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

YANG Data Model for a "Keystore" Mechanism
draft-ietf-netconf-keystore-04

Abstract

This document defines a YANG module called a "keystore", containing pinned certificates and pinned SSH host-keys. The module also defines a grouping for configuring public key pairs and a grouping for configuring certificates. The module also defines a notification that a system can use when one of its configured certificates is about to expire.

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.

Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements:

Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement:

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

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

This document defines a YANG [RFC7950] module for a system-level mechanism, herein called a "keystore". The keystore provides a centralized location for security sensitive data, as described below.

This module has the following characteristics:

Special consideration has been given for systems that have Trusted Protection Modules (TPMs). These systems are unique in that the TPM must be directed to generate new keys (it is not possible to load a key into a TPM) and it is not possible to backup/restore the TPM's private keys as configuration.

It is not required that a system has an operating system level keystore utility to implement this module.

1.1. Requirements Language

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

2. Tree Diagram

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

module: ietf-keystore
    +--rw keystore
       +--rw pinned-certificates* [name]
       |  +--rw name                  string
       |  +--rw description?          string
       |  +--rw pinned-certificate* [name]
       |     +--rw name    string
       |     +--rw data    binary
       +--rw pinned-host-keys* [name]
          +--rw name               string
          +--rw description?       string
          +--rw pinned-host-key* [name]
             +--rw name    string
             +--rw data    binary

  notifications:
    +---n certificate-expiration
       +--ro certificate        instance-identifier
       +--ro expiration-date    yang:date-and-time

  grouping certificate-grouping
    +---- 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
  grouping private-key-grouping
    +---- algorithm?              identityref
    +---- private-key?            union
    +---- public-key?             binary
    +---x generate-private-key
       +---w input
          +---w algorithm    identityref

3. Example Usage

The following example illustrates what a configured keystore might look like.

<keystore xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore">

  <!-- Manufacturer's trust root CA certs -->
  <pinned-certificates>
    <name>manufacturers-root-ca-certs</name>
    <description>
      Certificates built into the device for authenticating
      manufacturer-signed objects, such as TLS server certificates,
      vouchers, etc..  Note, though listed here, these are not
      configurable; any attempt to do so will be denied.
    </description>
    <pinned-certificate>
      <name>Manufacturer Root CA cert 1</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
    <pinned-certificate>
      <name>Manufacturer Root CA cert 2</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
  </pinned-certificates>

  <!-- pinned netconf/restconf client certificates -->
  <pinned-certificates>
    <name>explicitly-trusted-client-certs</name>
    <description>
      Specific client authentication certificates for explicitly
      trusted clients.  These are needed for client certificates
      that are not signed by a pinned CA.
    </description>
    <pinned-certificate>
      <name>George Jetson</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
  </pinned-certificates>

  <!-- pinned netconf/restconf server certificates -->
  <pinned-certificates>
    <name>explicitly-trusted-server-certs</name>
    <description>
      Specific server authentication certificates for explicitly
      trusted servers.  These are needed for server certificates
      that are not signed by a pinned CA.
    </description>
    <pinned-certificate>
      <name>Fred Flintstone</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
  </pinned-certificates>

  <!-- trust anchors (CA certs) for authenticating clients -->
  <pinned-certificates>
    <name>deployment-specific-ca-certs</name>
    <description>
      Trust anchors (i.e. CA certs) that are used to authenticate 
      client connections.  Clients are authenticated if their
      certificate has a chain of trust to one of these configured
      CA certificates.
    </description>
    <pinned-certificate>
      <name>ca.example.com</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
  </pinned-certificates>

  <!-- trust anchors for random HTTPS servers on Internet -->
  <pinned-certificates>
    <name>common-ca-certs</name>
    <description>
      Trusted certificates to authenticate common HTTPS servers.
      These certificates are similar to those that might be
      shipped with a web browser.
    </description>
    <pinned-certificate>
      <name>ex-certificate-authority</name>
      <data>base64encodedvalue==</data>
    </pinned-certificate>
  </pinned-certificates>

