YANG Groupings for SSH Clients and SSH Servers
draft-ietf-netconf-ssh-client-server-24
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Author | Kent Watsen | ||
| Last updated | 2021-05-18 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Last Call review
(of
-37)
by Elwyn Davies
Almost ready
SECDIR
will not review this version
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-netconf-ssh-client-server-24
";
}
identity encryption-alg-base {
description
"Base identity used to identify encryption algorithms.";
}
identity triple-des-cbc {
base encryption-alg-base;
description
"Three-key 3DES in CBC mode.";
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reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity aes128-cbc {
base encryption-alg-base;
description
"AES in CBC mode, with a 128-bit key.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity aes192-cbc {
base encryption-alg-base;
description
"AES in CBC mode, with a 192-bit key.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity aes256-cbc {
base encryption-alg-base;
description
"AES in CBC mode, with a 256-bit key.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity aes128-ctr {
if-feature "ssh-ctr";
base encryption-alg-base;
description
"AES in SDCTR mode, with 128-bit key.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
Modes";
}
identity aes192-ctr {
if-feature "ssh-ctr";
base encryption-alg-base;
description
"AES in SDCTR mode, with 192-bit key.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
Modes";
}
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identity aes256-ctr {
if-feature "ssh-ctr";
base encryption-alg-base;
description
"AES in SDCTR mode, with 256-bit key.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
Modes";
}
identity mac-alg-base {
description
"Base identity used to identify message authentication
code (MAC) algorithms.";
}
identity hmac-sha1 {
base mac-alg-base;
description
"HMAC-SHA1";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity hmac-sha2-256 {
if-feature "ssh-sha2";
base mac-alg-base;
description
"HMAC-SHA2-256";
reference
"RFC 6668: SHA-2 Data Integrity Verification for the
Secure Shell (SSH) Transport Layer Protocol";
}
identity hmac-sha2-512 {
if-feature "ssh-sha2";
base mac-alg-base;
description
"HMAC-SHA2-512";
reference
"RFC 6668: SHA-2 Data Integrity Verification for the
Secure Shell (SSH) Transport Layer Protocol";
}
// Groupings
grouping transport-params-grouping {
description
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"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 identityref {
base public-key-alg-base;
}
ordered-by user;
description
"Acceptable host key algorithms in order of descending
preference. The configured host key algorithms should
be compatible with the algorithm used by the configured
private key. Please see Section 5 of RFC EEEE for
valid combinations.
If this leaf-list is not configured (has zero elements)
the acceptable host key algorithms are implementation-
defined.";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
}
container key-exchange {
description
"Parameters regarding key exchange.";
leaf-list key-exchange-alg {
type identityref {
base key-exchange-alg-base;
}
ordered-by user;
description
"Acceptable key exchange algorithms in order of descending
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 identityref {
base encryption-alg-base;
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}
ordered-by user;
description
"Acceptable encryption algorithms in order of descending
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 identityref {
base mac-alg-base;
}
ordered-by user;
description
"Acceptable MAC algorithms in order of descending
preference.
If this leaf-list is not configured (has zero elements)
the acceptable MAC algorithms are implementation-
defined.";
}
}
}
}
<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
Examples (Section 3.2). 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.
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3.1.1. Features
The following diagram lists all the "feature" statements defined in
the "ietf-ssh-client" module:
Features:
+-- ssh-client-transport-params-config
+-- ssh-client-keepalives
+-- userauth-password
+-- userauth-publickey
+-- userauth-hostbased
+-- userauth-none
| The diagram above uses syntax that is similar to but not
| defined in [RFC8340].
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:
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=============== NOTE: '\' line wrapping per RFC 8792 ================
grouping ssh-client-grouping
+-- client-identity
| +-- username? string
| +-- public-key! {userauth-publickey}?
| | +---u ks:local-or-keystore-asymmetric-key-grouping
| +-- password! {userauth-password}?
| | +---u ct:password-grouping
| +-- hostbased! {userauth-hostbased}?
| | +---u ks:local-or-keystore-asymmetric-key-grouping
| +-- none? empty {userauth-none}?
| +-- certificate! {sshcmn:ssh-x509-certs}?
| +---u ks:local-or-keystore-end-entity-cert-with-key-groupi\
ng
+-- server-authentication
| +-- ssh-host-keys!
| | +---u ts:local-or-truststore-public-keys-grouping
| +-- ca-certs! {sshcmn:ssh-x509-certs}?
| | +---u ts:local-or-truststore-certs-grouping
| +-- ee-certs! {sshcmn:ssh-x509-certs}?
| +---u ts:local-or-truststore-certs-grouping
+-- transport-params {ssh-client-transport-params-config}?
| +---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 statement(s):
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- The "local-or-keystore-asymmetric-key-grouping" grouping is
discussed in Section 2.1.3.4 of [I-D.ietf-netconf-keystore].
