NETCONF Working Group K. Watsen Internet-Draft Watsen Networks Updates: 8572 (if approved) R. Housley Intended status: Standards Track Vigil Security, LLC Expires: 17 December 2021 S. Turner sn3rd 15 June 2021 Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request draft-ietf-netconf-sztp-csr-03 Abstract This draft extends the "get-bootstrapping-data" RPC defined in RFC 8572 to include an optional certificate signing request (CSR), enabling a bootstrapping device to additionally obtain an identity certificate (e.g., an LDevID, from IEEE 802.1AR) as part of the "onboarding information" response provided in the RPC-reply. Editorial Note (To be removed by RFC Editor) This draft contains many placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document. Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements: * "XXXX" --> the assigned numerical RFC value for this draft * "AAAA" --> the assigned RFC value for I-D.ietf-netconf-crypto- types Artwork in this document contains a placeholder value for the publication date of this draft. Please apply the following replacement: * "2021-06-15" --> the publication date of this draft This document contains references to other drafts in progress, both in the Normative References section, as well as in body text throughout. Please update the following references to reflect their final RFC assignments: * I-D.ietf-netconf-crypto-types Watsen, et al. Expires 17 December 2021 [Page 1] Internet-Draft Conveying a CSR in an SZTP Request June 2021 * I-D.ietf-netconf-keystore * I-D.ietf-netconf-trust-anchors * I-D.ietf-netmod-factory-default Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 17 December 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. The "ietf-sztp-csr" Module . . . . . . . . . . . . . . . . . 4 2.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 4 2.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 7 2.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 13 3. Security Considerations . . . . . . . . . . . . . . . . . . . 23 Watsen, et al. Expires 17 December 2021 [Page 2] Internet-Draft Conveying a CSR in an SZTP Request June 2021 3.1. SZTP-Client Considerations . . . . . . . . . . . . . . . 23 3.1.1. Ensuring the Integrity of Asymmetric Private Keys . . 23 3.1.2. Reuse of a Manufacturer-generated Private Key . . . . 23 3.1.3. Replay Attack Protection . . . . . . . . . . . . . . 23 3.1.4. Connecting to an Untrusted Bootstrap Server . . . . . 24 3.1.5. Selecting the Best Origin Authentication Mechanism . 24 3.1.6. Clearing the Private Key and Associated Certificate . . . . . . . . . . . . . . . . . . . . . 25 3.2. SZTP-Server Considerations . . . . . . . . . . . . . . . 25 3.2.1. Conveying Proof of Possession to a CA . . . . . . . . 25 3.2.2. Supporting SZTP-Clients that don't trust the SZTP-Server . . . . . . . . . . . . . . . . . . . . . 25 3.2.3. YANG Module Considerations . . . . . . . . . . . . . 26 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 4.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 26 4.2. The "YANG Module Names" Registry . . . . . . . . . . . . 26 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.1. Normative References . . . . . . . . . . . . . . . . . . 26 5.2. Informative References . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 1. Introduction 1.1. Overview This draft extends the "get-bootstrapping-data" RPC defined in [RFC8572] to include an optional certificate signing request (CSR) [RFC2986], enabling a bootstrapping device to additionally obtain an identity certificate (e.g., an LDevID [Std-802.1AR-2018]) as part of the "onboarding information" response provided in the RPC-reply. 1.2. Terminology This document uses the following terms from [RFC8572]: * Bootstrap Server * Bootstrapping Data * Conveyed Information * Device * Manufacturer * Onboarding Information * Signed Data This document defines the following new terms: SZTP-client The term "SZTP-client" refers to a "device" that is using a "bootstrap server" as a source of "bootstrapping data". Watsen, et al. Expires 17 December 2021 [Page 3] Internet-Draft Conveying a CSR in an SZTP Request June 2021 SZTP-server The term "SZTP-server" is an alternative term for "bootstrap server" that is symmetric with the "SZTP-client" term. 1.3. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. The "ietf-sztp-csr" Module This section defines a YANG 1.1 [RFC7950] module that augments the "ietf-sztp-bootstrap-server" module defined in [RFC8572] and defines a YANG "structure". The augmentation adds two nodes ("csr-support" and "csr") to the "input" parameter of the "get-bootstrapping-data" RPC defined in [RFC8572]. The YANG structure, "request-info", defines data returned in the "error-info" node defined in Section 7.1 of [RFC8040]. 