Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request
draft-ietf-netconf-sztp-csr-08

Document Type Active Internet-Draft (netconf WG)
Authors Kent Watsen  , Russ Housley  , Sean Turner 
Last updated 2021-08-24
Replaces draft-kwatsen-netconf-sztp-csr
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NETCONF Working Group                                          K. Watsen
Internet-Draft                                           Watsen Networks
Updates: 8572 (if approved)                                   R. Housley
Intended status: Standards Track                     Vigil Security, LLC
Expires: 25 February 2022                                      S. Turner
                                                                   sn3rd
                                                          24 August 2021

  Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch
               Provisioning (SZTP) Bootstrapping Request
                     draft-ietf-netconf-sztp-csr-08

Abstract

   This draft extends the "get-bootstrapping-data" RPC defined in RFC
   8572 to include an optional certificate signing request (CSR),
   enabling a bootstrapping device to additionally obtain an identity
   certificate (e.g., an LDevID, from IEEE 802.1AR) as part of the
   "onboarding information" response provided in the RPC-reply.

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:

   *  "XXXX" --> the assigned numerical RFC value for this draft

   *  "AAAA" --> the assigned RFC value for I-D.ietf-netconf-crypto-
      types

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

   *  "2021-08-24" --> the publication date of this draft

   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:

   *  I-D.ietf-netconf-crypto-types

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   *  I-D.ietf-netconf-keystore

   *  I-D.ietf-netconf-trust-anchors

   *  I-D.ietf-netmod-factory-default

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
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   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 25 February 2022.

Copyright Notice

   Copyright (c) 2021 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
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   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.4.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The "ietf-sztp-csr" Module  . . . . . . . . . . . . . . . . .   4
     2.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   5
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  14

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   3.  The "ietf-ztp-types" Module . . . . . . . . . . . . . . . . .  17
     3.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  17
     3.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  18
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
     4.1.  SZTP-Client Considerations  . . . . . . . . . . . . . . .  27
       4.1.1.  Ensuring the Integrity of Asymmetric Private Keys . .  27
       4.1.2.  Reuse of a Manufacturer-generated Private Key . . . .  27
       4.1.3.  Replay Attack Protection  . . . . . . . . . . . . . .  28
       4.1.4.  Connecting to an Untrusted Bootstrap Server . . . . .  28
       4.1.5.  Selecting the Best Origin Authentication Mechanism  .  29
       4.1.6.  Clearing the Private Key and Associated
               Certificate . . . . . . . . . . . . . . . . . . . . .  29
     4.2.  SZTP-Server Considerations  . . . . . . . . . . . . . . .  29
       4.2.1.  Verifying Proof of Possession . . . . . . . . . . . .  29
       4.2.2.  Supporting SZTP-Clients that don't trust the
               SZTP-Server . . . . . . . . . . . . . . . . . . . . .  30
     4.3.  Security Considerations for the "ietf-sztp-csr" YANG
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     4.4.  Security Considerations for the "ietf-ztp-types" YANG
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  30
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
     5.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  31
     5.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  31
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  31
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  33
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  34
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

1.1.  Overview

   This draft extends the "get-bootstrapping-data" RPC defined in
   [RFC8572] to include an optional certificate signing request (CSR)
   [RFC2986], enabling a bootstrapping device to additionally obtain an
   identity certificate (e.g., an LDevID [Std-802.1AR-2018]) as part of
   the "onboarding information" response provided in the RPC-reply.

   The ability to provision an identity certificate that is purpose-
   built for a production environment during the bootstrapping process
   removes reliance on the manufacturer CA, and it also enables the
   bootstraped device to join the production environment with an
   appropriate identity and other attributes in its LDevID certificate.

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   Two YANG [RFC7950] modules are defined.  The "ietf-ztp-types" module
   defines three YANG groupings for the various messages defined in this
   document.  The "ietf-sztp-csr" module augments two groupings into the
   "get-bootstrapping-data" RPC and defines a YANG Data Structure
   [RFC8791] around the third grouping.

1.2.  Terminology

   This document uses the following terms from [RFC8572]:

   *  Bootstrap Server
   *  Bootstrapping Data
   *  Conveyed Information
   *  Device
   *  Manufacturer
   *  Onboarding Information
   *  Signed Data

   This document defines the following new terms:

   SZTP-client  The term "SZTP-client" refers to a "device" that is
      using a "bootstrap server" as a source of "bootstrapping data".

   SZTP-server  The term "SZTP-server" is an alternative term for
      "bootstrap server" that is symmetric with the "SZTP-client" term.

1.3.  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.

1.4.  Conventions

   Various examples used in this document use a placeholder value for
   binary data that has been base64 encoded (e.g., "BASE64VALUE=").
   This placeholder value is used as real base64 encoded structures are
   often many lines long and hence distracting to the example being
   presented.

2.  The "ietf-sztp-csr" Module

   The "ietf-sztp-csr" module is a YANG 1.1 [RFC7950] module that
   augments the "ietf-sztp-bootstrap-server" module defined in [RFC8572]
   and defines a YANG "structure" that is to be conveyed in the "error-
   info" node defined in Section 7.1 of [RFC8040].

