Watsen Networks

kent+ietf@watsen.net

Vigil Security, LLC

housley@vigilsec.com

sn3rd

sean@sn3rd.com

ops netconf zerotouch bootstrap sztp ztp csr pkcs#10 p10 p10cr cmc cmp 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 .

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 () 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

• .  Introduction
  • .  Overview
  • .  Terminology
  • .  Requirements Language
  • .  Conventions
• .  The "ietf-sztp-csr" Module
  • .  Data Model Overview
  • .  Example Usage
  • .  YANG Module
• .  The "ietf-ztp-types" Module
  • .  Data Model Overview
  • .  YANG Module
• .  Security Considerations
  • .  SZTP-Client Considerations
    • .  Ensuring the Integrity of Asymmetric Private Keys
    • .  Reuse of a Manufacturer-Generated Private Key
    • .  Replay Attack Protection
    • .  Connecting to an Untrusted Bootstrap Server
    • .  Selecting the Best Origin Authentication Mechanism
    • .  Clearing the Private Key and Associated Certificate
  • .  SZTP-Server Considerations
    • .  Verifying Proof-of-Possession
    • .  Verifying Proof-of-Origin
    • .  Supporting SZTP-Clients That Don't Trust the SZTP-Server
  • .  Security Considerations for the "ietf-sztp-csr" YANG Module
  • .  Security Considerations for the "ietf-ztp-types" YANG Module
• .  IANA Considerations
  • .  The IETF XML Registry
  • .  The YANG Module Names Registry
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Contributors
• Authors' Addresses

Introduction

Overview This document extends the input to the "get-bootstrapping-data" RPC defined in to include an optional certificate signing request (CSR) , enabling a bootstrapping device to additionally obtain an identity certificate (e.g., an LDevID from ) 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 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 around the third grouping.

Terminology This document uses the following terms from :

• 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.

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 when, and only when, they appear in all capitals, as shown here.

Conventions Various examples in this document use "BASE64VALUE=" as a placeholder value for binary data that has been base64 encoded (per ). 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 .

The "ietf-sztp-csr" Module The "ietf-sztp-csr" module is a YANG 1.1 module that augments the "ietf-sztp-bootstrap-server" module defined in and defines a YANG "structure" that is to be conveyed in the "error-info" node defined in .

Data Model Overview The following tree diagram 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 .

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 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 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

Example Usage 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 . 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 . 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 ). 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 .

YANG Module This module augments an RPC defined in . The module uses data types and groupings defined in , , and . The module also has an informative reference to . 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: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. 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; } }

The "ietf-ztp-types" Module This section defines a YANG 1.1 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 .

Data Model Overview The following tree diagram 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

YANG Module This module uses data types and groupings defined in and . The module has additional normative references to , , , and and an informative reference to . 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:netconf@ietf.org> Authors: Kent Watsen <mailto:kent+ietf@watsen.net> Russ Housley <mailto:housley@vigilsec.com> Sean Turner <mailto:sean@sn3rd.com>"; description "This module defines three groupings that enable bootstrapping devices to 1) indicate if and how they support generating CSRs, 2) obtain a request to generate a CSR, and 3) communicate the requested CSR. The 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)"; } } } } }

Security Considerations This document builds on top of the solution presented in , and therefore all the security considerations discussed in apply here as well. For the various CSR formats, when using PKCS#10, the security considerations in apply; when using CMP, the security considerations in apply; and when using CMC, the security considerations in apply. For the various authentication mechanisms, when using TLS-level authentication, the security considerations in apply, and when using HTTP-level authentication, the security considerations in apply.

SZTP-Client Considerations

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 . 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.

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 , and some consequences of low-entropy random numbers are discussed in "Mining Your Ps and Qs" . The generation of quality random numbers is difficult. , , BSI AIS 31 , BCP 106 , 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 ). 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.

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.

Connecting to an Untrusted Bootstrap Server allows SZTP-clients to connect to untrusted SZTP-servers by blindly authenticating the SZTP-server's TLS end-entity certificate. As is discussed in , 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 . 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 , 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 .

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 , 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.

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 .

SZTP-Server Considerations

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.

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.

Supporting SZTP-Clients That Don't Trust the SZTP-Server allows SZTP-clients to connect to untrusted SZTP-servers by blindly authenticating the SZTP-server's TLS end-entity certificate. As is recommended in 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 .

Security Considerations for the "ietf-sztp-csr" YANG Module The recommended format for documenting the security considerations for YANG modules is described in . However, this module only augments two input parameters into the "get-bootstrapping-data" RPC in 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 .
• Security considerations for the "input" parameters passed inside the "get-bootstrapping-data" RPC are described in .

