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:

• 2022-08-30 --> the publication date of this draft

The following Appendix section is to be removed prior to publication:

• . Change Log

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 the clients and servers of both the NETCONF and RESTCONF protocols. The modules have been defined in a modular fashion to enable their use by other efforts, some of which are known to be in progress at the time of this writing, with many more expected to be defined in time. The normative dependency relationship between the various RFCs in the 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:

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@2022-08-30.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 2022-08-30 { 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. The configured host key algorithms should be compatible with the algorithm used by the configured private key. Please see Section 5 of RFC EEEE for valid combinations. If this leaf-list is not configured (has zero elements) the acceptable host key algorithms are implementation- defined."; reference "RFC EEEE: YANG Groupings for SSH Clients and SSH Servers"; } } container key-exchange { description "Parameters regarding key exchange."; leaf-list key-exchange-alg { type identityref { base 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:

Groupings The "ietf-ssh-client" module defines the following "grouping" statement:

• ssh-client-grouping

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@2022-08-30.yang" 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. 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 2022-08-30 { 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 TLS server is dropped after approximately max-wait * max-attempts seconds. Per Section 4 of RFC 4254, the SSH client SHOULD send an SSH_MSG_GLOBAL_REQUEST message with a purposely nonexistent 'request name' value (e.g., keepalive@ietf.org) and the 'want reply' value set to '1'."; reference "RFC 4254: The Secure Shell (SSH) Connection Protocol"; leaf max-wait { type uint16 { range "1..max"; } units "seconds"; default "30"; description "Sets the amount of time in seconds after which if no data has been received from the SSH server, a TLS-level message will be sent to test the aliveness of the SSH server."; } leaf max-attempts { type uint8; default "3"; description "Sets the maximum number of sequential keep-alive messages that can fail to obtain a response from the SSH server before assuming the SSH server is no longer alive."; } } // container keepalives } // grouping ssh-client-grouping } ]]> <CODE ENDS>

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:

Groupings The "ietf-ssh-server" module defines the following "grouping" statement:

• ssh-server-grouping

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 User A ct:ssh-public-key-format BASE64VALUE= User B 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@2022-08-30.yang" 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. 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 2022-08-30 { 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 SSL client. An unresponsive SSL client is dropped after approximately max-wait * max-attempts seconds. Per Section 4 of RFC 4254, the SSH server SHOULD send an SSH_MSG_GLOBAL_REQUEST message with a purposely nonexistent 'request name' value (e.g., keepalive@ietf.org) and the 'want reply' value set to '1'."; reference "RFC 4254: The Secure Shell (SSH) Connection Protocol"; leaf max-wait { type uint16 { range "1..max"; } units "seconds"; default "30"; description "Sets the amount of time in seconds after which if no data has been received from the SSL client, a SSL-level message will be sent to test the aliveness of the SSL client."; } leaf max-attempts { type uint8; default "3"; description "Sets the maximum number of sequential keep-alive messages that can fail to obtain a response from the SSL client before assuming the SSL client is no longer alive."; } } } // grouping ssh-server-grouping } ]]> <CODE ENDS>

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 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. 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 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. 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 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. 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 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. 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 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 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 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 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.

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 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 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. 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. 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. 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. 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 algortihm, and a "base" identity from which all of the other identities are derived. 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.
• Please also note that the "status" statement has been set to "deprecated" . It is recommended that IANA adds a column to the registry to more easily track the deprecation status of algorithms.

References Normative References 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. 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] 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] 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 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.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] 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] 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). 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. 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. Informative References 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 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) 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] 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 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] 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] 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. 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). 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. 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. 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.

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 . ]]>

Typedefs The following diagram illustrates the "typedef" statements defined in the "iana-ssh-encryption-algs" module: 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. <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 . ]]>

Typedefs The following diagram illustrates the "typedef" statements defined in the "iana-ssh-mac-algs" module: 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. <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 . ]]>

Typedefs The following diagram illustrates the "typedef" statements defined in the "iana-ssh-public-key-algs" module: 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. <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 . ]]>

Typedefs The following diagram illustrates the "typedef" statements defined in the "iana-ssh-key-exchange-algs" module: 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 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. <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.

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, Phil Shafer, Radek Krejci, Sean Turner, Tom Petch.

Contributors Special acknowledgement goes to Gary Wu for his work on the "ietf-ssh-common" module.