YANG Groupings for
SSH Clients and SSH Servers
Watsen Networks
kent+ietf@watsen.net
Operations
NETCONF Working Group
This document defines three YANG 1.1
modules: the first defines features and groupings common to both SSH
clients and SSH servers, the second defines a grouping for a generic
SSH client, and the third defines a grouping for a generic SSH server.
Editorial Note (To be removed by RFC Editor)
This draft contains 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.
Artwork in this document contains shorthand references to drafts in
progress. Please apply the following replacements:
-
AAAA --> the assigned RFC value for draft-ietf-netconf-crypto-types
-
BBBB --> the assigned RFC value for draft-ietf-netconf-trust-anchors
-
CCCC --> the assigned RFC value for draft-ietf-netconf-keystore
-
DDDD --> the assigned RFC value for draft-ietf-netconf-tcp-client-server
-
EEEE --> the assigned RFC value for this draft
Artwork in this document contains placeholder values for the date of
publication of this draft. Please apply the following replacement:
-
2022-12-12 --> the publication date of this draft
The "Relation to other RFCs" section contains
the text "one or more YANG modules" and, later, "modules". This text is sourced
from a file in a context where it is unknown how many modules a draft defines.
The text is not wrong as is, but it may be improved by stating more directly how
many modules are defined.
The "Relation to other RFCs" section contains
a self-reference to this draft, along with a corresponding Informative Reference in
the Appendix.
The following Appendix section is to be removed prior to publication:
Introduction
This document defines three YANG 1.1
modules: the first defines features and groupings common to both SSH
clients and SSH servers, the second defines a grouping for a generic
SSH client, and the third defines a grouping for a generic SSH 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.
Relation to other RFCs
This document presents one or more YANG modules
that are part of a collection of RFCs that work together
to, ultimately, enable the configuration of both the clients
and servers of both the NETCONF and
RESTCONF protocols.
The normative dependency relationship between the various RFCs
in this collection is presented in the below diagram. The labels
in the diagram represent the primary purpose provided by each
RFC. Hyperlinks to each RFC are provided below the diagram.
Label to RFC Mapping
Label in Diagram |
Originating RFC |
crypto-types |
|
truststore |
|
keystore |
|
tcp-client-server |
|
ssh-client-server |
|
tls-client-server |
|
http-client-server |
|
netconf-client-server |
|
restconf-client-server |
|
Specification Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
Adherence to the NMDA
This document is compliant with the Network Management Datastore
Architecture (NMDA) . For instance, as
described in and
, trust anchors and keys
installed during manufacturing are expected to appear
in <operational>.
Conventions
Various examples used in this document use a placeholder
value for binary data that has been base64 encoded (e.g.,
"BASE64VALUE="). This placeholder value is used as real
base64 encoded structures are often many lines long and
hence distracting to the example being presented.
The "ietf-ssh-common" Module
The SSH common model presented in this section contains features
and groupings common to both SSH clients and SSH servers. The
"transport-params-grouping" grouping can be used to configure
the list of SSH transport algorithms permitted by the SSH client
or SSH server. The lists of permitted algorithms are in decreasing
order of usage preference. The algorithm that appears first in
the client list that also appears in the server list is the one
that is used for the SSH transport layer connection. The ability
to restrict the algorithms allowed is provided in this grouping
for SSH clients and SSH servers that are capable of doing so
and may serve to make SSH clients and SSH servers compliant
with security policies.
Data Model Overview
This section provides an overview of the "ietf-ssh-common" module
in terms of its features, identities, and groupings.
Features
The following diagram lists all the "feature" statements
defined in the "ietf-ssh-common" module:
The diagram above uses syntax that is similar to but not
defined in .
Groupings
The "ietf-ssh-common" module defines the following "grouping" statement:
- transport-params-grouping
This grouping is presented in the following subsection.
The "transport-params-grouping" Grouping
The following tree diagram illustrates the
"transport-params-grouping" grouping:
Comments:
- This grouping is used by both the "ssh-client-grouping" and the
"ssh-server-grouping" groupings defined in
and , respectively.
- This grouping enables client and server configurations to
specify the algorithms that are to be used when establishing
SSH sessions.
- Each list is "ordered-by user".
Protocol-accessible Nodes
The following tree diagram lists all the
protocol-accessible nodes defined in the "ietf-ssh-common" module,
without expanding the "grouping" statements:
The following tree diagram lists all the
protocol-accessible nodes defined in the "ietf-ssh-common" module,
with all "grouping" statements expanded, enabling the module's full
structure to be seen:
Comments:
- Protocol-accessible nodes are those nodes that are accessible
when the module is "implemented", as described in .
- The protocol-accessible nodes for the "ietf-ssh-common" module
are limited to the RPC "generate-public-key", which is
additionally constrained by the feature "public-key-generation".
- The "encrypted-by-choice-grouping" grouping is discussed in
.
- The "asymmetric-key-pair-grouping" grouping is discussed in
.
Example Usage
The following example illustrates the "transport-params-grouping'
grouping when populated with some data.
sshpka:x509v3-rsa2048-sha256
sshpka:ssh-rsa
sshkea:diffie-hellman-group-exchange-sha256
sshea:aes256-ctr
sshea:aes192-ctr
sshea:aes128-ctr
sshea:aes256-cbc
sshea:aes192-cbc
sshea:aes128-cbc
sshma:hmac-sha2-256
sshma:hmac-sha2-512
]]>
The following example illustrates the "generate-public-key" RPC.
sshpka:ecdsa-sha2-nistp256
521
hidden-asymmetric-key
]]>
YANG Module
This YANG module has normative references to , , , , , and .
<CODE BEGINS> file "ietf-ssh-common@2022-12-12.yang"
Author: Kent Watsen
Author: Gary Wu ";
description
"This module defines a common features and groupings for
Secure Shell (SSH).
Copyright (c) 2022 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC EEEE
(https://www.rfc-editor.org/info/rfcEEEE); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2022-12-12 {
description
"Initial version";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-x509-certs {
description
"X.509v3 certificates are supported for SSH.";
reference
"RFC 6187: X.509v3 Certificates for Secure Shell
Authentication";
}
feature transport-params {
description
"SSH transport layer parameters are configurable.";
}
feature public-key-generation {
description
"Indicates that the server implements the
'generate-public-key' RPC.";
}
// 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 sshpka:public-key-alg-base;
}
ordered-by user;
description
"Acceptable host key algorithms in order of descending
preference.
If this leaf-list is not configured (has zero elements)
the acceptable host key algorithms are implementation-
defined.";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
}
container key-exchange {
description
"Parameters regarding key exchange.";
leaf-list key-exchange-alg {
type identityref {
base sshkea: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 sshea: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 sshma: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.";
}
}
}
// Protocol-accessible Nodes
rpc generate-public-key {
if-feature "public-key-generation";
description
"Requests the device to generate an public key using
the specified key algorithm.";
input {
leaf algorithm {
type sshpka:public-key-algorithm-ref;
mandatory true;
description
"The algorithm to be used when generating the key.";
}
leaf bits {
type uint16;
description
"Specifies the number of bits in the key to create.
