]> Watsen Networks

kent+ietf@watsen.net

Sandelman Software

mcr+ietf@sandelman.ca http://www.sandelman.ca/

Cisco Systems

pritikin@cisco.com

Futurewei Technologies Inc.

2330 Central Expy Santa Clara 95050 United States of America tte+ietf@cs.fau.de

Huawei

101 Software Avenue, Yuhua District Nanjing 210012 China maqiufang1@huawei.com

Operations ANIMA Working Group voucher This document defines a strategy to securely assign a pledge to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher". This document defines an artifact format as a YANG-defined JSON or CBOR document that has been signed using a variety of cryptographic systems. The voucher artifact is normally generated by the pledge's manufacturer (i.e., the Manufacturer Authorized Signing Authority (MASA)). This document updates RFC8366, merging a number of extensions into the YANG. The RFC8995 voucher request is also merged into this document. About This Document Status information for this document may be found at . Discussion of this document takes place on the anima Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction This document defines a strategy to securely assign a candidate device (pledge) to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer, i.e., the Manufacturer Authorized Signing Authority (MASA). This artifact is known as the "voucher". The voucher artifact is a JSON document that conforms with a data model described by YANG . It may also be serialized to CBOR . It is encoded using the rules defined in , and is signed using (by default) a CMS structure . The primary purpose of a voucher is to securely convey a certificate, the "pinned-domain-cert" (and constrained variations), that a pledge can use to authenticate subsequent interactions. A voucher may be useful in several contexts, but the driving motivation herein is to support secure onboarding mechanisms. Assigning ownership is important to device onboarding mechanisms so that the pledge can authenticate the network that is trying to take control of it. The lifetimes of vouchers may vary. In some onboarding protocols, the vouchers may include a nonce restricting them to a single use, whereas the vouchers in other onboarding protocols may have an indicated lifetime. In order to support long lifetimes, this document recommends using short lifetimes with programmatic renewal, see . This document only defines the voucher artifact, leaving it to other documents to describe specialized protocols for accessing it. Some onboarding protocols using the voucher artifact defined in this document include: , , and .

Terminology This document uses the following terms:

(Voucher) Artifact:

Used throughout to represent the voucher as instantiated in the form of a signed structure.

Bootstrapping:

The process where a pledge component obtains cryptographic key material to identify and trust future interactions within a specific domain network. Based on imprinted key material provided during manufacturing process (see imprinting).

Domain:

The set of entities or infrastructure under common administrative control. The goal of the onboarding protocol is to enable a pledge component to join a domain and obtain domain specific security credentials.

Imprint:

The process where a device obtains the cryptographic key material to identify and trust future interactions generally as part of the manufacturing. This term is taken from Konrad Lorenz's work in biology with new ducklings: "during a critical period, the duckling would assume that anything that looks like a mother duck is in fact their mother" . An equivalent for a device is to obtain the fingerprint of the manufacturer's root certification authority (root ca) certificate. A device that imprints on an attacker suffers a similar fate to a duckling that imprints on a hungry wolf. Imprinting is a term from psychology and ethology, as described in .

Join Registrar (and Coordinator):

A representative of the domain that is configured, perhaps autonomically, to decide whether a new device is allowed to join the domain. The administrator of the domain interfaces with a join registrar (and Coordinator) to control this process. Typically, a join registrar is "inside" its domain. For simplicity, this document often refers to this as just "registrar".

MASA (Manufacturer Authorized Signing Authority):

The entity that, for the purpose of this document, issues and signs the vouchers for a manufacturer's pledges. In some onboarding protocols, the MASA may have an Internet presence and be integral to the onboarding process, whereas in other protocols the MASA may be an offline service that has no active role in the onboarding process.

malicious registrar:

An on-path active attacker that presents itself as a legitimate registrar, but which is in fact under the control of an attacker.

Onboarding:

Onboarding describes the process to provide necessary operational data to pledge components and completes the process to bring a device into an operational state. This data may be configuration data, or also application specific cryptographic key material (application speciifc security credentials).

Owner:

The entity that controls the private key of the "pinned-domain-cert" certificate conveyed by the voucher.

Pledge:

The prospective component attempting to find and securely join a domain. When shipped or in factory reset mode, it only trusts authorized representatives of the manufacturer.

Registrar:

See join registrar.

TOFU (Trust on First Use):

Where a pledge component makes no security decisions but rather simply trusts the first domain entity it is contacted by. Used similarly to . This is also known as the "resurrecting duckling" model.

Voucher:

A short form for Voucher Artifact. It refers to the signed statement from the MASA service that indicates to a pledge the cryptographic identity of the domain it should trust. When clarity is needed, it may be preceeded by the type of the signature, such as CMS, JWS or COSE.

Voucher Data:

The raw (serialized) representation of the YANG without any enclosing signature. Current formats include JSON and CBOR.

Voucher Request:

A signed artifact sent from the Pledge to the Registrar, or from the Registrar to the MASA for Voucher acquisition.

Pledge Voucher Request (PVR):

A signed artifact sent from the Pledge to the Registrar. It is a special form of Voucher Request.

