Internet Engineering Task Force (IETF) K. Watsen

Internet Engineering Task Force (IETF) K. Watsen
Request for Comments: 9646 Watsen Networks
Updates: 8572 R. Housley
Category: Standards Track Vigil Security
ISSN: 2070-1721 S. Turner
sn3rd
October 2024

Conveying a Certificate Signing Request (CSR) in a Secure Zero-Touch
Provisioning (SZTP) Bootstrapping Request

Abstract

This document extends the input to 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., a Local Device Identifier (LDevID)
from IEEE 802.1AR) as part of the "onboarding information" response
provided in the RPC-reply.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9646.

Copyright Notice

Copyright (c) 2024 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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
1.1. Overview
1.2. Terminology
1.3. Requirements Language
1.4. Conventions
2. The "ietf-sztp-csr" Module
2.1. Data Model Overview
2.2. Example Usage
2.3. YANG Module
3. The "ietf-ztp-types" Module
3.1. Data Model Overview
3.2. YANG Module
4. Security Considerations
4.1. SZTP-Client Considerations
4.1.1. Ensuring the Integrity of Asymmetric Private Keys
4.1.2. Reuse of a Manufacturer-Generated Private Key
4.1.3. Replay Attack Protection
4.1.4. Connecting to an Untrusted Bootstrap Server
4.1.5. Selecting the Best Origin Authentication Mechanism
4.1.6. Clearing the Private Key and Associated Certificate
4.2. SZTP-Server Considerations
4.2.1. Verifying Proof-of-Possession
4.2.2. Verifying Proof-of-Origin
4.2.3. Supporting SZTP-Clients That Don't Trust the
SZTP-Server
4.3. Security Considerations for the "ietf-sztp-csr" YANG Module
4.4. Security Considerations for the "ietf-ztp-types" YANG
Module
5. IANA Considerations
5.1. The IETF XML Registry
5.2. The YANG Module Names Registry
6. References
6.1. Normative References
6.2. Informative References
Acknowledgements
Contributors
Authors' Addresses

1. Introduction

1.1. Overview

This document extends the input to 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 from
[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 Certification Authority (CA),
and it also enables the bootstrapped device to join the production
environment with an appropriate identity and other attributes in its
identity certificate (e.g., an LDevID).

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 in this document use "BASE64VALUE=" as a placeholder
value for binary data that has been base64 encoded (per Section 9.8
of [RFC7950]). This placeholder value is used because real
base64-encoded structures are often many lines long and hence
distracting to the example being presented.

Various examples in this document contain long lines that may be
folded, as described in [RFC8792].

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].

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:
+-- key-generation!
| +-- selected-algorithm
| +-- algorithm-identifier binary
+-- csr-generation
| +-- selected-format
| +-- format-identifier identityref
+-- cert-req-info? ct: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:

1. The SZTP-client sends a "csr-support" node, encoded in a first
"get-bootstrapping-data" request to the SZTP-server, to indicate
that it supports the ability to generate CSRs. This input
parameter conveys if the SZTP-client is able to generate a new
asymmetric key and, if so, which key algorithms it supports, as
well as what kinds of CSR structures the SZTP-client is able to
generate.

2. The SZTP-server responds with an error, containing the "csr-
request" structure, 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.

3. The SZTP-client sends one of the "*-csr" nodes, encoded in a
second "get-bootstrapping-data" request to the SZTP-server. This
node encodes the server-requested CSR.

4. The SZTP-server responds with onboarding information 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.

=============== 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.

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 sztp-csr:csr-request
+--ro sztp-csr:key-generation!
| +--ro sztp-csr:selected-algorithm
| +--ro sztp-csr:algorithm-identifier binary
+--ro sztp-csr:csr-generation
| +--ro sztp-csr:selected-format
| +--ro sztp-csr:format-identifier identityref
+--ro sztp-csr:cert-req-info? ct:csr-info

2.2. Example Usage

| NOTE: 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. In the
example below, the SZTP-client additionally indicates that it is able
to generate keys and provides a list of key algorithms it supports,
as well as provide a list of certificate formats it supports.

REQUEST

=============== 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.
In the example below, the SZTP-server specifies that it wishes the
SZTP-client to generate a key using a specific algorithm and generate
a PKCS#10-based CSR containing specific content.

RESPONSE

HTTP/1.1 400 Bad Request
Date: Sat, 31 Oct 2021 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

=============== 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 registration
authority (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 conveyed information (the "conveyed-
information" node shown below) that encodes "onboarding-information"
(inside the base64 value) containing a signed identity certificate
for the CSR provided by the SZTP-client:

RESPONSE

HTTP/1.1 200 OK
Date: Sat, 31 Oct 2021 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].

Below 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 [RFC9642].

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 Initial Device
Identifier (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:

=============== 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 [RFC9641].

