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NETCONF Working Group                                          K. Watsen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                                   G. Wu
Expires: May 3, 2018                                       Cisco Systems
                                                        October 30, 2017


             YANG Groupings for SSH Clients and SSH Servers
                draft-ietf-netconf-ssh-client-server-05

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  "2017-10-30" --> the publication date of this draft

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

   o  Appendix A.  Change Log




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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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2018.

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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The SSH Client Model  . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  The SSH Server Model  . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  12
     4.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  13
   5.  The SSH Common Model  . . . . . . . . . . . . . . . . . . . .  16
     5.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  17
     5.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  17
     5.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  18



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   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  29
     7.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  29
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  30
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  30
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  31
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  33
     A.1.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  33
     A.2.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  33
     A.3.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  33
     A.4.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  33
     A.5.  04 to 05  . . . . . . . . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

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.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.






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3.  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].

3.1.  Tree Diagram

   The following tree diagram [I-D.ietf-netmod-yang-tree-diagrams]
   provides an overview of the data model for the "ietf-ssh-client"
   module.

   module: ietf-ssh-client

     grouping ssh-client-grouping
       +---- client-identity
       |  +---- username?      string
       |  +---- (auth-type)
       |     +--:(certificate)
       |     |  +---- certificate {sshcmn:ssh-x509-certs}?
       |     |     +---- algorithm?
       |     |     |       identityref
       |     |     +---- private-key?                            union
       |     |     +---- public-key?                             binary
       |     |     +---x generate-private-key
       |     |     |  +---w input
       |     |     |     +---w algorithm    identityref
       |     |     +---- certificates
       |     |     |  +---- certificate* [name]
       |     |     |     +---- name?    string
       |     |     |     +---- value?   binary
       |     |     +---x generate-certificate-signing-request
       |     |        +---w input
       |     |        |  +---w subject       binary
       |     |        |  +---w attributes?   binary
       |     |        +--ro output
       |     |           +--ro certificate-signing-request    binary
       |     +--:(public-key)
       |     |  +---- public-key
       |     |     +---- algorithm?              identityref
       |     |     +---- private-key?            union



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       |     |     +---- public-key?             binary
       |     |     +---x generate-private-key
       |     |        +---w input
       |     |           +---w algorithm    identityref
       |     +--:(password)
       |        +---- password?      string
       +---- server-auth
       |  +---- pinned-ssh-host-keys?   ks:pinned-host-keys
       |  +---- pinned-ca-certs?        ks:pinned-certificates
       |  |       {sshcmn:ssh-x509-certs}?
       |  +---- pinned-server-certs?    ks:pinned-certificates
       |          {sshcmn:ssh-x509-certs}?
       +---- 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

3.2.  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].

   [ note: '\' line wrapping for formatting only]

   <!-- hypothetical example, as groupings don't have instance data -->\

   <ssh-client xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-client"
               xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common"\
   >

     <!-- how this client will authenticate itself to the server -->
     <client-identity>
       <username>foobar</username>
       <public-key>
         <algorithm xmlns:ks="urn:ietf:params:xml:ns:yang:ietf-keystore\
   ">ks:secp521r1</algorithm>
         <private-key>base64encodedvalue==</private-key>
         <public-key>base64encodedvalue==</public-key>
       </public-key>
     </client-identity>

     <!-- which host-keys will this client trust -->



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     <server-auth>
       <pinned-ssh-host-keys>explicitly-trusted-ssh-host-keys</pinned-s\
   sh-host-keys>
     </server-auth>

     <transport-params>
       <host-key>
         <host-key-alg>algs:ssh-rsa</host-key-alg>
       </host-key>
       <key-exchange>
         <key-exchange-alg>
           algs:diffie-hellman-group-exchange-sha256
         </key-exchange-alg>
       </key-exchange>
       <encryption>
         <encryption-alg>algs:aes256-ctr</encryption-alg>
         <encryption-alg>algs:aes192-ctr</encryption-alg>
         <encryption-alg>algs:aes128-ctr</encryption-alg>
         <encryption-alg>algs:aes256-cbc</encryption-alg>
         <encryption-alg>algs:aes192-cbc</encryption-alg>
         <encryption-alg>algs:aes128-cbc</encryption-alg>
       </encryption>
       <mac>
         <mac-alg>algs:hmac-sha2-256</mac-alg>
         <mac-alg>algs:hmac-sha2-512</mac-alg>
       </mac>
       <compression>
         <compression-alg>algs:none</compression-alg>
       </compression>