Registrar Voucher Request (RVR):

A signed artifact sent from the Registrar to the MASA. It is a special form of Voucher Request.

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.

Survey of Voucher Types A voucher is a cryptographically protected statement to the pledge device authorizing a zero-touch "imprint" on the join registrar of the domain. The specific information a voucher provides is influenced by the onboarding use case. The voucher can impart the following information to the join registrar and pledge:

Assertion Basis:

Indicates the method that protects the imprint (this is distinct from the voucher signature that protects the voucher itself). This might include manufacturer-asserted ownership verification, assured logging operations, or reliance on pledge endpoint behavior such as secure root of trust of measurement. The join registrar might use this information. Only some methods are normatively defined in this document. Other methods are left for future work.

Authentication of Join Registrar:

Indicates how the pledge can authenticate the join registrar. This document defines a mechanism to pin the domain certificate, or a raw public key. Pinning a symmetric key, or "CN-ID" or "DNS-ID" information (as defined in ) is left for future work.

Anti-Replay Protections:

Time- or nonce-based information to constrain the voucher to time periods or bootstrap attempts.

A number of onboarding scenarios can be met using differing combinations of this information. All scenarios address the primary threat of an on-path active attacker (or MiTM) impersonating the registrar. This would gain control over the pledge device. The following combinations are "types" of vouchers:

	Assertion		Registrar ID		Validity
Voucher Type	Logged	Verified	Trust Anchor	CN-ID or DNS-ID	RTC	Nonce
Audit	X		X			X
Nonceless Audit	X		X		X
Owner Audit	X	X	X		X	X
Owner ID		X	X	X	X
Bearer out-of-scope	X		wildcard	wildcard	optional	opt

NOTE: All voucher types include a 'pledge ID serial-number' (not shown here for space reasons).

Audit Voucher:

An Audit Voucher is named after the logging assertion mechanisms that the registrar then "audits" to enforce local policy. The registrar mitigates a malicious registrar by auditing that an unknown malicious registrar does not appear in the log entries. This does not directly prevent a malicious registrar but provides a response mechanism that ensures the MiTM is unsuccessful. The advantage is that actual ownership knowledge is not required on the MASA service.

Nonceless Audit Voucher:

An Audit Voucher without a validity period statement. Fundamentally, it is the same as an Audit Voucher except that it can be issued in advance to support network partitions or to provide a permanent voucher for remote deployments.

Ownership Audit Voucher:

An Audit Voucher where the MASA service has verified the registrar as the authorized owner. The MASA service mitigates a MiTM registrar by refusing to generate Audit Vouchers for unauthorized registrars. The registrar uses audit techniques to supplement the MASA. This provides an ideal sharing of policy decisions and enforcement between the vendor and the owner.

Ownership ID Voucher:

Named after inclusion of the pledge's CN-ID or DNS-ID within the voucher. The MASA service mitigates a MiTM registrar by identifying the specific registrar (via WebPKI) authorized to own the pledge.

Bearer Voucher:

A Bearer Voucher is named after the inclusion of a registrar ID wildcard. Because the registrar identity is not indicated, this voucher type must be treated as a secret and protected from exposure as any 'bearer' of the voucher can claim the pledge device. Publishing a nonceless bearer voucher effectively turns the specified pledge into a "TOFU" device with minimal mitigation against MiTM registrars. Bearer vouchers are out of scope.

Changes since RFC8366 was published in 2018 during the development of , and other work-in-progress efforts. Since then the industry has matured significantly, and the in-the-field activity which this document supports has become known as onboarding rather than bootstrapping. The focus of was onboarding of ISP and Enterprise owned wired routing and switching equipment, with IoT devices being a less important aspect. has focused upon onboarding of CPE equipment like cable modems and other larger IoT devices, again with smaller IoT devices being of less import. Since was published there is now a mature effort to do application-level onboarding of constrained IoT devices defined by The Thread and Fairhair (now OCF) consortia. The document has defined a version of that is useable over constrained 802.15.4 networks using CoAP and DTLS, while provides for using CoAP and EDHOC on even more constrained devices with very constrained networks. has created a new methodology for onboarding that does not depend upon a synchronous connection between the Pledge and the Registrar. This mechanism uses a mobile Registrar Agent that works to collect and transfer signed artifacts via physical travel from one network to another. Both and require extensions to the Voucher Request and the resulting Voucher. The new attribtes are required to carry the additional attributes and describe the extended semantics. In addition uses the serialization mechanism described in to produce significantly more compact artifacts. When the process to define and was started, there was a belief that the appropriate process was to use the augment mechanism to further extend both the voucher request and voucher artifacts. However, needs to extend an enumerated type with additional values and augment can not do this, so that was initially the impetus for this document. An attempt was then made to determine what would happen if one wanted to have a constrained version of the voucher artifact. The result was invalid YANG, with multiple definitions of the core attributes from the voucher artifact. After some discussion, it was determined that the augment mechanism did not work, nor did it work better when yang-data was replaced with the structure mechanisms. After significant discussion the decision was made to simply roll all of the needed extensions up into this document as "RFC8366bis". This document therefore represents a merge of YANG definitions from , the voucher-request from , and then extensions to each of these from , and . There are some difficulties with this approach: this document does not attempt to establish rigorous semantic definitions for how some attributes are to be used, referring normatively instead to the other relevant documents.

