| Internet-Draft | Voucher Artifact | January 2023 |
| Watsen, et al. | Expires 29 July 2023 | [Page] |
This document defines a strategy to securely assign a pledge to an ownerusing 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 documentthat has been signed using a variety of cryptographic systems.¶
The voucher artifact is normally generated bythe pledge's manufacturer (i.e., the Manufacturer Authorized SigningAuthority (MASA)).¶
This document updates RFC8366, merging a number of extensions into the YANG.The RFC8995 voucher request is also merged into this document.¶
This note is to be removed before publishing as an RFC.¶
Status information for this document may be found athttps://datatracker.ietf.org/doc/draft-ietf-anima-rfc8366bis/.¶
Discussion of this document takes place on the anima Working Group mailing list (mailto:anima@ietf.org), which is archived athttps://mailarchive.ietf.org/arch/browse/anima/. Subscribe athttps://www.ietf.org/mailman/listinfo/anima/.¶
Source for this draft and an issue tracker can be found athttps://github.com/anima-wg/voucher.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is athttps://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 29 July 2023.¶
Copyright (c) 2023 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 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 AuthorizedSigning Authority (MASA). This artifact is known as the "voucher".¶
The voucher artifact is a JSON[RFC8259] document thatconforms with a data model described by YANG[RFC7950].It may also be serialized to CBOR[CBOR].It is encoded using the rules defined in[RFC8259], andis signed using (by default) a CMS structure[RFC5652].¶
The primary purpose of a voucher is to securely convey acertificate, the "pinned-domain-cert" (and constrained variations), that a pledge canuse to authenticate subsequent interactions.A voucher may be useful in several contexts, but the driving motivationherein is to support secure onboarding mechanisms.Assigning ownership is important to device onboarding mechanisms so that the pledgecan 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 anindicated lifetime.In order to support long lifetimes, this document recommends using short lifetimes with programmatic renewal, seeSection 8.1.¶
This document only defines the voucher artifact, leaving it to otherdocuments to describe specialized protocols for accessing it.Some onboarding protocols using the voucher artifact defined inthis document include:[ZERO-TOUCH],[SECUREJOIN], and[BRSKI].¶
This document uses the following terms:¶
Used throughout to represent the voucher as instantiated in the formof a signed structure.¶
See Onboarding.¶
The set of entities or infrastructure under common administrativecontrol.The goal of the onboarding protocol is to enable a pledge todiscover and join a domain.¶
The process where a device obtains the cryptographic key material toidentify and trust future interactions with a network. This term istaken from Konrad Lorenz's work in biology with new ducklings:"during a critical period, the duckling would assume that anythingthat looks like a mother duck is in fact their mother"[Stajano99theresurrecting]. An equivalent for a device is toobtain the fingerprint of the network's root certification authoritycertificate. A device that imprints on an attacker suffers a similarfate to a duckling that imprints on a hungry wolf. Imprinting is aterm from psychology and ethology, as described in[imprinting].¶
A representative of the domain that is configured, perhapsautonomically, to decide whether a new device is allowed to join thedomain. The administrator of the domain interfaces with a joinregistrar (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".¶
The entity that, for the purpose of this document, signs thevouchers for a manufacturer's pledges.In some onboarding protocols, the MASA may have an Internetpresence and be integral to the onboarding process, whereas inother protocols the MASA may be an offline service that has noactive role in the onboarding process.¶
In previous documents the term "bootstrapping" has been used to describe mechanisms such as[BRSKI].The industry has however, converged upon the term "onboarding", and this document uses thatterm throughout.¶
The entity that controls the private key of the "pinned-domain-cert"certificate conveyed by the voucher.¶
The prospective device attempting to find and securely join adomain.When shipped, it only trusts authorized representatives of themanufacturer.¶
See join registrar.¶
Where a pledge device makes no security decisions but rather simplytrusts the first domain entity it is contacted by.Used similarly to[RFC7435].This is also known as the "resurrecting duckling" model.¶