     </transport-params>

   </ssh-client>

3.3.  YANG Module

   This YANG module has normative references to [RFC6991] and
   [I-D.ietf-netconf-keystore].

   <CODE BEGINS> file "ietf-ssh-client@2017-10-30.yang"
   module ietf-ssh-client {
     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-client";
     prefix "sshc";

     import ietf-ssh-common {
       prefix sshcmn;



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       revision-date 2017-10-30; // stable grouping definitions
       reference
         "RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
     }

     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";
     }

     organization
      "IETF NETCONF (Network Configuration) Working Group";

     contact
      "WG Web:   <http://tools.ietf.org/wg/netconf/>
       WG List:  <mailto:netconf@ietf.org>

       Author:   Kent Watsen
                 <mailto:kwatsen@juniper.net>

       Author:   Gary Wu
                 <mailto:garywu@cisco.com>";


     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) 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.";



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     revision "2017-10-30" {
       description
        "Initial version";
       reference
        "RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
     }

     // features

     feature ssh-client-transport-params-config {
       description
         "SSH transport layer parameters are configurable on an SSH
          client.";
     }

     // 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.";

       container client-identity {
         description
           "The credentials used by the client to authenticate to
            the SSH server.";

         leaf username {
           type string;
           description
             "The username of this user.  This will be the username
              used, for instance, to log into an SSH server.";
         }

         choice auth-type {
           mandatory true;
           description
             "The authentication type.";
           container certificate {
             if-feature sshcmn:ssh-x509-certs;
             uses ks:private-key-grouping;
             uses ks:certificate-grouping;
             description
               "A certificates to be used for client authentication.";
           }
           container public-key {
             uses ks:private-key-grouping;



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             description
               "A public key to be used for client authentication.";
           }
           leaf password {
             nacm:default-deny-all;
             type string;
             description
               "A password to be used for client authentication.";
           }
         }
       } // end client-auth

       container server-auth {
         must 'pinned-ssh-host-keys or pinned-ca-certs or '
              + 'pinned-server-certs';
         description
           "Trusted server identities.";
         leaf pinned-ssh-host-keys {
           type ks:pinned-host-keys;
           description
             "A reference to a list of SSH host keys used by the
              SSH client to authenticate SSH server host keys.
              A server host key is authenticated if it is an exact
              match to a configured SSH host key.";
         }

         leaf pinned-ca-certs {
           if-feature sshcmn:ssh-x509-certs;
           type ks:pinned-certificates;
           description
             "A reference to a list of certificate authority (CA)
              certificates used by the SSH client to authenticate
              SSH server certificates.  A server certificate is
              authenticated if it has a valid chain of trust to
              a configured CA certificate.";
         }

         leaf pinned-server-certs {
           if-feature sshcmn:ssh-x509-certs;
           type ks:pinned-certificates;
           description
             "A reference to a list of server certificates used by
              the SSH client to authenticate SSH server certificates.
              A server certificate is authenticated if it is an
              exact match to a configured server certificate.";
         }
       } // end server-auth




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       container transport-params {
         if-feature ssh-client-transport-params-config;
         description
           "Configurable parameters of the SSH transport layer.";
         uses sshcmn:transport-params-grouping;
       }

     }
   }
   <CODE ENDS>

4.  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.

4.1.  Tree Diagram

   The following tree diagram [I-D.ietf-netmod-yang-tree-diagrams]
   provides an overview of the data model for the "ietf-ssh-server"
   module.























