NETCONF Working Group K. Watsen Internet-Draft Juniper Networks Intended status: Standards Track G. Wu Expires: December 15, 2017 Cisco Systems June 13, 2017 SSH Client and Server Models draft-ietf-netconf-ssh-client-server-03 Abstract This document defines three YANG modules: the first defines groupings for a generic SSH client, the second defines groupings for a generic SSH server, and the third defines common identities and groupings used by both the client and the server. It is intended that these groupings will be used by applications using the SSH protocol. Editorial Note (To be removed by RFC Editor) This draft contains many placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document. This document contains references to other drafts in progress, both in the Normative References section, as well as in body text throughout. Please update the following references to reflect their final RFC assignments: o I-D.ietf-netconf-keystore Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements: o "XXXX" --> the assigned RFC value for this draft o "YYYY" --> the assigned RFC value for I-D.ietf-netconf-keystore Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement: o "2017-06-13" --> the publication date of this draft The following Appendix section is to be removed prior to publication: o Appendix A. Change Log Watsen & Wu Expires December 15, 2017 [Page 1] Internet-Draft SSH Client and Server Models June 2017 Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 15, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Tree Diagrams . . . . . . . . . . . . . . . . . . . . . . 4 2. The SSH Client Model . . . . . . . . . . . . . . . . . . . . 4 2.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 5 2.3. YANG Model . . . . . . . . . . . . . . . . . . . . . . . 6 3. The SSH Server Model . . . . . . . . . . . . . . . . . . . . 10 3.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 10 3.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 11 3.3. YANG Model . . . . . . . . . . . . . . . . . . . . . . . 11 4. The SSH Common Model . . . . . . . . . . . . . . . . . . . . 15 4.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 15 4.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 15 Watsen & Wu Expires December 15, 2017 [Page 2] Internet-Draft SSH Client and Server Models June 2017 4.3. YANG Model . . . . . . . . . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 26 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 6.1. The IETF XML Registry . . . . . . . . . . . . . . . . . . 27 6.2. The YANG Module Names Registry . . . . . . . . . . . . . 28 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 8.1. Normative References . . . . . . . . . . . . . . . . . . 29 8.2. Informative References . . . . . . . . . . . . . . . . . 30 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 31 A.1. server-model-09 to 00 . . . . . . . . . . . . . . . . . . 31 A.2. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 31 A.3. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 31 A.4. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 1. Introduction This document defines three YANG [RFC7950] modules: the first defines a grouping for a generic SSH client, the second defines a grouping for a generic SSH server, and the third defines identities and groupings common to both the client and the server (SSH is defined in [RFC4252], [RFC4253], and [RFC4254]). It is intended that these groupings will be used by applications using the SSH protocol. For instance, these groupings could be used to help define the data model for an OpenSSH [OPENSSH] server or a NETCONF over SSH [RFC6242] based server. The client and server YANG modules in this document each define one grouping, which is focused on just SSH-specific configuration, and specifically avoids any transport-level configuration, such as what ports to listen-on or connect-to. This enables applications the opportunity to define their own strategy for how the underlying TCP connection is established. For instance, applications supporting NETCONF Call Home [RFC8071] could use the grouping for the SSH parts it provides, while adding data nodes for the TCP-level call-home configuration. 1.1. Terminology The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Watsen & Wu Expires December 15, 2017 [Page 3] Internet-Draft SSH Client and Server Models June 2017 1.2. Tree Diagrams A simplified graphical representation of the data models is used in this document. The meaning of the symbols in these diagrams is as follows: o Brackets "[" and "]" enclose list keys. o Braces "{" and "}" enclose feature names, and indicate that the named feature must be present for the subtree to be present. o Abbreviations before data node names: "rw" means configuration (read-write) and "ro" state data (read-only). o Symbols after data node names: "?" means an optional node, "!" means a presence container, and "*" denotes a list and leaf-list. o Parentheses enclose choice and case nodes, and case nodes are also marked with a colon (":"). o Ellipsis ("...") stands for contents of subtrees that are not shown. 