Internet-Draft A YANG Data Model for a Keystore July 2020
Watsen Expires 9 January 2021 [Page]
Workgroup:
NETCONF Working Group
Internet-Draft:
draft-ietf-netconf-keystore-18
Published:
Intended Status:
Standards Track
Expires:
Author:
K. Watsen
Watsen Networks

A YANG Data Model for a Keystore

Abstract

This document defines a YANG 1.1 module called "ietf-keystore" that enables centralized configuration of both symmetric and asymmetric keys. The secret value for both key types may be encrypted. Asymmetric keys may be associated with certificates. 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:

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

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

Status of This Memo

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

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

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 9 January 2021.

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Table of Contents

1. Introduction

This document defines 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. 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 defined enabling a key to be either configured locally (within the defining data model) or be a reference to a key in the Keystore.

Special consideration has been given for systems that have cryptographic hardware, such as a Trusted Protection Module (TPM). These systems are unique in that the cryptographic hardware hides the secret key values. To support such hardware, symmetric keys may have the value "hidden-key" and asymmetric keys may have the value "hidden-private-key". While how such keys are created or destroyed is outside the scope of this document, the Keystore can contain entries for such keys, enabling them to be referenced by other configuration elements.

It is not required that a system has an operating system level keystore utility, with or without HSM backing, to implement this module. It is also possible that a system implementing the module to possess a multiplicity of operating system level keystore utilities and/or a multiplicity of HSMs.

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 define configuration modules for clients and servers of both the NETCONF [RFC6241] and RESTCONF [RFC8040] protocols.

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 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. Links the 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
Table 1: Label to RFC Mapping
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]

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 in compliant with Network Management Datastore Architecture (NMDA) [RFC8342]. For instance, keys and associated certificates installed during manufacturing (e.g., for an IDevID [Std-802.1AR-2009] certificate) are expected to appear in <operational> (see Section 3).

2. The "ietf-keystore" Module

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

2.1. Data Model Overview

2.1.1. Features

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

Features:
  +-- keystore-supported
  +-- local-definitions-supported

2.1.2. Typedefs

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

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

Comments:

  • All of 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 keystore. These typedefs are provided primarily as an aid to downstream modules that import the "ietf-keystore" module.

2.1.3. Groupings

The following diagram lists all the "grouping" statements defined in the "ietf-keystore" module:

Groupings:
  +-- encrypted-by-choice-grouping
  +-- asymmetric-key-certificate-ref-grouping
  +-- local-or-keystore-symmetric-key-grouping
  +-- local-or-keystore-asymmetric-key-grouping
  +-- local-or-keystore-asymmetric-key-with-certs-grouping
  +-- local-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-choice-grouping" Grouping

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

  grouping encrypted-by-choice-grouping
    +-- (encrypted-by-choice)
       +--:(symmetric-key-ref)
       |  +-- symmetric-key-ref?
       |          -> /keystore/symmetric-keys/symmetric-key/name
       +--:(asymmetric-key-ref)
          +-- asymmetric-key-ref?
                  -> /keystore/asymmetric-keys/asymmetric-key/name

Comments:

  • This grouping defines a "choice" statement with options to reference either a symmetric or an asymmetric key configured in the keystore.
2.1.3.2. The "asymmetric-key-certificate-ref-grouping" Grouping

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

  grouping asymmetric-key-certificate-ref-grouping
    +-- asymmetric-key?   ks:asymmetric-key-ref
    +-- 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.
2.1.3.3. The "local-or-keystore-symmetric-key-grouping" Grouping

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

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

Comments:

  • The "local-or-keystore-symmetric-key-grouping" grouping is provided soley as convenience to downstream modules that wish to offer an option as to if an symmetric key is defined locally 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 "local-definition" option, the defintion uses the "symmetric-key-grouping" grouping discussed in Section 2.1.3.2 of [I-D.ietf-netconf-crypto-types].
  • For the "keystore" option, the "keystore-reference" is an instance of the "symmetric-key-ref" discussed in Section 2.1.2.
2.1.3.4. The "local-or-keystore-asymmetric-key-grouping" Grouping

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

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

Comments:

  • The "local-or-keystore-asymmetric-key-grouping" grouping is provided soley as convenience to downstream modules that wish to offer an option as to if an asymmetric key is defined locally or as a reference to a 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 a asymmetric key in an alternate location.
  • For the "local-definition" option, the defintion uses the "asymmetric-key-pair-grouping" grouping discussed in Section 2.1.3.4 of [I-D.ietf-netconf-crypto-types].
  • For the "keystore" option, the "keystore-reference" is an instance of the "asymmetric-key-ref" typedef discussed in Section 2.1.2.
2.1.3.5. The "local-or-keystore-asymmetric-key-with-certs-grouping" Grouping