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   module: ietf-ssh-server

     grouping ssh-server-grouping
       +---- server-identity
       |  +---- host-key* [name]
       |     +---- name?          string
       |     +---- (host-key-type)
       |        +--:(public-key)
       |        |  +---- public-key
       |        |     +---- algorithm?              identityref
       |        |     +---- private-key?            union
       |        |     +---- public-key?             binary
       |        |     +---x generate-private-key
       |        |        +---w input
       |        |           +---w algorithm    identityref
       |        +--:(certificate)
       |           +---- certificate {sshcmn:ssh-x509-certs}?
       |              +---- algorithm?
       |              |       identityref
       |              +---- private-key?
       |              |       union
       |              +---- public-key?
       |              |       binary
       |              +---x generate-private-key
       |              |  +---w input
       |              |     +---w algorithm    identityref
       |              +---- certificates
       |              |  +---- certificate* [name]
       |              |     +---- name?    string
       |              |     +---- value?   binary
       |              +---x generate-certificate-signing-request
       |                 +---w input
       |                 |  +---w subject       binary
       |                 |  +---w attributes?   binary
       |                 +--ro output
       |                    +--ro certificate-signing-request    binary
       +---- client-cert-auth {sshcmn:ssh-x509-certs}?
       |  +---- pinned-ca-certs?       ks:pinned-certificates
       |  +---- pinned-client-certs?   ks:pinned-certificates
       +---- 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



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4.2.  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].

   [ note: '\' line wrapping for formatting only]

   <!-- hypothetical example, as groupings don't have instance data -->\

   <ssh-server xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-server"
               xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common"\
   >

     <!-- which host-keys will this SSH server present -->
     <server-identity>
       <host-key>
         <name>deployment-specific-certificate</name>
         <public-key>
           <algorithm xmlns:ks="urn:ietf:params:xml:ns:yang:ietf-keysto\
   re">ks:secp521r1</algorithm>
           <private-key>base64encodedvalue==</private-key>
           <public-key>base64encodedvalue==</public-key>
         </public-key>
       </host-key>
     </server-identity>

     <!-- which client-certs will this SSH server trust -->
     <client-cert-auth>
       <pinned-ca-certs>deployment-specific-ca-certs</pinned-ca-certs>
       <pinned-client-certs>explicitly-trusted-client-certs</pinned-cli\
   ent-certs>
     </client-cert-auth>

     <transport-params>
       <host-key>
         <host-key-alg>algs:ssh-rsa</host-key-alg>
       </host-key>
       <key-exchange>
         <key-exchange-alg>
           algs:diffie-hellman-group-exchange-sha256
         </key-exchange-alg>
       </key-exchange>
       <encryption>
         <encryption-alg>algs:aes256-ctr</encryption-alg>
         <encryption-alg>algs:aes192-ctr</encryption-alg>
         <encryption-alg>algs:aes128-ctr</encryption-alg>
         <encryption-alg>algs:aes256-cbc</encryption-alg>



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         <encryption-alg>algs:aes192-cbc</encryption-alg>
         <encryption-alg>algs:aes128-cbc</encryption-alg>
       </encryption>
       <mac>
         <mac-alg>algs:hmac-sha2-256</mac-alg>
         <mac-alg>algs:hmac-sha2-512</mac-alg>
       </mac>
       <compression>
         <compression-alg>algs:none</compression-alg>
       </compression>
     </transport-params>

   </ssh-server>

4.3.  YANG Module

   This YANG module has normative references to [RFC4253], [RFC6991],
   and [I-D.ietf-netconf-keystore].