2. The SSH Client Model The SSH client model presented in this section contains one YANG grouping, to just configure the SSH client omitting, for instance, any configuration for which IP address or port the client should connect to. This grouping references data nodes defined by the keystore model [I-D.ietf-netconf-keystore]. For instance, a reference to the keystore model is made to indicate which trusted CA certificate a client should use to authenticate X.509v3 certificate based host keys [RFC6187]. 2.1. Tree Diagram The following tree diagram presents the data model for the grouping defined in the ietf-ssh-client module. Please see Section 1.2 for tree diagram notation. Watsen & Wu Expires December 15, 2017 [Page 4] Internet-Draft SSH Client and Server Models June 2017 module: ietf-ssh-client groupings: ssh-client-grouping +---- server-auth | +---- trusted-ssh-host-keys? | | -> /ks:keystore/trusted-host-keys/name | +---- trusted-ca-certs? | | -> /ks:keystore/trusted-certificates/name | | {sshcom:ssh-x509-certs}? | +---- trusted-server-certs? | -> /ks:keystore/trusted-certificates/name | {sshcom:ssh-x509-certs}? +---- client-auth | +---- username? string | +---- (auth-type)? | +--:(certificate) | | +---- certificate? leafref {sshcom:ssh-x509-certs}? | +--:(public-key) | | +---- public-key? -> /ks:keystore/keys/key/name | +--:(password) | +---- password? string +---- transport-params {ssh-client-transport-params-config}? +---- host-key | +---- host-key-alg* identityref +---- key-exchange | +---- key-exchange-alg* identityref +---- encryption | +---- encryption-alg* identityref +---- mac | +---- mac-alg* identityref +---- compression +---- compression-alg* identityref 2.2. Example Usage This section shows how it would appear if the ssh-client-grouping were populated with some data. This example is consistent with the examples presented in Section 2.2 of [I-D.ietf-netconf-keystore]. Watsen & Wu Expires December 15, 2017 [Page 5] Internet-Draft SSH Client and Server Models June 2017 explicitly-trusted-ssh-host-keys foobar ex-rsa-key 2.3. YANG Model This YANG module has a normative references to [RFC6991] and [I-D.ietf-netconf-keystore]. file "ietf-ssh-client@2017-06-13.yang" module ietf-ssh-client { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-client"; prefix "sshc"; import ietf-ssh-common { prefix sshcom; revision-date 2017-06-13; // stable grouping definitions reference "RFC XXXX: SSH Client and Server Models"; } import ietf-netconf-acm { prefix nacm; reference "RFC 6536: Network Configuration Protocol (NETCONF) Access Control Model"; } import ietf-keystore { prefix ks; reference "RFC YYYY: Keystore Model"; Watsen & Wu Expires December 15, 2017 [Page 6] Internet-Draft SSH Client and Server Models June 2017 } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: WG List: Author: Kent Watsen Author: Gary Wu "; description "This module defines a reusable grouping for a SSH client that can be used as a basis for specific SSH client instances. Copyright (c) 2014 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision "2017-06-13" { description "Initial version"; reference "RFC XXXX: SSH Client and Server Models"; } feature ssh-client-transport-params-config { description "SSH transport layer parameters are configurable on an SSH client."; } grouping ssh-client-grouping { description Watsen & Wu Expires December 15, 2017 [Page 7] Internet-Draft SSH Client and Server Models June 2017 "A reusable grouping for configuring a SSH client without any consideration for how an underlying TCP session is established."; container server-auth { must 'trusted-ssh-host-keys or trusted-ca-certs or trusted-server-certs'; description "Trusted server identities."; leaf trusted-ssh-host-keys { type leafref { path "/ks:keystore/ks:trusted-host-keys/ks:name"; } description "A reference to a list of SSH host keys used by the SSH client to authenticate SSH server host keys. A server host key is authenticate if it is an exact match to a configured trusted SSH host key."; } leaf trusted-ca-certs { if-feature sshcom:ssh-x509-certs; type leafref { path "/ks:keystore/ks:trusted-certificates/ks:name"; } description "A reference to a list of certificate authority (CA) certificates used by the SSH client to authenticate SSH server certificates. A server certificate is authenticated if it has a valid chain of trust to a configured trusted CA certificate."; } leaf trusted-server-certs { if-feature sshcom:ssh-x509-certs; type leafref { path "/ks:keystore/ks:trusted-certificates/ks:name"; } description "A reference to a list of server certificates used by the SSH client to authenticate SSH server certificates. A server