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2.1.  Data Model Overview

   The following tree diagram [RFC8340] illustrates the "ietf-sztp-csr"
   module.

   module: ietf-sztp-csr

     augment /sztp-svr:get-bootstrapping-data/sztp-svr:input:
       +---w (msg-type)?
          +--:(csr-support)
          |  +---w csr-support
          |     +---w key-generation!
          |     |  +---w supported-algorithms
          |     |     +---w algorithm-identifier*   binary
          |     +---w csr-generation
          |        +---w supported-formats
          |           +---w format-identifier*   identityref
          +--:(csr)
             +---w (csr-type)
                +--:(p10-csr)
                |  +---w p10-csr?   ct:csr
                +--:(cmc-csr)
                |  +---w cmc-csr?   binary
                +--:(cmp-csr)
                   +---w cmp-csr?   binary

     structure: csr-request
        +--ro key-generation!
        |  +--ro selected-algorithm
        |     +--ro algorithm-identifier    binary
        +--ro csr-generation
        |  +--ro selected-format
        |     +--ro format-identifier    identityref
        +--ro cert-req-info?    ietf-crypto-types:csr-info

   The augmentation defines two kinds of parameters that an SZTP-client
   can send to an SZTP-server.  The YANG structure defines one
   collection of parameters that an SZTP-server can send to an SZTP-
   client.

   In the order of their intended use:

   *  The "csr-support" node is used by the SZTP-client to signal to the
      SZTP-server that it supports the ability the generate CSRs.  This
      parameter conveys if the SZTP-client is able to generate an new
      asymmetric key and, if so, which key algorithms it supports, as
      well as conveys what kinds of CSR structures the SZTP-client is
      able to generate.

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   *  The "csr-request" structure is used by the SZTP-server to request
      the SZTP-client to generate a CSR.  This structure is used to
      select the key algorithm the SZTP-client should use to generate a
      new asymmetric key, if supported, the kind of CSR structure the
      SZTP-client should generate and, optionally, the content for the
      CSR itself.

   *  The various "csr" nodes are used by the SZTP-client to communicate
      a CSR to the SZTP-server.

      |  No data model is defined enabling an SZTP-server to communicate
      |  the signed certificate to the SZTP-client.  How to do this is
      |  discussed in Section 2.2.

   To further illustrate how the augmentation and structure defined by
   the "ietf-sztp-csr" module are used, below are two additional tree
   diagrams showing these nodes placed where they are used.

   The following tree diagram [RFC8340] illustrates SZTP's "get-
   bootstrapping-data" RPC with the augmentation in place.

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   module: ietf-sztp-bootstrap-server

     rpcs:
       +---x get-bootstrapping-data
          +---w input
          |  +---w signed-data-preferred?          empty
          |  +---w hw-model?                       string
          |  +---w os-name?                        string
          |  +---w os-version?                     string
          |  +---w nonce?                          binary
          |  +---w (sztp-csr:msg-type)?
          |     +--:(sztp-csr:csr-support)
          |     |  +---w sztp-csr:csr-support
          |     |     +---w sztp-csr:key-generation!
          |     |     |  +---w sztp-csr:supported-algorithms
          |     |     |     +---w sztp-csr:algorithm-identifier*   bina\
   ry
          |     |     +---w sztp-csr:csr-generation
          |     |        +---w sztp-csr:supported-formats
          |     |           +---w sztp-csr:format-identifier*   identit\
   yref
          |     +--:(sztp-csr:csr)
          |        +---w (sztp-csr:csr-type)
          |           +--:(sztp-csr:p10-csr)
          |           |  +---w sztp-csr:p10-csr?   ct:csr
          |           +--:(sztp-csr:cmc-csr)
          |           |  +---w sztp-csr:cmc-csr?   binary
          |           +--:(sztp-csr:cmp-csr)
          |              +---w sztp-csr:cmp-csr?   binary
          +--ro output
             +--ro reporting-level?    enumeration {onboarding-server}?
             +--ro conveyed-information    cms
             +--ro owner-certificate?      cms
             +--ro ownership-voucher?      cms

   The following tree diagram [RFC8340] illustrates RESTCONF's "errors"
   RPC-reply message with the "csr-request" structure in place.

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   module: ietf-restconf
     +--ro errors
        +--ro error* []
           +--ro error-type       enumeration
           +--ro error-tag        string
           +--ro error-app-tag?   string
           +--ro error-path?      instance-identifier
           +--ro error-message?   string
           +--ro error-info
              +--ro csr-request
                 +--ro key-generation!
                 |  +--ro selected-algorithm
                 |     +--ro algorithm-identifier    binary
                 +--ro csr-generation
                 |  +--ro selected-format
                 |     +--ro format-identifier    identityref
                 +--ro cert-req-info?    ct:csr-info

2.2.  Example Usage

      |  The examples below are encoded using JSON, but they could
      |  equally well be encoded using XML, as is supported by SZTP.

   An SZTP-client implementing this specification would signal to the
   bootstrap server its willingness to generate a CSR by including the
   "csr-support" node in its "get-bootstrapping-data" RPC, as
   illustrated below.

   REQUEST

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\
   ng-data HTTP/1.1
   HOST: example.com
   Content-Type: application/yang.data+json

   {
     "ietf-sztp-bootstrap-server:input" : {
       "hw-model": "model-x",
       "os-name": "vendor-os",
       "os-version": "17.3R2.1",
       "nonce": "extralongbase64encodedvalue=",
       "ietf-sztp-csr:csr-support": {
         "key-generation": {
           "supported-algorithms": {
             "algorithm-identifier": [
               "BASE64VALUE1",
               "BASE64VALUE2",
               "BASE64VALUE3"
             ]
           }
         },
         "csr-generation": {
           "supported-formats": {
             "format-identifier": [
               "ietf-ztp-types:p10-csr",
               "ietf-ztp-types:cmc-csr",
               "ietf-ztp-types:cmp-csr"
             ]
           }
         }
       }
     }
   }

   Assuming the SZTP-server wishes to prompt the SZTP-client to provide
   a CSR, then it would respond with an HTTP 400 Bad Request error code:

