-fw2</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </public-key-bag>

       <!-- SSH Public Keys for Authenticating Application A -->
       <public-key-bag>
         <name>SSH Public Keys for Application A</name>
         <description>
           SSH public keys used to authenticate application A's SSH
           public keys.  An SSH public key is authenticated if it
           is an exact match to one of these public keys.
         </description>
         <public-key>
           <name>Application Instance #1</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
         <public-key>

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           <name>Application Instance #2</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </public-key-bag>

       <!-- Raw Public Keys for TLS Servers -->
       <public-key-bag>
         <name>Raw Public Keys for TLS Servers</name>
         <public-key>
           <name>Raw Public Key #1</name>
           <public-key-format>
             ct:subject-public-key-info-format</public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
         <public-key>
           <name>Raw Public Key #2</name>
           <public-key-format>
             ct:subject-public-key-info-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </public-key-bag>

       <!-- Raw Public Keys for TLS Clients -->
       <public-key-bag>
         <name>Raw Public Keys for TLS Clients</name>
         <public-key>
           <name>Raw Public Key #1</name>
           <public-key-format>
             ct:subject-public-key-info-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
         <public-key>
           <name>Raw Public Key #2</name>
           <public-key-format>
             ct:subject-public-key-info-format
         </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </public-key-bag>
     </public-key-bags>
   </truststore>

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2.2.2.  A Certificate Expiration Notification

   The following example illustrates the "certificate-expiration"
   notification (per Section 2.1.4.6 of [I-D.ietf-netconf-crypto-types])
   for a certificate configured in the truststore in Section 2.2.1.

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   <notification
     xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
     <eventTime>2018-05-25T00:01:00Z</eventTime>
     <truststore xmlns="urn:ietf:params:xml:ns:yang:ietf-truststore">
       <certificate-bags>
         <certificate-bag>
           <name>trusted-client-ee-certs</name>
           <certificate>
             <name>George Jetson</name>
             <certificate-expiration>
               <expiration-date>2018-08-05T14:18:53-05:00</expiration-d\
   ate>
             </certificate-expiration>
           </certificate>
         </certificate-bag>
       </certificate-bags>
     </truststore>
   </notification>

2.2.3.  The "Local or Truststore" Groupings

   This section illustrates the various "local-or-truststore" groupings
   defined in the "ietf-truststore" module, specifically the "local-or-
   truststore-certs-grouping" (Section 2.1.3.1) and "local-or-
   truststore-public-keys-grouping" (Section 2.1.3.2) groupings.

   These examples assume the existence of an example module called "ex-
   truststore-usage" having the namespace "http://example.com/ns/
   example-truststore-usage".

   The ex-truststore-usage module is first presented using tree diagrams
   [RFC8340], followed by an instance example illustrating all the
   "local-or-truststore" groupings in use, followed by the YANG module
   itself.

   The following tree diagram illustrates "ex-truststore-usage" without
   expanding the "grouping" statements:

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   module: ex-truststore-usage
     +--rw truststore-usage
        +--rw cert* [name]
        |  +--rw name                                     string
        |  +---u ts:local-or-truststore-certs-grouping
        +--rw public-key* [name]
           +--rw name                                           string
           +---u ts:local-or-truststore-public-keys-grouping

   The following tree diagram illustrates the "ex-truststore-usage"
   module, with all "grouping" statements expanded, enabling the
   truststore's full structure to be seen:

   module: ex-truststore-usage
     +--rw truststore-usage
        +--rw cert* [name]
        |  +--rw name                          string
        |  +--rw (local-or-truststore)
        |     +--:(local) {local-definitions-supported}?
        |     |  +--rw local-definition
        |     |     +--rw certificate* [name]
        |     |        +--rw name                      string
        |     |        +--rw cert-data
        |     |        |       trust-anchor-cert-cms
        |     |        +---n certificate-expiration
        |     |                {certificate-expiration-notification}?
        |     |           +-- expiration-date    yang:date-and-time
        |     +--:(truststore)
        |              {central-truststore-supported,certificates}?
        |        +--rw truststore-reference?   ts:certificate-bag-ref
        +--rw public-key* [name]
           +--rw name                          string
           +--rw (local-or-truststore)
              +--:(local) {local-definitions-supported}?
              |  +--rw local-definition
              |     +--rw public-key* [name]
              |        +--rw name                 string
              |        +--rw public-key-format    identityref
              |        +--rw public-key           binary
              +--:(truststore)
                       {central-truststore-supported,public-keys}?
                 +--rw truststore-reference?   ts:public-key-bag-ref

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   The following example provides two equivalent instances of each
   grouping, the first being a reference to a truststore and the second
   being locally-defined.  The instance having a reference to a
   truststore is consistent with the truststore defined in
   Section 2.2.1.  The two instances are equivalent, as the locally-
   defined instance example contains the same values defined by the
   truststore instance referenced by its sibling example.

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   <truststore-usage
     xmlns="http://example.com/ns/example-truststore-usage"
     xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">

     <!-- The following two equivalent examples illustrate   -->
     <!-- the "local-or-truststore-certs-grouping" grouping: -->

     <cert>
       <name>example 1a</name>
       <truststore-reference>trusted-client-ca-certs</truststore-refere\
   nce>
     </cert>

     <cert>
       <name>example 1b</name>
       <local-definition>
         <name>my-trusted-client-ca-certs</name>
         <certificate>
           <name>Client Identity Issuer #1</name>
           <cert>base64encodedvalue==</cert>
         </certificate>
         <certificate>
           <name>Client Identity Issuer #2</name>
           <cert>base64encodedvalue==</cert>
         </certificate>
       </local-definition>
     </cert>

     <!-- The following two equivalent examples illustrate the -->
     <!-- "local-or-truststore-public-keys-grouping" grouping: -->

     <public-key>
       <name>example 2a</name>
       <truststore-reference>trusted-ssh-public-keys</truststore-refere\
   nce>
     </public-key>

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     <public-key>
       <name>example 2b</name>
       <local-definition>
         <name>trusted-ssh-public-keys</name>
         <public-key>
           <name>corp-fw1</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
         <public-key>
           <name>corp-fw2</name>
           <public-key-format>
             ct:ssh-public-key-format
           </public-key-format>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </local-definition>
     </public-key>

   </truststore-usage>

   Following is the "ex-truststore-usage" module's YANG definition:

   module ex-truststore-usage {
     yang-version 1.1;
     namespace "http://example.com/ns/example-truststore-usage";
     prefix etu;

     import ietf-truststore {
       prefix ts;
       reference
         "RFC BBBB: A YANG Data Model for a Truststore";
     }

     organization
       "Example Corporation";

     contact
       "Author: YANG Designer <mailto:yang.designer@example.com>";

     description
       "This module illustrates notable groupings defined in
        the 'ietf-truststore' module.";

     revision 2021-05-18 {
       description

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         "Initial version";
       reference
         "RFC BBBB: A YANG Data Model for a Truststore";
     }

     container truststore-usage {
       description
         "An illustration of the various truststore groupings.";
       list cert {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this cert.";
         }
         uses ts:local-or-truststore-certs-grouping;
         description
           "An cert that may be configured locally or be
            a reference to a cert in the truststore.";
       }
       list public-key {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this cert.";
         }
         uses ts:local-or-truststore-public-keys-grouping;
         description
           "An public key that may be configured locally or be
            a reference to a public key in the truststore.";
       }
     }
   }

2.3.  YANG Module

   This YANG module imports modules from [RFC8341] and
   [I-D.ietf-netconf-crypto-types].