2.1. Data Model Overview The following tree diagram [RFC8340] illustrates the "ietf-sztp-csr" module. The diagram shows the definition of an augmentation adding descendent nodes "csr-support" and "csr" and the definition of a structure called "request-info". In the order of their intended use: * The "csr-support" node is used by the SZTP-client to signal to the SZTP-server that it supports the ability the generate CSRs, per this specification. The "csr-support" parameter carries details regarding the SZTP-client's ability to generate CSRs. * The "request-info" structure is used by the SZTP-server to signal back to the SZTP-client its desire to sign a CSR. The "request- info" structure additionally communicates details about the CSR the SZTP-client is to generate. * The "csr" node is used by the SZTP-client to communicate its CSR to the SZTP-server. Not shown is how the SZTP-server communicates the signed certificate to the SZTP-client; how to do this is discussed later in this document. Watsen, et al. Expires 17 December 2021 [Page 4] Internet-Draft Conveying a CSR in an SZTP Request June 2021 module: ietf-sztp-csr augment /sztp-svr:get-bootstrapping-data/sztp-svr:input: +---w csr-support! | +---w key-generation! | | +---w supported-algorithms | | +---w algorithm-identifier* binary | +---w csr-generation | +---w supported-formats | +---w format-identifier* identityref +---w csr! +---w (request-type) +--:(p10) | +---w p10? ct:csr +--:(cmc) | +---w cmc? binary +--:(cmp) +---w cmp? binary structure: request-info +--ro key-generation! | +--ro selected-algorithm | +--ro algorithm-identifier binary +--ro csr-generation | +--ro selected-format | +--ro format-identifier identityref +--ro cert-req-info? ietf-crypto-types:csr-info To further illustrate how the augmentation and structure defined by the "ietf-sztp-csr" module are used, below are two additional tree diagrams showing these nodes placed where they are used. The following tree diagram [RFC8340] illustrates SZTP's "get- bootstrapping-data" RPC with the augmentation in place. Watsen, et al. Expires 17 December 2021 [Page 5] Internet-Draft Conveying a CSR in an SZTP Request June 2021 module: ietf-sztp-bootstrap-server rpcs: +---x get-bootstrapping-data +---w input | +---w signed-data-preferred? empty | +---w hw-model? string | +---w os-name? string | +---w os-version? string | +---w nonce? binary | +---w sztp-csr:csr-support! | | +---w sztp-csr:key-generation! | | | +---w sztp-csr:supported-algorithms | | | +---w sztp-csr:algorithm-identifier* binary | | +---w sztp-csr:csr-generation | | +---w sztp-csr:supported-formats | | +---w sztp-csr:format-identifier* identityref | +---w sztp-csr:csr! | +---w (sztp-csr:request-type) | +--:(sztp-csr:p10) | | +---w sztp-csr:p10? ct:csr | +--:(sztp-csr:cmc) | | +---w sztp-csr:cmc? binary | +--:(sztp-csr:cmp) | +---w sztp-csr:cmp? binary +--ro output +--ro reporting-level? enumeration {onboarding-server}? +--ro conveyed-information cms +--ro owner-certificate? cms +--ro ownership-voucher? cms The following tree diagram [RFC8340] illustrates RESTCONF's "errors" RPC-reply message with the "request-info" structure in place. Watsen, et al. Expires 17 December 2021 [Page 6] Internet-Draft Conveying a CSR in an SZTP Request June 2021 module: ietf-restconf +--ro errors +--ro error* [] +--ro error-type enumeration +--ro error-tag string +--ro error-app-tag? string +--ro error-path? instance-identifier +--ro error-message? string +--ro error-info +--ro request-info +--ro key-generation! | +--ro selected-algorithm | +--ro algorithm-identifier binary +--ro csr-generation | +--ro selected-format | +--ro format-identifier identityref +--ro cert-req-info? ct:csr-info 2.2. Example Usage | The examples below are encoded using JSON, but they could | equally well be encoded using XML, as is supported by SZTP. An SZTP-client implementing this specification would signal to the bootstrap server its willingness to generate a CSR by including the "csr-support" node in its "get-bootstrapping-data" RPC, as illustrated below. REQUEST Watsen, et al. Expires 17 December 2021 [Page 7] Internet-Draft Conveying a CSR in an SZTP Request June 2021 =============== NOTE: '\' line wrapping per RFC 8792 ================ POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\ ng-data HTTP/1.1 HOST: example.com Content-Type: application/yang.data+json { "ietf-sztp-bootstrap-server:input" : { "hw-model": "model-x", "os-name": "vendor-os", "os-version": "17.3R2.1", "nonce": "extralongbase64encodedvalue=", "ietf-sztp-csr:csr-support": { "key-generation": { "supported-algorithms": { "algorithm-identifier": [ "base64encodedvalue1=", "base64encodedvalue2=", "base64encodedvalue3=" ] } }, "csr-generation": { "supported-formats": { "format-identifier": [ "ietf-sztp-csr:p10", "ietf-sztp-csr:cmc", "ietf-sztp-csr:cmp" ] } } } } } Assuming the SZTP-server wishes to prompt the SZTP-client to provide a CSR, then it would respond with an HTTP 400 (Bad Request) error code: RESPONSE Watsen, et al. Expires 17 December 2021 [Page 8] Internet-Draft Conveying a CSR in an SZTP Request June 2021 HTTP/1.1 400 Bad Request Date: Sat, 31 Oct 2015 17:02:40 GMT Server: example-server Content-Type: application/yang.data+json { "ietf-restconf:errors" : { "error" : [ { "error-type": "application", "error-tag": "missing-attribute", "error-message": "Missing input parameter", "error-info": { "ietf-sztp-csr:request-info": { "key-generation": { "selected-algorithm": { "algorithm-identifier": "base64EncodedValue==" } }, "csr-generation": { "selected-format": { "format-identifier": "ietf-sztp-csr:cmc" } }, "cert-req-info": "base64EncodedValue==" } } } ] } } Upon being prompted to provide a CSR, the SZTP-client would POST another "get-bootstrapping-data" request, but this time including the "csr" node to convey its CSR to the SZTP-server: REQUEST Watsen, et al. Expires 17 December 2021 [Page 9] Internet-Draft Conveying a CSR in an SZTP Request June 2021 =============== NOTE: '\' line wrapping per RFC 8792 ================ POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\ ng-data HTTP/1.1 HOST: example.com Content-Type: application/yang.data+json { "ietf-sztp-bootstrap-server:input" : { "hw-model": "model-x", "os-name": "vendor-os", "os-version": "17.3R2.1", "nonce": "extralongbase64encodedvalue=", "ietf-sztp-csr:csr": { "p10": "base64encodedvalue==" } } } The SZTP-server responds with "onboarding-information" (encoded inside the "conveyed-information" node) containing a signed identity certificate for the CSR provided by the SZTP-client: RESPONSE HTTP/1.1 200 OK Date: Sat, 31 Oct 2015 17:02:40 GMT Server: example-server Content-Type: application/yang.data+json { "ietf-sztp-bootstrap-server:output" : { "reporting-level": "verbose", "conveyed-information": "base64encodedvalue==" } } How the signed certificate is conveyed inside the onboarding information is outside the scope of this document. Some implementations may choose to convey it inside a script (e.g., SZTP's "pre-configuration-script"), while other implementations may choose to convey it inside the SZTP "configuration" node. SZTP onboarding information is described in Section 2.2 of [RFC8572]. Following are two examples of conveying the signed certificate inside the "configuration" node. Both examples assume that the SZTP-client understands the "ietf-keystore" module defined in [I-D.ietf-netconf-keystore]. Watsen, et al. Expires 17 December 2021 [Page 10] Internet-Draft Conveying a CSR in an SZTP Request June 2021 This first example illustrates the case where the signed certificate is for the same asymmetric key used by the SZTP-client's manufacturer-generated identity certificate (e.g., an IDevID, from [Std-802.1AR-2018]). As such, the configuration needs to associate the newly signed certificate with the existing asymmetric key: =============== NOTE: '\' line wrapping per RFC 8792 ================ { "ietf-keystore:keystore": { "asymmetric-keys": { "asymmetric-key": [ { "name": "Manufacturer-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\ -info-format", "public-key": "base64encodedvalue==", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Manufacturer-Generated IDevID Cert", "cert-data": "base64encodedvalue==" }, { "name": "Newly-Generated LDevID Cert", "cert-data": "base64encodedvalue==" } ] } } ] } } } This second example illustrates the case where the signed certificate is for a newly generated asymmetric key. As such, the configuration needs to associate the newly signed certificate with the newly generated asymmetric key: Watsen, et al. Expires 17 December 2021 [Page 11] Internet-Draft Conveying a CSR in an SZTP Request June 2021 =============== NOTE: '\' line wrapping per RFC 8792 ================ { "ietf-keystore:keystore": { "asymmetric-keys": { "asymmetric-key": [ { "name": "Manufacturer-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\ -info-format", "public-key": "base64encodedvalue==", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Manufacturer-Generated IDevID Cert", "cert-data": "base64encodedvalue==" } ] } }, { "name": "Newly-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\ -info-format", "public-key": "base64encodedvalue==", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Newly-Generated LDevID Cert", "cert-data": "base64encodedvalue==" } ] } } ] } } } In addition to configuring the signed certificate, it is often necessary to also configure the Issuer's signing certificate so that the device (i.e., STZP-client) can authenticate certificates presented by peer devices signed by the same issuer as its own. While outside the scope of this document, one way to do this would be to use the "ietf-truststore" module defined in [I-D.ietf-netconf-trust-anchors]. Watsen, et al. Expires 17 December 2021 [Page 12] Internet-Draft Conveying a CSR in an SZTP Request June 2021 2.3. YANG Module This module augments an RPC defined in [RFC8572], uses a data type defined in [I-D.ietf-netconf-crypto-types], has an normative references to [RFC2986] and [ITU.X690.2015], and an informative reference to [Std-802.1AR-2018]. file "ietf-sztp-csr@2021-06-15.yang" module ietf-sztp-csr { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-sztp-csr"; prefix sztp-csr; import ietf-sztp-bootstrap-server { prefix sztp-svr; reference "RFC 8572: Secure Zero Touch Provisioning (SZTP)"; } import ietf-yang-structure-ext { prefix sx; reference "RFC 8791: YANG Data Structure Extensions"; } import ietf-crypto-types { prefix ct; reference "RFC AAAA: YANG Data Types and Groupings for Cryptography"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: http://tools.ietf.org/wg/netconf WG List: Authors: Kent Watsen Russ Housley Sean Turner "; 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 Watsen, et al. Expires 17 December 2021 [Page 13] Internet-Draft Conveying a CSR in an SZTP Request June 2021 response. Copyright (c) 2020 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2021-06-15 { description "Initial version"; reference "RFC XXXX: Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request"; } identity certificate-request-format { description "A base identity for the request formats supported by the SZTP-client. Additional derived identities MAY be defined by future efforts."; } identity p10 { base certificate-request-format; description "Indicates that the SZTP-client supports generating requests using the 'CertificationRequest' structure defined in RFC 2986."; reference Watsen, et al. Expires 17 December 2021 [Page 14] Internet-Draft Conveying a CSR in an SZTP Request June 2021 "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7"; } identity cmc { base certificate-request-format; description "Indicates that the SZTP-client supports generating requests using a constrained version of the 'Full PKI Request' structure defined in RFC 5272."; reference "RFC 5272: Certificate Management over CMS (CMC)"; } identity cmp { base certificate-request-format; description "Indicates that the SZTP-client supports generating requests that contain a PKCS#10 Certificate Signing Request (p10cr), as defined in RFC 2986, encapsulated in a Nested Message Content (nested), as defined in RFC 4210."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7 RFC 4210: Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP)"; } // Protocol-accessible nodes augment "/sztp-svr:get-bootstrapping-data/sztp-svr:input" { description "This augmentation adds the 'csr-support' and 'csr' nodes to the SZTP (RFC 8572) 'get-bootstrapping-data' request message, enabling the SZTP-client to obtain an identity certificate (e.g., an LDevID from IEEE 802.1AR) as part of the onboarding information response provided by the SZTP-server. The 'csr-support' node enables the SZTP-client to indicate that it supports generating certificate signing requests (CSRs), and to provide details around the CSRs it is able to generate. The 'csr' node enables the SZTP-client to relay a CSR to the SZTP-server."; reference "IEEE 802.1AR: IEEE Standard for Local and metropolitan Watsen, et al. Expires 17 December 2021 [Page 15] Internet-Draft Conveying a CSR in an SZTP Request June 2021 area networks - Secure Device Identity RFC 8572: Secure Zero Touch Provisioning (SZTP)"; container csr-support { presence "Indicates that the SZTP-client is capable of sending CSRs."; description "The 'csr-support' node enables the SZTP-client to indicate that it supports generating certificate signing requests (CSRs), and provide details around the CSRs it is able to generate. When present, the SZTP-server MAY respond with the HTTP error 400 (Bad Request) with an 'ietf-restconf:errors' document having the 'error-tag' value 'missing-attribute' and the 'error-info' node containing the 'request-info' structure described in this module."; container key-generation { presence "Indicates that the SZTP-client is capable