Internet Engineering Task Force (IETF) K. Watsen
Request for Comments: 9644 Watsen Networks
Category: Standards Track August 2024
ISSN: 2070-1721
YANG Groupings for SSH Clients and SSH Servers
Abstract
This document presents YANG 1.1 modules -- three IETF modules and the
script used to create four supporting IANA modules.
The three IETF modules are ietf-ssh-common, ietf-ssh-client, and
ietf-ssh-server. The "ietf-ssh-client" and "ietf-ssh-server" modules
are the primary productions of this work, supporting the
configuration and monitoring of Secure Shell (SSH) clients and
servers.
The four IANA modules are iana-ssh-encryption-algs, iana-ssh-key-
exchange-algs, iana-ssh-mac-algs, and iana-ssh-public-key-algs.
These modules each define YANG enumerations providing support for an
IANA-maintained algorithm registry.
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/rfc9644.
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. Regarding the IETF Modules
1.2. Relation to Other RFCs
1.3. Specification Language
1.4. Adherence to the NMDA
1.5. Conventions
2. The "ietf-ssh-common" Module
2.1. Data Model Overview
2.2. Example Usage
2.3. YANG Module
3. The "ietf-ssh-client" Module
3.1. Data Model Overview
3.2. Example Usage
3.3. YANG Module
4. The "ietf-ssh-server" Module
4.1. Data Model Overview
4.2. Example Usage
4.3. YANG Module
5. Security Considerations
5.1. Considerations for the "iana-ssh-key-exchange-algs" Module
5.2. Considerations for the "iana-ssh-encryption-algs" Module
5.3. Considerations for the "iana-ssh-mac-algs" Module
5.4. Considerations for the "iana-ssh-public-key-algs" Module
5.5. Considerations for the "ietf-ssh-common" YANG Module
5.6. Considerations for the "ietf-ssh-client" YANG Module
5.7. Considerations for the "ietf-ssh-server" YANG Module
6. IANA Considerations
6.1. The IETF XML Registry
6.2. The YANG Module Names Registry
6.3. Considerations for the "iana-ssh-encryption-algs" Module
6.4. Considerations for the "iana-ssh-mac-algs" Module
6.5. Considerations for the "iana-ssh-public-key-algs" Module
6.6. Considerations for the "iana-ssh-key-exchange-algs" Module
7. References
7.1. Normative References
7.2. Informative References
Appendix A. Script to Generate IANA-Maintained YANG Modules
Acknowledgements
Contributors
Author's Address
1. Introduction
This document presents YANG 1.1 [RFC7950] modules -- three IETF
modules and the script to create four IANA modules.
The three IETF modules are ietf-ssh-common (Section 2), ietf-ssh-
client (Section 3), and ietf-ssh-server (Section 4). The "ietf-ssh-
client" and "ietf-ssh-server" modules are the primary productions of
this work, supporting the configuration and monitoring of SSH clients
and servers.
The groupings defined in this document are expected to be used in
conjunction with the groupings defined in an underlying transport-
level module, such as the groupings defined in [RFC9643]. The
transport-level data model enables the configuration of transport-
level values, such as a remote address, a remote port, a local
address, and a local port.
The four IANA modules are: iana-ssh-encryption-algs, iana-ssh-key-
exchange-algs, iana-ssh-mac-algs, and iana-ssh-public-key-algs.
These modules each define YANG enumerations providing support for an
IANA-maintained algorithm registry.
This document assumes that the four IANA modules exist and presents a
script in Appendix A that IANA may use to generate the YANG modules.
This document does not publish the initial versions of these four
modules. IANA publishes these modules.
1.1. Regarding the IETF Modules
The three IETF modules define features and groupings to model
"generic" SSH clients and SSH servers, where "generic" should be
interpreted as "least common denominator" rather than "complete."
Support for the basic SSH protocol [RFC4252] [RFC4253] [RFC4254] is
afforded by these modules, leaving configuration of advanced features
(e.g., multiple channels) to augmentations made by consuming modules.
It is intended that the YANG groupings will be used by applications
needing to configure SSH client and server protocol stacks. For
instance, these groupings are used to help define the data model models in
[NETCONF-CLIENT-SERVER], for clients and servers using the Network
Configuration Protocol (NETCONF) over SSH [RFC6242] based
clients and servers in [NETCONF-CLIENT-SERVER]. [RFC6242].
The "ietf-ssh-client" and "ietf-ssh-server" YANG modules each define
one grouping, which is focused on just SSH-specific configuration,
and specifically avoid any transport-level configuration, such as
what ports to listen on or connect to. This affords applications the
opportunity to define their own strategy for how the underlying TCP
connection is established. For instance, applications supporting
NETCONF Call Home [RFC8071] could use the "ssh-server-grouping"
grouping for the SSH parts it provides while adding data nodes for
the TCP-level call-home configuration.
The modules defined in this document optionally support [RFC6187],
which describes enabling host keys and public keys based on X.509v3
certificates.
1.2. Relation to Other RFCs
This document presents three YANG modules [RFC7950] that are part of
a collection of RFCs that work together to ultimately support the
configuration of both the clients and servers of both the NETCONF
[RFC6241] and RESTCONF [RFC8040] protocols.
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 | [RFC9641] |
+------------------------+--------------------------+
| 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
1.3. 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.
1.4. Adherence to the NMDA
This document is compliant with the Network Management Datastore
Architecture (NMDA) [RFC8342]. For instance, as described in
[RFC9641] and [RFC9642], trust anchors and keys installed during
manufacturing are expected to appear in <operational> (Section 5.3 of
[RFC8342]) and <system> [SYSTEM-CONFIG] if implemented.
1.5. Conventions
Various examples in this document use "BASE64VALUE=" as a placeholder
value for binary data that has been base64 encoded (per Section 9.8
of [RFC7950]). This placeholder value is used because real
base64-encoded structures are often many lines long and hence
distracting to the example being presented.
2. The "ietf-ssh-common" Module
The SSH common model presented in this section contains features and
groupings common to both SSH clients and SSH servers. The
"transport-params-grouping" grouping can be used to configure the
list of SSH transport algorithms permitted by the SSH client or SSH
server. The lists of permitted algorithms are in decreasing order of
usage preference. The algorithm that appears first in the client
list that also appears in the server list is the one that is used for
the SSH transport layer connection. The ability to restrict the
algorithms allowed is provided in this grouping for SSH clients and
SSH servers that are capable of doing so and may serve to make SSH
clients and SSH servers compliant with security policies.
2.1. Data Model Overview
This section provides an overview of the "ietf-ssh-common" module in
terms of its features, identities, and groupings.
2.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-ssh-common" module:
Features:
+-- ssh-x509-certs
+-- transport-params
+-- asymmetric-key-pair-generation
+-- algorithm-discovery
The diagram above uses syntax that is similar to but not defined in
[RFC8340].
Please refer to the YANG module for a description of each feature.
2.1.2. Groupings
The "ietf-ssh-common" module defines the following "grouping"
statement:
* transport-params-grouping
This grouping is presented in the following subsection.
2.1.2.1. The "transport-params-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "transport-
params-grouping" grouping:
grouping transport-params-grouping:
+-- host-key
| +-- host-key-alg* ssh-public-key-algorithm
+-- key-exchange
| +-- key-exchange-alg* ssh-key-exchange-algorithm
+-- encryption
| +-- encryption-alg* ssh-encryption-algorithm
+-- mac
+-- mac-alg* ssh-mac-algorithm
Comments:
* This grouping is used by both the "ssh-client-grouping" and the
"ssh-server-grouping" groupings defined in Sections 3.1.2.1 and
4.1.2.1, respectively.
* This grouping enables client and server configurations to specify
the algorithms that are to be used when establishing SSH sessions.
* Each list is "ordered-by user".
2.1.3. Protocol-Accessible Nodes
The following tree diagram [RFC8340] lists all the protocol-
accessible nodes defined in the "ietf-ssh-common" module without
expanding the "grouping" statements:
module: ietf-ssh-common
+--ro supported-algorithms {algorithm-discovery}?
+--ro public-key-algorithms
| +--ro supported-algorithm* ssh-public-key-algorithm
+--ro encryption-algorithms
| +--ro supported-algorithm* ssh-encryption-algorithm
+--ro key-exchange-algorithms
| +--ro supported-algorithm* ssh-key-exchange-algorithm
+--ro mac-algorithms
+--ro supported-algorithm* ssh-mac-algorithm
rpcs:
+---x generate-asymmetric-key-pair
{asymmetric-key-pair-generation}?
+---w input
| +---w algorithm ssh-public-key-algorithm
| +---w num-bits? uint16
| +---w private-key-encoding
| +---w (private-key-encoding)
| +--:(cleartext) {ct:cleartext-private-keys}?
| | +---w cleartext? empty
| +--:(encrypted) {ct:encrypted-private-keys}?
| | +---w encrypted
| | +---w ks:encrypted-by-grouping
| +--:(hidden) {ct:hidden-private-keys}?
| +---w hidden? empty
+--ro output
+--ro (key-or-hidden)?
+--:(key)
| +---u ct:asymmetric-key-pair-grouping
+--:(hidden)
+--ro location?
instance-identifier
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-ssh-common" module are
limited to the "supported-algorithms" container, which is
constrained by the "algorithm-discovery" feature, and the
"generate-asymmetric-key-pair" RPC, which is constrained by the
"asymmetric-key-pair-generation" feature.
* The "encrypted-by-grouping" grouping is discussed in
Section 2.1.3.1 of [RFC9642].
* The "asymmetric-key-pair-grouping" grouping is discussed in
Section 2.1.4.6 of [RFC9640].
2.2. Example Usage
The following example illustrates the "transport-params-grouping'
grouping when populated with some data.