   <CODE BEGINS> file "ietf-truststore@2021-05-18.yang"

   module ietf-truststore {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-truststore";
     prefix ts;

     import ietf-netconf-acm {

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       prefix nacm;
       reference
         "RFC 8341: Network Configuration Access Control Model";
     }

     import ietf-crypto-types {
       prefix ct;
       reference
         "RFC AAAA: YANG Data Types and Groupings for Cryptography";
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group";

     contact
       "WG Web  : <http://datatracker.ietf.org/wg/netconf/>
        WG List : <mailto:netconf@ietf.org>
        Author  : Kent Watsen <kent+ietf@watsen.net>";

     description
       "This module defines a 'truststore' to centralize management
        of trust anchors including certificates and public keys.

        Copyright (c) 2021 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 BBBB
        (https://www.rfc-editor.org/info/rfcBBBB); 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 2021-05-18 {
       description
         "Initial version";
       reference

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         "RFC BBBB: A YANG Data Model for a Truststore";
     }

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

     feature central-truststore-supported {
       description
         "The 'central-truststore-supported' feature indicates that
          the server supports the truststore (i.e., implements the
          'ietf-truststore' module).";
     }

     feature local-definitions-supported {
       description
         "The 'local-definitions-supported' feature indicates that
          the server supports locally-defined trust anchors.";
     }

     feature certificates {
       description
         "The 'certificates' feature indicates that the server
          implements the /truststore/certificate-bags subtree.";
     }

     feature public-keys {
       description
         "The 'public-keys' feature indicates that the server
          implements the /truststore/public-key-bags subtree.";
     }

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

     typedef certificate-bag-ref {
       type leafref {
         path "/ts:truststore/ts:certificate-bags/"
            + "ts:certificate-bag/ts:name";
       }
       description
         "This typedef defines a reference to a certificate bag
          in the truststore, when this module is implemented.";
     }

     typedef certificate-ref {
       type leafref {

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         path "/ts:truststore/ts:certificate-bags/ts:certificate-bag"
            + "[ts:name = current()/../ts:certificate-bag]/"
            + "ts:certificate/ts:name";
       }
       description
         "This typedef defines a reference to a specific certificate
          in a certificate bag in the truststore, when this module
          is implemented.  This typedef requires that there exist a
          sibling 'leaf' node called 'certificate-bag' that SHOULD
          have the typedef 'certificate-bag-ref'.";
     }

     typedef public-key-bag-ref {
       type leafref {
         path "/ts:truststore/ts:public-key-bags/"
            + "ts:public-key-bag/ts:name";
       }
       description
         "This typedef defines a reference to a public key bag
          in the truststore, when this module is implemented.";
     }

     typedef public-key-ref {
       type leafref {
         path "/ts:truststore/ts:public-key-bags/ts:public-key-bag"
            + "[ts:name = current()/../ts:public-key-bag]/"
            + "ts:public-key/ts:name";
       }
       description
         "This typedef defines a reference to a specific public key
          in a public key bag in the truststore, when this module is
          implemented.  This typedef requires that there exist a
          sibling 'leaf' node called 'public-key-bag' that SHOULD
          have the typedef 'public-key-bag-ref'.";
     }

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

     grouping local-or-truststore-certs-grouping {
       description
         "A grouping that allows the certificates to be either
          configured locally, within the using data model, or be a
          reference to a certificate bag stored in the truststore.

          Servers that do not 'implement' this module, and hence
          'central-truststore-supported' is not defined, SHOULD

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          augment in custom 'case' statements enabling references
          to the alternate truststore locations.";
       choice local-or-truststore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the truststore.";
         case local {
           if-feature "local-definitions-supported";
           container local-definition {
             description
               "A container for locally configured trust anchor
                certificates.";
             list certificate {
               key "name";
               min-elements 1;
               description
                 "A trust anchor certificate.";
               leaf name {
                 type string;
                 description
                   "An arbitrary name for this certificate.";
               }
               uses ct:trust-anchor-cert-grouping {
                 refine "cert-data" {
                   mandatory true;
                 }
               }
             }
           }
         }
         case truststore {
           if-feature "central-truststore-supported";
           if-feature "certificates";
           leaf truststore-reference {
             type ts:certificate-bag-ref;
             description
               "A reference to a certificate bag that exists in the
                truststore, when this module is implemented.";
           }
         }
       }
     }

     grouping local-or-truststore-public-keys-grouping {
       description
         "A grouping that allows the public keys to be either

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          configured locally, within the using data model, or be a
          reference to a public key bag stored in the truststore.