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

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

Comments:

  • The "local-or-keystore-asymmetric-key-with-certs-grouping" grouping is provided soley as convenience to downstream modules that wish to offer an option as to if an asymmetric key is defined locally or as a reference to a 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 a asymmetric key in an alternate location.
  • For the "local-definition" option, the defintion uses the "asymmetric-key-pair-with-certs-grouping" grouping discussed in Section 2.1.3.10 of [I-D.ietf-netconf-crypto-types].
  • For the "keystore" option, the "keystore-reference" is an instance of the "asymmetric-key-ref" typedef discussed in Section 2.1.2.
2.1.3.6. The "local-or-keystore-end-entity-cert-with-key-grouping" Grouping

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

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

Comments:

  • The "local-or-keystore-end-entity-cert-with-key-grouping" grouping is provided soley as convenience to downstream modules that wish to offer an option as to if an symmetric key is defined locally 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 "local-definition" option, the defintion uses the "asymmetric-key-pair-with-certs-grouping" grouping discussed in Section 2.1.3.10 of [I-D.ietf-netconf-crypto-types].
  • For the "keystore" option, the "keystore-reference" uses the "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-key* [name]
    |     +-- name?                                         string
    |     +---u ct:asymmetric-key-pair-with-certs-grouping
    +-- symmetric-keys
       +-- symmetric-key* [name]
          +-- name?                        string
          +---u ct:symmetric-key-grouping

Comments:

  • The "keystore-grouping" grouping is defines a keystore instance as being composed of symmetric and asymmetric keys. The stucture for the symmetric and asymmetric keys is essentially the same, being a "list" inside a "container".
  • For asymmetric keys, each "asymmetric-key" uses the "asymmetric-key-pair-with-certs-grouping" grouping discussed Section 2.1.3.10 of [I-D.ietf-netconf-crypto-types].
  • For symmetric keys, each "symmetric-key" uses the "symmetric-key-grouping" grouping discussed Section 2.1.3.2 of [I-D.ietf-netconf-crypto-types].

2.1.4. Protocol-accessible Nodes

The following diagram lists all the protocol-accessible nodes defined in the "ietf-keystore" module:

module: ietf-keystore
  +--rw keystore
     +--rw 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)
     |     |  +--:(private-key)
     |     |  |  +--rw private-key?                      binary
     |     |  +--:(hidden-private-key)
     |     |  |  +--rw hidden-private-key?               empty
     |     |  +--:(encrypted-private-key)
     |     |     +--rw encrypted-private-key
     |     |        +--rw encrypted-by
     |     |        |  +--rw (encrypted-by-choice)
     |     |        |     +--:(symmetric-key-ref)
     |     |        |     |  +--rw symmetric-key-ref?    leafref
     |     |        |     +--:(asymmetric-key-ref)
     |     |        |        +--rw asymmetric-key-ref?   leafref
     |     |        +--rw encrypted-value    binary
     |     +--rw certificates
     |     |  +--rw certificate* [name]
     |     |     +--rw name                      string
     |     |     +--rw cert-data                 end-entity-cert-cms
     |     |     +---n certificate-expiration
     |     |        +-- expiration-date    yang:date-and-time
     |     +---x generate-certificate-signing-request
     |             {certificate-signing-request-generation}?
     |        +---w input
     |        |  +---w csr-info    ct:csr-info
     |        +--ro output
     |           +--ro certificate-signing-request    ct:csr
     +--rw symmetric-keys
        +--rw symmetric-key* [name]
           +--rw name                   string
           +--rw key-format?            identityref
           +--rw (key-type)
              +--:(key)
              |  +--rw key?             binary
              +--:(hidden-key)
              |  +--rw hidden-key?      empty
              +--:(encrypted-key)
                 +--rw encrypted-key
                    +--rw encrypted-by
                    |  +--rw (encrypted-by-choice)
                    |     +--:(symmetric-key-ref)
                    |     |  +--rw symmetric-key-ref?    leafref
                    |     +--:(asymmetric-key-ref)
                    |        +--rw asymmetric-key-ref?   leafref
                    +--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].
  • For the "ietf-keystore" module, the protcol-accessible nodes are an instance of the "keystore-grouping" discussed in Section 2.1.3.7 grouping. Note that, in this diagram, all the used groupings have been expanded, enabling the keystore's full structure to be seen.
  • The reason for why "keystore-grouping" exists separate from the protocol-accessible nodes definition is so as 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>
         <key>base64encodedvalue==</key>
      </symmetric-key>
      <symmetric-key>
         <name>hidden-symmetric-key</name>
         <hidden-key/>
      </symmetric-key>
      <symmetric-key>
         <name>encrypted-symmetric-key</name>
         <key-format>
            ct:encrypted-one-symmetric-key-format
         </key-format>
         <encrypted-key>
           <encrypted-by>
             <asymmetric-key-ref>hidden-asymmetric-key</asymmetric-k\
ey-ref>
           </encrypted-by>
           <encrypted-value>base64encodedvalue==</encrypted-value>
         </encrypted-key>
      </symmetric-key>
   </symmetric-keys>

