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Versions: (draft-kwatsen-netconf-sztp-csr) 00 01

NETCONF Working Group                                          K. Watsen
Internet-Draft                                           Watsen Networks
Updates: 8572 (if approved)                                   R. Housley
Intended status: Standards Track                     Vigil Security, LLC
Expires: 5 April 2021                                          S. Turner
                                                                   sn3rd
                                                          2 October 2020


  Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch
               Provisioning (SZTP) Bootstrapping Request
                     draft-ietf-netconf-sztp-csr-00

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:

   *  "2020-10-02" --> 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
   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 5 April 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  The "ietf-sztp-csr" Module  . . . . . . . . . . . . . . . . .   4
     2.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   4
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  13
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .  23



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     3.1.  SZTP-Client Considerations  . . . . . . . . . . . . . . .  23
       3.1.1.  Ensuring the Integrity of Asymmetric Private Keys . .  23
       3.1.2.  Reuse of a Manufacturer-generated Private Key . . . .  23
       3.1.3.  Replay Attack Protection  . . . . . . . . . . . . . .  24
       3.1.4.  Connecting to an Untrusted Bootstrap Server . . . . .  24
       3.1.5.  Selecting the Best Origin Authentication Mechanism  .  25
       3.1.6.  Clearing the Private Key and Associated
               Certificate . . . . . . . . . . . . . . . . . . . . .  25
     3.2.  SZTP-Server Considerations  . . . . . . . . . . . . . . .  25
       3.2.1.  Conveying Proof of Possession to a CA . . . . . . . .  25
       3.2.2.  Supporting SZTP-Clients that don't trust the
               SZTP-Server . . . . . . . . . . . . . . . . . . . . .  25
       3.2.3.  YANG Module Considerations  . . . . . . . . . . . . .  26
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     4.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  26
     4.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  26
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

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.

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".




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   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.

2.  The "ietf-sztp-csr" Module

   This section defines a YANG 1.1 [RFC7950] module that augments the
   "ietf-sztp-bootstrap-server" module defined in [RFC8572] and defines
   a YANG "structure".

   The augmentation adds two nodes ("csr-support" and "csr") to the
   "input" parameter of the "get-bootstrapping-data" RPC defined in
   [RFC8572].

   The YANG structure, "request-info", defines data returned in the
   "error-info" node defined in Section 7.1 of [RFC8040].

2.1.  Data Model Overview

   The following tree diagram [RFC8340] illustrates the "ietf-sztp-csr"
   module.  The diagram shows the definition of an augmentation adding
   descendent nodes "csr-support" and "csr" and the definition of a
   structure called "request-info".

   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, per
      this specification.  The "csr-support" parameter carries details
      regarding the SZTP-client's ability to generate CSRs.

   *  The "request-info" structure is used by the SZTP-server to signal
      back to the SZTP-client its desire to sign a CSR.  The "request-
      info" structure additionally communicates details about the CSR
      the SZTP-client is to generate.

   *  The "csr" node is used by the SZTP-client to communicate its CSR
      to the SZTP-server.  Not shown is how the SZTP-server communicates
      the signed certificate to the SZTP-client; how to do this is
      discussed later in this document.




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

   module: ietf-sztp-csr

     augment /ietf-sztp-bootstrap-server:get-bootstrapping-data/ietf-sz\
   tp-bootstrap-server:input:
       +---- csr-support!
       |  +---- key-generation!
       |  |  +---- supported-algorithms
       |  |     +---- algorithm-identifier*   binary
       |  +---- csr-generation
       |     +---- supported-formats
       |        +---- format-identifier*   identityref
       +---- csr!
          +---- (request-type)
             +--:(p10)
             |  +---- p10?   ietf-crypto-types:csr
             +--:(cmc)
             |  +---- cmc?   binary
             +--:(cmp)
                +---- cmp?   binary

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

   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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   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:csr-support!
          |  |  +---w sztp-csr:key-generation!
          |  |  |  +---w sztp-csr:supported-algorithms
          |  |  |     +---w sztp-csr:algorithm-identifier*   binary
          |  |  +---w sztp-csr:csr-generation
          |  |     +---w sztp-csr:supported-formats
          |  |        +---w sztp-csr:format-identifier*   identityref
          |  +---w sztp-csr:csr!
          |     +---w (sztp-csr:request-type)
          |        +--:(sztp-csr:p10)
          |        |  +---w sztp-csr:p10?   ct:csr
          |        +--:(sztp-csr:cmc)
          |        |  +---w sztp-csr:cmc?   binary
          |        +--:(sztp-csr:cmp)
          |           +---w sztp-csr:cmp?   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 "request-info" 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 request-info
                 +--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": [
               "base64encodedvalue1=",
               "base64encodedvalue2=",
               "base64encodedvalue3="
             ]
           }
         },
         "csr-generation": {
           "supported-formats": {
             "format-identifier": [
               "ietf-sztp-csr:p10",
               "ietf-sztp-csr:cmc",
               "ietf-sztp-csr:cmp"
             ]
           }
         }
       }
     }
   }