- The "local-or-keystore-end-entity-cert-with-key-grouping"
grouping is discussed in Section 2.1.3.6 of
[I-D.ietf-netconf-keystore].
- The "local-or-truststore-public-keys-grouping" grouping is
discussed in Section 2.1.3.2 of
[I-D.ietf-netconf-trust-anchors].
- The "local-or-truststore-certs-grouping" grouping is discussed
in Section 2.1.3.1 of [I-D.ietf-netconf-trust-anchors].
- The "transport-params-grouping" grouping is discussed in
Section 2.1.3.1 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.
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 a
local key while the second uses a key configured in a keystore. Both
examples are consistent with the examples presented in Section 2 of
[I-D.ietf-netconf-trust-anchors] and Section 3.2 of
[I-D.ietf-netconf-keystore].
The following configuration example uses local-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"
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>
<local-definition>
<public-key-format>ct:ssh-public-key-format</public-key-form\
at>
<public-key>base64encodedvalue==</public-key>
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<private-key-format>ct:rsa-private-key-format</private-key-f\
ormat>
<cleartext-private-key>base64encodedvalue==</cleartext-priva\
te-key>
</local-definition>
</public-key>
</client-identity>
<!-- which host keys will this client trust -->
<server-authentication>
<ssh-host-keys>
<local-definition>
<public-key>
<name>corp-fw1</name>
<public-key-format>ct:ssh-public-key-format</public-key-fo\
rmat>
<public-key>base64encodedvalue==</public-key>
</public-key>
<public-key>
<name>corp-fw2</name>
<public-key-format>ct:ssh-public-key-format</public-key-fo\
rmat>
<public-key>base64encodedvalue==</public-key>
</public-key>
</local-definition>
</ssh-host-keys>
<ca-certs>
<local-definition>
<certificate>
<name>Server Cert Issuer #1</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
<certificate>
<name>Server Cert Issuer #2</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
</local-definition>
</ca-certs>
<ee-certs>
<local-definition>
<certificate>
<name>My Application #1</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
<certificate>
<name>My Application #2</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
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</local-definition>
</ee-certs>
</server-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
The following configuration example uses keystore-references for the
client identity and truststore-references for server authentication:
from the keystore:
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=============== 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>
<!-- can an SSH client have move than one key?
<public-key>
<keystore-reference>ssh-rsa-key</keystore-reference>
</public-key>
-->
<certificate>
<keystore-reference>
<asymmetric-key>ssh-rsa-key-with-cert</asymmetric-key>
<certificate>ex-rsa-cert2</certificate>
</keystore-reference>
</certificate>
</client-identity>
<!-- which host-keys will this client trust -->
<server-authentication>
<ssh-host-keys>
<truststore-reference>trusted-ssh-public-keys</truststore-refe\
rence>
</ssh-host-keys>
<ca-certs>
<truststore-reference>trusted-server-ca-certs</truststore-refe\
rence>
</ca-certs>
<ee-certs>
<truststore-reference>trusted-server-ee-certs</truststore-refe\
rence>
</ee-certs>
</server-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
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3.3. YANG Module
This YANG module has normative references to
[I-D.ietf-netconf-trust-anchors], and [I-D.ietf-netconf-keystore].
<CODE BEGINS> file "ietf-ssh-client@2021-05-18.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 AAAA: YANG Data Types and Groupings for Cryptography";
}
import ietf-truststore {
prefix ts;
reference
"RFC BBBB: A YANG Data Model for a Truststore";
}
import ietf-keystore {
prefix ks;
reference
"RFC CCCC: A YANG Data Model for a Keystore";
}
import ietf-ssh-common {
prefix sshcmn;
revision-date 2021-05-18; // stable grouping definitions
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http://datatracker.ietf.org/wg/netconf/>
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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 reusable groupings for SSH clients that
can be used as a basis for specific SSH client instances.