For RSA keys, the minimum size is 1024 bits and
the default is 3072 bits. Generally, 3072 bits is
considered sufficient. DSA keys must be exactly 1024
bits as specified by FIPS 186-2. For ECDSA keys, the
'bits' value determines the key length by selecting
from one of three elliptic curve sizes: 256, 384 or
521 bits. Attempting to use bit lengths other than
these three values for ECDSA keys will fail. ECDSA-SK,
Ed25519 and Ed25519-SK keys have a fixed length and
the 'bits' value, if specified, will be ignored.";
}
choice private-key-encoding {
default cleartext;
description
"A choice amongst optional private key handling.";
case cleartext {
leaf cleartext {
type empty;
description
"Indicates that the private key is to be returned
as a cleartext value.";
}
}
case encrypt {
if-feature "ct:private-key-encryption";
container encrypt-with {
description
"Indicates that the key is to be encrypted using
the specified symmetric or asymmetric key.";
uses ks:encrypted-by-choice-grouping;
}
}
case hide {
if-feature "ct:hidden-keys";
leaf hide {
type empty;
description
"Indicates that the private key is to be hidden.
Unlike the 'cleartext' and 'encrypt' options, the
key returned is a placeholder for an internally
stored key. See the 'Support for Built-in Keys'
section in RFC CCCC for information about hidden
keys.";
}
}
}
}
output {
uses ct:asymmetric-key-pair-grouping;
}
} // end generate-public-key
}
]]>
<CODE ENDS>
The "ietf-ssh-client" Module
This section defines a YANG 1.1 module called
"ietf-ssh-client". A high-level overview of the module is provided in
. Examples illustrating the module's use
are provided in Examples. The YANG
module itself is defined in .
Data Model Overview
This section provides an overview of the "ietf-ssh-client" module
in terms of its features and groupings.
Features
The following diagram lists all the "feature" statements
defined in the "ietf-ssh-client" module:
The diagram above uses syntax that is similar to but not
defined in .
Groupings
The "ietf-ssh-client" module defines the following "grouping" statement:
This grouping is presented in the following subsection.
The "ssh-client-grouping" Grouping
The following tree diagram illustrates the
"ssh-client-grouping" grouping:
Comments:
- The "client-identity" node configures a "username" and authentication methods,
each enabled by a "feature" statement defined in .
- The "server-authentication" node configures trust anchors for
authenticating the SSH server, with each option enabled by a "feature" statement.
- The "transport-params" node, which must be enabled by a feature, configures
parameters for the SSH sessions established by this configuration.
- The "keepalives" node, which must be enabled by a feature, configures
a "presence" container for testing the aliveness of the SSH server. The
aliveness-test occurs at the SSH protocol layer.
-
For the referenced grouping statement(s):
- The "local-or-keystore-asymmetric-key-grouping" grouping is
discussed in .
- The "local-or-keystore-end-entity-cert-with-key-grouping" grouping is
discussed in .
- The "local-or-truststore-public-keys-grouping" grouping is
discussed in .
- The "local-or-truststore-certs-grouping" grouping is
discussed in .
- The "transport-params-grouping" grouping is discussed in
in this document.
Protocol-accessible Nodes
The "ietf-ssh-client" module defines only "grouping" statements that are
used by other modules to instantiate protocol-accessible nodes.
Example Usage
This section presents two examples showing the "ssh-client-grouping"
grouping populated with some data. These examples are effectively the same
except the first configures the client identity using a local key
while the second uses a key configured in a keystore. Both examples
are consistent with the examples presented in Section 2 of and Section 3.2 of .
The following configuration example uses local-definitions for the
client identity and server authentication:
foobar
ct:ssh-public-key-format
BASE64VALUE=
ct:rsa-private-key-format
BASE64VALUE=
corp-fw1
ct:ssh-public-key-format
BASE64VALUE=
corp-fw2
ct:ssh-public-key-format
BASE64VALUE=
Server Cert Issuer #1
BASE64VALUE=
Server Cert Issuer #2
BASE64VALUE=
My Application #1
BASE64VALUE=
My Application #2
BASE64VALUE=
30
3
]]>
The following configuration example uses keystore-references for the
client identity and truststore-references for server authentication:
from the keystore:
foobar
ssh-rsa-key
ssh-rsa-key-with-cert
ex-rsa-cert2
trusted-ssh-public-keys
trusted-server-ca-certs
trusted-server-ee-certs
30
3
]]>
YANG Module
This YANG module has normative references to ,
, , ,
, and .
<CODE BEGINS> file "ietf-ssh-client@2022-12-12.yang"
Author: Kent Watsen ";
description
"This module defines reusable groupings for SSH clients that
can be used as a basis for specific SSH client instances.
Copyright (c) 2022 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC EEEE
(https://www.rfc-editor.org/info/rfcEEEE); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2022-12-12 {
description
"Initial version";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-client-keepalives {
description
"Per socket SSH keepalive parameters are configurable for
SSH clients on the server implementing this feature.";
}
feature client-ident-publickey {
description
"Indicates that the 'publickey' authentication type, per
RFC 4252, is supported for client identification.
The 'publickey' authentication type is required by
RFC 4252, but common implementations enable it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-password {
description
"Indicates that the 'password' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-hostbased {
description
"Indicates that the 'hostbased' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature client-ident-none {
description
"Indicates that the 'none' authentication type, per
RFC 4252, is supported for client identification.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
// Groupings
grouping ssh-client-grouping {
description
"A reusable grouping for configuring a SSH client without
any consideration for how an underlying TCP session is
established.
Note that this grouping uses fairly typical descendant
node names such that a stack of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'ssh-client-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
container client-identity {
nacm:default-deny-write;
description
"The username and authentication methods for the client.
The authentication methods are unordered. Clients may
initially send any configured method or, per RFC 4252,
Section 5.2, send the 'none' method to prompt the server
to provide a list of productive methods. Whenever a
choice amongst methods arises, implementations SHOULD
use a default ordering that prioritizes automation
over human-interaction.";
leaf username {
type string;
description
"The username of this user. This will be the username
used, for instance, to log into an SSH server.";
}
container public-key {
if-feature "client-ident-publickey";
presence
"Indicates that publickey-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A locally-defined or referenced asymmetric key
pair to be used for client identification.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "local-or-keystore/keystore/keystore-reference" {
must 'derived-from-or-self(deref(.)/../ks:public-key-'
+ 'format, "ct:ssh-public-key-format")';
}
}
}
container password {
if-feature "client-ident-password";
presence
"Indicates that password-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A password to be used to authenticate the client's
identity.";
uses ct:password-grouping;
}
container hostbased {
if-feature "client-ident-hostbased";
presence
"Indicates that hostbased authentication is configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A locally-defined or referenced asymmetric key
pair to be used for host identification.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "local-or-keystore/keystore/keystore-reference" {
must 'derived-from-or-self(deref(.)/../ks:public-key-'
+ 'format, "ct:ssh-public-key-format")';
}
}
}
leaf none {
if-feature "client-ident-none";
type empty;
description
"Indicates that 'none' algorithm is used for client
identification.";
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that certificate-based authentication has been
configured. This statement is present so the mandatory
descendant nodes do not imply that this node must be
configured.";
description
"A locally-defined or referenced certificate
to be used for client identification.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-end-entity-cert-with-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:subject-public-key-info-format")';
}
refine "local-or-keystore/keystore/keystore-reference"
+ "/asymmetric-key" {
must 'derived-from-or-self(deref(.)/../ks:public-key-'
+ 'format, "ct:subject-public-key-info-format")';
}
}
}
} // container client-identity
container server-authentication {
nacm:default-deny-write;
must 'ssh-host-keys or ca-certs or ee-certs';
description
"Specifies how the SSH client can authenticate SSH servers.
