Internet Engineering Task Force (IETF) K. Watsen

Internet Engineering Task Force (IETF) K. Watsen
Request for Comments: 9641 Watsen Networks
Category: Standards Track October 2024
ISSN: 2070-1721

A YANG Data Model for a Truststore

Abstract

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

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/rfc9641.

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. Adherence to the NMDA
1.4. Conventions
2. The "ietf-truststore" Module
2.1. Data Model Overview
2.2. Example Usage
2.3. YANG Module
3. Support for Built-In Trust Anchors
4. Security Considerations
4.1. Security of Data at Rest
4.2. Unconstrained Public Key Usage
4.3. Considerations for the "ietf-truststore" YANG Module
5. IANA Considerations
5.1. The IETF XML Registry
5.2. The YANG Module Names Registry
6. References
6.1. Normative References
6.2. Informative References
Acknowledgements
Author's Address

1. Introduction

This document presents a YANG 1.1 [RFC7950] module that has the
following characteristics:

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

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

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

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

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

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 both 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 below diagram. 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 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 | Reference |
+========================+==========================+
| crypto-types | [RFC9640] |
+------------------------+--------------------------+
| truststore | RFC 9641 |
+------------------------+--------------------------+
| keystore | [RFC9642] |
+------------------------+--------------------------+
| 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: Label 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. Adherence to the NMDA

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

1.4. Conventions

Various examples in this document use "BASE64VALUE=" as a placeholder
value for binary data that has been base64 encoded (see 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" with the word "truststore"
to refer to the top-level instance of the "truststore-grouping"
grouping when the "central-truststore-supported" feature is enabled.
Please be aware that consuming YANG modules MAY instantiate the
"truststore-grouping" grouping in other locations. All such other
instances are not the "central" instance.

2. The "ietf-truststore" Module

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

2.1. Data Model Overview

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

2.1.1. Features

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

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

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

2.1.2. Typedefs

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

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

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

Comments:

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

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

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

2.1.3. Groupings

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

* central-certificate-ref-grouping

* central-public-key-ref-grouping

* inline-or-truststore-certs-grouping

* inline-or-truststore-public-keys-grouping

* truststore-grouping

Each of these groupings are presented in the following subsections.

2.1.3.1. The "central-certificate-ref-grouping" Grouping

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

grouping central-certificate-ref-grouping:
+-- certificate-bag? ts:central-certificate-bag-ref
| {central-truststore-supported,certificates}?
+-- certificate? ts:central-certificate-ref
{central-truststore-supported,certificates}?

Comments:

* The "central-certificate-ref-grouping" grouping is provided solely
as a convenience to consuming modules that wish to enable the
configuration of a reference to a certificate in a certificate-bag
in the truststore.

* The "certificate-bag" leaf uses the "central-certificate-bag-ref"
typedef defined in Section 2.1.2.

* The "certificate" leaf uses the "central-certificate-ref" typedef
defined in Section 2.1.2.

2.1.3.2. The "central-public-key-ref-grouping" Grouping

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

grouping central-public-key-ref-grouping:
+-- public-key-bag? ts:central-public-key-bag-ref
| {central-truststore-supported,public-keys}?
+-- public-key? ts:central-public-key-ref
{central-truststore-supported,public-keys}?

Comments:

* The "central-public-key-ref-grouping" grouping is provided solely
as a convenience to consuming modules that wish to enable the
configuration of a reference to a public-key in a public-key-bag
in the truststore.

* The "public-key-bag" leaf uses the "central-public-key-bag-ref"
typedef defined in Section 2.1.2.

* The "public-key" leaf uses the "central-public-key-ref" typedef
defined in Section 2.1.2.

2.1.3.3. The "inline-or-truststore-certs-grouping" Grouping

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

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

Comments:

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

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

* For the "inline-definition" option, the "certificate" node uses
the "trust-anchor-cert-grouping" grouping discussed in
Section 2.1.4.8 of [RFC9640].

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

2.1.3.4. The "inline-or-truststore-public-keys-grouping" Grouping

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

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

Comments:

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

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

* For the "inline-definition" option, the "public-key" node uses the
"public-key-grouping" grouping discussed in Section 2.1.4.4 of
[RFC9640].