   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:request-info": {
               "key-generation": {
                 "selected-algorithm": {
                   "algorithm-identifier": "base64EncodedValue=="
                 }
               },
               "csr-generation": {
                 "selected-format": {
                   "format-identifier": "ietf-sztp-csr:cmc"
                 }
               },
               "cert-req-info": "base64EncodedValue=="
             }
           }
         }
       ]
     }
   }

   Upon being prompted to provide a CSR, the SZTP-client would POST
   another "get-bootstrapping-data" request, but this time including the
   "csr" node 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:csr": {
         "p10": "base64encodedvalue=="
       }
     }
   }

   The SZTP-server responds with "onboarding-information" (conveyed
   encoded inside the "conveyed-information" node) 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": "base64encodedvalue=="
     }
   }

   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 convey it
   inside the SZTP "configuration" node.

   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].




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   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).  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": "base64encodedvalue==",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Manufacturer-Generated IDevID Cert",
                   "cert-data": "base64encodedvalue=="
                 },
                 {
                   "name": "Newly-Generated LDevID Cert",
                   "cert-data": "base64encodedvalue=="
                 }
               ]
             }
           }
         ]
       }
     }
   }

   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": "base64encodedvalue==",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Manufacturer-Generated IDevID Cert",
                   "cert-data": "base64encodedvalue=="
                 }
               ]
             }
           },
           {
             "name": "Newly-Generated Hidden Key",
             "public-key-format": "ietf-crypto-types:subject-public-key\
   -info-format",
             "public-key": "base64encodedvalue==",
             "hidden-private-key": [null],
             "certificates": {
               "certificate": [
                 {
                   "name": "Newly-Generated LDevID Cert",
                   "cert-data": "base64encodedvalue=="
                 }
               ]
             }
           }
         ]
       }
     }
   }

   In addition to configuring the signed certificate, it is often
   necessary to also configure the Issuer's signing certificate so that
   the 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], uses a data type
   defined in [I-D.ietf-netconf-crypto-types], has an normative
   references to [RFC2986] and [ITU.X690.2015], and an informative
   reference to [Std-802.1AR-2018].

   <CODE BEGINS> file "ietf-sztp-csr@2020-10-02.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 BBBB:YANG Data Structure Extensions";
     }

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




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       Copyright (c) 2020 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 2020-10-02 {
       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 SZTP-client.

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

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



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     }

     identity cmc {
       base "certificate-request-format";
       description
         "Indicates that the SZTP-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)";
     }

     identity cmp {
       base "certificate-request-format";
       description
         "Indicates that the SZTP-client supports generating
          requests that contain a PKCS#10 Certificate Signing
          Request (p10cr), as defined in RFC 2986, encapsulated
          in a Nested Message Content (nested), as defined in
          RFC 4210.";
       reference
         "RFC 2986: PKCS #10: Certification Request Syntax
                    Specification Version 1.7
          RFC 4210: Internet X.509 Public Key Infrastructure
                    Certificate Management Protocol (CMP)";
     }


     // 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
          to generate.

          The 'csr' node enables the SZTP-client to relay a CSR to
          the SZTP-server.";

        reference



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          "IEEE 802.1AR: IEEE Standard for Local and metropolitan
                         area networks - Secure Device Identity
           RFC 8572: Secure Zero Touch Provisioning (SZTP)";

       container csr-support {
         presence
           "Indicates that the SZTP-client is capable of sending CSRs.";
         description
           "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
            to generate.

            When present, the SZTP-server MAY respond with the HTTP
            error 400 (Bad Request) with an 'ietf-restconf:errors'
            document having the 'error-tag' value 'missing-attribute'
            and the 'error-info' node containing the 'request-info'
            structure described in this module.";
         container key-generation {
           presence
             "Indicates that the SZTP-client is capable of
              generating a new asymmetric key pair.