   RESPONSE

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   HTTP/1.1 400 Bad Request
   Date: Sat, 31 Oct 2015 17:02:40 GMT
   Server: example-server
   Content-Type: application/yang.data+json

   {
     "ietf-restconf:errors" : {
       "error" : [
         {
           "error-type": "application",
           "error-tag": "missing-attribute",
           "error-message": "Missing input parameter",
           "error-info": {
             "ietf-sztp-csr:csr-request": {
               "key-generation": {
                 "selected-algorithm": {
                   "algorithm-identifier": "BASE64VALUE="
                 }
               },
               "csr-generation": {
                 "selected-format": {
                   "format-identifier": "ietf-ztp-types:p10-csr"
                 }
               },
               "cert-req-info": "BASE64VALUE="
             }
           }
         }
       ]
     }
   }

   Upon being prompted to provide a CSR, the SZTP-client would POST
   another "get-bootstrapping-data" request, but this time including one
   of the "csr" nodes to convey its CSR to the SZTP-server:

   REQUEST

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\
   ng-data HTTP/1.1
   HOST: example.com
   Content-Type: application/yang.data+json

   {
     "ietf-sztp-bootstrap-server:input" : {
       "hw-model": "model-x",
       "os-name": "vendor-os",
       "os-version": "17.3R2.1",
       "nonce": "extralongbase64encodedvalue=",
       "ietf-sztp-csr:p10-csr": "BASE64VALUE="
     }
   }

   At this point, it is expected that the SZTP-server, perhaps in
   conjunction with other systems, such as a backend CA or RA, will
   validate the CSR's origin and proof-of-possession and, assuming the
   CSR is approved, issue a signed certificate for the bootstrapping
   device.

   The SZTP-server responds with "onboarding-information" (encoded
   inside the "conveyed-information" node, shown below) containing a
   signed identity certificate for the CSR provided by the SZTP-client:

   RESPONSE

   HTTP/1.1 200 OK
   Date: Sat, 31 Oct 2015 17:02:40 GMT
   Server: example-server
   Content-Type: application/yang.data+json

   {
     "ietf-sztp-bootstrap-server:output" : {
       "reporting-level": "verbose",
       "conveyed-information": "BASE64VALUE="
     }
   }

   How the signed certificate is conveyed inside the onboarding
   information is outside the scope of this document.  Some
   implementations may choose to convey it inside a script (e.g., SZTP's
   "pre-configuration-script"), while other implementations may choose
   to convey it inside the SZTP "configuration" node.  SZTP onboarding
   information is described in Section 2.2 of [RFC8572].

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   Following are two examples of conveying the signed certificate inside
   the "configuration" node.  Both examples assume that the SZTP-client
   understands the "ietf-keystore" module defined in
   [I-D.ietf-netconf-keystore].

   This first example illustrates the case where the signed certificate
   is for the same asymmetric key used by the SZTP-client's
   manufacturer-generated identity certificate (e.g., an IDevID, from
   [Std-802.1AR-2018]).  As such, the configuration needs to associate
   the newly signed certificate with the existing asymmetric key:

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "ietf-keystore:keystore": {
       "asymmetric-keys": {
         "asymmetric-key": [
           {
             "name": "Manufacturer-Generated Hidden Key",
             "public-key-format": "ietf-crypto-types:subject-public-key\
   -info-format",
             "public-key": "BASE64VALUE=",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Manufacturer-Generated IDevID Cert",
                   "cert-data": "BASE64VALUE="
                 },
                 {
                   "name": "Newly-Generated LDevID Cert",
                   "cert-data": "BASE64VALUE="
                 }
               ]
             }
           }
         ]
       }
     }
   }

   This second example illustrates the case where the signed certificate
   is for a newly generated asymmetric key.  As such, the configuration
   needs to associate the newly signed certificate with the newly
   generated asymmetric key:

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "ietf-keystore:keystore": {
       "asymmetric-keys": {
         "asymmetric-key": [
           {
             "name": "Manufacturer-Generated Hidden Key",
             "public-key-format": "ietf-crypto-types:subject-public-key\
   -info-format",
             "public-key": "BASE64VALUE=",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Manufacturer-Generated IDevID Cert",
                   "cert-data": "BASE64VALUE="
                 }
               ]
             }
           },
           {
             "name": "Newly-Generated Hidden Key",
             "public-key-format": "ietf-crypto-types:subject-public-key\
   -info-format",
             "public-key": "BASE64VALUE=",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Newly-Generated LDevID Cert",
                   "cert-data": "BASE64VALUE="
                 }
               ]
             }
           }
         ]
       }
     }
   }

   In addition to configuring the signed certificate, it is often
   necessary to also configure the Issuer's signing certificate so that
   the device (i.e., STZP-client) can authenticate certificates
   presented by peer devices signed by the same issuer as its own.
   While outside the scope of this document, one way to do this would be
   to use the "ietf-truststore" module defined in
   [I-D.ietf-netconf-trust-anchors].

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2.3.  YANG Module

   This module augments an RPC defined in [RFC8572].  The module uses a
   data types and groupings defined in [RFC8572], [RFC8791], and
   [I-D.ietf-netconf-crypto-types].  The module has additional normative
   references to [RFC2986], [RFC5272], [RFC4210], and [ITU.X690.2015],
   and an informative reference to [Std-802.1AR-2018].