Any combination of authentication methods is additive and
unordered.";
container ssh-host-keys {
presence
"Indicates that the SSH host key have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A bag of SSH host keys used by the SSH client to
authenticate SSH server host keys. A server host key
is authenticated if it is an exact match to a
configured SSH host key.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine
"local-or-truststore/local/local-definition/public-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine
"local-or-truststore/truststore/truststore-reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
container ca-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that the CA certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A set of certificate authority (CA) certificates used by
the SSH client to authenticate SSH servers. A server
is authenticated if its certificate has a valid chain
of trust to a configured CA certificate.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
container ee-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that the EE certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be configured.";
description
"A set of end-entity certificates used by the SSH client
to authenticate SSH servers. A server is authenticated
if its certificate is an exact match to a configured
end-entity certificate.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
} // container server-authentication
container transport-params {
nacm:default-deny-write;
if-feature "sshcmn:transport-params";
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
} // container transport-parameters
container keepalives {
nacm:default-deny-write;
if-feature "ssh-client-keepalives";
presence
"Indicates that the SSH client proactively tests the
aliveness of the remote SSH server.";
description
"Configures the keep-alive policy, to proactively test
the aliveness of the SSH server. An unresponsive SSH
server is dropped after approximately max-wait *
max-attempts seconds. Per Section 4 of RFC 4254,
the SSH client SHOULD send an SSH_MSG_GLOBAL_REQUEST
message with a purposely nonexistent 'request name'
value (e.g., keepalive@ietf.org) and the 'want reply'
value set to '1'.";
reference
"RFC 4254: The Secure Shell (SSH) Connection Protocol";
leaf max-wait {
type uint16 {
range "1..max";
}
units "seconds";
default "30";
description
"Sets the amount of time in seconds after which if
no data has been received from the SSH server, a
SSH-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>
The "ietf-ssh-server" Module
This section defines a YANG 1.1 module called
"ietf-ssh-server". A high-level overview of the module is provided in
. Examples illustrating the module's use
are provided in Examples. The YANG
module itself is defined in .
Data Model Overview
This section provides an overview of the "ietf-ssh-server" module
in terms of its features and groupings.
Features
The following diagram lists all the "feature" statements
defined in the "ietf-ssh-server" module:
The diagram above uses syntax that is similar to but not
defined in .
Groupings
The "ietf-ssh-server" module defines the following "grouping" statement:
This grouping is presented in the following subsection.
The "ssh-server-grouping" Grouping
The following tree diagram illustrates the
"ssh-server-grouping" grouping:
Comments:
- The "server-identity" node configures the authentication methods the
server can use to identify itself to clients. The ability to use a
certificate is enabled by a "feature".
- The "client-authentication" node configures trust anchors for
authenticating the SSH client, with each option enabled by a "feature" statement.
- The "transport-params" node, which must be enabled by a feature, configures
parameters for the SSH sessions established by this configuration.
- The "keepalives" node, which must be enabled by a feature, configures
a "presence" container for testing the aliveness of the SSH client. The
aliveness-test occurs at the SSH protocol layer.
-
For the referenced grouping statement(s):
- The "local-or-keystore-asymmetric-key-grouping" grouping is
discussed in .
- The "local-or-keystore-end-entity-cert-with-key-grouping" grouping is
discussed in .
- The "local-or-truststore-public-keys-grouping" grouping is
discussed in .
- The "local-or-truststore-certs-grouping" grouping is
discussed in .
- The "transport-params-grouping" grouping is discussed in
in this document.
Protocol-accessible Nodes
The "ietf-ssh-server" module defines only "grouping" statements that are
used by other modules to instantiate protocol-accessible nodes.
Example Usage
This section presents two examples showing the "ssh-server-grouping"
grouping populated with some data. These examples are effectively the same
except the first configures the server identity using a local key
while the second uses a key configured in a keystore. Both examples
are consistent with the examples presented in Section 2 of and Section 3.2 of .
The following configuration example uses local-definitions for the
server identity and client authentication:
my-pubkey-based-host-key
ct:ssh-public-key-format
BASE64VALUE=
ct:rsa-private-key-format
BASE64VALUE=
my-cert-based-host-key
ct:subject-public-key-info-format
BASE64VALUE=
ct:rsa-private-key-format
BASE64VALUE=
BASE64VALUE=
mary
$0$secret
Mary-Key-1
ct:ssh-public-key-format
BASE64VALUE=
Mary-Key-2
ct:ssh-public-key-format
BASE64VALUE=
Identity Cert Issuer #1
BASE64VALUE=
Identity Cert Issuer #2
BASE64VALUE=
Application #1
BASE64VALUE=
Application #2
BASE64VALUE=
30
3
]]>
The following configuration example uses keystore-references for the
server identity and truststore-references for client authentication:
from the keystore:
my-pubkey-based-host-key
ssh-rsa-key
my-cert-based-host-key
ssh-rsa-key-with-cert
ex-rsa-cert2
mary
$0$secret
SSH Public Keys for Application A
trusted-client-ca-certs
trusted-client-ee-certs
30
3
]]>
YANG Module
This YANG module has normative references to ,
, , ,
, and ,
and informative references to and .
<CODE BEGINS> file "ietf-ssh-server@2022-12-12.yang"
Author: Kent Watsen ";
description
"This module defines reusable groupings for SSH servers that
can be used as a basis for specific SSH server instances.
Copyright (c) 2022 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC EEEE
(https://www.rfc-editor.org/info/rfcEEEE); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2022-12-12 {
description
"Initial version";
reference
"RFC EEEE: YANG Groupings for SSH Clients and SSH Servers";
}
// Features
feature ssh-server-keepalives {
description
"Per socket SSH keepalive parameters are configurable for
SSH servers on the server implementing this feature.";
}
feature local-users-supported {
description
"Indicates that the configuration for users can be
configured herein, as opposed to in an application
specific location.";
}
feature local-user-auth-publickey {
if-feature "local-users-supported";
description
"Indicates that the 'publickey' authentication type,
per RFC 4252, is supported for locally-defined users.
The 'publickey' authentication type is required by
RFC 4252, but common implementations enable it to
be disabled.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-password {
if-feature "local-users-supported";
description
"Indicates that the 'password' authentication type,
per RFC 4252, is supported for locally-defined users.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-hostbased {
if-feature "local-users-supported";
description
"Indicates that the 'hostbased' authentication type,
per RFC 4252, is supported for locally-defined users.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
feature local-user-auth-none {
if-feature "local-users-supported";
description
"Indicates that the 'none' authentication type, per
RFC 4252, is supported. It is NOT RECOMMENDED to
enable this feature.";
reference
"RFC 4252:
The Secure Shell (SSH) Authentication Protocol";
}
// Groupings
grouping ssh-server-grouping {
description
"A reusable grouping for configuring a SSH server without
any consideration for how underlying TCP sessions are
established.
Note that this grouping uses fairly typical descendant
node names such that a stack of 'uses' statements will
have name conflicts. It is intended that the consuming
data model will resolve the issue (e.g., by wrapping
the 'uses' statement in a container called
'ssh-server-parameters'). This model purposely does
not do this itself so as to provide maximum flexibility
to consuming models.";
container server-identity {
nacm:default-deny-write;
description
"The list of host keys the SSH server will present when
establishing a SSH connection.";
list host-key {
key "name";
min-elements 1;
ordered-by user;
description
"An ordered list of host keys the SSH server will use to
construct its ordered list of algorithms, when sending
its SSH_MSG_KEXINIT message, as defined in Section 7.1
of RFC 4253.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer
Protocol";
leaf name {
type string;
description
"An arbitrary name for this host key";
}
choice host-key-type {
mandatory true;
description
"The type of host key being specified";
container public-key {
description
"A locally-defined or referenced asymmetric key pair
to be used for the SSH server's host key.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses ks:local-or-keystore-asymmetric-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "local-or-keystore/keystore/"
+ "keystore-reference" {
must 'derived-from-or-self(deref(.)/../ks:public-'
+ 'key-format, "ct:ssh-public-key-format")';
}
}
}
container certificate {
if-feature "sshcmn:ssh-x509-certs";
description
"A locally-defined or referenced end-entity
certificate to be used for the SSH server's
host key.";
reference
"RFC CCCC: A YANG Data Model for a Keystore";
uses
ks:local-or-keystore-end-entity-cert-with-key-grouping {
refine "local-or-keystore/local/local-definition" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:subject-public-key-info-format")';
}
refine "local-or-keystore/keystore/keystore-reference"
+ "/asymmetric-key" {
must
'derived-from-or-self(deref(.)/../ks:public-key-'
+ 'format, "ct:subject-public-key-info-format")';
}
}
}
}
}
} // container server-identity
container client-authentication {
nacm:default-deny-write;
description
"Specifies how the SSH server can authenticate SSH clients.";
container users {
if-feature "local-users-supported";
description
"A list of locally configured users.";
list user {
key "name";
description
"A locally configured user.
