| NETCONF Working Group | K. Watsen |
| Internet-Draft | Watsen Networks |
| Intended status: Standards Track | G. Wu |
| Expires: October 31, 2019 | Cisco Systems |
| L. Xia | |
| Huawei | |
| April 29, 2019 |
YANG Groupings for SSH Clients and SSH Servers
draft-ietf-netconf-ssh-client-server-13
This document defines three YANG modules: the first defines groupings for a generic SSH client, the second defines groupings for a generic SSH server, and the third defines common identities and groupings used by both the client and the server. It is intended that these groupings will be used by applications using the SSH protocol.
This draft contains many placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document.
This document contains references to other drafts in progress, both in the Normative References section, as well as in body text throughout. Please update the following references to reflect their final RFC assignments:
Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements:
Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement:
The following Appendix section is to be removed prior to publication:
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 31, 2019.
Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document defines three YANG 1.1 [RFC7950] modules: the first defines a grouping for a generic SSH client, the second defines a grouping for a generic SSH server, and the third defines identities and groupings common to both the client and the server. It is intended that these groupings will be used by applications using the SSH protocol [RFC4252], [RFC4253], and [RFC4254]. For instance, these groupings could be used to help define the data model for an OpenSSH [OPENSSH] server or a NETCONF over SSH [RFC6242] based server.
The client and server YANG modules in this document each define one grouping, which is focused on just SSH-specific configuration, and specifically avoids 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 use groupings defined in [I-D.ietf-netconf-keystore] enabling keys to be either locally defined or a reference to globally configured values.
The modules defined in this document optionally support [RFC6187] enabling X.509v3 certificate based host keys and public keys.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This section provides a tree diagram [RFC8340] for the "ietf-ssh-client" module that does not have groupings expanded.
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
module: ietf-ssh-client
grouping ssh-client-grouping
+-- client-identity
| +-- username? string
| +-- (auth-type)
| +--:(password)
| | +-- password? string
| +--:(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-key-\
grouping
+-- server-authentication
| +-- pinned-ssh-host-keys? ta:pinned-host-keys-ref
| | {ta:ssh-host-keys}?
| +-- pinned-ca-certs? ta:pinned-certificates-ref
| | {sshcmn:ssh-x509-certs,ta:x509-certificates}?
| +-- pinned-server-certs? ta:pinned-certificates-ref
| {sshcmn:ssh-x509-certs,ta:x509-certificates}?
+-- transport-params {ssh-client-transport-params-config}?
| +---u sshcmn:transport-params-grouping
+-- keepalives! {ssh-client-keepalives}?
+-- max-wait? uint16
+-- max-attempts? uint8
This section presents two examples showing the ssh-client-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].
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
<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>
<local-definition>
<algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto\
-types">ct:rsa2048</algorithm>
<private-key>base64encodedvalue==</private-key>
<public-key>base64encodedvalue==</public-key>
</local-definition>
</public-key>
</client-identity>
<!-- which host-keys will this client trust -->
<server-authentication>
<pinned-ssh-host-keys>explicitly-trusted-ssh-host-keys</pinned-s\
sh-host-keys>
</server-authentication>
<transport-params>
<host-key>
<host-key-alg>algs:ssh-rsa</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>
algs:diffie-hellman-group-exchange-sha256
</key-exchange-alg>
</key-exchange>
<encryption>
<encryption-alg>algs:aes256-ctr</encryption-alg>
<encryption-alg>algs:aes192-ctr</encryption-alg>
<encryption-alg>algs:aes128-ctr</encryption-alg>
<encryption-alg>algs:aes256-cbc</encryption-alg>
<encryption-alg>algs:aes192-cbc</encryption-alg>
<encryption-alg>algs:aes128-cbc</encryption-alg>
</encryption>
<mac>
<mac-alg>algs:hmac-sha2-256</mac-alg>
<mac-alg>algs:hmac-sha2-512</mac-alg>
</mac>
</transport-params>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
The following example configures the client identity using a local key:
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
<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>
<keystore-reference>ex-rsa-key</keystore-reference>
</public-key>
</client-identity>
<!-- which host-keys will this client trust -->
<server-authentication>
<pinned-ssh-host-keys>explicitly-trusted-ssh-host-keys</pinned-s\
sh-host-keys>
</server-authentication>
<transport-params>
<host-key>
<host-key-alg>algs:ssh-rsa</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>
algs:diffie-hellman-group-exchange-sha256
</key-exchange-alg>
</key-exchange>
<encryption>
<encryption-alg>algs:aes256-ctr</encryption-alg>
<encryption-alg>algs:aes192-ctr</encryption-alg>
<encryption-alg>algs:aes128-ctr</encryption-alg>
<encryption-alg>algs:aes256-cbc</encryption-alg>
<encryption-alg>algs:aes192-cbc</encryption-alg>
<encryption-alg>algs:aes128-cbc</encryption-alg>
</encryption>
<mac>
<mac-alg>algs:hmac-sha2-256</mac-alg>
<mac-alg>algs:hmac-sha2-512</mac-alg>
</mac>
</transport-params>
<keepalives>
<max-wait>30</max-wait>
<max-attempts>3</max-attempts>
</keepalives>
</ssh-client>
The following example configures the client identity using a key from the keystore:
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@2019-04-29.yang"
module ietf-ssh-client {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-client";
prefix sshc;
import ietf-ssh-common {
prefix sshcmn;
revision-date 2019-04-29; // stable grouping definitions
reference
"RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
}
import ietf-trust-anchors {
prefix ta;
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
import ietf-keystore {
prefix ks;
reference
"RFC ZZZZ:
YANG Data Model for a Centralized Keystore Mechanism";
}
import ietf-netconf-acm {
prefix nacm;
reference
"RFC 8341: Network Configuration Access Control Model";
}
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 clients that
can be used as a basis for specific SSH client instances.
Copyright (c) 2019 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 XXXX
(https://www.rfc-editor.org/info/rfcXXXX); 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 2019-04-29 {
description
"Initial version";
reference
"RFC XXXX: 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.";
}
// Groupings
grouping ssh-client-grouping {
description
"A reusable grouping for configuring a SSH client without
any consideration for how an underlying TCP session is
established.
Note that this grouping uses fairly typical descendent
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 credentials used by the client to authenticate to
the SSH server.";
leaf username {
type string;
description
"The username of this user. This will be the username
used, for instance, to log into an SSH server.";
}
choice auth-type {
mandatory true;
description
"The authentication type.";
leaf password {
nacm:default-deny-all;
type string;
description
"A password to be used for client authentication.";
}
container public-key {
uses ks:local-or-keystore-asymmetric-key-grouping;
description
"A locally-defined or referenced asymmetric key
pair to be used for client authentication.";
reference
"RFC ZZZZ: YANG Data Model for a Centralized
Keystore Mechanism";
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
uses
ks:local-or-keystore-end-entity-cert-with-key-grouping;
description
"A locally-defined or referenced certificate
to be used for client authentication.";
reference
"RFC ZZZZ: YANG Data Model for a Centralized
Keystore Mechanism";
}
}
} // container client-identity
container server-authentication {
nacm:default-deny-write;
must 'pinned-ssh-host-keys or pinned-ca-certs or '
+ 'pinned-server-certs';
description
"Trusted server identities.";
leaf pinned-ssh-host-keys {
if-feature "ta:ssh-host-keys";
type ta:pinned-host-keys-ref;
description
"A reference to a list 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 YYYY: YANG Data Model for Global Trust Anchors";
}
leaf pinned-ca-certs {
if-feature "sshcmn:ssh-x509-certs";
if-feature "ta:x509-certificates";
type ta:pinned-certificates-ref;
description
"A reference to a list of certificate authority (CA)
certificates used by the SSH client to authenticate
SSH server certificates. A server certificate is
authenticated if it has a valid chain of trust to
a configured CA certificate.";
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
leaf pinned-server-certs {
if-feature "sshcmn:ssh-x509-certs";
if-feature "ta:x509-certificates";
type ta:pinned-certificates-ref;
description
"A reference to a list of server certificates used by
the SSH client to authenticate SSH server certificates.