   <asymmetric-keys>
      <asymmetric-key>
         <name>ssh-rsa-key</name>
         <public-key-format>
            ct:ssh-public-key-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:rsa-private-key-format
         </private-key-format>
         <private-key>base64encodedvalue==</private-key>
      </asymmetric-key>
      <asymmetric-key>
         <name>ssh-rsa-key-with-cert</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:rsa-private-key-format
         </private-key-format>
         <private-key>base64encodedvalue==</private-key>
         <certificates>
            <certificate>
               <name>ex-rsa-cert2</name>
               <cert-data>base64encodedvalue==</cert-data>
            </certificate>
         </certificates>
      </asymmetric-key>
      <asymmetric-key>
         <name>raw-private-key</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:rsa-private-key-format
         </private-key-format>
         <private-key>base64encodedvalue==</private-key>
      </asymmetric-key>
      <asymmetric-key>
         <name>rsa-asymmetric-key</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:rsa-private-key-format
         </private-key-format>
         <private-key>base64encodedvalue==</private-key>
         <certificates>
            <certificate>
               <name>ex-rsa-cert</name>
               <cert-data>base64encodedvalue==</cert-data>
            </certificate>
         </certificates>
      </asymmetric-key>
      <asymmetric-key>
         <name>ec-asymmetric-key</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:ec-private-key-format
         </private-key-format>
         <private-key>base64encodedvalue==</private-key>
         <certificates>
            <certificate>
               <name>ex-ec-cert</name>
               <cert-data>base64encodedvalue==</cert-data>
            </certificate>
         </certificates>
      </asymmetric-key>
      <asymmetric-key>
         <name>hidden-asymmetric-key</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <hidden-private-key/>
         <certificates>
            <certificate>
               <name>builtin-idevid-cert</name>
               <cert-data>base64encodedvalue==</cert-data>
            </certificate>
            <certificate>
               <name>my-ldevid-cert</name>
               <cert-data>base64encodedvalue==</cert-data>
            </certificate>
         </certificates>
      </asymmetric-key>
      <asymmetric-key>
         <name>encrypted-asymmetric-key</name>
         <public-key-format>
            ct:subject-public-key-info-format
         </public-key-format>
         <public-key>base64encodedvalue==</public-key>
         <private-key-format>
            ct:encrypted-one-asymmetric-key-format
         </private-key-format>
         <encrypted-private-key>
           <encrypted-by>
             <symmetric-key-ref>encrypted-symmetric-key</symmetric-k\
ey-ref>
           </encrypted-by>
           <encrypted-value>base64encodedvalue==</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 a 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 "Local or Keystore" Groupings

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

The following non-normative module is defined to illustrate these groupings:

module ex-keystore-usage {
  yang-version 1.1;

  namespace "http://example.com/ns/example-keystore-usage";
  prefix "eku";

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

  organization
   "Example Corporation";

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

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

  revision "2020-07-08" {
    description
     "Initial version";
    reference
     "RFC CCCC: 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:local-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:local-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:local-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:local-or-keystore-end-entity-cert-with-key-grouping;
      description
        "An end-entity certificate, and its associated private key,
         that may be configured locally or be a reference to a
         specific certificate (and its associated private key) in
         the keystore.";
    }
  }

}

The tree diagram [RFC8340] for this example module follows:

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

The following example provides two equivalent instances of each grouping, the first being a reference to a keystore and the second being locally-defined. 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 locally-defined instance example contains the same values defined by the keystore instance referenced by its sibling example.

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

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

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

  <symmetric-key>
    <name>example 1b</name>
    <local-definition>
      <key-format>ct:octet-string-key-format</key-format>
      <key>base64encodedvalue==</key>
    </local-definition>
  </symmetric-key>


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

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

  <asymmetric-key>
    <name>example 2b</name>
    <local-definition>
      <public-key-format>
        ct:subject-public-key-info-format
      </public-key-format>
      <public-key>base64encodedvalue==</public-key>
      <private-key-format>
        ct:rsa-private-key-format
      </private-key-format>
      <private-key>base64encodedvalue==</private-key>
    </local-definition>
  </asymmetric-key>