Signature mechanisms Three signature systems have been defined for vouchers and voucher-requests. defines a mechanism that uses COSE , with the voucher data encoded using . However, as the SID processe requires up-to-date YANG, the SID values for this mechanism are presented in this document. defines a mechanism that uses JSON and . The CMS mechanism first defined in continues to be defined here.

CMS Format Voucher Artifact The IETF evolution of PKCS#7 is CMS . A CMS-signed voucher, the default type, contains a ContentInfo structure with the voucher content. An eContentType of 40 indicates that the content is a JSON-encoded voucher. The signing structure is a CMS SignedData structure, as specified by Section 5.1 of , encoded using ASN.1 Distinguished Encoding Rules (DER), as specified in ITU-T X.690 . To facilitate interoperability, in this document registers the media type "application/voucher-cms+json" and the filename extension ".vcj". The CMS structure MUST contain a 'signerInfo' structure, as described in Section 5.1 of , containing the signature generated over the content using a private key trusted by the recipient. Normally, the recipient is the pledge and the signer is the MASA. In the Voucher Request, the signer is the pledge, or the Registrar. Within this document, the signer is assumed to be the MASA. Note that Section 5.1 of includes a discussion about how to validate a CMS object, which is really a PKCS7 object (cmsVersion=1). Intermediate systems (such the Bootstrapping Remote Secure Key Infrastructures registrar) that might need to evaluate the voucher in flight MUST be prepared for such an older format. No signaling is necessary, as the manufacturer knows the capabilities of the pledge and will use an appropriate format voucher for each pledge. The CMS structure SHOULD also contain all of the certificates leading up to and including the signer's trust anchor certificate known to the recipient. The inclusion of the trust anchor is unusual in many applications, but third parties cannot accurately audit the transaction without it. The CMS structure MAY also contain revocation objects for any intermediate certificate authorities (CAs) between the voucher issuer and the trust anchor known to the recipient. However, the use of CRLs and other validity mechanisms is discouraged, as the pledge is unlikely to be able to perform online checks and is unlikely to have a trusted clock source. As described below, the use of short-lived vouchers and/or a pledge-provided nonce provides a freshness guarantee.

Voucher Artifact The voucher's primary purpose is to securely assign a pledge to an owner. The voucher informs the pledge which entity it should consider to be its owner. This document defines a voucher that is a JSON-encoded or CBOR-encoded instance of the YANG module defined in . This format is described here as a practical basis for some uses (such as in NETCONF), but more to clearly indicate what vouchers look like in practice. This description also serves to validate the YANG data model. defined a media type and a filename extension for the CMS-encoded JSON type. Which type of voucher is expected is signaled (where possible) in the form of a MIME Content-Type, an HTTP Accept: header, or more mundane methods like use of a filename extension when a voucher is transferred on a USB key.

Tree Diagram The following tree diagram illustrates a high-level view of a voucher document. The notation used in this diagram is described in . Each node in the diagram is fully described by the YANG module in . Please review the YANG module for a detailed description of the voucher format.

Examples This section provides voucher examples for illustration purposes. These examples conform to the encoding rules defined in . The following example illustrates an ephemeral voucher (uses a nonce). The MASA generated this voucher using the 'logged' assertion type, knowing that it would be suitable for the pledge making the request. The following example illustrates a non-ephemeral voucher (no nonce). While the voucher itself expires after two weeks, it presumably can be renewed for up to a year. The MASA generated this voucher using the 'verified' assertion type, which should satisfy all pledges.