A server certificate is authenticated if it is an
exact match to a configured server certificate.";
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
} // 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 keepalives are enabled.";
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.";
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>
This section provides a tree diagram [RFC8340] for the "ietf-ssh-server" module that does not have groupings expanded.
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
module: ietf-ssh-server
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
| +-- supported-authentication-methods
| | +-- publickey? empty
| | +-- passsword? empty
| | +-- hostbased? empty
| | +-- none? empty
| | +-- other* string
| +-- (local-or-external)
| +--:(local) {local-client-auth-supported}?
| | +-- users
| | +-- user* [name]
| | +-- name? string
| | +-- password? ianach:crypt-hash
| | +-- authorized-key* [name]
| | +-- name? string
| | +-- algorithm string
| | +-- key-data binary
| +--:(external) {external-client-auth-supported}?
| +-- client-auth-defined-elsewhere? empty
+-- transport-params {ssh-server-transport-params-config}?
| +---u sshcmn:transport-params-grouping
+-- keepalives! {ssh-server-keepalives}?
+-- max-wait? uint16
+-- max-attempts? uint8
This section presents two examples showing the ssh-server-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].
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
<ssh-server
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-server"
xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<!-- which host-keys will this SSH server present -->
<server-identity>
<host-key>
<name>deployment-specific-certificate</name>
<public-key>
<local-definition>
<algorithm xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-cryp\
to-types">ct:rsa2048</algorithm>
<private-key>base64encodedvalue==</private-key>
<public-key>base64encodedvalue==</public-key>
</local-definition>
</public-key>
</host-key>
</server-identity>
<!-- which client credentials will this SSH server trust -->
<client-authentication>
<supported-authentication-methods>
<publickey/>
</supported-authentication-methods>
<!--<local-definition>-->
<users>
<user>
<name>mary</name>
</user>
</users>
<!--</local-definition>-->
<!--
<pinned-ca-certs>explicitly-trusted-client-ca-certs</pinned-ca-c\
erts>
<pinned-client-certs>explicitly-trusted-client-certs</pinned-cli\
ent-certs>
-->
</client-authentication>
<transport-params>
<host-key>
<host-key-alg>algs:ssh-rsa</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>
algs:diffie-hellman-group-exchange-sha256
</key-exchange-alg>
</key-exchange>
<encryption>
<encryption-alg>algs:aes256-ctr</encryption-alg>
<encryption-alg>algs:aes192-ctr</encryption-alg>
<encryption-alg>algs:aes128-ctr</encryption-alg>
<encryption-alg>algs:aes256-cbc</encryption-alg>
<encryption-alg>algs:aes192-cbc</encryption-alg>
<encryption-alg>algs:aes128-cbc</encryption-alg>
</encryption>
<mac>
<mac-alg>algs:hmac-sha2-256</mac-alg>
<mac-alg>algs:hmac-sha2-512</mac-alg>
</mac>
</transport-params>
</ssh-server>
The following example configures the server identity using a local key:
=========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===========
<ssh-server
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-server"
xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<!-- which host-keys will this SSH server present -->
<server-identity>
<host-key>
<name>deployment-specific-certificate</name>
<public-key>
<keystore-reference>ex-rsa-key</keystore-reference>
</public-key>
</host-key>
</server-identity>
<!-- which client credentials will this SSH server trust -->
<client-authentication>
<supported-authentication-methods>
<publickey/>
</supported-authentication-methods>
<!--<local-definition>-->
<users>
<user>
<name>mary</name>
</user>
</users>
<!--</local-definition>-->
<!--
<pinned-ca-certs>explicitly-trusted-client-ca-certs</pinned-ca-c\
erts>
<pinned-client-certs>explicitly-trusted-client-certs</pinned-cli\
ent-certs>
-->
</client-authentication>
<transport-params>
<host-key>
<host-key-alg>algs:ssh-rsa</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>
algs:diffie-hellman-group-exchange-sha256
</key-exchange-alg>
</key-exchange>
<encryption>
<encryption-alg>algs:aes256-ctr</encryption-alg>
<encryption-alg>algs:aes192-ctr</encryption-alg>
<encryption-alg>algs:aes128-ctr</encryption-alg>
<encryption-alg>algs:aes256-cbc</encryption-alg>
<encryption-alg>algs:aes192-cbc</encryption-alg>