              If this node is not present, the SZTP-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 SZTP-client's ability to
              generate a new asymmetric key pair.";
           container supported-algorithms {
             description
               "A list of public key algorithms supported by the
                SZTP-client for generating a new key.";
             leaf-list algorithm-identifier {
               type binary;
               min-elements 1;
               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



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                    Encoding Rules (DER).";
             }
           }
         }
         container csr-generation {
           description
             "Specifies details for the SZTP-client's ability to
              generate a certificate signing requests.";
           container supported-formats {
             description
               "A list of certificate request formats supported
                by the SZTP-client for generating a new key.";
             leaf-list format-identifier {
               type identityref {
                 base certificate-request-format;
               }
               min-elements 1;
               description
                 "A certificate request format supported by the
                  SZTP-client.";
             }
           }
         }
       }

       container csr {
         presence
           "Indicates that the SZTP-client has sent a CSR.";
         description
           "The 'csr' node enables the SZTP-client to convey
            a certificate signing request, using the encoding
            format selected by the SZT-server's 'request-info'
            response to the SZTP-client's previously sent
            'get-bootstrapping-data' request containing the
            'csr-support' node.

            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 'request-info', in
            which case the SZTP-client MUST invalidate the CSR
            sent in this node.";
         choice request-type {
           mandatory true;
           description
             "A choice amongst certificate signing request formats.




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              Additional formats MAY be augmented into this 'choice'
              statement by future efforts.";
           case p10 {
             leaf p10 {
               type ct:csr;
               description
                 "A CertificationRequest structure, per RFC 2986.
                  Please see 'csr' in RFC AAAA for encoding details.";
               reference
                 "RFC 2986:
                    PKCS #10: Certification Request Syntax Specification
                  RFC AAAA:
                    YANG Data Types and Groupings for Cryptography";
             }
           }
           case cmc {
             leaf cmc {
               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 controlSequence,
                  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.

                  For asymmetric key-based origin authentication
                  based on the IDevID's private key that encapsulates
                  a CSR signed by the LDevID's private key, the
                  PKIData contains one cmsSequence element and no
                  controlSequence, reqSequence, or otherMsgSequence
                  elements. 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 controlSequence, cmsSequence, or
                  otherMsgSequence elements. The reqSequence is
                  the TaggedRequest and it is the tcr CHOICE. The
                  tcr is the TaggedCertificationRequest and it a



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                  bodyPartId and the certificateRequest elements.
                  The certificateRequest is signed with the LDevID's
                  private key.

                  For shared secret-based origin authentication of
                  a CSR signed by the LDevID's private key, the
                  PKIData contains one cmsSequence element and no
                  controlSequence, 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 controlSequence, 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.";
               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 {
             leaf cmp {
               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.

                  The PKIMessage structure contains a PKCS#10
                  Certificate Signing Request (p10cr), as defined in
                  RFC 2986, encapsulated in a Nested Message Content
                  (nested) structure, as defined in RFC 4210.

                  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 one body element, a header
                  element that is an empty sequence, and no protection
                  or extraCerts elements. The body element contains a
                  p10cr CHOICE.



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                  For asymmetric key-based origin authentication based
                  on the IDevID's private key that encapsulates a CSR
                  signed by the LDevID's private key, PKIMessages
                  contains one PKIMessage with one header element,
                  one body element, one protection element, and one
                  extraCerts element.  The header element contains
                  pvno, sender, recipient, and protectionAlg elements
                  and no other elements. The body element contains the
                  nested CHOICE. The nested element's PKIMessages
                  contains one PKIMessage with one body element, one
                  header element that is an empty sequence, and no
                  protection or extraCerts elements. The nested
                  element's body element contains a p10cr CHOICE. The
                  protection element contains the digital signature
                  generated with the IDevID's private key. The
                  extraCerts element contains the IDevID certificate.

                  For shared secret-based origin authentication of a
                  CSR signed by the LDevID's private key, PKIMessages
                  contains one PKIMessage with one header element,
                  one body element, one protection element, and no
                  extraCerts element. The header element contains
                  pvno, sender, recipient, and protectionAlg elements
                  and no other elements. The body element contains
                  the nested CHOICE. The nested element's PKIMessages
                  contains one PKIMessage with one body element, one
                  header element that is an empty sequence, and no
                  protection or extraCerts elements. The body element
                  contains a p10cr CHOICE. The protection element
                  contains the MAC value generated with the shared
                  secret.";
               reference
                 "RFC 2986:
                    PKCS #10: Certification Request Syntax
                    Specification Version 1.7
                  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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     sx:structure request-info {
       container key-generation {
         presence
           "Indicates that the SZTP-client is to generate a new
            asymmetric key.  If missing, then the SZTP-client
            MUST reuse the key associated with its existing
            identity certificate (e.g., IDevID).