The server SHOULD derive the list of authentication
'method names' returned to the SSH client from the
descendant nodes configured herein, per Sections
5.1 and 5.2 in RFC 4252.
The authentication methods are unordered. Clients
must authenticate to all configured methods.
Whenever a choice amongst methods arises,
implementations SHOULD use a default ordering
that prioritizes automation over human-interaction.";
leaf name {
type string;
description
"The 'user name' for the SSH client, as defined in
the SSH_MSG_USERAUTH_REQUEST message in RFC 4253.";
}
container public-keys {
if-feature "local-user-auth-publickey";
presence
"Indicates that public keys have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be
configured.";
description
"A set of SSH public keys may be used by the SSH
server to authenticate this user. A user is
authenticated if its public key is an exact
match to a configured public key.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine "local-or-truststore/local/local-definition/"
+ "public-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "local-or-truststore/truststore/truststore-"
+ "reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
leaf password {
if-feature "local-user-auth-password";
type ianach:crypt-hash;
description
"The password for this user.";
}
container hostbased {
if-feature "local-user-auth-hostbased";
presence
"Indicates that hostbased keys have been configured.
This statement is present so the mandatory descendant
nodes do not imply that this node must be
configured.";
description
"A set of SSH host keys used by the SSH server to
authenticate this user's host. A user's host is
authenticated if its host key is an exact match
to a configured host key.";
reference
"RFC 4253: The Secure Shell (SSH) Transport Layer
RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-public-keys-grouping {
refine "local-or-truststore/local/local-definition/"
+ "public-key" {
must 'derived-from-or-self(public-key-format,'
+ ' "ct:ssh-public-key-format")';
}
refine "local-or-truststore/truststore/truststore-"
+ "reference" {
must 'not(deref(.)/../ts:public-key/ts:public-key-'
+ 'format[not(derived-from-or-self(., "ct:ssh-'
+ 'public-key-format"))])';
}
}
}
leaf none {
if-feature "local-user-auth-none";
type empty;
description
"Indicates that the 'none' method is configured
for this user.";
reference
"RFC 4252: The Secure Shell (SSH) Authentication
Protocol.";
}
}
}
container ca-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that CA certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply this node must be configured.";
description
"A set of certificate authority (CA) certificates used by
the SSH server to authenticate SSH client certificates.
A client certificate is authenticated if it has a valid
chain of trust to a configured CA certificate.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
container ee-certs {
if-feature "sshcmn:ssh-x509-certs";
presence
"Indicates that EE certificates have been configured.
This statement is present so the mandatory descendant
nodes do not imply this node must be configured.";
description
"A set of client certificates (i.e., end entity
certificates) used by the SSH server to authenticate
the certificates presented by SSH clients. A client
certificate is authenticated if it is an exact match
to a configured end-entity certificate.";
reference
"RFC BBBB: A YANG Data Model for a Truststore";
uses ts:local-or-truststore-certs-grouping;
}
} // container client-authentication
container transport-params {
nacm:default-deny-write;
if-feature "sshcmn:transport-params";
description
"Configurable parameters of the SSH transport layer.";
uses sshcmn:transport-params-grouping;
} // container transport-params
container keepalives {
nacm:default-deny-write;
if-feature "ssh-server-keepalives";
presence
"Indicates that the SSH server proactively tests the
aliveness of the remote SSH client.";
description
"Configures the keep-alive policy, to proactively test
the aliveness of the SSH client. An unresponsive SSH
client is dropped after approximately max-wait *
max-attempts seconds. Per Section 4 of RFC 4254,
the SSH server SHOULD send an SSH_MSG_GLOBAL_REQUEST
message with a purposely nonexistent 'request name'
value (e.g., keepalive@ietf.org) and the 'want reply'
value set to '1'.";
reference
"RFC 4254: The Secure Shell (SSH) Connection Protocol";
leaf max-wait {
type uint16 {
range "1..max";
}
units "seconds";
default "30";
description
"Sets the amount of time in seconds after which
if no data has been received from the SSH client,
a SSH-level message will be sent to test the
aliveness of the SSH client.";
}
leaf max-attempts {
type uint8;
default "3";
description
"Sets the maximum number of sequential keep-alive
messages that can fail to obtain a response from
the SSH client before assuming the SSH client is
no longer alive.";
}
}
} // grouping ssh-server-grouping
}
]]>
<CODE ENDS>
Security Considerations
The "iana-ssh-key-exchange-algs" Module
The "iana-ssh-key-exchange-algs" YANG module defines a data model
that is designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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.
This YANG module defines YANG identities, for a public IANA-maintained
registry, and a single protocol-accessible read-only node for the subset
of those identities supported by a server.
YANG identities are not security-sensitive, as they are statically
defined in the publicly-accessible YANG module.
The protocol-accessible read-only node for the algorithms supported
by a server is mildly sensitive, but not to the extent that special
NACM annotations are needed to prevent read-access to regular
authenticated administrators.
This module does not define any writable-nodes, RPCs, actions,
or notifications, and thus the security consideration for such
is not provided here.
The "iana-ssh-encryption-algs" Module
The "iana-ssh-encryption-algs" YANG module defines a data model
that is designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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.
This YANG module defines YANG identities, for a public IANA-maintained
registry, and a single protocol-accessible read-only node for the subset
of those identities supported by a server.
YANG identities are not security-sensitive, as they are statically
defined in the publicly-accessible YANG module.
The protocol-accessible read-only node for the algorithms supported
by a server is mildly sensitive, but not to the extent that special
NACM annotations are needed to prevent read-access to regular
authenticated administrators.
This module does not define any writable-nodes, RPCs, actions,
or notifications, and thus the security consideration for such
is not provided here.
The "iana-ssh-mac-algs" Module
The "iana-ssh-mac-algs" YANG module defines a data model
that is designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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.
This YANG module defines YANG identities, for a public IANA-maintained
registry, and a single protocol-accessible read-only node for the subset
of those identities supported by a server.
YANG identities are not security-sensitive, as they are statically
defined in the publicly-accessible YANG module.
The protocol-accessible read-only node for the algorithms supported
by a server is mildly sensitive, but not to the extent that special
NACM annotations are needed to prevent read-access to regular
authenticated administrators.
This module does not define any writable-nodes, RPCs, actions,
or notifications, and thus the security consideration for such
is not provided here.
The "iana-ssh-public-key-algs" Module
The "iana-ssh-public-key-algs" YANG module defines a data model
that is designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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.
This YANG module defines YANG identities, for a public IANA-maintained
registry, and a single protocol-accessible read-only node for the subset
of those identities supported by a server.
YANG identities are not security-sensitive, as they are statically
defined in the publicly-accessible YANG module.