certificate is authenticated if it is an exact match to a configured trusted server certificate."; } } container client-auth { description "The credentials used by the client to authenticate to Watsen & Wu Expires December 15, 2017 [Page 8] Internet-Draft SSH Client and Server Models June 2017 the SSH server."; leaf username { type string; description "The username of this user. This will be the username used, for instance, to log into an SSH server."; } choice auth-type { description "The authentication type."; leaf certificate { if-feature sshcom:ssh-x509-certs; type leafref { path "/ks:keystore/ks:keys/ks:key/ks:certificates/" + "ks:certificate/ks:name"; } description "A certificates to be used for user authentication."; } leaf public-key { type leafref { path "/ks:keystore/ks:keys/ks:key/ks:name"; } description "A public keys to be used for user authentication."; } leaf password { nacm:default-deny-all; type string; description "A password to be used for user authentication."; } } } // end client-auth container transport-params { if-feature ssh-client-transport-params-config; uses sshcom:transport-params-grouping; description "Configurable parameters for the SSH transport layer."; } } // ssh-client-grouping } Watsen & Wu Expires December 15, 2017 [Page 9] Internet-Draft SSH Client and Server Models June 2017 3. The SSH Server Model The SSH server model presented in this section contains one YANG grouping, for just the SSH-level configuration omitting, for instance, configuration for which ports to open to listen for connections on. This grouping references data nodes defined by the keystore model [I-D.ietf-netconf-keystore]. For instance, a reference to the keystore model is made to indicate which host key a server should present. 3.1. Tree Diagram The following tree diagram presents the data model for the grouping defined in the ietf-ssh-server module. Please see Section 1.2 for tree diagram notation. module: ietf-ssh-server groupings: ssh-server-grouping +---- host-keys | +---- host-key* [name] | +---- name? string | +---- (host-key-type) | +--:(public-key) | | +---- public-key? -> /ks:keystore/keys/key/name | +--:(certificate) | +---- certificate? leafref {sshcom:ssh-x509-certs}? +---- client-cert-auth {sshcom:ssh-x509-certs}? | +---- trusted-ca-certs? | | -> /ks:keystore/trusted-certificates/name | +---- trusted-client-certs? | -> /ks:keystore/trusted-certificates/name +---- transport-params {ssh-server-transport-params-config}? +---- host-key | +---- host-key-alg* identityref +---- key-exchange | +---- key-exchange-alg* identityref +---- encryption | +---- encryption-alg* identityref +---- mac | +---- mac-alg* identityref +---- compression +---- compression-alg* identityref Watsen & Wu Expires December 15, 2017 [Page 10] Internet-Draft SSH Client and Server Models June 2017 3.2. Example Usage This section shows how it would appear if the ssh-server-grouping were populated with some data. This example is consistent with the examples presented in Section 2.2 of [I-D.ietf-netconf-keystore]. deployment-specific-certificate ex-rsa-cert deployment-specific-ca-certs explicitly-trusted-client-certs 3.3. YANG Model This YANG module has a normative references to [RFC4253], [RFC6991], and [I-D.ietf-netconf-keystore]. file "ietf-ssh-server@2017-06-13.yang" module ietf-ssh-server { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-server"; prefix "sshs"; import ietf-ssh-common { prefix sshcom; revision-date 2017-06-13; // stable grouping definitions reference "RFC XXXX: SSH Client and Server Models"; Watsen & Wu Expires December 15, 2017 [Page 11] Internet-Draft SSH Client and Server Models June 2017 } import ietf-keystore { prefix ks; reference "RFC YYYY: Keystore Model"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: WG List: Author: Kent Watsen "; description "This module defines a reusable grouping for a SSH server that can be used as a basis for specific SSH server instances. Copyright (c) 2014 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision "2017-06-13" { description "Initial version"; reference "RFC XXXX: SSH Client and Server Models"; } // features feature ssh-server-transport-params-config { description "SSH transport layer parameters are configurable on an SSH server."; Watsen & Wu Expires December 15, 2017 [Page 12] Internet-Draft SSH Client and Server Models June 2017 } // grouping grouping ssh-server-grouping { description "A reusable grouping for configuring a SSH server without any consideration for how underlying TCP sessions are established."; container host-keys { 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"; leaf public-key { type leafref { path "/ks:keystore/ks:keys/ks:key/ks:name"; } description "The public key is actually identified by the name of its cooresponding private-key in the keystore."; } leaf certificate { if-feature sshcom:ssh-x509-certs; type leafref { path "/ks:keystore/ks:keys/ks:key/ks:certificates/" + "ks:certificate/ks:name"; } description "The name of a certificate in the keystore."; Watsen & Wu Expires December 15, 2017 [Page 13] Internet-Draft SSH Client and Server Models June 2017 } } } } container client-cert-auth { if-feature sshcom:ssh-x509-certs; description "A reference to a list of trusted certificate authority (CA) certificates and a reference to a list of trusted client certificates."; leaf trusted-ca-certs { type leafref { path "/ks:keystore/ks:trusted-certificates/ks:name"; } description "A reference to a list of certificate authority (CA) certificates used by the SSH server to authenticate SSH client certificates."; } leaf trusted-client-certs { type leafref { path "/ks:keystore/ks:trusted-certificates/ks:name"; } description "A reference to a list of client certificates used by the SSH server to authenticate SSH client certificates. A clients certificate is authenticated if it is an exact match to a configured trusted client certificate."; } } container transport-params { if-feature ssh-server-transport-params-config; uses sshcom:transport-params-grouping; description "Configurable parameters for the SSH transport layer."; } } // ssh-server-grouping } Watsen & Wu Expires December 15, 2017 [Page 14] Internet-Draft SSH Client and Server Models June 2017 4. The SSH Common Model The SSH common model presented in this section contains identities and groupings common to both SSH clients and SSH servers. The transport-params-grouping can be used to configure the list of SSH transport algorithms permitted by the SSH client or SSH server. The lists of algorithms are ordered such that, if multiple algorithms are permitted by the client, the algorithm that appears first in its list that is also permitted by the server is used for the SSH transport layer connection. The ability to restrict the 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. Features are defined for algorithms that are OPTIONAL or are not widely supported by popular implementations. Note that the list of algorithms is not exhaustive. As well, some algorithms that are REQUIRED by [RFC4253] are missing, notably "ssh-dss" and "diffie- hellman-group1-sha1" due to their weak security and there being alternatives that are widely supported. 4.1. Tree Diagram The following tree diagram presents the data model for the grouping defined in the ietf-ssh-common module. Please see Section 1.2 for tree diagram notation. module: ietf-ssh-common groupings: transport-params-grouping +---- host-key | +---- host-key-alg* identityref +---- key-exchange | +---- key-exchange-alg* identityref +---- encryption | +---- encryption-alg* identityref +---- mac | +---- mac-alg* identityref +---- compression +---- compression-alg* identityref 4.2. Example Usage This section shows how it would appear if the transport-params- grouping were populated with some data. Watsen & Wu Expires December 15, 2017 [Page 15] Internet-Draft SSH Client and Server Models June 2017 x509v3-rsa2048-sha256 ssh-rsa diffie-hellman-group-exchange-sha256 aes256-ctr aes192-ctr aes128-ctr aes256-cbc aes192-cbc aes128-cbc hmac-sha2-256 hmac-sha2-512 none 4.3. YANG Model This YANG module has a normative references to [RFC4344], [RFC4419], and [RFC5656]. file "ietf-ssh-common@2017-06-13.yang" module ietf-ssh-common { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-common"; prefix "sshcom"; organization "IETF NETCONF (Network Configuration) Working Group"; contact Watsen & Wu Expires December 15, 2017 [Page 16] Internet-Draft SSH Client and Server Models June 2017 "WG Web: WG List: Author: Kent Watsen Author: Gary Wu "; description "This module defines a common features, identities, and groupings for Secure Shell (SSH). Copyright (c) 2017 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision "2017-06-13" { description "Initial version"; reference "RFC XXXX: SSH Client and Server Models"; } // features feature ssh-ecc { description "Elliptic Curve Cryptography is supported for SSH."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } feature ssh-x509-certs { description "X.509v3 certificates are supported for SSH as per RFC 6187."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Watsen & Wu Expires December 15, 2017 [Page 17] Internet-Draft SSH Client and Server Models June 2017 Authentication"; } feature ssh-dh-group-exchange { description "Diffie-Hellman Group Exchange is supported for SSH."; reference "RFC 4419: Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"; } feature ssh-ctr { description "SDCTR encryption mode is supported for SSH."; reference "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption Modes"; } feature ssh-sha2 { description "The SHA2 family of cryptographic hash functions is supported for SSH."; reference "FIPS PUB 180-4: Secure Hash Standard (SHS)"; } feature ssh-zlib { description "ZLIB (LZ77) compression is supported for SSH."