            This leaf MUST only appear if the SZTP-clients
            'csr-support' included the 'key-generation' node.";
         description
           "Specifies details for the key that the SZTP-client
            is to generate.";
         container selected-algorithm {
           description
             "The key algorithm selected by the SZTP-server. The
              algorithm MUST be one of the algorithms specified
              by the 'supported-algorithms' node in the
              SZTP-client's request message.";
           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 SZTP-client
            is to generate.";
         container selected-format {
           description
             "The CSR format selected by the SZTP-server. The
              format MUST be one of the formats specified by
              the 'supported-formats' node in the SZTP-client's
              request message.";
           leaf format-identifier {



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             type identityref {
               base certificate-request-format;
             }
             mandatory true;
             description
               "A certificate request format to be used by the
                SZTP-client.";
           }
         }
       }
       leaf cert-req-info {
         type ct:csr-info;
         description
           "A CertificationRequestInfo structure, as defined in
            RFC 2986.

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

            When provided, the SZTP-client SHOULD use this
            structure to generate its CSR; failure to do so MAY
            result in another 400 (Bad Request) response.

            When not provided, the SZTP-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";
       }
     }
   }

   <CODE ENDS>







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3.  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.

3.1.  SZTP-Client Considerations

3.1.1.  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 device 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.

3.1.2.  Reuse of a Manufacturer-generated Private Key

   It is RECOMMENDED in [RFC8572] that devices are shipped from
   manufacturing with a secure device identity certificate (e.g., an
   IDevID, from [Std-802.1AR-2018]).  It is also RECOMMENDED that the
   private key for these necessarily long-lived certificates be stored
   in an HSM, such as a TPM.  Lastly, per the FIXME: guy says that the
   the keys/certs aren't always stored in the TPM (see private email
   from Aug 13th) previous consideration, when devices generate a new
   private key, it is also RECOMMENDED that the private key is protected
   by the HSM.










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   However, it is understood that space on an HSM chip may be limited,
   potentially to the point of not being able to store an additional
   private key for the CSR described in this document, and that it may
   not be possible to store hardware-protected keys outside the TPM
   (e.g., a TPM-encrypted key stored in non-volatile memory).  In such
   cases, it is RECOMMENDED to reuse the existing hardware-protected
   private key rather than generate a second private key outside of
   protection afforded by the hardware.

3.1.3.  Replay Attack Protection

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

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

   Generating a new key each time enables the random bytes used to
   create the key to serve the dual-purpose of also 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 IDevID 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.

3.1.4.  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 passed 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].

3.1.5.  Selecting the Best Origin Authentication Mechanism

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

   All of the certificate request formats defined in this document
   (e.g., CMC, CMP, etc.), not including a raw PKCS#10, support origin
   authentication.

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

3.1.6.  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 device is reset to its factory default state, such as by the
   "factory-reset" RPC defined in [I-D.ietf-netmod-factory-default].

3.2.  SZTP-Server Considerations

3.2.1.  Conveying Proof of Possession to a CA

3.2.2.  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.



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   As is recommended in Section 3.1.4 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].

3.2.3.  YANG Module Considerations

   The recommended format for documenting the Security Considerations
   for YANG modules is described in Section 3.7 of [RFC8407].  However,
   the module defined in this document 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.  IANA Considerations

4.1.  The "IETF XML" Registry

   This document registers one URI 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 registration is
   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.

4.2.  The "YANG Module Names" Registry

   This document registers one YANG module 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 registration is requested:







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

5.  References

5.1.  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-18, 20 August 2020,
              <https://tools.ietf.org/html/draft-ietf-netconf-crypto-
              types-18>.

   [ITU.X690.2015]
              International Telecommunication 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, 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>.

   [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>.





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   [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>.

   [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>.

5.2.  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-20,
              20 August 2020, <https://tools.ietf.org/html/draft-ietf-
              netconf-keystore-20>.

   [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-13, 20 August 2020, <https://tools.ietf.org/html/
              draft-ietf-netconf-trust-anchors-13>.

   [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://tools.ietf.org/html/draft-ietf-netmod-
              factory-default-15>.

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

   [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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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

































Watsen, et al.            Expires 5 April 2021                 [Page 29]


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