]> 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 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. Discussion Venues Discussion of this document takes place on the Autonomic Networking Integrated Model and Approach Working Group mailing list (anima@ietf.org), which is archived 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 , 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", 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 bootstrapping mechanisms. Assigning ownership is important to bootstrapping 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 bootstrapping protocols, the vouchers may include a nonce restricting them to a single use, whereas the vouchers in other bootstrapping 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 bootstrapping protocols using the voucher artifact defined in this document include: , , and .

Terminology This document uses the following terms:

Artifact:

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

Domain:

The set of entities or infrastructure under common administrative control. The goal of the bootstrapping protocol is to enable a pledge to discover and join a domain.

Imprint:

The process where a device obtains the cryptographic key material to identify and trust future interactions with a network. 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 network's root certification authority 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, signs the vouchers for a manufacturer's pledges. In some bootstrapping protocols, the MASA may have an Internet presence and be integral to the bootstrapping process, whereas in other protocols the MASA may be an offline service that has no active role in the bootstrapping process.

Owner:

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

Pledge:

The prospective device attempting to find and securely join a domain. When shipped, it only trusts authorized representatives of the manufacturer.

Registrar:

See join registrar.

TOFU (Trust on First Use):

Where a pledge device 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 signed statement from the MASA service that indicates to a pledge the cryptographic identity of the domain it should trust.

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 bootstrapping 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. Pinning a symmetric key, a raw 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 bootstrapping scenarios can be met using differing combinations of this information. All scenarios address the primary threat of a Man-in-The-Middle (MiTM) registrar gaining control over the pledge device. The following combinations are "types" of vouchers:

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 MiTM registrar by auditing that an unknown MiTM registrar does not appear in the log entries. This does not directly prevent the MiTM 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.

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 instance of the YANG module defined in that has been, by default, CMS signed. 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. Future work is expected to define new mappings of the voucher to Concise Binary Object Representation (CBOR) (from JSON) and to change the signature container from CMS to JSON Object Signing and Encryption (JOSE) or CBOR Object Signing and Encryption (COSE). XML or ASN.1 formats are also conceivable. This document defines a media type and a filename extension for the CMS-encoded JSON type. Future documents on additional formats would define additional media types. Signaling is 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) 2018 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 (pinned-domain-cert)\ ."; leaf created-on { type yang:date-and-time; mandatory false; must 'not(../created-on-integer)'; 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."; } } } 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 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 } ]]>

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 provides for extensions. CBOR integers for the "assertion" attribute enum

Integer	Assertion Type
0	verified
1	logged
2	proximity

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. Another possible use could be as a "signed voucher request" format originating from the pledge or registrar toward the MASA. 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 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 bootstrapping protocols, the vouchers may be created and consumed immediately, whereas in other bootstrapping 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 This section deals with actions and processes necessary for IANA to undertake to maintain the "iana-voucher-assertion-type" YANG module. The iana-voucher-assertion-type YANG module is intended to reflect the "voucher assertion types" registry in [TBD]. IANA is asked to create the "iana-voucher-assertion-type YANG module" registry. Voucher assertion types must not be directly added to the iana-voucher-type YANG module. They must instead be added to the "voucher assertion types" registry. Whenever a new enumerated type is added to the "voucher assertion types" registry, IANA must also update the "ietf-voucher-assertion-type" YANG module and add a new "enum" statement to the "voucher-assertion-type" type. The assigned name defined by the "enum" statement SHALL be the same as the mnemonic name of the new assertion type. The following substatements to the "enum" statement SHALL be defined:

• "value":

  Use the decimal value from the registry.

  "status":

  Include only if a class or type registration has been deprecated or obsoleted. IANA "deprecated" maps to YANG status "deprecated", and IANA "obsolete" maps to YANG status "obsolete".

  "description":

  Replicate the corresponding information from the registry, namely the full name of the new assertion type.

  "reference":

  Replicate the reference(s) from the registry.

Each time the "iana-voucher-assertion-type" YANG module is updated, a new "revision" statement SHALL be added before the existing "revision" statements. IANA has added this note to the "voucher assertion types" registries: When this registry is modified, the YANG module "iana-voucher-assertion-type" must be updated as defined in [RFCXXXX]. The "Reference" text in the "voucher assertion types" registry has been updated as follows: OLD: | NEW: | [RFC8366][RFCXXX]

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.

IANA is asked to register a second URI as follows:

• URI:

  urn:ietf:params:xml:ns:yang:iana-voucher-assertion-type

  Registrant Contact:

  The ANIMA WG of the IETF.

  XML:

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

The YANG Module Names Registry This document registers two YANG module in the "YANG Module Names" registry . IANA is asked to registrar the following:

• name:

  ietf-voucher

  namespace:

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

  prefix:

  vch

  reference: :RFC 8366

IANA is asked to register a second YANG module as follows:

• name:

  iana-voucher-assertion-type

  namespace:

  urn:ietf:params:xml:ns:yang:iana-voucher-assertion-type

  prefix:

  ianavat

  reference:

  RFC XXXX

The Media Types Registry This document requests IANA to update the following "Media Types" entry to point to the RFC number that will be assigned to this document:

Type name:

application

Subtype name:

voucher-cms+json

Required parameters:

none

Optional parameters:

none

Encoding considerations:

CMS-signed JSON vouchers are ASN.1/DER encoded.

Security considerations:

See

Interoperability considerations:

The format is designed to be broadly interoperable.

Published specification:

RFC 8366

Applications that use this media type:

ANIMA, 6tisch, and NETCONF zero-touch imprinting systems.

Fragment identifier considerations:

none

Additional information:

Deprecated alias names for this type:

none

Magic number(s):

None

File extension(s):

.vcj

Macintosh file type code(s):

none

Person and email address to contact for further information:

IETF ANIMA WG

Intended usage:

LIMITED

Restrictions on usage:

NONE

Author:

ANIMA WG

Change controller:

IETF

Provisional registration? (standards tree only):

NO

The SMI Security for S/MIME CMS Content Type Registry 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

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. Acklio 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 (-19) adds in draft text about objectives, // parties, and roles. This attempts to record discussions at side // meetings before, at, and after IETF 113. 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. International Telecommunication Union 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. 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. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. 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 describes the use of the Bidirectional Forwarding Detection (BFD) protocol in point-to-point Virtual eXtensible Local Area Network (VXLAN) tunnels used to form an overlay network. 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. 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 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.

Acknowledgements The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): William Atwood, Toerless Eckert, and Sheng Jiang. Russ Housley provided the upgrade from PKCS7 to CMS (RFC 5652) along with the detailed CMS structure diagram.