   <CODE BEGINS> file "ietf-sztp-csr@2021-08-24.yang"

   module ietf-sztp-csr {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-sztp-csr";
     prefix sztp-csr;

     import ietf-sztp-bootstrap-server {
       prefix sztp-svr;
       reference
         "RFC 8572: Secure Zero Touch Provisioning (SZTP)";
     }

     import ietf-yang-structure-ext {
       prefix sx;
       reference
         "RFC 8791: YANG Data Structure Extensions";
     }

     import ietf-ztp-types {
       prefix zt;
       reference
         "RFC XXXX: Conveying a Certificate Signing Request (CSR)
                    in a Secure Zero Touch Provisioning (SZTP)
                    Bootstrapping Request";
     }

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

     contact
       "WG Web:   http://tools.ietf.org/wg/netconf
        WG List:  <mailto:netconf@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Russ Housley <mailto:housley@vigilsec.com>
                  Sean Turner <mailto:sean@sn3rd.com>";

     description
       "This module augments the 'get-bootstrapping-data' RPC,
        defined in the 'ietf-sztp-bootstrap-server' module from

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        SZTP (RFC 8572), enabling the SZTP-client to obtain a
        signed identity certificate (e.g., an LDevID from IEEE
        802.1AR) as part of the SZTP onboarding information
        response.

        Copyright (c) 2021 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
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
        itself for full legal notices.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
        'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
        'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this
        document are to be interpreted as described in BCP 14
        (RFC 2119) (RFC 8174) when, and only when, they appear
        in all capitals, as shown here.";

     revision 2021-08-24 {
       description
         "Initial version";
       reference
         "RFC XXXX: Conveying a Certificate Signing Request (CSR)
                    in a Secure Zero Touch Provisioning (SZTP)
                    Bootstrapping Request";
     }

     // Protocol-accessible nodes

     augment "/sztp-svr:get-bootstrapping-data/sztp-svr:input" {
       description
         "This augmentation adds the 'csr-support' and 'csr' nodes to
          the SZTP (RFC 8572) 'get-bootstrapping-data' request message,
          enabling the SZTP-client to obtain an identity certificate
          (e.g., an LDevID from IEEE 802.1AR) as part of the onboarding
          information response provided by the SZTP-server.

          The 'csr-support' node enables the SZTP-client to indicate
          that it supports generating certificate signing requests
          (CSRs), and to provide details around the CSRs it is able

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          to generate.

          The 'csr' node enables the SZTP-client to relay a CSR to
          the SZTP-server.";
       reference
         "IEEE 802.1AR: IEEE Standard for Local and metropolitan
                        area networks - Secure Device Identity
          RFC 8572: Secure Zero Touch Provisioning (SZTP)";
       choice msg-type {
         description
           "Messages are mutually exclusive.";
         case csr-support {
           description
             "Indicates how the SZTP-client supports generating CSRs.

              If present and a SZTP-server wishes to request the
              SZTP-client generate a CSR, the SZTP-server MUST
              respond with HTTP code 400 Bad Request with an
              'ietf-restconf:errors' message having the 'error-tag'
              value 'missing-attribute' and the 'error-info' node
              containing the 'csr-request' structure described
              in this module.";
           uses zt:csr-support-grouping;
         }
         case csr {
           description
             "Provides the CSR generated by the SZTP-client.

              When present, the SZTP-server SHOULD respond with
              an SZTP onboarding information message containing
              a signed certificate for the conveyed CSR.  The
              SZTP-server MAY alternatively respond with another
              HTTP error containing another 'csr-request', in
              which case the SZTP-client MUST invalidate the
              previously generated CSR.";
           uses zt:csr-grouping;
         }
       }
     }

     sx:structure csr-request {
       description
         "A YANG data structure, per RFC 8791, that specifies
          details for the CSR that the ZTP-client is to generate.";
       reference
         "RFC 8791: YANG Data Structure Extensions";
       uses zt:csr-request-grouping;
     }

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   }

   <CODE ENDS>

3.  The "ietf-ztp-types" Module

   This section defines a YANG 1.1 [RFC7950] module that defines three
   YANG groupings, one each for messages sent between a ZTP-client and
   ZTP-server.  This module is defines independently of the "ietf-sztp-
   csr" module so that it's groupings may be used by bootstrapping
   protocols other than SZTP [RFC8572].

3.1.  Data Model Overview

   The following tree diagram [RFC8340] illustrates the three groupings
   defined in the "ietf-ztp-types" module.

   module: ietf-ztp-types

     grouping csr-support-grouping
       +-- csr-support
          +-- key-generation!
          |  +-- supported-algorithms
          |     +-- algorithm-identifier*   binary
          +-- csr-generation
             +-- supported-formats
                +-- format-identifier*   identityref
     grouping csr-request-grouping
       +-- key-generation!
       |  +-- selected-algorithm
       |     +-- algorithm-identifier    binary
       +-- csr-generation
       |  +-- selected-format
       |     +-- format-identifier    identityref
       +-- cert-req-info?    ct:csr-info
     grouping csr-grouping
       +-- (csr-type)
          +--:(p10-csr)
          |  +-- p10-csr?   ct:csr
          +--:(cmc-csr)
          |  +-- cmc-csr?   binary
          +--:(cmp-csr)
             +-- cmp-csr?   binary

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3.2.  YANG Module

   This module uses a data types and groupings [RFC8791] and
   [I-D.ietf-netconf-crypto-types].  The module has additional normative
   references to [RFC2986], [RFC4210], [RFC5272], and [ITU.X690.2015],
   and an informative reference to [Std-802.1AR-2018].

   <CODE BEGINS> file "ietf-ztp-types@2021-08-24.yang"

   module ietf-ztp-types {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-ztp-types";
     prefix zt;

     import ietf-crypto-types {
       prefix ct;
       reference
         "RFC AAAA: YANG Data Types and Groupings for Cryptography";
     }

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

     contact
       "WG Web:   http://tools.ietf.org/wg/netconf
        WG List:  <mailto:netconf@ietf.org>
        Authors:  Kent Watsen <mailto:kent+ietf@watsen.net>
                  Russ Housley <mailto:housley@vigilsec.com>
                  Sean Turner <mailto:sean@sn3rd.com>";

     description
       "This module defines three groupings that enable
        bootstrapping devices to 1) indicate if and how they
        support generating CSRs, 2) obtain a request to
        generate a CSR, and 3) communicate the requested CSR.

