Internet-Draft BRSKI-PRM October 2022
Fries, et al. Expires 27 April 2023 [Page]
Workgroup:
ANIMA WG
Internet-Draft:
draft-ietf-anima-brski-prm-05
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Fries
Siemens
T. Werner
Siemens
E. Lear
Cisco Systems
M. Richardson
Sandelman Software Works

BRSKI with Pledge in Responder Mode (BRSKI-PRM)

Abstract

This document defines enhancements to bootstrapping a remote secure key infrastructure (BRSKI, RFC8995) to facilitate bootstrapping in domains featuring no or only time limited connectivity between a pledge and the domain registrar. It specifically targets situations, in which the interaction model changes from a pledge-initiated-mode, as used in BRSKI, to a pledge-responding-mode as described in this document. To support the pledge-responding mode, BRSKI-PRM introduces a new component, the registrar-agent, which facilitates the communication between pledge and registrar during the bootstrapping phase. To establishment the trust relation between pledge and domain registrar, BRSKI-PRM relies on object security rather than transport security.

The approach defined here is agnostic with respect to the underlying enrollment protocol which connects the pledge and the domain registrar to the Domain CA.

About This Document

This note is to be removed before publishing as an RFC.

Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-anima-brski-prm/.

Source for this draft and an issue tracker can be found at https://github.com/anima-wg/anima-brski-prm.

Status of This Memo

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 at https://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 27 April 2023.

Table of Contents

1. Introduction

BRSKI as defined in [RFC8995] specifies a solution for secure zero-touch (automated) bootstrapping of devices (pledges) in a (customer) site domain. This includes the discovery of network elements in the customer site/domain and the exchange of security information necessary to establish trust between a pledge and the domain.

Security information about the customer site/domain, specifically the customer site/domain certificate, is exchanged utilizing voucher request objects and voucher response objects as defined in [RFC8995]. Voucher objects are specified in [RFC8366]. Vouchers are signed objects from the Manufacturer's Authorized Signing Authority (MASA). The MASA issues the voucher object and provides it via the domain registrar to the pledge.

For the certificate enrollment of devices, BRSKI relies on EST [RFC7030] to request and distribute customer site/domain specific device certificates. EST in turn relies on a binding of the certification request to an underlying TLS connection between the EST client and the EST server.

BRSKI addresses scenarios in which the pledge initiates the bootstrapping acting as a client (this document refers to this approach as pledge-initiator-mode). In industrial environments the pledge may behave as a server and thus does not initiate the bootstrapping with the domain registrar. In this scenarios it is expected that the pledge will be triggered to generate bootstrapping requests in the customer site/domain. This document refers to this approach as pledge-responder-mode and

  • introduces the registrar-agent as new component to facilitate the communication between the pledge and the registrar, as the pledge is in responder mode, and acts as server. For the interaction with the domain registrar the registrar-agent will use existing BRSKI [RFC8995] endpoints as well as additional endpoints defined i this document.
  • specifies the interaction (data exchange and data objects) between a pledge acting as server and a registrar-agent and the domain registrar. The security is addressed on application layer only to enable usage of arbitrary transport means between the pledge and the domain registrar via the registrar-agent. Connectivity between the pledge and the registrar-agent may be via IP-based networks (wired or wireless) but also via Bluetooth or NFC.
  • allows the application of registrar-agent credentials to establish TLS connections to the domain registrar. These registrar-agent credentials are different from the pledge's IDevID.

The term endpoint used in the context of this document is similar to resources in CoAP [RFC7252] and also in HTTP [RFC9110]. It is not used to describe a device. Endpoints are accessible via .well-known URIs.

To utilize the EST server endpoints on the domain registrar, the registrar-agent will act as client towards the domain registrar.

The registrar-agent also acts as a client when communicating with a pledge in responder mode. Here, TLS with server-side, certificate-based authentication is not directly applicable, as the pledge only possesses an IDevID certificate. The IDevID does not contain any anchor for which any kind of [RFC6125] validation can be done. Second, the registrar-agent may not be aware of manufacturer trust anchors to validate the IDevIDs. Finally, IDevID do not typically set Extended Key Usage (EKU) for TLS WWW Server authentication.

The inability to effectively do TLS in responder mode is one reason for relying on object security. Another reason is the application on different transports channels, for which TLS may not be available, such as Bluetooth and NFC.

Therefore, BRSKI-PRM relies on an additional signature wrapping of the exchanged data objects . For EST [RFC7030] the registrar then needs to do some pre-processing to verify this signature, which is not present in EST.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document relies on the terminology defined in [RFC8995], section 1.2. The following terms are defined additionally:

authenticated self-contained object:

Describes an object, which is cryptographically bound to the end entity (EE) certificate (IDevID certificate or LDEVID certificate). The binding is assumed to be provided through a digital signature of the actual object using the corresponding private key of the EE certificate.

CA:

Certification authority, issues certificates.

Commissioning tool:

Tool to interact with devices to provide configuration data

CSR:

Certificate Signing Request

EE:

End entity

mTLS:

Mutual authenticated Transport Layer Security.

on-site:

Describes a component or service or functionality available in the customer site/domain.

off-site:

Describes a component or service or functionality not available within the customer site/domain. It may be at a central site or an internet resident "cloud" service. The connection may also be a temporary and, e.g., only available at times when workers are present on a construction side, for instance.

PER:

Pledge-enrollment-request is a signature wrapped CSR, signed by the pledge that requests enrollment to a domain

POP:

Proof of possession (of a private key)

POI:

Proof of identity (see Section 4)

PVR:

Pledge-Voucher-Request is a request for a voucher signed by the Pledge to the Registrar.

RA:

Registration authority, an optional system component to which a CA delegates certificate management functions such as authorization checks.

RER:

Registrar-enrollment-request is the CSR of PER send to the CA by the registrar (RA/LRA)

RVR:

Registrar-Voucher-Request is a request for a voucher signed by the Registrar to the MASA. It may contain the PVR received from the pledge.

This document includes many examples that would contain many long sequences of base64 encoded objects with no content directly comprehensible to a human reader. In order to keep them readable the examples use the token "base64encodedvalue==" whenever such a thing occurs. This token is in fact valid base64. The full examples are in appendix.

This protocol unavoidably has a mix of both base64 encoded data (as is normal for many JSON encoded protocols), and also BASE64URL encoded data, as specified by JWS. The later is indicated by a string like "BASE64URL(THING)"

3. Scope of Solution

3.1. Supported Environments and Use Case Examples

BRSKI-PRM is applicable to environments where pledges may have different behavior: pledge-responder-mode, or pledges may have no direct connection to the domain registrar. Either way pledges are expected to be managed by the same registrar.

This can be motivated by pledges deployed in environments not yet connected to the operational customer site/domain network, e.g., at a construction site where a building is going up.

Another environment relates to the assembly of cabinets, which are prepared in advance to be installed on a customer site/domain.

As there is no direct connection to the registrar available in these environments the solution specified allows the pledges to act in a server role so they can be triggered for bootstrapping e.g., by a commissioning tool.

As BRSKI focuses on the pledge in a client role, initiating the bootstrapping (pledge-initiated-mode), BRSKI-PRM defines pledges acting as a server (pledge-responder-mode) responding to PVR and PER and consumption of the results.

The following examples motivate support of BRSKI-PRM to support pledges acting as server as well as pledges with limited connectivity to the registrar.

While BRSKI-PRM defines support for pledges in responder mode, there may be pledges, which can act as both initiator or responder. In these cases BRSKI-PRM can be combined with BRSKI as defined in [RFC8995] or BRSKI-AE [I-D.ietf-anima-brski-ae] to allow for more bootstrapping flexibility.

A pledge which can initiate, SHOULD listen for BRSKI messages as describe in [RFC8995], Section 4.1. Upon discovery of a potential Registrar, it SHOULD initiate to that Registrar. At the same time (so as to avoid the Slowloris-attack described in [RFC8995]), it SHOULD also respond to the pledge-responder-mode connections described in this document.

Once a pledge with such combined functionality has been bootstrapped, it may act as client for enrollment or re-enrollment of further certificates needed, e.g., using the enrollment protocol of choice. If it still acts as server, the defined endpoints can be used to trigger a Pledge-Enrollment-Request (PER) for further certificates.

3.1.1. Building Automation

In building automation a typical use case exists where a detached building (or a cabinet) or the basement of a building is equipped with sensors, actuators and controllers, but with only limited or no connection to the central building management system. This limited connectivity may exist during installation time or also during operation time.

During the installation, for instance, in the basement, a service technician collects the device specific information from the basement network and provides them to the central building management system. This could be done using a laptop, common mobile device, or dedicated commissioning tool to transport the information. The service technician may visit every new house in a subdivision collecting device specific information before connecting to the Registrar.

A domain registrar may be part of the central building management system and already be operational in the installation network. The central building management system can then provide operational parameters for the specific devices in the basement. This operational parameters may comprise values and settings required in the operational phase of the sensors/actuators, among them a certificate issued by the operator to authenticate against other components and services. These operational parameters are then provided to the devices in the basement facilitated by the service technician's laptop.

3.1.2. Infrastructure Isolation Policy

This refers to any case in which the network infrastructure is normally isolated from the Internet as a matter of policy, most likely for security reasons. In such a case, limited access to a domain registrar may be allowed in carefully controlled short periods of time, for example when a batch of new devices are deployed, but prohibited at other times.

3.1.3. Less Operational Security in the Target-Domain

The registration authority (RA) performing the authorization of a certificate request is a critical PKI component and therefore requires higher operational security than other components utilizing the issued certificates. CAs may also require higher security in the registration procedures. There may be situations in which the customer site/domain does not offer enough security to operate a RA/CA and therefore this service is transferred to a backend that offers a higher level of operational security.

3.2. Limitations

The mechanism described in this document presume the availability of the pledge to communicate with the registrar-agent. This may not be possible in constrained environments where, in particular, power must be conserved. In these situations, it is anticipated that the transceiver will be powered down most of the time. This presents a rendezvous problem: the pledge is unavailable for certain periods of time, and the registrar-agent is similarly presumed to be unavailable for certain periods of time.

4. Requirements Discussion and Mapping to Solution-Elements

Based on the intended target environment described in Section 3.1 the following requirements are derived to support bootstrapping of pledges in responder mode (acting as server).

  • To facilitate the communication between a pledge in responder mode and registrar, additional functionality is needed either on the registrar or as a stand-alone component. This new functionality is defined as registrar-agent and acts as an agent of the registrar to trigger the pledge to generate requests for voucher and enrollment. These requests are than provided by the registrar-agent to the registrar. This requires the definition of pledge endpoints to allow interaction with the registrar-agent.
  • The communication between the registrar-agent and the pledge MUST NOT rely on transport layer security (TLS) because the pledge does not have certificate a that can easily be verified by [RFC6125] methods. It is also more difficult to use TLS over other technology stacks (e.g., BTLE).
  • The use of authenticated self-contained objects provides a work around for both the TLS challenges, and the technology stack challenge.
  • By contrast, the registrar-agent can be authenticated by the registrar as a component, acting on behalf of the registrar. In addition the registrar must be able to verify, which registrar-agent was in direct contact with the pledge.
  • It would be inaccurate for the voucher request and voucher response to use an assertion with value "proximity" in the voucher, as the pledge was not in direct contact with the registrar for bootstrapping. Therefore a new "agent-proximity" assertion value is necessary for distinguishing assertions the MASA can state.