Copyright (c) 2021 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Simplified
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC EEEE
(https://www.rfc-editor.org/info/rfcEEEE); see the RFC
itself for full legal notices.;
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2021-05-18 {
description
"Initial version";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-client-transport-params-config {
description
"SSH transport layer parameters are configurable on an SSH
client.";
}
feature ssh-client-keepalives {
description
"Per socket SSH keepalive parameters are configurable for
SSH clients on the server implementing this feature.";
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}
feature userauth-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 enable it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature userauth-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 userauth-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 userauth-none {
description
"Indicates that the 'none' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
// Groupings
grouping ssh-client-grouping {
description
"A reusable grouping for configuring a SSH client without
any consideration for how an underlying TCP session is
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established.
Note that this grouping uses fairly typical descendant
node names such that a stack 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 RFC 4252,
Section 5.2, 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 "userauth-publickey";
presence
"Indicates that publickey-based authentication has been
configured. This statement is present so the mandatory
descendent 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 CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'public-key-format = "ct:ssh-public-key-format"';
}
refine "local-or-keystore/keystore/keystore-reference" {
must 'deref(.)/../ks:public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
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}
}
container password {
if-feature "userauth-password";
presence
"Indicates that password-based authentication has been
configured. This statement is present so the mandatory
descendent 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 "userauth-hostbased";
presence
"Indicates that hostbased authentication is configured.
This statement is present so the mandatory descendent
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 CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'public-key-format = "ct:ssh-public-key-format"';
}
refine "local-or-keystore/keystore/keystore-reference" {
must 'deref(.)/../ks:public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
}
}
leaf none {
if-feature "userauth-none";
type empty;
description
"Indicates that '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
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configured.";
description
"A locally-defined or referenced certificate
to be used for client identification.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-end-entity-cert-with-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'public-key-format'
+ ' = "ct:subject-public-key-info-format"';
}
refine "local-or-keystore/keystore/keystore-reference"
+ "/asymmetric-key" {
must '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 BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine
"local-or-truststore/local/local-definition/public-key" {
must 'public-key-format = "ct:ssh-public-key-format"';
}
refine
"local-or-truststore/truststore/truststore-reference" {
must 'deref(.)/../*/ts:public-key-format'
+ ' = "ct:ssh-public-key-format"';
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}
}
}
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 BBBB: A YANG Data Model for a Truststore";
uses ts:local-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 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 BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
} // container server-authentication
container transport-params {
nacm:default-deny-write;
if-feature "ssh-client-transport-params-config";
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
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aliveness of the remote SSH server.";
description
"Configures the keep-alive policy, to proactively test
the aliveness of the SSH server. An unresponsive TLS
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) 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 if
no data has been received from the SSH server, a
TLS-level message will be sent to test the
aliveness of 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 Examples
(Section 4.2). The YANG module itself is defined in Section 4.3.
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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-transport-params-config
+-- ssh-server-keepalives
+-- local-users-supported
+-- userauth-publickey
+-- userauth-password
+-- userauth-hostbased
+-- userauth-none
| The diagram above uses syntax that is similar to but not
| defined in [RFC8340].
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:
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=============== NOTE: '\' line wrapping per RFC 8792 ================
grouping ssh-server-grouping
+-- server-identity
| +-- host-key* [name]
| +-- name? string
| +-- (host-key-type)
| +--:(public-key)
| | +-- public-key
| | +---u ks:local-or-keystore-asymmetric-key-grouping
| +--:(certificate)
| +-- certificate {sshcmn:ssh-x509-certs}?
| +---u ks:local-or-keystore-end-entity-cert-with-k\
ey-grouping
+-- client-authentication
| +-- users {local-users-supported}?
| | +-- user* [name]
| | +-- name? string
| | +-- public-keys! {userauth-publickey}?
| | | +---u ts:local-or-truststore-public-keys-grouping
| | +-- password? ianach:crypt-hash
| | | {userauth-password}?
| | +-- hostbased! {userauth-hostbased}?
| | | +---u ts:local-or-truststore-public-keys-grouping
| | +-- none? empty {userauth-none}?
| +-- ca-certs! {sshcmn:ssh-x509-certs}?
| | +---u ts:local-or-truststore-certs-grouping
| +-- ee-certs! {sshcmn:ssh-x509-certs}?
| +---u ts:local-or-truststore-certs-grouping
+-- transport-params {ssh-server-transport-params-config}?
| +---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.
