path: root/doc/rfc/rfc9642.txt

Internet Engineering Task Force (IETF)                         K. Watsen
Request for Comments: 9642                               Watsen Networks
Category: Standards Track                                   October 2024
ISSN: 2070-1721


                    A YANG Data Model for a Keystore

Abstract

   This document presents a YANG module called "ietf-keystore" that
   enables centralized configuration of both symmetric and asymmetric
   keys.  The secret value for both key types may be encrypted or
   hidden.  Asymmetric keys may be associated with certificates.
   Notifications are sent when certificates are about to expire.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9642.

Copyright Notice

   Copyright (c) 2024 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Relation to Other RFCs
     1.2.  Specification Language
     1.3.  Terminology
     1.4.  Adherence to the NMDA
     1.5.  Conventions
   2.  The "ietf-keystore" Module
     2.1.  Data Model Overview
     2.2.  Example Usage
     2.3.  YANG Module
   3.  Support for Built-In Keys
   4.  Encrypting Keys in Configuration
   5.  Security Considerations
     5.1.  Security of Data at Rest and in Motion
     5.2.  Unconstrained Private Key Usage
     5.3.  Security Considerations for the "ietf-keystore" YANG Module
   6.  IANA Considerations
     6.1.  The IETF XML Registry
     6.2.  The YANG Module Names Registry
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgements
   Author's Address

1.  Introduction

   This document presents a YANG 1.1 [RFC7950] module called "ietf-
   keystore" that enables centralized configuration of both symmetric
   and asymmetric keys.  The secret value for both key types may be
   encrypted or hidden (see [RFC9640]).  Asymmetric keys may be
   associated with certificates.  Notifications are sent when
   certificates are about to expire.

   The "ietf-keystore" module defines many "grouping" statements
   intended for use by other modules that may import it.  For instance,
   there are groupings that define enabling a key to be configured
   either inline (within the defining data model) or as a reference to a
   key in the central keystore.

   Special consideration has been given for servers that have
   cryptographic hardware, such as a trusted platform module (TPM).
   These servers are unique in that the cryptographic hardware hides the
   secret key values.  Additionally, such hardware is commonly
   initialized when manufactured to protect a "built-in" asymmetric key
   for which its public half is conveyed in an identity certificate
   (e.g., an Initial Device Identifier (IDevID) [Std-802.1AR-2018]
   certificate).  See how built-in keys are supported in Section 3.

   This document is intended to reflect existing practices that many
   server implementations support at the time of writing.  To simplify
   implementation, advanced key formats may be selectively implemented.

   Implementations may utilize operating-system level keystore utilities
   (e.g., "Keychain Access" on MacOS) and/or cryptographic hardware
   (e.g., TPMs).

1.1.  Relation to Other RFCs

   This document presents a YANG module [RFC7950] that is part of a
   collection of RFCs that work together to ultimately support the
   configuration of both the clients and servers of the Network
   Configuration Protocol (NETCONF) [RFC6241] and RESTCONF [RFC8040].

   The dependency relationship between the primary YANG groupings
   defined in the various RFCs is presented in the diagram below.  In
   some cases, a document may define secondary groupings that introduce
   dependencies not illustrated in the diagram.  The labels in the
   diagram are shorthand names for the defining RFCs.  The citation
   references for the shorthand names are provided below the diagram.

   Please note that the arrows in the diagram point from referencer to
   referenced.  For example, the "crypto-types" RFC does not have any
   dependencies, whilst the "keystore" RFC depends on the "crypto-types"
   RFC.

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

   +========================+==========================+
   | Label in Diagram       | Originating RFC          |
   +========================+==========================+
   | crypto-types           | [RFC9640]                |
   +------------------------+--------------------------+
   | truststore             | [RFC9641]                |
   +------------------------+--------------------------+
   | keystore               | RFC 9642                 |
   +------------------------+--------------------------+
   | tcp-client-server      | [RFC9643]                |
   +------------------------+--------------------------+
   | ssh-client-server      | [RFC9644]                |
   +------------------------+--------------------------+
   | tls-client-server      | [RFC9645]                |
   +------------------------+--------------------------+
   | http-client-server     | [HTTP-CLIENT-SERVER]     |
   +------------------------+--------------------------+
   | netconf-client-server  | [NETCONF-CLIENT-SERVER]  |
   +------------------------+--------------------------+
   | restconf-client-server | [RESTCONF-CLIENT-SERVER] |
   +------------------------+--------------------------+

         Table 1: Labels in Diagram 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.  Terminology

   The terms "client" and "server" are defined in [RFC6241] and are not
   redefined here.

   The term "keystore" is defined in this document as a mechanism that
   intends to safeguard secrets.

   The nomenclatures "<running>" and "<operational>" are defined in
   [RFC8342].

   The sentence fragments "augmented" and "augmented in" are used herein
   as the past tense verbified form of the "augment" statement defined
   in Section 7.17 of [RFC7950].

   The term "key" may be used to mean one of three things in this
   document: 1) the YANG-defined "asymmetric-key" or "symmetric-key"
   node defined in this document, 2) the raw key data possessed by the
   aforementioned key nodes, or 3) the "key" of a YANG "list" statement.
   This document qualifies types '2' and '3' using "raw key value" and
   "YANG list key" where needed.  In all other cases, an unqualified
   "key" refers to a YANG-defined "asymmetric-key" or "symmetric-key"
   node.

1.4.  Adherence to the NMDA

   This document is compliant with Network Management Datastore
   Architecture (NMDA) [RFC8342].  For instance, keys and associated
   certificates installed during manufacturing (e.g., for an IDevID
   certificate) are expected to appear in <operational> (see Section 3).

1.5.  Conventions

   Various examples in this document use "BASE64VALUE=" as a placeholder
   value for binary data that has been base64 encoded (per Section 9.8
   of [RFC7950]).  This placeholder value is used because real
   base64-encoded structures are often many lines long and hence
   distracting to the example being presented.

   Various examples in this document use the XML [W3C.REC-xml-20081126]
   encoding.  Other encodings, such as JSON [RFC8259], could
   alternatively be used.

   Various examples in this document contain long lines that may be
   folded, as described in [RFC8792].

   This document uses the adjective "central" to the word "keystore" to
   refer to the top-level instance of the "keystore-grouping", when the
   "central-keystore-supported" feature is enabled.  Please be aware
   that consuming YANG modules MAY instantiate the "keystore-grouping"
   in other locations.  All such other instances are not the "central"
   instance.

2.  The "ietf-keystore" Module

   This section defines a YANG 1.1 [RFC7950] module called "ietf-
   keystore".  A high-level overview of the module is provided in
   Section 2.1.  Examples illustrating the module's use are provided in
   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-keystore" 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-keystore" module:

   Features:
     +-- central-keystore-supported
     +-- inline-definitions-supported
     +-- asymmetric-keys
     +-- symmetric-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-keystore" module:

   Typedefs:
     leafref
       +-- central-symmetric-key-ref
       +-- central-asymmetric-key-ref

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

   Comments:

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

   *  The leafrefs refer to symmetric and asymmetric keys in the central
      keystore when this module is implemented.

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

2.1.3.  Groupings

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

   *  encrypted-by-grouping
   *  central-asymmetric-key-certificate-ref-grouping
   *  inline-or-keystore-symmetric-key-grouping
   *  inline-or-keystore-asymmetric-key-grouping
   *  inline-or-keystore-asymmetric-key-with-certs-grouping
   *  inline-or-keystore-end-entity-cert-with-key-grouping
   *  keystore-grouping

   Each of these groupings are presented in the following subsections.