        The terms 'IDevID' and 'LDevID' are used herein to
        mean 'initial device identifier' and 'local device
        identifer'.  These terms are defined consistent with
        the IEEE 802.1AR specification, though there is no
        requirement that a ZTP-client's identity certificate
        conform to IEEE 802.1AR.

        Copyright (c) 2021 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

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        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
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
        itself for full legal notices.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
        'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
        'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this
        document are to be interpreted as described in BCP 14
        (RFC 2119) (RFC 8174) when, and only when, they appear
        in all capitals, as shown here.";

     revision 2021-08-24 {
       description
         "Initial version";
       reference
         "RFC XXXX: Conveying a Certificate Signing Request (CSR)
                    in a Secure Zero Touch Provisioning (SZTP)
                    Bootstrapping Request";
     }

     identity certificate-request-format {
       description
         "A base identity for the request formats supported
          by the ZTP-client.

          Additional derived identities MAY be defined by
          future efforts.";
     }

     identity p10-csr {
       base certificate-request-format;
       description
         "Indicates that the ZTP-client supports generating
          requests using the 'CertificationRequest' structure
          defined in RFC 2986.";
       reference
         "RFC 2986: PKCS #10: Certification Request Syntax
                    Specification Version 1.7";
     }

     identity cmp-csr {
       base certificate-request-format;
       description

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         "Indicates that the ZTP-client supports generating
          requests using a constrained version of the PKIMessage
          containing a p10cr structure defined in RFC 4210.";
       reference
         "RFC 4210: Internet X.509 Public Key Infrastructure
                    Certificate Management Protocol (CMP)";
     }

     identity cmc-csr {
       base certificate-request-format;
       description
         "Indicates that the ZTP-client supports generating
          requests using a constrained version of the 'Full
          PKI Request' structure defined in RFC 5272.";
       reference
         "RFC 5272: Certificate Management over CMS (CMC)";
     }

     // Protocol-accessible nodes

     grouping csr-support-grouping {
       description
         "A grouping enabling use by other efforts.";
       container csr-support {
         description
         "Enables a ZTP-client to indicate that it supports
          generating certificate signing requests (CSRs) and
          provides details about the CSRs it is able to
          generate.";
         container key-generation {
           presence
             "Indicates that the ZTP-client is capable of
              generating a new asymmetric key pair.

              If this node is not present, the ZTP-server MAY
              request a CSR using the asymmetric key associated
              with the device's existing identity certificate
              (e.g., an IDevID from IEEE 802.1AR).";
           description
             "Specifies details for the ZTP-client's ability to
              generate a new asymmetric key pair.";
           container supported-algorithms {
             description
               "A list of public key algorithms supported by the
                ZTP-client for generating a new asymmetric key.";
             leaf-list algorithm-identifier {
               type binary;
               min-elements 1;

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               description
                 "An AlgorithmIdentifier, as defined in RFC 2986,
                  encoded using 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).";
             }
           }
         }
         container csr-generation {
           description
             "Specifies details for the ZTP-client's ability to
              generate a certificate signing requests.";
           container supported-formats {
             description
               "A list of certificate request formats supported
                by the ZTP-client for generating a new key.";
             leaf-list format-identifier {
               type identityref {
                 base zt:certificate-request-format;
               }
               min-elements 1;
               description
                 "A certificate request format supported by the
                  ZTP-client.";
             }
           }
         }
       }
     }

     grouping csr-request-grouping {
       description
         "A grouping enabling use by other efforts.";
       container key-generation {
         presence
           "Provided by a ZTP-server to indicate that it wishes
            the ZTP-client to generate a new asymmetric key.

            This statement is present so the mandatory descendant
            nodes do not imply that this node must be configured.";
         description

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           "The key generation parameters selected by the ZTP-server.

            This leaf MUST only appear if the ZTP-client's
            'csr-support' included the 'key-generation' node.";
         container selected-algorithm {
           description
             "The key algorithm selected by the ZTP-server. The
              algorithm MUST be one of the algorithms specified by
              the 'supported-algorithms' node in the ZTP-client's
              message containing the 'csr-support' structure.";
           leaf algorithm-identifier {
             type binary;
             mandatory true;
             description
               "An AlgorithmIdentifier, as defined in RFC 2986,
                encoded using 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).";
           }
         }
       }
       container csr-generation {
         description
           "Specifies details for the CSR that the ZTP-client
            is to generate.";
         container selected-format {
           description
             "The CSR format selected by the ZTP-server. The
              format MUST be one of the formats specified by
              the 'supported-formats' node in the ZTP-client's
              request message.";
           leaf format-identifier {
             type identityref {
               base zt:certificate-request-format;
             }
             mandatory true;
             description
               "A certificate request format to be used by the
                ZTP-client.";
           }
         }

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       }
       leaf cert-req-info {
         type ct:csr-info;
         description
           "A CertificationRequestInfo structure, as defined in
            RFC 2986, and modeled via a 'typedef' statement by
            RFC AAAA.

            Enables the ZTP-server to provide a fully-populated
            CertificationRequestInfo structure that the ZTP-client
            only needs to sign in order to generate the complete
            'CertificationRequest' structure to send to ZTP-server
            in its next 'get-bootstrapping-data' request message.

            When provided, the ZTP-client SHOULD use this
            structure to generate its CSR; failure to do so MAY
            result in a 400 Bad Request response containing
            another 'csr-request' structure.