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* 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 statement(s):
- The "local-or-keystore-asymmetric-key-grouping" grouping is
discussed in Section 2.1.3.4 of [I-D.ietf-netconf-keystore].
- The "local-or-keystore-end-entity-cert-with-key-grouping"
grouping is discussed in Section 2.1.3.6 of
[I-D.ietf-netconf-keystore].
- The "local-or-truststore-public-keys-grouping" grouping is
discussed in Section 2.1.3.2 of
[I-D.ietf-netconf-trust-anchors].
- The "local-or-truststore-certs-grouping" grouping is discussed
in Section 2.1.3.1 of [I-D.ietf-netconf-trust-anchors].
- The "transport-params-grouping" grouping is discussed in
Section 2.1.3.1 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.
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 a
local key while the second uses a key configured in a keystore. Both
examples are consistent with the examples presented in Section 2 of
[I-D.ietf-netconf-trust-anchors] and Section 3.2 of
[I-D.ietf-netconf-keystore].
The following configuration example uses local-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"
xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<!-- the host-key this SSH server will present -->
<server-identity>
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<host-key>
<name>my-pubkey-based-host-key</name>
<public-key>
<local-definition>
<public-key-format>ct:ssh-public-key-format</public-key-fo\
rmat>
<public-key>base64encodedvalue==</public-key>
<private-key-format>ct:rsa-private-key-format</private-key\
-format>
<cleartext-private-key>base64encodedvalue==</cleartext-pri\
vate-key>
</local-definition>
</public-key>
</host-key>
<host-key>
<name>my-cert-based-host-key</name>
<certificate>
<local-definition>
<public-key-format>ct:subject-public-key-info-format</publ\
ic-key-format>
<public-key>base64encodedvalue==</public-key>
<private-key-format>ct:rsa-private-key-format</private-key\
-format>
<cleartext-private-key>base64encodedvalue==</cleartext-pri\
vate-key>
<cert-data>base64encodedvalue==</cert-data>
</local-definition>
</certificate>
</host-key>
</server-identity>
<!-- the client credentials this SSH server will trust -->
<client-authentication>
<users>
<user>
<name>mary</name>
<password>$0$secret</password>
<public-keys>
<local-definition>
<public-key>
<name>User A</name>
<public-key-format>ct:ssh-public-key-format</public-ke\
y-format>
<public-key>base64encodedvalue==</public-key>
</public-key>
<public-key>
<name>User B</name>
<public-key-format>ct:ssh-public-key-format</public-ke\
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y-format>
<public-key>base64encodedvalue==</public-key>
</public-key>
</local-definition>
</public-keys>
</user>
</users>
<ca-certs>
<local-definition>
<certificate>
<name>Identity Cert Issuer #1</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
<certificate>
<name>Identity Cert Issuer #2</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
</local-definition>
</ca-certs>
<ee-certs>
<local-definition>
<certificate>
<name>Application #1</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
<certificate>
<name>Application #2</name>
<cert-data>base64encodedvalue==</cert-data>
</certificate>
</local-definition>
</ee-certs>
</client-authentication>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-server>
The following configuration example uses keystore-references for the
server identity and truststore-references for client authentication:
from the keystore:
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=============== 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:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<!-- the host-key this SSH server will present -->
<server-identity>
<host-key>
<name>my-pubkey-based-host-key</name>
<public-key>
<keystore-reference>ssh-rsa-key</keystore-reference>
</public-key>
</host-key>
<host-key>
<name>my-cert-based-host-key</name>
<certificate>
<keystore-reference>
<asymmetric-key>ssh-rsa-key-with-cert</asymmetric-key>
<certificate>ex-rsa-cert2</certificate>
</keystore-reference>
</certificate>
</host-key>
</server-identity>
<!-- the client credentials this SSH server will trust -->
<client-authentication>
<users>
<user>
<name>mary</name>
<password>$0$secret</password>
<public-keys>
<truststore-reference>SSH Public Keys for Application A</t\
ruststore-reference>
</public-keys>
</user>
</users>
<ca-certs>
<truststore-reference>trusted-client-ca-certs</truststore-refe\
rence>
</ca-certs>
<ee-certs>
<truststore-reference>trusted-client-ee-certs</truststore-refe\
rence>
</ee-certs>
</client-authentication>
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<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
[I-D.ietf-netconf-trust-anchors] and [I-D.ietf-netconf-keystore] and
informative references to [RFC4253] and [RFC7317].
