| RFC 9646 | Conveying a CSR in an SZTP Request | October 2024 |
| Watsen, et al. | Standards Track | [Page] |
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.¶
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 athttps://www.rfc-editor.org/info/rfc9646.¶
Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
This document extends the input to the "get-bootstrapping-data" RPC defined in[RFC8572] to include an optional certificate signing request (CSR)[RFC2986], enabling a bootstrapping device to additionally obtain an identity certificate (e.g., an LDevID from[Std-802.1AR-2018]) as part of the "onboarding information" response provided in the RPC-reply.¶
The ability to provision an identity certificate that is purpose-built for a production environment during the bootstrapping process removes reliance on the manufacturer Certification Authority (CA), and it also enables the bootstrapped device to join the production environment with an appropriate identity and other attributes in its identity certificate (e.g., an LDevID).¶
Two YANG[RFC7950] modules are defined. The "ietf-ztp-types" module defines three YANG groupings for the various messages defined in this document. The "ietf-sztp-csr" module augments two groupings into the "get-bootstrapping-data" RPC and defines a YANG data structure[RFC8791] around the third grouping.¶
This document uses the following terms from[RFC8572]:¶
This document defines the following new terms:¶
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.¶
Various examples in this document use "BASE64VALUE=" as a placeholder value for binary data that has been base64 encoded (perSection 9.8 of [RFC7950]). This placeholder value is used because real base64-encoded structures are often many lines long and hence distracting to the example being presented.¶
Various examples in this document contain long lines that may be folded, as described in[RFC8792].¶
The "ietf-sztp-csr" module is a YANG 1.1[RFC7950] module that augments the "ietf-sztp-bootstrap-server" module defined in[RFC8572] and defines a YANG "structure" that is to be conveyed in the "error-info" node defined inSection 7.1 of [RFC8040].¶
The following tree diagram[RFC8340] illustrates the "ietf-sztp-csr" module.¶
module: ietf-sztp-csr augment /sztp-svr:get-bootstrapping-data/sztp-svr:input: +---w (msg-type)? +--:(csr-support) | +---w csr-support | +---w key-generation! | | +---w supported-algorithms | | +---w algorithm-identifier* binary | +---w csr-generation | +---w supported-formats | +---w format-identifier* identityref +--:(csr) +---w (csr-type) +--:(p10-csr) | +---w p10-csr? ct:csr +--:(cmc-csr) | +---w cmc-csr? binary +--:(cmp-csr) +---w cmp-csr? binary structure csr-request: +-- key-generation! | +-- selected-algorithm | +-- algorithm-identifier binary +-- csr-generation | +-- selected-format | +-- format-identifier identityref +-- cert-req-info? ct:csr-info¶
The augmentation defines two kinds of parameters that an SZTP-client can send to an SZTP-server. The YANG structure defines one collection of parameters that an SZTP-server can send to an SZTP-client.¶
In the order of their intended use:¶
To further illustrate how the augmentation and structure defined by the "ietf-sztp-csr" module are used, below are two additional tree diagrams showing these nodes placed where they are used.¶
The following tree diagram[RFC8340] illustrates SZTP's "get-bootstrapping-data" RPC with the augmentation in place.¶
=============== NOTE: '\' line wrapping per RFC 8792 ================module: ietf-sztp-bootstrap-server rpcs: +---x get-bootstrapping-data +---w input | +---w signed-data-preferred? empty | +---w hw-model? string | +---w os-name? string | +---w os-version? string | +---w nonce? binary | +---w (sztp-csr:msg-type)? | +--:(sztp-csr:csr-support) | | +---w sztp-csr:csr-support | | +---w sztp-csr:key-generation! | | | +---w sztp-csr:supported-algorithms | | | +---w sztp-csr:algorithm-identifier* bina\ry | | +---w sztp-csr:csr-generation | | +---w sztp-csr:supported-formats | | +---w sztp-csr:format-identifier* identit\yref | +--:(sztp-csr:csr) | +---w (sztp-csr:csr-type) | +--:(sztp-csr:p10-csr) | | +---w sztp-csr:p10-csr? ct:csr | +--:(sztp-csr:cmc-csr) | | +---w sztp-csr:cmc-csr? binary | +--:(sztp-csr:cmp-csr) | +---w sztp-csr:cmp-csr? binary +--ro output +--ro reporting-level? enumeration {onboarding-server}? +--ro conveyed-information cms +--ro owner-certificate? cms +--ro ownership-voucher? cms¶The following tree diagram[RFC8340] illustrates RESTCONF's "errors" RPC-reply message with the "csr-request" structure in place.¶
module: ietf-restconf +--ro errors +--ro error* [] +--ro error-type enumeration +--ro error-tag string +--ro error-app-tag? string +--ro error-path? instance-identifier +--ro error-message? string +--ro error-info +--ro sztp-csr:csr-request +--ro sztp-csr:key-generation! | +--ro sztp-csr:selected-algorithm | +--ro sztp-csr:algorithm-identifier binary +--ro sztp-csr:csr-generation | +--ro sztp-csr:selected-format | +--ro sztp-csr:format-identifier identityref +--ro sztp-csr:cert-req-info? ct:csr-info¶
NOTE: The examples below are encoded using JSON, but they could equally well be encoded using XML, as is supported by SZTP.¶