of generating a new asymmetric key pair. If this node is not present, the SZTP-server MAY request a CSR using the asymmetric key associated with the device's existing identity certificate (e.g., an IDevID from IEEE 802.1AR)."; description "Specifies details for the SZTP-client's ability to generate a new asymmetric key pair."; container supported-algorithms { description "A list of public key algorithms supported by the SZTP-client for generating a new key."; leaf-list algorithm-identifier { type binary; min-elements 1; description "An AlgorithmIdentifier, as defined in RFC 2986, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7 ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } Watsen, et al. Expires 17 December 2021 [Page 16] Internet-Draft Conveying a CSR in an SZTP Request June 2021 } } container csr-generation { description "Specifies details for the SZTP-client's ability to generate a certificate signing requests."; container supported-formats { description "A list of certificate request formats supported by the SZTP-client for generating a new key."; leaf-list format-identifier { type identityref { base certificate-request-format; } min-elements 1; description "A certificate request format supported by the SZTP-client."; } } } } container csr { presence "Indicates that the SZTP-client has sent a CSR."; description "The 'csr' node enables the SZTP-client to convey a certificate signing request, using the encoding format selected by the SZT-server's 'request-info' response to the SZTP-client's previously sent 'get-bootstrapping-data' request containing the 'csr-support' node. When present, the SZTP-server SHOULD respond with an SZTP onboarding information message containing a signed certificate for the conveyed CSR. The SZTP-server MAY alternatively respond with another HTTP error containing another 'request-info', in which case the SZTP-client MUST invalidate the CSR sent in this node."; choice request-type { mandatory true; description "A choice amongst certificate signing request formats. Additional formats MAY be augmented into this 'choice' statement by future efforts."; case p10 { leaf p10 { Watsen, et al. Expires 17 December 2021 [Page 17] Internet-Draft Conveying a CSR in an SZTP Request June 2021 type ct:csr; description "A CertificationRequest structure, per RFC 2986. Please see 'csr' in RFC AAAA for encoding details."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification RFC AAAA: YANG Data Types and Groupings for Cryptography"; } } case cmc { leaf cmc { type binary; description "A constrained version of the 'Full PKI Request' message defined in RFC 5272, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690. For asymmetric key-based origin authentication of a CSR based on the IDevID's private key for the associated IDevID's public key, the PKIData contains one reqSequence element and no controlSequence, cmsSequence, or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the IDevID's private key. For asymmetric key-based origin authentication based on the IDevID's private key that encapsulates a CSR signed by the LDevID's private key, the PKIData contains one cmsSequence element and no controlSequence, reqSequence, or otherMsgSequence elements. The cmsSequence is the TaggedContentInfo and it includes a bodyPartID element and a contentInfo. The contentInfo is a SignedData encapsulating a PKIData with one reqSequence element and no controlSequence, cmsSequence, or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the LDevID's private key. Watsen, et al. Expires 17 December 2021 [Page 18] Internet-Draft Conveying a CSR in an SZTP Request June 2021 For shared secret-based origin authentication of a CSR signed by the LDevID's private key, the PKIData contains one cmsSequence element and no controlSequence, reqSequence, or otherMsgSequence elements. The cmsSequence is the TaggedContentInfo and it includes a bodyPartID element and a contentInfo. The contentInfo is an AuthenticatedData encapsulating a PKIData with one reqSequence element and no controlSequence, cmsSequence, or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the LDevID's private key."; reference "RFC 5272: Certificate Management over CMS (CMC) ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } case cmp { leaf cmp { type binary; description "A PKIMessage structure, as defined in RFC 4210, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690. The PKIMessage structure contains a PKCS#10 Certificate Signing Request (p10cr), as defined in RFC 2986, encapsulated in a Nested Message Content (nested) structure, as defined in RFC 4210. For asymmetric key-based origin authentication of