            When not provided, the ZTP-client SHOULD generate a
            CSR using the same structure defined in its existing
            identity certificate (e.g., IDevID).

            It is an error if the 'AlgorithmIdentifier' field
            contained inside the 'SubjectPublicKeyInfo' field
            does not match the algorithm identified by the
            'selected-algorithm' node.";
         reference
           "RFC 2986:
              PKCS #10: Certification Request Syntax Specification
            RFC AAAA:
              YANG Data Types and Groupings for Cryptography";
       }
     }

     grouping csr-grouping {
       description
         "Enables a ZTP-client to convey a certificate signing
          request, using the encoding format selected by a
          ZTP-server's 'csr-request' response to the ZTP-client's
          previously sent 'get-bootstrapping-data' request
          containing the 'csr-support' node.";
       choice csr-type {
         mandatory true;
         description
           "A choice amongst certificate signing request formats.

            Additional formats MAY be augmented into this 'choice'

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            statement by future efforts.";
         case p10-csr {
           leaf p10-csr {
             type ct:csr;
             description
               "A CertificationRequest structure, per RFC 2986.";
             reference
               "RFC 2986: PKCS #10: Certification
                          Request Syntax Specification";
           }
         }
         case cmc-csr {
           leaf cmc-csr {
             type binary;
             description
               "A constrained version of the 'Full PKI Request'
                message defined in RFC 5272, encoded using ASN.1
                distinguished encoding rules (DER), as specified
                in ITU-T X.690.

                For asymmetric key-based origin authentication of
                a CSR based on the IDevID's private key for the
                associated IDevID's public key, the PKIData
                contains one reqSequence element and no cmsSequence
                or otherMsgSequence elements. The reqSequence is
                the TaggedRequest and it is the tcr CHOICE. The
                tcr is the TaggedCertificationRequest and it a
                bodyPartId and the certificateRequest elements.
                The certificateRequest is signed with the IDevID's
                private key. The IDevID certificate and optionally
                its certificate chain is included in the SignedData
                certificates that encapsulates the PKIData.

                For asymmetric key-based origin authentication
                based on the IDevID's private key that signs the
                encapsulated CSR signed by the LDevID's private key,
                the PKIData contains one cmsSequence element and no
                otherMsgSequence element.  The cmsSequence is the
                TaggedContentInfo and it includes a bodyPartID
                element and a contentInfo.  The contentInfo is
                a SignedData encapsulating a PKIData with one
                reqSequence element and no cmsSequence or
                otherMsgSequence elements. The reqSequence is
                the TaggedRequest and it is the tcr CHOICE. The
                tcr is the TaggedCertificationRequest and it a
                bodyPartId and the certificateRequest elements.
                The certificateRequest is signed with the LDevID's
                private key. The IDevID certificate and optionally

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                its certificate chain is included in the SignedData
                certificates that encapsulates the PKIData.

                For shared secret-based origin authentication of a
                CSR signed by the LDevID's private key, the PKIData
                contains one cmsSequence element and no reqSequence
                or otherMsgSequence elements. The cmsSequence is
                the TaggedContentInfo and it includes a bodyPartID
                element and a contentInfo.  The contentInfo is an
                AuthenticatedData encapsulating a PKIData with one
                reqSequence element and no cmsSequences or
                otherMsgSequence elements. The reqSequence is the
                TaggedRequest and it is the tcr CHOICE. The tcr is
                the TaggedCertificationRequest and it a bodyPartId
                and the certificateRequest elements.  The
                certificateRequest is signed with the LDevID's
                private key. The IDevID certificate and optionally
                its certificate chain is included in the SignedData
                certificates that encapsulates the PKIData.";
             reference
               "RFC 5272: Certificate Management over CMS (CMC)
                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).";
           }
         }
         case cmp-csr {
           leaf cmp-csr {
             type binary;
             description
               "A PKIMessage structure, as defined in RFC 4210,
                encoded using ASN.1 distinguished encoding rules
                (DER), as specified in ITU-T X.690.

                For asymmetric key-based origin authentication of
                a CSR based on the IDevID's private key for the
                associated IDevID's public key, PKIMessages
                contains one PKIMessage with the header and body
                elements, no protection element, and should contain
                the extraCerts element. The header element contains
                the pvno, sender, and recipient elements. The pvno
                contains cmp2000, and the sender contains the
                subject of the IDevID certificate. The body element
                contains a p10cr CHOICE of type CertificationRequet.
                It is signed with the IDevID's private key. The
                extraCerts element contains the IDevID certificate,

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                optionally followed by its certificate chain
                excluding the trust anchor.

                For asymmetric key-based origin authentication
                based on the IDevID's private key that signs the
                encapsulated CSR signed by the LDevID's private
                key, PKIMessages contains one PKIMessage with the
                header, body, and protection elements, and should
                contain the extraCerts element. The header element
                contains the pvno, sender, recipient, protectionAlg,
                and optionally senderKID elements. The pvno contains
                cmp2000, the sender contains the subject of the
                IDevID certificate, the protectionAlg contains the
                AlgorithmIdentifier of the used signature algorithm,
                and the senderKID contains the subject key
                identifier of the IDevID certificate. The body
                element contains a p10cr CHOICE of type
                CertificationRequet. It is signed with the LDevID's
                private key.  The protection element contains the
                digital signature generated with the IDevID's
                private key. The extraCerts element contains the
                IDevID certificate, optionally followed by its
                certificate chain excluding the trust anchor.