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

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

  <asymmetric-key-with-certs>
    <name>example 3b</name>
    <local-definition>
      <public-key-format>
          ct:subject-public-key-info-format
      </public-key-format>
      <public-key>base64encodedvalue==</public-key>
      <private-key-format>
        ct:rsa-private-key-format
      </private-key-format>
      <private-key>base64encodedvalue==</private-key>
      <certificates>
        <certificate>
          <name>a locally-defined cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
      </certificates>
    </local-definition>
  </asymmetric-key-with-certs>


  <!-- The following two equivalent examples illustrate       -->
  <!-- "local-or-keystore-end-entity-cert-with-key-grouping": -->

  <end-entity-cert-with-key>
    <name>example 4a</name>
    <keystore-reference>
      <asymmetric-key>rsa-asymmetric-key</asymmetric-key>
      <certificate>ex-rsa-cert</certificate>
    </keystore-reference>
  </end-entity-cert-with-key>

  <end-entity-cert-with-key>
    <name>example 4b</name>
    <local-definition>
      <public-key-format>
        ct:subject-public-key-info-format
      </public-key-format>
      <public-key>base64encodedvalue==</public-key>
      <private-key-format>
        ct:rsa-private-key-format
      </private-key-format>
      <private-key>base64encodedvalue==</private-key>
      <cert-data>base64encodedvalue==</cert-data>
    </local-definition>
  </end-entity-cert-with-key>

</keystore-usage>

2.3. YANG Module

This YANG module has normative references to [RFC8341] and [I-D.ietf-netconf-crypto-types].

<CODE BEGINS> file "ietf-keystore@2020-07-08.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 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 <mailto:kent+ietf@watsen.net>";

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

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

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

     This version of this YANG module is part of RFC CCCC
     (https://www.rfc-editor.org/info/rfcCCCC); 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 2020-07-08 {
    description
      "Initial version";
    reference
      "RFC CCCC: A YANG Data Model for a Keystore";
  }

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

  feature keystore-supported {
    description
      "The 'keystore-supported' feature indicates that the server
       supports the Keystore.";
  }

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

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

  typedef 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 Keystore.";
  }

  typedef 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 Keystore.";
  }

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

  grouping encrypted-by-choice-grouping {
    description
      "A grouping that defines a choice enabling references
       to other keys.";
    choice encrypted-by-choice {
      nacm:default-deny-write;
      mandatory true;
      description
        "A choice amongst other symmetric or asymmetric keys.";
      case symmetric-key-ref {
        leaf symmetric-key-ref {
          type leafref {
            path "/ks:keystore/ks:symmetric-keys/"
                 + "ks:symmetric-key/ks:name";
          }
          description
           "Identifies the symmetric key used to encrypt this key.";
        }
      }
      case asymmetric-key-ref {
        leaf asymmetric-key-ref {
          type leafref {
            path "/ks:keystore/ks:asymmetric-keys/"
                 + "ks:asymmetric-key/ks:name";
          }
          description
           "Identifies the asymmetric key used to encrypt this key.";
        }
      }
    }
  }

  grouping asymmetric-key-certificate-ref-grouping {
    description
      "This grouping defines a reference to a specific certificate
       associated with an asymmetric key stored in the Keystore.";
    leaf asymmetric-key {
      nacm:default-deny-write;
      type ks: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.";
    }
  }


  // local-or-keystore-* groupings

  grouping local-or-keystore-symmetric-key-grouping {
    description
      "A grouping that expands to allow the symmetric key to be
       either stored locally, within the using data model, or be
       a reference to a symmetric key stored in the Keystore.";
    choice local-or-keystore {
      nacm:default-deny-write;
      mandatory true;
      description
        "A choice between an inlined definition and a definition
         that exists in the Keystore.";
      case local {
        if-feature "local-definitions-supported";
        container local-definition {
          description
            "Container to hold the local key definition.";
          uses ct:symmetric-key-grouping;
        }
      }
      case keystore {
        if-feature "keystore-supported";
        leaf keystore-reference {
          type ks:symmetric-key-ref;
          description
            "A reference to an symmetric key that exists in
             the Keystore.";
        }
      }
    }
  }

  grouping local-or-keystore-asymmetric-key-grouping {
    description
      "A grouping that expands to allow the asymmetric key to be
       either stored locally, within the using data model, or be
       a reference to an asymmetric key stored in the Keystore.";
    choice local-or-keystore {
      nacm:default-deny-write;
      mandatory true;
      case local {
        if-feature "local-definitions-supported";
        container local-definition {
          description
            "Container to hold the local key definition.";
          uses ct:asymmetric-key-pair-grouping;
        }
      }
      case keystore {
        if-feature "keystore-supported";
        leaf keystore-reference {
          type ks:asymmetric-key-ref;
          description
            "A reference to an asymmetric key that exists in
             the Keystore.  The intent is to reference just the
             asymmetric key without any regard for any certificates
             that may be associated with it.";
        }
      }
      description
        "A choice between an inlined definition and a definition
         that exists in the Keystore.";
    }
  }