a CSR based on the IDevID's private key for the associated IDevID's public key, PKIMessages contains one PKIMessage with one body element, a header element that is an empty sequence, and no protection or extraCerts elements. The body element contains a p10cr CHOICE. For asymmetric key-based origin authentication based on the IDevID's private key that encapsulates a CSR signed by the LDevID's private key, PKIMessages Watsen, et al. Expires 17 December 2021 [Page 19] Internet-Draft Conveying a CSR in an SZTP Request June 2021 contains one PKIMessage with one header element, one body element, one protection element, and one extraCerts element. The header element contains pvno, sender, recipient, and protectionAlg elements and no other elements. The body element contains the nested CHOICE. The nested element's PKIMessages contains one PKIMessage with one body element, one header element that is an empty sequence, and no protection or extraCerts elements. The nested element's body element contains a p10cr CHOICE. The protection element contains the digital signature generated with the IDevID's private key. The extraCerts element contains the IDevID certificate. For shared secret-based origin authentication of a CSR signed by the LDevID's private key, PKIMessages contains one PKIMessage with one header element, one body element, one protection element, and no extraCerts element. The header element contains pvno, sender, recipient, and protectionAlg elements and no other elements. The body element contains the nested CHOICE. The nested element's PKIMessages contains one PKIMessage with one body element, one header element that is an empty sequence, and no protection or extraCerts elements. The body element contains a p10cr CHOICE. The protection element contains the MAC value generated with the shared secret."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7 RFC 4210: Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP) ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } } } } sx:structure request-info { container key-generation { Watsen, et al. Expires 17 December 2021 [Page 20] Internet-Draft Conveying a CSR in an SZTP Request June 2021 presence "Indicates that the SZTP-client is to generate a new asymmetric key. If missing, then the SZTP-client MUST reuse the key associated with its existing identity certificate (e.g., IDevID). This leaf MUST only appear if the SZTP-clients 'csr-support' included the 'key-generation' node."; description "A YANG data structure, per RFC 8791, that specifies details for the key that the SZTP-client is to generate."; reference "RFC 8791: YANG Data Structure Extensions"; container selected-algorithm { description "The key algorithm selected by the SZTP-server. The algorithm MUST be one of the algorithms specified by the 'supported-algorithms' node in the SZTP-client's request message."; leaf algorithm-identifier { type binary; mandatory true; description "An AlgorithmIdentifier, as defined in RFC 2986, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7 ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } } container csr-generation { description "Specifies details for the CSR that the SZTP-client is to generate."; container selected-format { description "The CSR format selected by the SZTP-server. The format MUST be one of the formats specified by the 'supported-formats' node in the SZTP-client's request message."; Watsen, et al. Expires 17 December 2021 [Page 21] Internet-Draft Conveying a CSR in an SZTP Request June 2021 leaf format-identifier { type identityref { base certificate-request-format; } mandatory true; description "A certificate request format to be used by the SZTP-client."; } } } leaf cert-req-info { type ct:csr-info; description "A CertificationRequestInfo structure, as defined in RFC 2986, and modeled via a 'typedef' statement by RFC AAAA. Enables the SZTP-server to provide a fully-populated CertificationRequestInfo structure that the SZTP-client only needs to sign in order to generate the complete 'CertificationRequest' structure to send to SZTP-server in its next 'get-bootstrapping-data' request message. When provided, the SZTP-client SHOULD use this structure to generate its CSR; failure to do so MAY result in a 400 (Bad Request) response containing another 'request-info' structure. When not provided, the SZTP-client SHOULD generate a CSR using the same structure defined in its existing identity certificate (e.g., IDevID). It is an error if the 'AlgorithmIdentifier' field contained inside the 'SubjectPublicKeyInfo' field does not match the algorithm identified by the 'selected-algorithm' node."