At least the following properties are required for the voucher and enrollment processing:

  • Proof of Identity (POI): provides data-origin authentication of a data object, e.g., a voucher request or an enrollment request, utilizing an existing IDevID. Certificate updates may utilize the certificate that is to be updated.
  • Proof of Possession (POP): proves that an entity possesses and controls the private key corresponding to the public key contained in the certification request, typically by adding a signature using the private key to the certification request.

Solution examples based on existing technology are provided with the focus on existing IETF RFCs:

  • Voucher requests and responses as used in [RFC8995] already provide both, POP and POI, through a digital signature to protect the integrity of the voucher, while the corresponding signing certificate contains the identity of the signer.
  • Certification requests are data structures containing the information from a requester for a CA to create a certificate. The certification request format in BRSKI is PKCS#10 [RFC2986]. In PKCS#10, the structure is signed to ensure integrity protection and proof of possession of the private key of the requester that corresponds to the contained public key. In the application examples, this POP alone is not sufficient. A POI is also required for the certification request and therefore needs to be additionally bound to the existing credential of the pledge (IDevID). This binding supports the authorization decision for the certification request may be provided directly with the certification request. While BRSKI uses the binding to TLS, BRSKI-PRM aims at an additional signature of the PKCS#10 using existing credentials on the pledge (IDevID). This allows the process to be independent of the selected transport.

5. Architectural Overview

For BRSKI with pledge in responder mode, the base system architecture defined in BRSKI [RFC8995] is enhanced to facilitate the new use cases in which the pledge acts as server. The pledge-responder-mode allows delegated bootstrapping using a registrar-agent instead of a direct connection between the pledge and the domain registrar.

Necessary enhancements to support authenticated self-contained objects for certificate enrollment are kept at a minimum to enable reuse of already defined architecture elements and interactions.

For the authenticated self-contained objects used for the certification request, BRSKI-PRM relies on the defined message wrapping mechanisms of the enrollment protocols stated in Section 4 above.

The security used within the document for bootstrapping objects produced or consumed by the pledge bases on JOSE [RFC7515]. In constraint environments it may provided based on COSE [RFC9052].

An abstract overview of the BRSKI-PRM protocol can be found in [BRSKI-PRM-abstract].

5.1. Pledge-Responder-Mode (PRM): Registrar-Agent Communication with Pledges

To support mutual trust establishment between the domain registrar and pledges not directly connected to the customer site/domain, this document specifies the exchange of authenticated self-contained objects (the voucher request/response as known from BRSKI and the enrollment request/response as introduced by BRSKI-PRM) with the help of a registrar-agent.

This leads to extensions of the logical components in the BRSKI architecture as shown in Figure 1. Note that the Join Proxy is neglected in the figure as not needed by the registrar-agent. The registrar-agent interacts with the pledge to transfer the required data objects for bootstrapping, which are then also exchanged between the registrar-agent and the domain registrar. The addition of the registrar-agent influences the sequences of the data exchange between the pledge and the domain registrar as described in [RFC8995]. To enable reuse of BRSKI defined functionality as much as possible, BRSKI-PRM:

  • uses existing endpoints were the required functionality is provided
  • enhances existing with new supported media types, e.g., for JWS voucher
  • defines new endpoints were additional functionality is required, e.g., for wrapped certification request, CA certificates, or new status information.
Drop Ship Vendor Service M anufacturer A uthorized Ownership S igning Tracker A uthority BRSKI- BRSKI-PRM MASA ............................. ......... . . . . . . Pledge . Registrar BRSKI Domain . . Agent EST Registrar . (PKI RA) . . LDevID . . . IDevID . . . . . Key Infrastructure . . (e.g., PKI Certificate . . Authority) . . . ....................................... "Domain" components
Figure 1: Architecture overview using registrar-agent

The following list describes the components in a (customer) site domain:

  • Pledge: The pledge is expected to respond with the necessary data objects for bootstrapping to the registrar-agent. The protocol used between the pledge and the registrar-agent is assumed to be HTTP in the context of this document. Other protocols may be used like CoAP, Bluetooth, or NFC, but are out of scope of this document. A pledge acting as a server during bootstrapping leads to some differences to BRSKI:

    • Discovery of the pledge by the registrar-agent must be possible.
    • As the registrar-agent must be able to request data objects for bootstrapping of the pledge, the pledge must offer corresponding endpoints.
    • The registrar-agent may provide additional data to the pledge in the context of the voucher triggering request, to make itself visible to the domain registrar.
    • Order of exchanges in the call flow may be different as the registrar-agent collects both, PVR and PER, at once and provides them to the registrar. This approach is used in order to allow for bulk bootstrapping of several devices in a single pass through a new site by the commissioning personnel.
    • The data objects utilized for the data exchange between the pledge and the registrar are self-contained authenticated objects (signature-wrapped objects).
  • Registrar-agent: provides a communication path to exchange data objects between the pledge and the domain registrar. The registrar-agent brokers in situations in which the domain registrar is not directly reachable by the pledge. This may be due to a different technology stack or due to missing connectivity. The registrar-agent triggers a pledge to create bootstrapping artifacts such as the voucher-request and the enrollment-request on one or multiple pledges and performs a (bulk) bootstrapping based on the collected data. The registrar-agent is expected to possess information about the domain registrar: the registrar EE certificate, LDevID(CA) certificate, IP address, either by configuration or by using the discovery mechanism defined in [RFC8995]. There is no trust assumption between the pledge and the registrar-agent as only authenticated self-contained objects are used, which are transported via the registrar-agent and provided either by the pledge or the registrar. The trust assumption between the registrar-agent and the registrar is based on the LDevID of the registrar-agent, provided by the PKI responsible for the domain. This allows the registrar-agent to authenticate towards the registrar, e.g., in a TLS handshake. Based on this, the registrar is able to distinguish a pledge from a registrar-agent during the TLS session establishment and also to verify that the registrar-agent is authorized to perform the bootstrapping of the distinct pledge. The registrar-agent may be implemented as an integrated functionality of a commissioning tool or be co-located with the registrar itself.
  • Join Proxy (not shown): same functionality as described in [RFC8995] if needed. Note that a registrar-agent may use a join proxy to facilitate the TLS connection to the registrar, in the same way that a BRSKI pledge would use a join proxy. This is useful in cases where the registrar-agent does not have full IP connectivity via the domain network, or cases where it has no other means to locate the registrar on the network.
  • Domain Registrar: In general the domain registrar fulfills the same functionality regarding the bootstrapping of the pledge in a (customer) site domain by facilitating the communication of the pledge with the MASA service and the domain PKI service. In contrast to [RFC8995], the domain registrar does not interact with a pledge directly but through the registrar-agent. The registrar detects if the bootstrapping is performed by the pledge directly or by the registrar-agent.
  • The manufacturer provided components/services (MASA and Ownership tracker) are used as defined in [RFC8995]. For issuing a voucher, the MASA may perform additional checks on a voucher-request, to issue a voucher indicating agent-proximity instead of (registrar-)proximity.

5.2. Agent-Proximity Assertion

"Agent-proximity" is a statement, that the proximity registrar certificate was provided via the registrar-agent as defined in Section 6 and not directly to the pledge. "Agent-proximity" is therefore a weaker assertion then "proximity". It is defined as additional assertion type in [I-D.ietf-anima-rfc8366bis]. This can be verified by the registrar and also by the MASA during the voucher-request processing. Note that at the time of creating the voucher-request, the pledge cannot verify the registrar's registrar EE certificate and has no proof-of-possession of the corresponding private key for the certificate. The pledge therefore accepts the registrar EE certificate provisionally until it receives the voucher as described in Section 6.3. See also [RFC8995] "PROVISIONAL accept of server cert".

Trust handover to the domain is established via the "pinned-domain-certificate" in the voucher.

In contrast to the above, "proximity" provides a statement, that the pledge was in direct contact with the registrar and was able to verify proof-of-possession of the private key in the context of the TLS handshake. The provisionally accepted registrar EE certificate can be verified after the voucher has been processed by the pledge. As the returned voucher includes an additional signature by the registrar as defined in Section 6.2.5, the pledge can also verify that the registrar possesses the corresponding private key.

5.3. Behavior of Pledge in Pledge-Responder-Mode

The pledge is triggered by the registrar-agent to generate the PVR and PER as well as for the processing of the responses and the generation of status information. Due to the use of the registrar-agent, the interaction with the domain registrar is changed as shown in Figure 3. To enable interaction with the registrar-agent, the pledge provides endpoints using the BRSKI defined endpoints based on the "/.well-known/brski" URI tree.

The following endpoints are defined for the pledge in this document. The URI path begins with "http://www.example.com/.well-known/brski" followed by a path-suffix that indicates the intended operation.

Operations and their corresponding URIs:

Table 1: Endpoints on the pledge
Operation Operation path Details
Trigger pledge-voucher-request creation - Returns PVR /pledge-voucher-request Section 6.1
Trigger pledge-enrollment-request - Returns PER /pledge-enrollment-request Section 6.1
Provide voucher to pledge - Returns pledge-voucher-status /pledge-voucher Section 6.3
Provide enrollment response to pledge - Returns pledge-enrollment-status /pledge-enrollment Section 6.3
Provide CA certs to pledge /pledge-CACerts Section 6.3
Query bootstrapping status of pledge - Returns pledge-status /pledge-bootstrap-status Section 6.4

5.4. Behavior of Registrar-Agent

The registrar-agent as a new component provides connectivity between the pledge and the domain registrar and reuses the endpoints of the domain registrar side already specified in [RFC8995]. It facilitates the exchange of data between the pledge and the domain registrar, which are the voucher request/response, the enrollment request/response, as well as related telemetry and status information. For the communication with the pledge the registrar-agent utilizes communication endpoints provided by the pledge. The transport in this specification is based on HTTP but may also be done using other transport mechanisms. This new component changes the general interaction between the pledge and the domain registrar as shown in Figure 1.

For authentication to the domain registrar, the registrar-agent uses its LDevID(RegAgt). The provisioning of the registrar-agent LDevID is out of scope for this document, but may be done in advance using a separate BRSKI run or by other means like configuration. It is recommended to use short lived registrar-agent LDevIDs in the range of days or weeks as outlined in Section 10.3.

The registrar-agent will use its LDevID(RegAgt) when establishing a TLS session with the domain registrar for TLS client authentication. The LDevID(RegAgt) certificate MUST include a SubjectKeyIdentifier (SKID), which is used as reference in the context of an agent-signed-data object as defined in Section 6.1. Note that this is an additional requirement for issuing the certificate, as [IEEE-802.1AR] only requires the SKID to be included for intermediate CA certificates. [RFC8995] makes a similar requirement. In BRSKI-PRM, the SKID is used in favor of a certificate fingerprint to avoid additional computations.

Using an LDevID for TLS client authentication of the registrar-agent is a deviation from [RFC8995], in which the pledge's IDevID credential is used to perform TLS client authentication. The use of the LDevID(RegAgt) allows the domain registrar to distinguish, if bootstrapping is initiated from a pledge or from a registrar-agent and to adopt different internal handling accordingly. If a registrar detects a request that originates from a registrar-agent it is able to switch the operational mode from BRSKI to BRSKI-PRM. This may be supported by a specific naming in the SAN (subject alternative name) component of the LDevID(RegAgt) certificate. Alternatively, the domain may feature a CA specifically for issuing registrar-agent LDevID certificates. This allows the registrar to detect registrar-agents based on the issuing CA.