  grouping local-or-keystore-asymmetric-key-with-certs-grouping {
    description
      "A grouping that expands to allow an asymmetric key and its
       associated certificates to be either stored locally, within
       the using data model, or be a reference to an asymmetric key
       (and its associated certificates) stored in the Keystore.";
    choice local-or-keystore {
      nacm:default-deny-write;
      mandatory true;
      case local {
        if-feature "local-definitions-supported";
        container local-definition {
          description
            "Container to hold the local key definition.";
          uses ct:asymmetric-key-pair-with-certs-grouping;
        }
      }
      case keystore {
        if-feature "keystore-supported";
        leaf keystore-reference {
          type ks:asymmetric-key-ref;
          description
            "A reference to an asymmetric-key (and all of its
             associated certificates) in the Keystore.";
        }
      }
      description
        "A choice between an inlined definition and a definition
         that exists in the Keystore.";
    }
  }

  grouping local-or-keystore-end-entity-cert-with-key-grouping {
    description
      "A grouping that expands to allow an end-entity certificate
       (and its associated private key) to be either stored locally,
       within the using data model, or be a reference to a specific
       certificate in the Keystore.";
    choice local-or-keystore {
      nacm:default-deny-write;
      mandatory true;
      case local {
        if-feature "local-definitions-supported";
        container local-definition {
          description
            "Container to hold the local key definition.";
          uses ct:asymmetric-key-pair-with-cert-grouping;
        }
      }
      case keystore {
        if-feature "keystore-supported";
        container keystore-reference {
          uses asymmetric-key-certificate-ref-grouping;
          description
            "A reference to a specific certificate (and its
             associated private key) in the Keystore.";
        }
      }
      description
        "A choice between an inlined definition and a definition
         that exists in the Keystore.";
    }
  }

  grouping keystore-grouping {
    description
      "Grouping definition enables use in other contexts.  If ever
       done, implementations SHOULD augment new 'case' statements
       into local-or-keystore 'choice' statements to supply leafrefs
       to the new location.";
    container asymmetric-keys {
      nacm:default-deny-write;
      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;
      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;
      }
    }
  } // grouping keystore-grouping



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

  container keystore {
    description
      "The Keystore contains 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-key/"
              + "encrypted-key/encrypted-by" {
        description
          "Augments in a choice statement enabling the encrypting
           key to be any other symmetric or asymmetric key in the
           keystore.";
        uses encrypted-by-choice-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
           keystore.";
        uses encrypted-by-choice-grouping;
      }
    }
  }

}

<CODE ENDS>

3. Support for Built-in Keys

In some implementations, a server may support built-in keys. Built-in 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., SSH) is enabled.

The key characteristic of the built-in keys is that they are provided by the system, as opposed to configuration. As such, they are present in <operational>. The example below illustrates what the keystore in <operational> might look like for a server in its factory default state.

<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-key-format>
      <public-key>base64encodedvalue==</public-key>
      <hidden-private-key/>
      <certificates>
        <certificate>
          <name>Manufacturer-Generated IDevID Cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
      </certificates>
    </asymmetric-key>
  </asymmetric-keys>
</keystore>

In order for the built-in keys (and/or their associated built-in certificates) to be referenced by configuration, the referenced keys MUST first be copied into <running>. The keys SHOULD be copied into <running> using the same "key" values, so that the server can bind the references to the built-in entries.

Built-in "hidden" keys cannot be copied into other parts of the configuration because their private parts are hidden, and therefore impossible to replicate. Built-in "encrypted" keys MAY be copied into other parts of the configuration so long as they maintain their reference to the other built-in key that encrypted them.

Only the referenced keys need to be copied; that is, the keys in <running> MAY be a subset of the built-in keys define in <operational>. No keys may be added or changed (with exception to associating additional certificates to a built-in key); that is, the keys in <running> MUST be a subset (which includes the whole of the set) of the built-in keys define in <operational>.

A server MUST reject attempts to modify any aspect of built-in keys, with exception to associating additional certificates to a built-in key. That these keys are "configured" in <running> is an illusion, as they are strictly a read-only subset of that which must already exist in <operational>.