YANG Module WG List: Author: Kent Watsen Author: Max Pritikin Author: Michael Richardson Author: Toerless Eckert "; description "This module defines the format for a voucher, which is produced by a pledge's manufacturer or delegate (MASA) to securely assign a pledge to an 'owner', so that the pledge may establish a secure connection to the owner's network infrastructure. 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) 2023 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 8366; see the RFC itself for full legal notices."; revision 2023-01-10 { description "updated to support new assertion enumerated type"; reference "RFC ZZZZ Voucher Profile for Bootstrapping Protocols"; } // Top-level statement sx:structure voucher { uses voucher-artifact-grouping; } // Grouping defined for future augmentations grouping voucher-artifact-grouping { description "Grouping to allow reuse/extensions in future work."; container voucher { description "A voucher assigns a pledge to an owner using the (pinned-domain-cert) value."; leaf created-on { type yang:date-and-time; mandatory false; description "A value indicating the date this voucher was created. This node is primarily for human consumption and auditing. Future work MAY create verification requirements based on this node."; } leaf expires-on { type yang:date-and-time; must 'not(../nonce)'; description "A value indicating when this voucher expires. The node is optional as not all pledges support expirations, such as pledges lacking a reliable clock. If this field exists, then the pledges MUST ensure that the expires-on time has not yet passed. A pledge without an accurate clock cannot meet this requirement. The expires-on value MUST NOT exceed the expiration date of any of the listed 'pinned-domain-cert' certificates."; } leaf assertion { type enumeration { enum verified { value 0; description "Indicates that the ownership has been positively verified by the MASA (e.g., through sales channel integration)."; } enum logged { value 1; description "Indicates that the voucher has been issued after minimal verification of ownership or control. The issuance has been logged for detection of potential security issues (e.g., recipients of vouchers might verify for themselves that unexpected vouchers are not in the log). This is similar to unsecured trust-on-first-use principles but with the logging providing a basis for detecting unexpected events."; } enum proximity { value 2; description "Indicates that the voucher has been issued after the MASA verified a proximity proof provided by the device and target domain. The issuance has been logged for detection of potential security issues."; } enum agent-proximity { value 3; description "Mostly identical to proximity, but indicates that the voucher has been issued after the MASA has verified a statement that a registrar agent has made contact with the device."; } } } leaf serial-number { type string; mandatory true; description "The serial-number of the hardware. When processing a voucher, a pledge MUST ensure that its serial-number matches this value. If no match occurs, then the pledge MUST NOT process this voucher."; } leaf idevid-issuer { type binary; description "The Authority Key Identifier OCTET STRING (as defined in Section 4.2.1.1 of RFC 5280) from the pledge's IDevID certificate. Optional since some serial-numbers are already unique within the scope of a MASA. Inclusion of the statistically unique key identifier ensures statistically unique identification of the hardware. When processing a voucher, a pledge MUST ensure that its IDevID Authority Key Identifier matches this value. If no match occurs, then the pledge MUST NOT process this voucher. When issuing a voucher, the MASA MUST ensure that this field is populated for serial-numbers that are not otherwise unique within the scope of the MASA."; } leaf pinned-domain-cert { type binary; mandatory false; description "An X.509 v3 certificate structure, as specified by RFC 5280, using Distinguished Encoding Rules (DER) encoding, as defined in ITU-T X.690. This certificate is used by a pledge to trust a Public Key Infrastructure in order to verify a domain certificate supplied to the pledge separately by the bootstrapping protocol. The domain certificate MUST have this certificate somewhere in its chain of certificates. This certificate MAY be an end-entity certificate, including a self-signed entity."; reference "RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. 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)."; } leaf domain-cert-revocation-checks { type boolean; description "A processing instruction to the pledge that it MUST (true) or MUST NOT (false) verify the revocation status for the pinned domain certificate. If this field is not set, then normal PKIX behavior applies to validation of the domain certificate."; } leaf nonce { type binary { length "8..32"; } must 'not(../expires-on)'; description "A value that can be used by a pledge in some bootstrapping protocols to enable anti-replay protection. This node is optional because it is not used by all bootstrapping protocols. When present, the pledge MUST compare the provided nonce value with another value that the pledge randomly generated and sent to a bootstrap server in an earlier bootstrapping message. If the value is present, but the values do not match, then the pledge MUST NOT process this voucher."; } leaf pinned-domain-pubk { type binary; description "The pinned-domain-pubk may replace the pinned-domain-cert in constrained uses of the voucher. The pinned-domain-pubk is the Raw Public Key of the Registrar. This field is encoded as a Subject Public Key Info block as specified in RFC7250, in section 3. The ECDSA algorithm MUST be supported. The EdDSA algorithm as specified in draft-ietf-tls-rfc4492bis-17 SHOULD be supported. Support for the DSA algorithm is not recommended. Support for the RSA algorithm is a MAY."; } leaf pinned-domain-pubk-sha256 { type binary; description "The pinned-domain-pubk-sha256 is a second alternative to pinned-domain-cert. In many cases the public key of the domain has already been transmitted during the key agreement process, and it is wasteful to transmit the public key another two times. The use of a hash of public key info, at 32-bytes for sha256 is a significant savings compared to an RSA public key, but is only a minor savings compared to a 256-bit ECDSA public-key. Algorithm agility is provided by extensions to this specification which can define a new leaf for another hash type."; } leaf last-renewal-date { type yang:date-and-time; must '../expires-on'; description "The date that the MASA projects to be the last date it will renew a voucher on. This field is merely informative; it is not processed by pledges. Circumstances may occur after a voucher is generated that may alter a voucher's validity period. For instance, a vendor may associate validity periods with support contracts, which may be terminated or extended over time."; } // from BRSKI-CLOUD leaf est-domain { type ietf:uri; description "The est-domain is a URL to which the Pledge should continue doing enrollment rather than with the Cloud Registrar. The pinned-domain-cert contains a trust-anchor which is to be used to authenticate the server found at this URI. "; } leaf additional-configuration { type ietf:uri; description "The additional-configuration attribute contains a URL to which the Pledge can retrieve additional configuration information. The contents of this URL are vendor specific. This is intended to do things like configure a VoIP phone to point to the correct hosted PBX, for example."; } } // end voucher } // end voucher-grouping } ]]>

ietf-voucher SID values explains how to serialize YANG into CBOR, and for this a series of SID values are required. While defines the management process for these values, due to the immaturity of the tooling around this YANG-SID mechanisms, the following values are considered normative. It is believed, however, that they will not change. The "assertion" attribute is an enumerated type , and the current PYANG tooling does not document the valid values for this attribute. In the JSON serialization, the literal strings from the enumerated types are used so there is no ambiguity. In the CBOR serialization, a small integer is used. This following values are documented here, but the YANG module should be considered authoritative. No IANA registry is provided or necessary because the YANG module (and this document) would be extended when there are new entries to make. CBOR integers for the "assertion" attribute enum