2.3. YANG Module

This module augments an RPC defined in [RFC8572]. The module uses
data types and groupings defined in [RFC8572], [RFC8791], and
[RFC9640]. The module also has an informative reference to
[Std-802.1AR-2018].

<CODE BEGINS> file "[email protected]"
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 9646: 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: https://datatracker.ietf.org/wg/netconf
WG List: NETCONF WG list <mailto:[email protected]>
Authors: Kent Watsen <mailto:[email protected]>
Russ Housley <mailto:[email protected]>
Sean Turner <mailto:[email protected]>";

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.

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.

Copyright (c) 2024 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 Revised 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 9646
(https://www.rfc-editor.org/info/rfc9646); see the
RFC itself for full legal notices.";

revision 2024-10-10 {
description
"Initial version.";
reference
"RFC 9646: 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
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 an HTTP 400 Bad Request error code 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 delete any key
generated for 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;
}

}
<CODE ENDS>

3. The "ietf-ztp-types" Module

This section defines a YANG 1.1 [RFC7950] module that defines three
YANG groupings, one for each message sent between a ZTP-client and
ZTP-server. This module is defined independently of the "ietf-sztp-
csr" module so that its 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

3.2. YANG Module

This module uses data types and groupings defined in [RFC8791] and
[RFC9640]. The module has additional normative references to
[RFC2986], [RFC4210], [RFC5272], and [ITU.X690.2021] and an
informative reference to [Std-802.1AR-2018].

<CODE BEGINS> file "[email protected]"
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 9640: YANG Data Types and Groupings for Cryptography";
}

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

contact
"WG Web: https://datatracker.ietf.org/wg/netconf
WG List: NETCONF WG list <mailto:[email protected]>
Authors: Kent Watsen <mailto:[email protected]>
Russ Housley <mailto:[email protected]>
Sean Turner <mailto:[email protected]>";

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 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.

Copyright (c) 2024 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 Revised 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 9646
(https://www.rfc-editor.org/info/rfc9646); see the
RFC itself for full legal notices.";

revision 2024-10-10 {
description
"Initial version.";
reference
"RFC 9646: 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
"Indicates that the ZTP-client supports generating
requests using a profiled version of the PKIMessage
that MUST contain a PKIHeader followed by a PKIBody
containing only the ir, cr, kur, or p10cr structures
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 profiled 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;
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 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
"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.";
}
}
}
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 9640.

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 the ZTP-server
in its next 'get-bootstrapping-data' request message.

When provided, the ZTP-client MUST use this structure
to generate its CSR; failure to do so will 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., an IDevID from IEEE 802.1AR).

If the 'AlgorithmIdentifier' field contained inside the
certificate 'SubjectPublicKeyInfo' field does not match
the algorithm identified by the 'selected-algorithm' node,
then the client MUST reject the certificate and raise an
error.";

reference
"RFC 2986:
PKCS #10: Certification Request Syntax Specification
Version 1.7
RFC 9640:
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 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'
statement by future efforts.";
case p10-csr {
leaf p10-csr {
type ct:p10-csr;
description
"A CertificationRequest structure, per RFC 2986.
Encoding details are defined in the 'ct:csr'
typedef defined in RFC 9640.

A raw P10 does not support origin authentication in
the CSR structure. External origin authentication
may be provided via the ZTP-client's authentication
to the ZTP-server at the transport layer (e.g., TLS).";
reference
"RFC 2986: PKCS #10: Certification Request Syntax
Specification Version 1.7
RFC 9640: YANG Data Types and Groupings for
Cryptography";
}
}
case cmc-csr {
leaf cmc-csr {
type binary;
description
"A profiled 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 initial device identity certificate's
private key for the associated identity certificate'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 branch. The tcr is the
TaggedCertificationRequest, and it is the bodyPartID
and the certificateRequest elements. The
certificateRequest is signed with the initial device
identity certificate's private key. The initial device
identity certificate, and optionally its certificate
chain is included in the SignedData certificates that
encapsulate the PKIData.

For asymmetric-key-based origin authentication based on
the initial device identity certificate's private key
that signs the encapsulated CSR signed by the local
device identity certificate'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 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 is the bodyPartID and
the certificateRequest elements. PKIData contains one
cmsSequence element and no controlSequence, reqSequence,
or otherMsgSequence elements. The certificateRequest
is signed with the local device identity certificate's
private key. The initial device identity certificate
and optionally its certificate chain is included in
the SignedData certificates that encapsulate the
PKIData.