  <!-- pinned SSH host keys -->
  <pinned-host-keys>
    <name>explicitly-trusted-ssh-host-keys</name>
    <description>
      Trusted SSH host keys used to authenticate SSH servers.
      These host keys would be analogous to those stored in
      a known_hosts file in OpenSSH.
    </description>
    <pinned-host-key>
      <name>corp-fw1</name>
      <data>base64encodedvalue==</data>
    </pinned-host-key>
  </pinned-host-keys>

</keystore>

The following example illustrates the "certificate-expiration" notification in use with the NETCONF protocol.

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

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2016-07-08T00:01:00Z</eventTime>
  <certificate-expiration 
    xmlns="urn:ietf:params:xml:ns:yang:ietf-keystore">
    <certificate xmlns:ks="urn:ietf:params:xml:ns:yang:ietf-keystore\
">
      /ks:keystore/ks:keys/ks:key[ks:name='ex-rsa-key']/ks:certifica\
tes/ks:certificate[ks:name='ex-rsa-cert']
    </certificate>
    <expiration-date>2016-08-08T14:18:53-05:00</expiration-date>
  </certificate-expiration>
</notification>

The following example module has been constructed to illustrate the groupings defined in the "ietf-keystore" module.

module ex-keystore-usage {
  yang-version 1.1;

  namespace "http://example.com/ns/example-keystore-usage";
  prefix "eku";

  import ietf-keystore {
    prefix ks;
    reference 
      "RFC VVVV: YANG Data Model for a 'Keystore' Mechanism";
  }

  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>";

  description
   "This module uses the groupings defines the keystore draft
    for illustration.";

  revision "YYYY-MM-DD" {
    description
     "Initial version";
  }

  container key {
    uses ks:private-key-grouping;
    uses ks:certificate-grouping;
    description
      "A container of certificates, and an action to generate
       a certificate signing request.";
  }
}

The following example illustrates what a configured key might look like. This example uses the "ex-keystore-usage" module above.

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

<key xmlns="http://example.com/ns/example-keystore-usage">
  <algorithm xmlns:ks="urn:ietf:params:xml:ns:yang:ietf-keystore">ks:\
secp521r1</algorithm>
  <private-key>base64encodedvalue==</private-key>
  <public-key>base64encodedvalue==</public-key>
  <certificates>
    <certificate>
      <name>domain certificate</name>
      <value>base64encodedvalue==</value>
    </certificate>
  </certificates>
 </key>

The following example illustrates the "generate-certificate-signing-request" action in use with the NETCONF protocol. This example uses the "ex-keystore-usage" module above.

REQUEST
-------
<rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <action xmlns="urn:ietf:params:xml:ns:yang:1">
    <key xmlns="http://example.com/ns/example-keystore-usage">
      <generate-certificate-signing-request>
        <subject>base64encodedvalue==</subject>
        <attributes>base64encodedvalue==</attributes>
      </generate-certificate-signing-request>
    </key>
  </action>
</rpc>

RESPONSE
--------
<rpc-reply message-id="101"
   xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <certificate-signing-request
     xmlns="http://example.com/ns/example-keystore-usage">
     base64encodedvalue==
   </certificate-signing-request>
</rpc-reply>

The following example illustrates the "generate-private-key" action in use with the NETCONF protocol. This example uses the "ex-keystore-usage" module above.