2.1.3.1.  The "encrypted-by-grouping" Grouping

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

     grouping encrypted-by-grouping:
       +-- (encrypted-by)
          +--:(central-symmetric-key-ref)
          |        {central-keystore-supported,symmetric-keys}?
          |  +-- symmetric-key-ref?    ks:central-symmetric-key-ref
          +--:(central-asymmetric-key-ref)
                   {central-keystore-supported,asymmetric-keys}?
             +-- asymmetric-key-ref?   ks:central-asymmetric-key-ref

   Comments:

   *  This grouping defines a "choice" statement with options to
      reference either a symmetric or an asymmetric key configured in
      the keystore.

   *  This grouping is usable only when the keystore module is
      implemented.  Servers defining custom keystore locations MUST
      augment in alternate "encrypted-by" references to the alternate
      locations.

2.1.3.2.  The "central-asymmetric-key-certificate-ref-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "central-
   asymmetric-key-certificate-ref-grouping" grouping:

     grouping central-asymmetric-key-certificate-ref-grouping:
       +-- asymmetric-key?   ks:central-asymmetric-key-ref
       |       {central-keystore-supported,asymmetric-keys}?
       +-- certificate?      leafref

   Comments:

   *  This grouping defines a reference to a certificate in two parts:
      the first being the name of the asymmetric key the certificate is
      associated with, and the second being the name of the certificate
      itself.

   *  This grouping is usable only when the keystore module is
      implemented.  Servers defining custom keystore locations can
      define an alternate grouping for references to the alternate
      locations.

2.1.3.3.  The "inline-or-keystore-symmetric-key-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "inline-or-
   keystore-symmetric-key-grouping" grouping:

     grouping inline-or-keystore-symmetric-key-grouping:
       +-- (inline-or-keystore)
          +--:(inline) {inline-definitions-supported}?
          |  +-- inline-definition
          |     +---u ct:symmetric-key-grouping
          +--:(central-keystore)
                   {central-keystore-supported,symmetric-keys}?
             +-- central-keystore-reference?
                     ks:central-symmetric-key-ref

   Comments:

   *  The "inline-or-keystore-symmetric-key-grouping" grouping is
      provided solely as convenience to consuming modules that wish to
      offer an option for a symmetric key that is defined either inline
      or as a reference to a symmetric key in the keystore.

   *  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 symmetric key in an alternate location.

   *  For the "inline-definition" option, the definition uses the
      "symmetric-key-grouping" grouping discussed in Section 2.1.4.3 of
      [RFC9640].

   *  For the "central-keystore" option, the "central-keystore-
      reference" is an instance of the "symmetric-key-ref" discussed in
      Section 2.1.2.

2.1.3.4.  The "inline-or-keystore-asymmetric-key-grouping" Grouping

   The following tree diagram [RFC8340] illustrates the "inline-or-
   keystore-asymmetric-key-grouping" grouping:

     grouping inline-or-keystore-asymmetric-key-grouping:
       +-- (inline-or-keystore)
          +--:(inline) {inline-definitions-supported}?
          |  +-- inline-definition
          |     +---u ct:asymmetric-key-pair-grouping
          +--:(central-keystore)
                   {central-keystore-supported,asymmetric-keys}?
             +-- central-keystore-reference?
                     ks:central-asymmetric-key-ref

   Comments:

   *  The "inline-or-keystore-asymmetric-key-grouping" grouping is
      provided solely as convenience to consuming modules that wish to
      offer an option for an asymmetric key that is defined either
      inline or as a reference to an asymmetric key in the keystore.

   *  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 an asymmetric key in an alternate location.

   *  For the "inline-definition" option, the definition uses the
      "asymmetric-key-pair-grouping" grouping discussed in
      Section 2.1.4.6 of [RFC9640].

   *  For the "central-keystore" option, the "central-keystore-
      reference" is an instance of the "asymmetric-key-ref" typedef
      discussed in Section 2.1.2.

2.1.3.5.  The "inline-or-keystore-asymmetric-key-with-certs-grouping"
          Grouping

   The following tree diagram [RFC8340] illustrates the "inline-or-
   keystore-asymmetric-key-with-certs-grouping" grouping:

     grouping inline-or-keystore-asymmetric-key-with-certs-grouping:
       +-- (inline-or-keystore)
          +--:(inline) {inline-definitions-supported}?
          |  +-- inline-definition
          |     +---u ct:asymmetric-key-pair-with-certs-grouping
          +--:(central-keystore)
                   {central-keystore-supported,asymmetric-keys}?
             +-- central-keystore-reference?
                     ks:central-asymmetric-key-ref

   Comments:

   *  The "inline-or-keystore-asymmetric-key-with-certs-grouping"
      grouping is provided solely as convenience to consuming modules
      that wish to offer an option for an asymmetric key that is defined
      either inline or as a reference to an asymmetric key in the
      keystore.

   *  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 an asymmetric key in an alternate location.

   *  For the "inline-definition" option, the definition uses the
      "asymmetric-key-pair-with-certs-grouping" grouping discussed in
      Section 2.1.4.12 of [RFC9640].

   *  For the "central-keystore" option, the "central-keystore-
      reference" is an instance of the "asymmetric-key-ref" typedef
      discussed in Section 2.1.2.

2.1.3.6.  The "inline-or-keystore-end-entity-cert-with-key-grouping"
          Grouping

   The following tree diagram [RFC8340] illustrates the "inline-or-
   keystore-end-entity-cert-with-key-grouping" grouping:

     grouping inline-or-keystore-end-entity-cert-with-key-grouping:
       +-- (inline-or-keystore)
          +--:(inline) {inline-definitions-supported}?
          |  +-- inline-definition
          |     +---u ct:asymmetric-key-pair-with-cert-grouping
          +--:(central-keystore)
                   {central-keystore-supported,asymmetric-keys}?
             +-- central-keystore-reference
                +---u central-asymmetric-key-certificate-ref-grouping

   Comments:

   *  The "inline-or-keystore-end-entity-cert-with-key-grouping"
      grouping is provided solely as convenience to consuming modules
      that wish to offer an option for a symmetric key that is defined
      either inline or as a reference to a symmetric key in the
      keystore.

   *  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 symmetric key in an alternate location.

   *  For the "inline-definition" option, the definition uses the
      "asymmetric-key-pair-with-certs-grouping" grouping discussed in
      Section 2.1.4.12 of [RFC9640].

   *  For the "central-keystore" option, the "central-keystore-
      reference" uses the "central-asymmetric-key-certificate-ref-
      grouping" grouping discussed in Section 2.1.3.2.

2.1.3.7.  The "keystore-grouping" Grouping

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

     grouping keystore-grouping:
       +-- asymmetric-keys {asymmetric-keys}?
       |  +-- asymmetric-key* [name]
       |     +-- name                                          string
       |     +---u ct:asymmetric-key-pair-with-certs-grouping
       +-- symmetric-keys {symmetric-keys}?
          +-- symmetric-key* [name]
             +-- name                         string
             +---u ct:symmetric-key-grouping

   Comments:

   *  The "keystore-grouping" grouping defines a keystore instance as
      being composed of symmetric and asymmetric keys.  The structure
      for the symmetric and asymmetric keys is essentially the same: a
      "list" inside a "container".

   *  For asymmetric keys, each "asymmetric-key" uses the "asymmetric-
      key-pair-with-certs-grouping" grouping discussed in
      Section 2.1.4.12 of [RFC9640].

   *  For symmetric keys, each "symmetric-key" uses the "symmetric-key-
      grouping" grouping discussed in Section 2.1.4.3 of [RFC9640].

