Watsen Networks

kent+ietf@watsen.net

Vigil Security, LLC

housley@vigilsec.com

sn3rd

sean@sn3rd.com

Operations NETCONF Working Group zerotouch bootstrap sztp ztp csr pkcs#10 p10 p10cr cmc cmp This draft extends the "get-bootstrapping-data" RPC defined in RFC 8572 to include an optional certificate signing request (CSR), enabling a bootstrapping device to additionally obtain an identity certificate (e.g., an LDevID, from IEEE 802.1AR) as part of the "onboarding information" response provided in the RPC-reply. Editorial Note (To be removed by RFC Editor) This draft contains many placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document. Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements:

• XXXX --> the assigned numerical RFC value for this draft
• AAAA --> the assigned RFC value for I-D.ietf-netconf-crypto-types

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

• 2021-08-15 --> 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
• I-D.ietf-netconf-keystore
• I-D.ietf-netconf-trust-anchors
• I-D.ietf-netmod-factory-default

Introduction

Overview This draft extends 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 ) as part of the "onboarding information" response provided in the RPC-reply. The ability to provision an identity certificate that is purpose-built for a production environment during the bootstrapping process removes reliance on the manufacturer CA, and it also enables the bootstraped device to join the production environment with an appropriate identity and other attributes in its LDevID certificate. 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 used in this document use a placeholder value for binary data that has been base64 encoded (e.g., "BASE64VALUE="). This placeholder value is used as real base64 encoded structures are often many lines long and hence distracting to the example being presented.

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. The augmentation defines two kinds of parameters that an SZTP-client can send to an SZTP-server. The YANG structure defines one collection of parameters that an SZTP-server can send to an SZTP-client. In the order of their intended use:

• The "csr-support" node is used by the SZTP-client to signal to the SZTP-server that it supports the ability the generate CSRs. This parameter conveys if the SZTP-client is able to generate an new asymmetric key and, if so, which key algorithms it supports, as well as conveys what kinds of CSR structures the SZTP-client is able to generate.
• The "csr-request" structure is used by the SZTP-server to request the SZTP-client to generate a CSR. This structure is used to select the key algorithm the SZTP-client should use to generate a new asymmetric key, if supported, the kind of CSR structure the SZTP-client should generate and, optionally, the content for the CSR itself.
• The various "csr" nodes are used by the SZTP-client to communicate a CSR to the SZTP-server.

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

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, as illustrated below. REQUEST 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 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 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 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 . 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 . 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 ). As such, the configuration needs to associate the newly signed certificate with the existing asymmetric key: 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: 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 a data types and groupings defined in , , and . The module has additional normative references to , , , and , and an informative reference to . <CODE BEGINS> file "ietf-sztp-csr@2021-08-15.yang" 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 response. Copyright (c) 2021 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2021-08-15 { description "Initial version"; reference "RFC XXXX: Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request"; } // Protocol-accessible nodes augment "/sztp-svr:get-bootstrapping-data/sztp-svr:input" { description "This augmentation adds the 'csr-support' and 'csr' nodes to the SZTP (RFC 8572) 'get-bootstrapping-data' request message, enabling the SZTP-client to obtain an identity certificate (e.g., an LDevID from IEEE 802.1AR) as part of the onboarding information response provided by the SZTP-server. The 'csr-support' node enables the SZTP-client to indicate that it supports generating certificate signing requests (CSRs), and to provide details around the CSRs it is able to generate. The 'csr' node enables the SZTP-client to relay a CSR to the SZTP-server."; reference "IEEE 802.1AR: IEEE Standard for Local and metropolitan area networks - Secure Device Identity RFC 8572: Secure Zero Touch Provisioning (SZTP)"; choice msg-type { description "Messages are mutually exclusive."; case csr-support { description "Indicates how the SZTP-client supports generating CSRs. If present and a SZTP-server wishes to request the SZTP-client generate a CSR, the SZTP-server MUST respond with HTTP code 400 Bad Request with an 'ietf-restconf:errors' message having the 'error-tag' value 'missing-attribute' and the 'error-info' node containing the 'csr-request' structure described in this module."; uses zt:csr-support-grouping; } case csr { description "Provides the CSR generated by the SZTP-client. When present, the SZTP-server SHOULD respond with an SZTP onboarding information message containing a signed certificate for the conveyed CSR. The SZTP-server MAY alternatively respond with another HTTP error containing another 'csr-request', in which case the SZTP-client MUST invalidate the previously generated CSR."; uses zt:csr-grouping; } } } sx:structure csr-request { description "A YANG data structure, per RFC 8791, that specifies details for the CSR that the ZTP-client is to generate."; reference "RFC 8791: YANG Data Structure Extensions"; uses zt:csr-request-grouping; } } ]]> <CODE ENDS>

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

Data Model Overview The following tree diagram illustrates the three groupings defined in the "ietf-ztp-types" module.

