YANG Groupings for
SSH Clients and SSH ServersWatsen Networkskent+ietf@watsen.netCisco Systemsgarywu@cisco.comHuaweifrank.xialiang@huawei.com
Operations
NETCONF Working GroupThis 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: I-D.ietf-netconf-trust-anchorsI-D.ietf-netconf-keystoreArtwork in this document contains shorthand references to drafts in
progress. Please apply the following replacements: XXXX --> the assigned RFC value
for this draftYYYY --> the assigned RFC value
for I-D.ietf-netconf-trust-anchorsZZZZ --> the assigned RFC value
for I-D.ietf-netconf-keystoreArtwork in this document contains placeholder values for the date of
publication of this draft. Please apply the following replacement: 2019-03-09 --> the publication
date of this draftThe following Appendix section is to be removed prior to publication:
Appendix A. Change LogThis document defines three YANG 1.1
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 , , and . For instance, these
groupings could be used to help define the data model for an OpenSSH
server or a NETCONF over SSH 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 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 enabling keys
to be either locally defined or
a reference to globally configured values.The modules defined in this document optionally support 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
when, and only when,
they appear in all capitals, as shown here.This section provides a tree diagram for
the "ietf-ssh-client" module that does not have groupings
expanded.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 3 of and Section 3.2 of .The following example configures the client identity using a local
key: foobarct:rsa2048base64encodedvalue==base64encodedvalue==explicitly-trusted-ssh-host-keys
algs:ssh-rsa
algs:diffie-hellman-group-exchange-sha256
algs:aes256-ctralgs:aes192-ctralgs:aes128-ctralgs:aes256-cbcalgs:aes192-cbcalgs:aes128-cbcalgs:hmac-sha2-256algs:hmac-sha2-512303
]]>The following example configures the client identity using a key
from the keystore: foobarex-rsa-keyexplicitly-trusted-ssh-host-keys
algs:ssh-rsa
algs:diffie-hellman-group-exchange-sha256
algs:aes256-ctralgs:aes192-ctralgs:aes128-ctralgs:aes256-cbcalgs:aes192-cbcalgs:aes128-cbcalgs:hmac-sha2-256algs:hmac-sha2-512303
]]>This YANG module has normative references to , and . file "ietf-ssh-client@2019-03-09.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 2019-03-09; // 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";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web:
WG List:
Author: Kent Watsen
Author: Gary Wu ";
description
"This module defines reusable groupings for SSH clients that
can be used as a basis for specific SSH client instances.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision "2019-03-09" {
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.";
uses client-identity-grouping;
uses server-auth-grouping;
uses transport-params-grouping;
uses keepalives-grouping;
}
grouping client-identity-grouping {
description
"A reusable grouping for configuring a SSH client identity.";
container ssh-client-identity {
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 {
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";
}
} // auth-type
} // client-identity
} // client-identity-grouping
grouping server-auth-grouping {
description
"A reusable grouping for configuring SSH server
authentication.";
container ssh-server-auth {
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";
}
} // server-auth
} // server-auth-grouping
grouping transport-params-grouping {
description
"A reusable grouping for configuring a SSH transport
parameters.";
container ssh-transport-params {
if-feature ssh-client-transport-params-config;
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
}
} // transport-params-grouping
grouping keepalives-grouping {
description
"A reusable grouping for configuring SSH client keepalive
parameters.";
container ssh-keepalives {
if-feature "ssh-client-keepalives";
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.";
}
}
} // keepalives-grouping
}
]]>This section provides a tree diagram for
the "ietf-ssh-server" module that does not have groupings
expanded.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 3 of and Section 3.2 of .The following example configures the server identity using a local
key: deployment-specific-certificatect:rsa2048base64encodedvalue==base64encodedvalue==explicitly-trusted-client-ca-certs
explicitly-trusted-client-certs
algs:ssh-rsa
algs:diffie-hellman-group-exchange-sha256
algs:aes256-ctralgs:aes192-ctralgs:aes128-ctralgs:aes256-cbcalgs:aes192-cbcalgs:aes128-cbcalgs:hmac-sha2-256algs:hmac-sha2-512
]]>The following example configures the server identity using a key
from the keystore: deployment-specific-certificateex-rsa-keyexplicitly-trusted-client-ca-certs
explicitly-trusted-client-certs
algs:ssh-rsa
algs:diffie-hellman-group-exchange-sha256
algs:aes256-ctralgs:aes192-ctralgs:aes128-ctralgs:aes256-cbcalgs:aes192-cbcalgs:aes128-cbcalgs:hmac-sha2-256algs:hmac-sha2-512
]]>This YANG module has normative references to and and informative references to
and . file "ietf-ssh-server@2019-03-09.yang"
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) ===========
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 2019-03-09; // 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";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web:
WG List:
Author: Kent Watsen
Author: Gary Wu ";
description
"This module defines reusable groupings for SSH servers that
can be used as a basis for specific SSH server instances.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision "2019-03-09" {
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.";
}
// Groupings
grouping ssh-server-grouping {
description
"A reusable grouping for configuring a SSH server without
any consideration for how underlying TCP sessions are
established.";
uses server-identity-grouping;
uses client-auth-grouping;
uses transport-params-grouping;
uses keepalives-grouping;
}
grouping server-identity-grouping {
description
"A reusable grouping for configuring an SSH server identity.";
container ssh-server-identity {
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";
}
}
}
} // server-identity
} // server-identity-grouping
grouping client-auth-grouping {
description
"A reusable grouping for configuring a SSH client
authentication.";
container ssh-client-cert-auth {
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.