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification RFC AAAA: YANG Data Types and Groupings for Cryptography"; } } } Watsen, et al. Expires 17 December 2021 [Page 22] Internet-Draft Conveying a CSR in an SZTP Request June 2021 3. Security Considerations This document builds on top of the solution presented in [RFC8572] and therefore all the Security Considerations discussed in RFC 8572 apply here as well. 3.1. SZTP-Client Considerations 3.1.1. Ensuring the Integrity of Asymmetric Private Keys The private key the SZTP-client uses for the dynamically-generated identity certificate MUST be protected from inadvertent disclosure in order to prevent identity fraud. The security of this private key is essential in order to ensure the associated identity certificate can be used as a root of trust. It is RECOMMENDED that devices are manufactured with an HSM (hardware security module), such as a TPM (trusted platform module), to generate and forever contain the private key within the security perimeter of the HSM. In such cases, the private key, and its associated certificates, MAY have long validity periods. In cases where the device does not possess an HSM, or otherwise is unable to use an HSM for the private key, it is RECOMMENDED to regenerate the private key (and associated identity certificates) periodically. Details for how to generate a new private key and associate a new identity certificate are outside the scope of this document. 3.1.2. Reuse of a Manufacturer-generated Private Key It is RECOMMENDED that a new private key is generated for each CSR described in this document. This private key SHOULD be protected as well as the built-in private key associated with the device's initial secure 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. 3.1.3. Replay Attack Protection This RFC enables an SZTP-client to announce an ability to generate new key to use for its CSR. Watsen, et al. Expires 17 December 2021 [Page 23] Internet-Draft Conveying a CSR in an SZTP Request June 2021 When the SZTP-server responds with a request for the device to generate a new key, it is essential that the device actually generates a new key. Generating a new key each time enables the random bytes used to create the key to serve the dual-purpose of also acting like a "nonce" used in other mechanisms to detect replay attacks. When a fresh public/private key pair is generated for the request, confirmation to the SZTP-client that the response has not been replayed is enabled by the SZTP-client's fresh public key appearing in the signed certificate provided by the SZTP-server. When a public/private key pair associated with the IDevID used for the request, there may not be confirmation to the SZTP-client that the response has not been replayed; however, the worst case result is a lost certificate that is associated to the private key known only to the SZTP-client. 3.1.4. Connecting to an Untrusted Bootstrap Server [RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers, by blindly authenticating the SZTP-server's TLS end-entity certificate. As is discussed in Section 9.5 of [RFC8572], in such cases the SZTP- client MUST assert that the bootstrapping data returned is signed, if the SZTP-client is to trust it. However, the HTTP error message used in this document cannot be signed data, as described in RFC 8572. Therefore, the solution presented in this document cannot be used when the SZTP-client connects to an untrusted SZTP-server. Consistent with the recommendation presented in Section 9.6 of [RFC8572], SZTP-clients SHOULD NOT passed the "csr-support" input parameter to an untrusted SZTP-server. SZTP-clients SHOULD pass instead the "signed-data-preferred" input parameter, as discussed in Appendix B of [RFC8572]. 3.1.5. Selecting the Best Origin Authentication Mechanism When generating a new key, it is important that the client be able to provide additional proof to the CA that it was the entity that generated the key. Watsen, et al. Expires 17 December 2021 [Page 24] Internet-Draft Conveying a CSR in an SZTP Request June 2021 All of the certificate request formats defined in this document (e.g., CMC, CMP, etc.), not including a raw PKCS#10, support origin authentication. These formats support origin authentication using both PKI and shared secret. Typically only one possible origin authentication mechanism can possibly be used but, in the case that the SZTP-client authenticates itself using both TLS-level (e.g., IDevID) and HTTP-level credentials (e.g., Basic), as is allowed by Section 5.3 of [RFC8572], then the SZTP-client may need to choose between the two options. In the case the SZTP-client must choose between the asymmetric key option versus a shared secret for origin authentication, it is RECOMMENDED that the SZTP-client choose using the asymmetric key option. 