YANG Module This module uses a data types and groupings and . The module has additional normative references to , , , and , and an informative reference to . <CODE BEGINS> file "ietf-ztp-types@2021-08-15.yang" Authors: Kent Watsen Russ Housley Sean Turner "; description "This module defines three groupings that enable bootstrapping devices to 1) indicate if and how they support generating CSRs, 2) obtain a request to generate a CSR, and 3) communicate the requested CSR. The terms 'IDevID' and 'LDevID' are used herein to mean 'initial device identifier' and 'local device identifer'. These terms are defined consistent with the IEEE 802.1AR specification, though there is no requirement that a ZTP-client's identity certificate conform to IEEE 802.1AR. Copyright (c) 2021 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2021-08-15 { 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 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 constrained version of the PKIMessage containing a p10cr structure defined in RFC 4210."; reference "RFC 4210: Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP)"; } identity cmc-csr { base certificate-request-format; description "Indicates that the ZTP-client supports generating requests using a constrained version of the 'Full PKI Request' structure defined in RFC 5272."; reference "RFC 5272: Certificate Management over CMS (CMC)"; } // Protocol-accessible nodes grouping csr-support-grouping { description "A grouping enabling use by other efforts."; container csr-support { description "Enables a ZTP-client to indicate that it supports generating certificate signing requests (CSRs) and provides details about the CSRs it is able to generate."; container key-generation { presence "Indicates that the ZTP-client is capable of generating a new asymmetric key pair. If this node is not present, the ZTP-server MAY request a CSR using the asymmetric key associated with the device's existing identity certificate (e.g., an IDevID from IEEE 802.1AR)."; description "Specifies details for the ZTP-client's ability to generate a new asymmetric key pair."; container supported-algorithms { description "A list of public key algorithms supported by the ZTP-client for generating a new asymmetric key."; leaf-list algorithm-identifier { type binary; min-elements 1; description "An AlgorithmIdentifier, as defined in RFC 2986, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification Version 1.7 ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } } container csr-generation { description "Specifies details for the ZTP-client's ability to generate a certificate signing requests."; container supported-formats { description "A list of certificate request formats supported by the ZTP-client for generating a new key."; leaf-list format-identifier { type identityref { base zt:certificate-request-format; } min-elements 1; description "A certificate request format supported by the ZTP-client."; } } } } } grouping csr-request-grouping { description "A grouping enabling use by other efforts."; container key-generation { presence "Provided by a ZTP-server to indicate that it wishes the ZTP-client to generate a new asymmetric key. This statement is present so the mandatory descendant nodes do not imply that this node must be configured."; description "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 csr-parameters { type ct:csr-info; description "A CertificationRequestInfo structure, as defined in RFC 2986, and modeled via a 'typedef' statement by RFC AAAA. Enables the ZTP-server to provide a fully-populated CertificationRequestInfo structure that the ZTP-client only needs to sign in order to generate the complete 'CertificationRequest' structure to send to ZTP-server in its next 'get-bootstrapping-data' request message. When provided, the ZTP-client SHOULD use this structure to generate its CSR; failure to do so MAY result in a 400 Bad Request response containing another 'csr-request' structure. When not provided, the ZTP-client SHOULD generate a CSR using the same structure defined in its existing identity certificate (e.g., IDevID). It is an error if the 'AlgorithmIdentifier' field contained inside the 'SubjectPublicKeyInfo' field does not match the algorithm identified by the 'selected-algorithm' node."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification RFC AAAA: YANG Data Types and Groupings for Cryptography"; } } grouping csr-grouping { description "Enables a ZTP-client to convey a certificate signing request, using the encoding format selected by a ZTP-server's 'csr-request' response to the ZTP-client's previously sent 'get-bootstrapping-data' request containing the 'csr-support' node."; choice csr-type { mandatory true; description "A choice amongst certificate signing request formats. Additional formats MAY be augmented into this 'choice' statement by future efforts."; case p10-csr { leaf p10-csr { type ct:csr; description "A CertificationRequest structure, per RFC 2986."; reference "RFC 2986: PKCS #10: Certification Request Syntax Specification"; } } case cmc-csr { leaf cmc-csr { type binary; description "A constrained version of the 'Full PKI Request' message defined in RFC 5272, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690. For asymmetric key-based origin authentication of a CSR based on the IDevID's private key for the associated IDevID's public key, the PKIData contains one reqSequence element and no cmsSequence or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the IDevID's private key. The IDevID certificate and optionally its certificate chain is included in the SignedData certificates that encapsulates the PKIData. For asymmetric key-based origin authentication based on the IDevID's private key that signs the encapsulated CSR signed by the LDevID's private key, the PKIData contains one cmsSequence element and no otherMsgSequence element. The cmsSequence is the TaggedContentInfo and it includes a bodyPartID element and a contentInfo. The contentInfo is a SignedData encapsulating a PKIData with one reqSequence element and no cmsSequence or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the LDevID's private key. The IDevID certificate and optionally its certificate chain is included in the SignedData certificates that encapsulates the PKIData. For shared secret-based origin authentication of a CSR signed by the LDevID's private key, the PKIData contains one cmsSequence element and no reqSequence or otherMsgSequence elements. The cmsSequence is the TaggedContentInfo and it includes a bodyPartID element and a contentInfo. The contentInfo is an AuthenticatedData encapsulating a PKIData with one reqSequence element and no cmsSequences or otherMsgSequence elements. The reqSequence is the TaggedRequest and it is the tcr CHOICE. The tcr is the TaggedCertificationRequest and it a bodyPartId and the certificateRequest elements. The certificateRequest is signed with the LDevID's private key. The IDevID certificate and optionally its certificate chain is included in the SignedData certificates that encapsulates the PKIData."; reference "RFC 5272: Certificate Management over CMS (CMC) ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } case cmp-csr { leaf cmp-csr { type binary; description "A PKIMessage structure, as defined in RFC 4210, encoded using ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690. For asymmetric key-based origin authentication of a CSR based on the IDevID's private key for the associated IDevID's public key, PKIMessages contains one PKIMessage with the header and body elements, no protection element, and should contain the extraCerts element. The header element contains the pvno, sender, and recipient elements. The pvno contains cmp2000, and the sender contains the subject of the IDevID certificate. The body element contains a p10cr CHOICE of type CertificationRequet. It is signed with the IDevID's private key. The extraCerts element contains the IDevID certificate, optionally followed by its certificate chain excluding the trust anchor. For asymmetric key-based origin authentication based on the IDevID's private key that signs the encapsulated CSR signed by the LDevID's private key, PKIMessages contains one PKIMessage with the header, body, and protection elements, and should contain the extraCerts element. The header element contains the pvno, sender, recipient, protectionAlg, and optionally senderKID elements. The pvno contains cmp2000, the sender contains the subject of the IDevID certificate, the protectionAlg contains the AlgorithmIdentifier of the used signature algorithm, and the senderKID contains the subject key identifier of the IDevID certificate. The body element contains a p10cr CHOICE of type CertificationRequet. It is signed with the LDevID's private key. The protection element contains the digital signature generated with the IDevID's private key. The extraCerts element contains the IDevID certificate, optionally followed by its certificate chain excluding the trust anchor. For shared secret-based origin authentication of a CSR signed by the LDevID's private key, PKIMessages contains one PKIMessage with the header, body, and protection element, and no extraCerts element. The header element contains the pvno, sender, recipient, protectionAlg, and senderKID elements. The pvno contains cmp2000, the protectionAlg contains the AlgorithmIdentifier of the used MAC algorithm, and the senderKID contains a reference the recipient can use to identify the shared secret. The body element contains a p10cr CHOICE of type CertificationRequet. It is signed with the LDevID's private key. The protection element contains the MAC value generated with the shared secret."; reference "RFC 4210: Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP) ITU-T X.690: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } } } } } ]]> <CODE ENDS>