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

<rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0\
">
  <action xmlns="urn:ietf:params:xml:ns:yang:1">
    <key xmlns="http://example.com/ns/example-keystore-usage">
      <generate-private-key>
        <algorithm xmlns:ks="urn:ietf:params:xml:ns:yang:ietf-keysto\
re">ks:secp521r1</algorithm>
      </generate-private-key>
    </key>
  </action>
</rpc>

RESPONSE
--------
<rpc-reply message-id="101"
   xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <ok/>
</rpc-reply>

4. YANG Module

This YANG module imports modules defined in [RFC6536] and [RFC6991]. This module uses data types defined in [RFC2315], [RFC2986], [RFC3447], [RFC4253], [RFC5280], [RFC5915], and [ITU.X690.1994]. This module uses algorithms defined in [RFC3447] and [RFC5480].

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

  namespace "urn:ietf:params:xml:ns:yang:ietf-keystore";
  prefix "ks";

  import ietf-yang-types {
    prefix yang;
    reference 
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 6536: Network Configuration Protocol (NETCONF) Access
       Control 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>";


  description
   "This module defines a keystore to centralize management
    of security credentials.

    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 VVVV; see
    the RFC itself for full legal notices.";

  revision "2017-10-30" {
    description
     "Initial version";
    reference
     "RFC VVVV: YANG Data Model for a 'Keystore' Mechanism";
  }

  // Identities

  identity key-algorithm {
    description
      "Base identity from which all key-algorithms are derived.";
  }

  identity rsa1024 {
    base key-algorithm;
    description
      "The RSA algorithm using a 1024-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity rsa2048 {
    base key-algorithm;
    description
      "The RSA algorithm using a 2048-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity rsa3072 {
    base key-algorithm;
    description
      "The RSA algorithm using a 3072-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity rsa4096 {
    base key-algorithm;
    description
      "The RSA algorithm using a 4096-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity rsa7680 {
    base key-algorithm;
    description
      "The RSA algorithm using a 7680-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity rsa15360 {
    base key-algorithm;
    description
      "The RSA algorithm using a 15360-bit key.";
    reference
      "RFC3447: Public-Key Cryptography Standards (PKCS) #1:
                RSA Cryptography Specifications Version 2.1.";
  }

  identity secp192r1 {
    base key-algorithm;
    description
      "The secp192r1 algorithm.";
    reference
      "RFC5480: 
         Elliptic Curve Cryptography Subject Public Key Information.";
  }

  identity secp256r1 {
    base key-algorithm;
    description
      "The secp256r1 algorithm.";
    reference
      "RFC5480: 
         Elliptic Curve Cryptography Subject Public Key Information.";
  }

  identity secp384r1 {
    base key-algorithm;
    description
      "The secp384r1 algorithm.";
    reference
      "RFC5480: 
         Elliptic Curve Cryptography Subject Public Key Information.";
  }

  identity secp521r1 {
    base key-algorithm;
    description
      "The secp521r1 algorithm.";
    reference
      "RFC5480: 
         Elliptic Curve Cryptography Subject Public Key Information.";
  }


  // typedefs 

  typedef pinned-certificates {
    type leafref {
      path "/ks:keystore/ks:pinned-certificates/ks:name";
    }
    description
      "This typedef enables importing modules to easily define a
       reference to pinned-certificates.  Use of this type also
       impacts the YANG tree diagram output.";
    reference
      "I-D.ietf-netmod-yang-tree-diagrams: YANG Tree Diagrams";
  }

  typedef pinned-host-keys {
    type leafref {
      path "/ks:keystore/ks:pinned-host-keys/ks:name";
    }
    description
      "This typedef enables importing modules to easily define a
       reference to pinned-host-keys.  Use of this type also
       impacts the YANG tree diagram output.";
    reference
      "I-D.ietf-netmod-yang-tree-diagrams: YANG Tree Diagrams";
  }