As BRSKI-PRM uses authenticated self-contained data objects between the pledge and the domain registrar, the binding of the pledge identity to the requests is provided by the data object signature employing the pledge's IDevID. The objects exchanged between the pledge and the domain registrar used in the context of this specifications are JOSE objects.

In addition to the LDevID(RegAgt), the registrar-agent is provided with the product-serial-number(s) of the pledge(s) to be bootstrapped. This is necessary to allow the discovery of pledge(s) by the registrar-agent using mDNS (see Section 5.4.2) The list may be provided by administrative means or the registrar agent may get the information via an interaction with the pledge. For instance, [RFC9238] describes scanning of a QR code, the product-serial-number would be initialized from the 12N B005 Product Serial Number.

According to [RFC8995] section 5.3, the domain registrar performs the pledge authorization for bootstrapping within his domain based on the pledge voucher-request object.

The following information MUST be available at the registrar-agent:

  • LDevID(RegAgt): own operational key pair.
  • Registrar EE certificate: certificate of the domain registrar.
  • Serial-number(s): product-serial-number(s) of pledge(s) to be bootstrapped.

5.4.1. Discovery of Registrar by Registrar-Agent

The discovery of the domain registrar may be done as specified in [RFC8995] with the deviation that it is done between the registrar-agent and the domain registrar. Alternatively, the registrar-agent may be configured with the address of the domain registrar and the certificate of the domain registrar.

5.4.2. Discovery of Pledge by Registrar-Agent

The discovery of the pledge by registrar-agent should be done by using DNS-based Service Discovery [RFC6763] over Multicast DNS [RFC6762] to discover the pledge. The pledge constructs a local host name based on device local information (product-serial-number), which results in "product-serial-number._brski-pledge._tcp.local".

The registrar-agent MAY use

  • "product-serial-number._brski-pledge._tcp.local", to discover a specific pledge, e.g., when connected to a local network.
  • "_brski-pledge._tcp.local" to get a list of pledges to be bootstrapped.

A manufacturer may allow the pledge to react on mDNS discovery without his product-serial-number contained. This allows a commissioning tool to discover pledges to be bootstrapped in the domain. The manufacturer may opt out of this functionality as outlined in Section 10.4.

To be able to detect the pledge using mDNS, network connectivity is required. For Ethernet it is provided by simply connecting the network cable. For WiFi networks, connectivity can be provided by using a pre-agreed SSID for bootstrapping. The same approach can be used by 6LoWPAN/mesh using a pre-agreed PAN ID. How to gain network connectivity is out of scope of this document.

6. Bootstrapping Data Objects and Corresponding Exchanges

The interaction of the pledge with the registrar-agent may be accomplished using different transport means (protocols and/or network technologies). This specification descibes the usage of HTTP as in BRSKI [RFC8995]. Alternative transport channels may be CoAP, Bluetooth Low Energy (BLE), or Nearfield Communication (NFC). These transport means may differ from, and are independent of, the ones used between the registrar-agent and the registrar. Transport channel independence is realized by data objects which are not bound to specific transport security. Therefore, authenticated self-contained objects (here: signature-wrapped objects) are applied for data exchanges between the pledge and the registrar.

The registrar-agent provides the domain registrar certificate (registrar EE certificate) to the pledge to be included in the PVR leaf "agent-provided-proximity-registrar-certificate". This enables the registrar to verify that it is the desired registrar for handling the request.

The registrar certificate may be configured at the registrar-agent or may be fetched by the registrar-agent based on a prior TLS connection with this domain registrar. In addition, the registrar-agent provides agent-signed-data containing the pledge product-serial-number, signed with the LDevID(RegAgt). This enables the registrar to verify and log, which registrar-agent was in contact with the pledge, when verifying the PVR.

The registrar MUST fetch the LDevID(RegAgt) certificate based on the SubjectKeyIdentifier (SKID) in the header of the agent-signed-data from the PVR. The registrar includes the LDevID(RegAgt) certificate information into the RVR if the PVR asked for the assertion "agent-proximity".

The MASA in turn verifies the registrar EE certificate is included in the PVR ("prior-signed-voucher-request" of RVR) in the "agent-provided-proximity-registrar-certificate" leaf and may assert the PVR as "verified" or "logged" instead of "proximity", as there is no direct connection between the pledge and the registrar.

In addition, the MASA can state the assertion "agent-proximity" as follows: The MASA can verify the signature of the agent-signed-data contained in the prior-signed-voucher-request, based on the provided LDevID(RegAgt) certificate in the "agent-sign-cert" leaf of the RVR. If both can be verified successfully, the MASA can assert "agent-proximity" in the voucher.

Depending on the MASA verification policy, it may also respond with a suitable 4xx or 5xx status code as described in section 5.6 of [RFC8995]. The voucher then can be supplied via the registrar to the registrar-agent.

Figure 2 provides an overview of the exchanges detailed in the following sub sections.

Pledge Registrar Domain Domain Vendor Agent Registrar CA Service (RegAgt) (JRC) (MASA) Internet discover pledge mDNS query trigger PVR (tPVR) and PER (tPER) generation on pledge tPVR PVR tPER PER ~ ~ ~ ~ ~ provide PVR to infrastructure TLS | [Reg-Agt authenticated and authorized?] PVR | [Reg-Agt authorized?] [accept device?] [contact vendor] RVR [extract DomainID] [update audit log] Voucher Voucher provide PER to infrastructure PER CSR Cert Enroll-Resp query cACerts from infrastructure cACert-Req cACert-Resp ~ ~ ~ ~ ~ provide voucher and certificate and collect status info Voucher vStatus cACerts Enroll-Resp eStatus ~ ~ ~ ~ ~ provide voucher status and enroll status to registrar TLS vStatus req device audit log device audit log [verify audit log] eStatus
Figure 2: Overview pledge-responder-mode exchanges

The following sub sections split the interactions between the different components into:

  • Section 6.1 describes the request object acquisition by the registrar-agent from pledge.
  • Section 6.2 describes the request object processing initiated by the registrar-agent to the registrar and also the interaction of the registrar with the MASA and the domain CA including the response object processing by these entities.
  • Section 6.3 describes the supply of response objects between the registrar-agent and the pledge including the status information.
  • Section 6.4 describes the general status handling and addresses corresponding exchanges between the registrar-agent and the registrar.

6.1. Request Objects Acquisition by Registrar-Agent from Pledge

The following description assumes that the registrar-agent has already discovered the pledge. This may be done as described in Section 5.4.2 based on mDNS or similar.

The focus is on the exchange of signature-wrapped objects using endpoints defined for the pledge in Section 5.3.

Preconditions:

  • Pledge: possesses IDevID
  • Registrar-agent: possesses/trusts IDevID CA certificate and has own LDevID(RegAgt) credentials for the registrar domain (site). In addition, the registrar-agent MUST know the product-serial-number(s) of the pledge(s) to be bootstrapped. The registrar-agent MAY be provided with the product-serial-number(s) in different ways:

    • configured, e.g., as a list of pledges to be bootstrapped via QR code scanning
    • discovered by using standard approaches like mDNS as described in Section 5.4.2
    • discovered by using a vendor specific approach, e.g., RF beacons The registrar-agent SHOULD have synchronized time.
  • Registrar: possesses/trusts IDevID CA certificate and has own registrar EE credentials.
Pledge Registrar Agent (RegAgt) -create agent-signed-data trigger pledge-voucher-request -agent-provided-proximity-registrar-cert -agent-signed-data pledge-voucher-request -store PVR trigger enrollment request (empty) pledge-enrollment-request -store (PER)
Figure 3: Request collection (registrar-agent - pledge)

Note: The registrar-agent may trigger the pledge for the PVR or the PER or both. It is expected that this will be aligned with a service technician workflow, visiting and installing each pledge.

6.1.1. Pledge-Voucher-Request (PVR) - Trigger

Triggering the pledge to create the PVR is done using HTTP POST on the defined pledge endpoint: "/.well-known/brski/pledge-voucher-request"

The registrar-agent PVR trigger Content-Type header is: application/json. Following parameters are provided in the JSON object:

  • agent-provided-proximity-registrar-cert: base64-encoded registrar EE TLS certificate.
  • agent-signed-data: base64-encoded JSON-in-JWS object.

The trigger for the pledge to create a PVR is depicted in the following figure:

{
  "agent-provided-proximity-registrar-cert": "base64encodedvalue==",
  "agent-signed-data": "base64encodedvalue=="
}
Figure 4: Representation of trigger to create PVR

The pledge provisionally accepts the agent-provided-proximity-registrar-cert, it SHOULD verify it after a voucher is received. The pledge will be unable to verify the agent-signed-data itself as it does not possess the LDevID(RegAgt) certificate and the domain trust has not been established at this point of the communication. It SHOULD be done, after the voucher has been received.

The agent-signed-data is a JSON-in-JWS object and contains the following information:

The header of the agent-signed-data contains:

  • alg: algorithm used for creating the object signature.
  • kid: MUST contain the base64-encoded bytes of the SubjectKeyIdentifier (the "KeyIdentifier" OCTET STRING value), excluding the ASN.1 encoding of "OCTET STRING" of the LDevID(RegAgt) certificate.

The body of the agent-signed-data contains an "ietf-voucher-request-prm:agent-signed-data" element (defined in Section 7.1):

  • created-on: MUST contain the creation date and time in yang:date-and-time format.
  • serial-number: MUST contain the product-serial-number as type string as defined in [RFC8995], section 2.3.1. The serial-number corresponds with the product-serial-number contained in the X520SerialNumber field of the IDevID certificate of the pledge.
# The agent-signed-data in General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-voucher-request-prm:agent-signed-data)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "ietf-voucher-request-prm:agent-signed-data"
  representation in JSON syntax

"ietf-voucher-request-prm:agent-signed-data": {
  "created-on": "2021-04-16T00:00:01.000Z",
  "serial-number": "callee4711"
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "kid": "base64encodedvalue=="
}
Figure 5: Representation of agent-signed-data in General JWS Serialization syntax

6.1.2. Pledge-Voucher-Request (PVR) - Response

Upon receiving the voucher-request trigger, the pledge SHALL construct the body of the PVR as defined in [RFC8995]. It will contain additional information provided by the registrar-agent as specified in the following. This PVR becomes a JSON-in-JWS object as defined in [I-D.ietf-anima-jws-voucher]. If the pledge is unable to construct the PVR it SHOULD respond with a HTTP error code to the registrar-agent to indicate that it is not able to create the PVR.

The following client error responses MAY be used:

  • 400 Bad Request: if the pledge detected an error in the format of the request, e.g. missing field, wrong data types, etc. or it's not valid JSON even though the PVR media type was set to application/json.
  • 403 Forbidden: if the pledge detected that one or more security parameters from the trigger message to create the PVR were not valid, e.g., the LDevID (Reg) certificate.

The header of the PVR SHALL contain the following parameters as defined in [RFC7515]:

  • alg: algorithm used for creating the object signature.
  • x5c: contains the base64-encoded pledge IDevID certificate. It may optionally contain the certificate chain for this certificate.

The payload of the PVR MUST contain the following parameters as part of the ietf-voucher-request-prm:voucher as defined in [RFC8995]:

  • created-on: SHALL contain the current date and time in yang:date-and-time format. If the pledge does not have synchronized the time, it SHALL use the created-on time from the agent-signed-data, received in the trigger to create a PVR.
  • nonce: SHALL contain a cryptographically strong pseudo-random number.
  • serial-number: SHALL contain the pledge product-serial-number as X520SerialNumber.
  • assertion: SHALL contain the requested voucher assertion "agent-proximity".