          Servers that do not 'implement' this module, and hence
          'central-truststore-supported' is not defined, SHOULD
          augment in custom 'case' statements enabling references
          to the alternate truststore locations.";
       choice local-or-truststore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the truststore.";
         case local {
           if-feature "local-definitions-supported";
           container local-definition {
             description
               "A container to hold local public key definitions.";
             list public-key {
               key "name";
               description
                 "A public key definition.";
               leaf name {
                 type string;
                 description
                   "An arbitrary name for this public key.";
               }
               uses ct:public-key-grouping;
             }
           }
         }
         case truststore {
           if-feature "central-truststore-supported";
           if-feature "public-keys";
           leaf truststore-reference {
             type ts:public-key-bag-ref;
             description
               "A reference to a bag of public keys that exists
                in the truststore, when this module is implemented.";
           }
         }
       }
     }

     grouping truststore-grouping {
       description
         "A grouping definition that enables use in other contexts.
          Where used, implementations MUST augment new 'case'

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          statements into the various local-or-truststore 'choice'
          statements to supply leafrefs to the model-specific
          location(s).";
       container certificate-bags {
         nacm:default-deny-write;
         if-feature "certificates";
         description
           "A collection of certificate bags.";
         list certificate-bag {
           key "name";
           description
             "A bag of certificates.  Each bag of certificates SHOULD
              be for a specific purpose.  For instance, one bag could
              be used to authenticate a specific set of servers, while
              another could be used to authenticate a specific set of
              clients.";
           leaf name {
             type string;
             description
               "An arbitrary name for this bag of certificates.";
           }
           leaf description {
             type string;
             description
               "A description for this bag of certificates.  The
                intended purpose for the bag SHOULD be described.";
           }
           list certificate {
             key "name";
             description
               "A trust anchor certificate.";
             leaf name {
               type string;
               description
                 "An arbitrary name for this certificate.";
             }
             uses ct:trust-anchor-cert-grouping {
               refine "cert-data" {
                 mandatory true;
               }
             }
           }
         }
       }
       container public-key-bags {
         nacm:default-deny-write;
         if-feature "public-keys";
         description

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           "A collection of public key bags.";
         list public-key-bag {
           key "name";
           description
             "A bag of public keys.  Each bag of keys SHOULD be for
              a specific purpose.  For instance, one bag could be used
              authenticate a specific set of servers, while another
              could be used to authenticate a specific set of clients.";
           leaf name {
             type string;
             description
               "An arbitrary name for this bag of public keys.";
           }
           leaf description {
             type string;
             description
               "A description for this bag public keys.  The
                intended purpose for the bag SHOULD be described.";
           }
           list public-key {
             key "name";
             description
               "A public key.";
             leaf name {
               type string;
               description
                 "An arbitrary name for this public key.";
             }
             uses ct:public-key-grouping;
           }
         }
       }
     }

     /*********************************/
     /*   Protocol accessible nodes   */
     /*********************************/

     container truststore {
       nacm:default-deny-write;
       description
         "The truststore contains bags of certificates and
          public keys.";
       uses truststore-grouping;
     }
   }

   <CODE ENDS>

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3.  Support for Built-in Trust Anchors

   In some implementations, a server may define some built-in trust
   anchors.  For instance, there may be built-in trust anchors enabling
   the server to securely connect to well-known services (e.g., an SZTP
   [RFC8572] bootstrap server) or public CA certificates to connect to
   arbitrary services using public PKI.

   Built-in trust anchors are expected to be set by a vendor-specific
   process.  Any ability for operators to modify built-in trust anchors
   is outside the scope of this document.