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

<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-key-format>
      <public-key>base64encodedvalue==</public-key>
      <hidden-private-key/>
      <certificates>
        <certificate>
          <name>Manufacturer-Generated IDevID Cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
        <certificate>
          <name>Deployment-Specific LDevID Cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
      </certificates>
    </asymmetric-key>
  </asymmetric-keys>
</keystore>

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

<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-key-format>
      <public-key>base64encodedvalue==</public-key>
      <hidden-private-key/>
      <certificates>
        <certificate>
          <name>Manufacturer-Generated IDevID Cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
        <certificate or:origin="or:intended">
          <name>Deployment-Specific LDevID Cert</name>
          <cert-data>base64encodedvalue==</cert-data>
        </certificate>
      </certificates>
    </asymmetric-key>
  </asymmetric-keys>
</keystore>

4. Encrypting Keys in Configuration

This section describes an approach that enables all the private keys on a server to be encrypted, such that traditional backup/restore procedures can be used without concern for keys being compromised when in transit.

4.1. Root Key

The cornerstone to this solution is the existence of a "root" key that can be used to encrypt all the other keys. The server MUST be able to use this key to decrypt the other keys in the configuration.

The root key SHOULD be a hidden key, i.e., one whose private data has no presence in <running> or <operational> (see "hidden-key" and "hidden-private-key" in "ietf-crypto-types" [I-D.ietf-netconf-crypto-types]). If the server implementation does not support hidden keys, then the private data part of key MUST be protected by access control with access granted only to an administrator with special access control rights (e.g., an organization's crypto officer). Given the long lifetime of built-in keys (see Section 3), built-in keys MUST be hidden.

A hidden root key MAY be either a symmetric key or an asymmetric key. If the hidden root key is symmetric, then the server MUST provide APIs enabling other keys (ideally generated by the server) to be encrypted. If the hidden root key is asymmetric, then the server SHOULD provide APIs enabling other keys to be both generated and encrypted by it, but MAY alternatively enable administrators with special access control rights to generate and encrypt the other keys themselves, using the hidden key's public part. For practical reasons, an unhidden root key SHOULD be asymmetric, so that its public part can be accessed by other administrators without concern.

4.2. Configuring Encrypting Keys

Each time a new key is to be configured, it SHOULD be encrypted by the root key.

In "ietf-crypto-types" [I-D.ietf-netconf-crypto-types], the format for an encrypted symmetric key is described by the "encrypted-one-symmetric-key-format" identity, while the format for an encrypted asymmetric key is described by the "encrypted-one-asymmetric-key-format" identity

Ideally, the server implementation provides an API to generate a symmetric or asymmetric key, and encrypt the generated key using another key known to the system (e.g., the root key). Thusly administrators can safely call this API to configure new keys.

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.

In either case, the encrypted key can be configured into the Keystore using either the "encrypted-key" (for symmetric keys) or the "encrypted-private-key" (for asymmetric keys) nodes. These two nodes contain both the encrypted value as well as a reference to the other key in the Keystore that it was encrypted by.

4.3. Migrating Configuration to Another Server

In the case a server's root key is used to encrypt other keys, migrating the configuration to another server may entail additional effort, assuming the second server has a different root key than the first server, in order for the second server to decrypt the other encrypted keys.

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

Another option is to introduce a "shared root" key that acts as a portable intermediate root key. This shared root key would only need to be known to an organization's crypto officer. The shared root key SHOULD be encrypted offline by the crypto officer using each server's public key, which may be, e.g., in the server's IDevID certificate. The crypto officer can then safely handoff the encrypted shared key to other administrators responsible for server installations, including migrations. In order to migrate 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 shared key's Keystore entry from the first server (an encrypted key), with the shared key encrypted by the second server's root key. The following diagram illustrates this idea:

 +-------------+                                 +---------------+
 | shared key  |                                 |shared root key|
 |(unencrypted)|-------------------------------> |  (encrypted)  |
 +-------------+     encrypts offline using      +---------------+
        ^            each server's root key          |
        |                                            |
        |                                            |
        |  possesses    \o                           |
        +--------------  |\                          |
                        / \         shares with      |
                      crypto    +--------------------+
                      officer   |
                                |
                                |
+----------------------+        |         +----------------------+
|       server-1       |        |         |       server-2       |
|    configuration     |        |         |    configuration     |
|                      |        |         |                      |
|                      |        |         |                      |
|  +----------------+  |        |         |  +----------------+  |
|  |   root key-1   |  |        |         |  |   root key-2   |  |
|  |    (hidden)    |  |        |         |  |    (hidden)    |  |
|  +----------------+  |        |         |  +----------------+  |
|      ^               |        |         |      ^               |
|      |               |        |         |      |               |
|      |               |        |         |      |               |
|      |  encrypted    |        |         |      |  encrypted    |
|      |  by           |        |         |      |  by           |
|      |               |        |         |      |               |
|      |               |        |         |      |               |
|  +----------------+  |        |         |  +----------------+  |
|  |shared root key |  |        |         |  |shared root key |  |
|  |  (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. Data at Rest

The YANG module defined in this document defines a mechanism called a "keystore" that, by its name, suggests that it will protect its contents from unauthorized disclosure and modification.