   <CODE BEGINS> file "ietf-ssh-server@2017-10-30.yang"
   module ietf-ssh-server {
     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-server";
     prefix "sshs";

     import ietf-ssh-common {
       prefix sshcmn;
       revision-date 2017-10-30; // stable grouping definitions
       reference
         "RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
     }

     import ietf-keystore {
       prefix ks;
       reference
         "RFC YYYY: Keystore Model";
     }

     organization
      "IETF NETCONF (Network Configuration) Working Group";

     contact
      "WG Web:   <http://tools.ietf.org/wg/netconf/>
       WG List:  <mailto:netconf@ietf.org>

       Author:   Kent Watsen
                 <mailto:kwatsen@juniper.net>



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       Author:   Gary Wu
                 <mailto:garywu@cisco.com>";


     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) 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 "2017-10-30" {
       description
        "Initial version";
       reference
        "RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
     }

     // features

     feature ssh-server-transport-params-config {
       description
         "SSH transport layer parameters are configurable on an SSH
          server.";
     }

     // groupings

     grouping ssh-server-grouping {
       description
         "A reusable grouping for configuring a SSH server without
          any consideration for how underlying TCP sessions are
          established.";
       container server-identity {
         description
           "The list of host-keys the SSH server will present when
            establishing a SSH connection.";
         list host-key {



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           key name;
           min-elements 1;
           ordered-by user;
           description
             "An ordered list of host keys the SSH server will use to
              construct its ordered list of algorithms, when sending
              its SSH_MSG_KEXINIT message, as defined in Section 7.1
              of RFC 4253.";
           reference
             "RFC 4253: The Secure Shell (SSH) Transport Layer
                        Protocol";
           leaf name {
             type string;
             description
               "An arbitrary name for this host-key";
           }
           choice host-key-type {
             mandatory true;
             description
               "The type of host key being specified";
             container public-key {
               uses ks:private-key-grouping;
               description
                 "The SSH server uses a public-key for its host key.";
             }
             container certificate {
               if-feature sshcmn:ssh-x509-certs;
               uses ks:private-key-grouping;
               uses ks:certificate-grouping;
               description
                 "The SSH server uses a certificate for its host key.";
             }
           }
         }
       }

       container client-cert-auth {
         if-feature sshcmn:ssh-x509-certs;
         description
           "A reference to a list of pinned certificate authority (CA)
            certificates and a reference to a list of pinned client
            certificates.";
         leaf pinned-ca-certs {
           type ks:pinned-certificates;
           description
             "A reference to a list of certificate authority (CA)
              certificates used by the SSH server to authenticate
              SSH client certificates.  A client certificate is



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              authenticated if it has a valid chain of trust to
              a configured pinned CA certificate.";
         }
         leaf pinned-client-certs {
           type ks:pinned-certificates;
           description
             "A reference to a list of client certificates used by
              the SSH server to authenticate SSH client certificates.
              A clients certificate is authenticated if it is an
              exact match to a configured pinned client certificate.";
         }
       }

       container transport-params {
         if-feature ssh-server-transport-params-config;
         description
           "Configurable parameters of the SSH transport layer.";
         uses sshcmn:transport-params-grouping;
       }

     }
   }
   <CODE ENDS>

5.  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.







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5.1.  Tree Diagram

   The following tree diagram [I-D.ietf-netmod-yang-tree-diagrams]
   provides an overview of the data model for the "ietf-ssh-common"
   module.

   module: ietf-ssh-common

     grouping transport-params-grouping
       +---- host-key
       |  +---- host-key-alg*   identityref
       +---- key-exchange
       |  +---- key-exchange-alg*   identityref
       +---- encryption
       |  +---- encryption-alg*   identityref
       +---- mac
          +---- mac-alg*   identityref

5.2.  Example Usage

   This section shows how it would appear if the transport-params-
   grouping were populated with some data.

   <!-- hypothetical example, as groupings don't have instance data -->
   <transport-params
     xmlns="urn:ietf:params:xml:ns:yang:ietf-ssh-common"
     xmlns:algs="urn:ietf:params:xml:ns:yang:ietf-ssh-common">