An SZTP-client implementing this specification would signal to the bootstrap server its willingness to generate a CSR by including the "csr-support" node in its "get-bootstrapping-data" RPC. In the example below, the SZTP-client additionally indicates that it is able to generate keys and provides a list of key algorithms it supports, as well as provide a list of certificate formats it supports.¶
REQUEST¶
=============== NOTE: '\' line wrapping per RFC 8792 ================POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\ng-data HTTP/1.1HOST: example.comContent-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 RequestDate: Sat, 31 Oct 2021 17:02:40 GMTServer: example-serverContent-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/1.1HOST: example.comContent-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 OKDate: Sat, 31 Oct 2021 17:02:40 GMTServer: example-serverContent-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 inSection 2.2 of [RFC8572].¶
Below are two examples of conveying the signed certificate inside the "configuration" node. Both examples assume that the SZTP-client understands the "ietf-keystore" module defined in[RFC9642].¶
This first example illustrates the case where the signed certificate is for the same asymmetric key used by the SZTP-client's manufacturer-generated identity certificate (e.g., an Initial Device Identifier (IDevID) from[Std-802.1AR-2018]). As such, the configuration needs to associate the newly signed certificate with the existing asymmetric key:¶
=============== NOTE: '\' line wrapping per RFC 8792 ================{ "ietf-keystore:keystore": { "asymmetric-keys": { "asymmetric-key": [ { "name": "Manufacturer-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\-info-format", "public-key": "BASE64VALUE=", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Manufacturer-Generated IDevID Cert", "cert-data": "BASE64VALUE=" }, { "name": "Newly-Generated LDevID Cert", "cert-data": "BASE64VALUE=" } ] } } ] } }}¶This second example illustrates the case where the signed certificate is for a newly generated asymmetric key. As such, the configuration needs to associate the newly signed certificate with the newly generated asymmetric key:¶
=============== NOTE: '\' line wrapping per RFC 8792 ================{ "ietf-keystore:keystore": { "asymmetric-keys": { "asymmetric-key": [ { "name": "Manufacturer-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\-info-format", "public-key": "BASE64VALUE=", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Manufacturer-Generated IDevID Cert", "cert-data": "BASE64VALUE=" } ] } }, { "name": "Newly-Generated Hidden Key", "public-key-format": "ietf-crypto-types:subject-public-key\-info-format", "public-key": "BASE64VALUE=", "hidden-private-key": [null], "certificates": { "certificate": [ { "name": "Newly-Generated LDevID Cert", "cert-data": "BASE64VALUE=" } ] } } ] } }}¶In addition to configuring the signed certificate, it is often necessary to also configure the issuer's signing certificate so that the device (i.e., STZP-client) can authenticate certificates presented by peer devices signed by the same issuer as its own. While outside the scope of this document, one way to do this would be to use the "ietf-truststore" module defined in[RFC9641].¶
This module augments an RPC defined in[RFC8572]. The module uses data types and groupings defined in[RFC8572],[RFC8791], and[RFC9640]. The module also has an informative reference to[Std-802.1AR-2018].¶
<CODE BEGINS> file "ietf-sztp-csr@2024-10-10.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-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; }}<CODE ENDS>¶This section defines a YANG 1.1[RFC7950] module that defines three YANG groupings, one for each message sent between a ZTP-client and ZTP-server. This module is defined independently of the "ietf-sztp-csr" module so that its groupings may be used by bootstrapping protocols other than SZTP[RFC8572].¶
The following tree diagram[RFC8340] illustrates the three groupings defined in the "ietf-ztp-types" module.¶
module: ietf-ztp-types grouping csr-support-grouping +-- csr-support +-- key-generation! | +-- supported-algorithms | +-- algorithm-identifier* binary +-- csr-generation +-- supported-formats +-- format-identifier* identityref grouping csr-request-grouping +-- key-generation! | +-- selected-algorithm | +-- algorithm-identifier binary +-- csr-generation | +-- selected-format | +-- format-identifier identityref +-- cert-req-info? ct:csr-info grouping csr-grouping +-- (csr-type) +--:(p10-csr) | +-- p10-csr? ct:csr +--:(cmc-csr) | +-- cmc-csr? binary +--:(cmp-csr) +-- cmp-csr? binary¶
This module uses data types and groupings defined in[RFC8791] and[RFC9640]. The module has additional normative references to[RFC2986],[RFC4210],[RFC5272], and[ITU.X690.2021] and an informative reference to[Std-802.1AR-2018].¶
<CODE BEGINS> file "ietf-ztp-types@2024-10-10.yang"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)"; } } } }}<CODE ENDS>¶This document builds on top of the solution presented in[RFC8572], and therefore all the security considerations discussed in[RFC8572] apply here as well.¶
For the various CSR formats, when using PKCS#10, the security considerations in[RFC2986] apply; when using CMP, the security considerations in[RFC4210] apply; and when using CMC, the security considerations in[RFC5272] apply.¶
For the various authentication mechanisms, when using TLS-level authentication, the security considerations in[RFC8446] apply, and when using HTTP-level authentication, the security considerations in[RFC9110] apply.¶