<CODE BEGINS> file "ietf-ssh-server@2021-05-18.yang"
module ietf-ssh-server {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-server";
prefix sshs;
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 AAAA: YANG Data Types and Groupings for Cryptography";
}
import ietf-truststore {
prefix ts;
reference
"RFC BBBB: A YANG Data Model for a Truststore";
}
import ietf-keystore {
prefix ks;
reference
"RFC CCCC: A YANG Data Model for a Keystore";
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}
import ietf-ssh-common {
prefix sshcmn;
revision-date 2021-05-18; // stable grouping definitions
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Author: Kent Watsen <mailto:kent+ietf@watsen.net>
Author: Gary Wu <mailto:garywu@cisco.com>";
description
"This module defines reusable groupings for SSH servers that
can be used as a basis for specific SSH server instances.
Copyright (c) 2021 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Simplified
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC EEEE
(https://www.rfc-editor.org/info/rfcEEEE); see the RFC
itself for full legal notices.;
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2021-05-18 {
description
"Initial version";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
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}
// Features
feature ssh-server-transport-params-config {
description
"SSH transport layer parameters are configurable on an SSH
server.";
}
feature ssh-server-keepalives {
description
"Per socket SSH keepalive 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 userauth-publickey {
description
"Indicates that the 'publickey' authentication type, per
RFC 4252, is supported.
The 'publickey' authentication type is required by
RFC 4252, but common implementations enable it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature userauth-password {
description
"Indicates that the 'password' authentication type, per
RFC 4252, is supported.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature userauth-hostbased {
description
"Indicates that the 'hostbased' authentication type, per
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RFC 4252, is supported.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature userauth-none {
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 a 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 stack 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 a SSH connection.";
list host-key {
key "name";
min-elements 1;
ordered-by user;
description
"An ordered list of host keys 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
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"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 CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must
'public-key-format = "ct:ssh-public-key-format"';
}
refine "local-or-keystore/keystore/"
+ "keystore-reference" {
must '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 CCCC: A YANG Data Model for a Keystore";
uses
ks:local-or-keystore-end-entity-cert-with-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'public-key-format'
+ ' = "ct:subject-public-key-info-format"';
}
refine "local-or-keystore/keystore/keystore-reference"
+ "/asymmetric-key" {
must 'deref(.)/../ks:public-key-format'
+ ' = "ct:subject-public-key-info-format"';
}
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}
}
}
}
} // container server-identity
container client-authentication {
nacm:default-deny-write;
description
"Specifies how the SSH server can authenticate SSH clients.";
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 in 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 'user name' for the SSH client, as defined in
the SSH_MSG_USERAUTH_REQUEST message in RFC 4253.";
}
container public-keys {
if-feature "userauth-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
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"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine "local-or-truststore/local/local-definition"
+ "/public-key" {
must 'public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
refine "local-or-truststore/truststore/"
+ "truststore-reference" {
must 'deref(.)/../*/ts:public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
}
}
leaf password {
if-feature "userauth-password";
type ianach:crypt-hash;
description
"The password for this user.";
}
container hostbased {
if-feature "userauth-hostbased";
presence
"Indicates that hostbased 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 4253: The Secure Shell (SSH) Transport Layer
RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine "local-or-truststore/local/local-definition"
+ "/public-key" {
must 'public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
refine "local-or-truststore/truststore"
+ "/truststore-reference" {
must 'deref(.)/../*/ts:public-key-format'
+ ' = "ct:ssh-public-key-format"';
}
}
}
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leaf none {
if-feature "userauth-none";
type empty;
description
"Indicates that the 'none' method is supported.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
}
}
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 BBBB: A YANG Data Model for a Truststore";
uses ts:local-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 BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
} // container client-authentication
container transport-params {
nacm:default-deny-write;
if-feature "ssh-server-transport-params-config";
description
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"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 SSL client. An unresponsive SSL
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) 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
if no data has been received from the SSL client,
a SSL-level message will be sent to test the
aliveness of the SSL 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 SSL client before assuming the SSL client is
no longer alive.";
}
}
} // grouping ssh-server-grouping
}
<CODE ENDS>
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5. Security Considerations
5.1. The "ietf-ssh-common" YANG Module
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 NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
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 does not define any RPCs, actions, or notifications, and
thus the security consideration for such is not provided here.