A signed statement from the MASA service that indicates to a pledgethe cryptographic identity of the domain it should trust.¶
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 asdescribed in BCP 14[RFC2119][RFC8174] when, and only when, theyappear in all capitals, as shown here.¶
A voucher is a cryptographically protected statement to the pledgedevice authorizing a zero-touch "imprint" on the join registrar of thedomain. The specific information a voucher provides is influenced by theonboarding use case.¶
The voucher can impart the following information tothe join registrar and pledge:¶
Indicates the method that protectsthe imprint (this is distinct from the voucher signature thatprotects the voucher itself). This might includemanufacturer-asserted ownership verification, assuredlogging operations, or reliance on pledge endpoint behaviorsuch as secure root of trustof measurement. The join registrar might use this information.Only some methods are normatively defined in thisdocument. Other methods are left for future work.¶
Indicates how the pledgecan authenticate the join registrar. This document definesa mechanism to pin the domain certificate.Pinning a symmetric key, a raw key, or "CN-ID" or "DNS-ID"information (as defined in[RFC6125]) is left for future work.¶
Time- or nonce-basedinformation to constrain the voucher to time periods or bootstrapattempts.¶
A number of onboarding scenarios can be met using differingcombinations of this information. All scenarios address the primarythreat of a Man-in-The-Middle (MiTM) registrar gaining control overthe 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).¶
An Audit Voucher is named after the logging assertion mechanismsthat the registrar then "audits" to enforce local policy. Theregistrar mitigates a MiTM registrar by auditing that an unknownMiTM registrar does not appear in the log entries. This does notdirectly prevent the MiTM but provides a response mechanism thatensures the MiTM is unsuccessful. The advantage is that actualownership knowledge is not required on the MASA service.¶
An Audit Voucher without a validity period statement. Fundamentally,it is the same as an Audit Voucher except that it can be issued inadvance to support network partitions or to provide a permanentvoucher for remote deployments.¶
An Audit Voucher where the MASA service has verified the registraras the authorized owner.The MASA service mitigates a MiTM registrar by refusing to generateAudit Vouchers for unauthorized registrars. The registrar uses audittechniques to supplement the MASA. This provides an ideal sharing ofpolicy decisions and enforcement between the vendor and the owner.¶
Named after inclusion of the pledge's CN-ID or DNS-ID within thevoucher. The MASA service mitigates a MiTM registrar by identifyingthe specific registrar (via WebPKI) authorized to own the pledge.¶
A Bearer Voucher is named after the inclusion of a registrar IDwildcard. Because the registrar identity is not indicated, thisvoucher type must be treated as a secret and protected from exposureas any 'bearer' of the voucher can claim the pledgedevice. Publishing a nonceless bearer voucher effectively turns thespecified pledge into a "TOFU" device with minimal mitigationagainst MiTM registrars. Bearer vouchers are out of scope.¶
[RFC8366] was published in 2018 during the development of[BRSKI],[ZERO-TOUCH] 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 asonboarding rather thanbootstrapping.¶
The focus of[BRSKI] was onboarding of ISP and Enterprise owned wired routing and switching equipment, with IoT devices being a less important aspect.[ZERO-TOUCH] 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[BRSKI] 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[cBRSKI] document has defined a version of[BRSKI] that is useable over constrained 802.15.4 networks using CoAP and DTLS, while[I-D.selander-ace-ake-authz] provides for using CoAP and EDHOC on even more constrained devices with very constrained networks.¶
[PRM] 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[cBRSKI] and[PRM] 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[cBRSKI] uses the serialization mechanism described in[YANGCBOR] to produce significantly more compact artifacts.¶