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

2.1.3.5. The "truststore-grouping" Grouping

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

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

Comments:

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

* For certificates, each certificate is defined by the "trust-
anchor-cert-grouping" grouping (Section 2.1.4.8 of [RFC9640]).
The "cert-data" node is a Cryptographic Message Syntax (CMS)
structure that can be composed of a chain of one or more
certificates. Additionally, the "certificate-expiration"
notification enables the server to alert clients when certificates
are nearing expiration or have already expired.

* For public keys, each public key is defined by the "public-key-
grouping" grouping (Section 2.1.4.4 of [RFC9640]). The "public-
key" node can be one of any number of structures specified by the
"public-key-format" identity node.

2.1.4. Protocol-Accessible Nodes

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

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

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

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

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-truststore" module are
instances of the "truststore-grouping" grouping discussed in
Section 2.1.3.5.

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

* The "truststore-grouping" grouping is discussed in
Section 2.1.3.5.

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

2.2. Example Usage

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

2.2.1. A Truststore Instance

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

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

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

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

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

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


<certificate-bags>


<certificate-bag>
<name>trusted-server-ca-certs</name>
<description>
Trust anchors (i.e., CA certs) used to authenticate server
certificates. A server certificate is authenticated if its
end-entity certificate has a chain of trust to one of these
certificates.
</description>
<certificate>
<name>Server Cert Issuer #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Server Cert Issuer #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>


<certificate-bag>
<name>trusted-server-ee-certs</name>
<description>
Specific end-entity certificates used to authenticate server
certificates. A server certificate is authenticated if its
end-entity certificate is an exact match to one of these
certificates.
</description>
<certificate>
<name>My Application #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>My Application #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>


<certificate-bag>
<name>trusted-client-ca-certs</name>
<description>
Trust anchors (i.e., CA certs) used to authenticate client
certificates. A client certificate is authenticated if its
end-entity certificate has a chain of trust to one of these
certificates.
</description>
<certificate>
<name>Client Identity Issuer #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Client Identity Issuer #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>


<certificate-bag>
<name>trusted-client-ee-certs</name>
<description>
Specific end-entity certificates used to authenticate client
certificates. A client certificate is authenticated if its
end-entity certificate is an exact match to one of these
certificates.
</description>
<certificate>
<name>George Jetson</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Fred Flintstone</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>
</certificate-bags>


<public-key-bags>


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

This list of SSH public keys is analogous to OpenSSH's
"/etc/ssh/ssh_known_hosts" file.
</description>
<public-key>
<name>corp-fw1</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>corp-fw2</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
</public-key-bag>


<public-key-bag>
<name>SSH Public Keys for Application A</name>
<description>
SSH public keys used to authenticate application A's SSH
public keys. An SSH public key is authenticated if it
is an exact match to one of these public keys.
</description>
<public-key>
<name>Application Instance #1</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>Application Instance #2</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
</public-key-bag>


<public-key-bag>
<name>Raw Public Keys for TLS Servers</name>
<public-key>
<name>Raw Public Key #1</name>
<public-key-format>ct:subject-public-key-info-format</public\
-key-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>Raw Public Key #2</name>
<public-key-format>ct:subject-public-key-info-format</public\
-key-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
</public-key-bag>


<public-key-bag>
<name>Raw Public Keys for TLS Clients</name>
<public-key>
<name>Raw Public Key #1</name>
<public-key-format>ct:subject-public-key-info-format</public\
-key-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>Raw Public Key #2</name>
<public-key-format>ct:subject-public-key-info-format</public\
-key-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
</public-key-bag>
</public-key-bags>
</truststore>

2.2.2. A Certificate Expiration Notification

The following example illustrates the "certificate-expiration"
notification (per Section 2.1.4.7 of [RFC9640]) for a certificate
configured in the truststore described in Section 2.2.1.