Integer	Assertion Type
0	verified
1	logged
2	proximity
3	agent-proximity

Voucher Request Artifact defined a Voucher-Request Artifact as an augmented artifact from the Voucher Artifact originally defined in . That definition has been moved to this document, and translated from YANG-DATA to the SX:STRUCTURE extension .

Tree Diagram The following tree diagram illustrates a high-level view of a voucher request document. The notation used in this diagram is described in . Each node in the diagram is fully described by the YANG module in .

"ietf-voucher-request" Module The ietf-voucher-request YANG module is derived from the ietf-voucher module. WG List: Author: Kent Watsen Author: Michael H. Behringer Author: Toerless Eckert Author: Max Pritikin Author: Michael Richardson "; description "This module defines the format for a voucher request. It is a superset of the voucher itself. It provides content to the MASA for consideration during a voucher request. 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) 2019 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 (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2023-01-10 { description "Initial version"; reference "RFC XXXX: Bootstrapping Remote Secure Key Infrastructure"; } // Top-level statement sx:structure voucher { uses voucher-request-grouping; } // Grouping defined for future usage grouping voucher-request-grouping { description "Grouping to allow reuse/extensions in future work."; uses vch:voucher-artifact-grouping { refine "voucher/created-on" { mandatory false; } refine "voucher/pinned-domain-cert" { mandatory false; description "A pinned-domain-cert field is not valid in a voucher request, and any occurrence MUST be ignored"; } refine "voucher/last-renewal-date" { description "A last-renewal-date field is not valid in a voucher request, and any occurrence MUST be ignored"; } refine "voucher/domain-cert-revocation-checks" { description "The domain-cert-revocation-checks field is not valid in a voucher request, and any occurrence MUST be ignored"; } refine "voucher/assertion" { mandatory false; description "Any assertion included in registrar voucher requests SHOULD be ignored by the MASA."; } augment "voucher" { description "Adds leaf nodes appropriate for requesting vouchers."; leaf prior-signed-voucher-request { type binary; description "If it is necessary to change a voucher, or re-sign and forward a voucher that was previously provided along a protocol path, then the previously signed voucher SHOULD be included in this field. For example, a pledge might sign a voucher request with a proximity-registrar-cert, and the registrar then includes it as the prior-signed-voucher-request field. This is a simple mechanism for a chain of trusted parties to change a voucher request, while maintaining the prior signature information. The Registrar and MASA MAY examine the prior signed voucher information for the purposes of policy decisions. For example this information could be useful to a MASA to determine that both pledge and registrar agree on proximity assertions. The MASA SHOULD remove all prior-signed-voucher-request information when signing a voucher for imprinting so as to minimize the final voucher size."; } leaf proximity-registrar-cert { type binary; description "An X.509 v3 certificate structure as specified by RFC 5280, Section 4 encoded using the ASN.1 distinguished encoding rules (DER), as specified in [ITU.X690.1994]. The first certificate in the Registrar TLS server certificate_list sequence (the end-entity TLS certificate, see [RFC8446]) presented by the Registrar to the Pledge. This MUST be populated in a Pledge's voucher request when a proximity assertion is requested."; } leaf proximity-registrar-pubk { type binary; description "The proximity-registrar-pubk replaces the proximity-registrar-cert in constrained uses of the voucher-request. The proximity-registrar-pubk is the Raw Public Key of the Registrar. This field is encoded as specified in RFC7250, section 3. The ECDSA algorithm MUST be supported. The EdDSA algorithm as specified in draft-ietf-tls-rfc4492bis-17 SHOULD be supported. Support for the DSA algorithm is not recommended. Support for the RSA algorithm is a MAY, but due to size is discouraged."; } leaf proximity-registrar-pubk-sha256 { type binary; description "The proximity-registrar-pubk-sha256 is an alternative to both proximity-registrar-pubk and pinned-domain-cert. In many cases the public key of the domain has already been transmitted during the key agreement protocol, and it is wasteful to transmit the public key another two times. The use of a hash of public key info, at 32-bytes for sha256 is a significant savings compared to an RSA public key, but is only a minor savings compared to a 256-bit ECDSA public-key. Algorithm agility is provided by extensions to this specification which may define a new leaf for another hash type."; } leaf agent-signed-data { type binary; description "The agent-signed-data field contains a JOSE [RFC7515] object provided by the Registrar-Agent to the Pledge. This artifact is signed by the Registrar-Agent and contains a copy of the pledge's serial-number."; } leaf agent-provided-proximity-registrar-cert { type binary; description "An X.509 v3 certificate structure, as specified by RFC 5280, Section 4, encoded using the ASN.1 distinguished encoding rules (DER), as specified in ITU X.690. The first certificate in the registrar TLS server certificate_list sequence (the end-entity TLS certificate; see RFC 8446) presented by the registrar to the registrar-agent and provided to the pledge. This MUST be populated in a pledge's voucher-request when an agent-proximity assertion is requested."; reference "ITU X.690: Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3"; } leaf agent-sign-cert { type binary; description "An X.509 v3 certificate structure, as specified by RFC 5280, Section 4, encoded using the ASN.1 distinguished encoding rules (DER), as specified in ITU X.690. This certificate can be used by the pledge, the registrar, and the MASA to verify the signature of agent-signed-data. It is an optional component for the pledge-voucher request. This MUST be populated in a registrar's voucher-request when an agent-proximity assertion is requested."; reference "ITU X.690: Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile"; } } } } } ]]>