When the process to define[cBRSKI] and[PRM] was started, there was a belief that the appropriate process was to use the[RFC8040]augment mechanism to further extend both the voucher request[BRSKI] and voucher[RFC8366] artifacts.However,[PRM] needs to extend an enumerated type with additional values andaugment 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[PRM] voucher artifact.The result was invalid YANG, with multiple definitions of the core attributes from the[RFC8366] voucher artifact.After some discussion, it was determined that theaugment mechanism did not work, nor did it work better when[RFC8040] yang-data was replaced with the[RFC8971] 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[RFC8366], the voucher-request from[BRSKI], and then extensions to each of these from[cBRSKI] and[PRM].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.¶
The voucher's primary purpose is to securely assign a pledge to anowner.The voucher informs the pledge which entity it should consider to beits owner.¶
This document defines a voucher that is a JSON-encoded or CBOR-encoded instance of theYANG module defined inSection 6.3 that has been, by default, CMS signed.[cBRSKI] definies how to encode with CBOR and sign the voucher with[COSE], while[jBRSKI] explains how to use[JWS] to do JSON signatures.¶
This format is described here as a practical basis for some uses (suchas in NETCONF), but more to clearly indicate what vouchers look likein practice.This description also serves to validate the YANG data model.¶
[RFC8366] defined a media type and a filename extension for theCMS-encoded JSON type.Which type of voucher is expected is signaled (where possible) in the form of a MIMEContent-Type, an HTTP Accept: header, or more mundane methods like use of a filename extension when a voucher is transferred on a USB key.¶
The following tree diagram illustrates a high-level view of a voucherdocument.The notation used in this diagram is described in[RFC8340].Each node in the diagram is fully described by the YANG module inSection 6.3.Please review the YANG module for a detailed description of thevoucher format.¶
module: ietf-voucher structure voucher: +-- voucher +-- created-on? yang:date-and-time +-- expires-on? yang:date-and-time +-- assertion? enumeration +-- serial-number string +-- idevid-issuer? binary +-- pinned-domain-cert? binary +-- domain-cert-revocation-checks? boolean +-- nonce? binary +-- pinned-domain-pubk? binary +-- pinned-domain-pubk-sha256? binary +-- last-renewal-date? yang:date-and-time¶
This section provides voucher examples for illustrationpurposes. These examples conform to the encoding rulesdefined in[RFC8259].¶
The following example illustrates an ephemeral voucher (uses a nonce).The MASA generated this voucher using the 'logged' assertion type, knowingthat it would be suitable for the pledge making the request.¶
{ "ietf-voucher:voucher": { "created-on": "2016-10-07T19:31:42Z", "assertion": "logged", "serial-number": "JADA123456789", "idevid-issuer": "base64encodedvalue==", "pinned-domain-cert": "base64encodedvalue==", "nonce": "base64encodedvalue==" }}¶The following example illustrates a non-ephemeral voucher (no nonce).While the voucher itself expires after two weeks, it presumably canbe renewed for up to a year. The MASA generated this voucherusing the 'verified' assertion type, which should satisfy all pledges.¶
{ "ietf-voucher:voucher": { "created-on": "2016-10-07T19:31:42Z", "expires-on": "2016-10-21T19:31:42Z", "assertion": "verified", "serial-number": "JADA123456789", "idevid-issuer": "base64encodedvalue==", "pinned-domain-cert": "base64encodedvalue==", "domain-cert-revocation-checks": "true", "last-renewal-date": "2017-10-07T19:31:42Z" }}¶<CODE BEGINS>module ietf-voucher { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-voucher"; prefix vch; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-yang-structure-ext { prefix sx; } organization "IETF ANIMA Working Group"; contact "WG Web: <https://datatracker.ietf.org/wg/anima/> WG List: <mailto:anima@ietf.org> Author: Kent Watsen <mailto:kwatsen@juniper.net> Author: Max Pritikin <mailto:pritikin@cisco.com> Author: Michael Richardson <mailto:mcr+ietf@sandelman.ca> Author: Toerless Eckert <mailto:tte+ietf@cs.fau.de>"; 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. This is stronger than just logging, because it requires some verification that the pledge and owner are in communication but is still dependent on analysis of the logs to detect unexpected events."; } enum agent-proximity { value 3; description "Indicates that the voucher has been issued after the MASA has verified a statement that a registrar agent has made contact with the device. This type of voucher is weaker than straight proximity, but stronger than logged."; } } } 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."; } } // end voucher } // end voucher-grouping}<CODE ENDS>¶[RFC9148] explains how to serialize YANG into CBOR, and for this a series of SID values are required.While[I-D.ietf-core-sid] 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.¶