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } // identities identity public-key-alg-base { description "Base identity used to identify public key algorithms."; } identity ssh-dss { base public-key-alg-base; description "Digital Signature Algorithm using SHA-1 as the hashing algorithm."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } Watsen & Wu Expires December 15, 2017 [Page 18] Internet-Draft SSH Client and Server Models June 2017 identity ssh-rsa { base public-key-alg-base; description "RSASSA-PKCS1-v1_5 signature scheme using SHA-1 as the hashing algorithm."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity ecdsa-sha2-nistp256 { base public-key-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the nistp256 curve and the SHA2 family of hashing algorithms."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity ecdsa-sha2-nistp384 { base public-key-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the nistp384 curve and the SHA2 family of hashing algorithms."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity ecdsa-sha2-nistp521 { base public-key-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the nistp521 curve and the SHA2 family of hashing algorithms."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity x509v3-ssh-rsa { base public-key-alg-base; if-feature ssh-x509-certs; description "RSASSA-PKCS1-v1_5 signature scheme using a public key stored in an X.509v3 certificate and using SHA-1 as the hashing Watsen & Wu Expires December 15, 2017 [Page 19] Internet-Draft SSH Client and Server Models June 2017 algorithm."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Authentication"; } identity x509v3-rsa2048-sha256 { base public-key-alg-base; if-feature "ssh-x509-certs and ssh-sha2"; description "RSASSA-PKCS1-v1_5 signature scheme using a public key stored in an X.509v3 certificate and using SHA-256 as the hashing algorithm. RSA keys conveyed using this format MUST have a modulus of at least 2048 bits."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Authentication"; } identity x509v3-ecdsa-sha2-nistp256 { base public-key-alg-base; if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the nistp256 curve with a public key stored in an X.509v3 certificate and using the SHA2 family of hashing algorithms."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Authentication"; } identity x509v3-ecdsa-sha2-nistp384 { base public-key-alg-base; if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the nistp384 curve with a public key stored in an X.509v3 certificate and using the SHA2 family of hashing algorithms."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Authentication"; } identity x509v3-ecdsa-sha2-nistp521 { base public-key-alg-base; if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2"; description "Elliptic Curve Digital Signature Algorithm (ECDSA) using the Watsen & Wu Expires December 15, 2017 [Page 20] Internet-Draft SSH Client and Server Models June 2017 nistp521 curve with a public key stored in an X.509v3 certificate and using the SHA2 family of hashing algorithms."; reference "RFC 6187: X.509v3 Certificates for Secure Shell Authentication"; } identity key-exchange-alg-base { description "Base identity used to identify key exchange algorithms."; } identity diffie-hellman-group14-sha1 { base key-exchange-alg-base; description "Diffie-Hellman key exchange with SHA-1 as HASH and Oakley Group 14 (2048-bit MODP Group)."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity diffie-hellman-group-exchange-sha1 { base key-exchange-alg-base; if-feature ssh-dh-group-exchange; description "Diffie-Hellman Group and Key Exchange with SHA-1 as HASH."; reference "RFC 4419: Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"; } identity diffie-hellman-group-exchange-sha256 { base key-exchange-alg-base; if-feature "ssh-dh-group-exchange and ssh-sha2"; description "Diffie-Hellman Group and Key Exchange with SHA-256 as HASH."; reference "RFC 4419: Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"; } identity ecdh-sha2-nistp256 { base key-exchange-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the nistp256 curve and the SHA2 family of hashing algorithms."; reference Watsen & Wu Expires December 15, 2017 [Page 21] Internet-Draft SSH Client and Server Models June 2017 "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity ecdh-sha2-nistp384 { base key-exchange-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the nistp384 curve and the SHA2 family of hashing algorithms."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity ecdh-sha2-nistp521 { base key-exchange-alg-base; if-feature "ssh-ecc and ssh-sha2"; description "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the nistp521 curve and the SHA2 family of hashing algorithms."; reference "RFC 5656: Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer"; } identity encryption-alg-base { description "Base identity used to identify encryption algorithms."; } identity triple-des-cbc { base encryption-alg-base; description "Three-key 3DES in CBC mode."