2.1.4.  Protocol-Accessible Nodes

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

   module: ietf-keystore
     +--rw keystore {central-keystore-supported}?
        +---u keystore-grouping

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

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

   module: ietf-keystore
     +--rw keystore {central-keystore-supported}?
        +--rw asymmetric-keys {asymmetric-keys}?
        |  +--rw asymmetric-key* [name]
        |     +--rw name                           string
        |     +--rw public-key-format?             identityref
        |     +--rw public-key?                    binary
        |     +--rw private-key-format?            identityref
        |     +--rw (private-key-type)
        |     |  +--:(cleartext-private-key) {cleartext-private-keys}?
        |     |  |  +--rw cleartext-private-key?   binary
        |     |  +--:(hidden-private-key) {hidden-private-keys}?
        |     |  |  +--rw hidden-private-key?      empty
        |     |  +--:(encrypted-private-key) {encrypted-private-keys}?
        |     |     +--rw encrypted-private-key
        |     |        +--rw encrypted-by
        |     |        |  +--rw (encrypted-by)
        |     |        |     +--:(central-symmetric-key-ref)
        |     |        |     |        {central-keystore-supported,symme\
   tric-keys}?
        |     |        |     |  +--rw symmetric-key-ref?
        |     |        |     |          ks:central-symmetric-key-ref
        |     |        |     +--:(central-asymmetric-key-ref)
        |     |        |              {central-keystore-supported,asymm\
   etric-keys}?
        |     |        |        +--rw asymmetric-key-ref?
        |     |        |                ks:central-asymmetric-key-ref
        |     |        +--rw encrypted-value-format    identityref
        |     |        +--rw encrypted-value           binary
        |     +--rw certificates
        |     |  +--rw certificate* [name]
        |     |     +--rw name                      string
        |     |     +--rw cert-data                 end-entity-cert-cms
        |     |     +---n certificate-expiration
        |     |             {certificate-expiration-notification}?
        |     |        +-- expiration-date    yang:date-and-time
        |     +---x generate-csr {csr-generation}?
        |        +---w input
        |        |  +---w csr-format    identityref
        |        |  +---w csr-info      csr-info
        |        +--ro output
        |           +--ro (csr-type)
        |              +--:(p10-csr)
        |                 +--ro p10-csr?   p10-csr
        +--rw symmetric-keys {symmetric-keys}?
           +--rw symmetric-key* [name]
              +--rw name                             string
              +--rw key-format?                      identityref
              +--rw (key-type)
                 +--:(cleartext-symmetric-key)
                 |  +--rw cleartext-symmetric-key?   binary
                 |          {cleartext-symmetric-keys}?
                 +--:(hidden-symmetric-key) {hidden-symmetric-keys}?
                 |  +--rw hidden-symmetric-key?      empty
                 +--:(encrypted-symmetric-key)
                          {encrypted-symmetric-keys}?
                    +--rw encrypted-symmetric-key
                       +--rw encrypted-by
                       |  +--rw (encrypted-by)
                       |     +--:(central-symmetric-key-ref)
                       |     |        {central-keystore-supported,symme\
   tric-keys}?
                       |     |  +--rw symmetric-key-ref?
                       |     |          ks:central-symmetric-key-ref
                       |     +--:(central-asymmetric-key-ref)
                       |              {central-keystore-supported,asymm\
   etric-keys}?
                       |        +--rw asymmetric-key-ref?
                       |                ks:central-asymmetric-key-ref
                       +--rw encrypted-value-format    identityref
                       +--rw encrypted-value           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 protocol-accessible nodes for the "ietf-keystore" module are
      instances of the "keystore-grouping" grouping discussed in
      Section 2.1.3.7.

   *  The top-level node "keystore" is additionally constrained by the
      feature "central-keystore-supported".

   *  The "keystore-grouping" grouping is discussed in Section 2.1.3.7.

   *  The reason for why "keystore-grouping" exists separate from the
      protocol-accessible nodes definition is to enable instances of the
      keystore 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 Keystore Instance

   The following example illustrates keys in <running>.  Please see
   Section 3 for an example illustrating built-in values in
   <operational>.

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

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

      <symmetric-keys>
         <symmetric-key>
            <name>cleartext-symmetric-key</name>
            <key-format>ct:octet-string-key-format</key-format>
            <cleartext-symmetric-key>BASE64VALUE=</cleartext-symmetric-\
   key>
         </symmetric-key>
         <symmetric-key>
            <name>hidden-symmetric-key</name>
            <hidden-symmetric-key/>
         </symmetric-key>
         <symmetric-key>
            <name>encrypted-symmetric-key</name>
            <key-format>ct:one-symmetric-key-format</key-format>
            <encrypted-symmetric-key>
              <encrypted-by>
                <asymmetric-key-ref>hidden-asymmetric-key</asymmetric-k\
   ey-ref>
              </encrypted-by>
              <encrypted-value-format>ct:cms-enveloped-data-format</enc\
   rypted-value-format>
              <encrypted-value>BASE64VALUE=</encrypted-value>
            </encrypted-symmetric-key>
         </symmetric-key>
      </symmetric-keys>

      <asymmetric-keys>
         <asymmetric-key>
            <name>ssh-rsa-key</name>
            <private-key-format>ct:rsa-private-key-format</private-key-\
   format>
            <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
         </asymmetric-key>
         <asymmetric-key>
            <name>ssh-rsa-key-with-cert</name>
            <private-key-format>ct:rsa-private-key-format</private-key-\
   format>
            <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
            <certificates>
               <certificate>
                  <name>ex-rsa-cert2</name>
                  <cert-data>BASE64VALUE=</cert-data>
               </certificate>
            </certificates>
         </asymmetric-key>
         <asymmetric-key>
            <name>raw-private-key</name>
            <private-key-format>ct:rsa-private-key-format</private-key-\
   format>
            <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
         </asymmetric-key>
         <asymmetric-key>
            <name>rsa-asymmetric-key</name>
            <private-key-format>ct:rsa-private-key-format</private-key-\
   format>
            <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
            <certificates>
               <certificate>
                  <name>ex-rsa-cert</name>
                  <cert-data>BASE64VALUE=</cert-data>
               </certificate>
            </certificates>
         </asymmetric-key>
         <asymmetric-key>
            <name>ec-asymmetric-key</name>
            <private-key-format>ct:ec-private-key-format</private-key-f\
   ormat>
            <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
            <certificates>
               <certificate>
                  <name>ex-ec-cert</name>
                  <cert-data>BASE64VALUE=</cert-data>
               </certificate>
            </certificates>
         </asymmetric-key>
         <asymmetric-key>
            <name>hidden-asymmetric-key</name>
            <public-key-format>ct:subject-public-key-info-format</publi\
   c-key-format>
            <public-key>BASE64VALUE=</public-key>
            <hidden-private-key/>
            <certificates>
               <certificate>
                  <name>builtin-idevid-cert</name>
                  <cert-data>BASE64VALUE=</cert-data>
               </certificate>
               <certificate>
                  <name>my-ldevid-cert</name>
                  <cert-data>BASE64VALUE=</cert-data>
               </certificate>
            </certificates>
         </asymmetric-key>
         <asymmetric-key>
            <name>encrypted-asymmetric-key</name>
            <private-key-format>ct:one-asymmetric-key-format</private-k\
   ey-format>
            <encrypted-private-key>
              <encrypted-by>
                <symmetric-key-ref>encrypted-symmetric-key</symmetric-k\
   ey-ref>
              </encrypted-by>
              <encrypted-value-format>ct:cms-encrypted-data-format</enc\
   rypted-value-format>
              <encrypted-value>BASE64VALUE=</encrypted-value>
            </encrypted-private-key>
         </asymmetric-key>
      </asymmetric-keys>
   </keystore>

2.2.2.  A Certificate Expiration Notification

   The following example illustrates a "certificate-expiration"
   notification for a certificate associated with an asymmetric key
   configured in the keystore.