5.2. The "ietf-ssh-client" YANG Module
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 NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
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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.
| Please be aware that this module uses the "key" and "private-
| key" nodes from the "ietf-crypto-types" module
| [I-D.ietf-netconf-crypto-types], where said nodes have the NACM
| extension "default-deny-all" set, thus preventing unrestricted
| read-access to the cleartext key values.
All of 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 consideration for such is not provided here.
5.3. The "ietf-ssh-server" YANG Module
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 NETCONF access control model (NACM) [RFC8341] provides the means
to restrict access for particular users to a pre-configured subset of
all available protocol operations and content.
Since the module in this document only define groupings, these
considerations are primarily for the designers of other modules that
use these groupings.
None of the readable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments. The NACM
"default-deny-all" extension has not been set for any data nodes
defined in this module.
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| Please be aware that this module uses the "key" and "private-
| key" nodes from the "ietf-crypto-types" module
| [I-D.ietf-netconf-crypto-types], where said nodes have the NACM
| extension "default-deny-all" set, thus preventing unrestricted
| read-access to the cleartext key values.
All of 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 keepalive 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 consideration for such is not provided here.
6. IANA Considerations
6.1. The "IETF XML" Registry
This document registers three URIs in the "ns" subregistry of the
IETF XML Registry [RFC3688]. Following the format in [RFC3688], the
following registrations are requested:
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
This document registers three YANG modules in the YANG Module Names
registry [RFC6020]. Following the format in [RFC6020], the following
registrations are requested:
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name: ietf-ssh-common
namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-common
prefix: sshcmn
reference: RFC EEEE
name: ietf-ssh-client
namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-client
prefix: sshc
reference: RFC EEEE
name: ietf-ssh-server
namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-server
prefix: sshs
reference: RFC EEEE
7. References
7.1. Normative References
[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for
Cryptography", Work in Progress, Internet-Draft, draft-
ietf-netconf-crypto-types-19, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-crypto-
types-19>.
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore", Work in
Progress, Internet-Draft, draft-ietf-netconf-keystore-21,
10 February 2021, <https://tools.ietf.org/html/draft-ietf-
netconf-keystore-21>.
[I-D.ietf-netconf-trust-anchors]
Watsen, K., "A YANG Data Model for a Truststore", Work in
Progress, Internet-Draft, draft-ietf-netconf-trust-
anchors-14, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-trust-
anchors-14>.
[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>.
[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>.
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[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>.
[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>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
7.2. Informative References
[I-D.ietf-netconf-http-client-server]
Watsen, K., "YANG Groupings for HTTP Clients and HTTP
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-http-client-server-06, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-http-
client-server-06>.
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[I-D.ietf-netconf-netconf-client-server]
Watsen, K., "NETCONF Client and Server Models", Work in
Progress, Internet-Draft, draft-ietf-netconf-netconf-
client-server-22, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-netconf-
client-server-22>.
[I-D.ietf-netconf-restconf-client-server]
Watsen, K., "RESTCONF Client and Server Models", Work in
Progress, Internet-Draft, draft-ietf-netconf-restconf-
client-server-22, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-restconf-
client-server-22>.
[I-D.ietf-netconf-ssh-client-server]
Watsen, K., "YANG Groupings for SSH Clients and SSH
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-ssh-client-server-23, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-ssh-
client-server-23>.
[I-D.ietf-netconf-tcp-client-server]
Watsen, K. and M. Scharf, "YANG Groupings for TCP Clients
and TCP Servers", Work in Progress, Internet-Draft, draft-
ietf-netconf-tcp-client-server-09, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-tcp-
client-server-09>.