3.1.6. Clearing the Private Key and Associated Certificate Unlike a manufacturer-generated identity certificate (e.g., IDevID), the deployment-generated identity certificate (e.g., LDevID) and the associated private key (assuming a new private key was generated for the purpose), are considered user data and SHOULD be cleared whenever the device is reset to its factory default state, such as by the "factory-reset" RPC defined in [I-D.ietf-netmod-factory-default]. 3.2. SZTP-Server Considerations 3.2.1. Conveying Proof of Possession to a CA 3.2.2. Supporting SZTP-Clients that don't trust the SZTP-Server [RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers, by blindly authenticating the SZTP-server's TLS end-entity certificate. As is recommended in Section 3.1.4 in this document, in such cases, SZTP-clients SHOULD pass the "signed-data-preferred" input parameter. The reciprocal of this statement is that SZTP-servers, wanting to support SZTP-clients that don't trust them, SHOULD support the "signed-data-preferred" input parameter, as discussed in Appendix B of [RFC8572]. Watsen, et al. Expires 17 December 2021 [Page 25] Internet-Draft Conveying a CSR in an SZTP Request June 2021 3.2.3. YANG Module Considerations The recommended format for documenting the Security Considerations for YANG modules is described in Section 3.7 of [RFC8407]. However, the module defined in this document only augments two input parameters into the "get-bootstrapping-data" RPC in [RFC8572], and therefore only needs to point to the relevant Security Considerations sections in that RFC. * Security considerations for the "get-bootstrapping-data" RPC are described in Section 9.16 of [RFC8572]. * Security considerations for the "input" parameters passed inside the "get-bootstrapping-data" RPC are described in Section 9.6 of [RFC8572]. 4. IANA Considerations 4.1. The "IETF XML" Registry This document registers one URI in the "ns" subregistry of the IETF XML Registry [RFC3688] maintained at https://www.iana.org/assignments/xml-registry/xml-registry.xhtml#ns. Following the format in [RFC3688], the following registration is requested: URI: urn:ietf:params:xml:ns:yang:ietf-sztp-csr Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. 4.2. The "YANG Module Names" Registry This document registers one YANG module in the YANG Module Names registry [RFC6020] maintained at https://www.iana.org/assignments/ yang-parameters/yang-parameters.xhtml. Following the format defined in [RFC6020], the below registration is requested: name: ietf-sztp-csr namespace: urn:ietf:params:xml:ns:yang:ietf-sztp-csr prefix: sztp-csr reference: RFC XXXX 5. References 5.1. Normative References Watsen, et al. Expires 17 December 2021 [Page 26] Internet-Draft Conveying a CSR in an SZTP Request June 2021 [I-D.ietf-netconf-crypto-types] Watsen, K., "YANG Data Types and Groupings for Cryptography", Work in Progress, Internet-Draft, draft- ietf-netconf-crypto-types-19, 10 February 2021, . [ITU.X690.2015] International Telecommunication Union, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1, August 2015, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, November 2000, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero Touch Provisioning (SZTP)", RFC 8572, DOI 10.17487/RFC8572, April 2019, . 5.2. Informative References Watsen, et al. Expires 17 December 2021 [Page 27] Internet-Draft Conveying a CSR in an SZTP Request June 2021 [I-D.ietf-netconf-keystore] Watsen, K., "A YANG Data Model for a Keystore", Work in Progress, Internet-Draft, draft-ietf-netconf-keystore-21, 10 February 2021, . [I-D.ietf-netconf-trust-anchors] Watsen, K., "A YANG Data Model for a Truststore", Work in Progress, Internet-Draft, draft-ietf-netconf-trust- anchors-14, 10 February 2021, . [I-D.ietf-netmod-factory-default] Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for Factory Default Settings", Work in Progress, Internet- Draft, draft-ietf-netmod-factory-default-15, 25 April 2020, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018, . [Std-802.1AR-2018] Group, W. -. H. L. L. P. W., "IEEE Standard for Local and metropolitan area networks - Secure Device Identity", 14 June 2018, . Authors' Addresses Kent Watsen Watsen Networks Email: kent+ietf@watsen.net Watsen, et al. Expires 17 December 2021 [Page 28] Internet-Draft Conveying a CSR in an SZTP Request June 2021 Russ Housley Vigil Security, LLC Email: housley@vigilsec.com Sean Turner sn3rd Email: sean@sn3rd.com Watsen, et al. Expires 17 December 2021 [Page 29]