Security Considerations for the "ietf-ztp-types" YANG Module The recommended format for documenting the security considerations for YANG modules is described in . 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.

IANA Considerations

The IETF XML Registry IANA has registered two URIs in the "ns" registry of the "IETF XML Registry" maintained at .

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.

The YANG Module Names Registry IANA has registered two YANG modules in the "YANG Module Names" registry maintained at .

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

References Normative References ITU In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community. This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas. This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides on-line interactions between PKI components, including an exchange between a Certification Authority (CA) and a client system. [STANDARDS-TRACK] This document defines the base syntax for CMC, a Certificate Management protocol using the Cryptographic Message Syntax (CMS). This protocol addresses two immediate needs within the Internet Public Key Infrastructure (PKI) community: 1. The need for an interface to public key certification products and services based on CMS and PKCS #10 (Public Key Cryptography Standard), and 2. The need for a PKI enrollment protocol for encryption only keys due to algorithm or hardware design. CMC also requires the use of the transport document and the requirements usage document along with this document for a full definition. [STANDARDS-TRACK] YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS-TRACK] YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF). This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document presents a technique to securely provision a networking device when it is booting in a factory-default state. Variations in the solution enable it to be used on both public and private networks. The provisioning steps are able to update the boot image, commit an initial configuration, and execute arbitrary scripts to address auxiliary needs. The updated device is subsequently able to establish secure connections with other systems. For instance, a device may establish NETCONF (RFC 6241) and/or RESTCONF (RFC 8040) connections with deployment-specific network management systems. This document describes YANG mechanisms for defining abstract data structures with YANG. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. Watsen Networks Informative References T-Systems GEI GmbH Bundesamt für Sicherheit in der Informationstechnik (BSI) National Institute of Science and Technology (NIST) International Organization for Standardization (ISO) UC San Diego University of Michigan University of Michigan University of Michigan Security'12: Proceedings of the 21st USENIX Conference on Security Symposium Information Technology Laboratory Information Technology Laboratory Security systems are built on strong cryptographic algorithms that foil pattern analysis attempts. However, the security of these systems is dependent on generating secret quantities for passwords, cryptographic keys, and similar quantities. The use of pseudo-random processes to generate secret quantities can result in pseudo-security. A sophisticated attacker may find it easier to reproduce the environment that produced the secret quantities and to search the resulting small set of possibilities than to locate the quantities in the whole of the potential number space. Choosing random quantities to foil a resourceful and motivated adversary is surprisingly difficult. This document points out many pitfalls in using poor entropy sources or traditional pseudo-random number generation techniques for generating such quantities. It recommends the use of truly random hardware techniques and shows that the existing hardware on many systems can be used for this purpose. It provides suggestions to ameliorate the problem when a hardware solution is not available, and it gives examples of how large such quantities need to be for some applications. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. PKCS #12 v1.1 describes a transfer syntax for personal identity information, including private keys, certificates, miscellaneous secrets, and extensions. Machines, applications, browsers, Internet kiosks, and so on, that support this standard will allow a user to import, export, and exercise a single set of personal identity information. This standard supports direct transfer of personal information under several privacy and integrity modes. This document represents a republication of PKCS #12 v1.1 from RSA Laboratories' Public Key Cryptography Standard (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document captures the current syntax used in YANG module tree diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language. This memo provides guidelines for authors and reviewers of specifications containing YANG modules. Recommendations and procedures are defined, which are intended to increase interoperability and usability of Network Configuration Protocol (NETCONF) and RESTCONF protocol implementations that utilize YANG modules. This document obsoletes RFC 6087. This document defines two strategies for handling long lines in width-bounded text content. One strategy, called the "single backslash" strategy, is based on the historical use of a single backslash ('\') character to indicate where line-folding has occurred, with the continuation occurring with the first character that is not a space character (' ') on the next line. The second strategy, called the "double backslash" strategy, extends the first strategy by adding a second backslash character to identify where the continuation begins and is thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content. This document defines a YANG data model with the "factory-reset" RPC to allow clients to reset a server back to its factory default condition. It also defines an optional "factory-default" datastore to allow clients to read the factory default configuration for the device. The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in RFC 8342. Watsen Networks Watsen Networks IEEE

Acknowledgements The authors would like to thank for following for lively discussions on list and in the halls (ordered by first name): , , , , , , , , , , , , , , and .

Contributors Special thanks go to and for helping with the descriptions for the "cmc-csr" and "cmp-csr" nodes.

Authors' Addresses Watsen Networks

kent+ietf@watsen.net

Vigil Security, LLC

housley@vigilsec.com

sn3rd

sean@sn3rd.com