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

   <notification
     xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
     <eventTime>2018-05-25T00:01:00Z</eventTime>
     <keystore xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore">
       <asymmetric-keys>
         <asymmetric-key>
           <name>hidden-asymmetric-key</name>
           <certificates>
             <certificate>
               <name>my-ldevid-cert</name>
               <certificate-expiration>
                 <expiration-date>2018-08-05T14:18:53-05:00</expiration\
   -date>
               </certificate-expiration>
             </certificate>
           </certificates>
         </asymmetric-key>
       </asymmetric-keys>
     </keystore>
   </notification>

2.2.3.  The "Inline or Keystore" Groupings

   This section illustrates the various "inline-or-keystore" groupings
   defined in the "ietf-keystore" module, specifically the "inline-or-
   keystore-symmetric-key-grouping" (Section 2.1.3.3), "inline-or-
   keystore-asymmetric-key-grouping" (Section 2.1.3.4), "inline-or-
   keystore-asymmetric-key-with-certs-grouping" (Section 2.1.3.5), and
   "inline-or-keystore-end-entity-cert-with-key-grouping"
   (Section 2.1.3.6) groupings.

   These examples assume the existence of an example module called "ex-
   keystore-usage" that has the namespace "https://example.com/ns/
   example-keystore-usage".

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

2.2.3.1.  Tree Diagrams for the "ex-keystore-usage" Module

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

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

   module: ex-keystore-usage
     +--rw keystore-usage
        +--rw symmetric-key* [name]
        |  +--rw name                                            string
        |  +---u ks:inline-or-keystore-symmetric-key-grouping
        +--rw asymmetric-key* [name]
        |  +--rw name                                             string
        |  +---u ks:inline-or-keystore-asymmetric-key-grouping
        +--rw asymmetric-key-with-certs* [name]
        |  +--rw name
        |  |       string
        |  +---u ks:inline-or-keystore-asymmetric-key-with-certs-groupi\
   ng
        +--rw end-entity-cert-with-key* [name]
           +--rw name
           |       string
           +---u ks:inline-or-keystore-end-entity-cert-with-key-grouping

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

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

   module: ex-keystore-usage
     +--rw keystore-usage
        +--rw symmetric-key* [name]
        |  +--rw name                                string
        |  +--rw (inline-or-keystore)
        |     +--:(inline) {inline-definitions-supported}?
        |     |  +--rw inline-definition
        |     |     +--rw key-format?                      identityref
        |     |     +--rw (key-type)
        |     |        +--:(cleartext-symmetric-key)
        |     |        |  +--rw cleartext-symmetric-key?   binary
        |     |        |          {cleartext-symmetric-keys}?
        |     |        +--:(hidden-symmetric-key)
        |     |        |        {hidden-symmetric-keys}?
        |     |        |  +--rw hidden-symmetric-key?      empty
        |     |        +--:(encrypted-symmetric-key)
        |     |                 {encrypted-symmetric-keys}?
        |     |           +--rw encrypted-symmetric-key
        |     |              +--rw encrypted-by
        |     |              +--rw encrypted-value-format    identityref
        |     |              +--rw encrypted-value           binary
        |     +--:(central-keystore)
        |              {central-keystore-supported,symmetric-keys}?
        |        +--rw central-keystore-reference?
        |                ks:central-symmetric-key-ref
        +--rw asymmetric-key* [name]
        |  +--rw name                                string
        |  +--rw (inline-or-keystore)
        |     +--:(inline) {inline-definitions-supported}?
        |     |  +--rw inline-definition
        |     |     +--rw public-key-format?             identityref
        |     |     +--rw public-key?                    binary
        |     |     +--rw private-key-format?            identityref
        |     |     +--rw (private-key-type)
        |     |        +--:(cleartext-private-key)
        |     |        |        {cleartext-private-keys}?
        |     |        |  +--rw cleartext-private-key?   binary
        |     |        +--:(hidden-private-key) {hidden-private-keys}?
        |     |        |  +--rw hidden-private-key?      empty
        |     |        +--:(encrypted-private-key)
        |     |                 {encrypted-private-keys}?
        |     |           +--rw encrypted-private-key
        |     |              +--rw encrypted-by
        |     |              +--rw encrypted-value-format    identityref
        |     |              +--rw encrypted-value           binary
        |     +--:(central-keystore)
        |              {central-keystore-supported,asymmetric-keys}?
        |        +--rw central-keystore-reference?
        |                ks:central-asymmetric-key-ref
        +--rw asymmetric-key-with-certs* [name]
        |  +--rw name                                string
        |  +--rw (inline-or-keystore)
        |     +--:(inline) {inline-definitions-supported}?
        |     |  +--rw inline-definition
        |     |     +--rw public-key-format?             identityref
        |     |     +--rw public-key?                    binary
        |     |     +--rw private-key-format?            identityref
        |     |     +--rw (private-key-type)
        |     |     |  +--:(cleartext-private-key)
        |     |     |  |        {cleartext-private-keys}?
        |     |     |  |  +--rw cleartext-private-key?   binary
        |     |     |  +--:(hidden-private-key) {hidden-private-keys}?
        |     |     |  |  +--rw hidden-private-key?      empty
        |     |     |  +--:(encrypted-private-key)
        |     |     |           {encrypted-private-keys}?
        |     |     |     +--rw encrypted-private-key
        |     |     |        +--rw encrypted-by
        |     |     |        +--rw encrypted-value-format    identityref
        |     |     |        +--rw encrypted-value           binary
        |     |     +--rw certificates
        |     |     |  +--rw certificate* [name]
        |     |     |     +--rw name                      string
        |     |     |     +--rw cert-data
        |     |     |     |       end-entity-cert-cms
        |     |     |     +---n certificate-expiration
        |     |     |             {certificate-expiration-notification}?
        |     |     |        +-- expiration-date    yang:date-and-time
        |     |     +---x generate-csr {csr-generation}?
        |     |        +---w input
        |     |        |  +---w csr-format    identityref
        |     |        |  +---w csr-info      csr-info
        |     |        +--ro output
        |     |           +--ro (csr-type)
        |     |              +--:(p10-csr)
        |     |                 +--ro p10-csr?   p10-csr
        |     +--:(central-keystore)
        |              {central-keystore-supported,asymmetric-keys}?
        |        +--rw central-keystore-reference?
        |                ks:central-asymmetric-key-ref
        +--rw end-entity-cert-with-key* [name]
           +--rw name                                string
           +--rw (inline-or-keystore)
              +--:(inline) {inline-definitions-supported}?
              |  +--rw inline-definition
              |     +--rw public-key-format?             identityref
              |     +--rw public-key?                    binary
              |     +--rw private-key-format?            identityref
              |     +--rw (private-key-type)
              |     |  +--:(cleartext-private-key)
              |     |  |        {cleartext-private-keys}?
              |     |  |  +--rw cleartext-private-key?   binary
              |     |  +--:(hidden-private-key) {hidden-private-keys}?
              |     |  |  +--rw hidden-private-key?      empty
              |     |  +--:(encrypted-private-key)
              |     |           {encrypted-private-keys}?
              |     |     +--rw encrypted-private-key
              |     |        +--rw encrypted-by
              |     |        +--rw encrypted-value-format    identityref
              |     |        +--rw encrypted-value           binary
              |     +--rw cert-data?
              |     |       end-entity-cert-cms
              |     +---n certificate-expiration
              |     |       {certificate-expiration-notification}?
              |     |  +-- expiration-date    yang:date-and-time
              |     +---x generate-csr {csr-generation}?
              |        +---w input
              |        |  +---w csr-format    identityref
              |        |  +---w csr-info      csr-info
              |        +--ro output
              |           +--ro (csr-type)
              |              +--:(p10-csr)
              |                 +--ro p10-csr?   p10-csr
              +--:(central-keystore)
                       {central-keystore-supported,asymmetric-keys}?
                 +--rw central-keystore-reference
                    +--rw asymmetric-key?
                    |       ks:central-asymmetric-key-ref
                    |       {central-keystore-supported,asymmetric-keys\
   }?
                    +--rw certificate?      leafref