The private key the SZTP-client uses for the dynamically generated identity certificateMUST 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 isRECOMMENDED 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 certificatesMAY 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 isRECOMMENDED to periodically reset the private key (and associated identity certificates) in order to minimize the lifetime of unprotected private keys. For instance, a Network Management System (NMS) controller/orchestrator application could periodically prompt the SZTP-client to generate a new private key and provide a certificate signing request (CSR) or, alternatively, push both the key and an identity certificate to the SZTP-client using, e.g., a PKCS#12 message[RFC7292]. In another example, the SZTP-client could be configured to periodically reset the configuration to its factory default, thus causing removal of the private key and associated identity certificates and re-execution of the SZTP protocol.¶
It isRECOMMENDED that a new private key is generated for each CSR described in this document.¶
Implementations must randomly generate nonces and private keys. The use of inadequate pseudorandom number generators (PRNGs) to generate cryptographic keys can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. As an example of predictable random numbers, see CVE-2008-0166[CVE-2008-0166], and some consequences of low-entropy random numbers are discussed in "Mining Your Ps and Qs"[MiningPsQs]. The generation of quality random numbers is difficult.[ISO.20543-2019],[NIST.SP.800-90Ar1], BSI AIS 31[AIS31], BCP 106[RFC4086], and others offer valuable guidance in this area.¶
This private keySHOULD be protected as well as the built-in private key associated with the SZTP-client's initial device identity certificate (e.g., the IDevID from[Std-802.1AR-2018]).¶
In cases where it is not possible to generate a new private key that is protected as well as the built-in private key, it isRECOMMENDED to reuse the built-in private key rather than generate a new private key that is not as well protected.¶
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.¶
[RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers by blindly authenticating the SZTP-server's TLS end-entity certificate.¶
As is discussed inSection 9.5 of [RFC8572], in such cases, the SZTP-clientMUST assert that the bootstrapping data returned is signed if the SZTP-client is to trust it.¶
However, the HTTP error message used in this document cannot be signed data, as described in[RFC8572].¶
Therefore, the solution presented in this document cannot be used when the SZTP-client connects to an untrusted SZTP-server.¶
Consistent with the recommendation presented inSection 9.6 of [RFC8572], SZTP-clientsSHOULD NOT pass the "csr-support" input parameter to an untrusted SZTP-server. SZTP-clientsSHOULD instead pass the "signed-data-preferred" input parameter, as discussed inAppendix B of [RFC8572].¶
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 bySection 5.3 of [RFC8572], then the SZTP-client may need to choose between the two options.¶
In the case that the SZTP-client must choose between an asymmetric key option versus a shared secret for origin authentication, it isRECOMMENDED that the SZTP-client choose using the asymmetric key.¶
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 andSHOULD be cleared whenever the SZTP-client is reset to its factory default state, such as by the "factory-reset" RPC defined in[RFC8808].¶
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.¶
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.¶
[RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers by blindly authenticating the SZTP-server's TLS end-entity certificate.¶
As is recommended inSection 4.1.4 of this document, in such cases, SZTP-clientsSHOULD 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 inAppendix B of [RFC8572].¶
The recommended format for documenting the security considerations for YANG modules is described inSection 3.7 of [RFC8407]. However, this module only augments two input parameters into the "get-bootstrapping-data" RPC in[RFC8572] and therefore only needs to point to the relevant Security Considerations sections in that RFC.¶
The recommended format for documenting the security considerations for YANG modules is described inSection 3.7 of [RFC8407]. However, this module does not define any protocol-accessible nodes (it only defines "identity" and "grouping" statements), and therefore there are no security considerations to report.¶
IANA has registered two URIs in the "ns" registry of the "IETF XML Registry"[RFC3688] maintained at<https://www.iana.org/assignments/xml-registry/>.¶
IANA has registered two YANG modules in the "YANG Module Names" registry[RFC6020] maintained at<https://www.iana.org/assignments/yang-parameters/>.¶
The authors would like to thank for following for lively discussions on list and in the halls (ordered by first name):Benjamin Kaduk,Dan Romascanu,David von Oheimb,Éric Vyncke,Guy Fedorkow,Hendrik Brockhaus,Joe Clarke,Meral Shirazipour,Murray Kucherawy,Rich Salz,Rob Wilton,Roman Danyliw,Qin Wu,Yaron Sheffer, andZaheduzzaman Sarkar.¶
Special thanks go toDavid von Oheimb andHendrik Brockhaus for helping with the descriptions for the "cmc-csr" and "cmp-csr" nodes.¶