The protocol-accessible read-only node for the algorithms supported
by a server is mildly sensitive, but not to the extent that special
NACM annotations are needed to prevent read-access to regular
authenticated administrators.
This module does not define any writable-nodes, RPCs, actions,
or notifications, and thus the security consideration for such
is not provided here.
The "ietf-ssh-common" YANG Module
The "ietf-ssh-common" YANG module defines "grouping" statements
that are designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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 this module only define groupings,
these considerations are primarily for the designers of other
modules that use these groupings.
None of the readable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments.
The NACM "default-deny-all" extension has not been set for
any data nodes defined in this module.
None of the writable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments.
The NACM "default-deny-write" extension has not been set for
any data nodes defined in this module.
This module does not define any RPCs, actions, or notifications,
and thus the security consideration for such is not provided here.
The "ietf-ssh-client" YANG Module
The "ietf-ssh-client" YANG module defines "grouping" statements
that are designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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 this module only define groupings,
these considerations are primarily for the designers of other
modules that use these groupings.
One readable data node defined in this YANG module may be considered
sensitive or vulnerable in some network environments. This
node is as follows:
-
The "client-identity/password" node:
- The cleartext "password" node defined in the "ssh-client-grouping"
grouping is additionally sensitive to read operations such that,
in normal use cases, it should never be returned to a client.
For this reason, the NACM extension "default-deny-all" has been
applied to it.
Please be aware that this module uses the "key" and "private-key"
nodes from the "ietf-crypto-types" module ,
where said nodes have the NACM extension "default-deny-all" set, thus
preventing unrestricted read-access to the cleartext key values.
All the writable data nodes defined by this module may be
considered sensitive or vulnerable in some network environments.
For instance, any modification to a key or reference to a key
may dramatically alter the implemented security policy. For
this reason, the NACM extension "default-deny-write" has been
set for all data nodes defined in this module.
This module does not define any RPCs, actions, or notifications,
and thus the security consideration for such is not provided here.
The "ietf-ssh-server" YANG Module
The "ietf-ssh-server" YANG module defines "grouping" statements
that are designed to be accessed via YANG based management
protocols, such as NETCONF and RESTCONF
. Both of these protocols have
mandatory-to-implement secure transport layers (e.g., SSH, TLS)
with mutual authentication.
The Network 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 this module only define groupings,
these considerations are primarily for the designers of other
modules that use these groupings.
None of the readable data nodes defined in this YANG module are
considered sensitive or vulnerable in network environments.
The NACM "default-deny-all" extension has not been set for
any data nodes defined in this module.
Please be aware that this module uses the "key" and "private-key"
nodes from the "ietf-crypto-types" module ,
where said nodes have the NACM extension "default-deny-all" set, thus
preventing unrestricted read-access to the cleartext key values.
All the writable data nodes defined by this module may be
considered sensitive or vulnerable in some network environments.
For instance, the addition or removal of references to keys,
certificates, trusted anchors, etc., or even the modification
of transport or keepalive parameters can dramatically alter
the implemented security policy. For this reason, the NACM
extension "default-deny-write" has been set for all data nodes
defined in this module.
This module does not define any RPCs, actions, or notifications,
and thus the security consideration for such is not provided here.
IANA Considerations
The "IETF XML" Registry
This document registers seven URIs in the "ns" subregistry of the
IETF XML Registry . Following the format in
, the following registrations are
requested:
The "YANG Module Names" Registry
This document registers seven YANG modules in the YANG Module Names
registry . Following the format in , the following registrations are requested:
The "iana-ssh-encryption-algs" Module
IANA is requested to maintain a YANG module called "iana-ssh-encryption-algs"
that shadows the "Encryption Algorithm Names" sub-registry of the
"Secure Shell (SSH) Protocol Parameters" registry .
This registry defines a YANG identity for each encryption algorithm, and a "base"
identity from which all of the other identities are derived. Identities are chosen
over enumerations for extensibility reasons.
An initial version of this module can be found in
- Please note that this module was created on June 16th, 2022, and that additional
entries may have been added in the interim before this document's publication.
If this is that case, IANA may either publish just an updated module containing
the new entries, or publish the initial module that is immediately followed by a
"revision" containing the additional algorithm names.
The "iana-ssh-mac-algs" Module
IANA is requested to maintain a YANG module called "iana-ssh-mac-algs"
that shadows the "MAC Algorithm Names" sub-registry of the
"Secure Shell (SSH) Protocol Parameters" registry .
This registry defines a YANG identity for each MAC algorithm, and a "base"
identity from which all of the other identities are derived. Identities are chosen
over enumerations for extensibility reasons.
An initial version of this module can be found in .
- Please note that this module was created on June 16th, 2022, and that additional
entries may have been added in the interim before this document's publication.
If this is that case, IANA may either publish just an updated module containing
the new entries, or publish the initial module that is immediately followed by a
"revision" containing the additional algorithm names.
The "iana-ssh-public-key-algs" Module
IANA is requested to maintain a YANG module called "iana-ssh-public-key-algs"
that shadows the "Public Key Algorithm Names" sub-registry of the
"Secure Shell (SSH) Protocol Parameters" registry .
This registry defines a YANG identity for each public key algorithm, and a "base"
identity from which all of the other identities are derived. Identities are chosen
over enumerations for extensibility reasons.
Registry entries for which the '*All values beginning with the specified string
and not containing "@".' note applies MUST be expanded so that there is a distinct
YANG identity for each enumeration.
An initial version of this module can be found in .
- Please note that this module was created on June 16th, 2022, and that additional
entries may have been added in the interim before this document's publication.
If this is that case, IANA may either publish just an updated module containing
the new entries, or publish the initial module that is immediately followed by a
"revision" containing the additional algorithm names.
The "iana-ssh-key-exchange-algs" Module
IANA is requested to maintain a YANG module called "iana-ssh-key-exchange-algs"
that shadows the "Key Exchange Method Names" sub-registry of the
"Secure Shell (SSH) Protocol Parameters" registry .
This registry defines a YANG identity for each key exchange algorithm, and a "base"
identity from which all of the other identities are derived. Identities are chosen
over enumerations for extensibility reasons.
Registry entries for which the '*All values beginning with the specified string
and not containing "@".' note applies MUST be expanded so that there is a distinct
YANG identity for each enumeration.
An initial version of this module can be found in .
- Please note that this module was created on June 16th, 2022, and that additional
entries may have been added in the interim before this document's publication.
If this is that case, IANA may either publish just an updated module containing
the new entries, or publish the initial module that is immediately followed by a
"revision" containing the additional algorithm names.
References
Normative References
Key words for use in RFCs to Indicate Requirement Levels
In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
The Secure Shell (SSH) Authentication Protocol
The Secure Shell Protocol (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH authentication protocol framework and public key, password, and host-based client authentication methods. Additional authentication methods are described in separate documents. The SSH authentication protocol runs on top of the SSH transport layer protocol and provides a single authenticated tunnel for the SSH connection protocol. [STANDARDS-TRACK]
The Secure Shell (SSH) Connection Protocol
Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network.
This document describes the SSH Connection Protocol. It provides interactive login sessions, remote execution of commands, forwarded TCP/IP connections, and forwarded X11 connections. All of these channels are multiplexed into a single encrypted tunnel.
The SSH Connection Protocol has been designed to run on top of the SSH transport layer and user authentication protocols. [STANDARDS-TRACK]
The Secure Shell (SSH) Transport Layer Encryption Modes
Researchers have discovered that the authenticated encryption portion of the current SSH Transport Protocol is vulnerable to several attacks.