     <host-key>
       <host-key-alg>algs:x509v3-rsa2048-sha256</host-key-alg>
       <host-key-alg>algs:ssh-rsa</host-key-alg>
     </host-key>
     <key-exchange>
       <key-exchange-alg>
         algs:diffie-hellman-group-exchange-sha256
       </key-exchange-alg>
     </key-exchange>
     <encryption>
       <encryption-alg>algs:aes256-ctr</encryption-alg>
       <encryption-alg>algs:aes192-ctr</encryption-alg>
       <encryption-alg>algs:aes128-ctr</encryption-alg>
       <encryption-alg>algs:aes256-cbc</encryption-alg>
       <encryption-alg>algs:aes192-cbc</encryption-alg>
       <encryption-alg>algs:aes128-cbc</encryption-alg>
     </encryption>
     <mac>
       <mac-alg>algs:hmac-sha2-256</mac-alg>
       <mac-alg>algs:hmac-sha2-512</mac-alg>



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     </mac>
     <compression>
       <compression-alg>algs:none</compression-alg>
     </compression>

     <host-key>
       <host-key-alg>sshcmn:x509v3-rsa2048-sha256</host-key-alg>
       <host-key-alg>sshcmn:ssh-rsa</host-key-alg>
     </host-key>
     <key-exchange>
       <key-exchange-alg>
         sshcmn:diffie-hellman-group-exchange-sha256
       </key-exchange-alg>
     </key-exchange>
     <encryption>
       <encryption-alg>sshcmn:aes256-ctr</encryption-alg>
       <encryption-alg>sshcmn:aes192-ctr</encryption-alg>
       <encryption-alg>sshcmn:aes128-ctr</encryption-alg>
       <encryption-alg>sshcmn:aes256-cbc</encryption-alg>
       <encryption-alg>sshcmn:aes192-cbc</encryption-alg>
       <encryption-alg>sshcmn:aes128-cbc</encryption-alg>
     </encryption>
     <mac>
       <mac-alg>sshcmn:hmac-sha2-256</mac-alg>
       <mac-alg>sshcmn:hmac-sha2-512</mac-alg>
     </mac>
   >>>>>>> f4046cc2ee2316422f0a1e2589efdc91c1d491ce

   </transport-params>

5.3.  YANG Module

   This YANG module has normative references to [RFC4344], [RFC4419],
   [RFC5656], and [RFC6668].

   <CODE BEGINS> file "ietf-ssh-common@2017-10-30.yang"
   module ietf-ssh-common {
     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-ssh-common";
     prefix "sshcmn";

     organization
      "IETF NETCONF (Network Configuration) Working Group";

     contact
      "WG Web:   <http://tools.ietf.org/wg/netconf/>
       WG List:  <mailto:netconf@ietf.org>



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       Author:   Kent Watsen
                 <mailto:kwatsen@juniper.net>

       Author:   Gary Wu
                 <mailto:garywu@cisco.com>";

     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 "2017-10-30" {
       description
        "Initial version";
       reference
        "RFC XXXX: YANG Groupings for SSH Clients and SSH Servers";
     }

     // features

     feature ssh-ecc {
       description
         "Elliptic Curve Cryptography is supported for SSH.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     feature ssh-x509-certs {
       description
         "X.509v3 certificates are supported for SSH as per RFC 6187.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }




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     feature ssh-dh-group-exchange {
       description
         "Diffie-Hellman Group Exchange is supported for SSH.";
       reference
         "RFC 4419: Diffie-Hellman Group Exchange for the
                    Secure Shell (SSH) Transport Layer Protocol";
     }

     feature ssh-ctr {
       description
         "SDCTR encryption mode is supported for SSH.";
       reference
         "RFC 4344: The Secure Shell (SSH) Transport Layer
                    Encryption Modes";
     }

     feature ssh-sha2 {
       description
         "The SHA2 family of cryptographic hash functions is supported
          for SSH.";
       reference
         "FIPS PUB 180-4: Secure Hash Standard (SHS)";
     }

     // identities

     identity public-key-alg-base {
       description
         "Base identity used to identify public key algorithms.";
     }

     identity ssh-dss {
       base public-key-alg-base;
       description
         "Digital Signature Algorithm using SHA-1 as the hashing
          algorithm.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity ssh-rsa {
       base public-key-alg-base;
       description
         "RSASSA-PKCS1-v1_5 signature scheme using SHA-1 as the hashing
          algorithm.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }



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     identity ecdsa-sha2-nistp256 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp256 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity ecdsa-sha2-nistp384 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp384 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity ecdsa-sha2-nistp521 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp521 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity x509v3-ssh-rsa {
       base public-key-alg-base;
       if-feature ssh-x509-certs;
       description
         "RSASSA-PKCS1-v1_5 signature scheme using a public key stored
          in an X.509v3 certificate and using SHA-1 as the hashing
          algorithm.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }

     identity x509v3-rsa2048-sha256 {
       base public-key-alg-base;
       if-feature "ssh-x509-certs and ssh-sha2";



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       description
         "RSASSA-PKCS1-v1_5 signature scheme using a public key stored
          in an X.509v3 certificate and using SHA-256 as the hashing
          algorithm.  RSA keys conveyed using this format MUST have a
          modulus of at least 2048 bits.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }

     identity x509v3-ecdsa-sha2-nistp256 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp256 curve with a public key stored in an X.509v3
          certificate and using the SHA2 family of hashing algorithms.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }

     identity x509v3-ecdsa-sha2-nistp384 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp384 curve with a public key stored in an X.509v3
          certificate and using the SHA2 family of hashing algorithms.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }

     identity x509v3-ecdsa-sha2-nistp521 {
       base public-key-alg-base;
       if-feature "ssh-ecc and ssh-x509-certs and ssh-sha2";
       description
         "Elliptic Curve Digital Signature Algorithm (ECDSA) using the
          nistp521 curve with a public key stored in an X.509v3
          certificate and using the SHA2 family of hashing algorithms.";
       reference
         "RFC 6187: X.509v3 Certificates for Secure Shell
                    Authentication";
     }

     identity key-exchange-alg-base {
       description



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         "Base identity used to identify key exchange algorithms.";
     }

     identity diffie-hellman-group14-sha1 {
       base key-exchange-alg-base;
       description
         "Diffie-Hellman key exchange with SHA-1 as HASH and
          Oakley Group 14 (2048-bit MODP Group).";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity diffie-hellman-group-exchange-sha1 {
       base key-exchange-alg-base;
       if-feature ssh-dh-group-exchange;
       description
         "Diffie-Hellman Group and Key Exchange with SHA-1 as HASH.";
       reference
         "RFC 4419: Diffie-Hellman Group Exchange for the
                    Secure Shell (SSH) Transport Layer Protocol";
     }

     identity diffie-hellman-group-exchange-sha256 {
       base key-exchange-alg-base;
       if-feature "ssh-dh-group-exchange and ssh-sha2";
       description
         "Diffie-Hellman Group and Key Exchange with SHA-256 as HASH.";
       reference
         "RFC 4419: Diffie-Hellman Group Exchange for the
                    Secure Shell (SSH) Transport Layer Protocol";
     }

     identity ecdh-sha2-nistp256 {
       base key-exchange-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the
          nistp256 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity ecdh-sha2-nistp384 {
       base key-exchange-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the



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          nistp384 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity ecdh-sha2-nistp521 {
       base key-exchange-alg-base;
       if-feature "ssh-ecc and ssh-sha2";
       description
         "Elliptic Curve Diffie-Hellman (ECDH) key exchange using the
          nistp521 curve and the SHA2 family of hashing algorithms.";
       reference
         "RFC 5656: Elliptic Curve Algorithm Integration in the
                    Secure Shell Transport Layer";
     }

     identity encryption-alg-base {
       description
         "Base identity used to identify encryption algorithms.";
     }

     identity triple-des-cbc {
       base encryption-alg-base;
       description
         "Three-key 3DES in CBC mode.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity aes128-cbc {
       base encryption-alg-base;
       description
        "AES in CBC mode, with a 128-bit key.";
       reference
        "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity aes192-cbc {
       base encryption-alg-base;
       description
         "AES in CBC mode, with a 192-bit key.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity aes256-cbc {
       base encryption-alg-base;