The ietf-voucher-request:voucher is enhanced with additional parameters:

  • agent-provided-proximity-registrar-cert: MUST be included and contains the base64-encoded registrar EE certificate (provided as trigger parameter by the registrar-agent).
  • agent-signed-data: MUST contain the base64-encoded agent-signed-data (as defined in Figure 5) and provided as trigger parameter.

The enhancements of the YANG module for the ietf-voucher-request with these new leaves are defined in Section 7.1.

The PVR is signed using the pledge's IDevID credential contained as x5c parameter of the JOSE header.

# The PVR in General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-voucher-request-prm:voucher)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded Payload "ietf-voucher-request-prm:voucher" Representation
  in JSON syntax
"ietf-voucher-request-prm:voucher": {
   "created-on": "2021-04-16T00:00:02.000Z",
   "nonce": "eDs++/FuDHGUnRxN3E14CQ==",
   "serial-number": "callee4711",
   "assertion": "agent-proximity",
   "agent-provided-proximity-registrar-cert": "base64encodedvalue==",
   "agent-signed-data": "base64encodedvalue=="
}

# Decoded "JWS Protected Header" Representation in JSON syntax
{
    "alg": "ES256",
    "x5c": [
      "base64encodedvalue==",
      "base64encodedvalue=="
    ],
    "typ": "voucher-jws+json"
}
Figure 6: Representation of PVR

The PVR Content-Type is defined in [I-D.ietf-anima-jws-voucher] as application/voucher-jws+json.

The pledge SHOULD include this Content-Type header field indicating the included media type for the PVR. Note that this is also an indication regarding the acceptable format of the voucher response. This format is included by the registrar as described in Section 6.2.

6.1.3. Pledge-Enrollment-Request (PER) - Trigger

Once the registrar-agent has received the PVR it can trigger the pledge to generate a PER. As in BRSKI the PER contains a PKCS#10, but additionally signed using the pledge's IDevID. Note, as the initial enrollment aims to request a generic certificate, no certificate attributes are provided to the pledge.

Triggering the pledge to create the enrollment-request is done using HTTP POST on the defined pledge endpoint: "/.well-known/brski/pledge-enrollment-request"

The registrar-agent PER trigger Content-Type header is: application/json with an empty body by default. Note that using HTTP POST allows for an empty body, but also to provide additional data, like CSR attributes or information about the enroll type "enroll-generic-cert" or "re-enroll-generic-cert". The "enroll-generic-cert" case is shown in Figure 7.

{
  "enroll-type" : "enroll-generic-cert"
}
Figure 7: Example of trigger to create a PER

6.1.4. Pledge-Enrollment-Request (PER) - Response

In the following the enrollment is described as initial enrollment with an empty HTTP POST body.

Upon receiving the enrollment-trigger, the pledge SHALL construct the PER as authenticated self-contained object. The CSR already assures proof of possession of the private key corresponding to the contained public key. In addition, based on the additional signature using the IDevID, proof of identity is provided. Here, a JOSE object is being created in which the body utilizes the YANG module ietf-ztp-types with the grouping for csr-grouping for the CSR as defined in [I-D.ietf-netconf-sztp-csr].

Depending on the capability of the pledge, it constructs the enrollment request (PER) as plain PKCS#10. Note, the focus in this use case is placed on PKCS#10 as PKCS#10 can be transmitted in different enrollment protocols in the infrastructure like EST, CMP, CMS, and SCEP. If the pledge has already implemented an enrollment protocol, it may leverage that functionality for the creation of the CSR. Note, [I-D.ietf-netconf-sztp-csr] also allows for inclusion of certification requests in different formats used by CMP or CMC.

The pledge SHOULD construct the PER as PKCS#10. In BRSKI-PRM it MUST sign it additionally with its IDevID credentials to provide proof-of-identity bound to the PKCS#10 as described below.

If the pledge is unable to construct the PER it SHOULD respond with a HTTP 4xx/5xx error code to the registrar-agent to indicate that it is not able to create the PER.

The following 4xx client error codes MAY be used:

  • 400 Bad Request: if the pledge detected an error in the format of the request or detected invalid JSON even though the PER media type was set to application/json.
  • 403 Forbidden: if the pledge detected that one or more security parameters (if provided) from the trigger message to create the PER are not valid.
  • 406 Not Acceptable: if the request's Accept header indicates a type that is unknown or unsupported. For example, a type other than application/jose+json.
  • 415 Unsupported Media Type: if the request's Content-Type header indicates a type that is unknown or unsupported. For example, a type other than 'application/json'.

A successful enrollment will result in a generic LDevID certificate for the pledge in the new domain, which can be used to request further (application specific) LDevID certificates if necessary for operation. The registrar-agent SHALL use the endpoints specified in this document.

[I-D.ietf-netconf-sztp-csr] considers PKCS#10 but also CMP and CMC as certification request format. Note that the wrapping signature is only necessary for plain PKCS#10 as other request formats like CMP and CMS support the signature wrapping as part of their own certificate request format.

The registrar-agent enrollment-request Content-Type header for a signature-wrapped PKCS#10 is: application/jose+json

The header of the pledge enrollment-request SHALL contain the following parameter as defined in [RFC7515]:

  • alg: algorithm used for creating the object signature.
  • x5c: contains the base64-encoded pledge IDevID certificate. It may optionally contain the certificate chain for this certificate.

The body of the pledge enrollment-request SHOULD contain a P10 parameter (for PKCS#10) as defined for ietf-ztp-types:p10-csr in [I-D.ietf-netconf-sztp-csr]:

  • P10: contains the base64-encoded PKCS#10 of the pledge.

The JOSE object is signed using the pledge's IDevID credential, which corresponds to the certificate signaled in the JOSE header.

# The PER in General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-ztp-types)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded Payload "ietf-ztp-types" Representation in JSON Syntax
"ietf-ztp-types": {
  "p10-csr": "base64encodedvalue=="
}

# Decoded "JWS Protected Header" Representation in JSON Syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ],
  "crit":["created-on"],
  "created-on": "2022-09-13T00:00:02.000Z"
}
Figure 8: Representation of PER

With the collected PVR and PER, the registrar-agent starts the interaction with the domain registrar.

The new protected header field "created-on" is introduced to reflect freshness of the PER. The field is marked critical "crit" to ensure that it must be understood and validated by the receiver (here the domain registrar) according to section 4.1.11 of [RFC7515]. It allows the registrar to verify the timely correlation between the PER and previously exchanged messages, i.e., created-on of PER >= created-on of PVR >= created-on of PVR trigger.

As the registrar-agent is intended to facilitate communication between the pledge and the domain registrar, a collection of requests from more than one pledge is possible. This allows bulk bootstrapping of several pledges using the same connection between the registrar-agent and the domain registrar.

6.2. Request Object Handling initiated by the Registrar-Agent on Registrar, MASA and Domain CA

The BRSKI-PRM bootstrapping exchanges between registrar-agent and domain registrar resemble the BRSKI exchanges between pledge and domain registrar (pledge-initiator-mode) with some deviations.

Preconditions:

  • Registrar-agent: possesses it's own LDevID(RegAgt) credentials of the site domain. In addition, it may possess the IDevID CA certificate of the pledge vendor/manufacturer to verify the pledge certificate in the received request messages. It has the address of the domain registrar through configuration or by discovery, e.g., mDNS/DNSSD. The registrar-agent has acquired one or more PVR and PER objects.
  • Registrar: possesses the IDevID CA certificate of the pledge vendor/manufacturer and it's own registrar EE credentials of the site domain.
  • MASA: possesses it's own vendor/manufacturer credentials (voucher signing key, TLS server certificate) related to pledges IDevID and MAY possess the site-specific domain CA certificate. The latter is only necessary if the MASA needs to verify that the domain of the Registrar is a-priori authorized to enroll a particular pledge, or a particular type of pledge. In such case is out of scope of this document how the MASA will obtain the domain CA certificate. In other cases, a MASA may allow the pledge to enroll into an anonymous and/or yet-unknown domain and then the a-priori possession of the domain CA certificate is not needed.
Registrar- Domain Domain Vendor agent Registrar CA Service (RegAgt) (JRC) (MASA) | Internet [voucher + enrollment] [PVR PER available ] mTLS [Reg-Agt authenticated and authorized?] Voucher-Req (PVR) [Reg-Agt authorized?] [accept device?] [contact vendor] mTLS Voucher-Req (RVR) [extract DomainID] [update audit log] Voucher Voucher Enroll-Req (PER) mTLS Enroll-Req (RER) Enroll-Resp Enroll-Resp caCerts-Req caCerts-Res
Figure 9: Request processing between registrar-agent and bootstrapping services

The registrar-agent establishes a TLS connection to the registrar. As already stated in [RFC8995], the use of TLS 1.3 (or newer) is encouraged. TLS 1.2 or newer is REQUIRED on the registrar-agent side. TLS 1.3 (or newer) SHOULD be available on the registrar, but TLS 1.2 MAY be used. TLS 1.3 (or newer) SHOULD be available on the MASA, but TLS 1.2 MAY be used.

6.2.1. Connection Establishment (Registrar-Agent to Registrar)

In contrast to BRSKI [RFC8995] TLS client authentication to the registrar is achieved by using registrar-agent LDevID(RegAgt) credentials instead of pledge IDevID credentials. Consequently BRSKI (pledge-initiator-mode) is distinguishable from BRSKI-PRM (pledge-responder-mode) by the registrar. The registrar SHOULD verify that the registrar-agent is authorized to establish a connection to the registrar by TLS client authentication using LDevID(RegAgt) credentials. If the connection from registrar-agent to registrar is established, the authorization SHALL be verified again based on agent-signed-data contained in the PVR. This ensures that the pledge has been triggered by an authorized registrar-agent.

The registrar can receive request objects in different formats as defined in [RFC8995]. Specifically, the registrar will receive JSON-in-JWS objects generated by the pledge for voucher-request and enrollment-request (instead of BRSKI voucher-request as CMS-signed JSON and enrollment-request as PKCS#10).

The registrar-agent SHALL send the PVR by HTTP POST to the registrar endpoint: "/.well-known/brski/requestvoucher"

The Content-Type header field for JSON-in-JWS PVR is: application/voucher-jws+json (see Figure 6 for the content definition), as defined in [I-D.ietf-anima-jws-voucher].

The registrar-agent SHOULD set the Accept field in the request-header indicating the acceptable Content-Type for the voucher-response. The voucher-response Content-Type header field SHOULD be set to application/voucher-jws+json as defined in [I-D.ietf-anima-jws-voucher].

6.2.2. Pledge-Voucher-Request (RVR) Processing by Registrar

After receiving the PVR from registrar-agent, the registrar SHALL perform the verification as defined in section 5.3 of [RFC8995]. In addition, the registrar SHALL verify the following parameters from the PVR:

  • agent-provided-proximity-registrar-cert: MUST contain registrar's own registrar EE certificate to ensure the registrar in proximity of the registrar-agent is the desired registrar for this PVR.
  • agent-signed-data: The registrar MUST verify that the agent provided data has been signed with the LDevID(RegAgt) credentials indicated in the "kid" JOSE header parameter. The registrar MUST verify that the LDevID(ReAgt) certificate, corresponding to the signature, is still valid. If the certificate is already expired, the registrar SHALL reject the request. Validity of used signing certificates at the time of signing the agent-signed-data is necessary to avoid that a rogue registrar-agent generates agent-signed-data objects to onboard arbitrary pledges at a later point in time, see also Section 10.3. The registrar MUST fetch the LDevID(RegAgt) certificate, based on the provided SubjectKeyIdentifier (SKID) contained in the "kid" header parameter of the agent-signed-data, and perform this verification. This requires, that the registrar can fetch the LDevID(RegAgt) certificate data (including intermediate CA certificates if existent) based on the SKID.