SID Assigned to--------- -------------------------------------------------- 2451 data /ietf-voucher:voucher/voucher 2452 data /ietf-voucher:voucher/voucher/assertion 2453 data /ietf-voucher:voucher/voucher/created-on 2454 data .../domain-cert-revocation-checks 2455 data /ietf-voucher:voucher/voucher/expires-on 2456 data /ietf-voucher:voucher/voucher/idevid-issuer 2457 data /ietf-voucher:voucher/voucher/last-renewal-date 2458 data /ietf-voucher:voucher/voucher/nonce 2459 data /ietf-voucher:voucher/voucher/pinned-domain-cert 2460 data /ietf-voucher:voucher/voucher/pinned-domain-pubk 2461 data .../pinned-domain-pubk-sha256 2462 data /ietf-voucher:voucher/voucher/serial-number WARNING, obsolete definitions¶
The "assertion" attribute is an enumerated type[RFC8366], 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 provides for extensions.¶
| Integer | Assertion Type |
|---|---|
| 0 | verified |
| 1 | logged |
| 2 | proximity |
| 3 | agent-proximity |
The IETF evolution of PKCS#7 is CMS[RFC5652].A CMS-signed voucher, the default type, contains a ContentInfostructure with the voucher content. An eContentType of 40indicates that the content is a JSON-encoded voucher.¶
The signing structure is a CMS SignedData structure, as specified bySection 5.1 of[RFC5652], encoded using ASN.1 Distinguished EncodingRules (DER), as specified in ITU-T X.690[ITU-T.X690.2015].¶
To facilitate interoperability,Section 10.3 in this document registers themedia type "application/voucher-cms+json" and the filename extension".vcj".¶
The CMS structureMUST contain a 'signerInfo' structure, asdescribed in Section 5.1 of[RFC5652], containing thesignature generated over the content using a private keytrusted by the recipient. Normally, the recipient is the pledge and thesigner is the MASA. Another possible use could be as a "signedvoucher request" format originating from the pledge or registrartoward the MASA.Within this document, the signer is assumed to be the MASA.¶
Note that Section 5.1 of[RFC5652] includes adiscussion about how to validate a CMS object, which is really aPKCS7 object (cmsVersion=1). Intermediate systems (such theBootstrapping Remote Secure Key Infrastructures[BRSKI] registrar)that might need to evaluate the voucher in flightMUST be prepared forsuch an older format.No signaling is necessary, as the manufacturer knows the capabilitiesof the pledge and will use an appropriate format voucher for eachpledge.¶
The CMS structureSHOULD also contain all of the certificatesleading up to and including the signer's trust anchor certificateknown to the recipient. The inclusion of the trust anchor isunusual in many applications, but third parties cannot accuratelyaudit the transaction without it.¶
The CMS structureMAY also contain revocation objects for anyintermediate certificate authorities (CAs) between thevoucher issuer and the trust anchor known to the recipient.However, the use of CRLs and other validity mechanisms isdiscouraged, as the pledge is unlikely to be able to performonline checks and is unlikely to have a trusted clock source.As described below, the use of short-lived vouchers and/or apledge-provided nonce provides a freshness guarantee.¶
[BRSKI],Section 3 defined a Voucher-Request Artifact as an augmented artifact from the Voucher Artifact originally defined in[RFC8366].That definition has been moved to this document, and translated from YANG-DATA[RFC8040] to the SX:STRUCTURE extension[RFC8971].¶
The following tree diagram illustrates a high-level view of a voucherrequest document.The notation used in this diagram is described in[RFC8340].Each node in the diagram is fully described by the YANG module inSection 7.2.¶
module: ietf-voucher-request structure voucher: +-- voucher +-- created-on? | yang:date-and-time +-- expires-on? | yang:date-and-time +-- assertion? enumeration +-- serial-number string +-- idevid-issuer? binary +-- pinned-domain-cert? binary +-- domain-cert-revocation-checks? boolean +-- nonce? binary +-- pinned-domain-pubk? binary +-- pinned-domain-pubk-sha256? binary +-- last-renewal-date? | yang:date-and-time +-- prior-signed-voucher-request? binary +-- proximity-registrar-cert? binary +-- proximity-registrar-pubk? binary +-- proximity-registrar-pubk-sha256? binary +-- agent-signed-data? binary +-- agent-provided-proximity-registrar-cert? binary +-- agent-sign-cert? binary¶
The ietf-voucher-request YANG module is derived from the ietf-voucher module.¶