For shared-secret-based origin authentication of a
CSR signed by the local device identity certificate'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 is the bodyPartID and the certificateRequest
elements. The certificateRequest is signed with the
local device identity certificate's private key. The
initial device identity certificate and optionally its
certificate chain is included in the SignedData
certificates that encapsulate 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 initial device identity certificate's
private key for the associated initial device identity
certificate's public key, PKIMessages contain one
PKIMessage with the header and body elements, do not
contain a 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
initial device identity certificate. The body element
contains an ir, cr, kur, or p10cr CHOICE of type
CertificationRequest. It is signed with the initial
device identity certificate's private key. The
extraCerts element contains the initial device identity
certificate, optionally followed by its certificate
chain excluding the trust anchor.

For asymmetric-key-based origin authentication based
on the initial device identity certificate's private
key that signs the encapsulated CSR signed by the local
device identity certificate's private key, PKIMessages
contain 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 initial device identity
certificate, the protectionAlg contains the
AlgorithmIdentifier of the used signature algorithm,
and the senderKID contains the subject key identifier
of the initial device identity certificate. The body
element contains an ir, cr, kur, or p10cr CHOICE of
type CertificationRequest. It is signed with the local
device identity certificate's private key. The
protection element contains the digital signature
generated with the initial device identity
certificate's private key. The extraCerts element
contains the initial device identity certificate,
optionally followed by its certificate chain excluding
the trust anchor.

For shared-secret-based origin authentication of a
CSR signed by the local device identity certificate's
private key, PKIMessages contain 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 Message
Authentication Code (MAC) algorithm, and the senderKID
contains a reference the recipient can use to identify
the shared secret. The body element contains an ir, cr,
kur, or p10cr CHOICE of type CertificationRequest. It
is signed with the local device identity certificate'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)";
}
}
}
}

}
<CODE ENDS>

4. Security Considerations

This document builds on top of the solution presented in [RFC8572],
and therefore all the security considerations discussed in [RFC8572]
apply here as well.

For the various CSR formats, when using PKCS#10, the security
considerations in [RFC2986] apply; when using CMP, the security
considerations in [RFC4210] apply; and when using CMC, the security
considerations in [RFC5272] apply.

For the various authentication mechanisms, when using TLS-level
authentication, the security considerations in [RFC8446] apply, and
when using HTTP-level authentication, the security considerations in
[RFC9110] apply.

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 to authenticate the
device it is issued to.

It is RECOMMENDED that devices are manufactured with a hardware
security module (HSM), such as a trusted platform module (TPM), to
generate and 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 is unable
to use an HSM to protect the private key, it is RECOMMENDED to
periodically reset the private key (and associated identity
certificates) in order to minimize the lifetime of unprotected
private keys. For instance, a Network Management System (NMS)
controller/orchestrator application could periodically prompt the
SZTP-client to generate a new private key and provide a certificate
signing request (CSR) or, alternatively, push both the key and an
identity certificate to the SZTP-client using, e.g., a PKCS#12
message [RFC7292]. In another example, the SZTP-client could be
configured to periodically reset the configuration to its factory
default, thus causing removal of the private key and associated
identity certificates and re-execution of the SZTP protocol.

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.

Implementations must randomly generate nonces and private keys. The
use of inadequate pseudorandom number generators (PRNGs) to generate
cryptographic keys can result in little or no security. An attacker
may find it much easier to reproduce the PRNG environment that
produced the keys, searching the resulting small set of
possibilities, rather than brute force searching the whole key space.
As an example of predictable random numbers, see CVE-2008-0166
[CVE-2008-0166], and some consequences of low-entropy random numbers
are discussed in "Mining Your Ps and Qs" [MiningPsQs]. The
generation of quality random numbers is difficult. [ISO.20543-2019],
[NIST.SP.800-90Ar1], BSI AIS 31 [AIS31], BCP 106 [RFC4086], and
others offer valuable guidance in this area.

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]).

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. Protection of the private-key information is vital
to public-key cryptography. Disclosure of the private-key material
to another entity can lead to masquerades.

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 [RFC8572].

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

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 instead
pass the "signed-data-preferred" input parameter, as discussed in
Appendix B of [RFC8572].

4.1.5. Selecting the Best Origin Authentication Mechanism

The origin of the CSR must 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 CSR does not support
origin authentication.

The CMP and CMC request formats support origin authentication using
both PKI and a 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 [RFC8808].

4.2. SZTP-Server Considerations

4.2.1. Verifying Proof-of-Possession

Regardless, if using a new asymmetric key or the bootstrapping
device's manufacturer-generated key (e.g., the IDevID key), the
public key is placed in the CSR and the CSR is signed by that private
key. Proof-of-possession of the private key is verified by ensuring
the signature over the CSR using the public key placed in the CSR.

4.2.2. Verifying Proof-of-Origin

When the bootstrapping device's manufacturer-generated private key
(e.g., the IDevID key) is reused for the CSR, proof-of-origin is
verified by validating the IDevID-issuer cert and ensuring that the
CSR uses the same key pair.