If the validation fails the registrar SHOULD respond with HTTP 404 Not Found status code to the registrar-agent. HTTP 406 Not Acceptable status code SHOULD be used if the Content-Type indicated by the Accept header is unknown or unsupported.

If the validation succeeds, the registrar SHOULD accept the PVR to join the domain as defined in section 5.3 of [RFC8995]. The registrar then establishes a TLS connection to MASA as described in section 5.4 of [RFC8995] to obtain a voucher for the pledge.

6.2.3. Registrar-Voucher-Request (RVR) Processing (Registrar to MASA)

The registrar SHALL construct the payload of the RVR as defined in [RFC8995]. The RVR encoding SHALL be JSON-in-JWS as defined in [I-D.ietf-anima-jws-voucher].

The header of the RVR SHALL contain the following parameter as defined for JWS [RFC7515]:

  • alg: algorithm used to create the object signature
  • x5c: base64-encoded registrar LDevID certificate(s) (It optionally contains the certificate chain for this certificate)

The payload of the RVR MUST contain the following parameter as part of the voucher-request as defined in [RFC8995]:

  • created-on: current date and time in yang:date-and-time format of RVR creation
  • nonce: copied form the PVR
  • serial-number: product-serial-number of pledge The registrar MUST verify that the IDevID certificate subject serialNumber of the pledge (X520SerialNumber) matches the serial-number value in the PVR. In addition, it MUST be equal to the serial-number value contained in the agent-signed data of PVR.
  • assertion: voucher assertion requested by the pledge (agent-proximity). The registrar provides this information to assure successful verification of agent proximity based on the agent-signed-data.
  • prior-signed-voucher-request: PVR as in [RFC8995]

The RVR MUST be enhanced with the following parameter, when the assertion "agent-proximity" is requested, as defined in Section 7.1:

  • agent-sign-cert: LDevID(RegAgt) certificate or the LDevID(RegAgt) certificate including certificate chain. In the context of this document it is a JSON array of base64encoded certificate information and handled in the same way as x5c header objects.

If only a single object is contained in the x5c it MUST be the base64-encoded LDevID(RegAgt) certificate. If multiple certificates are included in the x5c, the first MUST be the base64-encoded LDevID(RegAgt) certificate.

The MASA uses this information for verification that the registrar-agent is in proximity to the registrar to state the corresponding assertion "agent-proximity".

The object is signed using the registrar EE credentials, which corresponds to the certificate referenced in the JOSE header.

# The RVR in General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-voucher-request-prm:voucher)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "ietf-voucher-request-prm:voucher" representation
  in JSON syntax
"ietf-voucher-request-prm:voucher": {
   "created-on": "2022-01-04T02:37:39.235Z",
   "nonce": "eDs++/FuDHGUnRxN3E14CQ==",
   "serial-number": "callee4711",
   "assertion": "agent-proximity",
   "prior-signed-voucher-request": "base64encodedvalue==",
   "agent-sign-cert": [
     "base64encodedvalue==",
     "base64encodedvalue==",
     "..."
   ]
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ],
  "typ": "voucher-jws+json"
}
Figure 10: Representation of RVR

The registrar SHALL send the RVR to the MASA endpoint by HTTP POST: "/.well-known/brski/requestvoucher"

The RVR Content-Type header field is defined in [I-D.ietf-anima-jws-voucher] as: application/voucher-jws+json

The registrar SHOULD set the Accept header of the RVR indicating the desired media type for the voucher-response. The media type is application/voucher-jws+json as defined in [I-D.ietf-anima-jws-voucher].

Once the MASA receives the RVR it SHALL perform the verification as described in section 5.5 in [RFC8995].

In addition, the following processing SHALL be performed for PVR contained in RVR "prior-signed-voucher-request" field:

  • agent-provided-proximity-registrar-cert: The MASA MAY verify that this field contains the registrar EE certificate. If so, it MUST correspond to the registrar EE credentials used to sign the RVR. Note: Correspond here relates to the case that a single registrar EE certificate is used or that different registrar EE certificates are used, which are issued by the same CA.
  • agent-signed-data: The MASA MAY verify this data to issue "agent-proximity" assertion. If so, the agent-signed-data MUST contain the pledge product-serial-number, contained in the "serial-number" field of the PVR (from "prior-signed-voucher-request" field) and also in "serial-number" field of the RVR. The LDevID(RegAgt) certificate to be used for signature verification is identified by the "kid" parameter of the JOSE header. If the assertion "agent-proximity" is requested, the RVR MUST contain the corresponding LDevID(RegAgt) certificate data in the "agent-sign-cert" field of the RVR. It MUST be verified by the MASA to the same domain CA as the registrar EE certificate. If the "agent-sign-cert" field is not set, the MASA MAY state a lower level assertion value, e.g.: "logged" or "verified". Note: Sub-CA certificate(s) MUST also be carried by "agent-sign-cert", in case the LDevID(RegAgt) certificate is issued by a sub-CA and not the domain CA known to the MASA. As the "agent-sign-cert" field is defined as array (x5c), it can handle multiple certificates.

If validation fails, the MASA SHOULD respond with an HTTP 4xx client error status code to the registrar. The HTTP error status codes are kept the same as defined in section 5.6 of [RFC8995] and comprise the codes: 403, 404, 406, and 415.

6.2.4. Voucher Issuance by MASA

The expected voucher-response format for BRSKI-PRM (pledge-responder-mode) application/voucher-jws+json as defined in [I-D.ietf-anima-jws-voucher] SHOULD be applied. If the MASA detects that the Accept header of the PVR does not match the application/voucher-jws+json it SHOULD respond with the HTTP status code 406 Not Acceptable as the pledge will not be able to parse the response. The voucher syntax is described in detail by [RFC8366]. Figure 11 shows an example of the contents of a voucher.

# The MASA issued voucher in General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-voucher:voucher)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "ietf-voucher:voucher" representation in
  JSON syntax
"ietf-voucher:voucher": {
  "assertion": "agent-proximity",
  "serial-number": "callee4711",
  "nonce": "base64encodedvalue==",
  "created-on": "2022-01-04T00:00:02.000Z",
  "pinned-domain-cert": "base64encodedvalue=="
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ],
  "typ": "voucher-jws+json"
}
Figure 11: Representation of MASA issued voucher

The MASA returns the voucher-response (voucher) to the registrar.

6.2.5. MASA issued Voucher Processing by Registrar

After receiving the voucher the registrar SHOULD evaluate it for transparency and logging purposes as outlined in section 5.6 of [RFC8995]. The registrar MUST add an additional signature to the MASA provided voucher using its registrar credentials. The signature is created by signing the original "JWS Payload" produced by MASA and the registrar added "JWS Protected Header" using the registrar EE credentials (see[RFC7515], section 5.2 point 8. The x5c component of the "JWS Protected Header" MUST contain registrar EE certificate as well as potential intermediate CA certificates up to the pinned domain certificate. The pinned domain certificate is already contained in the voucher payload ("pinned-domain-cert").

This signature provides a proof of possession of the private key corresponding to the registrar EE certificate the pledge received in the trigger for the PVR (see Figure 4). The registrar MUST use the same registrar EE credentials used for authentication in the TLS handshake to authenticate towards the registrar-agent. This ensures that the same registrar EE certificate can be used to verify the signature as transmitted in the voucher request as also transferred in the PVR in the "agent-provided-proximity-registrar-cert". Figure 12 below provides an example of the voucher with two signatures.

# The MASA issued voucher with additional registrar signature in
  General JWS Serialization syntax
{
  "payload": "BASE64URL(ietf-voucher:voucher)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header (MASA)))",
      "signature": "base64encodedvalue=="
    },
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header (Reg)))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "ietf-voucher:voucher" representation in
  JSON syntax
"ietf-voucher:voucher": {
   "assertion": "agent-proximity",
   "serial-number": "callee4711",
   "nonce": "base64encodedvalue==",
   "created-on": "2022-01-04T00:00:02.000Z",
   "pinned-domain-cert": "base64encodedvalue=="
}

# Decoded "JWS Protected Header (MASA)" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ],
  "typ": "voucher-jws+json"
}

# Decoded "JWS Protected Header (Reg)" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}
Figure 12: Representation of MASA issued voucher with additional registrar signature

Depending on the security policy of the operator, this signature can also be interpreted by the pledge as explicit authorization of the registrar to install the contained trust anchor. The registrar sends the voucher to the registrar-agent.

6.2.6. Pledge-Enrollment-Request (PER) Processing (Registrar-Agent to Registrar)

After receiving the voucher, the registrar-agent sends the PER to the registrar. Deviating from BRSKI the PER is not a raw PKCS#10. As the registrar-agent is involved in the exchange, the PKCS#10 is wrapped in a JWS object by the pledge and signed with pledge's IDevID to ensure proof-of-identity as outlined in Figure 8.

EST [RFC7030] standard endpoints (/simpleenroll, /simplereenroll, /serverkeygen, /cacerts) on the registrar cannot be used for BRSKI-PRM. This is caused by the utilization of signature wrapped-objects in BRSKI-PRM. As EST requires to sent a raw PKCS#10 request to e.g., "/.well-known/est/simpleenroll" endpoint, this document makes an enhancement by utilizing EST but with the exception to transport a signature wrapped PKCS#10 request. Therefore a new endpoint for BRSKI-PRM on the registrar is defined as "/.well-known/brski/requestenroll"

The Content-Type header of PER is: application/jose+json.

This is a deviation from the Content-Type header values used in [RFC7030] and results in additional processing at the domain registrar (as EST server). Note, the registrar is already aware that the bootstrapping is performed in a pledge-responder-mode due to the use of the LDevID(RegAgt) certificate for TLS and the provided PVR as JSON-in-JWS object.

  • If the registrar receives a PER with Content-Type header: application/jose+json, it MUST verify the wrapping signature using the certificate indicated in the JOSE header.
  • The registrar verifies that the pledge's certificate (here IDevID), carried in "x5c" header field, is accepted to join the domain after successful validation of the PVR.
  • If both succeed, the registrar utilizes the PKCS#10 request contained in the JWS object body as "P10" parameter of "ietf-sztp-csr:csr" for further processing of the enrollment request with the corresponding domain CA. It creates a registrar-enrollment-request (RER) by utilizing the protocol expected by the domain CA. The domain registrar may either directly forward the provided PKCS#10 request to the CA or provide additional information about attributes to be included by the CA into the requested LDevID certificate. The approach of sending this information to the CA depends on the utilized certificate management protocol between the RA and the CA and is out of scope for this document.

The registrar-agent SHALL send the PER to the registrar by HTTP POST to the endpoint: "/.well-known/brski/requestenroll"

The registrar SHOULD respond with an HTTP 200 OK in the success case or fail with HTTP 4xx/5xx status codes as defined by the HTTP standard.

A successful interaction with the domain CA will result in a pledge LDevID certificate, which is then forwarded by the registrar to the registrar-agent using the Content-Type header: application/pkcs7-mime.