ietf-voucher-request SID values explains how to serialize YANG into CBOR, and for this a series of SID values are required. While defines the management process for these values, due to the immaturity of the tooling around this YANG-SID mechanisms, the following values are considered normative. It is believed, however, that they will not change. The "assertion" attribute is an enumerated type, and has values as defined above in .

Design Considerations

Renewals Instead of Revocations The lifetimes of vouchers may vary. In some onboarding protocols, the vouchers may be created and consumed immediately, whereas in other onboarding solutions, there may be a significant time delay between when a voucher is created and when it is consumed. In cases when there is a time delay, there is a need for the pledge to ensure that the assertions made when the voucher was created are still valid. A revocation artifact is generally used to verify the continued validity of an assertion such as a PKIX certificate, web token, or a "voucher". With this approach, a potentially long-lived assertion is paired with a reasonably fresh revocation status check to ensure that the assertion is still valid. However, this approach increases solution complexity, as it introduces the need for additional protocols and code paths to distribute and process the revocations. Addressing the shortcomings of revocations, this document recommends instead the use of lightweight renewals of short-lived non-revocable vouchers. That is, rather than issue a long-lived voucher, where the 'expires-on' leaf is set to some distant date, the expectation is for the MASA to instead issue a short-lived voucher, where the 'expires-on' leaf is set to a relatively near date, along with a promise (reflected in the 'last-renewal-date' field) to reissue the voucher again when needed. Importantly, while issuing the initial voucher may incur heavyweight verification checks ("Are you who you say you are?" "Does the pledge actually belong to you?"), reissuing the voucher should be a lightweight process, as it ostensibly only updates the voucher's validity period. With this approach, there is only the one artifact, and only one code path is needed to process it; there is no possibility of a pledge choosing to skip the revocation status check because, for instance, the OCSP Responder is not reachable. While this document recommends issuing short-lived vouchers, the voucher artifact does not restrict the ability to create long-lived voucher, if required; however, no revocation method is described. Note that a voucher may be signed by a chain of intermediate CAs leading up to the trust anchor certificate known by the pledge. Even though the voucher itself is not revocable, it may still be revoked, per se, if one of the intermediate CA certificates is revoked.

Voucher Per Pledge The solution described herein originally enabled a single voucher to apply to many pledges, using lists of regular expressions to represent ranges of serial-numbers. However, it was determined that blocking the renewal of a voucher that applied to many devices would be excessive when only the ownership for a single pledge needed to be blocked. Thus, the voucher format now only supports a single serial-number to be listed.

Security Considerations

Clock Sensitivity An attacker could use an expired voucher to gain control over a device that has no understanding of time. The device cannot trust NTP as a time reference, as an attacker could control the NTP stream. There are three things to defend against this: 1) devices are required to verify that the expires-on field has not yet passed, 2) devices without access to time can use nonces to get ephemeral vouchers, and 3) vouchers without expiration times may be used, which will appear in the audit log, informing the security decision. This document defines a voucher format that contains time values for expirations, which require an accurate clock in order to be processed correctly. Vendors planning on issuing vouchers with expiration values must ensure that devices have an accurate clock when shipped from manufacturing facilities and take steps to prevent clock tampering. If it is not possible to ensure clock accuracy, then vouchers with expirations should not be issued.

Protect Voucher PKI in HSM Pursuant the recommendation made in Section 6.1 for the MASA to be deployed as an online voucher signing service, it is RECOMMENDED that the MASA's private key used for signing vouchers is protected by a hardware security module (HSM).

Test Domain Certificate Validity When Signing If a domain certificate is compromised, then any outstanding vouchers for that domain could be used by the attacker. The domain administrator is clearly expected to initiate revocation of any domain identity certificates (as is normal in PKI solutions). Similarly, they are expected to contact the MASA to indicate that an outstanding (presumably short lifetime) voucher should be blocked from automated renewal. Protocols for voucher distribution are RECOMMENDED to check for revocation of domain identity certificates before the signing of vouchers.