This document describes new symmetric encryption methods for the Secure Shell (SSH) Transport Protocol and gives specific recommendations on how frequently SSH implementations should rekey. [STANDARDS-TRACK]
Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
This memo describes a new key exchange method for the Secure Shell (SSH) protocol. It allows the SSH server to propose new groups on which to perform the Diffie-Hellman key exchange to the client. The proposed groups need not be fixed and can change with time. [STANDARDS-TRACK]
RSA Key Exchange for the Secure Shell (SSH) Transport Layer Protocol
This memo describes a key-exchange method for the Secure Shell (SSH) protocol based on Rivest-Shamir-Adleman (RSA) public-key encryption. It uses much less client CPU time than the Diffie-Hellman algorithm specified as part of the core protocol, and hence is particularly suitable for slow client systems. [STANDARDS-TRACK]
Generic Security Service Application Program Interface (GSS-API) Authentication and Key Exchange for the Secure Shell (SSH) Protocol
The Secure Shell protocol (SSH) is a protocol for secure remote login and other secure network services over an insecure network.
The Generic Security Service Application Program Interface (GSS-API) provides security services to callers in a mechanism-independent fashion.
This memo describes methods for using the GSS-API for authentication and key exchange in SSH. It defines an SSH user authentication method that uses a specified GSS-API mechanism to authenticate a user, and a family of SSH key exchange methods that use GSS-API to authenticate a Diffie-Hellman key exchange.
This memo also defines a new host public key algorithm that can be used when no operations are needed using a host's public key, and a new user authentication method that allows an authorization name to be used in conjunction with any authentication that has already occurred as a side-effect of GSS-API-based key exchange. [STANDARDS-TRACK]
AES Galois Counter Mode for the Secure Shell Transport Layer Protocol
Secure shell (SSH) is a secure remote-login protocol. SSH provides for algorithms that provide authentication, key agreement, confidentiality, and data-integrity services. The purpose of this document is to show how the AES Galois Counter Mode can be used to provide both confidentiality and data integrity to the SSH Transport Layer Protocol. This memo provides information for the Internet community.
Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
This document describes algorithms based on Elliptic Curve Cryptography (ECC) for use within the Secure Shell (SSH) transport protocol. In particular, it specifies Elliptic Curve Diffie-Hellman (ECDH) key agreement, Elliptic Curve Menezes-Qu-Vanstone (ECMQV) key agreement, and Elliptic Curve Digital Signature Algorithm (ECDSA) for use in the SSH Transport Layer protocol. [STANDARDS-TRACK]
YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)
YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS-TRACK]
X.509v3 Certificates for Secure Shell Authentication
X.509 public key certificates use a signature by a trusted certification authority to bind a given public key to a given digital identity. This document specifies how to use X.509 version 3 public key certificates in public key algorithms in the Secure Shell protocol. [STANDARDS-TRACK]
SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol
This memo defines algorithm names and parameters for use in some of the SHA-2 family of secure hash algorithms for data integrity verification in the Secure Shell (SSH) protocol. It also updates RFC 4253 by specifying a new RECOMMENDED data integrity algorithm. [STANDARDS-TRACK]
The YANG 1.1 Data Modeling Language
YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF).
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words
RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.
More Modular Exponentiation (MODP) Diffie-Hellman (DH) Key Exchange (KEX) Groups for Secure Shell (SSH)
This document defines added Modular Exponentiation (MODP) groups for the Secure Shell (SSH) protocol using SHA-2 hashes. This document updates RFC 4250. This document updates RFC 4253 by correcting an error regarding checking the Peer's DH Public Key.
Extension Negotiation in the Secure Shell (SSH) Protocol
This memo updates RFCs 4251, 4252, 4253, and 4254 by defining a mechanism for Secure Shell (SSH) clients and servers to exchange information about supported protocol extensions confidentially after SSH key exchange.
Use of RSA Keys with SHA-256 and SHA-512 in the Secure Shell (SSH) Protocol
This memo updates RFCs 4252 and 4253 to define new public key algorithms for use of RSA keys with SHA-256 and SHA-512 for server and client authentication in SSH connections.
Network Configuration Access Control Model
The standardization of network configuration interfaces for use with the Network Configuration Protocol (NETCONF) or the RESTCONF protocol requires a structured and secure operating environment that promotes human usability and multi-vendor interoperability. There is a need for standard mechanisms to restrict NETCONF or RESTCONF protocol access for particular users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. This document defines such an access control model.
This document obsoletes RFC 6536.
Ed25519 and Ed448 Public Key Algorithms for the Secure Shell (SSH) Protocol
This document describes the use of the Ed25519 and Ed448 digital signature algorithms in the Secure Shell (SSH) protocol. Accordingly, this RFC updates RFC 4253.
Secure Shell (SSH) Key Exchange Method Using Curve25519 and Curve448
This document describes the specification for using Curve25519 and Curve448 key exchange methods in the Secure Shell (SSH) protocol.
Generic Security Service Application Program Interface (GSS-API) Key Exchange with SHA-2
This document specifies additions and amendments to RFC 4462. It defines a new key exchange method that uses SHA-2 for integrity and deprecates weak Diffie-Hellman (DH) groups. The purpose of this specification is to modernize the cryptographic primitives used by Generic Security Service (GSS) key exchanges.
Deprecating RC4 in Secure Shell (SSH)
This document deprecates RC4 in Secure Shell (SSH). Therefore, this document formally moves RFC 4345 to Historic status.
Informative References
The IETF XML Registry
This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas.
The Secure Shell (SSH) Transport Layer Protocol
The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network.
This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression.
Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated.
This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. [STANDARDS-TRACK]
Network Configuration Protocol (NETCONF)
The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK]
Using the NETCONF Protocol over Secure Shell (SSH)
This document describes a method for invoking and running the Network Configuration Protocol (NETCONF) within a Secure Shell (SSH) session as an SSH subsystem. This document obsoletes RFC 4742. [STANDARDS-TRACK]
A YANG Data Model for System Management
This document defines a YANG data model for the configuration and identification of some common system properties within a device containing a Network Configuration Protocol (NETCONF) server. This document also includes data node definitions for system identification, time-of-day management, user management, DNS resolver configuration, and some protocol operations for system management.
RESTCONF Protocol
This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF).
NETCONF Call Home and RESTCONF Call Home
This RFC presents NETCONF Call Home and RESTCONF Call Home, which enable a NETCONF or RESTCONF server to initiate a secure connection to a NETCONF or RESTCONF client, respectively.
YANG Tree Diagrams
This document captures the current syntax used in YANG module tree diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language.
Network Management Datastore Architecture (NMDA)
Datastores are a fundamental concept binding the data models written in the YANG data modeling language to network management protocols such as the Network Configuration Protocol (NETCONF) and RESTCONF. This document defines an architectural framework for datastores based on the experience gained with the initial simpler model, addressing requirements that were not well supported in the initial model. This document updates RFC 7950.
OpenSSH
IANA "Key Exchange Method Names" Sub-registry of the "Secure Shell (SSH) Protocol Parameters" Registry
IANA "Encryption Algorithm Names" Sub-registry of the "Secure Shell (SSH) Protocol Parameters" Registry
IANA "MAC Algorithm Names" Sub-registry of the "Secure Shell (SSH) Protocol Parameters" Registry
IANA "Public Key Algorithm Names" Sub-registry of the "Secure Shell (SSH) Protocol Parameters" Registry
YANG Modules for IANA
The modules contained in this section were generated by scripts using the contents of the
associated sub-registry as they existed on June 16th, 2022.
Initial Module for the "Encryption Algorithm Names" Registry
Data Model Overview
This section provides an overview of the "iana-ssh-encryption-algs" module
in terms of its identities and protocol-accessible nodes.