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity aes128-cbc { base encryption-alg-base; description "AES in CBC mode, with a 128-bit key."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity aes192-cbc { Watsen & Wu Expires December 15, 2017 [Page 22] Internet-Draft SSH Client and Server Models June 2017 base encryption-alg-base; description "AES in CBC mode, with a 192-bit key."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity aes256-cbc { base encryption-alg-base; description "AES in CBC mode, with a 256-bit key."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity aes128-ctr { base encryption-alg-base; if-feature ssh-ctr; description "AES in SDCTR mode, with 128-bit key."; reference "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption Modes"; } identity aes192-ctr { base encryption-alg-base; if-feature ssh-ctr; description "AES in SDCTR mode, with 192-bit key."; reference "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption Modes"; } identity aes256-ctr { base encryption-alg-base; if-feature ssh-ctr; description "AES in SDCTR mode, with 256-bit key."; reference "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption Modes"; } identity mac-alg-base { description "Base identity used to identify message authentication Watsen & Wu Expires December 15, 2017 [Page 23] Internet-Draft SSH Client and Server Models June 2017 code (MAC) algorithms."; } identity hmac-sha1 { base mac-alg-base; description "HMAC-SHA1"; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity hmac-sha2-256 { base mac-alg-base; if-feature "ssh-sha2"; description "HMAC-SHA2-256"; reference "RFC 6668: SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol"; } identity hmac-sha2-512 { base mac-alg-base; if-feature "ssh-sha2"; description "HMAC-SHA2-512"; reference "RFC 6668: SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol"; } identity compression-alg-base { description "Base identity used to identify compression algorithms."; } identity none { base compression-alg-base; description "No compression."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } identity zlib { base compression-alg-base; if-feature ssh-zlib; description Watsen & Wu Expires December 15, 2017 [Page 24] Internet-Draft SSH Client and Server Models June 2017 "ZLIB (LZ77) compression."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; } // groupings grouping transport-params-grouping { description "A reusable grouping for SSH transport parameters. For configurable parameters, a zero-element leaf-list of algorithms indicates the system default configuration for that parameter."; reference "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol"; container host-key { description "Parameters regarding host key."; leaf-list host-key-alg { type identityref { base public-key-alg-base; } ordered-by user; description "Host key algorithms in order of descending preference."; } } container key-exchange { description "Parameters regarding key exchange."; leaf-list key-exchange-alg { type identityref { base key-exchange-alg-base; } ordered-by user; description "Key exchange algorithms in order of descending preference."; } } container encryption { description "Parameters regarding encryption."; leaf-list encryption-alg { type identityref { base encryption-alg-base; } ordered-by user; description Watsen & Wu Expires December 15, 2017 [Page 25] Internet-Draft SSH Client and Server Models June 2017 "Encryption algorithms in order of descending preference."; } } container mac { description "Parameters regarding message authentication code (MAC)."; leaf-list mac-alg { type identityref { base mac-alg-base; } ordered-by user; description "MAC algorithms in order of descending preference."; } } container compression { description "Parameters regarding compression."; leaf-list compression-alg { type identityref { base compression-alg-base; } ordered-by user; description "Compression algorithms in order of descending preference."; } } } } 5. Security Considerations The YANG module defined in this document is designed to be accessed via YANG based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to- implement secure transport layers (e.g., SSH, TLS) with mutual authentication. The NETCONF access control model (NACM) [RFC6536] provides the means to restrict access for particular users to a pre-configured subset of all available protocol operations and content. There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) Watsen & Wu Expires December 15, 2017 [Page 26] Internet-Draft SSH Client and Server Models June 2017 to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability: /: The entire data tree defined by this module is sensitive to write operations. For instance, the addition or removal of references to keys, certificates, trusted anchors, etc., can dramatically alter the implemented security policy. However, no NACM annotations are applied as the data SHOULD be editable by users other than a designated 'recovery session'. Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability: /client-auth/password: This node is additionally sensitive to read operations such that, in normal use cases, it should never be returned to a client. The best reason for returning this node is to support backup/restore type workflows. This being the case, this node is marked with the NACM value 'default- deny-all'. Some of the RPC operations in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability: NONE 6. IANA Considerations 6.1. The IETF XML Registry This document registers three URIs in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registrations are requested: Watsen & Wu Expires December 15, 2017 [Page 27] Internet-Draft SSH Client and Server Models June 2017 URI: urn:ietf:params:xml:ns:yang:ietf-ssh-client Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. URI: urn:ietf:params:xml:ns:yang:ietf-ssh-server Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. URI: urn:ietf:params:xml:ns:yang:ietf-ssh-common Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. 6.2. The YANG Module Names Registry This document registers three YANG modules in the YANG Module Names registry [RFC7950]. Following the format in [RFC7950], the the following registrations are requested: name: ietf-ssh-client namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-client prefix: sshc reference: RFC XXXX name: ietf-ssh-server namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-server prefix: sshs reference: RFC XXXX name: ietf-ssh-common namespace: urn:ietf:params:xml:ns:yang:ietf-ssh-common prefix: sshcom reference: RFC XXXX 7. Acknowledgements The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): Andy Bierman, Martin Bjorklund, Benoit Claise, Mehmet Ersue, Balazs Kovacs, David Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch, Juergen Schoenwaelder, Phil Shafer, Sean Turner, Michal Vasko, and Bert Wijnen. 8. References Watsen & Wu Expires December 15, 2017 [Page 28] Internet-Draft SSH Client and Server Models June 2017 8.1. Normative References [I-D.ietf-netconf-keystore] Watsen, K., "Keystore Model", draft-ietf-netconf- keystore-01 (work in progress), March 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4344] Bellare, M., Kohno, T., and C. Namprempre, "The Secure Shell (SSH) Transport Layer Encryption Modes", RFC 4344, DOI 10.17487/RFC4344, January 2006, . [RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006, . [RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer", RFC 5656, DOI 10.17487/RFC5656, December 2009, . [RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure Shell Authentication", RFC 6187, DOI 10.17487/RFC6187, March 2011, . [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012, . [RFC6668] Bider, D. and M. Baushke, "SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol", RFC 6668, DOI 10.17487/RFC6668, July 2012, . [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . Watsen & Wu Expires December 15, 2017 [Page 29] Internet-Draft SSH Client and Server Models June 2017 8.2. Informative References [OPENSSH] "OpenSSH", 2016, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252, January 2006, . [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006, . [RFC4254] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Connection Protocol", RFC 4254, DOI 10.17487/RFC4254, January 2006, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, February 2017, . Watsen & Wu Expires December 15, 2017 [Page 30] Internet-Draft SSH Client and Server Models June 2017 Appendix A. Change Log A.1. server-model-09 to 00 o This draft was split out from draft-ietf-netconf-server-model-09. o Added in previously missing ietf-ssh-client module. o Noted that '0.0.0.0' and '::' might have special meanings. A.2. 00 to 01 o Renamed "keychain" to "keystore". A.3. 01 to 02 o Removed the groupings 'listening-ssh-client-grouping' and 'listening-ssh-server-grouping'. Now modules only contain the transport-independent groupings. o Simplified the "client-auth" part in the ietf-ssh-client module. It now inlines what it used to point to keystore for. o Added cipher suites for various algorithms into new 'ietf-ssh- common' module. A.4. 02 to 03 o Removed 'RESTRICTED' enum from 'password' leaf type. o Added a 'must' statement to container 'server-auth' asserting that at least one of the various auth mechanisms must be specified. o Fixed description statement for leaf 'trusted-ca-certs'. Authors' Addresses Kent Watsen Juniper Networks EMail: kwatsen@juniper.net Gary Wu Cisco Systems EMail: garywu@cisco.com Watsen & Wu Expires December 15, 2017 [Page 31]