=============== NOTE: '\' line wrapping per RFC 8792 ================
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<transport-params
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<host-key>
<host-key-alg>x509v3-rsa2048-sha256</host-key-alg>
<host-key-alg>ssh-rsa</host-key-alg>
<host-key-alg>ssh-rsa@openssh.com</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>diffie-hellman-group-exchange-sha256</key-exch\
ange-alg>
</key-exchange>
<encryption>
<encryption-alg>aes256-ctr</encryption-alg>
<encryption-alg>aes192-ctr</encryption-alg>
<encryption-alg>aes128-ctr</encryption-alg>
<encryption-alg>aes256-gcm@openssh.com</encryption-alg>
</encryption>
<mac>
<mac-alg>hmac-sha2-256</mac-alg>
<mac-alg>hmac-sha2-512</mac-alg>
</mac>
</transport-params>
The following example illustrates operational state data indicating
the SSH algorithms supported by the server.
=============== NOTE: '\' line wrapping per RFC 8792 ================
<supported-algorithms
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<encryption-algorithms>
<supported-algorithm>aes256-ctr</supported-algorithm>
<supported-algorithm>arcfour256</supported-algorithm>
<supported-algorithm>serpent256-ctr</supported-algorithm>
<supported-algorithm>AEAD_AES_128_GCM</supported-algorithm>
<supported-algorithm>AEAD_AES_256_GCM</supported-algorithm>
<supported-algorithm>aes256-gcm@openssh.com</supported-algorithm>
</encryption-algorithms>
<key-exchange-algorithms>
<supported-algorithm>ecdh-sha2-nistp256</supported-algorithm>
<supported-algorithm>rsa2048-sha256</supported-algorithm>
<supported-algorithm>gss-group14-sha1-nistp256</supported-algori\
thm>
<supported-algorithm>gss-gex-sha1-nistp256</supported-algorithm>
<supported-algorithm>gss-group14-sha256-1.2.840.10045.3.1.1</sup\
ported-algorithm>
<supported-algorithm>curve25519-sha256</supported-algorithm>
</key-exchange-algorithms>
<mac-algorithms>
<supported-algorithm>hmac-sha2-256</supported-algorithm>
<supported-algorithm>hmac-sha2-512</supported-algorithm>
<supported-algorithm>AEAD_AES_256_GCM</supported-algorithm>
</mac-algorithms>
<public-key-algorithms>
<supported-algorithm>rsa-sha2-256</supported-algorithm>
<supported-algorithm>rsa-sha2-512</supported-algorithm>
<supported-algorithm>spki-sign-rsa</supported-algorithm>
<supported-algorithm>pgp-sign-dss</supported-algorithm>
<supported-algorithm>x509v3-rsa2048-sha256</supported-algorithm>
<supported-algorithm>ecdsa-sha2-nistp256</supported-algorithm>
<supported-algorithm>ecdsa-sha2-1.3.132.0.37</supported-algorith\
m>
<supported-algorithm>ssh-ed25519</supported-algorithm>
<supported-algorithm>ssh-rsa@openssh.com</supported-algorithm>
</public-key-algorithms>
</supported-algorithms>
The following example illustrates the "generate-asymmetric-key-pair"
RPC.
REQUEST
=============== NOTE: '\' line wrapping per RFC 8792 ================
<rpc message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<generate-asymmetric-key-pair
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<algorithm>ecdsa-sha2-nistp256</algorithm>
<num-bits>521</num-bits>
<private-key-encoding>
<encrypted>
<asymmetric-key-ref>hidden-asymmetric-key</asymmetric-key-re\
f>
</encrypted>
</private-key-encoding>
</generate-asymmetric-key-pair>
</rpc>
RESPONSE
=============== NOTE: '\' line wrapping per RFC 8792 ================
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types"
xmlns:sshcmn="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<sshcmn:public-key-format>ct:subject-public-key-info-format</sshcm\
n:public-key-format>
<sshcmn:public-key>BASE64VALUE=</sshcmn:public-key>
<sshcmn:private-key-format>ct:ec-private-key-format</sshcmn:privat\
e-key-format>
<sshcmn:cleartext-private-key>BASE64VALUE=</sshcmn:cleartext-priva\
te-key>
</rpc-reply>
2.3. YANG Module
This YANG module has normative references to [RFC4250], [RFC4253],
[RFC4344], [RFC4419], [RFC5656],
[RFC6187], [RFC6668], and [FIPS_186-5].
<CODE BEGINS> file "ietf-ssh-common@2024-03-16.yang"
module ietf-ssh-common {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-common";
prefix sshcmn;
import iana-ssh-encryption-algs {
prefix sshea;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
import iana-ssh-key-exchange-algs {
prefix sshkea;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
import iana-ssh-mac-algs {
prefix sshma;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
import iana-ssh-public-key-algs {
prefix sshpka;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
import ietf-crypto-types {
prefix ct;
reference
"RFC 9640: YANG Data Types and Groupings for Cryptography";
}
import ietf-keystore {
prefix ks;
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
WG List: NETCONF WG list <mailto:netconf@ietf.org>
Author: Kent Watsen <mailto:kent+ietf@watsen.net>
Author: Gary Wu <mailto:garywu@cisco.com>";
description
"This module defines common features and groupings for
Secure Shell (SSH).
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 9644
(https://www.rfc-editor.org/info/rfc9644); see the RFC
itself for full legal notices.";
revision 2024-03-16 {
description
"Initial version.";
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-x509-certs {
description
"X.509v3 certificates are supported for SSH.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
feature transport-params {
description
"SSH transport layer parameters are configurable.";
}
feature asymmetric-key-pair-generation {
description
"Indicates that the server implements the
'generate-asymmetric-key-pair' RPC.";
}
feature algorithm-discovery {
description
"Indicates that the server implements the
'supported-algorithms' container.";
}
// Typedefs
typedef ssh-public-key-algorithm {
type union {
type sshpka:ssh-public-key-algorithm;
type string {
length "1..64" {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
pattern '.*@.*' {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
}
}
description
"A type that enables the public key algorithm to be
either an IANA-maintained public key algorithm in
the 'iana-ssh-public-key-algs' YANG module (RFC 9644)
or a locally defined algorithm, per Section 4.6.1
of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned Numbers
RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
typedef ssh-key-exchange-algorithm {
type union {
type sshkea:ssh-key-exchange-algorithm;
type string {
length "1..64" {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
pattern '.*@.*' {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
}
}
description
"A type that enables the key exchange algorithm to be
either an IANA-maintained key exchange algorithm in
the 'iana-ssh-key-exchange-algs' YANG module (RFC 9644)
or a locally defined algorithm, per Section 4.6.1
of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned Numbers
RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
typedef ssh-encryption-algorithm {
type union {
type sshea:ssh-encryption-algorithm;
type string {
length "1..64" {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
pattern '.*@.*' {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
}
}
description
"A type that enables the encryption algorithm to be
either an IANA-maintained encryption algorithm in
the 'iana-ssh-encryption-algs' YANG module (RFC 9644)
or a locally defined algorithm, per Section 4.6.1
of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned Numbers
RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
typedef ssh-mac-algorithm {
type union {
type sshma:ssh-mac-algorithm;
type string {
length "1..64" {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
pattern '.*@.*' {
description
"Non-IANA-maintained algorithms must include the
at sign (@) in them, per Section 4.6.1 of RFC
4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned
Numbers";
}
}
}
description
"A type that enables the message authentication code (MAC)
algorithm to be either an IANA-maintained MAC algorithm
in the 'iana-ssh-mac-algs' YANG module (RFC 9644)
or a locally defined algorithm, per Section 4.6.1
of RFC 4250.";
reference
"RFC 4250: The Secure Shell (SSH) Protocol Assigned Numbers
RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
// Groupings
grouping transport-params-grouping {
description
"A reusable grouping for SSH transport parameters.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
container host-key {
description
"Parameters regarding host key.";
leaf-list host-key-alg {
type ssh-public-key-algorithm;
ordered-by user;
description
"Acceptable host key algorithms in order of decreasing
preference.
If this leaf-list is not configured (has zero
elements), the acceptable host key algorithms are
implementation-defined.";
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
}
container key-exchange {
description
"Parameters regarding key exchange.";
leaf-list key-exchange-alg {
type ssh-key-exchange-algorithm;
ordered-by user;
description
"Acceptable key exchange algorithms in order of decreasing
preference.
If this leaf-list is not configured (has zero
elements), the acceptable key exchange algorithms are
implementation-defined.";
}
}
container encryption {
description
"Parameters regarding encryption.";
leaf-list encryption-alg {
type ssh-encryption-algorithm;
ordered-by user;
description
"Acceptable encryption algorithms in order of decreasing
preference.
If this leaf-list is not configured (has zero
elements), the acceptable encryption algorithms are
implementation-defined.";
}
}
container mac {
description
"Parameters regarding message authentication code (MAC).";
leaf-list mac-alg {
type ssh-mac-algorithm;
ordered-by user;
description
"Acceptable MAC algorithms in order of decreasing
preference.
If this leaf-list is not configured (has zero
elements), the acceptable MAC algorithms are
implementation-defined.";
}
}
}
// Protocol-accessible Nodes
container supported-algorithms {
if-feature "algorithm-discovery";
config false;
description
"Identifies all of the supported algorithms.";
container public-key-algorithms {
description
"A container for a list of public key algorithms
supported by the server.";
leaf-list supported-algorithm {
type ssh-public-key-algorithm;
description
"A public key algorithm supported by the server.";
}
}
container encryption-algorithms {
description
"A container for a list of encryption algorithms
supported by the server.";
leaf-list supported-algorithm {
type ssh-encryption-algorithm;
description
"An encryption algorithm supported by the server.";
}
}
container key-exchange-algorithms {
config false;
description
"A container for a list of key exchange algorithms
supported by the server.";
leaf-list supported-algorithm {
type ssh-key-exchange-algorithm;
description
"A key exchange algorithm supported by the server.";
}
}
container mac-algorithms {
config false;
description
"A container for a list of MAC algorithms
supported by the server.";
leaf-list supported-algorithm {
type ssh-mac-algorithm;
description
"A MAC algorithm supported by the server.";
}
}
}
rpc generate-asymmetric-key-pair {
if-feature "asymmetric-key-pair-generation";
description
"Requests the device to generate a public key using
the specified key algorithm.";
input {
leaf algorithm {
type ssh-public-key-algorithm;
mandatory true;
description
"The algorithm to be used when generating the key.";
}
leaf num-bits {
type uint16;
description
"Specifies the number of bits in the key to create.