Identities
The following diagram lists the base "identity" statements defined in the
module, of which there is just one, and illustrates that all the derived identity
statements are generated from the associated IANA-maintained registry
.
]]>
The diagram above uses syntax that is similar to but not
defined in .
Typedefs
The following diagram illustrates the "typedef" statements
defined in the "iana-ssh-encryption-algs" module:
The diagram above uses syntax that is similar to but not
defined in .
Comments:
- The typedef defined in the "iana-ssh-encryption-algs" module
extends the "identityref" type defined in .
Protocol-accessible Nodes
The following tree diagram lists all the
protocol-accessible nodes defined in the "iana-ssh-encryption-algs"
module:
Comments:
- Protocol-accessible nodes are those nodes that are accessible
when the module is "implemented", as described in .
Example Usage
The following example illustrates operational state data indicating
the SSH encryption algorithms supported by the server:
sshea:aes256-ctr
sshea:aes256-cbc
sshea:twofish256-cbc
sshea:serpent256-cbc
sshea:arcfour256
sshea:serpent256-ctr
sshea:aead-aes-256-gcm
]]>
YANG Module
Following are the complete contents to the initial IANA-maintained YANG module.
Please note that the date "2022-06-16" reflects the day on which the extraction
occurred.
This YANG module has normative references to [FIPS 46-3], ,
, , and .
<CODE BEGINS> file "iana-ssh-encryption-algs@2022-06-16.yang"
<CODE ENDS>
Initial Module for the "MAC Algorithm Names" Registry
Data Model Overview
This section provides an overview of the "iana-ssh-mac-algs" module
in terms of its identities and protocol-accessible nodes.
Identities
The following diagram lists the base "identity" statements defined in the
module, of which there is just one, and illustrates that all the derived identity
statements are generated from the associated IANA-maintained registry
.
]]>
The diagram above uses syntax that is similar to but not
defined in .
Typedefs
The following diagram illustrates the "typedef" statements
defined in the "iana-ssh-mac-algs" module:
The diagram above uses syntax that is similar to but not
defined in .
Comments:
- The typedef defined in the "iana-ssh-mac-algs" module
extends the "identityref" type defined in .
Protocol-accessible Nodes
The following tree diagram lists all the
protocol-accessible nodes defined in the "iana-ssh-mac-algs"
module:
Comments:
- Protocol-accessible nodes are those nodes that are accessible
when the module is "implemented", as described in .
Example Usage
The following example illustrates operational state data indicating
the SSH MAC algorithms supported by the server:
sshma:hmac-sha2-256
sshma:hmac-sha2-512
sshma:aead-aes-256-gcm
]]>
YANG Module
Following are the complete contents to the initial IANA-maintained YANG module.
Please note that the date "2022-06-16" reflects the day on which the extraction
occurred.
This YANG module has normative references ,
, and .
<CODE BEGINS> file "iana-ssh-mac-algs@2022-06-16.yang"
<CODE ENDS>
Initial Module for the "Public Key Algorithm Names" Registry
Data Model Overview
This section provides an overview of the "iana-ssh-public-key-algs" module
in terms of its identities and protocol-accessible nodes.
Identities
The following diagram lists the base "identity" statements defined in the
module, of which there is just one, and illustrates that all the derived identity
statements are generated from the associated IANA-maintained registry
.
]]>
The diagram above uses syntax that is similar to but not
defined in .
Typedefs
The following diagram illustrates the "typedef" statements
defined in the "iana-ssh-public-key-algs" module:
The diagram above uses syntax that is similar to but not
defined in .
Comments:
- The typedef defined in the "iana-ssh-public-key-algs" module
extends the "identityref" type defined in .
Protocol-accessible Nodes
The following tree diagram lists all the
protocol-accessible nodes defined in the "iana-ssh-public-key-algs"
module:
Comments:
- Protocol-accessible nodes are those nodes that are accessible
when the module is "implemented", as described in .
Example Usage
The following example illustrates operational state data indicating
the SSH public key algorithms supported by the server:
sshpka:rsa-sha2-256
sshpka:rsa-sha2-512
sshpka:spki-sign-rsa
sshpka:pgp-sign-dss
sshpka:x509v3-rsa2048-sha256
sshpka:ecdsa-sha2-nistp256
sshpka:ecdsa-sha2-1.3.132.0.37
sshpka:ssh-ed25519
]]>
YANG Module
Following are the complete contents to the initial IANA-maintained YANG module.
Please note that the date "2022-06-16" reflects the day on which the extraction
occurred.
This YANG module has normative references ,
, , ,
, and .
<CODE BEGINS> file "iana-ssh-public-key-algs@2022-06-16.yang"
<CODE ENDS>
Initial Module for the "Key Exchange Method Names" Registry
Data Model Overview
This section provides an overview of the "iana-ssh-key-exchange-algs" module
in terms of its identities and protocol-accessible nodes.
Identities
The following diagram lists the base "identity" statements defined in the
module, of which there is just one, and illustrates that all the derived identity
statements are generated from the associated IANA-maintained registry
.
]]>
The diagram above uses syntax that is similar to but not
defined in .
Typedefs
The following diagram illustrates the "typedef" statements
defined in the "iana-ssh-key-exchange-algs" module:
The diagram above uses syntax that is similar to but not
defined in .
Comments:
- The typedef defined in the "iana-ssh-key-exchange-algs" module
extends the "identityref" type defined in .
Protocol-accessible Nodes
The following tree diagram lists all the
protocol-accessible nodes defined in the "iana-ssh-key-exchange-algs"
module:
Comments:
- Protocol-accessible nodes are those nodes that are accessible
when the module is "implemented", as described in .
Example Usage
The following example illustrates operational state data indicating
the SSH key exchange algorithms supported by the server:
sshkea:diffie-hellman-group-exchange-sha256\
supported-algorithm>
sshkea:ecdh-sha2-nistp256
sshkea:rsa2048-sha256
sshkea:gss-group1-sha1-curve25519-sha256
sshkea:gss-group14-sha1-nistp256
sshkea:gss-gex-sha1-nistp256
sshkea:gss-group14-sha256-1.2.840.10045.3.1.1\
sshkea:curve25519-sha256
]]>
YANG Module
Following are the complete contents to the initial IANA-maintained YANG module.
Please note that the date "2022-06-16" reflects the day on which the extraction
occurred.
This YANG module has normative references to ,
, , ,
, , .
<CODE BEGINS> file "iana-ssh-key-exchange-algs@2022-06-16.yang"
<CODE ENDS>
Change Log
00 to 01
- Noted that '0.0.0.0' and '::' might have special meanings.
- Renamed "keychain" to "keystore".
01 to 02
- 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.
02 to 03
- Removed 'RESTRICTED' enum from 'password' leaf type.
- Added a 'must' statement to container 'server-auth' asserting
that at least one of the various auth mechanisms must be
specified.
- Fixed description statement for leaf 'trusted-ca-certs'.
03 to 04
- Change title to "YANG Groupings for SSH Clients and SSH
Servers"
- Added reference to RFC 6668
- Added RFC 8174 to Requirements Language Section.
- Enhanced description statement for ietf-ssh-server's
"trusted-ca-certs" leaf.
- Added mandatory true to ietf-ssh-client's "client-auth"
'choice' statement.
- Changed the YANG prefix for module ietf-ssh-common from
'sshcom' to 'sshcmn'.
- Removed the compression algorithms as they are not commonly
configurable in vendors' implementations.
- Updating descriptions in transport-params-grouping and the
servers's usage of it.