Security controls for the API (i.e., data in motion) are discussed in Section 5.2, but controls for the data at rest cannot be specified by the YANG module.

In order to satisfy the expectations of a "keystore", it is RECOMMENDED that implementations ensure that the keystore contents are encrypted when persisted to non-volatile memory.

5.2. The "ietf-keystore" 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.

All of the writable data nodes defined by this 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 module does not define any RPCs, actions, or notifications, and thus the security consideration for such is not provided here.

6. IANA Considerations

6.1. 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-keystore
   Registrant Contact: The NETCONF WG of the IETF.
   XML: N/A, the requested URI is an XML namespace.

6.2. The YANG Module Names Registry

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

   name:         ietf-keystore
   namespace:    urn:ietf:params:xml:ns:yang:ietf-keystore
   prefix:       ks
   reference:    RFC CCCC

7. References

7.1. Normative References

[I-D.ietf-netconf-crypto-types]
Watsen, K., "Common YANG Data Types for Cryptography", Work in Progress, Internet-Draft, draft-ietf-netconf-crypto-types-15, , <https://tools.ietf.org/html/draft-ietf-netconf-crypto-types-15>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC6020]
Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://www.rfc-editor.org/info/rfc6020>.
[RFC7950]
Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <https://www.rfc-editor.org/info/rfc7950>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/info/rfc8341>.

7.2. 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-03, , <https://tools.ietf.org/html/draft-ietf-netconf-http-client-server-03>.
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-17, , <https://tools.ietf.org/html/draft-ietf-netconf-keystore-17>.
[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-19, , <https://tools.ietf.org/html/draft-ietf-netconf-netconf-client-server-19>.
[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-19, , <https://tools.ietf.org/html/draft-ietf-netconf-restconf-client-server-19>.
[I-D.ietf-netconf-ssh-client-server]
Watsen, K. and G. Wu, "YANG Groupings for SSH Clients and SSH Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-ssh-client-server-19, , <https://tools.ietf.org/html/draft-ietf-netconf-ssh-client-server-19>.
[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-06, , <https://tools.ietf.org/html/draft-ietf-netconf-tcp-client-server-06>.
[I-D.ietf-netconf-tls-client-server]
Watsen, K. and G. Wu, "YANG Groupings for TLS Clients and TLS Servers", Work in Progress, Internet-Draft, draft-ietf-netconf-tls-client-server-19, , <https://tools.ietf.org/html/draft-ietf-netconf-tls-client-server-19>.
[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-10, , <https://tools.ietf.org/html/draft-ietf-netconf-trust-anchors-10>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <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, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8340]
Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <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, , <https://www.rfc-editor.org/info/rfc8342>.
[Std-802.1AR-2009]
Group, W. -. H. L. L. P. W., "IEEE Standard for Local and metropolitan area networks - Secure Device Identity", , <http://standards.ieee.org/findstds/standard/802.1AR-2009.html>.

Appendix A. Change Log

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

A.1. 00 to 01

  • Replaced the 'certificate-chain' structures with PKCS#7 structures. (Issue #1)
  • Added 'private-key' as a configurable data node, and removed the 'generate-private-key' and 'load-private-key' actions. (Issue #2)
  • Moved 'user-auth-credentials' to the ietf-ssh-client module. (Issues #4 and #5)

A.2. 01 to 02

  • Added back 'generate-private-key' action.
  • Removed 'RESTRICTED' enum from the 'private-key' leaf type.
  • Fixed up a few description statements.

A.3. 02 to 03

  • Changed draft's title.
  • Added missing references.
  • Collapsed sections and levels.
  • Added RFC 8174 to Requirements Language Section.
  • Renamed 'trusted-certificates' to 'pinned-certificates'.
  • Changed 'public-key' from config false to config true.
  • Switched 'host-key' from OneAsymmetricKey to definition from RFC 4253.

A.4. 03 to 04

  • Added typedefs around leafrefs to common keystore paths
  • Now tree diagrams reference ietf-netmod-yang-tree-diagrams
  • Removed Design Considerations section
  • Moved key and certificate definitions from data tree to groupings

A.5. 04 to 05

  • Removed trust anchors (now in their own draft)
  • Added back global keystore structure
  • Added groupings enabling keys to either be locally defined or a reference to the keystore.