2.2.3.2.  Example Usage for the "ex-keystore-usage" Module

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

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

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

     <!-- The following two equivalent examples illustrate the  -->
     <!-- "inline-or-keystore-symmetric-key-grouping" grouping: -->

     <symmetric-key>
       <name>example 1a</name>
       <central-keystore-reference>cleartext-symmetric-key</central-key\
   store-reference>
     </symmetric-key>

     <symmetric-key>
       <name>example 1b</name>
       <inline-definition>
         <key-format>ct:octet-string-key-format</key-format>
         <cleartext-symmetric-key>BASE64VALUE=</cleartext-symmetric-key>
       </inline-definition>
     </symmetric-key>


     <!-- The following two equivalent examples illustrate the   -->
     <!-- "inline-or-keystore-asymmetric-key-grouping" grouping: -->

     <asymmetric-key>
       <name>example 2a</name>
       <central-keystore-reference>rsa-asymmetric-key</central-keystore\
   -reference>
     </asymmetric-key>

     <asymmetric-key>
       <name>example 2b</name>
       <inline-definition>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <private-key-format>ct:rsa-private-key-format</private-key-for\
   mat>
         <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
       </inline-definition>
     </asymmetric-key>


     <!-- The following two equivalent examples illustrate the     -->
     <!-- "inline-or-keystore-asymmetric-key-with-certs-grouping"  -->
     <!-- grouping:                                                -->

     <asymmetric-key-with-certs>
       <name>example 3a</name>
       <central-keystore-reference>rsa-asymmetric-key</central-keystore\
   -reference>
     </asymmetric-key-with-certs>

     <asymmetric-key-with-certs>
       <name>example 3b</name>
       <inline-definition>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <private-key-format>ct:rsa-private-key-format</private-key-for\
   mat>
         <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
         <certificates>
           <certificate>
             <name>a locally defined cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
         </certificates>
       </inline-definition>
     </asymmetric-key-with-certs>


     <!-- The following two equivalent examples illustrate the    -->
     <!-- "inline-or-keystore-end-entity-cert-with-key-grouping"  -->
     <!-- grouping:                                               -->
     <end-entity-cert-with-key>
       <name>example 4a</name>
       <central-keystore-reference>
         <asymmetric-key>rsa-asymmetric-key</asymmetric-key>
         <certificate>ex-rsa-cert</certificate>
       </central-keystore-reference>
     </end-entity-cert-with-key>

     <end-entity-cert-with-key>
       <name>example 4b</name>
       <inline-definition>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <private-key-format>ct:rsa-private-key-format</private-key-for\
   mat>
         <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
         <cert-data>BASE64VALUE=</cert-data>
       </inline-definition>
     </end-entity-cert-with-key>

   </keystore-usage>

2.2.3.3.  The "ex-keystore-usage" YANG Module

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

   module ex-keystore-usage {
     yang-version 1.1;
     namespace "https://example.com/ns/example-keystore-usage";
     prefix ex-keystore-usage;

     import ietf-keystore {
       prefix ks;
       reference
         "RFC 9642: A YANG Data Model for a Keystore";
     }

     organization
       "Example Corporation";

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

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

     revision 2024-10-10 {
       description
         "Initial version";
       reference
         "RFC 9642: A YANG Data Model for a Keystore";
     }

     container keystore-usage {
       description
         "An illustration of the various keystore groupings.";
       list symmetric-key {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this key.";
         }
         uses ks:inline-or-keystore-symmetric-key-grouping;
         description
           "An symmetric key that may be configured locally or be a
            reference to a symmetric key in the keystore.";
       }
       list asymmetric-key {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this key.";
         }
         uses ks:inline-or-keystore-asymmetric-key-grouping;
         description
           "An asymmetric key, with no certs, that may be configured
            locally or be a reference to an asymmetric key in the
            keystore.  The intent is to reference just the asymmetric
            key, not any certificates that may also be associated
            with the asymmetric key.";
       }
       list asymmetric-key-with-certs {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this key.";
         }
         uses ks:inline-or-keystore-asymmetric-key-with-certs-grouping;
         description
           "An asymmetric key and its associated certs that may be
            configured locally or be a reference to an asymmetric
            key (and its associated certs) in the keystore.";
       }
       list end-entity-cert-with-key {
         key "name";
         leaf name {
           type string;
           description
             "An arbitrary name for this key.";
         }
         uses ks:inline-or-keystore-end-entity-cert-with-key-grouping;
         description
           "An end-entity certificate and its associated asymmetric
            key that may be configured locally or be a reference
            to another certificate (and its associated asymmetric
            key) in the keystore.";
       }
     }
   }

2.3.  YANG Module

   This YANG module has normative references to [RFC8341] and [RFC9640].

   <CODE BEGINS> file "ietf-keystore@2024-10-10.yang"
   module ietf-keystore {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-keystore";
     prefix ks;

     import ietf-netconf-acm {
       prefix nacm;
       reference
         "RFC 8341: Network Configuration Access Control Model";
     }

     import ietf-crypto-types {
       prefix ct;
       reference
         "RFC 9640: YANG Data Types and Groupings for Cryptography";
     }

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

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

     description
       "This module defines a 'keystore' to centralize management
        of security credentials.

        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.

        Copyright (c) 2024 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 9642
        (https://www.rfc-editor.org/info/rfc9642); see the RFC
        itself for full legal notices.";

     revision 2024-10-10 {
       description
         "Initial version";
       reference
         "RFC 9642: A YANG Data Model for a Keystore";
     }

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

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

     feature inline-definitions-supported {
       description
         "The 'inline-definitions-supported' feature indicates that
          the server supports locally defined keys.";
     }

     feature asymmetric-keys {
       description
         "The 'asymmetric-keys' feature indicates that the server
          implements the /keystore/asymmetric-keys subtree.";

     }

     feature symmetric-keys {
       description
         "The 'symmetric-keys' feature indicates that the server
          implements the /keystore/symmetric-keys subtree.";
     }

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

     typedef central-symmetric-key-ref {
       type leafref {
         path "/ks:keystore/ks:symmetric-keys/ks:symmetric-key"
            + "/ks:name";
       }
       description
         "This typedef enables modules to easily define a reference
          to a symmetric key stored in the central keystore.";
     }

     typedef central-asymmetric-key-ref {
       type leafref {
         path "/ks:keystore/ks:asymmetric-keys/ks:asymmetric-key"
            + "/ks:name";
       }
       description
         "This typedef enables modules to easily define a reference
          to an asymmetric key stored in the central keystore.";
     }

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

     grouping encrypted-by-grouping {
       description
         "A grouping that defines a 'choice' statement that can be
          augmented into the 'encrypted-by' node, present in the
          'symmetric-key-grouping' and 'asymmetric-key-pair-grouping'
          groupings defined in RFC 9640, enabling references to keys
          in the central keystore.";
       choice encrypted-by {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice amongst other symmetric or asymmetric keys.";
         case central-symmetric-key-ref {
           if-feature "central-keystore-supported";
           if-feature "symmetric-keys";
           leaf symmetric-key-ref {
             type ks:central-symmetric-key-ref;
             description
               "Identifies the symmetric key used to encrypt the
                associated key.";
           }
         }
         case central-asymmetric-key-ref {
           if-feature "central-keystore-supported";
           if-feature "asymmetric-keys";
           leaf asymmetric-key-ref {
             type ks:central-asymmetric-key-ref;
             description
               "Identifies the asymmetric key whose public key
                encrypted the associated key.";
           }
         }
       }
     }

     // *-ref groupings

     grouping central-asymmetric-key-certificate-ref-grouping {
       description
         "A grouping for the reference to a certificate associated
          with an asymmetric key stored in the central keystore.";
       leaf asymmetric-key {
         nacm:default-deny-write;
         if-feature "central-keystore-supported";
         if-feature "asymmetric-keys";
         type ks:central-asymmetric-key-ref;
         must '../certificate';
         description
           "A reference to an asymmetric key in the keystore.";
       }
       leaf certificate {
         nacm:default-deny-write;
         type leafref {
           path "/ks:keystore/ks:asymmetric-keys/ks:asymmetric-key"
              + "[ks:name = current()/../asymmetric-key]/"
              + "ks:certificates/ks:certificate/ks:name";
         }
         must '../asymmetric-key';
         description
           "A reference to a specific certificate of the
            asymmetric key in the keystore.";
       }
     }

     // inline-or-keystore-* groupings

     grouping inline-or-keystore-symmetric-key-grouping {
       description
         "A grouping for the configuration of a symmetric key.  The
          symmetric key may be defined inline or as a reference to
          a symmetric key stored in the central keystore.