For RSA keys, the minimum size is 1024 bits and
the default is 3072 bits. Generally, 3072 bits is
considered sufficient. DSA keys must be exactly 1024
bits, as specified by FIPS 186-5. For Elliptic Curve
Digital Signature Algorithm (ECDSA) keys, the
'num-bits' value determines the key length by selecting
from one of three elliptic curve sizes: 256, 384, or
521 bits. Attempting to use bit lengths other than
these three values for ECDSA keys will fail. ECDSA-SK,
Ed25519, and Ed25519-SK keys have a fixed length, and
thus, the 'num-bits' value is not specified.";
reference
"FIPS 186-5: Digital Signature Standard (DSS)";
}
container private-key-encoding {
description
"Indicates how the private key is to be encoded.";
choice private-key-encoding {
mandatory true;
description
"A choice amongst optional private key handling.";
case cleartext {
if-feature "ct:cleartext-private-keys";
leaf cleartext {
type empty;
description
"Indicates that the private key is to be returned
as a cleartext value.";
}
}
case encrypted {
if-feature "ct:encrypted-private-keys";
container encrypted {
description
"Indicates that the private key is to be encrypted
using the specified symmetric or asymmetric key.";
uses ks:encrypted-by-grouping;
}
}
case hidden {
if-feature "ct:hidden-private-keys";
leaf hidden {
type empty;
description
"Indicates that the private key is to be hidden.
Unlike the 'cleartext' and 'encrypt' options, the
key returned is a placeholder for an internally
stored key. See the 'Support for Built-in Keys'
section in RFC 9642 for information about hidden
keys.
It is expected that the server will instantiate
the hidden key in the same location where built-in
keys are located. Rather than returning the key,
just the key's location is returned in the output.";
}
}
}
}
}
output {
choice key-or-hidden {
case key {
uses ct:asymmetric-key-pair-grouping;
}
case hidden {
leaf location {
type instance-identifier;
description
"The location to where a hidden key was created.";
}
}
description
"The output can be either a key (for cleartext and
encrypted keys) or the location to where the key
was created (for hidden keys).";
}
}
} // end generate-asymmetric-key-pair
}
<CODE ENDS>
3. The "ietf-ssh-client" Module
This section defines a YANG 1.1 [RFC7950] module called "ietf-ssh-
client". A high-level overview of the module is provided in
Section 3.1. Examples illustrating the module's use are provided in
Section 3.2 ("Example Usage"). The YANG module itself is defined in
Section 3.3.
3.1. Data Model Overview
This section provides an overview of the "ietf-ssh-client" module in
terms of its features and groupings.
3.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-ssh-client" module:
Features:
+-- ssh-client-keepalives
+-- client-ident-password
+-- client-ident-publickey
+-- client-ident-hostbased
+-- client-ident-none
The diagram above uses syntax that is similar to but not defined in
[RFC8340].
Please refer to the YANG module for a description of each feature.
3.1.2. Groupings
The "ietf-ssh-client" module defines the following "grouping"
statement:
* ssh-client-grouping
This grouping is presented in the following subsection.
3.1.2.1. The "ssh-client-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "ssh-client-
grouping" grouping:
=============== NOTE: '\' line wrapping per RFC 8792 ================
grouping ssh-client-grouping:
+-- client-identity
| +-- username? string
| +-- public-key! {client-ident-publickey}?
| | +---u ks:inline-or-keystore-asymmetric-key-grouping
| +-- password! {client-ident-password}?
| | +---u ct:password-grouping
| +-- hostbased! {client-ident-hostbased}?
| | +---u ks:inline-or-keystore-asymmetric-key-grouping
| +-- none? empty {client-ident-none}?
| +-- certificate! {sshcmn:ssh-x509-certs}?
| +---u ks:inline-or-keystore-end-entity-cert-with-key-group\
ing
+-- server-authentication
| +-- ssh-host-keys!
| | +---u ts:inline-or-truststore-public-keys-grouping
| +-- ca-certs! {sshcmn:ssh-x509-certs}?
| | +---u ts:inline-or-truststore-certs-grouping
| +-- ee-certs! {sshcmn:ssh-x509-certs}?
| +---u ts:inline-or-truststore-certs-grouping
+-- transport-params {sshcmn:transport-params}?
| +---u sshcmn:transport-params-grouping
+-- keepalives! {ssh-client-keepalives}?
+-- max-wait? uint16
+-- max-attempts? uint8
Comments:
* The "client-identity" node configures a "username" and
authentication methods, each enabled by a "feature" statement
defined in Section 3.1.1.
* The "server-authentication" node configures trust anchors for
authenticating the SSH server, with each option enabled by a
"feature" statement.
* The "transport-params" node, which must be enabled by a feature,
configures parameters for the SSH sessions established by this
configuration.
* The "keepalives" node, which must be enabled by a feature,
configures a "presence" container for testing the aliveness of the
SSH server. The aliveness-test occurs at the SSH protocol layer.
* For the referenced grouping statements:
- The "inline-or-keystore-asymmetric-key-grouping" grouping is
discussed in Section 2.1.3.4 of [RFC9642].
- The "inline-or-keystore-end-entity-cert-with-key-grouping"
grouping is discussed in Section 2.1.3.6 of [RFC9642].
- The "inline-or-truststore-public-keys-grouping" grouping is
discussed in Section 2.1.3.4 of [RFC9641].
- The "inline-or-truststore-certs-grouping" grouping is discussed
in Section 2.1.3.3 of [RFC9641].
- The "transport-params-grouping" grouping is discussed in
Section 2.1.2.1 in this document.
3.1.3. Protocol-Accessible Nodes
The "ietf-ssh-client" module defines only "grouping" statements that
are used by other modules to instantiate protocol-accessible nodes.
Thus, this module, when implemented, does not itself define any
protocol-accessible nodes.
3.2. Example Usage
This section presents two examples showing the "ssh-client-grouping"
grouping populated with some data. These examples are effectively
the same, except the first configures the client identity using an
inlined key, while the second uses a key configured in a keystore.
Both examples are consistent with the examples presented in
Section 2.2.1 of [RFC9641] and Section 2.2.1 of [RFC9642].
The following configuration example uses inline-definitions for the
client identity and server authentication:
=============== NOTE: '\' line wrapping per RFC 8792 ================
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<ssh-client
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-client"
xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
<!-- how this client will authenticate itself to the server -->
<client-identity>
<username>foobar</username>
<public-key>
<inline-definition>
<private-key-format>ct:rsa-private-key-format</private-key-f\
ormat>
<cleartext-private-key>BASE64VALUE=</cleartext-private-key>
</inline-definition>
</public-key>
</client-identity>
<!-- which host keys will this client trust -->
<server-authentication>
<ssh-host-keys>
<inline-definition>
<public-key>
<name>corp-fw1</name>
<public-key-format>ct:ssh-public-key-format</public-key-fo\
rmat>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>corp-fw2</name>
<public-key-format>ct:ssh-public-key-format</public-key-fo\
rmat>
<public-key>BASE64VALUE=</public-key>
</public-key>
</inline-definition>
</ssh-host-keys>
<ca-certs>
<inline-definition>
<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>
</inline-definition>
</ca-certs>
<ee-certs>
<inline-definition>
<certificate>
<name>My Application #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>My Application #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</inline-definition>
</ee-certs>
</server-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
The following configuration example uses central-keystore-references
for the client identity and central-truststore-references for server
authentication from the keystore:
=============== NOTE: '\' line wrapping per RFC 8792 ================
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<ssh-client
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-client"
xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<!-- how this client will authenticate itself to the server -->
<client-identity>
<username>foobar</username>
<public-key>
<central-keystore-reference>ssh-rsa-key</central-keystore-refe\
rence>
</public-key>
<certificate>
<central-keystore-reference>
<asymmetric-key>ssh-rsa-key-with-cert</asymmetric-key>
<certificate>ex-rsa-cert2</certificate>
</central-keystore-reference>
</certificate>
</client-identity>
<!-- which host-keys will this client trust -->
<server-authentication>
<ssh-host-keys>
<central-truststore-reference>trusted-ssh-public-keys</central\
-truststore-reference>
</ssh-host-keys>
<ca-certs>
<central-truststore-reference>trusted-server-ca-certs</central\
-truststore-reference>
</ca-certs>
<ee-certs>
<central-truststore-reference>trusted-server-ee-certs</central\
-truststore-reference>
</ee-certs>
</server-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
3.3. YANG Module
This YANG module has normative references to [RFC4252], [RFC4254],
[RFC8341], [RFC9640], [RFC9641], and [RFC9642].
<CODE BEGINS> file "ietf-ssh-client@2024-03-16.yang"
module ietf-ssh-client {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-client";
prefix sshc;
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";
}
import ietf-truststore {
prefix ts;
reference
"RFC 9641: A YANG Data Model for a Truststore";
}
import ietf-keystore {
prefix ks;
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
}
import ietf-ssh-common {
prefix sshcmn;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
WG List: NETCONF WG list <mailto:netconf@ietf.org>
Author: Kent Watsen <mailto:kent+ietf@watsen.net>";
description
"This module defines a reusable grouping for SSH clients that
can be used as a basis for specific SSH client instances.
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 9644
(https://www.rfc-editor.org/info/rfc9644); see the RFC
itself for full legal notices.";
revision 2024-03-16 {
description
"Initial version.";
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-client-keepalives {
description
"Per socket SSH keep-alive parameters are configurable for
SSH clients on the server implementing this feature.";
}
feature client-ident-publickey {
description
"Indicates that the 'publickey' authentication type, per
RFC 4252, is supported for client identification.
The 'publickey' authentication type is required by
RFC 4252, but common implementations allow it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-password {
description
"Indicates that the 'password' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-hostbased {
description
"Indicates that the 'hostbased' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-none {
description
"Indicates that the 'none' authentication type, per
RFC 4252, is supported for client identification.
It is NOT RECOMMENDED to enable this feature.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
// Groupings
grouping ssh-client-grouping {
description
"A reusable grouping for configuring an SSH client without
any consideration for how an underlying TCP session is
established.