   As built-in trust anchors are provided by the server, they are
   present in <operational>.  The example below illustrates what the
   truststore in <operational> might look like for a server in its
   factory default state.

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   <truststore
     xmlns="urn:ietf:params:xml:ns:yang:ietf-truststore"
     xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types"
     xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
     or:origin="or:intended">
     <certificate-bags>

       <certificate-bag or:origin="or:system">
         <name>Built-In Manufacturer Trust Anchor Certificates</name>
         <description>
           Certificates built into the device for authenticating
           manufacturer-signed objects, such as TLS server certificates,
           vouchers, etc.
         </description>
         <certificate>
           <name>Manufacturer Root CA Cert</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

       <certificate-bag or:origin="or:system">
         <name>Built-In Public Trust Anchor Certificates</name>
         <description>
           Certificates built into the device for authenticating
           certificates issued by public certificate authorities,
           such as the end-entity certificate for web servers.
         </description>
         <certificate>
           <name>Public Root CA Cert 1</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>Public Root CA Cert 2</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
         <certificate>
           <name>Public Root CA Cert 3</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

     </certificate-bags>
   </truststore>

   In order for the built-in bags of trust anchors and/or their trust
   anchors to be referenced by configuration, they MUST first be copied
   into <running>.

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   The built-in bags and/or their trust anchors MUST be copied into
   <running> using the same "key" values if it is desired for the server
   to maintain/update them (e.g., a software update may update a bag of
   trusted public CA certificates used for TLS-client connections).

   Built-in bags and/or their trust anchors MAY be copied into other
   parts of the configuration but, by doing so, they lose their
   association to the built-in entries and any assurances afforded by
   knowing they are/were built-in.

   The built-in bags and/or their trust anchors are immutable by
   configuration operations.  Servers MUST ignore attempts to modify any
   aspect of built-in bags and/or their trust anchors from <running>.

   The following example illustrates how a single built-in public CA
   certificate from the previous example has been propagated to
   <running>:

   <truststore
     xmlns="urn:ietf:params:xml:ns:yang:ietf-truststore"
     xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
     <certificate-bags>

       <certificate-bag>
         <name>Built-In Public Trust Anchor Certificates</name>
         <description>
           Certificates built into the device for authenticating
           certificates issued by public certificate authorities,
           such as the end-entity certificate for web servers.

           Only the subset of the certificates that are referenced
           by other configuration nodes need to be copied.  For
           instance, only "Public Root CA Cert 3" is present here.

           No new certificates can be added, nor existing certificate
           values changed.  Missing certificates have no effect on
           "operational" when the configuration is applied.
         </description>
         <certificate>
           <name>Public Root CA Cert 3</name>
           <cert-data>base64encodedvalue==</cert-data>
         </certificate>
       </certificate-bag>

     </certificate-bags>
   </truststore>

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4.  Security Considerations

4.1.  Security of Data at Rest

   The YANG module defined in this document defines a mechanism called a
   "truststore" that, by its name, suggests that its contents are
   protected from unauthorized modification.

   Security controls for the API (i.e., data in motion) are discussed in
   Section 4.3, but controls for the data at rest cannot be specified by
   the YANG module.

   In order to satisfy the expectations of a "truststore", it is
   RECOMMENDED that implementations ensure that the truststore contents
   are protected from unauthorized modifications when at rest.

4.2.  Unconstrained Public Key Usage

   This module enables the configuration of public keys without
   constraints on their usage, e.g., what operations the key is allowed
   to be used for (encryption, verification, both).

   This module also enables the configuration of certificates, where
   each certificate may constrain the usage of the public key according
   to local policy.

4.3.  The "ietf-truststore" YANG Module

   The YANG module defined in this document is designed to be accessed
   via YANG based management protocols, such as NETCONF [RFC6241] and
   RESTCONF [RFC8040].  Both of these protocols have mandatory-to-
   implement secure transport layers (e.g., SSH, TLS) with mutual
   authentication.