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       description
         "AES in CBC mode, with a 256-bit key.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
     }

     identity aes128-ctr {
       base encryption-alg-base;
       if-feature ssh-ctr;
       description
         "AES in SDCTR mode, with 128-bit key.";
       reference
         "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
                    Modes";
     }

     identity aes192-ctr {
       base encryption-alg-base;
       if-feature ssh-ctr;
       description
         "AES in SDCTR mode, with 192-bit key.";
       reference
         "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
                    Modes";
     }

     identity aes256-ctr {
       base encryption-alg-base;
       if-feature ssh-ctr;
       description
         "AES in SDCTR mode, with 256-bit key.";
       reference
         "RFC 4344: The Secure Shell (SSH) Transport Layer Encryption
            Modes";
     }

     identity mac-alg-base {
       description
         "Base identity used to identify message authentication
          code (MAC) algorithms.";
     }

     identity hmac-sha1 {
       base mac-alg-base;
       description
         "HMAC-SHA1";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";



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     }

     identity hmac-sha2-256 {
       base mac-alg-base;
       if-feature "ssh-sha2";
       description
         "HMAC-SHA2-256";
       reference
         "RFC 6668: SHA-2 Data Integrity Verification for the
                    Secure Shell (SSH) Transport Layer Protocol";
     }

     identity hmac-sha2-512 {
       base mac-alg-base;
       if-feature "ssh-sha2";
       description
         "HMAC-SHA2-512";
       reference
         "RFC 6668: SHA-2 Data Integrity Verification for the
                    Secure Shell (SSH) Transport Layer Protocol";
     }

     // groupings

     grouping transport-params-grouping {
       description
         "A reusable grouping for SSH transport parameters.";
       reference
         "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
       container host-key {
         description
           "Parameters regarding host key.";
         leaf-list host-key-alg {
           type identityref {
             base public-key-alg-base;
           }
           ordered-by user;
           description
             "Acceptable host key algorithms in order of descending
              preference.

              If this leaf-list is not configured (has zero elements)
              the acceptable host key algorithms are implementation-
              defined.";
         }
       }
       container key-exchange {
         description



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           "Parameters regarding key exchange.";
         leaf-list key-exchange-alg {
           type identityref {
             base key-exchange-alg-base;
           }
           ordered-by user;
           description
             "Acceptable key exchange algorithms in order of descending
              preference.

              If this leaf-list is not configured (has zero elements)
              the acceptable key exchange algorithms are implementation-
              defined.";
         }
       }
       container encryption {
         description
           "Parameters regarding encryption.";
         leaf-list encryption-alg {
           type identityref {
             base encryption-alg-base;
           }
           ordered-by user;
           description
             "Acceptable encryption algorithms in order of descending
              preference.

              If this leaf-list is not configured (has zero elements)
              the acceptable encryption algorithms are implementation-
              defined.";
         }
       }
       container mac {
         description
           "Parameters regarding message authentication code (MAC).";
         leaf-list mac-alg {
           type identityref {
             base mac-alg-base;
           }
           ordered-by user;
           description
             "Acceptable MAC algorithms in order of descending
              preference.

              If this leaf-list is not configured (has zero elements)
              the acceptable MAC algorithms are implementation-
              defined.";
         }



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       }

     } // transport-params-grouping

   }
   <CODE ENDS>

6.  Security Considerations

   The YANG modules defined in this document are designed to be accessed
   via YANG based management protocols, such as NETCONF [RFC6241] and
   RESTCONF [RFC8040].  Both of these protocols have mandatory-to-
   implement secure transport layers (e.g., SSH, TLS) with mutual
   authentication.

   The NETCONF access control model (NACM) [RFC6536] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

   Since the modules defined in this document define only groupings,
   these considerations are primarily for the designers of other modules
   that use these groupings.

   There are a number of data nodes defined in the YANG modules that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

      /: The entire data tree defined by all the modules defined in this
         draft are sensitive to write operations.  For instance, the
         addition or removal of references to keys, certificates,
         trusted anchors, etc., can dramatically alter the implemented
         security policy.  However, no NACM annotations are applied as
         the data SHOULD be editable by users other than a designated
         'recovery session'.