- Now tree diagrams reference ietf-netmod-yang-tree-diagrams
- Updated YANG to use typedefs around leafrefs to common keystore
paths
- Now inlines key and certificates (no longer a leafref to
keystore)
04 to 05
- Merged changes from co-author.
05 to 06
- Updated to use trust anchors from trust-anchors draft (was
keystore draft)
- Now uses new keystore grouping enabling asymmetric key to be
either locally defined or a reference to the keystore.
06 to 07
- factored the ssh-[client|server]-groupings into more reusable
groupings.
- added if-feature statements for the new "ssh-host-keys" and
"x509-certificates" features defined in
draft-ietf-netconf-trust-anchors.
07 to 08
- Added a number of compatibility matrices to Section 5 (thanks Frank!)
- Clarified that any configured "host-key-alg" values need to be
compatible with the configured private key.
08 to 09
- Updated examples to reflect update to groupings defined in the keystore -09 draft.
- Add SSH keepalives features and groupings.
- Prefixed top-level SSH grouping nodes with 'ssh-' and support mashups.
- Updated copyright date, boilerplate template, affiliation, and folding algorithm.
09 to 10
- Reformatted the YANG modules.
10 to 11
- Reformatted lines causing folding to occur.
11 to 12
- Collapsed all the inner groupings into the top-level grouping.
- Added a top-level "demux container" inside the top-level grouping.
- Added NACM statements and updated the Security Considerations section.
- Added "presence" statements on the "keepalive" containers, as was
needed to address a validation error that appeared after adding the
"must" statements into the NETCONF/RESTCONF client/server modules.
- Updated the boilerplate text in module-level "description" statement
to match copyeditor convention.
12 to 13
- Removed the "demux containers", floating the
nacm:default-deny-write to each descendant node, and
adding a note to model designers regarding the potential
need to add their own demux containers.
- Fixed a couple references (section 2 --> section 3)
- In the server model, replaced <client-cert-auth>
with <client-authentication> and introduced
'local-or-external' choice.
13 to 14
- Updated to reflect changes in trust-anchors drafts
(e.g., s/trust-anchors/truststore/g + s/pinned.//)
14 to 15
- Updated examples to reflect ietf-crypto-types change
(e.g., identities --> enumerations)
- Updated "server-authentication" and "client-authentication" nodes from
being a leaf of type "ts:host-keys-ref" or "ts:certificates-ref" to a
container that uses "ts:local-or-truststore-host-keys-grouping" or
"ts:local-or-truststore-certs-grouping".
15 to 16
- Removed unnecessary if-feature statements in the -client and -server modules.
- Cleaned up some description statements in the -client and -server modules.
- Fixed a canonical ordering issue in ietf-ssh-common detected by new pyang.
16 to 17
- Removed choice local-or-external by removing the 'external' case and flattening
the 'local' case and adding a "local-users-supported" feature.
- Updated examples to include the "*-key-format" nodes.
- Augmented-in "must" expressions ensuring that locally-defined public-key-format
are "ct:ssh-public-key-format" (must expr for ref'ed keys are TBD).
17 to 18
- Removed leaf-list 'other' from ietf-ssh-server.
- Removed unused 'external-client-auth-supported' feature.
- Added features client-auth-password, client-auth-hostbased, and client-auth-none.
- Renamed 'host-key' to 'public-key' for when refering to 'publickey' based auth.
- Added new feature-protected 'hostbased' and 'none' to the 'user' node's config.
- Added new feature-protected 'hostbased' and 'none' to the 'client-identity' node's config.
- Updated examples to reflect new "bag" addition to truststore.
- Refined truststore/keystore groupings to ensure the key formats "must" be particular values.
- Switched to using truststore's new "public-key" bag (instead of separate "ssh-public-key"
and "raw-public-key" bags.
- Updated client/server examples to cover ALL cases (local/ref x cert/raw-key/psk).
18 to 19
- Updated the "keepalives" containers to address Michal Vasko's request to
align with RFC 8071.
- Removed algorithm-mapping tables from the "SSH Common Model" section
- Removed 'algorithm' node from examples.
- Added feature "userauth-publickey"
- Removed "choice auth-type", as auth-types are not exclusive.
- Renamed both "client-certs" and "server-certs" to "ee-certs"
- Switch "must" to assert the public-key-format is "subject-public-key-info-format" when certificates are used.
- Added a "Note to Reviewers" note to first page.
19 to 20
- Added a "must 'public-key or password or hostbased or none or certificate'"
statement to the "user" node in ietf-ssh-client
- Expanded "Data Model Overview section(s) [remove "wall" of tree diagrams].
- Moved the "ietf-ssh-common" module section to proceed the other two module sections.
- Updated the Security Considerations section.
20 to 21
- Updated examples to reflect new "cleartext-" prefix in the crypto-types draft.
21 to 22
- Cleaned up the SSH-client examples (i.e., removing FIXMEs)
- Fixed issues found by the SecDir review of the "keystore" draft.
- Updated the "ietf-ssh-client" module to use the new "password-grouping"
grouping from the "crypto-types" module.
22 to 23
- Addressed comments raised by YANG Doctor in the ct/ts/ks drafts.
23 to 24
- Removed the 'supported-authentication-methods' from {grouping ssh-server-grouping}/client-authentication.
- Added XML-comment above examples explaining the reason for the unexepected top-most element's presence.
- Added RFC-references to various 'feature' statements.
- Renamed "credentials" to "authentication methods"
- Renamed "client-auth-*" to "userauth-*"
- Renamed "client-identity-*" to "userauth-*"
- Fixed nits found by YANG Doctor reviews.
- Aligned modules with `pyang -f` formatting.
- Added a 'Contributors' section.
24 to 25
- Moved algorithms in ietf-ssh-common (plus more) to IANA-maintained modules
- Added "config false" lists for algorithms supported by the server.
- Renamed "{ietf-ssh-client}userauth-*" to "client-ident-*"
- Renamed "{ietf-ssh-server}userauth-*" to "local-user-auth-*"
- Fixed issues found during YANG Doctor review.
- Fixed issues found during Secdir review.
25 to 26
- Replaced "base64encodedvalue==" with "BASE64VALUE=" in examples.
- Minor editorial nits
26 to 27
- Fixed up the 'WG Web' and 'WG List' lines in YANG module(s)
- Fixed up copyright (i.e., s/Simplified/Revised/) in YANG module(s)
- Created identityref-based typedefs for each of the four IANA alg identity bases.
- Added ietf-ssh-common:generate-public-key() RPC for discussion.
27 to 28
- Fixed example to not have line-returns around "identity" values.
- Fixed examples to not include "xmlns:algs".
- Added an example for the "generate-public-key" RPC.
28 to 29
- Updated modules to IANA-maintained modules in Appendix A to 2022-06-16.
29 to 30
- Fixed 'must' expressions.
- Added missing 'revision' statement.
30 to 31
- Updated per Shepherd reviews impacting the suite of drafts.
31 to 32
- Updated per Shepherd reviews impacting the suite of drafts.
Acknowledgements
The authors would like to thank for following for lively discussions
on list and in the halls (ordered by first name):
Alan Luchuk,
Andy Bierman,
Balazs Kovacs,
Barry Leiba,
Benoit Claise,
Bert Wijnen,
David Lamparter,
Gary Wu,
Juergen Schoenwaelder,
Ladislav Lhotka,
Liang Xia,
Martin Bjoerklund,
Mehmet Ersue,
Michal Vasko,
Per Andersson,
Phil Shafer,
Radek Krejci,
Sean Turner,
Tom Petch.
Contributors
Special acknowledgement goes to Gary Wu for his work on the
"ietf-ssh-common" module.