                For shared secret-based origin authentication of a
                CSR signed by the LDevID's private key, PKIMessages
                contains one PKIMessage with the header, body, and
                protection element, and no extraCerts element. The
                header element contains the pvno, sender, recipient,
                protectionAlg, and senderKID elements. The pvno
                contains cmp2000, the protectionAlg contains the
                AlgorithmIdentifier of the used MAC algorithm, and
                the senderKID contains a reference the recipient
                can use to identify the shared secret. The body
                element contains a p10cr CHOICE of type
                CertificationRequet. It is signed with the LDevID's
                private key.  The protection element contains the
                MAC value generated with the shared secret.";
             reference
               "RFC 4210:
                  Internet X.509 Public Key Infrastructure
                  Certificate Management Protocol (CMP)
                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).";
           }

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         }
       }
     }

   }

   <CODE ENDS>

4.  Security Considerations

   This document builds on top of the solution presented in [RFC8572]
   and therefore all the Security Considerations discussed in RFC 8572
   apply here as well.

4.1.  SZTP-Client Considerations

4.1.1.  Ensuring the Integrity of Asymmetric Private Keys

   The private key the SZTP-client uses for the dynamically-generated
   identity certificate MUST be protected from inadvertent disclosure in
   order to prevent identity fraud.

   The security of this private key is essential in order to ensure the
   associated identity certificate can be used as a root of trust.

   It is RECOMMENDED that devices are manufactured with an HSM (hardware
   security module), such as a TPM (trusted platform module), to
   generate and forever contain the private key within the security
   perimeter of the HSM.  In such cases, the private key, and its
   associated certificates, MAY have long validity periods.

   In cases where the SZTP-client does not possess an HSM, or otherwise
   is unable to use an HSM for the private key, it is RECOMMENDED to
   regenerate the private key (and associated identity certificates)
   periodically.  Details for how to generate a new private key and
   associate a new identity certificate are outside the scope of this
   document.

4.1.2.  Reuse of a Manufacturer-generated Private Key

   It is RECOMMENDED that a new private key is generated for each CSR
   described in this document.

   This private key SHOULD be protected as well as the built-in private
   key associated with the SZTP-client's initial device identity
   certificate (e.g., the IDevID, from [Std-802.1AR-2018]).

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   In cases where it is not possible to generate a new private key that
   is protected as well as the built-in private key, it is RECOMMENDED
   to reuse the built-in private key rather than generate a new private
   key that is not as well protected.

4.1.3.  Replay Attack Protection

   This RFC enables an SZTP-client to announce an ability to generate a
   new key to use for its CSR.

   When the SZTP-server responds with a request for the SZTP-client to
   generate a new key, it is essential that the SZTP-client actually
   generates a new key.

   Generating a new key each time enables the random bytes used to
   create the key to also serve the dual-purpose of acting like a
   "nonce" used in other mechanisms to detect replay attacks.

   When a fresh public/private key pair is generated for the request,
   confirmation to the SZTP-client that the response has not been
   replayed is enabled by the SZTP-client's fresh public key appearing
   in the signed certificate provided by the SZTP-server.

   When a public/private key pair associated with the manufacturer-
   generated identity certificate (e.g., IDevID) is used for the
   request, there may not be confirmation to the SZTP-client that the
   response has not been replayed; however, the worst case result is a
   lost certificate that is associated to the private key known only to
   the SZTP-client.

4.1.4.  Connecting to an Untrusted Bootstrap Server

   [RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers,
   by blindly authenticating the SZTP-server's TLS end-entity
   certificate.

   As is discussed in Section 9.5 of [RFC8572], in such cases the SZTP-
   client MUST assert that the bootstrapping data returned is signed, if
   the SZTP-client is to trust it.

   However, the HTTP error message used in this document cannot be
   signed data, as described in RFC 8572.

   Therefore, the solution presented in this document cannot be used
   when the SZTP-client connects to an untrusted SZTP-server.

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   Consistent with the recommendation presented in Section 9.6 of
   [RFC8572], SZTP-clients SHOULD NOT pass the "csr-support" input
   parameter to an untrusted SZTP-server.  SZTP-clients SHOULD pass
   instead the "signed-data-preferred" input parameter, as discussed in
   Appendix B of [RFC8572].

4.1.5.  Selecting the Best Origin Authentication Mechanism

   A The CSR's origin SHOULD be verified before a certificate is issued.

   When generating a new key, it is important that the SZTP-client be
   able to provide additional proof that it was the entity that
   generated the key.

   The CMP and CMC certificate request formats defined in this document
   support origin authentication.  A raw PKCS#10 does not support origin
   authentication.

   The CMP and CMC request formats support origin authentication using
   both PKI and shared secret.

   Typically, only one possible origin authentication mechanism can
   possibly be used but, in the case that the SZTP-client authenticates
   itself using both TLS-level (e.g., IDevID) and HTTP-level credentials
   (e.g., Basic), as is allowed by Section 5.3 of [RFC8572], then the
   SZTP-client may need to choose between the two options.

   In the case that the SZTP-client must choose between an asymmetric
   key option versus a shared secret for origin authentication, it is
   RECOMMENDED that the SZTP-client choose using the asymmetric key.

4.1.6.  Clearing the Private Key and Associated Certificate

   Unlike a manufacturer-generated identity certificate (e.g., IDevID),
   the deployment-generated identity certificate (e.g., LDevID) and the
   associated private key (assuming a new private key was generated for
   the purpose), are considered user data and SHOULD be cleared whenever
   the SZTP-client is reset to its factory default state, such as by the
   "factory-reset" RPC defined in [I-D.ietf-netmod-factory-default].

4.2.  SZTP-Server Considerations

4.2.1.  Verifying Proof of Possession

   When the bootstrapping device's manufacturer-generated private key
   (e.g., the IDevID key) is reused for the CSR, proof-of-possession is
   verified by ensuring the CSR was signed by that key.