[I-D.ietf-netconf-tls-client-server]
Watsen, K., "YANG Groupings for TLS Clients and TLS
Servers", Work in Progress, Internet-Draft, draft-ietf-
netconf-tls-client-server-23, 10 February 2021,
<https://tools.ietf.org/html/draft-ietf-netconf-tls-
client-server-23>.
[OPENSSH] Project, T. O., "OpenSSH", 2016, <http://www.openssh.com>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[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>.
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[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>.
[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>.
[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>.
[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>.
[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>.
Appendix A. Change Log
This section is to be removed before publishing as an RFC.
A.1. 00 to 01
* Noted that '0.0.0.0' and '::' might have special meanings.
* Renamed "keychain" to "keystore".
A.2. 01 to 02
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* Removed the groupings 'listening-ssh-client-grouping' and
'listening-ssh-server-grouping'. Now modules only contain the
transport-independent groupings.
* Simplified the "client-auth" part in the ietf-ssh-client module.
It now inlines what it used to point to keystore for.
* Added cipher suites for various algorithms into new 'ietf-ssh-
common' module.
A.3. 02 to 03
* Removed 'RESTRICTED' enum from 'password' leaf type.
* Added a 'must' statement to container 'server-auth' asserting that
at least one of the various auth mechanisms must be specified.
* Fixed description statement for leaf 'trusted-ca-certs'.
A.4. 03 to 04
* Change title to "YANG Groupings for SSH Clients and SSH Servers"
* Added reference to RFC 6668
* Added RFC 8174 to Requirements Language Section.
* Enhanced description statement for ietf-ssh-server's "trusted-ca-
certs" leaf.
* Added mandatory true to ietf-ssh-client's "client-auth" 'choice'
statement.
* Changed the YANG prefix for module ietf-ssh-common from 'sshcom'
to 'sshcmn'.
* Removed the compression algorithms as they are not commonly
configurable in vendors' implementations.
* Updating descriptions in transport-params-grouping and the
servers's usage of it.
* Now tree diagrams reference ietf-netmod-yang-tree-diagrams
* Updated YANG to use typedefs around leafrefs to common keystore
paths
* Now inlines key and certificates (no longer a leafref to keystore)
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A.5. 04 to 05
* Merged changes from co-author.
A.6. 05 to 06
* Updated to use trust anchors from trust-anchors draft (was
keystore draft)
* Now uses new keystore grouping enabling asymmetric key to be
either locally defined or a reference to the keystore.
A.7. 06 to 07
* factored the ssh-[client|server]-groupings into more reusable
groupings.
* added if-feature statements for the new "ssh-host-keys" and
"x509-certificates" features defined in draft-ietf-netconf-trust-
anchors.
A.8. 07 to 08
* Added a number of compatibility matrices to Section 5 (thanks
Frank!)
* Clarified that any configured "host-key-alg" values need to be
compatible with the configured private key.
A.9. 08 to 09
* Updated examples to reflect update to groupings defined in the
keystore -09 draft.
* Add SSH keepalives features and groupings.
* Prefixed top-level SSH grouping nodes with 'ssh-' and support
mashups.
* Updated copyright date, boilerplate template, affiliation, and
folding algorithm.
A.10. 09 to 10
* Reformatted the YANG modules.
A.11. 10 to 11
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* Reformatted lines causing folding to occur.
A.12. 11 to 12
* Collapsed all the inner groupings into the top-level grouping.
* Added a top-level "demux container" inside the top-level grouping.
* Added NACM statements and updated the Security Considerations
section.
* Added "presence" statements on the "keepalive" containers, as was
needed to address a validation error that appeared after adding
the "must" statements into the NETCONF/RESTCONF client/server
modules.
* Updated the boilerplate text in module-level "description"
statement to match copyeditor convention.
A.13. 12 to 13
* Removed the "demux containers", floating the nacm:default-deny-
write to each descendent node, and adding a note to model
designers regarding the potential need to add their own demux
containers.
* Fixed a couple references (section 2 --> section 3)
* In the server model, replaced <client-cert-auth> with <client-
authentication> and introduced 'local-or-external' choice.
A.14. 13 to 14
* Updated to reflect changes in trust-anchors drafts (e.g., s/trust-
anchors/truststore/g + s/pinned.//)
A.15. 14 to 15
* Updated examples to reflect ietf-crypto-types change (e.g.,
identities --> enumerations)
* Updated "server-authentication" and "client-authentication" nodes
from being a leaf of type "ts:host-keys-ref" or "ts:certificates-
ref" to a container that uses "ts:local-or-truststore-host-keys-
grouping" or "ts:local-or-truststore-certs-grouping".