<encryption-alg>algs:aes128-cbc</encryption-alg>
</encryption>
<mac>
<mac-alg>algs:hmac-sha2-256</mac-alg>
<mac-alg>algs:hmac-sha2-512</mac-alg>
</mac>
</transport-params>
</ssh-server>
The following example configures the server identity using a key from the keystore:
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@2019-04-29.yang"
module ietf-ssh-server {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-server";
prefix sshs;
import ietf-ssh-common {
prefix sshcmn;
revision-date 2019-04-29; // stable grouping definitions
reference
"RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
}
/*
import ietf-trust-anchors {
prefix ta;
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
*/
import ietf-keystore {
prefix ks;
reference
"RFC ZZZZ:
YANG Data Model for a Centralized Keystore Mechanism";
}
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";
}
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) 2019 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 XXXX
(https://www.rfc-editor.org/info/rfcXXXX); 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 2019-04-29 {
description
"Initial version";
reference
"RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
}
// 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-client-auth-supported {
description
"Indicates that the SSH server supports local configuration
of client credentials.";
}
feature external-client-auth-supported {
description
"Indicates that the SSH server supports external configuration
of client credentials.";
}
// 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 descendent
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
"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 {
uses ks:local-or-keystore-asymmetric-key-grouping;
description
"A locally-defined or referenced asymmetric key pair
to be used for the SSH server's host key.";
reference
"RFC ZZZZ: YANG Data Model for a Centralized
Keystore Mechanism";
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
uses
ks:local-or-keystore-end-entity-cert-with-key-grouping;
description
"A locally-defined or referenced end-entity
certificate to be used for the SSH server's
host key.";
reference
"RFC ZZZZ: YANG Data Model for a Centralized
Keystore Mechanism";
}
}
}
} // container server-identity
container client-authentication {
nacm:default-deny-write;
description
"Specifies if SSH client authentication is required or
optional, and specifies if the SSH client authentication
credentials are configured locally or externally.";
container supported-authentication-methods {
description
"Indicates which authentication methods the server
supports.";
leaf publickey {
type empty;
description
"Indicates that the 'publickey' method is supported.
Note that RFC 6187 X.509v3 Certificates for SSH uses
the 'publickey' method name.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.
RFC 6187: X.509v3 Certificates for Secure Shell
Authentication.";
}
leaf passsword {
type empty;
description
"Indicates that the 'password' method is supported.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
leaf hostbased {
type empty;
description
"Indicates that the 'hostbased' method is supported.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
leaf none {
type empty;
description
"Indicates that the 'none' method is supported.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
leaf-list other {
type string;
description
"Indicates a supported method name not defined by
RFC 4253.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
}
choice local-or-external {
mandatory true;
description
"Indicates if the client credentials are configured
locally or externally.";
case local {
if-feature "local-client-auth-supported";
description
"Client credentials are configured locally.";
container users {
description
"A list of locally configured users.";
list user {
key name;
description
"The list of local users configured on this device.";
leaf name {
type string;
description
"The user name string identifying this entry.";
}
leaf password {
type ianach:crypt-hash;
description
"The password for this entry.";
}
list authorized-key {
key name;
description
"A list of public SSH keys for this user. These
keys are allowed for SSH authentication, as
described in RFC 4253.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer
Protocol";
leaf name {
type string;
description
"An arbitrary name for the SSH key.";
}
leaf algorithm {
type string;
mandatory true;
description
"The public key algorithm name for this SSH key.