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

<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2018-05-25T00:01:00Z</eventTime>
<truststore xmlns="urn:ietf:params:xml:ns:yang:ietf-truststore">
<certificate-bags>
<certificate-bag>
<name>trusted-client-ee-certs</name>
<certificate>
<name>George Jetson</name>
<certificate-expiration>
<expiration-date>2024-01-05T14:18:53-05:00</expiration-d\
ate>
</certificate-expiration>
</certificate>
</certificate-bag>
</certificate-bags>
</truststore>
</notification>

2.2.3. The "Inline or Truststore" Groupings

This section illustrates the various "inline-or-truststore" groupings
defined in the "ietf-truststore" module, specifically the "inline-or-
truststore-certs-grouping" (Section 2.1.3.3) and "inline-or-
truststore-public-keys-grouping" (Section 2.1.3.4) groupings.

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

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

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

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

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

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

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

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

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




<cert>
<name>example 1a</name>
<central-truststore-reference>trusted-client-ca-certs</central-t\
ruststore-reference>
</cert>

<cert>
<name>example 1b</name>
<inline-definition>
<certificate>
<name>Client Identity Issuer #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Client Identity Issuer #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</inline-definition>
</cert>




<public-key>
<name>example 2a</name>
<central-truststore-reference>trusted-ssh-public-keys</central-t\
ruststore-reference>
</public-key>

<public-key>
<name>example 2b</name>
<inline-definition>
<public-key>
<name>corp-fw1</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>corp-fw2</name>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>BASE64VALUE=</public-key>
</public-key>
</inline-definition>
</public-key>

</truststore-usage>

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

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

import ietf-truststore {
prefix ts;
reference
"RFC 9641: A YANG Data Model for a Truststore";
}

organization
"Example Corporation";

contact
"Author: YANG Designer <mailto:[email protected]>";

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

revision 2024-10-10 {
description
"Initial version.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
}

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

2.3. YANG Module

This YANG module imports modules from [RFC8341] and [RFC9640].

<CODE BEGINS> file "[email protected]"
module ietf-truststore {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-truststore";
prefix ts;

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:[email protected]>
Author: Kent Watsen <[email protected]>";
description
"This module defines a 'truststore' to centralize management
of trust anchors, including certificates and public keys.

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 9641
(https://www.rfc-editor.org/info/rfc9641); see the RFC
itself for full legal notices.";

revision 2024-10-10 {
description
"Initial version.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
}

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

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

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

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

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

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

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

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

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

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

/*****************/
/* Groupings */
/*****************/
// *-ref groupings

grouping central-certificate-ref-grouping {
description
"Grouping for the reference to a certificate in a
certificate-bag in the central truststore.";
leaf certificate-bag {
nacm:default-deny-write;
if-feature "central-truststore-supported";
if-feature "certificates";
type ts:central-certificate-bag-ref;
must '../certificate';
description
"Reference to a certificate-bag in the truststore.";
}
leaf certificate {
nacm:default-deny-write;
if-feature "central-truststore-supported";
if-feature "certificates";
type ts:central-certificate-ref;
must '../certificate-bag';
description
"Reference to a specific certificate in the
referenced certificate-bag.";
}
}

grouping central-public-key-ref-grouping {
description
"Grouping for the reference to a public key in a
public-key-bag in the central truststore.";
leaf public-key-bag {
nacm:default-deny-write;
if-feature "central-truststore-supported";
if-feature "public-keys";
type ts:central-public-key-bag-ref;
description
"Reference of a public key bag in the truststore, including
the certificate to authenticate the TLS client.";
}
leaf public-key {
nacm:default-deny-write;
if-feature "central-truststore-supported";
if-feature "public-keys";
type ts:central-public-key-ref;
description
"Reference to a specific public key in the
referenced public-key-bag.";
}
}

// inline-or-truststore-* groupings

grouping inline-or-truststore-certs-grouping {
description
"A grouping for the configuration of a list of certificates.
The list of certificates may be defined inline or as a
reference to a certificate bag in the central truststore.

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

grouping inline-or-truststore-public-keys-grouping {
description
"A grouping that allows the public keys to either be
configured locally, within the data model being used, or be a
reference to a public key bag stored in the truststore.