<CODE BEGINS>=============== NOTE: '\' line wrapping per RFC 8792 ================module ietf-voucher-request { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-voucher-request"; prefix vcr; import ietf-yang-structure-ext { prefix sx; } import ietf-voucher { prefix vch; 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"; reference "RFC 8366: Voucher Artifact for Bootstrapping Protocols"; } organization "IETF ANIMA Working Group"; contact "WG Web: <https://datatracker.ietf.org/wg/anima/> WG List: <mailto:anima@ietf.org> Author: Kent Watsen <mailto:kent+ietf@watsen.net> Author: Michael H. Behringer <mailto:Michael.H.Behringer@gmail.com> Author: Toerless Eckert <mailto:tte+ietf@cs.fau.de> Author: Max Pritikin <mailto:pritikin@cisco.com> Author: Michael Richardson <mailto:mcr+ietf@sandelman.ca>"; 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"; } } } }}<CODE ENDS>¶[RFC9148] explains how to serialize YANG into CBOR, and for this a series of SID values are required.While[I-D.ietf-core-sid] 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.¶
SID Assigned to--------- -------------------------------------------------- 2501 data /ietf-voucher-request:voucher/voucher 2515 data .../agent-provided-proximity-registrar-cert 2516 data .../agent-sign-cert 2517 data .../agent-signed-data 2502 data /ietf-voucher-request:voucher/voucher/assertion 2503 data /ietf-voucher-request:voucher/voucher/created-on 2504 data .../domain-cert-revocation-checks 2505 data /ietf-voucher-request:voucher/voucher/expires-on 2506 data .../idevid-issuer 2507 data .../last-renewal-date 2508 data /ietf-voucher-request:voucher/voucher/nonce 2509 data .../pinned-domain-cert 2518 data .../pinned-domain-pubk 2519 data .../pinned-domain-pubk-sha256 2510 data .../prior-signed-voucher-request 2511 data .../proximity-registrar-cert 2513 data .../proximity-registrar-pubk 2512 data .../proximity-registrar-pubk-sha256 2514 data .../serial-number WARNING, obsolete definitions¶
The "assertion" attribute is an enumerated type, and has values as defined above inTable 2.¶
The lifetimes of vouchers may vary. In some onboarding protocols,the vouchers may be created and consumed immediately, whereas in otheronboarding solutions, there may be a significant time delay betweenwhen a voucher is created and when it is consumed.In cases when there is a time delay, there is a need for the pledgeto ensure that the assertions made when the voucher was created arestill valid.¶
A revocation artifact is generally used to verify the continued validityof an assertion such as a PKIX certificate, web token, or a "voucher". Withthis approach, a potentially long-lived assertion is paired with a reasonablyfresh revocation status check to ensure that the assertion is still valid.However, this approach increases solution complexity, as it introduces theneed for additional protocols and code paths to distribute and process therevocations.¶
Addressing the shortcomings of revocations, this document recommendsinstead the use of lightweight renewals of short-lived non-revocablevouchers. That is, rather than issue a long-lived voucher, where the'expires-on' leaf is set to some distant date, the expectationis 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 againwhen needed. Importantly, while issuing the initial voucher may incurheavyweight verification checks ("Are you who you say you are?" "Does thepledge actually belong to you?"), reissuing the voucher should be alightweight process, as it ostensibly only updates the voucher'svalidity period.With this approach, there isonly the one artifact, and only one code path is needed to processit; there is no possibility of a pledge choosing to skip therevocation status check because, for instance, the OCSP Responder isnot reachable.¶
While this document recommends issuing short-lived vouchers, thevoucher artifact does not restrict the ability to create long-livedvoucher, if required; however, no revocation method is described.¶
Note that a voucher may be signed by a chain of intermediate CAsleading up to the trust anchor certificate known by the pledge. Eventhough the voucher itself is not revocable, it may still be revoked,per se, if one of the intermediate CA certificates is revoked.¶
The solution described herein originally enabled a single voucher toapply to many pledges, using lists of regular expressions to representranges of serial-numbers. However, it was determined that blocking therenewal of a voucher that applied to many devices would be excessivewhen only the ownership for a single pledge needed to be blocked.Thus, the voucher format now only supports a single serial-numberto be listed.¶
An attacker could use an expired voucher to gain control overa device that has no understanding of time. The device cannottrust NTP as a time reference, as an attacker could controlthe NTP stream.¶