Note that this grouping uses fairly typical descendant
node names such that a nesting of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'ssh-client-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
container client-identity {
nacm:default-deny-write;
description
"The username and authentication methods for the client.
The authentication methods are unordered. Clients may
initially send any configured method or, per Section 5.2 of
RFC 4252, send the 'none' method to prompt the server
to provide a list of productive methods. Whenever a
choice amongst methods arises, implementations SHOULD
use a default ordering that prioritizes automation
over human interaction.";
leaf username {
type string;
description
"The username of this user. This will be the username
used, for instance, to log into an SSH server.";
}
container public-key {
if-feature "client-ident-publickey";
presence
"Indicates that public-key-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A locally defined or referenced asymmetric key
pair to be used for client identification.";
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
uses ks:inline-or-keystore-asymmetric-key-grouping {
refine "inline-or-keystore/inline/inline-definition" {
must 'not(public-key-format) or derived-from-or-self'
+ '(public-key-format, "ct:ssh-public-key-format")';
}
refine "inline-or-keystore/central-keystore/"
+ "central-keystore-reference" {
must 'not(deref(.)/../ks:public-key-format) or derived-'
+ 'from-or-self(deref(.)/../ks:public-key-format, '
+ '"ct:ssh-public-key-format")';
}
}
}
container password {
if-feature "client-ident-password";
presence
"Indicates that password-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A password to be used to authenticate the client's
identity.";
uses ct:password-grouping;
}
container hostbased {
if-feature "client-ident-hostbased";
presence
"Indicates that host-based authentication is configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A locally defined or referenced asymmetric key
pair to be used for host identification.";
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
uses ks:inline-or-keystore-asymmetric-key-grouping {
refine "inline-or-keystore/inline/inline-definition" {
must 'not(public-key-format) or derived-from-or-self('
+ 'public-key-format, "ct:ssh-public-key-format")';
}
refine "inline-or-keystore/central-keystore/"
+ "central-keystore-reference" {
must 'not(deref(.)/../ks:public-key-format) or derived-'
+ 'from-or-self(deref(.)/../ks:public-key-format, '
+ '"ct:ssh-public-key-format")';
}
}
}
leaf none {
if-feature "client-ident-none";
type empty;
description
"Indicates that the 'none' algorithm is used for client
identification.";
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that certificate-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A locally defined or referenced certificate
to be used for client identification.";
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
uses
ks:inline-or-keystore-end-entity-cert-with-key-grouping {
refine "inline-or-keystore/inline/inline-definition" {
must 'not(public-key-format) or derived-from-or-self('
+ 'public-key-format, "ct:subject-public-key-info-'
+ 'format")';
}
refine "inline-or-keystore/central-keystore/"
+ "central-keystore-reference/asymmetric-key" {
must 'not(deref(.)/../ks:public-key-format) or derived-'
+ 'from-or-self(deref(.)/../ks:public-key-format, '
+ '"ct:subject-public-key-info-format")';
}
}
}
} // container client-identity
container server-authentication {
nacm:default-deny-write;
must 'ssh-host-keys or ca-certs or ee-certs';
description
"Specifies how the SSH client can authenticate SSH servers.
Any combination of authentication methods is additive and
unordered.";
container ssh-host-keys {
presence
"Indicates that the SSH host key have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A bag of SSH host keys used by the SSH client to
authenticate SSH server host keys. A server host key
is authenticated if it is an exact match to a
configured SSH host key.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-public-keys-grouping {
refine
"inline-or-truststore/inline/inline-definition/public"
+ "-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "inline-or-truststore/central-truststore/"
+ "central-truststore-reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
container ca-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that the CA certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A set of certificate authority (CA) certificates used by
the SSH client to authenticate SSH servers. A server
is authenticated if its certificate has a valid chain
of trust to a configured CA certificate.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-certs-grouping;
}
container ee-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that the EE certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A set of end-entity (EE) certificates used by the SSH
client to authenticate SSH servers. A server is
authenticated if its certificate is an exact match to a
configured end-entity certificate.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-certs-grouping;
}
} // container server-authentication
container transport-params {
nacm:default-deny-write;
if-feature "sshcmn:transport-params";
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
} // container transport-parameters
container keepalives {
nacm:default-deny-write;
if-feature "ssh-client-keepalives";
presence
"Indicates that the SSH client proactively tests the
aliveness of the remote SSH server.";
description
"Configures the keep-alive policy to proactively test
the aliveness of the SSH server. An unresponsive SSH
server is dropped after approximately max-wait *
max-attempts seconds. Per Section 4 of RFC 4254,
the SSH client SHOULD send an SSH_MSG_GLOBAL_REQUEST
message with a purposely nonexistent 'request name'
value (e.g., keepalive@ietf.org) keepalive@example.com) and the 'want reply'
value set to '1'.";
reference
"RFC 4254: The Secure Shell (SSH) Connection Protocol";
leaf max-wait {
type uint16 {
range "1..max";
}
units "seconds";
default "30";
description
"Sets the amount of time in seconds after which an
SSH-level message will be sent to test the aliveness
of the SSH server if no data has been received from the
SSH server.";
}
leaf max-attempts {
type uint8;
default "3";
description
"Sets the maximum number of sequential keep-alive
messages that can fail to obtain a response from
the SSH server before assuming the SSH server is
no longer alive.";
}
} // container keepalives
} // grouping ssh-client-grouping
}
<CODE ENDS>
4. The "ietf-ssh-server" Module
This section defines a YANG 1.1 module called "ietf-ssh-server". A
high-level overview of the module is provided in Section 4.1.
Examples illustrating the module's use are provided in Section 4.2
("Example Usage"). The YANG module itself is defined in Section 4.3.
4.1. Data Model Overview
This section provides an overview of the "ietf-ssh-server" module in
terms of its features and groupings.
4.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-ssh-server" module:
Features:
+-- ssh-server-keepalives
+-- local-users-supported
+-- local-user-auth-publickey {local-users-supported}?
+-- local-user-auth-password {local-users-supported}?
+-- local-user-auth-hostbased {local-users-supported}?
+-- local-user-auth-none {local-users-supported}?
The diagram above uses syntax that is similar to but not defined in
[RFC8340].
Please refer to the YANG module for a description of each feature.
4.1.2. Groupings
The "ietf-ssh-server" module defines the following "grouping"
statement:
* ssh-server-grouping
This grouping is presented in the following subsection.
4.1.2.1. The "ssh-server-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "ssh-server-
grouping" grouping:
=============== NOTE: '\' line wrapping per RFC 8792 ================
grouping ssh-server-grouping:
+-- server-identity
| +-- host-key* [name]
| +-- name? name string
| +-- (host-key-type)
| +--:(public-key)
| | +-- public-key
| | +---u ks:inline-or-keystore-asymmetric-key-groupi\
ng
| +--:(certificate)
| +-- certificate {sshcmn:ssh-x509-certs}?
| +---u ks:inline-or-keystore-end-entity-cert-with-\
key-grouping
+-- client-authentication
| +-- users {local-users-supported}?
| | +-- user* [name]
| | +-- name? name string
| | +-- public-keys! {local-user-auth-publickey}?
| | | +---u ts:inline-or-truststore-public-keys-grouping
| | +-- password
| | | +-- hashed-password? ianach:crypt-hash
| | | | {local-user-auth-password}?
| | | +--ro last-modified? yang:date-and-time
| | +-- hostbased! {local-user-auth-hostbased}?
| | | +---u ts:inline-or-truststore-public-keys-grouping
| | +-- none? empty {local-user-auth-none}?
| +-- ca-certs! {sshcmn:ssh-x509-certs}?
| | +---u ts:inline-or-truststore-certs-grouping
| +-- ee-certs! {sshcmn:ssh-x509-certs}?
| +---u ts:inline-or-truststore-certs-grouping
+-- transport-params {sshcmn:transport-params}?
| +---u sshcmn:transport-params-grouping
+-- keepalives! {ssh-server-keepalives}?
+-- max-wait? uint16
+-- max-attempts? uint8
Comments:
* The "server-identity" node configures the authentication methods
the server can use to identify itself to clients. The ability to
use a certificate is enabled by a "feature".
* The "client-authentication" node configures trust anchors for
authenticating the SSH client, with each option enabled by a
"feature" statement.
* The "transport-params" node, which must be enabled by a feature,
configures parameters for the SSH sessions established by this
configuration.
* The "keepalives" node, which must be enabled by a feature,
configures a "presence" container for testing the aliveness of the
SSH client. The aliveness-test occurs at the SSH protocol layer.
* For the referenced grouping statements:
- The "inline-or-keystore-asymmetric-key-grouping" grouping is
discussed in Section 2.1.3.4 of [RFC9642].
- The "inline-or-keystore-end-entity-cert-with-key-grouping"
grouping is discussed in Section 2.1.3.6 of [RFC9642].
- The "inline-or-truststore-public-keys-grouping" grouping is
discussed in Section 2.1.3.4 of [RFC9641].
- The "inline-or-truststore-certs-grouping" grouping is discussed
in Section 2.1.3.3 of [RFC9641].
- The "transport-params-grouping" grouping is discussed in
Section 2.1.2.1 in this document.
4.1.3. Protocol-Accessible Nodes
The "ietf-ssh-server" module defines only "grouping" statements that
are used by other modules to instantiate protocol-accessible nodes.
Thus, this module, when implemented, does not itself define any
protocol-accessible nodes.
4.2. Example Usage
This section presents two examples showing the "ssh-server-grouping"
grouping populated with some data. These examples are effectively
the same, except the first configures the server identity using an
inlined key, while the second uses a key configured in a keystore.
Both examples are consistent with the examples presented in
Section 2.2.1 of [RFC9641] and Section 2.2.1 of [RFC9642].