Servers that wish to define alternate truststore locations
SHOULD augment in custom 'case' statement, enabling
references to those alternate truststore locations.";
choice inline-or-truststore {
nacm:default-deny-write;
mandatory true;
description
"A choice between an inlined definition and a definition
that exists in the truststore.";
case inline {
if-feature "inline-definitions-supported";
container inline-definition {
description
"A container to hold local public key definitions.";
list public-key {
key "name";
description
"A public key definition.";
leaf name {
type string;
description
"An arbitrary name for this public key.";
}
uses ct:public-key-grouping;
}
}
}
case central-truststore {
if-feature "central-truststore-supported";
if-feature "public-keys";
leaf central-truststore-reference {
type ts:central-public-key-bag-ref;
description
"A reference to a bag of public keys that exists
in the central truststore.";
}
}
}
}

// the truststore grouping

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

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

container truststore {
if-feature "central-truststore-supported";
nacm:default-deny-write;
description
"The truststore contains bags of certificates and
public keys.";
uses truststore-grouping;
}
}
<CODE ENDS>

3. Support for Built-In Trust Anchors

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

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

The primary characteristic of the built-in trust anchors is that they
are provided by the server, as opposed to configuration. 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 truststore in <operational>
might look like for a server in its factory default state. Note that
the built-in trust anchor bags have the "or:origin" annotation value
"or:system".

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

<certificate-bag or:origin="or:system">
<name>Built-In Manufacturer Trust Anchor Certificates</name>
<description>
Certificates built into the device for authenticating
manufacturer-signed objects, such as TLS server certificates,
vouchers, etc.
</description>
<certificate>
<name>Manufacturer Root CA Cert</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>

<certificate-bag or:origin="or:system">
<name>Built-In Public Trust Anchor Certificates</name>
<description>
Certificates built into the device for authenticating
certificates issued by public certificate authorities,
such as the end-entity certificate for web servers.
</description>
<certificate>
<name>Public Root CA Cert 1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Public Root CA Cert 2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Public Root CA Cert 3</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</certificate-bag>

</certificate-bags>
</truststore>

4. Security Considerations

4.1. Security of Data at Rest

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

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

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

4.2. Unconstrained Public Key Usage

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

Trust anchors configured via this module are implicitly trusted to
validate certification paths that may include any name, be used for
any purpose, or be subject to constraints imposed by an intermediate
CA or by context in which the truststore is used. Implementations
are free to use alternative or auxiliary structures and validation
rules to define constraints that limit the applicability of a trust
anchor.

4.3. Considerations for the "ietf-truststore" YANG Module

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

The "ietf-truststore" YANG module defines "grouping" and "container"
statements that are 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.,
Secure Shell (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.

Most of the readable data nodes defined in this YANG module are not
considered sensitive or vulnerable in network environments. However,
the "cert-data" node uses the NACM "default-deny-all" extension for
reasons described in Section 3.8 of [RFC9640].

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

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

5. IANA Considerations

5.1. The IETF XML Registry

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

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

5.2. The YANG Module Names Registry

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

Name: ietf-truststore
Namespace: urn:ietf:params:xml:ns:yang:ietf-truststore
Prefix: ts
Reference: RFC 9641

6. References

6.1. 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>.

[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>.

6.2. 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., 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>.

[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>.

[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>.

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

[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>.

[RFC9642] Watsen, K., "A YANG Data Model for a Keystore", RFC 9642,
DOI 10.17487/RFC9642, October 2024,
<https://www.rfc-editor.org/info/rfc9642>.

[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>.

[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)", World Wide Web Consortium
Recommendation REC-xml-20081126, November 2008,
<https://www.w3.org/TR/2008/REC-xml-20081126/>.

Acknowledgements

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

The authors additionally thank the following for helping give shape
to this work (ordered by first name): Balázs Kovács, Carl Wallace,
Eric Voit, Éric Vyncke, Francesca Palombini, Jensen Zhang, Jürgen
Schönwälder, Lars Eggert, Liang Xia, Martin Björklund, Murray
Kucherawy, Nick Hancock, Paul Kyzivat, Qin Wu, Rob Wilton, Robert
Varga, Roman Danyliw, and Yoav Nir.

Author's Address

Kent Watsen
Watsen Networks
Email: [email protected]