  // groupings

  grouping private-key-grouping {
    description
      "A private/public key pair, and an action to request the
       system to generate a private key.";
    leaf algorithm {
      type identityref {
        base "key-algorithm";
      }
      description
        "Identifies the key's algorithm.  More specifically, this
         leaf specifies how the 'private-key' and 'public-key'
         binary leafs are encoded.";
    }
    leaf private-key {
      nacm:default-deny-all;
      type union {
        type binary;
        type enumeration {
          enum "hardware-protected" {
            description
             "The private key is inaccessible due to being
              protected by a cryptographic hardware module
              (e.g., a TPM).";
          }
        }
      }
      must "../algorithm";
      description
        "A binary that contains the value of the private key.  The
         interpretation of the content is defined by the key
         algorithm.  For example, a DSA key is an integer, an RSA
         key is represented as RSAPrivateKey as defined in 
         [RFC3447], and an Elliptic Curve Cryptography (ECC) key
         is represented as ECPrivateKey as defined in [RFC5915]";
      reference
        "RFC 3447: Public-Key Cryptography Standards (PKCS) #1:
                   RSA Cryptography Specifications Version 2.1.
         RFC 5915: Elliptic Curve Private Key Structure.";
    }
    leaf public-key {
      type binary;
      must "../algorithm";
      must "../private-key";
      description
        "A binary that contains the value of the public key.  The
         interpretation of the content is defined by the key
         algorithm.  For example, a DSA key is an integer, an RSA
         key is represented as RSAPublicKey as defined in 
         [RFC3447], and an Elliptic Curve Cryptography (ECC) key
         is represented using the 'publicKey' described in 
         [RFC5915]";
      reference
        "RFC 3447: Public-Key Cryptography Standards (PKCS) #1:
                   RSA Cryptography Specifications Version 2.1.
         RFC 5915: Elliptic Curve Private Key Structure.";
    }
    action generate-private-key {
      description
        "Requests the device to generate a private key using the
         specified key algorithm.  This action is primarily to
         support cryptographic processors that must generate
         the private key themselves.  The resulting key is
         considered operational state and hence only present
         in the <operational>.";
      input {
        leaf algorithm {
          type identityref {
            base "key-algorithm";
          }
          mandatory true;
          description
            "The algorithm to be used when generating the key.";
        }
      }
    } // end generate-private-key
  }

  grouping certificate-grouping {
    description
      "A container of certificates, and an action to generate
       a certificate signing request.";
    container certificates {
      description
        "Certificates associated with this key.  More than one
         certificate supports, for instance, a TPM-protected
         key that has both IDevID and LDevID certificates
         associated.";
      list certificate {
        key name;
        description
          "A certificate for this private key.";
        leaf name {
          type string;
          description
            "An arbitrary name for the certificate.";
        }
        leaf value {
          type binary;
          description
           "A PKCS #7 SignedData structure, as specified by 
            Section 9.1 in RFC 2315, containing just certificates
            (no content, signatures, or CRLs), encoded using ASN.1
            distinguished encoding rules (DER), as specified in
            ITU-T X.690.
    