Valid values are the values in the IANA 'Secure
Shell (SSH) Protocol Parameters' registry,
Public Key Algorithm Names.";
reference
"IANA 'Secure Shell (SSH) Protocol Parameters'
registry, Public Key Algorithm Names";
}
leaf key-data {
type binary;
mandatory true;
description
"The binary public key data for this SSH key, as
specified by RFC 4253, Section 6.6, i.e.:
string certificate or public key format
identifier
byte[n] key/certificate data.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer
Protocol";
}
}
} // list user
/*
if-feature "sshcmn:ssh-x509-certs";
description
"A reference to a list of pinned certificate authority
(CA) certificates and a reference to a list of pinned
client certificates.";
leaf pinned-ca-certs {
if-feature "ta:x509-certificates";
type ta:pinned-certificates-ref; // local or remote
description
"A reference to a list 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 pinned CA certificate.";
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
leaf pinned-client-certs {
if-feature "ta:x509-certificates";
type ta:pinned-certificates-ref; // local or remote
description
"A reference to a list of client certificates
used by the SSH server to authenticate SSH
client certificates. A clients certificate
is authenticated if it is an exact match to
a configured pinned client certificate.";
reference
"RFC YYYY: YANG Data Model for Global Trust Anchors";
}
*/
} // container users
} // case local
case external {
if-feature "external-client-auth-supported";
description
"Client credentials are configured externally, such
as via RADIUS, RFC 7317, or another mechanism.";
leaf client-auth-defined-elsewhere {
type empty;
description
"Indicates that client credentials are configured
elsewhere.";
}
}
} // choice local-or-external
} // container client-authentication
container transport-params {
nacm:default-deny-write;
if-feature "ssh-server-transport-params-config";
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 keepalives are enabled.";
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.";
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.";
}
} // container keepalives
} // grouping server-identity-grouping
}
<CODE ENDS>
The SSH common model presented in this section contains identities and groupings common to both SSH clients and SSH servers. The transport-params-grouping can be used to configure the list of SSH transport algorithms permitted by the SSH client or SSH server. The lists of algorithms are ordered such that, if multiple algorithms are permitted by the client, the algorithm that appears first in its list that is also permitted by the server 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.
+-------------------------------+-------------------------------+ | sshcmn:host-key-alg | ct:signature-algorithm | +-------------------------------+-------------------------------+ | dsa-sha1 | dsa-sha1 | | rsa-pkcs1-sha1 | rsa-pkcs1-sha1 | | rsa-pkcs1-sha256 | rsa-pkcs1-sha256 | | rsa-pkcs1-sha512 | rsa-pkcs1-sha512 | | ecdsa-secp256r1-sha256 | ecdsa-secp256r1-sha256 | | ecdsa-secp384r1-sha384 | ecdsa-secp384r1-sha384 | | ecdsa-secp521r1-sha512 | ecdsa-secp521r1-sha512 | | x509v3-rsa-pkcs1-sha1 | x509v3-rsa-pkcs1-sha1 | | x509v3-rsa2048-pkcs1-sha256 | x509v3-rsa2048-pkcs1-sha1 | | x509v3-ecdsa-secp256r1-sha256 | x509v3-ecdsa-secp256r1-sha256 | | x509v3-ecdsa-secp384r1-sha384 | x509v3-ecdsa-secp384r1-sha384 | | x509v3-ecdsa-secp521r1-sha512 | x509v3-ecdsa-secp521r1-sha512 | +-------------------------------+-------------------------------+
Table 1 The SSH Host-key-alg Compatibility Matrix
+-------------------------------+-------------------------------+ | sshcmn:key-exchange-alg | ct:key-negotiation-algorithm | +-------------------------------+-------------------------------+ | diffie-hellman-group14-sha1 | diffie-hellman-group14-sha1 | | diffie-hellman-group14-sha256 | diffie-hellman-group14-sha256 | | diffie-hellman-group15-sha512 | diffie-hellman-group15-sha512 | | diffie-hellman-group16-sha512 | diffie-hellman-group16-sha512 | | diffie-hellman-group17-sha512 | diffie-hellman-group17-sha512 | | diffie-hellman-group18-sha512 | diffie-hellman-group18-sha512 | | ecdh-sha2-secp256r1 | ecdh-sha2-secp256r1 | | ecdh-sha2-secp384r1 | ecdh-sha2-secp384r1 | +-------------------------------+-------------------------------+