YANG Module Security Considerations The YANG module specified in this document defines the schema for data that is subsequently encapsulated by a CMS signed-data content type, as described in Section 5 of . As such, all of the YANG modeled data is protected from modification. Implementations should be aware that the signed data is only protected from external modification; the data is still visible. This potential disclosure of information doesn't affect security so much as privacy. In particular, adversaries can glean information such as which devices belong to which organizations and which CRL Distribution Point and/or OCSP Responder URLs are accessed to validate the vouchers. When privacy is important, the CMS signed-data content type SHOULD be encrypted, either by conveying it via a mutually authenticated secure transport protocol (e.g., TLS ) or by encapsulating the signed-data content type with an enveloped-data content type (Section 6 of ), though details for how to do this are outside the scope of this document. The use of YANG to define data structures, via the 'yang-data' statement, is relatively new and distinct from the traditional use of YANG to define an API accessed by network management protocols such as NETCONF and RESTCONF . For this reason, these guidelines do not follow template described by Section 3.7 of .

IANA Considerations

The IETF XML Registry This document registers two URIs in the "IETF XML Registry" . IANA has registered the following:

• URI:

  urn:ietf:params:xml:ns:yang:ietf-voucher

  Registrant Contact:

  The ANIMA WG of the IETF.

  XML:

  N/A, the requested URI is an XML namespace.

This reference should be updated to point to this document.

The YANG Module Names Registry This document registers two YANG module in the "YANG Module Names" registry . IANA has registred the following:

• name:

  ietf-voucher

  namespace:

  urn:ietf:params:xml:ns:yang:ietf-voucher

  prefix:

  vch

  reference: :RFC 8366

This reference should be updated to point to this document.

The Media Types Registry IANA has registered the media type: voucher-cms+json, and this registration should be updated to point to this document.

The SMI Security for S/MIME CMS Content Type Registry IANA has registered the OID 1.2.840.113549.1.9.16.1.40, id-ct-animaJSONVoucher. This registration should be updated to point to this document.