The following configuration example uses inline-definitions for the
server identity and client authentication:
=============== NOTE: '\' line wrapping per RFC 8792 ================
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<ssh-server
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-server"
xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
<!-- the host-key this SSH server will present -->
<server-identity>
<host-key>
<name>my-pubkey-based-host-key</name>
<public-key>
<inline-definition>
<private-key-format>ct:rsa-private-key-format</private-key\
-format>
<cleartext-private-key>BASE64VALUE=</cleartext-private-key>
</inline-definition>
</public-key>
</host-key>
<host-key>
<name>my-cert-based-host-key</name>
<certificate>
<inline-definition>
<private-key-format>ct:rsa-private-key-format</private-key\
-format>
<cleartext-private-key>BASE64VALUE=</cleartext-private-key>
<cert-data>BASE64VALUE=</cert-data>
</inline-definition>
</certificate>
</host-key>
</server-identity>
<!-- the client credentials this SSH server will trust -->
<client-authentication>
<users>
<user>
<name>mary</name>
<password>
<hashed-password>$0$example-secret</hashed-password>
</password>
<public-keys>
<inline-definition>
<public-key>
<name>Mary-Key-1</name>
<public-key-format>ct:ssh-public-key-format</public-ke\
y-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
<public-key>
<name>Mary-Key-2</name>
<public-key-format>ct:ssh-public-key-format</public-ke\
y-format>
<public-key>BASE64VALUE=</public-key>
</public-key>
</inline-definition>
</public-keys>
</user>
</users>
<ca-certs>
<inline-definition>
<certificate>
<name>Identity Cert Issuer #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Identity Cert Issuer #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</inline-definition>
</ca-certs>
<ee-certs>
<inline-definition>
<certificate>
<name>Application #1</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
<certificate>
<name>Application #2</name>
<cert-data>BASE64VALUE=</cert-data>
</certificate>
</inline-definition>
</ee-certs>
</client-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-server>
The following configuration example uses central-keystore-references
for the server identity and central-truststore-references for client
authentication from the keystore:
=============== NOTE: '\' line wrapping per RFC 8792 ================
<!-- The outermost element below doesn't exist in the data model. -->
<!-- It simulates if the "grouping" were a "container" instead. -->
<ssh-server
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-server">
<!-- the host-key this SSH server will present -->
<server-identity>
<host-key>
<name>my-pubkey-based-host-key</name>
<public-key>
<central-keystore-reference>ssh-rsa-key</central-keystore-re\
ference>
</public-key>
</host-key>
<host-key>
<name>my-cert-based-host-key</name>
<certificate>
<central-keystore-reference>
<asymmetric-key>ssh-rsa-key-with-cert</asymmetric-key>
<certificate>ex-rsa-cert2</certificate>
</central-keystore-reference>
</certificate>
</host-key>
</server-identity>
<!-- the client credentials this SSH server will trust -->
<client-authentication>
<users>
<user>
<name>mary</name>
<password>
<hashed-password>$0$example-secret</hashed-password>
</password>
<public-keys>
<central-truststore-reference>SSH Public Keys for Applicat\
ion A</central-truststore-reference>
</public-keys>
</user>
</users>
<ca-certs>
<central-truststore-reference>trusted-client-ca-certs</central\
-truststore-reference>
</ca-certs>
<ee-certs>
<central-truststore-reference>trusted-client-ee-certs</central\
-truststore-reference>
</ee-certs>
</client-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-server>
4.3. YANG Module
This YANG module has normative references to [RFC4251], [RFC4252],
[RFC4253], [RFC4254], [RFC6991], [RFC7317], [RFC8341], [RFC9640],
[RFC9641], and [RFC9642].
<CODE BEGINS> file "ietf-ssh-server@2024-03-16.yang"
module ietf-ssh-server {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-server";
prefix sshs;
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
import iana-crypt-hash {
prefix ianach;
reference
"RFC 7317: A YANG Data Model for System Management";
}
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";
}
import ietf-truststore {
prefix ts;
reference
"RFC 9641: A YANG Data Model for a Truststore";
}
import ietf-keystore {
prefix ks;
reference
"RFC 9642: A YANG Data Model for a Keystore and Keystore
Operations";
}
import ietf-ssh-common {
prefix sshcmn;
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/netconf
WG List: NETCONF WG list <mailto:netconf@ietf.org>
Author: Kent Watsen <mailto:kent+ietf@watsen.net>";
description
"This module defines a reusable grouping for SSH servers that
can be used as a basis for specific SSH server instances.
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 9644
(https://www.rfc-editor.org/info/rfc9644); see the RFC
itself for full legal notices.";
revision 2024-03-16 {
description
"Initial version.";
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-server-keepalives {
description
"Per socket SSH keep-alive parameters are configurable for
SSH servers on the server implementing this feature.";
}
feature local-users-supported {
description
"Indicates that the configuration for users can be
configured herein, as opposed to in an application-
specific location.";
}
feature local-user-auth-publickey {
if-feature "local-users-supported";
description
"Indicates that the 'publickey' authentication type,
per RFC 4252, is supported for locally defined users.
The 'publickey' authentication type is required by
RFC 4252, but common implementations allow it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-password {
if-feature "local-users-supported";
description
"Indicates that the 'password' authentication type,
per RFC 4252, is supported for locally defined users.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-hostbased {
if-feature "local-users-supported";
description
"Indicates that the 'hostbased' authentication type,
per RFC 4252, is supported for locally defined users.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-none {
if-feature "local-users-supported";
description
"Indicates that the 'none' authentication type, per
RFC 4252, is supported. It is NOT RECOMMENDED to
enable this feature.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
// Groupings
grouping ssh-server-grouping {
description
"A reusable grouping for configuring an SSH server without
any consideration for how underlying TCP sessions are
established.
Note that this grouping uses fairly typical descendant
node names such that a nesting of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'ssh-server-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
container server-identity {
nacm:default-deny-write;
description
"The list of host keys the SSH server will present when
establishing an SSH connection.";
list host-key {
key "name";
min-elements 1;
ordered-by user;
description
"An ordered list of host keys (see RFC 4251) the SSH
server will use to construct its ordered list of
algorithms when sending its SSH_MSG_KEXINIT message,
as defined in Section 7.1 of RFC 4253.";
reference
"RFC 4251: The Secure Shell (SSH) Protocol Architecture
RFC 4253: The Secure Shell (SSH) Transport Layer
Protocol";
leaf name {
type string;
description
"An arbitrary name for this host key.";
}
choice host-key-type {
mandatory true;
description
"The type of host key being specified.";
container public-key {
description
"A locally defined or referenced asymmetric key pair
to be used for the SSH server's host key.";
reference
"RFC 9642: A YANG Data Model for a Keystore and
Keystore Operations";
uses ks:inline-or-keystore-asymmetric-key-grouping {
refine "inline-or-keystore/inline/inline-definition" {
must 'not(public-key-format) or derived-from-or-self'
+ '(public-key-format, "ct:ssh-public-key-format")';
}
refine "inline-or-keystore/central-keystore/"
+ "central-keystore-reference" {
must 'not(deref(.)/../ks:public-key-format) or '
+ 'derived-from-or-self(deref(.)/../ks:public-'
+ 'key-format, "ct:ssh-public-key-format")';
}
}
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
description
"A locally defined or referenced end-entity
certificate to be used for the SSH server's
host key.";
reference
"RFC 9642: A YANG Data Model for a Keystore and
Keystore Operations";
uses
ks:inline-or-keystore-end-entity-cert-with-key-grouping{
refine "inline-or-keystore/inline/inline-definition" {
must 'not(public-key-format) or derived-from-or-self'
+ '(public-key-format, "ct:subject-public-key-'
+ 'info-format")';
}
refine "inline-or-keystore/central-keystore/"
+ "central-keystore-reference/asymmetric-key" {
must 'not(deref(.)/../ks:public-key-format) or '
+ 'derived-from-or-self(deref(.)/../ks:public-key'
+ '-format, "ct:subject-public-key-info-format")';
}
}
}
}
}
} // container server-identity
container client-authentication {
nacm:default-deny-write;
description
"Specifies how the SSH server can be configured to
authenticate SSH clients. See RFC 4252 for a general
discussion about SSH authentication.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication Protocol";
container users {
if-feature "local-users-supported";
description
"A list of locally configured users.";
list user {
key "name";
description
"A locally configured user.
The server SHOULD derive the list of authentication
'method names' returned to the SSH client from the
descendant nodes configured herein, per Sections
5.1 and 5.2 of RFC 4252.
The authentication methods are unordered. Clients
must authenticate to all configured methods.
Whenever a choice amongst methods arises,
implementations SHOULD use a default ordering
that prioritizes automation over human interaction.";
leaf name {
type string;
description
"The 'username' for the SSH client, as defined in
the SSH_MSG_USERAUTH_REQUEST message in RFC 4253.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer
Protocol";
}
container public-keys {
if-feature "local-user-auth-publickey";
presence
"Indicates that public keys have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be
configured.";
description
"A set of SSH public keys may be used by the SSH
server to authenticate this user. A user is
authenticated if its public key is an exact
match to a configured public key.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-public-keys-grouping {
refine "inline-or-truststore/inline/inline-definition/"
+ "public-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "inline-or-truststore/central-truststore/"
+ "central-truststore-reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
container password {
description
"A password the SSH server may use to authenticate
this user. A user is authenticated if the hash
of the supplied password matches this value.";
leaf hashed-password {
if-feature "local-user-auth-password";
type ianach:crypt-hash;
description
"The password for this user.";
}
leaf last-modified {
type yang:date-and-time;
config false;
description
"Identifies when the password was last set.";
}
}
container hostbased {
if-feature "local-user-auth-hostbased";
presence
"Indicates that host-based (RFC 4252) keys have been
configured. This statement is present so the
mandatory descendant nodes do not imply that this
node must be configured.";
description
"A set of SSH host keys used by the SSH server to
authenticate this user's host. A user's host is
authenticated if its host key is an exact match
to a configured host key.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol
RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-public-keys-grouping {
refine "inline-or-truststore/inline/inline-definition/"
+ "public-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "inline-or-truststore/central-truststore/"
+ "central-truststore-reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
leaf none {
if-feature "local-user-auth-none";
type empty;
description
"Indicates that the 'none' method is configured
for this user.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol";
}
}
} // users
container ca-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that CA certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply this node must be configured.";
description
"A set of certificate authority (CA) certificates used by
the SSH server to authenticate SSH client certificates.