When the bootstrapping device's manufacturer-generated private key
(e.g., an IDevID key from IEEE 802.1AR) is reused for the CSR, proof-
of-origin is verified by validating the IDevID certification path and
ensuring that the CSR uses the same key pair.

When a fresh asymmetric key is used with the CMP or CMC formats, the
authentication is part of the protocols, which could employ either
the manufacturer-generated private key or a shared secret. In
addition, CMP and CMC support processing by an RA before the request
is passed to the CA, which allows for more robust handling of errors.

4.2.3. 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 of 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

5.1. The IETF XML Registry

IANA has registered two URIs in the "ns" registry of the "IETF XML
Registry" [RFC3688] maintained at <https://www.iana.org/assignments/
xml-registry/>.

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

IANA has registered two YANG modules in the "YANG Module Names"
registry [RFC6020] maintained at <https://www.iana.org/assignments/
yang-parameters/>.

Name: ietf-sztp-csr
Namespace: urn:ietf:params:xml:ns:yang:ietf-sztp-csr
Prefix: sztp-csr
Reference: RFC 9646

Name: ietf-ztp-types
Namespace: urn:ietf:params:xml:ns:yang:ietf-ztp-types
Prefix: ztp-types
Reference: RFC 9646

6. References

6.1. Normative References

[ITU.X690.2021]
ITU, "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,
February 2021, <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>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

[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>.

[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.

[RFC9640] Watsen, K., "YANG Data Types and Groupings for
Cryptography", RFC 9640, DOI 10.17487/RFC9640, October
2024, <https://www.rfc-editor.org/info/rfc9640>.

6.2. Informative References

[AIS31] Killmann, W. and W. Schindler, "A proposal for:
Functionality classes for random number generators -
Version 2.0", September 2011,
<https://www.bsi.bund.de/SharedDocs/Downloads/DE/BSI/
Zertifizierung/Interpretationen/AIS_31_Functionality_class
es_for_random_number_generators_e.pdf>.

[CVE-2008-0166]
National Institute of Science and Technology (NIST),
"National Vulnerability Database - CVE-2008-0166 Detail",
May 2008,
<https://nvd.nist.gov/vuln/detail/CVE-2008-0166>.

[ISO.20543-2019]
International Organization for Standardization (ISO),
"Information technology -- Security techniques -- Test and
analysis methods for random bit generators within ISO/IEC
19790 and ISO/IEC 15408", ISO/IEC 20543:2019, October
2019.

[MiningPsQs]
Heninger, N., Durumeric, Z., Wustrow, E., and J.
Halderman, "Mining Your Ps and Qs: Detection of Widespread
Weak Keys in Network Devices", Security'12: Proceedings of
the 21st USENIX Conference on Security Symposium, August
2012, <https://www.usenix.org/conference/usenixsecurity12/
technical-sessions/presentation/heninger>.

[NIST.SP.800-90Ar1]
Barker, E. and J. Kelsey, "Recommendation for Random
Number Generation Using Deterministic Random Bit
Generators", DOI 10.6028/NIST.SP.800-90Ar1, NIST
SP 800-90Ar1, June 2015,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-90Ar1.pdf>.

[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.

[RFC7292] Moriarty, K., Ed., Nystrom, M., Parkinson, S., Rusch, A.,
and M. Scott, "PKCS #12: Personal Information Exchange
Syntax v1.1", RFC 7292, DOI 10.17487/RFC7292, July 2014,
<https://www.rfc-editor.org/info/rfc7292>.

[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>.

[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.

[RFC8808] Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
Factory Default Settings", RFC 8808, DOI 10.17487/RFC8808,
August 2020, <https://www.rfc-editor.org/info/rfc8808>.

[RFC9641] Watsen, K., "A YANG Data Model for a Truststore",
RFC 9641, DOI 10.17487/RFC9641, October 2024,
<https://www.rfc-editor.org/info/rfc9641>.

[RFC9642] Watsen, K., "A YANG Data Model for a Keystore", RFC 9642,
DOI 10.17487/RFC9642, October 2024,
<https://www.rfc-editor.org/info/rfc9642>.

[Std-802.1AR-2018]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Secure Device Identity", August 2018,
<https://standards.ieee.org/ieee/802.1AR/6995/>.

Acknowledgements

The authors would like to thank for following for lively discussions
on list and in the halls (ordered by first name): Benjamin Kaduk, Dan
Romascanu, David von Oheimb, Éric Vyncke, Guy Fedorkow, Hendrik
Brockhaus, Joe Clarke, Meral Shirazipour, Murray Kucherawy, Rich
Salz, Rob Wilton, Roman Danyliw, Qin Wu, Yaron Sheffer, and
Zaheduzzaman Sarkar.

Contributors

Special thanks go 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: [email protected]

Russ Housley
Vigil Security, LLC
Email: [email protected]

Sean Turner
sn3rd
Email: [email protected]