Table 2 The SSH Key-exchange-alg Compatibility Matrix
+-----------------------+---------------------------------------+ | sshcmn:encryption-alg | ct:symmetric-key-encryption-algorithm | +-----------------------+---------------------------------------+ | aes-128-cbc | aes-128-cbc | | aes-192-cbc | aes-192-cbc | | aes-256-cbc | aes-256-cbc | | aes-128-ctr | aes-128-ctr | | aes-192-ctr | aes-192-ctr | | aes-256-ctr | aes-256-ctr | +-----------------------+---------------------------------------+
Table 3 The SSH Encryption-alg Compatibility Matrix
+----------------+-------------------+ | sshcmn:mac-alg | ct:mac-algorithm | +----------------+-------------------+ | hmac-sha1 | hmac-sha1 | | hmac-sha1-96 | hmac-sha1-96 | | hmac-sha2-256 | hmac-sha2-256 | | hmac-sha2-512 | hmac-sha2-512 | +----------------+-------------------+
Table 4 The SSH Mac-alg Compatibility Matrix
[I-D.ietf-netconf-crypto-types] defines six categories of cryptographic algorithms (hash-algorithm, symmetric-key-encryption-algorithm, mac-algorithm, asymmetric-key-encryption-algorithm, signature-algorithm, key-negotiation-algorithm) and lists several widely accepted algorithms for each of them. The SSH client and server models use one or more of these algorithms. The SSH common model includes four parameters for configuring its permitted SSH algorithms, which are: host-key-alg, key-exchange-alg, encryption-alg and mac-alg. The following tables are provided, in part, to define the subset of algorithms defined in the crypto-types model used by SSH and, in part, to ensure compatibility of configured SSH cryptographic parameters for configuring its permitted SSH algorithms ("sshcmn" representing SSH common model, and "ct" representing crypto-types model which the SSH client/server model is based on):
As is seen in the tables above, the names of the “sshcmn” algorithms are all identical to the names of algorithms defined in [I-D.ietf-netconf-crypto-types]. While appearing to be redundant, it is important to realize that not all the algorithms defined in [I-D.ietf-netconf-crypto-types] are supported by SSH. That is, the algorithms supported by SSH are a subset of the algorithms defined in [I-D.ietf-netconf-crypto-types]. The algorithms used by SSH are redefined in this document in order to constrain the algorithms that may be selected to just the ones used by SSH.
Features are defined for algorithms that are OPTIONAL or are not widely supported by popular implementations. Note that the list of algorithms is not exhaustive. As well, some algorithms that are REQUIRED by [RFC4253] are missing, notably "ssh-dss" and "diffie-hellman-group1-sha1" due to their weak security and there being alternatives that are widely supported.
The following tree diagram [RFC8340] provides an overview of the data model for the "ietf-ssh-common" module.
module: ietf-ssh-common
grouping transport-params-grouping
+-- host-key
| +-- host-key-alg* identityref
+-- key-exchange
| +-- key-exchange-alg* identityref
+-- encryption
| +-- encryption-alg* identityref
+-- mac
+-- mac-alg* identityref
This following example illustrates how the transport-params-grouping appears when populated with some data.
<transport-params
xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-common"
xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">
<host-key>
<host-key-alg>algs:x509v3-rsa2048-sha256</host-key-alg>
<host-key-alg>algs:ssh-rsa</host-key-alg>
</host-key>
<key-exchange>
<key-exchange-alg>
algs:diffie-hellman-group-exchange-sha256
</key-exchange-alg>
</key-exchange>
<encryption>
<encryption-alg>algs:aes256-ctr</encryption-alg>
<encryption-alg>algs:aes192-ctr</encryption-alg>
<encryption-alg>algs:aes128-ctr</encryption-alg>
<encryption-alg>algs:aes256-cbc</encryption-alg>
<encryption-alg>algs:aes192-cbc</encryption-alg>
<encryption-alg>algs:aes128-cbc</encryption-alg>
</encryption>
<mac>
<mac-alg>algs:hmac-sha2-256</mac-alg>
<mac-alg>algs:hmac-sha2-512</mac-alg>
</mac>
</transport-params>
This YANG module has normative references to [RFC4253], [RFC4344], [RFC4419], [RFC5656], [RFC6187], and [RFC6668].