6.2.7. Request Wrapped-CA-certificate(s) (Registrar-Agent to Registrar)

As the pledge will verify it own certificate LDevID certificate when received, it also needs the corresponding CA certificates. This is done in EST [RFC7030] using the "/.well-known/est/cacerts" endpoint, which provides the CA certificates over a TLS protected connection. BRSKI-PRM requires a signature wrapped CA certificate object, to avoid that the pledge can be provided with arbitrary CA certificates in an authorized way. The registrar signed CA certificate object will allow the pledge to verify the authorization to install the received CA certificate(s). As the CA certificate(s) are provided to the pledge after the voucher, the pledge has the required information (the domain certificate) to verify the wrapped CA certificate object.

To support registrar-agents requesting a signature wrapped CA certificate(s) object, a new endpoint for BRSKI-PRM is defined on the registrar: "/.well-known/brski/wrappedcacerts"

The registrar-agent SHALL requests the EST CA trust anchor database information (in form of CA certificates) by HTTP GET.

The Content-Type header of the response SHALL be: application/jose+json.

This is a deviation from the Content-Type header values used in EST [RFC7030] and results in additional processing at the domain registrar (as EST server). The additional processing is to sign the CA certificate(s) information using the registrar EE credentials. This results in a signed CA certificate(s) object (JSON-in-JWS), the CA certificates are provided as base64 encoded "x5b" in the JWS payload.

# The CA certificates data with additional registrar signature in
  General JWS Serialization syntax
{
  "payload": "BASE64URL(certs)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "certs" representation in JSON syntax
{
  "x5b": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}


# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}
Figure 13: Representation of CA certificate(s) data with additional registrar signature

6.3. Response Object Supply by Registrar-Agent to Pledge

It is assumed that the registrar-agent already obtained the bootstrapping response objects from the domain registrar and can supply them to the pledge: * voucher-response - Voucher (from MASA via Registrar) * wrapped-CA-certificate(s)-response - CA certificates * enrollment-response - LDevID(Pledge) certificate (from CA via Registrar)

The registrar-agent will re-connect to the pledge. To contact the pledge, it may either discover the pledge as described in Section 5.4.2 or use stored information from the first contact with the pledge.

Preconditions in addition to Section 6.2:

  • Registrar-agent: possesses voucher and LDevID certificate and optionally CA certificates.
Pledge Registrar- Agent (RegAgt) [voucher and enrollment] [responses available] supply voucher voucher status - store pledge voucher status supply CA certificates supply enrollment response enroll status - store pledge enroll status supply CAcerts (optional)
Figure 14: Responses and status handling between pledge and registrar-agent

The registrar-agent provides the information via distinct pledge endpoints as following.

6.3.1. Pledge: Voucher Response Processing

The registrar-agent SHALL send the voucher-response to the pledge by HTTP POST to the endpoint: "/.well-known/brski/pledge-voucher".

The registrar-agent voucher-response Content-Type header is application/voucher-jws+json and contains the voucher as provided by the MASA. An example if given in Figure 11 for a MASA signed voucher and in Figure 12 for the voucher with the additional signature of the registrar.

A nonceless voucher may be accepted as in [RFC8995] and may be allowed by a manufactures pledge implementation.

To perform the validation of multiple signatures on the voucher object, the pledge SHALL perform the signature verification in the following order:

  1. Verify MASA signature as described in section 5.6.1 in [RFC8995]
  2. Install trust anchor contained in the voucher ("pinned-domain-cert") provisionally
  3. Verify registrar signature as described in section 5.6.1 in [RFC8995], but take the registrar certificate instead of the MASA certificate for the verification
  4. Validate the registrar certificate received in the agent-provided-proximity-registrar-cert in the pledge-voucher-request trigger request (in the field "agent-provided-proximity-registrar-cert").

If all steps stated above have been performed successfully, the pledge SHALL terminate the "PROVISIONAL accept" state for the domain trust anchor and the registrar EE certificate.

If an error occurs during the verification and validation of the voucher, this SHALL be reported in the reason field of the pledge voucher status.

6.3.2. Pledge: Voucher Status Telemetry

After voucher verification and validation the pledge MUST reply with a status telemetry message as defined in section 5.7 of [RFC8995]. The pledge generates the voucher-status and provides it as signed JSON-in-JWS object in response to the registrar-agent.

The response has the Content-Type application/jose+json and is signed using the IDevID of the pledge as shown in Figure 15. As the reason field is optional (see [RFC8995]), it MAY be omitted in case of success.

# The "pledge-voucher-status" telemetry in general JWS
  serialization syntax
{
  "payload": "BASE64URL(pledge-voucher-status)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "pledge-voucher-status" representation in JSON
  syntax
{
  "version": 1,
  "status": true,
  "reason": "Voucher successfully processed",
  "reason-context": {
    "additional": "JSON"
  }
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}
Figure 15: Representation of pledge voucher status telemetry

6.3.3. Pledge: Wrapped-CA-Certificate(s) Processing

The registrar-agent SHALL provide the set of CA certificates requested from the registrar to the pledge by HTTP POST to the endpoint: "/.well-known/brski/pledge-CAcerts".

As the CA certificate provisioning is crucial from a security perspective, this provisioning SHALL only be done, if the voucher-response has been successfully processed by pledge.

The supply CA certificates message has the Content-Type application/jose+json and is signed using the credential of the registrar pledge as shown in Figure 13.

The CA certificates are provided as base64 encoded "x5b". The pledge SHALL install the received CA certificates as trust anchor after successful verification of the registrar's signature.

If validation of the wrapping signature or another security check fails, the pledge SHOULD respond with the HTTP 403 Forbidden status code. The HTTP 415 Unsupported Media Type status code SHOULD be used, if the Content-Type of the request is in an unknown or unsupported format. The HTTP 400 Bad Request status code SHOULD be used, if the pledge detects errors in the encoding of the payload.

6.3.4. Pledge: Enrollment Response Processing

The registrar-agent SHALL send the enroll-response to the pledge by HTTP POST to the endpoint: "/.well-known/brski/pledge-enrollment".

The registrar-agent enroll-response Content-Type header, when using EST [RFC7030] as enrollment protocol between the registrar-agent and the infrastructure is: application/pkcs7-mime. Note: It only contains the LDevID certificate for the pledge, not the certificate chain.

Upon reception, the pledge SHALL verify the received LDevID certificate. The pledge SHALL generate the enroll status and provide it in the response to the registrar-agent. If the verification of the LDevID certificate succeeds, the status SHALL be set to true, otherwise to FALSE.

6.3.5. Pledge: Enrollment Status Telemetry

The pledge MUST reply with a status telemetry message as defined in section 5.9.4 of [RFC8995]. As for the other objects, the enroll-status is signed and results in a JSON-in-JWS object. If the pledge verified the received LDevID certificate successfully it SHALL sign the response using its new LDevID credentials as shown in Figure 16. In the failure case, the pledge SHALL use the available IDevID credentials. As the reason field is optional, it MAY be omitted in case of success.

The response has the Content-Type application/jose+json.

# The "pledge-enroll-status" telemetry in General JWS Serialization
  syntax
{
  "payload": "BASE64URL(pledge-enroll-status)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "pledge-enroll-status" representation in
  JSON syntax
{
  "version": 1,
  "status": true,
  "reason": "Enrollment response successfully processed",
  "reason-context": {
    "additional": "JSON"
  }
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}
Figure 16: Representation of pledge enroll status telemetry

Once the registrar-agent has collected the information, it can connect to the registrar-agent to provide the status responses to the registrar.

6.3.6. Telemetry Voucher Status and Enroll Status Handling (Registrar-Agent to Domain Registrar)

The following description requires that the registrar-agent has collected the status information from the pledge. It SHALL provide the status information to the registrar for further processing.

Preconditions in addition to Section 6.2:

  • Registrar-agent: possesses voucher status and enroll status from pledge.
Registrar Domain Domain Vendor Agent Registrar CA Service RegAgt) (JRC) (MASA) | Internet [voucher + enroll ] [status info available] mTLS Voucher Status req-device audit log device audit log [verify audit log ] Enroll Status
Figure 17: Bootstrapping status handling

The registrar-agent MUST provide the collected pledge voucher status to the registrar. This status indicates if the pledge could process the voucher successfully or not.

If the TLS connection to the registrar was closed, the registrar-agent establishes a TLS connection with the registrar as stated in Section 6.2.

The registrar-agent sends the pledge voucher status without modification to the registrar with an HTTP-over-TLS POST using the registrar endpoint "/.well-known/brski/voucher_status". The Content-Type header is kept as application/jose+json as described in Figure 14 and depicted in the example in Figure 15.

The registrar SHALL verify the signature of the pledge voucher status and validate that it belongs to an accepted device in his domain based on the contained "serial-number" in the IDevID certificate referenced in the header of the voucher status.

According to [RFC8995] section 5.7, the registrar SHOULD respond with an HTTP 200 OK in the success case or fail with HTTP 4xx/5xx status codes as defined by the HTTP standard. The registrar-agent may use the response to signal success / failure to the service technician operating the registrar agent. Within the server logs the server SHOULD capture this telemetry information.

The registrar SHOULD proceed with collecting and logging status information by requesting the MASA audit-log from the MASA service as described in section 5.8 of [RFC8995].

The registrar-agent MUST provide the pledge's enroll status to the registrar. The status indicates the pledge could process the enroll-response (certificate) and holds the corresponding private key.

The registrar-agent sends the pledge enroll status without modification to the registrar with an HTTP-over-TLS POST using the registrar endpoint "/.well-known/brski/enrollstatus". The Content-Type header is kept as application/jose+json as described in Figure 14 and depicted in the example in Figure 16.

The registrar MUST verify the signature of the pledge enroll status. Also, the registrar SHALL validate that the pledge is an accepted device in his domain based on the contained product-serial-number in the LDevID certificate referenced in the header of the enroll status. The registrar SHOULD log this event. In case the pledge enroll status indicates a failure, the pledge was unable to verify the received LDevID certificate and therefore signed the enroll status with its IDevID credential. Note that the verification of a signature of the status information is an addition to the described handling in section 5.9.4 of [RFC8995].

According to [RFC8995] section 5.9.4, the registrar SHOULD respond with an HTTP 200 OK in the success case or fail with HTTP 4xx/5xx status codes as defined by the HTTP standard. Based on the failure case the registrar MAY decide that for security reasons the pledge is not allowed to reside in the domain. In this case the registrar MUST revoke the certificate. The registrar-agent may use the response to signal success / failure to the service technician operating the registrar agent. Within the server log the registrar SHOULD capture this telemetry information.

6.4. Request Pledge-Status by Registrar-Agent from Pledge

The following assumes that a registrar-agent may need to query the status of a pledge. This information may be useful to solve errors, when the pledge was not able to connect to the target domain during the bootstrapping. The pledge MAY provide a dedicated endpoint to accept status-requests.

Preconditions:

  • Registrar-agent: possesses LDevID (RegAgt), list of serial numbers of pledges to be queried and a list of corresponding manufacturer trust anchors to be able to verify signatures performed with the IDevID credential.
  • Pledge: may already possess domain credentials and LDevID(Pledge), or may not possess one or both of these.
Pledge Registrar- Agent (RegAgt) pledge-status request pledge-status response
Figure 18: Pledge-status handling between registrar-agent and pledge

6.4.1. Pledge-Status - Trigger (Registrar-Agent to Pledge)

The registrar-agent requests the pledge-status via HTTP POST on the defined pledge endpoint: "/.well-known/brski/pledge-status"

The registrar-agent Content-Type header for the pledge-status request is: application/jose+json. It contains information on the requested status-type, the time and date the request is created, and the product serial-number of the pledge contacted as shown in Figure 19. The pledge-status request is signed by registrar-agent using the LDevID(RegAgt) credential.