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   When a new asymmetric key is used, proof-of-possession may be
   verified, with the CMP or CMC formats, by ensuring the parent ASN.1
   structure containing the CSR is signed by the manufacturer-generated
   key.

4.2.2.  Supporting SZTP-Clients that don't trust the SZTP-Server

   [RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers,
   by blindly authenticating the SZTP-server's TLS end-entity
   certificate.

   As is recommended in Section 4.1.4 in this document, in such cases,
   SZTP-clients SHOULD pass the "signed-data-preferred" input parameter.

   The reciprocal of this statement is that SZTP-servers, wanting to
   support SZTP-clients that don't trust them, SHOULD support the
   "signed-data-preferred" input parameter, as discussed in Appendix B
   of [RFC8572].

4.3.  Security Considerations for the "ietf-sztp-csr" YANG Module

   The recommended format for documenting the Security Considerations
   for YANG modules is described in Section 3.7 of [RFC8407].  However,
   this module only augments two input parameters into the "get-
   bootstrapping-data" RPC in [RFC8572], and therefore only needs to
   point to the relevant Security Considerations sections in that RFC.

   *  Security considerations for the "get-bootstrapping-data" RPC are
      described in Section 9.16 of [RFC8572].

   *  Security considerations for the "input" parameters passed inside
      the "get-bootstrapping-data" RPC are described in Section 9.6 of
      [RFC8572].

4.4.  Security Considerations for the "ietf-ztp-types" YANG Module

   The recommended format for documenting the Security Considerations
   for YANG modules is described in Section 3.7 of [RFC8407].  However,
   this module does not define any protocol-accessible nodes (it only
   defines "identity" and "grouping" statements) and therefore there are
   no Security considerations to report.

5.  IANA Considerations

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5.1.  The "IETF XML" Registry

   This document registers two URIs in the "ns" subregistry of the IETF
   XML Registry [RFC3688] maintained at
   https://www.iana.org/assignments/xml-registry/xml-registry.xhtml#ns.
   Following the format in [RFC3688], the following registrations are
   requested:

   URI: urn:ietf:params:xml:ns:yang:ietf-sztp-csr
   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-ztp-types
   Registrant Contact: The NETCONF WG of the IETF.
   XML: N/A, the requested URI is an XML namespace.

5.2.  The "YANG Module Names" Registry

   This document registers two YANG modules in the YANG Module Names
   registry [RFC6020] maintained at https://www.iana.org/assignments/
   yang-parameters/yang-parameters.xhtml.  Following the format defined
   in [RFC6020], the below registrations are requested:

   name:      ietf-sztp-csr
   namespace: urn:ietf:params:xml:ns:yang:ietf-sztp-csr
   prefix:    sztp-csr
   reference: RFC XXXX

   name:      ietf-ztp-types
   namespace: urn:ietf:params:xml:ns:yang:ietf-ztp-types
   prefix:    ztp-types
   reference: RFC XXXX

6.  References

6.1.  Normative References

   [I-D.ietf-netconf-crypto-types]
              Watsen, K., "YANG Data Types and Groupings for
              Cryptography", Work in Progress, Internet-Draft, draft-
              ietf-netconf-crypto-types-20, 18 May 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              crypto-types-20>.

   [ITU.X690.2015]
              International Telecommunication Union, "Information
              Technology - ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and

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              Distinguished Encoding Rules (DER)", ITU-T Recommendation
              X.690, ISO/IEC 8825-1, August 2015,
              <https://www.itu.int/rec/T-REC-X.690/>.

   [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>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/info/rfc2986>.

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

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <https://www.rfc-editor.org/info/rfc5272>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

   [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>.

   [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>.

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   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,
              <https://www.rfc-editor.org/info/rfc8572>.

   [RFC8791]  Bierman, A., Björklund, M., and K. Watsen, "YANG Data
              Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
              June 2020, <https://www.rfc-editor.org/info/rfc8791>.

6.2.  Informative References

   [I-D.ietf-netconf-keystore]
              Watsen, K., "A YANG Data Model for a Keystore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-keystore-22,
              18 May 2021, <https://datatracker.ietf.org/doc/html/draft-
              ietf-netconf-keystore-22>.

   [I-D.ietf-netconf-trust-anchors]
              Watsen, K., "A YANG Data Model for a Truststore", Work in
              Progress, Internet-Draft, draft-ietf-netconf-trust-
              anchors-15, 18 May 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              trust-anchors-15>.

   [I-D.ietf-netmod-factory-default]
              Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
              Factory Default Settings", Work in Progress, Internet-
              Draft, draft-ietf-netmod-factory-default-15, 25 April
              2020, <https://datatracker.ietf.org/doc/html/draft-ietf-
              netmod-factory-default-15>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

   [Std-802.1AR-2018]
              Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
              metropolitan area networks - Secure Device Identity", 14
              June 2018, <http://standards.ieee.org/findstds/
              standard/802.1AR-2018.html>.

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Acknowledgements

   The authors would like to thank for following for lively discussions
   on list and in the halls (ordered by first name): David von Oheimb,
   Hendrik Brockhaus, Guy Fedorkow, Joe Clarke, Rich Salz, Rob Wilton,
   and Qin Wu.

Contributors

   Special thanks goes to David von Oheimb and Hendrik Brockhaus for
   helping with the descriptions for the "cmc-csr" and "cmp-csr" nodes.

Authors' Addresses

   Kent Watsen
   Watsen Networks

   Email: kent+ietf@watsen.net

   Russ Housley
   Vigil Security, LLC

   Email: housley@vigilsec.com

   Sean Turner
   sn3rd

   Email: sean@sn3rd.com

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