   The NETCONF access control model (NACM) [RFC8341] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

   None of the readable data nodes defined in this YANG module are
   considered sensitive or vulnerable in network environments.  The NACM
   "default-deny-all" extension has not been set for any data nodes
   defined in this module.

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   All of the writable data nodes defined by this module, both in the
   "grouping" statements as well as the protocol-accessible "truststore"
   instance, may be considered sensitive or vulnerable in some network
   environments.  For instance, any modification to a trust anchor or
   reference to a trust anchor may dramatically alter the implemented
   security policy.  For this reason, the NACM extension "default-deny-
   write" has been set for all data nodes defined in this module.

   This module does not define any "rpc" or "action" statements, and
   thus the security considerations for such is not provided here.

5.  IANA Considerations

5.1.  The "IETF XML" Registry

   This document registers one URI in the "ns" subregistry of the IETF
   XML Registry [RFC3688].  Following the format in [RFC3688], the
   following registration is requested:

      URI: urn:ietf:params:xml:ns:yang:ietf-truststore
      Registrant Contact: The IESG
      XML: N/A, the requested URI is an XML namespace.

5.2.  The "YANG Module Names" Registry

   This document registers one YANG module in the YANG Module Names
   registry [RFC6020].  Following the format in [RFC6020], the following
   registration is requested:

      name:         ietf-truststore
      namespace:    urn:ietf:params:xml:ns:yang:ietf-truststore
      prefix:       ts
      reference:    RFC BBBB

6.  References

6.1.  Normative References

   [I-D.ietf-netconf-crypto-types]
              Watsen, K., "YANG Data Types and Groupings for
              Cryptography", Work in Progress, Internet-Draft, draft-
              ietf-netconf-crypto-types-19, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-crypto-
              types-19>.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

6.2.  Informative References

   [I-D.ietf-netconf-http-client-server]
              Watsen, K., "YANG Groupings for HTTP Clients and HTTP
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-http-client-server-06, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-http-
              client-server-06>.

   [I-D.ietf-netconf-keystore]
              Watsen, K., "A YANG Data Model for a Keystore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-keystore-21,
              10 February 2021, <https://tools.ietf.org/html/draft-ietf-
              netconf-keystore-21>.

   [I-D.ietf-netconf-netconf-client-server]
              Watsen, K., "NETCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-netconf-
              client-server-22, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-netconf-
              client-server-22>.

   [I-D.ietf-netconf-restconf-client-server]
              Watsen, K., "RESTCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-restconf-
              client-server-22, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-restconf-
              client-server-22>.

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   [I-D.ietf-netconf-ssh-client-server]
              Watsen, K., "YANG Groupings for SSH Clients and SSH
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-ssh-client-server-23, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-ssh-
              client-server-23>.

   [I-D.ietf-netconf-tcp-client-server]
              Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
              and TCP Servers", Work in Progress, Internet-Draft, draft-
              ietf-netconf-tcp-client-server-09, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-tcp-
              client-server-09>.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K., "YANG Groupings for TLS Clients and TLS
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-tls-client-server-23, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-tls-
              client-server-23>.

   [I-D.ietf-netconf-trust-anchors]
              Watsen, K., "A YANG Data Model for a Truststore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-trust-
              anchors-14, 10 February 2021,
              <https://tools.ietf.org/html/draft-ietf-netconf-trust-
              anchors-14>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/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, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

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   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,
              <https://www.rfc-editor.org/info/rfc8572>.

Appendix A.  Change Log

   This section is to be removed before publishing as an RFC.

A.1.  00 to 01

   *  Added features "x509-certificates" and "ssh-host-keys".

   *  Added nacm:default-deny-write to "trust-anchors" container.

A.2.  01 to 02

   *  Switched "list pinned-certificate" to use the "trust-anchor-cert-
      grouping" from crypto-types.  Effectively the same definition as
      before.

A.3.  02 to 03

   *  Updated copyright date, boilerplate template, affiliation, folding
      algorithm, and reformatted the YANG module.