The following Concise Data Definition Language (CDDL) [RFC8610] explains the structure of the format for the pledge-status request. It is defined following the status telemetry definitions in BRSKI [RFC8995]. Consequently, format and semantics of pledge-status requests below are for version 1. The version field is included to permit significant changes to the pledge-status request and response in the future. A pledge or a registrar-agent that receives a pledge-status request with a version larger than it knows about SHOULD log the contents and alert a human.

<CODE BEGINS>
  status-request = {
      "version": uint,
      "created-on": tdate ttime,
      "serial-number": text,
      "status-type": text
  }

<CODE ENDS>
Figure 19: CDDL for pledge-status request

The status-type defined for BRSKI-PRM is "bootstrap". This indicates the pledge to provide current status information regarding the bootstrapping status (voucher processing and enrollment of the pledge into the new domain). As the pledge-status request is defined generic, it may be used by other specifications to request further status information, e.g., for onboarding to get further information about enrollment of application specific LDevIDs or other parameters. This is out of scope for this specification.

Figure 20 below shows an example for querying pledge-status using status-type bootstrap.

# The registrar-agent request of "pledge-status" in general JWS
  serialization syntax
{
  "payload": "BASE64URL(status-request)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "status-request" representation in JSON syntax
{
  "version": 1,
  "created-on": "2022-08-12T02:37:39.235Z",
  "serial-number": "pledge-callee4711",
  "status-type": "bootstrap"
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ]
}
Figure 20: Example of registrar-agent request of pledge-status using status-type bootstrap

6.4.2. Pledge-Status - Response (Pledge - Registrar-Agent)

If the pledge receives the pledge-status request with status-type "bootstrap" it SHALL react with a status response message based on the telemetry information described in section Section 6.3.

The pledge-status response Content-Type header is application/jose+json.

The following CDDL explains the structure of the format for the status response, which is :

<CODE BEGINS>
  status-response = {
    "version": uint,
    "status":
      "factory-default" /
      "voucher-success" /
      "voucher-error" /
      "enroll-success" /
      "enroll-error" /
      "connect-success" /
      "connect-error",
    ?"reason" : text,
    ?"reason-context" : { $$arbitrary-map }
  }

<CODE ENDS>
Figure 21: CDDL for pledge-status response

Different cases for pledge bootstrapping status may occur, which SHOULD be reflected using the status enumeration. This document specifies the status values in the context of the bootstrapping process and credential application. Other documents may enhance the above enumeration to reflect further status information.

The pledge-status response message is signed with IDevID or LDevID, depending on bootstrapping state of the pledge.

  • "factory-default": Pledge has not been bootstrapped. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its IDevID(Pledge).
  • "voucher-success": Pledge processed the voucher exchange successfully. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its IDevID(Pledge).
  • "voucher-error": Pledge voucher processing terminated with error. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its IDevID(Pledge).
  • "enroll-success": Pledge has processed the enrollment exchange successfully. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its LDevID(Pledge).
  • "enroll-error": Pledge enrollment response processing terminated with error. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its IDevID(Pledge).

The reason and the reason-context SHOULD contain the telemetry information as described in section Section 6.3.

As the pledge is assumed to utilize the bootstrapped credential information in communication with other peers, additional status information is provided for the connectivity to other peers, which may be helpful in analyzing potential error cases.

  • "connect-success": Pledge could successfully establish a connection to another peer. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its LDevID(Pledge).
  • "connect-error": Pledge connection establishment terminated with error. Additional information may be provided in the reason or reason-context. The pledge signs the response message using its LDevID(Pledge).

The pledge-status responses are cumulative in the sense that connect-success implies enroll-success implies voucher-success.

Figure 22 provides an example for the bootstrapping-status information.

# The pledge "status-response" in General JWS Serialization syntax
{
  "payload": "BASE64URL(status-response)",
  "signatures": [
    {
      "protected": "BASE64URL(UTF8(JWS Protected Header))",
      "signature": "base64encodedvalue=="
    }
  ]
}

# Decoded payload "status-response" representation in JSON syntax
{
  "version": 1,
  "status": "enroll-success",
  "reason-context": {
    "additional" : "JSON"
  }
}

# Decoded "JWS Protected Header" representation in JSON syntax
{
  "alg": "ES256",
  "x5c": [
    "base64encodedvalue==",
    "base64encodedvalue=="
  ],
  "typ": "jose+json
}
Figure 22: Example of pledge-status response

In case "factory-default" the pledge does not possess the domain certificate resp. the domain trust-anchor. It will not be able to verify the signature of the registrar-agent in the bootstrapping-status request. In cases "vouchered" and "enrolled" the pledge already possesses the domain certificate (has domain trust-anchor) and can therefore validate the signature of the registrar-agent. If validation of the JWS signature fails, the pledge SHOULD respond with the HTTP 403 Forbidden status code. The HTTP 406 Not Acceptable status code SHOULD be used, if the Accept header in the request indicates an unknown or unsupported format. The HTTP 415 Unsupported Media Type status code SHOULD be used, if the Content-Type of the request is an unknown or unsupported format. The HTTP 400 Bad Request status code SHOULD be used, if the Accept/Content-Type headers are correct but nevertheless the status-request cannot be correctly parsed.

7. Artifacts

7.1. Voucher Request Artifact

The following enhancement extends the voucher-request as defined in [RFC8995] to include additional fields necessary for handling bootstrapping in the pledge-responder-mode.

7.1.1. Tree Diagram

The following tree diagram is mostly a duplicate of the contents of [RFC8995], with the addition of the fields agent-signed-data, the registrar-proximity-certificate, and agent-signing certificate. The tree diagram is described in [RFC8340]. Each node in the diagram is fully described by the YANG module in Section Section 7.1.2.

module: ietf-voucher-request-prm

 grouping voucher-request-prm-grouping
  +-- 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
     +-- last-renewal-date?                        yang:date-and-time
     +-- prior-signed-voucher-request?             binary
     +-- proximity-registrar-cert?                 binary
     +-- agent-signed-data?                        binary
     +-- agent-provided-proximity-registrar-cert?  binary
     +-- agent-sign-cert?                          binary

7.1.2. YANG Module

The following YANG module extends the [RFC8995] Voucher Request to include a signed artifact from the registrar-agent (agent-signed-data) as well as the registrar-proximity-certificate and the agent-signing certificate.

<CODE BEGINS> file "ietf-voucher-request-prm@2022-07-05.yang"


module ietf-voucher-request-prm {
  yang-version 1.1;

  namespace "urn:ietf:params:xml:ns:yang:ietf-voucher-request-prm";
  prefix vrprm;

  import ietf-restconf {
    prefix rc;
    description
      "This import statement is only present to access
       the yang-data extension defined in RFC 8040.";
    reference "RFC 8040: RESTCONF Protocol";
  }

  import ietf-voucher-request {
    prefix vcr;
    description
      "This module defines the format for a voucher request,
          which is produced by a pledge as part of the RFC8995
          onboarding process.";
    reference
      "RFC 8995: Bootstrapping Remote Secure Key Infrastructure";
  }

  organization
   "IETF ANIMA Working Group";

  contact
   "WG Web:   <http://tools.ietf.org/wg/anima/>
    WG List:  <mailto:anima@ietf.org>
    Author:   Steffen Fries
              <mailto:steffen.fries@siemens.com>
    Author:   Eliot Lear
              <mailto: lear@cisco.com>
    Author:   Thomas Werner
              <mailto: thomas-werner@siemens.com>
    Author:   Michael Richardson
              <mailto: mcr+ietf@sandelman.ca>";

  description
   "This module defines the format for a voucher-request form the
    pledge in responder mode. It bases on the voucher-request
    defined in RFC 8995, which 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) 2021 IETF Trust and the persons identified as
    authors of the code. All rights reserved.

    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (https://trustee.ietf.org/license-info).

    This version of this YANG module is part of RFC xxxx; see the
    RFC itself for full legal notices.";


  revision 2022-07-05 {
    description
     "Initial version";
    reference
     "RFC XXXX: BRSKI for Pledge in Responder Mode";
  }

  // Top-level statement
  rc:yang-data voucher-request-prm-artifact {
    // YANG data template for a voucher-request.
    uses voucher-request-prm-grouping;
  }
  // Grouping defined for future usage
  grouping voucher-request-prm-grouping {
    description
      "Grouping to allow reuse/extensions in future work.";
    uses vcr:voucher-request-grouping {

      augment voucher {
        description "Base the voucher-request-prm upon the
          regular one";

        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-list agent-sign-cert{
          type binary;
          min-elements 1;
          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.
             It is defined as list to enable inclusion of further
             certificates along the certificate chain if different
             issuing CAs have been used for the registrar-agent
             and the registrar.";
          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>

Examples for the PVR are provided in Section 6.2.

8. IANA Considerations

This document requires the following IANA actions.

8.1. BRSKI .well-known Registry

IANA is requested to enhance the Registry entitled: "BRSKI Well-Known URIs" with the following endpoints:

 URI                        Description                       Reference
 pledge-voucher-request     create pledge-voucher-request     [THISRFC]
 pledge-enrollment-request  create pledge-enrollment-request  [THISRFC]
 pledge-voucher             supply voucher response           [THISRFC]
 pledge-enrollment          supply enrollment response        [THISRFC]
 pledge-cacerts             supply CA certificates to pledge  [THISRFC]
 pledge-status              query pledge status               [THISRFC]
 requestenroll              supply PER to registrar           [THISRFC]
 wrappedcacerts             request wrapped CA certificates   [THISRFC]

9. Privacy Considerations

In general, the privacy considerations of [RFC8995] apply for BRSKI-PRM also. Further privacy aspects need to be considered for:

  • the introduction of the additional component registrar-agent
  • no transport layer security between registrar-agent and pledge

The credential used by the registrar-agent to sign the data for the pledge should not contain any personal information. Therefore, it is recommended to use an LDevID certificate associated with the commissioning device instead of an LDevID certificate associated with the service technician operating the device. This avoids revealing potentially included personal information to Registrar and MASA.

The communication between the pledge and the registrar-agent is performed over plain HTTP. Therefore, it is subject to disclosure by a Dolev-Yao attacker (a "oppressive observer")[onpath]. Depending on the requests and responses, the following information is disclosed.

  • the Pledge product-serial-number is contained in the trigger message for the PVR and in all responses from the pledge. This information reveals the identity of the devices being bootstrapped and allows deduction of which products an operator is using in their environment. As the communication between the pledge and the registrar-agent may be realized over wireless link, this information could be easily be eavesdropped, if the wireless network is unencrypted. Even if the wireless network is encrypted, if it uses a network-wide key, then layer-2 attacks (ARP/ND spoofing) could insert on-path observer into the path.
  • the Timestamp data could reveal the activation time of the device.
  • the Status data of the device could reveal information about the current state of the device in the domain network.

10. Security Considerations

In general, the security considerations of [RFC8995] apply for BRSKI-PRM also. Further security aspects are considered here related to:

  • the introduction of the additional component registrar-agent
  • the reversal of the pledge communication direction (push mode, compared to BRSKI)
  • no transport layer security between registrar-agent and pledge

10.1. Denial of Service (DoS) Attack on Pledge

Disrupting the pledge behavior by a DoS attack may prevent the bootstrapping of the pledge to a new domain.