<CODE BEGINS> file "ietf-ssh-common@2019-04-29.yang"
module ietf-ssh-common {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-common";
prefix sshcmn;
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 a common features, identities, and
groupings for Secure Shell (SSH).
Copyright (c) 2019 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 XXXX
(https://www.rfc-editor.org/info/rfcXXXX); 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 2019-04-29 {
description
"Initial version";
reference
"RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-ecc {
description
"Elliptic Curve Cryptography is supported for SSH.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
feature ssh-x509-certs {
description
"X.509v3 certificates are supported for SSH per RFC 6187.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
feature ssh-dh-group-exchange {
description
"Diffie-Hellman Group Exchange is supported for SSH.";
reference
"RFC 4419: Diffie-Hellman Group Exchange for the
Secure Shell (SSH) Transport Layer Protocol";
}
feature ssh-ctr {
description
"SDCTR encryption mode is supported for SSH.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer
Encryption Modes";
}
feature ssh-sha2 {
description
"The SHA2 family of cryptographic hash functions is
supported for SSH.";
reference
"FIPS PUB 180-4: Secure Hash Standard (SHS)";
}
// Identities
identity public-key-alg-base {
description
"Base identity used to identify public key algorithms.";
}
identity ssh-dss {
base public-key-alg-base;
description
"Digital Signature Algorithm using SHA-1 as the
hashing algorithm.";
reference
"RFC 4253:
The Secure Shell (SSH) Transport Layer Protocol";
}
identity ssh-rsa {
base public-key-alg-base;
description
"RSASSA-PKCS1-v1_5 signature scheme using SHA-1 as the
hashing algorithm.";
reference
"RFC 4253:
The Secure Shell (SSH) Transport Layer Protocol";
}
identity ecdsa-sha2-nistp256 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA) using the
nistp256 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
identity ecdsa-sha2-nistp384 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA) using the
nistp384 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
identity ecdsa-sha2-nistp521 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA) using the
nistp521 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
identity x509v3-ssh-rsa {
base public-key-alg-base;
if-feature "ssh-x509-certs";
description
"RSASSA-PKCS1-v1_5 signature scheme using a public key stored
in an X.509v3 certificate and using SHA-1 as the hashing
algorithm.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
identity x509v3-rsa2048-sha256 {
base public-key-alg-base;
if-feature "ssh-x509-certs and ssh-sha2";
description
"RSASSA-PKCS1-v1_5 signature scheme using a public key stored
in an X.509v3 certificate and using SHA-256 as the hashing
algorithm. RSA keys conveyed using this format MUST have a
modulus of at least 2048 bits.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
identity x509v3-ecdsa-sha2-nistp256 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA)
using the nistp256 curve with a public key stored in
an X.509v3 certificate and using the SHA2 family of
hashing algorithms.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
identity x509v3-ecdsa-sha2-nistp384 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA)
using the nistp384 curve with a public key stored in
an X.509v3 certificate and using the SHA2 family of
hashing algorithms.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
identity x509v3-ecdsa-sha2-nistp521 {
base public-key-alg-base;
if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
description
"Elliptic Curve Digital Signature Algorithm (ECDSA)
using the nistp521 curve with a public key stored in
an X.509v3 certificate and using the SHA2 family of
hashing algorithms.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
identity key-exchange-alg-base {
description
"Base identity used to identify key exchange algorithms.";
}
identity diffie-hellman-group14-sha1 {
base key-exchange-alg-base;
description
"Diffie-Hellman key exchange with SHA-1 as HASH and
Oakley Group 14 (2048-bit MODP Group).";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
}
identity diffie-hellman-group-exchange-sha1 {
base key-exchange-alg-base;
if-feature "ssh-dh-group-exchange";
description
"Diffie-Hellman Group and Key Exchange with SHA-1 as HASH.";
reference
"RFC 4419: Diffie-Hellman Group Exchange for the
Secure Shell (SSH) Transport Layer Protocol";
}
identity diffie-hellman-group-exchange-sha256 {
base key-exchange-alg-base;
if-feature "ssh-dh-group-exchange and ssh-sha2";
description
"Diffie-Hellman Group and Key Exchange with SHA-256 as HASH.";