   Some of the readable data nodes in the YANG modules may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

      /client-auth/password:  This node in the 'ietf-ssh-client' module
         is additionally sensitive to read operations such that, in
         normal use cases, it should never be returned to a client.  The



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         only time this node should be returned 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

7.  IANA Considerations

7.1.  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:

      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.

7.2.  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:















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      name:         ietf-ssh-client
      namespace:    urn:ietf:params:xml:ns:yang:ietf-ssh-client
      prefix:       sshc
      reference:    RFC XXXX

      name:         ietf-ssh-server
      namespace:    urn:ietf:params:xml:ns:yang:ietf-ssh-server
      prefix:       sshs
      reference:    RFC XXXX

      name:         ietf-ssh-common
      namespace:    urn:ietf:params:xml:ns:yang:ietf-ssh-common
      prefix:       sshcmn
      reference:    RFC XXXX

8.  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.

9.  References

9.1.  Normative References

   [I-D.ietf-netconf-keystore]
              Watsen, K., "Keystore Model", draft-ietf-netconf-
              keystore-02 (work in progress), June 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4344]  Bellare, M., Kohno, T., and C. Namprempre, "The Secure
              Shell (SSH) Transport Layer Encryption Modes", RFC 4344,
              DOI 10.17487/RFC4344, January 2006,
              <https://www.rfc-editor.org/info/rfc4344>.

   [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,
              <https://www.rfc-editor.org/info/rfc4419>.





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   [RFC5656]  Stebila, D. and J. Green, "Elliptic Curve Algorithm
              Integration in the Secure Shell Transport Layer",
              RFC 5656, DOI 10.17487/RFC5656, December 2009,
              <https://www.rfc-editor.org/info/rfc5656>.

   [RFC6187]  Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
              Shell Authentication", RFC 6187, DOI 10.17487/RFC6187,
              March 2011, <https://www.rfc-editor.org/info/rfc6187>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

   [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,
              <https://www.rfc-editor.org/info/rfc6668>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [I-D.ietf-netmod-yang-tree-diagrams]
              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
              ietf-netmod-yang-tree-diagrams-02 (work in progress),
              October 2017.

   [OPENSSH]  "OpenSSH", 2016, <http://www.openssh.com>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.




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   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <https://www.rfc-editor.org/info/rfc4253>.

   [RFC4254]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Connection Protocol", RFC 4254, DOI 10.17487/RFC4254,
              January 2006, <https://www.rfc-editor.org/info/rfc4254>.

   [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,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8071]  Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
              RFC 8071, DOI 10.17487/RFC8071, February 2017,
              <https://www.rfc-editor.org/info/rfc8071>.



























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Appendix A.  Change Log

A.1.  00 to 01

   o  Noted that '0.0.0.0' and '::' might have special meanings.

   o  Renamed "keychain" to "keystore".

A.2.  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.3.  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'.

A.4.  03 to 04

   o  Change title to "YANG Groupings for SSH Clients and SSH Servers"

   o  Added reference to RFC 6668

   o  Added RFC 8174 to Requirements Language Section.

   o  Enhanced description statement for ietf-ssh-server's "trusted-ca-
      certs" leaf.

   o  Added mandatory true to ietf-ssh-client's "client-auth" 'choice'
      statement.

   o  Changed the YANG prefix for module ietf-ssh-common from 'sshcom'
      to 'sshcmn'.

   o  Removed the compression algorithms as they are not commonly
      configurable in vendors' implementations.



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   o  Updating descriptions in transport-params-grouping and the
      servers's usage of it.

   o  Now tree diagrams reference ietf-netmod-yang-tree-diagrams

   o  Updated YANG to use typedefs around leafrefs to common keystore
      paths

   o  Now inlines key and certificates (no longer a leafref to keystore)

A.5.  04 to 05

   o  Merged changes from co-author.

Authors' Addresses

   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net


   Gary Wu
   Cisco Systems

   EMail: garywu@cisco.com

























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