A.4.  03 to 04

   *  Added groupings 'local-or-truststore-certs-grouping' and 'local-
      or-truststore-host-keys-grouping', matching similar definitions in
      the keystore draft.  Note new (and incomplete) "truststore" usage!

   *  Related to above, also added features 'truststore-supported' and
      'local-trust-anchors-supported'.

A.5.  04 to 05

   *  Renamed "trust-anchors" to "truststore"

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   *  Removed "pinned." prefix everywhere, to match truststore rename

   *  Moved everything under a top-level 'grouping' to enable use in
      other contexts.

   *  Renamed feature from 'local-trust-anchors-supported' to 'local-
      definitions-supported' (same name used in keystore)

   *  Removed the "require-instance false" statement from the "*-ref"
      typedefs.

   *  Added missing "ssh-host-keys" and "x509-certificates" if-feature
      statements

A.6.  05 to 06

   *  Editorial changes only.

A.7.  06 to 07

   *  Added Henk Birkholz as a co-author (thanks Henk!)

   *  Added PSKs and raw public keys to truststore.

A.8.  07 to 08

   *  Added new "Support for Built-in Trust Anchors" section.

   *  Removed spurious "uses ct:trust-anchor-certs-grouping" line.

   *  Removed PSK from model.

A.9.  08 to 09

   *  Removed remaining PSK references from text.

   *  Wrapped each top-level list with a container.

   *  Introduced "bag" term.

   *  Merged "SSH Public Keys" and "Raw Public Keys" in a single "Public
      Keys" bag.  Consuming downstream modules (i.e., "ietf-[ssh/tls]-
      [client/server]) refine the "public-key-format" to be either SSH
      or TLS specific as needed.

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A.10.  09 to 10

   *  Removed "algorithm" node from examples.

   *  Removed the no longer used statements supporting the old "ssh-
      public-key" and "raw-public-key" nodes.

   *  Added a "Note to Reviewers" note to first page.

A.11.  10 to 11

   *  Corrected module prefix registered in the IANA Considerations
      section.

   *  Modified 'local-or-truststore-certs-grouping' to use a list (not a
      leaf-list).

   *  Added new example section "The Local or Truststore Groupings".

   *  Clarified expected behavior for "built-in" certificates in
      <operational>

   *  Expanded "Data Model Overview section(s) [remove "wall" of tree
      diagrams].

   *  Updated the Security Considerations section.

A.12.  11 to 12

   *  Fixed a copy/paste issue in the "Data at Rest" Security
      Considerations section.

A.13.  12 to 13

   *  Fixed issues found by the SecDir review of the "keystore" draft.

A.14.  13 to 14

   *  Added an "Unconstrained Public Key Usage" Security Consideration
      to address concern raised by SecDir.

   *  Addressed comments raised by YANG Doctor.

A.15.  14 to 15

   *  Added prefixes to 'path' statements per trust-anchors/issues/1

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   *  Renamed feature "truststore-supported" to "central-truststore-
      supported".

   *  Associated with above, generally moved text to refer to a
      "central" truststore.

   *  Removed two unecessary/unwanted "min-elements 1" and associated
      "presence" statements.

   *  Aligned modules with `pyang -f` formatting.

   *  Fixed nits found by YANG Doctor reviews.

Acknowledgements

   The authors especially thank Henk Birkholz for contributing YANG to
   the ietf-truststore module supporting raw public keys and PSKs (pre-
   shared or pairwise-symmetric keys).  While these contributions were
   eventually replaced by reusing the existing support for asymmetric
   and symmetric trust anchors, respectively, it was only thru Henk's
   initiative that the WG was able to come to that result.

   The authors additionally thank the following for helping give shape
   to this work (ordered by first name): Balazs Kovacs, Eric Voit,
   Juergen Schoenwaelder, Liang Xia, Martin Bjoerklund, Nick Hancock,
   and Yoav Nir.

Author's Address

   Kent Watsen
   Watsen Networks

   Email: kent+ietf@watsen.net

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