There are three things to defend against this: 1) devices arerequired to verify that the expires-on field has not yet passed,2) devices without access to time can use nonces toget ephemeral vouchers, and 3) vouchers without expiration timesmay be used, which will appear in the audit log, informing thesecurity decision.¶
This document defines a voucher format that contains time valuesfor expirations, which require an accurate clockin order to be processed correctly. Vendors planning onissuing vouchers with expiration values must ensure that deviceshave an accurate clock when shipped from manufacturingfacilities and take steps to prevent clock tampering.If it is not possible to ensure clock accuracy, thenvouchers with expirations should not be issued.¶
Pursuant the recommendation made in Section 6.1 for the MASA to bedeployed as an online voucher signing service, it isRECOMMENDED thatthe MASA's private key used for signing vouchers is protected bya hardware security module (HSM).¶
If a domain certificate is compromised, then any outstandingvouchers for that domain could be used by the attacker. The domainadministrator is clearly expected to initiate revocation of anydomain identity certificates (as is normal in PKI solutions).¶
Similarly, they are expected to contact the MASA to indicate thatan outstanding (presumably short lifetime) voucher should be blocked fromautomated renewal.Protocols for voucher distribution areRECOMMENDED to check for revocation of domain identity certificatesbefore the signing of vouchers.¶
The YANG module specified in this document defines the schemafor data that is subsequently encapsulated by a CMS signed-datacontent type, as described in Section 5 of[RFC5652]. As such,all of the YANG modeled data is protected from modification.¶
Implementations should be aware that the signed data is onlyprotected from external modification; the data is still visible.This potential disclosure of information doesn't affect securityso much as privacy. In particular, adversaries can gleaninformation such as which devices belong to which organizationsand which CRL Distribution Point and/or OCSP Responder URLs areaccessed to validate the vouchers. When privacy is important,the CMS signed-data content typeSHOULD be encrypted, either byconveying it via a mutually authenticated secure transport protocol(e.g., TLS[RFC5246]) or by encapsulating the signed-datacontent type with an enveloped-data content type (Section 6of[RFC5652]), though details for how to do this are outsidethe 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 ofYANG to define an API accessed by network management protocols such asNETCONF[RFC6241] and RESTCONF[RFC8040]. For this reason, theseguidelines do not follow template described by Section 3.7 of[YANG-GUIDE].¶
This document registers two URIs in the "IETF XML Registry"[RFC3688].¶
IANA has registered the following:¶
This document registers two YANG module in the "YANG Module Names"registry[RFC6020].¶
IANA is asked to registrar the following:¶
reference: :RFC 8366¶
IANA is asked to register a second YANG module as follows:¶
This document requests IANA to update the following "Media Types" entry to point to the RFC number that will be assigned to this document:¶
application¶
voucher-cms+json¶
none¶
none¶
CMS-signed JSON vouchers are ASN.1/DER encoded.¶
The format is designed to be broadly interoperable.¶
RFC 8366¶
ANIMA, 6tisch, and NETCONF zero-touch imprinting systems.¶
none¶
IETF ANIMA WG¶
LIMITED¶
NONE¶
ANIMA WG¶
IETF¶
NO¶
This document requests IANA to update this registered OID in the "SMI Security for S/MIME CMS Content Type (1.2.840.113549.1.9.16.1)" registry to point to the RFC number to be assigned to this document:¶
| Decimal | Description | References |
|---|---|---|
| 40 | id-ct-animaJSONVoucher | RFC 8366 |
The authors would like to thank for following forlively discussions on list and in the halls (orderedby last name): William Atwood, Toerless Eckert, and Sheng Jiang.¶
Russ Housley provided the upgrade from PKCS7 to CMS (RFC 5652) alongwith the detailed CMS structure diagram.¶
draft-ietf-anima-rfc8366bis-05
| Document | Document type | This is an older version of an Internet-Draft whose latest revision state is "Active". | |
|---|---|---|---|
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| Authors | Kent Watsen,Michael Richardson,Max Pritikin,Toerless Eckert,Qiufang Ma | ||
| Replaces | draft-richardson-anima-rfc8366bis | ||
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| Additional resources | Mailing list discussion |