A client certificate is authenticated if it has a valid
chain of trust to a configured CA certificate.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-certs-grouping;
}
container ee-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that EE certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply this node must be configured.";
description
"A set of client certificates (i.e., end-entity
certificates) used by the SSH server to authenticate
the certificates presented by SSH clients. A client
certificate is authenticated if it is an exact match
to a configured end-entity certificate.";
reference
"RFC 9641: A YANG Data Model for a Truststore";
uses ts:inline-or-truststore-certs-grouping;
}
} // container client-authentication
container transport-params {
nacm:default-deny-write;
if-feature "sshcmn:transport-params";
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
} // container transport-params
container keepalives {
nacm:default-deny-write;
if-feature "ssh-server-keepalives";
presence
"Indicates that the SSH server proactively tests the
aliveness of the remote SSH client.";
description
"Configures the keep-alive policy to proactively test
the aliveness of the SSH client. An unresponsive SSH
client is dropped after approximately max-wait *
max-attempts seconds. Per Section 4 of RFC 4254,
the SSH server SHOULD send an SSH_MSG_GLOBAL_REQUEST
message with a purposely nonexistent 'request name'
value (e.g., keepalive@ietf.org) keepalive@example.com) and the 'want reply'
value set to '1'.";
reference
"RFC 4254: The Secure Shell (SSH) Connection Protocol";
leaf max-wait {
type uint16 {
range "1..max";
}
units "seconds";
default "30";
description
"Sets the amount of time in seconds after which
an SSH-level message will be sent to test the
aliveness of the SSH client if no data has been
received from the SSH client.";
}
leaf max-attempts {
type uint8;
default "3";
description
"Sets the maximum number of sequential keep-alive
messages that can fail to obtain a response from
the SSH client before assuming the SSH client is
no longer alive.";
}
}
} // grouping ssh-server-grouping
}
<CODE ENDS>
5. Security Considerations
The three IETF YANG modules in this document define groupings and
will not be deployed as standalone modules. Their security
implications may be context-dependent based on their use in other
modules. The designers of modules that import these groupings must
conduct their own analysis of the security considerations.
5.1. Considerations for the "iana-ssh-key-exchange-algs" Module
This section follows is modeled after the template defined in Section 3.7.1
of [RFC8407].
The "iana-ssh-key-exchange-algs" YANG module defines a data model
that 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 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.
This YANG module defines YANG enumerations for a public IANA-
maintained registry.
YANG enumerations are not security-sensitive, as they are statically
defined in the publicly accessible YANG module. IANA MAY deprecate
and/or obsolete enumerations over time as needed to address security
issues found in the algorithms.
This module does not define any writable nodes, RPCs, actions, or
notifications, and thus, the security considerations for such are not
provided here.
5.2. Considerations for the "iana-ssh-encryption-algs" Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "iana-ssh-encryption-algs" YANG module defines a data model that
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 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.
This YANG module defines YANG enumerations for a public IANA-
maintained registry.
YANG enumerations are not security-sensitive, as they are statically
defined in the publicly accessible YANG module.
This module does not define any writable nodes, RPCs, actions, or
notifications, and thus, the security considerations for such are not
provided here.
5.3. Considerations for the "iana-ssh-mac-algs" Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "iana-ssh-mac-algs" YANG module defines a data model that 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 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.
This YANG module defines YANG enumerations for a public IANA-
maintained registry.
YANG enumerations are not security-sensitive, as they are statically
defined in the publicly accessible YANG module.
This module does not define any writable nodes, RPCs, actions, or
notifications, and thus, the security considerations for such are not
provided here.
5.4. Considerations for the "iana-ssh-public-key-algs" Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "iana-ssh-public-key-algs" YANG module defines a data model that
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 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.
This YANG module defines YANG enumerations for a public IANA-
maintained registry.
YANG enumerations are not security-sensitive, as they are statically
defined in the publicly accessible YANG module.
This module does not define any writable nodes, RPCs, actions, or
notifications, and thus, the security considerations for such are not
provided here.
5.5. Considerations for the "ietf-ssh-common" YANG Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "ietf-ssh-common" YANG module defines "grouping" statements that
are 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 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.
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.
None of the writable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-write" extension has not been set for any data nodes
defined in this module.
This module defines the "generate-asymmetric-key-pair" RPC, which
may, if the "ct:cleartext-private-keys" feature is enabled and the
client requests it, return the private clear in cleartext form. It
is NOT RECOMMENDED for private keys to pass the server's security
perimeter.
This module does not define any actions or notifications, and thus,
the security considerations for such are not provided here.
5.6. Considerations for the "ietf-ssh-client" YANG Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "ietf-ssh-client" YANG module defines "grouping" statements that
are 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 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.
One readable data node defined in this YANG module may be considered
sensitive or vulnerable in some network environments. This node is
as follows:
* The "client-identity/password" node:
The cleartext "password" node defined in the "ssh-client-
grouping" grouping is additionally sensitive to read operations
such that, in normal use cases, it should never be returned to
a client. For this reason, the NACM extension "default-deny-
all" has been applied to it.
All the writable data nodes defined by this module 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 considerations for such are not provided here.
5.7. Considerations for the "ietf-ssh-server" YANG Module
This section follows the template defined in Section 3.7.1 of
[RFC8407].
The "ietf-ssh-server" YANG module defines "grouping" statements that
are 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 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.
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 the writable data nodes defined by this module may be considered
sensitive or vulnerable in some network environments. For instance,
the addition or removal of references to keys, certificates, trusted
anchors, etc., or even the modification of transport or keep-alive
parameters can 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 considerations for such are not provided here.
6. IANA Considerations
6.1. The IETF XML Registry
IANA has registered seven URIs in the "ns" registry of the "IETF XML
Registry" [RFC3688] as follows.
URI: urn:ietf:params:xml:ns:yang:iana-ssh-key-exchange-algs
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:iana-ssh-encryption-algs
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:iana-ssh-mac-algs
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:iana-ssh-public-key-algs
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-ssh-common
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-ssh-client
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-ssh-server
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
6.2. The YANG Module Names Registry
IANA has registered seven YANG modules in the "YANG Module Names"
registry [RFC6020] as follows.
Name: iana-ssh-key-exchange-algs
Namespace: urn:ietf:params:xml:ns:yang:iana-ssh-key-exchange-algs
Prefix: sshkea
Reference: RFC 9644
Name: iana-ssh-encryption-algs
Namespace: urn:ietf:params:xml:ns:yang:iana-ssh-encryption-algs
Prefix: sshea
Reference: RFC 9644
Name: iana-ssh-mac-algs
Namespace: urn:ietf:params:xml:ns:yang:iana-ssh-mac-algs
Prefix: sshma
Reference: RFC 9644
Name: iana-ssh-public-key-algs
Namespace: urn:ietf:params:xml:ns:yang:iana-ssh-public-key-algs
Prefix: sshpka
Reference: RFC 9644
Name: ietf-ssh-common
Namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-common
Prefix: sshcmn
Reference: RFC 9644
Name: ietf-ssh-client
Namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-client
Prefix: sshc
Reference: RFC 9644
Name: ietf-ssh-server
Namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-server
Prefix: sshs
Reference: RFC 9644
6.3. Considerations for the "iana-ssh-encryption-algs" Module
This section follows the template defined in Section 4.30.3.1 of
[YANG-GUIDE].
This document presents a script (see Appendix A) for IANA to use to
generate the IANA-maintained "iana-ssh-encryption-algs" YANG module.
The most recent version of the YANG module is available in the "YANG
Parameters" registry group [IANA-YANG-PARAMETERS].
IANA has added the following note to the registry:
| New values must not be directly added to the "iana-ssh-encryption-
| algs" YANG module. They must instead be added to the "Encryption
| Algorithm Names" registry of the "Secure Shell (SSH) Protocol
| Parameters" registry group [IANA-ENC-ALGS].
When a value is added to the "Encryption Algorithm Names" registry, a
new "enum" statement must be added to the "iana-ssh-encryption-algs"
YANG module. The "enum" statement, and substatements thereof, should
be defined as follows:
enum
Replicates a name from the registry.
value
Contains the decimal value of the IANA-assigned value.
status
Include only if a registration has been deprecated or obsoleted.
An IANA "Note" containing the word "HISTORIC" maps to YANG status
"obsolete". Since the registry is unable to express a "SHOULD
NOT" recommendation, there is no mapping to YANG status
"deprecated".
description
Contains "Enumeration for the 'foo-bar' algorithm.", where "foo-
bar" is a placeholder for the algorithm's name (e.g., "3des-cbc").
reference
Replicates the reference(s) from the registry with the title of
the document(s) added.
Unassigned or reserved values are not present in the module.
When the "iana-ssh-encryption-algs" YANG module is updated, a new
"revision" statement with a unique revision date must be added in
front of the existing revision statements. The "revision" must have
a "description" statement explaining why the update occurred and must
have a "reference" substatement that points to the document defining
the registry update that resulted in this change. For instance:
revision 2024-02-02 {
description
"This update reflects the update made to the underlying
Foo Bar registry per RFC XXXX.";
reference
"RFC XXXX: Extend the Foo Bars Registry
to Support Something Important";
}
IANA has added the following note to the "Encryption Algorithm Names"
registry.
| When this registry is modified, the YANG module "iana-ssh-
| encryption-algs" [IANA-YANG-PARAMETERS] must be updated as defined
| in RFC 9644.
6.4. Considerations for the "iana-ssh-mac-algs" Module
This section follows the template defined in Section 4.30.3.1 of
[YANG-GUIDE].
This document presents a script (see Appendix A) for IANA to use to
generate the IANA-maintained "iana-ssh-mac-algs" YANG module. The
most recent version of the YANG module is available in the "YANG
Parameters" registry group [IANA-YANG-PARAMETERS].
IANA has added the following note to the registry:
| New values must not be directly added to the "iana-ssh-mac-algs"
| YANG module. They must instead be added to the "MAC Algorithm
| Names" registry of the "Secure Shell (SSH) Protocol Parameters"
| registry group [IANA-MAC-ALGS].