          Servers that wish to define alternate keystore locations
          SHOULD augment in custom 'case' statements enabling
          references to those alternate keystore locations.";
       choice inline-or-keystore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the keystore.";
         case inline {
           if-feature "inline-definitions-supported";
           container inline-definition {
             description
               "A container to hold the local key definition.";
             uses ct:symmetric-key-grouping;
           }
         }
         case central-keystore {
           if-feature "central-keystore-supported";
           if-feature "symmetric-keys";
           leaf central-keystore-reference {
             type ks:central-symmetric-key-ref;
             description
               "A reference to a symmetric key that exists in
                the central keystore.";
           }
         }
       }
     }

     grouping inline-or-keystore-asymmetric-key-grouping {
       description
         "A grouping for the configuration of an asymmetric key.  The
          asymmetric key may be defined inline or as a reference to
          an asymmetric key stored in the central keystore.

          Servers that wish to define alternate keystore locations
          SHOULD augment in custom 'case' statements enabling
          references to those alternate keystore locations.";
       choice inline-or-keystore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the keystore.";
         case inline {
           if-feature "inline-definitions-supported";
           container inline-definition {
             description
               "A container to hold the local key definition.";
             uses ct:asymmetric-key-pair-grouping;
           }
         }
         case central-keystore {
           if-feature "central-keystore-supported";
           if-feature "asymmetric-keys";
           leaf central-keystore-reference {
             type ks:central-asymmetric-key-ref;
             description
               "A reference to an asymmetric key that exists in
                the central keystore.  The intent is to reference
                just the asymmetric key without any regard for
                any certificates that may be associated with it.";
           }
         }
       }
     }

     grouping inline-or-keystore-asymmetric-key-with-certs-grouping {
       description
         "A grouping for the configuration of an asymmetric key and
          its associated certificates.  The asymmetric key and its
          associated certificates may be defined inline or as a
          reference to an asymmetric key (and its associated
          certificates) in the central keystore.

          Servers that wish to define alternate keystore locations
          SHOULD augment in custom 'case' statements enabling
          references to those alternate keystore locations.";
       choice inline-or-keystore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the keystore.";
         case inline {
           if-feature "inline-definitions-supported";
           container inline-definition {
             description
               "A container to hold the local key definition.";
             uses ct:asymmetric-key-pair-with-certs-grouping;
           }
         }
         case central-keystore {
           if-feature "central-keystore-supported";
           if-feature "asymmetric-keys";
           leaf central-keystore-reference {
             type ks:central-asymmetric-key-ref;
             description
               "A reference to an asymmetric key (and all of its
                associated certificates) in the keystore, when
                this module is implemented.";
           }
         }
       }
     }

     grouping inline-or-keystore-end-entity-cert-with-key-grouping {
       description
         "A grouping for the configuration of an asymmetric key and
          its associated end-entity certificate.  The asymmetric key
          and its associated end-entity certificate may be defined
          inline or as a reference to an asymmetric key (and its
          associated end-entity certificate) in the central keystore.

          Servers that wish to define alternate keystore locations
          SHOULD augment in custom 'case' statements enabling
          references to those alternate keystore locations.";
       choice inline-or-keystore {
         nacm:default-deny-write;
         mandatory true;
         description
           "A choice between an inlined definition and a definition
            that exists in the keystore.";
         case inline {
           if-feature "inline-definitions-supported";
           container inline-definition {
             description
               "A container to hold the local key definition.";
             uses ct:asymmetric-key-pair-with-cert-grouping;
           }
         }
         case central-keystore {
           if-feature "central-keystore-supported";
           if-feature "asymmetric-keys";
           container central-keystore-reference {
             uses central-asymmetric-key-certificate-ref-grouping;
             description
               "A reference to a specific certificate associated with
                an asymmetric key stored in the central keystore.";
           }
         }
       }
     }

     // the keystore grouping

     grouping keystore-grouping {
       description
         "A grouping definition enables use in other contexts.  If ever
          done, implementations MUST augment new 'case' statements
          into the various inline-or-keystore 'choice' statements to
          supply leafrefs to the model-specific location(s).";
       container asymmetric-keys {
         nacm:default-deny-write;
         if-feature "asymmetric-keys";
         description
           "A list of asymmetric keys.";
         list asymmetric-key {
           key "name";
           description
             "An asymmetric key.";
           leaf name {
             type string;
             description
               "An arbitrary name for the asymmetric key.";
           }
           uses ct:asymmetric-key-pair-with-certs-grouping;
         }
       }
       container symmetric-keys {
         nacm:default-deny-write;
         if-feature "symmetric-keys";
         description
           "A list of symmetric keys.";
         list symmetric-key {
           key "name";
           description
             "A symmetric key.";
           leaf name {
             type string;
             description
               "An arbitrary name for the symmetric key.";
           }
           uses ct:symmetric-key-grouping;
         }
       }
     }

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

     container keystore {
       if-feature "central-keystore-supported";
       description
         "A central keystore containing a list of symmetric keys and
          a list of asymmetric keys.";
       nacm:default-deny-write;
       uses keystore-grouping {
         augment "symmetric-keys/symmetric-key/key-type/encrypted-"
               + "symmetric-key/encrypted-symmetric-key/encrypted-by" {
           description
             "Augments in a choice statement enabling the encrypting
              key to be any other symmetric or asymmetric key in the
              central keystore.";
           uses encrypted-by-grouping;
         }
         augment "asymmetric-keys/asymmetric-key/private-key-type/"
               + "encrypted-private-key/encrypted-private-key/"
               + "encrypted-by" {
           description
             "Augments in a choice statement enabling the encrypting
              key to be any other symmetric or asymmetric key in the
              central keystore.";
           uses encrypted-by-grouping;
         }
       }
     }
   }
   <CODE ENDS>

3.  Support for Built-In Keys

   In some implementations, a server may support keys built into the
   server.  Built-in keys MAY be set during the manufacturing process or
   be dynamically generated the first time the server is booted or a
   particular service (e.g., Secure Shell (SSH)) is enabled.

   Built-in keys are "hidden" keys expected to be set by a vendor-
   specific process.  Any ability for operators to set and/or modify
   built-in keys is outside the scope of this document.

   The primary characteristic of the built-in keys is that they are
   provided by the server, as opposed to being configured.  As such,
   they are present in <operational> (Section 5.3 of [RFC8342]) and
   <system> [NETMOD-SYSTEM-CONFIG], if implemented.

   The example below illustrates what the keystore in <operational>
   might look like for a server in its factory default state.  Note that
   the built-in keys have the "or:origin" annotation value "or:system".