A.6. 05 to 06

  • Added feature "local-keys-supported"
  • Added nacm:default-deny-all and nacm:default-deny-write
  • Renamed generate-asymmetric-key to generate-hidden-key
  • Added an install-hidden-key action
  • Moved actions inside fo the "asymmetric-key" container
  • Moved some groupings to draft-ietf-netconf-crypto-types

A.7. 06 to 07

  • Removed a "require-instance false"
  • Clarified some description statements
  • Improved the keystore-usage examples

A.8. 07 to 08

  • Added "local-definition" containers to avoid posibility of the action/notification statements being under a "case" statement.
  • Updated copyright date, boilerplate template, affiliation, folding algorithm, and reformatted the YANG module.

A.9. 08 to 09

  • Added a 'description' statement to the 'must' in the /keystore/asymmetric-key node explaining that the descendent values may exist in <operational> only, and that implementation MUST assert that the values are either configured or that they exist in <operational>.
  • Copied above 'must' statement (and description) into the local-or-keystore-asymmetric-key-grouping, local-or-keystore-asymmetric-key-with-certs-grouping, and local-or-keystore-end-entity-cert-with-key-grouping statements.

A.10. 09 to 10

  • Updated draft title to match new truststore draft title
  • Moved everything under a top-level 'grouping' to enable use in other contexts.
  • Renamed feature from 'local-keys-supported' to 'local-definitions-supported' (same name used in truststore)
  • Removed the either-all-or-none 'must' expressions for the key's 3-tuple values (since the values are now 'mandatory true' in crypto-types)
  • Example updated to reflect 'mandatory true' change in crypto-types draft

A.11. 10 to 11

  • Replaced typedef asymmetric-key-certificate-ref with grouping asymmetric-key-certificate-ref-grouping.
  • Added feature feature 'key-generation'.
  • Cloned groupings symmetric-key-grouping, asymmetric-key-pair-grouping, asymmetric-key-pair-with-cert-grouping, and asymmetric-key-pair-with-certs-grouping from crypto-keys, augmenting into each new case statements for values that have been encrypted by other keys in the keystore. Refactored keystore model to use these groupings.
  • Added new 'symmetric-keys' lists, as a sibling to the existing 'asymmetric-keys' list.
  • Added RPCs (not actions) 'generate-symmetric-key' and 'generate-asymmetric-key' to *return* a (potentially encrypted) key.

A.12. 11 to 12

  • Updated to reflect crypto-type's draft using enumerations over identities.
  • Added examples for the 'generate-symmetric-key' and 'generate-asymmetric-key' RPCs.
  • Updated the Introduction section.

A.13. 12 to 13

  • Updated examples to incorporate new "key-format" identities.
  • Made the two "generate-*-key" RPCs be "action" statements instead.

A.14. 13 to 14

  • Updated YANG module and examples to incorporate the new iana-*-algorithm modules in the crypto-types draft..

A.15. 14 to 15

  • Added new "Support for Built-in Keys" section.
  • Added 'must' expressions asserting that the 'key-format' leaf whenever an encrypted key is specified.
  • Added local-or-keystore-symmetric-key-grouping for PSK support.

A.16. 15 to 16

  • Moved the generate key actions to ietf-crypt-types as RPCs, which are augmented by ietf-keystore to support encrypted keys. Examples updated accordingly.
  • Added a SSH certificate-based key (RFC 6187) and a raw private key to the example instance document (partly so they could be referenced by examples in the SSH and TLS client/server drafts.

A.17. 16 to 17

  • Removed augments to the "generate-symmetric-key" and "generate-asymmetric-key" groupings.
  • Removed "generate-symmetric-key" and "generate-asymmetric-key" examples.
  • Removed the "algorithm" nodes from remaining examples.
  • Updated the "Support for Built-in Keys" section.
  • Added new section "Encrypting Keys in Configuration".
  • Added a "Note to Reviewers" note to first page.

A.18. 17 to 18

  • Removed dangling/unnecessary ref to RFC 8342.
  • r/MUST/SHOULD/ wrt strength of keys being configured over transports.
  • Added an example for the "certificate-expiration" notification.
  • Clarified that OS MAY have a multiplicity of underlying keystores and/or HSMs.
  • Clarified expected behavior for "built-in" keys in <operational>
  • Clarified the "Migrating Configuration to Another Server" section.
  • Expanded "Data Model Overview section(s) [remove "wall" of tree diagrams].
  • Updated the Security Considerations section.

Acknowledgements

The authors would like to thank for following for lively discussions on list and in the halls (ordered by first name): Alan Luchuk, Andy Bierman, Benoit Claise, Bert Wijnen, Balazs Kovacs, David Lamparter, Eric Voit, Ladislav Lhotka, Liang Xia, Juergen Schoenwaelder, Mahesh Jethanandani, Martin Bjorklund, Mehmet Ersue, Phil Shafer, Radek Krejci, Ramkumar Dhanapal, Reshad Rahman, Sean Turner, and Tom Petch.

Author's Address

Kent Watsen
Watsen Networks