When a value is added to the "MAC Algorithm Names" registry, a new
"enum" statement must be added to the "iana-ssh-mac-algs" YANG
module. The "enum" statement, and substatements thereof, should be
defined as follows:
enum
Replicates a name from the registry.
value
Contains the decimal value of the IANA-assigned value.
status
Include only if a registration has been deprecated or obsoleted.
description
Contains "Enumeration for the 'foo-bar' algorithm.", where "foo-
bar" is a placeholder for the algorithm's name (e.g., "3des-cbc").
reference
Replicates the reference(s) from the registry with the title of
the document(s) added.
Unassigned or reserved values are not present in the module.
When the "iana-ssh-mac-algs" YANG module is updated, a new "revision"
statement with a unique revision date must be added in front of the
existing revision statements. The "revision" must have a
"description" statement explaining why the update occurred and must
have a "reference" substatement that points to the document defining
the registry update that resulted in this change. For instance:
revision 2024-02-02 {
description
"This update reflects the update made to the underlying
Foo Bar registry per RFC XXXX.";
reference
"RFC XXXX: Extend the Foo Bars Registry
to Support Something Important";
}
IANA has added the following note to the "MAC Algorithm Names"
registry.
| When this registry is modified, the YANG module "iana-ssh-mac-
| algs" [IANA-YANG-PARAMETERS] must be updated as defined in RFC
| 9644.
6.5. Considerations for the "iana-ssh-public-key-algs" Module
This section follows the template defined in Section 4.30.3.1 of
[YANG-GUIDE].
This document presents a script (see Appendix A) for IANA to use to
generate the IANA-maintained "iana-ssh-public-key-algs" YANG module.
The most recent version of the YANG module is available in the "YANG
Parameters" registry group [IANA-YANG-PARAMETERS].
IANA has added the following note to the registry:
| New values must not be directly added to the "iana-ssh-public-key-
| algs" YANG module. They must instead be added to the "Public Key
| Algorithm Names" registry of the "Secure Shell (SSH) Protocol
| Parameters" registry group [IANA-PUBKEY-ALGS].
When a value is added to the "Public Key Algorithm Names" registry, a
new "enum" statement must be added to the "iana-ssh-public-key-algs"
YANG module. The "enum" statement, and substatements thereof, should
be defined as follows:
enum
Replicates a name from the registry.
value
Contains the decimal value of the IANA-assigned value.
status
Include only if a registration has been deprecated or obsoleted.
description
Contains "Enumeration for the 'foo-bar' algorithm.", where "foo-
bar" is a placeholder for the algorithm's name (e.g., "3des-cbc").
reference
Replicates the reference(s) from the registry with the title of
the document(s) added.
In the case that the algorithm name ends with "-*", the family of
enumerations must be added. The family of enum algorithm names are
generated by replacing the "*" character with these strings:
"nistp256", "nistp384", "nistp521", "1.3.132.0.1",
"1.2.840.10045.3.1.1", "1.3.132.0.33", "1.3.132.0.26",
"1.3.132.0.27", "1.3.132.0.16", "1.3.132.0.36", "1.3.132.0.37", and
"1.3.132.0.38".
Unassigned or reserved values are not present in the module.
When the "iana-ssh-public-key-algs" YANG module is updated, a new
"revision" statement with a unique revision date must be added in
front of the existing revision statements. The "revision" must have
a "description" statement explaining why the update occurred and must
have a "reference" substatement that points to the document defining
the registry update that resulted in this change. For instance:
revision 2024-02-02 {
description
"This update reflects the update made to the underlying
Foo Bar registry per RFC XXXX.";
reference
"RFC XXXX: Extend the Foo Bars Registry
to Support Something Important";
}
IANA has added the following note to the "Public Key Algorithm Names"
registry.
| When this registry is modified, the YANG module "iana-ssh-public-
| key-algs" [IANA-YANG-PARAMETERS] must be updated as defined in RFC
| 9644.
6.6. Considerations for the "iana-ssh-key-exchange-algs" Module
This section follows the template defined in Section 4.30.3.1 of
[YANG-GUIDE].
This document presents a script (see Appendix A) for IANA to use to
generate the IANA-maintained "iana-ssh-key-exchange-algs" YANG
module. The most recent version of the YANG module is available in
the "YANG Parameters" registry group [IANA-YANG-PARAMETERS].
IANA has added the following note to the registry:
| New values must not be directly added to the "iana-ssh-key-
| exchange-algs" YANG module. They must instead be added to the
| "Key Exchange Method Names" registry of the "Secure Shell (SSH)
| Protocol Parameters" registry group [IANA-KEYEX-ALGS].
When a value is added to the "Key Exchange Method Names" registry, a
new "enum" statement must be added to the "iana-ssh-key-exchange-
algs" YANG module. The "enum" statement, and substatements thereof,
should be defined as follows:
enum
Replicates a name from the registry.
value
Contains the decimal value of the IANA-assigned value.
status
Include only if a registration has been deprecated or obsoleted.
An IANA "OK to Implement" containing "SHOULD NOT" maps to YANG
status "deprecated". An IANA "OK to Implement" containing "MUST
NOT" maps to YANG status "obsolete".
description
Contains "Enumeration for the 'foo-bar' algorithm.", where "foo-
bar" is a placeholder for the algorithm's name (e.g., "3des-cbc").
reference
Replicates the reference(s) from the registry with the title of
the document(s) added.
In the case that the algorithm name ends with "-*", the family of
enumerations must be added. The family of enum algorithm names are
generated by replacing the "*" character with these strings:
"nistp256", "nistp384", "nistp521", "1.3.132.0.1",
"1.2.840.10045.3.1.1", "1.3.132.0.33", "1.3.132.0.26",
"1.3.132.0.27", "1.3.132.0.16", "1.3.132.0.36", "1.3.132.0.37", and
"1.3.132.0.38".
Unassigned or reserved values are not present in the module.
When the "iana-ssh-key-exchange-algs" YANG module is updated, a new
"revision" statement with a unique revision date must be added in
front of the existing revision statements. The "revision" must have
a "description" statement explaining why the update occurred, and
must have a "reference" substatement that points to the document
defining the registry update that resulted in this change. For
instance:
revision 2024-02-02 {
description
"This update reflects the update made to the underlying
Foo Bar registry per RFC XXXX.";
reference
"RFC XXXX: Extend the Foo Bars Registry
to Support Something Important";
}
IANA has added the following note to the "Key Exchange Method Names"
registry.
| When this registry is modified, the YANG module "iana-ssh-key-
| exchange-algs" [IANA-YANG-PARAMETERS] must be updated as defined
| in RFC 9644.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Assigned Numbers", RFC 4250,
DOI 10.17487/RFC4250, January 2006,
<https://www.rfc-editor.org/info/rfc4250>.
[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
January 2006, <https://www.rfc-editor.org/info/rfc4251>.
[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>.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>.
[RFC4254] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Connection Protocol", RFC 4254, DOI 10.17487/RFC4254,
January 2006, <https://www.rfc-editor.org/info/rfc4254>.
[RFC4344] Bellare, M., Kohno, T., and C. Namprempre, "The Secure
Shell (SSH) Transport Layer Encryption Modes", RFC 4344,
DOI 10.17487/RFC4344, January 2006,
<https://www.rfc-editor.org/info/rfc4344>.
[RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman
Group Exchange for the Secure Shell (SSH) Transport Layer
Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006,
<https://www.rfc-editor.org/info/rfc4419>.
[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm
Integration in the Secure Shell Transport Layer",
RFC 5656, DOI 10.17487/RFC5656, December 2009,
<https://www.rfc-editor.org/info/rfc5656>.
[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>.
[RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
Shell Authentication", RFC 6187, DOI 10.17487/RFC6187,
March 2011, <https://www.rfc-editor.org/info/rfc6187>.
[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>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC6668] Bider, D. and M. Baushke, "SHA-2 Data Integrity
Verification for the Secure Shell (SSH) Transport Layer
Protocol", RFC 6668, DOI 10.17487/RFC6668, July 2012,
<https://www.rfc-editor.org/info/rfc6668>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7317] Bierman, A. and M. Bjorklund, "A YANG Data Model for
System Management", RFC 7317, DOI 10.17487/RFC7317, August
2014, <https://www.rfc-editor.org/info/rfc7317>.
[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>.
[RFC9640] Watsen, K., "YANG Data Types and Groupings for
Cryptography", RFC 9640, DOI 10.17487/RFC9640, August
2024, <https://www.rfc-editor.org/info/rfc9640>.
[RFC9641] Watsen, K., "A YANG Data Model for a Truststore",
RFC 9641, DOI 10.17487/RFC9641, August 2024,
<https://www.rfc-editor.org/info/rfc9641>.
[RFC9642] Watsen, K., "A YANG Data Model for a Keystore and Keystore
Operations", RFC 9642, DOI 10.17487/RFC9642, August 2024,
<https://www.rfc-editor.org/info/rfc9642>.
7.2. Informative References
[FIPS_186-5]
NIST, "Digital Signature Standard (DSS)", FIPS PUB 186-5,
DOI 10.6028/NIST.FIPS.186-5, February 2023,
<https://csrc.nist.gov/pubs/fips/186-5/final>.
[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>.
[IANA-ENC-ALGS]
IANA, "Encryption Algorithm Names",
<https://www.iana.org/assignments/ssh-parameters/>.
[IANA-KEYEX-ALGS]
IANA, "Key Exchange Method Names",
<https://www.iana.org/assignments/ssh-parameters>.
[IANA-MAC-ALGS]
IANA, "MAC Algorithm Names",
<https://www.iana.org/assignments/ssh-parameters>.
[IANA-PUBKEY-ALGS]
IANA, "Public Key Algorithm Names",
<https://www.iana.org/assignments/ssh-parameters/>.
[IANA-YANG-PARAMETERS]
IANA, "YANG Parameters",
<https://www.iana.org/assignments/yang-parameters>.
[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>.
[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>.
[RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
RFC 8071, DOI 10.17487/RFC8071, February 2017,
<https://www.rfc-editor.org/info/rfc8071>.
[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>.