            This structure contains the certificate itself as well
            as any intermediate certificates leading up to a trust
            anchor certificate.  The trust anchor certificate MAY
            be included as well.";
          reference
            "RFC 2315:
               PKCS #7: Cryptographic Message Syntax Version 1.5.
             ITU-T X.690:
               Information technology – ASN.1 encoding rules:
               Specification of Basic Encoding Rules (BER),
               Canonical Encoding Rules (CER) and Distinguished
               Encoding Rules (DER).";
        }
      }
    }
    action generate-certificate-signing-request {
      description
        "Generates a certificate signing request structure for
         the associated private key using the passed subject and
         attribute values.  The specified assertions need to be
         appropriate for the certificate's use.  For example,
         an entity certificate for a TLS server SHOULD have
         values that enable clients to satisfy RFC 6125
         processing.";
      input {
        leaf subject {
          type binary;
          mandatory true;
          description
            "The 'subject' field from the CertificationRequestInfo
             structure as specified by RFC 2986, Section 4.1 encoded
             using the ASN.1 distinguished encoding rules (DER), as
             specified in ITU-T X.690.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
               Version 1.7.
             ITU-T X.690:
                Information technology – ASN.1 encoding rules:
                Specification of Basic Encoding Rules (BER), 
                Canonical Encoding Rules (CER) and Distinguished
                Encoding Rules (DER).";
        } 
        leaf attributes {
          type binary;
          description 
           "The 'attributes' field from the CertificationRequestInfo
            structure as specified by RFC 2986, Section 4.1 encoded
            using the ASN.1 distinguished encoding rules (DER), as
            specified in ITU-T X.690.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
               Version 1.7.
             ITU-T X.690:
                Information technology – ASN.1 encoding rules:
                Specification of Basic Encoding Rules (BER), 
                Canonical Encoding Rules (CER) and Distinguished
                Encoding Rules (DER).";
        }
      }
      output {
        leaf certificate-signing-request {
          type binary;
          mandatory true;
          description
            "A CertificationRequest structure as specified by RFC
             2986, Section 4.1 encoded using the ASN.1 distinguished
             encoding rules (DER), as specified in ITU-T X.690.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
               Version 1.7.
             ITU-T X.690:
                Information technology – ASN.1 encoding rules:
                Specification of Basic Encoding Rules (BER), 
                Canonical Encoding Rules (CER) and Distinguished
                Encoding Rules (DER).";

        }
      }
    }
  }


  // protocol accessible nodes

  container keystore {
    nacm:default-deny-write;
    description
      "The keystore contains X.509 certificates and SSH host keys.";

    list pinned-certificates {
      key name;
      description
        "A list of pinned certificates.  These certificates can be
         used by a server to authenticate clients, or by clients to
         authenticate servers.   Each list of pinned certificates
         SHOULD be specific to a purpose, as the list as a whole
         may be referenced by other modules.  For instance, a
         NETCONF server's configuration might use a specific list
         of pinned certificates for when authenticating NETCONF 
         client connections.";
      leaf name {
        type string;
        description
          "An arbitrary name for this list of pinned certificates.";
      }
      leaf description {
        type string;
        description
          "An arbitrary description for this list of pinned
           certificates.";
      }
      list pinned-certificate {
        key name;
        description
          "A pinned certificate.";
        leaf name {
          type string;
          description
            "An arbitrary name for this pinned certificate. The
             name must be unique across all lists of pinned 
             certificates (not just this list) so that leafrefs
             from another module can resolve to unique values.";
        }
        leaf data { 
          type binary;
          mandatory true;
          description
            "An X.509 v3 certificate structure as specified by RFC
             5280, Section 4 encoded using the ASN.1 distinguished
             encoding rules (DER), as specified in ITU-T X.690.";
          reference
            "RFC 5280:
               Internet X.509 Public Key Infrastructure Certificate
               and Certificate Revocation List (CRL) Profile.
             ITU-T X.690:
                Information technology – ASN.1 encoding rules:
                Specification of Basic Encoding Rules (BER), 
                Canonical Encoding Rules (CER) and Distinguished
                Encoding Rules (DER).";
        }
      }
    }

    list pinned-host-keys {
      key name;
      description
        "A list of pinned host keys.  These pinned host-keys can
         be used by clients to authenticate SSH servers.  Each
         list of pinned host keys SHOULD be specific to a purpose,
         so the list as a whole may be referenced by other modules.
         For instance, a NETCONF client's configuration might
         point to a specific list of pinned host keys for when 
         authenticating specific SSH servers.";
      leaf name {
        type string;
        description
          "An arbitrary name for this list of pinned SSH host keys.";
      }
      leaf description {
        type string;
        description
          "An arbitrary description for this list of pinned SSH host
           keys.";
      }
      list pinned-host-key {
        key name;
        description
          "A pinned host key.";
        leaf name {
          type string;
          description
            "An arbitrary name for this pinned host-key. Must be
             unique across all lists of pinned host-keys (not just
             this list) so that a leafref to it from another module
             can resolve to unique values.";
        }
        leaf data {
          type binary;
          mandatory true;
          description
            "The binary public key data for this SSH key, as
             specified by RFC 4253, Section 6.6, i.e.:

               string    certificate or public key format
                         identifier
               byte[n]   key/certificate data.";
          reference
            "RFC 4253: The Secure Shell (SSH) Transport Layer
                       Protocol";
        }
      }
    }
  }

  notification certificate-expiration {
    description
      "A notification indicating that a configured certificate is 
       either about to expire or has already expired.  When to send
       notifications is an implementation specific decision, but
       it is RECOMMENDED that a notification be sent once a month
       for 3 months, then once a week for four weeks, and then once
       a day thereafter.";
    leaf certificate {
      type instance-identifier;
      mandatory true;
      description
        "Identifies which certificate is expiring or is expired.";
    }
    leaf expiration-date {
      type yang:date-and-time;
      mandatory true;
      description
        "Identifies the expiration date on the certificate.";
    }
  }

}
<CODE ENDS>

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) 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 keys, certificates, trusted anchors, etc., can dramatically alter the implemented security policy. This being the case, the top-level node in this module is marked with the NACM value 'default-deny-write'.
/keystore/keys/key/private-key:
When writing this node, implementations MUST ensure that the strength of the key being configured is not greater than the strength of the underlying secure transport connection over which it is communicated. Implementations SHOULD fail the write-request if ever the strength of the private key is greater then the strength of the underlying transport, and alert the client that the strength of the key may have been compromised. Additionally, when deleting this node, implementations SHOULD automatically (without explicit request) zeroize these keys in the most secure manner available, so as to prevent the remnants of their persisted storage locations from being analyzed in any meaningful way.

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:

/keystore/keys/key/private-key:
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 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:

generate-certificate-signing-request:
For this action, it is RECOMMENDED that implementations assert channel binding [RFC5056], so as to ensure that the application layer that sent the request is the same as the device authenticated when the secure transport layer was established.

6. IANA Considerations

6.1. The IETF XML Registry

This document registers one URI in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested:

   URI: urn:ietf:params:xml:ns:yang:ietf-keystore
   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 one YANG module in the YANG Module Names registry [RFC6020]. Following the format in [RFC6020], the the following registration is requested:

   name:         ietf-keystore
   namespace:    urn:ietf:params:xml:ns:yang:ietf-keystore
   prefix:       ks
   reference:    RFC VVVV

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, Balázs Kovács, David Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch, Juergen Schoenwaelder; Phil Shafer, Sean Turner, and Bert Wijnen.

8. References

8.1. Normative References

[ITU.X690.1994] International Telecommunications Union, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, November 2000.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February 2003.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, January 2006.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R. and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R. and T. Polk, "Elliptic Curve Cryptography Subject Public Key Information", RFC 5480, DOI 10.17487/RFC5480, March 2009.
[RFC5915] Turner, S. and D. Brown, "Elliptic Curve Private Key Structure", RFC 5915, DOI 10.17487/RFC5915, June 2010.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012.
[RFC6991] Schoenwaelder, J., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.

8.2. Informative References

[I-D.ietf-netmod-yang-tree-diagrams] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", Internet-Draft draft-ietf-netmod-yang-tree-diagrams-02, October 2017.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, DOI 10.17487/RFC4211, September 2005.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007.
[RFC5914] Housley, R., Ashmore, S. and C. Wallace, "Trust Anchor Format", RFC 5914, DOI 10.17487/RFC5914, June 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC8040] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[Std-802.1AR-2009] IEEE SA-Standards Board, "IEEE Standard for Local and metropolitan area networks - Secure Device Identity", December 2009.

Appendix A. Change Log

A.1. 00 to 01

A.2. 01 to 02

A.3. 02 to 03

A.4. 03 to 04

Author's Address

Kent Watsen Juniper Networks EMail: kwatsen@juniper.net