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

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 as a root of trust. It is RECOMMENDED that devices are manufactured with an HSM (hardware security module), such as a TPM (trusted platform module), to generate and forever contain the private key within the security perimeter of the HSM. In such cases, the private key, and its associated certificates, MAY have long validity periods. In cases where the SZTP-client does not possess an HSM, or otherwise is unable to use an HSM for the private key, it is RECOMMENDED to regenerate the private key (and associated identity certificates) periodically. Details for how to generate a new private key and associate a new identity certificate are outside the scope of this document.

Reuse of a Manufacturer-generated Private Key It is RECOMMENDED that a new private key is generated for each CSR described in this document. This private key SHOULD be protected as well as the built-in private key associated with the SZTP-client's initial device identity certificate (e.g., the IDevID, from ). 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.

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 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 , SZTP-clients SHOULD NOT pass the "csr-support" input parameter to an untrusted SZTP-server. SZTP-clients SHOULD pass instead the "signed-data-preferred" input parameter, as discussed in .

Selecting the Best Origin Authentication Mechanism When generating a new key, it is important that the client be able to provide additional proof to the CA that it was the entity that generated the key. All 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 , then the SZTP-client may need to choose between the two options. In the case that 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.

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

Conveying Proof of Possession to a CA When the bootstrapping device's manufacturer-generated private key (e.g., the IDevID key) is reused, a CA may validate that the CSR was signed by that key. Both the CMP and CMC formats entail the bootstrapping device signing the request once with its (e.g., LDevID) key and then again with its (e.g., IDevID) key, which enables a downstream CA to be assured that the bootstrapping device possesses the public key being signed.

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 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 .

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 This document registers two URIs in the "ns" subregistry of the IETF XML Registry maintained at . Following the format in , the following registrations are requested:

The "YANG Module Names" Registry This document registers two YANG modules in the YANG Module Names registry maintained at . Following the format defined in , the below registrations are requested:

References Normative References 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 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. International Telecommunication Union Informative References IEEE SA-Standards Board 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.

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

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