Note: password and public-key based client authentication
are not configured in this YANG module as they are
expected to be configured by the ietf-system module
defined in RFC 7317.";
reference
"RFC 7317: A YANG Data Model for System Management";
leaf pinned-ca-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 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;
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";
}
}
} // client-auth-grouping
grouping transport-params-grouping {
description
"A reusable grouping for configuring a SSH transport
parameters.";
container ssh-transport-params {
if-feature ssh-server-transport-params-config;
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
}
} // transport-params-grouping
grouping keepalives-grouping {
description
"A reusable grouping for configuring SSH server keepalive
parameters.";
container ssh-keepalives {
if-feature "ssh-server-keepalives";
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.";
}
}
} // keepalives-grouping
}
]]>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. 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):+-------------------------------+-------------------------------+
| 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 |
+-------------------------------+-------------------------------++-------------------------------+-------------------------------+
| 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 |
+-------------------------------+-------------------------------++-----------------------+---------------------------------------+
| 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 |
+-----------------------+---------------------------------------++----------------+-------------------+
| 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 |
+----------------+-------------------+As is seen in the tables above, the names of the “sshcmn” algorithms
are all identical to the names of algorithms defined in . While appearing to be
redundant, it is important to realize that not all the algorithms
defined in are supported
by SSH. That is, the algorithms supported by SSH are a subset of the
algorithms defined in .
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 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 provides an
overview of the data model for the "ietf-ssh-common" module.This following example illustrates how the
transport-params-grouping appears when populated with some data.algs:x509v3-rsa2048-sha256algs:ssh-rsa
algs:diffie-hellman-group-exchange-sha256
algs:aes256-ctralgs:aes192-ctralgs:aes128-ctralgs:aes256-cbcalgs:aes192-cbcalgs:aes128-cbcalgs:hmac-sha2-256algs:hmac-sha2-512
]]>This YANG module has normative references to , , , , , and . file "ietf-ssh-common@2019-03-09.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:
WG List:
Author: Kent Watsen
Author: Gary Wu ";
description
"This module defines a common features, identities, and
groupings for Secure Shell (SSH).
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision "2019-03-09" {
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.";
}
}
} // transport-params-grouping
}
]]>The YANG modules defined in this document are designed to be accessed
via YANG based management protocols, such as NETCONF and RESTCONF . Both of these
protocols have mandatory-to-implement secure transport layers (e.g.,
SSH, TLS) with mutual authentication.The NETCONF access control model (NACM)
provides the means to restrict access for particular users to a
pre-configured subset of all available protocol operations and
content.Since the modules defined in this document define only 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: The entire data tree defined by all the modules
defined in this draft are sensitive to write operations. For
instance, the addition or removal of references to keys,
certificates, trusted anchors, etc., can dramatically alter the
implemented security policy. However, no NACM annotations are
applied as the data SHOULD be editable by users other than a
designated 'recovery session'.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: This node in the
'ietf-ssh-client' module is additionally sensitive to read
operations such that, in normal use cases, it should never be
returned to a client. The only time this node should be returned is
to support backup/restore type workflows. However, no NACM
annotations are applied as the data SHOULD be writable by users
other than a designated 'recovery session'.Some of the RPC 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 . Following the format in
, 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 . Following the format in , 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
OpenSSHNoted that '0.0.0.0' and '::' might have special meanings.Renamed "keychain" to "keystore".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.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'.Change title to "YANG Groupings for SSH Clients and SSH
Servers"Added reference to RFC 6668Added 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-diagramsUpdated YANG to use typedefs around leafrefs to common keystore
pathsNow inlines key and certificates (no longer a leafref to
keystore)Merged changes from co-author.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.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.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.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.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.