reference
"RFC 4419: Diffie-Hellman Group Exchange for the
Secure Shell (SSH) Transport Layer Protocol";
}
identity ecdh-sha2-nistp256 {
base key-exchange-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Diffie-Hellman (ECDH) key exchange using the
nistp256 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
identity ecdh-sha2-nistp384 {
base key-exchange-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Diffie-Hellman (ECDH) key exchange using the
nistp384 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
identity ecdh-sha2-nistp521 {
base key-exchange-alg-base;
if-feature "ssh-ecc and ssh-sha2";
description
"Elliptic Curve Diffie-Hellman (ECDH) key exchange using the
nistp521 curve and the SHA2 family of hashing algorithms.";
reference
"RFC 5656: Elliptic Curve Algorithm Integration in the
Secure Shell Transport Layer";
}
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.";
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 {
base encryption-alg-base;
if-feature "ssh-ctr";
description
"AES in SDCTR mode, with 128-bit key.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
Modes";
}
identity aes192-ctr {
base encryption-alg-base;
if-feature "ssh-ctr";
description
"AES in SDCTR mode, with 192-bit key.";
reference
"RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
Modes";
}
identity aes256-ctr {
base encryption-alg-base;
if-feature "ssh-ctr";
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 {
base mac-alg-base;
if-feature "ssh-sha2";
description
"HMAC-SHA2-256";
reference
"RFC 6668: SHA-2 Data Integrity Verification for the
Secure Shell (SSH) Transport Layer Protocol";
}
identity hmac-sha2-512 {
base mac-alg-base;
if-feature "ssh-sha2";
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
"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 XXXX for
valid combinations.
If this leaf-list is not configured (has zero elements)
the acceptable host key algorithms are implementation-
defined.";
reference
"RFC XXXX: 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;
}
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>
The YANG modules defined in this document 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 modules in this document only define groupings, these considerations are primarily for the designers of other modules that use these groupings.
There are a number of data nodes defined in the YANG modules that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability:
Some of the readable data nodes in the YANG modules may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:
Some of the operations in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability:
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-client Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. URI: urn:ietf:params:xml:ns:yang:ietf-ssh-server Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. URI: urn:ietf:params:xml:ns:yang:ietf-ssh-common Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace.
This document registers three YANG modules in the YANG Module Names registry [RFC6020]. Following the format in [RFC6020], the following registrations are requested:
name: ietf-ssh-client namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-client prefix: sshc reference: RFC XXXX name: ietf-ssh-server namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-server prefix: sshs reference: RFC XXXX name: ietf-ssh-common namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-common prefix: sshcmn reference: RFC XXXX
| [OPENSSH] | Project, T. O., "OpenSSH", 2016. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004. |
| [RFC4252] | Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252, January 2006. |
| [RFC4253] | Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006. |
| [RFC4254] | Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection Protocol", RFC 4254, DOI 10.17487/RFC4254, January 2006. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011. |
| [RFC6242] | Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011. |
| [RFC7317] | Bierman, A. and M. Bjorklund, "A YANG Data Model for System Management", RFC 7317, DOI 10.17487/RFC7317, August 2014. |
| [RFC8040] | Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017. |
| [RFC8071] | Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, February 2017. |
| [RFC8340] | Bjorklund, M. and L. Berger, "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018. |
The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): Andy Bierman, Martin Bjorklund, Benoit Claise, Mehmet Ersue, Balázs Kovács, David Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch, Juergen Schoenwaelder, Phil Shafer, Sean Turner, Michal Vaško, and Bert Wijnen.