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

   <keystore xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore"
     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">
     <asymmetric-keys>
       <asymmetric-key or:origin="or:system">
         <name>Manufacturer-Generated Hidden Key</name>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <hidden-private-key/>
         <certificates>
           <certificate>
             <name>Manufacturer-Generated IDevID Cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
         </certificates>
       </asymmetric-key>
     </asymmetric-keys>
   </keystore>

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

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

   <keystore xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore"
     xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
     <asymmetric-keys>
       <asymmetric-key>
         <name>Manufacturer-Generated Hidden Key</name>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <hidden-private-key/>
         <certificates>
           <certificate>
             <name>Manufacturer-Generated IDevID Cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
           <certificate>
             <name>Deployment-Specific LDevID Cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
         </certificates>
       </asymmetric-key>
     </asymmetric-keys>
   </keystore>

   After the above configuration is applied, <operational> should appear
   as follows:

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

   <keystore xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore"
     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">
     <asymmetric-keys>
       <asymmetric-key or:origin="or:system">
         <name>Manufacturer-Generated Hidden Key</name>
         <public-key-format>ct:subject-public-key-info-format</public-k\
   ey-format>
         <public-key>BASE64VALUE=</public-key>
         <hidden-private-key/>
         <certificates>
           <certificate>
             <name>Manufacturer-Generated IDevID Cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
           <certificate or:origin="or:intended">
             <name>Deployment-Specific LDevID Cert</name>
             <cert-data>BASE64VALUE=</cert-data>
           </certificate>
         </certificates>
       </asymmetric-key>
     </asymmetric-keys>
   </keystore>

4.  Encrypting Keys in Configuration

   This section describes an approach that enables both the symmetric
   and asymmetric keys on a server to be encrypted, such that backup/
   restore procedures can be used without concern for raw key data being
   compromised when in transit.

   The approach presented in this section is not normative.  This
   section answers how a configuration containing secrets that are
   encrypted by a built-in key (Section 3) can be backed up from one
   server and restored on a different server when each server has unique
   primary keys.  The API defined by the "ietf-keystore" YANG module
   presented in this document is sufficient to support the workflow
   described in this section.

4.1.  Key Encryption Key

   The ability to encrypt configured keys is predicated on the existence
   of a key encryption key (KEK).  There may be any number of KEKs in a
   server.  A KEK, by its namesake, is a key that is used to encrypt
   other keys.  A KEK MAY be either a symmetric key or an asymmetric
   key.

   If a KEK is a symmetric key, then the server MUST provide an API for
   administrators to encrypt other keys without needing to know the
   symmetric key's value.  If the KEK is an asymmetric key, then the
   server SHOULD provide an API enabling the encryption of other keys
   or, alternatively, assume the administrators can do so themselves
   using the asymmetric key's public half.

   A server MUST possess access to the KEK, or an API using the KEK, so
   that it can decrypt the other keys in the configuration at runtime.

4.2.  Configuring Encrypted Keys

   Each time a new key is configured, it SHOULD be encrypted by a KEK.

   In the "ietf-crypto-types" module [RFC9640], the format for encrypted
   values is described by identity statements derived from the
   "symmetrically-encrypted-value-format" and "asymmetrically-encrypted-
   value-format" identity statements.

   Implementations of servers implementing the "ietf-keystore" module
   SHOULD provide an API that simultaneously generates a key and
   encrypts the generated key using a KEK.  Thus, the cleartext value of
   the newly generated key may never be known to the administrators
   generating the keys.  Such an API is defined in the "ietf-ssh-common"
   and "ietf-tls-common" YANG modules defined in [RFC9644] and
   [RFC9645], respectively.

   In case the server implementation does not provide such an API, then
   the generating and encrypting steps MAY be performed outside the
   server, e.g., by an administrator with special access control rights
   (such as an organization's crypto officer).

   In either case, the encrypted key can be configured into the keystore
   using either the "encrypted-symmetric-key" (for symmetric keys) or
   the "encrypted-private-key" (for asymmetric keys) nodes.  These two
   nodes contain both the encrypted raw key value as well as a reference
   to the KEK that encrypted the key.

4.3.  Migrating Configuration to Another Server

   When a KEK is used to encrypt other keys, migrating the configuration
   to another server is only possible if the second server has the same
   KEK.  How the second server comes to have the same KEK is discussed
   in this section.

   In some deployments, mechanisms outside the scope of this document
   may be used to migrate a KEK from one server to another.  That said,
   beware that the ability to do so typically entails having access to
   the first server; however, in some scenarios, the first server may no
   longer be operational.

   In other deployments, an organization's crypto officer, possessing a
   KEK's cleartext value, configures the same KEK on the second server,
   presumably as a hidden key or a key protected by access control, so
   that the cleartext value is not disclosed to regular administrators.
   However, this approach creates high coupling to and dependency on the
   crypto officers that does not scale in production environments.

   In order to decouple the crypto officers from the regular
   administrators, a special KEK, called the "primary key" (PK), may be
   used.

   A PK is commonly a globally unique built-in (see Section 3)
   asymmetric key.  The private raw key value, due to its long lifetime,
   is hidden (i.e., "hidden-private-key"; see Section 2.1.4.5. of
   [RFC9640]).  The raw public key value is often contained in an
   identity certificate (e.g., IDevID).  How to configure a PK during
   the manufacturing process is outside the scope of this document.

   Assuming the server has a PK, the PK can be used to encrypt a "shared
   KEK", which is then used to encrypt the keys configured by regular
   administrators.

   With this extra level of indirection, it is possible for a crypto
   officer to encrypt the same KEK for a multiplicity of servers offline
   using the public key contained in their identity certificates.  The
   crypto officer can then safely hand off the encrypted KEKs to regular
   administrators responsible for server installations, including
   migrations.

   In order to migrate the configuration from a first server, an
   administrator would need to make just a single modification to the
   configuration before loading it onto a second server, which is to
   replace the encrypted KEK keystore entry from the first server with
   the encrypted KEK for the second server.  Upon doing this, the
   configuration (containing many encrypted keys) can be loaded into the
   second server while enabling the second server to decrypt all the
   encrypted keys in the configuration.

   The following diagram illustrates this idea:

    +-------------+                                 +-------------+
    | shared KEK  |                                 | shared KEK  |
    |(unencrypted)|-------------------------------> | (encrypted) |
    +-------------+     encrypts offline using      +-------------+
           ^            each server's PK                |
           |                                            |
           |                                            |
           |  possesses    \o                           |
           +--------------  |\                          |
                           / \         shares with      |
                         crypto    +--------------------+
                         officer   |
                                   |
                                   |
   +----------------------+        |         +----------------------+
   |       server-1       |        |         |       server-2       |
   |    configuration     |        |         |    configuration     |
   |                      |        |         |                      |
   |                      |        |         |                      |
   |  +----------------+  |        |         |  +----------------+  |
   |  |      PK-1      |  |        |         |  |      PK-2      |  |
   |  |    (hidden)    |  |        |         |  |    (hidden)    |  |
   |  +----------------+  |        |         |  +----------------+  |
   |      ^               |        |         |      ^               |
   |      |               |        |         |      |               |
   |      |               |        |         |      |               |
   |      |  encrypted    |        |         |      |  encrypted    |
   |      |  by           |        |         |      |  by           |
   |      |               |        |         |      |               |
   |      |               |        |         |      |               |
   |  +----------------+  |        |         |  +----------------+  |
   |  |  shared KEK    |  |        |         |  |  shared KEK    |  |
   |  |  (encrypted)   |  |        v         |  |  (encrypted)   |  |
   |  +----------------+  |                  |  +----------------+  |
   |      ^               |     regular      |      ^               |
   |      |               |      admin       |      |               |
   |      |               |                  |      |               |
   |      |  encrypted    |       \o         |      |  encrypted    |
   |      |  by           |        |\        |      |  by           |
   |      |               |       / \        |      |               |
   |      |               |                  |      |               |
   |  +----------------+  |----------------->|  +----------------+  |
   |  | all other keys |  |     migrate      |  | all other keys |  |
   |  |  (encrypted)   |  |  configuration   |  |  (encrypted)   |  |
   |  +----------------+  |                  |  +----------------+  |
   |                      |                  |                      |
   +----------------------+                  +----------------------+

5.  Security Considerations

5.1.  Security of Data at Rest and in Motion

   The YANG module defined in this document defines a mechanism called a
   "keystore" that intends to protect its contents from unauthorized
   disclosure and modification.