[RFC9643] Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
and TCP Servers", RFC 9643, DOI 10.17487/RFC9643, August
2024, <https://www.rfc-editor.org/info/rfc9643>.
[RFC9645] Watsen, K., "YANG Groupings for TLS Clients and TLS
Servers", RFC 9645, DOI 10.17487/RFC9645, August 2024,
<https://www.rfc-editor.org/info/rfc9645>.
[SYSTEM-CONFIG]
Ma, Q., Wu, Q., and C. Feng, "System-defined
Configuration", Work in Progress, Internet-Draft, draft-
ietf-netmod-system-config-08, 18 June 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
system-config-08>.
[YANG-GUIDE]
Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
Authors and Reviewers of Documents Containing YANG Data
Models", Work in Progress, Internet-Draft, draft-ietf-
netmod-rfc8407bis-14, 5 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
rfc8407bis-14>.
Appendix A. Script to Generate IANA-Maintained YANG Modules
This section is not normative.
The Python <https://www.python.org> script contained in this section
will create the four IANA-maintained modules that are described (but
not contained) in this document.
Run the script using the command "python gen-yang-modules.py" to
produce four YANG module files in the current directory.
Be aware that the script does not attempt to copy the "revision"
statements from the previous/current YANG module. Copying the
revision statements must be done manually.
<CODE BEGINS>
=============== NOTE: '\' line wrapping per RFC 8792 ================
import re
import csv
import textwrap
import requests
import requests_cache
from io import StringIO
from datetime import datetime
# Metadata for the four YANG modules produced by this script
MODULES = [
{
"csv_url": "https://www.iana.org/assignments/ssh-parameters/\
ssh-parameters-17.csv",
"spaced_name": "encryption",
"hypenated_name": "encryption",
"prefix": "sshea",
"description": """ "This module defines enumerations for \
the encryption algorithms
defined in the 'Encryption Algorithm Names' registry of the
'Secure Shell (SSH) Protocol Parameters' registry group
maintained by IANA.""",
},
{
"csv_url": "https://www.iana.org/assignments/ssh-parameters/\
ssh-parameters-19.csv",
"spaced_name": "public key",
"hypenated_name": "public-key",
"prefix": "sshpka",
"description": """ "This module defines enumerations for \
the public key algorithms
defined in the 'Public Key Algorithm Names' registry of the
'Secure Shell (SSH) Protocol Parameters' registry group
maintained by IANA."""
},
{
"csv_url": "https://www.iana.org/assignments/ssh-parameters/\
ssh-parameters-18.csv",
"spaced_name": "mac",
"hypenated_name": "mac",
"prefix": "sshma",
"description": """ "This module defines enumerations for \
the MAC algorithms
defined in the 'MAC Algorithm Names' registry of the
'Secure Shell (SSH) Protocol Parameters' registry group
maintained by IANA."""
},
{
"csv_url": "https://www.iana.org/assignments/ssh-parameters/\
ssh-parameters-16.csv",
"spaced_name": "key exchange",
"hypenated_name": "key-exchange",
"prefix": "sshkea",
"description": """ "This module defines enumerations for \
the key exchange algorithms
defined in the 'Key Exchange Method Names' registry of the
'Secure Shell (SSH) Protocol Parameters' registry group
maintained by IANA."""
},
]
def create_module_begin(module, f):
# Define template for all four modules
PREAMBLE_TEMPLATE="""
module iana-ssh-HNAME-algs {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:iana-ssh-HNAME-algs";
prefix PREFIX;
organization
"Internet Assigned Numbers Authority (IANA)";
contact
"Postal: ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States of America
Tel: +1 310 301 5800
Email: iana@iana.org";
description
DESCRIPTION
Copyright (c) YEAR 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).
The initial version of this YANG module is part of RFC 9644
(https://www.rfc-editor.org/info/rfc9644); see the RFC
itself for full legal notices.
All versions of this module are published by IANA at
https://www.iana.org/assignments/yang-parameters.";
revision DATE {
description
"This initial version of the module was created using
the script defined in RFC 9644 to reflect the contents
of the SNAME algorithms registry maintained by IANA.";
reference
"RFC 9644: YANG Groupings for SSH Clients and SSH Servers";
}
typedef ssh-HNAME-algorithm {
type enumeration {
"""
# Replacements
rep = {
"DATE": datetime.today().strftime('%Y-%m-%d'),
"YEAR": datetime.today().strftime('%Y'),
"SNAME": module["spaced_name"],
"HNAME": module["hypenated_name"],
"PREFIX": module["prefix"],
"DESCRIPTION": module["description"]
}
# Do the replacement
rep = dict((re.escape(k), v) for k, v in rep.items())
pattern = re.compile("|".join(rep.keys()))
text = pattern.sub(lambda m: rep[re.escape(m.group(0))], PREAMBL\
E_TEMPLATE)
# Write preamble into the file
f.write(text)
def create_module_body(module, f):
# Fetch the current CSV file from IANA
r = requests.get(module["csv_url"])
assert(r.status_code == 200)
# Ascertain the first CSV column's name
with StringIO(r.text) as csv_file:
csv_reader = csv.reader(csv_file)
for row in csv_reader:
first_colname = row[0]
break
# Parse each CSV line
with StringIO(r.text) as csv_file:
csv_reader = csv.DictReader(csv_file)
for row in csv_reader:
# Extract just the ref
refs = row["Reference"][1:-1] # remove the '[' and ']' \
chars
refs = refs.split("][")
# There may be more than one ref
titles = []
for ref in refs:
# Ascertain the ref's title
if ref.startswith("RFC"):
# Fetch the current BIBTEX entry
bibtex_url="https://datatracker.ietf.org/doc/"+ \
ref.lower() + "/bibtex/"
r = requests.get(bibtex_url)
assert r.status_code == 200, "Could not GET " + \
bibtex_url
# Append to 'titles' value from the "title" line
for item in r.text.split("\n"):
if "title =" in item:
titles.append(re.sub('.*{{(.*)}}.*', r'\\
g<1>', item))
break
else:
raise Exception("RFC title not found")
# Insert a space: "RFCXXXX" --> "RFC XXXX"
index = refs.index(ref)
refs[index] = "RFC " + ref[3:]
elif ref.startswith("FIPS"):
# Special case for FIPS, since no bibtex to fetch
if ref == "FIPS 46-3" or ref == "FIPS-46-3":
titles.append("Data Encryption Standard (DES\
)")
else:
raise Exception("FIPS ref not found")
else:
raise Exception("ref not found")
# Function used below
def write_enumeration(alg):
f.write('\n')
f.write(f' enum {alg} {{\n')
if "HISTORIC" in row["Note"]:
f.write(f' status obsolete;\n')
elif "OK to Implement" in row:
if "MUST NOT" in row["OK to Implement"]:
f.write(f' status obsolete;\n')
elif "SHOULD NOT" in row["OK to Implement"]:
f.write(f' status deprecated;\n')
f.write(f' description\n')
description = f' "Enumeration for the \'{al\
g}\' algorithm.'
if "Section" in row["Note"]:
description += " " + row["Note"]
description += '";'
description = textwrap.fill(description, width=69, s\
ubsequent_indent=" ")
f.write(f'{description}\n')
f.write(' reference\n')
f.write(' "')
if row["Reference"] == "":
f.write(' Missing in IANA registry.')
else:
ref_len = len(refs)
for i in range(ref_len):
ref = refs[i]
f.write(f'{ref}:\n')
title = " " + titles[i]
if i == ref_len - 1:
title += '";'
title = textwrap.fill(title, width=67, subse\
quent_indent=" ")
f.write(f'{title}')
if i != ref_len - 1:
f.write('\n ')
f.write('\n')
f.write(' }\n')
# Write one or more "enumeration" statements
if not row[first_colname].endswith("-*"): # just one enu\
meration
# Avoid duplicate entries caused by the "ecdh-sha2-*\
" family expansion
if not row[first_colname].startswith("ecdh-sha2-nist\
p"):
write_enumeration(row[first_colname])
else: # a family of enumerations
curve_ids = [
"nistp256",
"nistp384",
"nistp521",
"1.3.132.0.1",
"1.2.840.10045.3.1.1",
"1.3.132.0.33",
"1.3.132.0.26",
"1.3.132.0.27",
"1.3.132.0.16",
"1.3.132.0.36",
"1.3.132.0.37",
"1.3.132.0.38",
]
for curve_id in curve_ids:
write_enumeration(row[first_colname][:-1] + curv\
e_id)
def create_module_end(module, f):
# Close out the enumeration, typedef, and module
f.write(" }\n")
f.write(" description\n")
f.write(f' "An enumeration for SSH {module["spaced_name"]} \
algorithms.";\n')
f.write(" }\n")
f.write('\n')
f.write('}\n')
def create_module(module):
# Install cache for 8x speedup
requests_cache.install_cache()
# Ascertain YANG module's name
yang_module_name = "iana-ssh-" + module["hypenated_name"] + "-al\
gs.yang"
# Create YANG module file
with open(yang_module_name, "w") as f:
create_module_begin(module, f)
create_module_body(module, f)
create_module_end(module, f)
def main():
for module in MODULES:
create_module(module)
if __name__ == "__main__":
main()
<CODE ENDS>
Acknowledgements
The authors would like to thank the following for lively discussions
on list and in the halls (ordered by first name): Alan Luchuk, Andy
Bierman, Balázs Kovács, Barry Leiba, Benoit Claise, Bert Wijnen,
David Lamparter, Elwyn Davies, Gary Wu, Jürgen Schönwälder, Ladislav
Lhotka, Liang Xia, Martin Björklund, Martin Thomson, Mehmet Ersue,
Michal Vaško, Murray Kucherawy, Paul Wouters, Per Andersson, Phil
Shafer, Qin Wun, Radek Krejci, Rob Wilton, Roman Danyliw, Russ
Housley, Sean Turner, Thomas Martin, Tom Petch, and Warren Kumari.
Contributors
Special acknowledgement goes to Gary Wu for his work on the "ietf-
ssh-common" module.
Author's Address
Kent Watsen
Watsen Networks
Email: kent+ietf@watsen.net