References Normative References This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [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] JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. 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). Trilliant Networks Inc. IMT Atlantique Google Switzerland GmbH Universität Bremen TZI Sandelman Software Works YANG Schema Item iDentifiers (YANG SID) are globally unique 63-bit unsigned integers used to identify YANG items, as a more compact method to identify YANG items that can be used for efficiency and in constrained environments (RFC 7228). This document defines the semantics, the registration, and assignment processes of YANG SIDs for IETF managed YANG modules. To enable the implementation of these processes, this document also defines a file format used to persist and publish assigned YANG SIDs. // The present version (–24) is intended to address the remaining // IESG comments. Enrollment over Secure Transport (EST) is used as a certificate provisioning protocol over HTTPS. Low-resource devices often use the lightweight Constrained Application Protocol (CoAP) for message exchanges. This document defines how to transport EST payloads over secure CoAP (EST-coaps), which allows constrained devices to use existing EST functionality for provisioning certificates. Sandelman Software Works vanderstok consultancy Cisco Systems IoTconsultancy.nl This document defines the Constrained Bootstrapping Remote Secure Key Infrastructure (cBRSKI) protocol, which provides a solution for secure zero-touch onboarding of resource-constrained (IoT) devices into the network of a domain owner. This protocol is designed for constrained networks, which may have limited data throughput or may experience frequent packet loss. cBRSKI is a variant of the BRSKI protocol, which uses an artifact signed by the device manufacturer called the "voucher" which enables a new device and the owner's network to mutually authenticate. While the BRSKI voucher data is encoded in JSON, cBRSKI uses a compact CBOR-encoded voucher. The BRSKI voucher data definition is extended with new data types that allow for smaller voucher sizes. The Enrollment over Secure Transport (EST) protocol, used in BRSKI, is replaced with EST-over- CoAPS; and HTTPS used in BRSKI is replaced with DTLS-secured CoAP (CoAPS). This document Updates RFC 8995 and RFC 9148. Siemens AG Sandelman Software Works [TODO: I-D.draft-ietf-anima-rfc8366bis] defines a digital artifact called voucher as a YANG-defined JSON document that is signed using a Cryptographic Message Syntax (CMS) structure. This document introduces a variant of the voucher artifact in which CMS is replaced by the JSON Object Signing and Encryption (JOSE) mechanism described in RFC7515 to support deployments in which JOSE is preferred over CMS. In addition to explaining how the format is created, the "application/voucher-jws+json" media type is registered and examples are provided. International Telecommunication Union 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 specifies automated bootstrapping of an Autonomic Control Plane. To do this, a Secure Key Infrastructure is bootstrapped. This is done using manufacturer-installed X.509 certificates, in combination with a manufacturer's authorizing service, both online and offline. We call this process the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol. Bootstrapping a new device can occur when using a routable address and a cloud service, only link-local connectivity, or limited/disconnected networks. Support for deployment models with less stringent security requirements is included. Bootstrapping is complete when the cryptographic identity of the new key infrastructure is successfully deployed to the device. The established secure connection can be used to deploy a locally issued certificate to the device as well. Siemens AG Siemens AG Cisco Systems Sandelman Software Works This document defines enhancements to Bootstrapping a Remote Secure Key Infrastructure (BRSKI, RFC8995) to enable bootstrapping in domains featuring no or only limited connectivity between a pledge and the domain registrar. It specifically changes the interaction model from a pledge-initiated mode, as used in BRSKI, to a pledge- responding mode, where the pledge is in server role. For this, BRSKI with Pledge in Responder Mode (BRSKI-PRM) introduces a new component, the Registrar-Agent, which facilitates the communication between pledge and registrar during the bootstrapping phase. To establish the trust relation between pledge and registrar, BRSKI-PRM relies on object security rather than transport security. The approach defined here is agnostic to the enrollment protocol that connects the domain registrar to the domain CA. Cisco Auth0 Sandelman Software Works Bootstrapping Remote Secure Key Infrastructures defines how to onboard a device securely into an operator maintained infrastructure. It assumes that there is local network infrastructure for the device to discover and to help the device. This document extends the new device behaviour so that if no local infrastructure is available, such as in a home or remote office, that the device can use a well defined "call-home" mechanism to find the operator maintained infrastructure. To this, this document defines how to contact a well-known Cloud Registrar, and two ways in which the new device may be redirected towards the operator maintained infrastructure. This document describes YANG mechanisms for defining abstract data structures with YANG. This document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text. 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. 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. Sandelman Software Works vanderstok consultancy Cisco Systems IoTconsultancy.nl This document defines the Constrained Bootstrapping Remote Secure Key Infrastructure (cBRSKI) protocol, which provides a solution for secure zero-touch onboarding of resource-constrained (IoT) devices into the network of a domain owner. This protocol is designed for constrained networks, which may have limited data throughput or may experience frequent packet loss. cBRSKI is a variant of the BRSKI protocol, which uses an artifact signed by the device manufacturer called the "voucher" which enables a new device and the owner's network to mutually authenticate. While the BRSKI voucher data is encoded in JSON, cBRSKI uses a compact CBOR-encoded voucher. The BRSKI voucher data definition is extended with new data types that allow for smaller voucher sizes. The Enrollment over Secure Transport (EST) protocol, used in BRSKI, is replaced with EST-over- CoAPS; and HTTPS used in BRSKI is replaced with DTLS-secured CoAP (CoAPS). This document Updates RFC 8995 and RFC 9148. Siemens AG Sandelman Software Works [TODO: I-D.draft-ietf-anima-rfc8366bis] defines a digital artifact called voucher as a YANG-defined JSON document that is signed using a Cryptographic Message Syntax (CMS) structure. This document introduces a variant of the voucher artifact in which CMS is replaced by the JSON Object Signing and Encryption (JOSE) mechanism described in RFC7515 to support deployments in which JOSE is preferred over CMS. In addition to explaining how the format is created, the "application/voucher-jws+json" media type is registered and examples are provided. Informative References This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] 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. The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] 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). 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. Many application technologies enable secure communication between two entities by means of Internet Public Key Infrastructure Using X.509 (PKIX) certificates in the context of Transport Layer Security (TLS). This document specifies procedures for representing and verifying the identity of application services in such interactions. [STANDARDS-TRACK] This document defines the concept "Opportunistic Security" in the context of communications protocols. Protocol designs based on Opportunistic Security use encryption even when authentication is not available, and use authentication when possible, thereby removing barriers to the widespread use of encryption on the Internet. This document defines a strategy to securely assign a pledge to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher". This document defines an artifact format as a YANG-defined JSON document that has been signed using a Cryptographic Message Syntax (CMS) structure. Other YANG-derived formats are possible. The voucher artifact is normally generated by the pledge's manufacturer (i.e., the Manufacturer Authorized Signing Authority (MASA)). This document only defines the voucher artifact, leaving it to other documents to describe specialized protocols for accessing it. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. CBOR Object Signing and Encryption (COSE) defines a set of security services for CBOR. This document defines a countersignature algorithm along with the needed header parameters and CBOR tags for COSE. This document updates RFC 9052. JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. YANG (RFC 7950) is a data modeling language used to model configuration data, state data, parameters and results of Remote Procedure Call (RPC) operations or actions, and notifications. This document defines encoding rules for YANG in the Concise Binary Object Representation (CBOR) (RFC 8949). Sandelman Software Works This document describes a zero-touch mechanism to enroll a new device (the "pledge") into a IEEE802.15.4 TSCH network using the 6tisch signaling mechanisms. The resulting device will obtain a domain specific credential that can be used with either 802.15.9 per-host pair keying protocols, or to obtain the network-wide key from a coordinator. The mechanism describe her is an augmentation to the one-touch mechanism described in [I-D.ietf-6tisch-minimal-security]. 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. Wikipedia Ericsson AB Ericsson AB INRIA Sandelman Software Works Institute of Embedded Systems, ZHAW This document describes a procedure for augmenting the lightweight authenticated Diffie-Hellman key exchange protocol EDHOC with third party assisted authorization, targeting constrained IoT deployments (RFC 7228).

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