A.16. 15 to 16
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* Removed unnecessary if-feature statements in the -client and
-server modules.
* Cleaned up some description statements in the -client and -server
modules.
* Fixed a canonical ordering issue in ietf-ssh-common detected by
new pyang.
A.17. 16 to 17
* Removed choice local-or-external by removing the 'external' case
and flattening the 'local' case and adding a "local-users-
supported" feature.
* Updated examples to include the "*-key-format" nodes.
* Augmented-in "must" expressions ensuring that locally-defined
public-key-format are "ct:ssh-public-key-format" (must expr for
ref'ed keys are TBD).
A.18. 17 to 18
* Removed leaf-list 'other' from ietf-ssh-server.
* Removed unused 'external-client-auth-supported' feature.
* Added features client-auth-password, client-auth-hostbased, and
client-auth-none.
* Renamed 'host-key' to 'public-key' for when refering to
'publickey' based auth.
* Added new feature-protected 'hostbased' and 'none' to the 'user'
node's config.
* Added new feature-protected 'hostbased' and 'none' to the 'client-
identity' node's config.
* Updated examples to reflect new "bag" addition to truststore.
* Refined truststore/keystore groupings to ensure the key formats
"must" be particular values.
* Switched to using truststore's new "public-key" bag (instead of
separate "ssh-public-key" and "raw-public-key" bags.
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* Updated client/server examples to cover ALL cases (local/ref x
cert/raw-key/psk).
A.19. 18 to 19
* Updated the "keepalives" containers to address Michal Vasko's
request to align with RFC 8071.
* Removed algorithm-mapping tables from the "SSH Common Model"
section
* Removed 'algorithm' node from examples.
* Added feature "userauth-publickey"
* Removed "choice auth-type", as auth-types aren't exclusive.
* Renamed both "client-certs" and "server-certs" to "ee-certs"
* Switch "must" to assert the public-key-format is "subject-public-
key-info-format" when certificates are used.
* Added a "Note to Reviewers" note to first page.
A.20. 19 to 20
* Added a "must 'public-key or password or hostbased or none or
certificate'" statement to the "user" node in ietf-ssh-client
* Expanded "Data Model Overview section(s) [remove "wall" of tree
diagrams].
* Moved the "ietf-ssh-common" module section to proceed the other
two module sections.
* Updated the Security Considerations section.
A.21. 20 to 21
* Updated examples to reflect new "cleartext-" prefix in the crypto-
types draft.
A.22. 21 to 22
* Cleaned up the SSH-client examples (i.e., removing FIXMEs)
* Fixed issues found by the SecDir review of the "keystore" draft.
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* Updated the "ietf-ssh-client" module to use the new "password-
grouping" grouping from the "crypto-types" module.
A.23. 22 to 23
* Addressed comments raised by YANG Doctor in the ct/ts/ks drafts.
A.24. 23 to 24
* Removed the 'supported-authentication-methods' from {grouping ssh-
server-grouping}/client-authentication.
* Added XML-comment above examples explaining the reason for the
unexepected top-most element's presence.
* Added RFC-references to various 'feature' statements.
* Renamed "credentials" to "authentication methods"
* Renamed "client-auth-*" to "userauth-*"
* Renamed "client-identity-*" to "userauth-*"
* Fixed nits found by YANG Doctor reviews.
* Aligned modules with `pyang -f` formatting.
* Added a 'Contributors' section.
Acknowledgements
The authors would like to thank for following for lively discussions
on list and in the halls (ordered by first name): Alan Luchuk, Andy
Bierman, Balazs Kovacs, Benoit Claise, Bert Wijnen, David Lamparter,
Gary Wu, Juergen Schoenwaelder, Ladislav Lhotka, Liang Xia, Martin
Bjoerklund, Mehmet Ersue, Michal Vasko, Phil Shafer, Radek Krejci,
Sean Turner, Tom Petch.
Contributors
Special acknowledgement goes to Gary Wu for his work on the "ietf-
ssh-common" module.
Author's Address
Kent Watsen
Watsen Networks
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Email: kent+ietf@watsen.net
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