   In order to satisfy the expectations of a keystore, it is RECOMMENDED
   that server implementations ensure that the keystore contents are
   encrypted when persisted to non-volatile memory and that the keystore
   contents that have been decrypted in volatile memory are zeroized
   when not in use.

   The keystore contents may be encrypted by either encrypting the
   contents individually (e.g., using the "encrypted" value formats) or
   using persistence-layer-level encryption.  If storing cleartext
   values (which is NOT RECOMMENDED per Section 3.5 of [RFC9640]), then
   persistence-layer-level encryption SHOULD be used to protect the data
   at rest.

   If the keystore contents are not encrypted when persisted, then
   server implementations MUST ensure the persisted storage is
   inaccessible.

5.2.  Unconstrained Private Key Usage

   This module enables the configuration of private keys without
   constraints on their usage, e.g., what operations the key is allowed
   to be used for (such as signature, decryption, or both).

   This module also does not constrain the usage of the associated
   public keys other than in the context of a configured certificate
   (e.g., an identity certificate), in which case the key usage is
   constrained by the certificate.

5.3.  Security Considerations for the "ietf-keystore" YANG Module

   This section is modeled after the template defined in Section 3.7.1
   of [RFC8407].

   The ietf-keystore YANG module defines a data model that is designed
   to be accessed via YANG-based management protocols, such as NETCONF
   [RFC6241] and RESTCONF [RFC8040].  These protocols have mandatory-to-
   implement secure transport layers (e.g., SSH [RFC4252], TLS
   [RFC8446], and QUIC [RFC9000]) and mandatory-to-implement mutual
   authentication.

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular users to a
   preconfigured subset of all available protocol operations and
   content.

   Please be aware that this YANG module uses groupings from other YANG
   modules that define nodes that may be considered sensitive or
   vulnerable in network environments.  Please review the Security
   Considerations for dependent YANG modules for information as to which
   nodes may be considered sensitive or vulnerable in network
   environments.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   The "cleartext-symmetric-key" node:
      This node, imported from the "symmetric-key-grouping" grouping
      defined in [RFC9640], is additionally sensitive to read operations
      such that, in normal use cases, it should never be returned to a
      client.  For this reason, the NACM extension "default-deny-all"
      was applied to it in [RFC9640].

   The "cleartext-private-key" node:
      This node, defined in the "asymmetric-key-pair-grouping" grouping
      in [RFC9640], is additionally sensitive to read operations such
      that, in normal use cases, it should never be returned to a
      client.  For this reason, the NACM extension "default-deny-all" is
      applied to it in [RFC9640].

   All the writable data nodes defined by this YANG module, both in the
   "grouping" statements as well as the protocol-accessible "keystore"
   instance, may be considered sensitive or vulnerable in some network
   environments.  For instance, any modification to a key or reference
   to a key 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 YANG module does not define any "rpc" or "action" statements,
   and thus the security considerations for such is not provided here.

   Built-in key types SHOULD be hidden and/or encrypted (not cleartext).
   If this is not possible, access control mechanisms like NACM SHOULD
   be used to limit access to the key's secret data to only the most
   trusted authorized clients (e.g., belonging to an organization's
   crypto officer).

6.  IANA Considerations

6.1.  The IETF XML Registry

   IANA has registered the following URI in the "ns" registry of the
   "IETF XML Registry" [RFC3688].

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

6.2.  The YANG Module Names Registry

   IANA has registered the following YANG module in the "YANG Module
   Names" registry defined in [RFC6020].

   Name:  ietf-keystore
   Maintained by IANA:  N
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-keystore
   Prefix:  ks
   Reference:  RFC 9642

7.  References

7.1.  Normative References

   [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>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [RFC9640]  Watsen, K., "YANG Data Types and Groupings for
              Cryptography", RFC 9640, DOI 10.17487/RFC9640, October
              2024, <https://www.rfc-editor.org/info/rfc9640>.

7.2.  Informative References

   [HTTP-CLIENT-SERVER]
              Watsen, K., "YANG Groupings for HTTP Clients and HTTP
              Servers", Work in Progress, Internet-Draft, draft-ietf-
              netconf-http-client-server-23, 15 August 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              http-client-server-23>.

   [NETCONF-CLIENT-SERVER]
              Watsen, K., "NETCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-netconf-
              client-server-37, 14 August 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              netconf-client-server-37>.

   [NETMOD-SYSTEM-CONFIG]
              Ma, Q., Ed., Wu, Q., and C. Feng, "System-defined
              Configuration", Work in Progress, Internet-Draft, draft-
              ietf-netmod-system-config-09, 29 September 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              system-config-09>.

   [RESTCONF-CLIENT-SERVER]
              Watsen, K., "RESTCONF Client and Server Models", Work in
              Progress, Internet-Draft, draft-ietf-netconf-restconf-
              client-server-38, 14 August 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              restconf-client-server-38>.

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

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [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>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/info/rfc8792>.

   [RFC9641]  Watsen, K., "A YANG Data Model for a Truststore",
              RFC 9641, DOI 10.17487/RFC9641, October 2024,
              <https://www.rfc-editor.org/info/rfc9641>.

   [RFC9643]  Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
              and TCP Servers", RFC 9643, DOI 10.17487/RFC9643, October
              2024, <https://www.rfc-editor.org/info/rfc9643>.

   [RFC9644]  Watsen, K., "YANG Groupings for SSH Clients and SSH
              Servers", RFC 9644, DOI 10.17487/RFC9644, October 2024,
              <https://www.rfc-editor.org/info/rfc9644>.

   [RFC9645]  Watsen, K., "YANG Groupings for TLS Clients and TLS
              Servers", RFC 9645, DOI 10.17487/RFC9645, October 2024,
              <https://www.rfc-editor.org/info/rfc9645>.

   [Std-802.1AR-2018]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks - Secure Device Identity", IEEE Std 802.1AR-2018,
              DOI 10.1109/IEEESTD.2018.8423794, August 2018,
              <https://standards.ieee.org/standard/802_1AR-2018.html>.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, C. M., Maler, E.,
              and F. Yergeau, "Extensible Markup Language (XML) 1.0
              (Fifth Edition)", W3C Recommendation REC-xml-20081126,
              November 2008, <https://www.w3.org/TR/xml/>.

Acknowledgements

   The authors would like to thank the following for lively discussions
   on list and in the halls (ordered by first name): Alan Luchuk, Andy
   Bierman, Balázs Kovács, Benoit Claise, Bert Wijnen, David Lamparter,
   Eric Voit, Éric Vyncke, Francesca Palombini, Jürgen Schönwälder,
   Ladislav Lhotka, Liang Xia, Magnus Nyström, Mahesh Jethanandani,
   Martin Björklund, Mehmet Ersue, Murray Kucherawy, Paul Wouters, Phil
   Shafer, Qin Wu, Radek Krejci, Ramkumar Dhanapal, Reese Enghardt,
   Reshad Rahman, Rob Wilton, Roman Danyliw, Sandra Murphy, Sean Turner,
   Tom Petch, Warren Kumari, and Zaheduzzaman Sarker.

Author's Address

   Kent Watsen
   Watsen Networks
   Email: kent+ietf@watsen.net