A DoS attack with a faked registrar-agent may block the bootstrapping of the pledge due to state creation on the pledge (the pledge may produce a voucher, and refuse to produce another one). One mitigation may be that the pledge does does not limited the number of voucher requests it creates until at least one has finished, or a single onboarding state may expire after a certain time.

10.2. Misuse of acquired PVR and PER by Registrar-Agent

A registrar-agent that uses previously requested PVR and PER for domain-A, may attempt to onboard the device into domain-B. This can be detected by the domain registrar while PVR processing. The domain registrar needs to verify that the "proximity-registrar-cert" field in the PVR matches its own registrar EE certificate. In addition, the domain registrar needs to verify the association of the pledge to its domain based on the product-serial-number contained in the PVR and in the IDevID certificate of the pledge. (This is just part of the supply chain integration) Moreover, the domain registrar verifies if the registrar-agent is authorized to interact with the pledge for voucher-requests and enroll-requests, based on the LDevID(RegAgt) certificate data contained in the PVR.

Misbinding of a pledge by a faked domain registrar is countered as described in BRSKI security considerations [RFC8995] (section 11.4).

10.3. Misuse of Registrar-Agent Credentials

Concerns on misusage of an registrar-agent with a valid LDevID(RegAgt), may be addressed by utilizing short-lived certificates (e.g., valid for a day) to authenticate the registrar-agent against the domain registrar. The LDevID(RegAgt) certificate may be acquired by a prior BRSKI run for the registrar-agent, if an IDevID is available on registrar-agent. Alternatively, the LDevID may be acquired by a service technician from the domain PKI system in an authenticated way.

In addition it is required that the LDevID(RegAgt) certificate is valid for the complete bootstrapping phase. This avoids that a registrar-agent could be misused to create arbitrary "agent-signed-data" objects to perform an authorized bootstrapping of a rouge pledge at a later point in time. In this misuse "agent-signed-data" could be dated after the validity time of the LDevID(RegAgt) certificate, due to missing trusted timestamp in the registrar-agents signature. To address this, the registrar SHOULD verify the certificate used to create the signature on "agent-signed-data". Furthermore the registrar also verifies the LDevID(RegAgt) certificate used in the TLS handshake with the registrar-agent. If both certificates are verified successfully, the registrar-agent's signature can be considered as valid.

10.4. Misuse of mDNS to obtain list of pledges

To discover a specific pledge a registrar-agent may request the service name in combination with the product-serial-number of a specific pledge. The pledge reacts on this if his product-serial-number is part of the request message.

If the registrar-agent performs DNS-based Service Discovery without a specific product-serial-number, all pledges in the domain react if the functionality is supported. This functionality enumerates and reveals the information of devices available in the domain. The information about this is provided here as a feature to support the commissioning of devices. A manufacturer may decide to support this feature only for devices not possessing a LDevID or to not support this feature at all, to avoid an enumeration in an operative domain.

10.5. YANG Module Security Considerations

The enhanced voucher-request described in section Section 7.1 is bases on [RFC8995], but uses a different encoding based on [I-D.ietf-anima-jws-voucher]. Therefore similar considerations as described in [RFC8995] section 11.7 (Security Considerations) apply. The YANG module specified in this document defines the schema for data that is subsequently encapsulated by a JOSE signed-data Content-type as described in [I-D.ietf-anima-jws-voucher]. As such, all of the YANG-modeled data is protected against modification. 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 [RFC6241] and RESTCONF [RFC8040]. For this reason these guidelines do not follow the template described by [RFC8407] section 3.7 (Security Considerations Section).

11. Acknowledgments

We would like to thank the various reviewers, in particular Brian E. Carpenter, Oskar Camenzind, and Hendrik Brockhaus for their input and discussion on use cases and call flows. Special thanks to Esko Dijk for the in deep review and the improving proposals.

12. References

12.1. Normative References

[I-D.ietf-anima-jws-voucher]
Werner, T. and M. Richardson, "JWS signed Voucher Artifacts for Bootstrapping Protocols", Work in Progress, Internet-Draft, draft-ietf-anima-jws-voucher-05, , <https://www.ietf.org/archive/id/draft-ietf-anima-jws-voucher-05.txt>.
[I-D.ietf-anima-rfc8366bis]
Watsen, K., Richardson, M., Pritikin, M., Eckert, T. T., and Q. Ma, "A Voucher Artifact for Bootstrapping Protocols", Work in Progress, Internet-Draft, draft-ietf-anima-rfc8366bis-00, , <https://www.ietf.org/archive/id/draft-ietf-anima-rfc8366bis-00.txt>.
[I-D.ietf-netconf-sztp-csr]
Watsen, K., Housley, R., and S. Turner, "Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request", Work in Progress, Internet-Draft, draft-ietf-netconf-sztp-csr-14, , <https://www.ietf.org/archive/id/draft-ietf-netconf-sztp-csr-14.txt>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC5280]
Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, , <https://www.rfc-editor.org/info/rfc5280>.
[RFC6762]
Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, , <https://www.rfc-editor.org/info/rfc6762>.
[RFC6763]
Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, , <https://www.rfc-editor.org/info/rfc6763>.
[RFC7030]
Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, , <https://www.rfc-editor.org/info/rfc7030>.
[RFC7515]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, , <https://www.rfc-editor.org/info/rfc7515>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8366]
Watsen, K., Richardson, M., Pritikin, M., and T. Eckert, "A Voucher Artifact for Bootstrapping Protocols", RFC 8366, DOI 10.17487/RFC8366, , <https://www.rfc-editor.org/info/rfc8366>.
[RFC8610]
Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, , <https://www.rfc-editor.org/info/rfc8610>.
[RFC8995]
Pritikin, M., Richardson, M., Eckert, T., Behringer, M., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995, , <https://www.rfc-editor.org/info/rfc8995>.

12.2. Informative References

[BRSKI-PRM-abstract]
"Abstract BRSKI-PRM Protocol Overview", , <https://raw.githubusercontent.com/anima-wg/anima-brski-prm/main/pics/brski_prm_overview.png>.
[I-D.ietf-anima-brski-ae]
von Oheimb, D., Fries, S., Brockhaus, H., and E. Lear, "BRSKI-AE: Alternative Enrollment Protocols in BRSKI", Work in Progress, Internet-Draft, draft-ietf-anima-brski-ae-02, , <https://www.ietf.org/archive/id/draft-ietf-anima-brski-ae-02.txt>.
[IEEE-802.1AR]
Institute of Electrical and Electronics Engineers, "IEEE 802.1AR Secure Device Identifier", IEEE 802.1AR, .
[onpath]
"can an on-path attacker drop traffic?", n.d., <https://mailarchive.ietf.org/arch/msg/saag/m1r9uo4xYznOcf85Eyk0Rhut598/>.
[RFC2986]
Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, , <https://www.rfc-editor.org/info/rfc2986>.
[RFC6125]
Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, , <https://www.rfc-editor.org/info/rfc6125>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC7252]
Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, , <https://www.rfc-editor.org/info/rfc7252>.
[RFC8340]
Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/info/rfc8340>.
[RFC8407]
Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, , <https://www.rfc-editor.org/info/rfc8407>.
[RFC8792]
Watsen, K., Auerswald, E., Farrel, A., and Q. Wu, "Handling Long Lines in Content of Internet-Drafts and RFCs", RFC 8792, DOI 10.17487/RFC8792, , <https://www.rfc-editor.org/info/rfc8792>.
[RFC9052]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, , <https://www.rfc-editor.org/info/rfc9052>.
[RFC9110]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/info/rfc9110>.
[RFC9238]
Richardson, M., Latour, J., and H. Habibi Gharakheili, "Loading Manufacturer Usage Description (MUD) URLs from QR Codes", RFC 9238, DOI 10.17487/RFC9238, , <https://www.rfc-editor.org/info/rfc9238>.

Appendix A. Examples

These examples are folded according to [RFC8792] Single Backslash rule.

A.1. Example Pledge Voucher Request - PVR (from Pledge to Registrar-agent)

The following is an example request sent from a Pledge to the Registrar-agent, in "General JWS JSON Serialization".
The message size of this PVR is: 4649 bytes

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
  "payload":
    "eyJpZXRmLXZvdWNoZXItcmVxdWVzdC1wcm06dm91Y2hlciI6eyJhc3NlcnRpb24\
iOiJhZ2VudC1wcm94aW1pdHkiLCJzZXJpYWwtbnVtYmVyIjoiMDEyMzQ1Njc4OSIsIm5\
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teFIzQ1hvWktHUXJVPSJdfX0",
    "signatures":[{
      "protected":"eyJ4NWMiOlsiTUlJQitUQ0NBYUNnQXdJQkFnSUdBWG5WanNVN\
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      "signature":"Y_ohapnmvbwjLuUicOB7NAmbGM7igBfpUlkKUuSNdG-eDI4BQ\
yuXZ2aw93zZId45R7XxAK-12YKIx6qLjiPjMw"
  }]
}
Figure 23: Example Pledge Voucher Request - PVR

A.2. Example Parboiled Registrar Voucher Request - RVR (from Registrar to MASA)

The term parboiled refers to food which is partially cooked. In [RFC8995], the term refers to a Pledge voucher-request (PVR) which has been received by the Registrar, and then has been processed by the Registrar ("cooked"), and is now being forwarded to the MASA.

The following is an example Registrar voucher-request (RVR) sent from the Registrar to the MASA, in "General JWS JSON Serialization". Note that the previous PVR can be seen in the payload as "prior-signed-voucher-request". The message size of this RVR is: 13257 bytes

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
  "payload":
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  "signatures":[{
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    "signature":"67t3n8zyEek4IM2Ko3Y_UvE1hzp794QFNTqG-HzTrBQtE4_4-yS\
yyFd3kP6YCn35YYJ7yK35d3styo_yoiPfKA"
  }]
}
Figure 24: Example Registrar Voucher Request - RVR

A.3. Example Voucher Response (from MASA to Pledge, via Registrar and Registrar-agent)

The following is an example voucher response from MASA to Pledge via Registrar and Registrar-agent, in "General JWS JSON Serialization". The message size of this Voucher is: 1916 bytes

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
  "payload":"eyJpZXRmLXZvdWNoZXI6dm91Y2hlciI6eyJhc3NlcnRpb24iOiJhZ2V\
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  "signatures":[{
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    "signature":"0TB5lr-cs1jqka2vNbQm3bBYWfLJd8zdVKIoV53eo2YgSITnKKY\
TvHMUw0wx9wdyuNVjNoAgLysNIgEvlcltBw"
  }]
}
Figure 25: Example Voucher Response from MASA

A.4. Example Voucher Response, MASA issued Voucher with additional Registrar signature (from MASA to Pledge, via Registrar and Registrar-agent)

The following is an example voucher response from MASA to Pledge via Registrar and Registrar-agent, in "General JWS JSON Serialization". The message size of this Voucher is: 3006 bytes

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
  "payload":"eyJpZXRmLXZvdWNoZXI6dm91Y2hlciI6eyJhc3NlcnRpb24iOiJhZ2V\
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  "signatures":[{
    "protected":"eyJ4NWMiOlsiTUlJQmt6Q0NBVGlnQXdJQkFnSUdBV0ZCakNrWU1\
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",
    "signature":"ShqW8uFRkuAXIzjAhB4bolMMndcY7GYq3Kbo94yvGtjCaxEX3Hp\
6QXZUTEJ_kulQ1G7DnaU4igDPdUGtcV9Lkw"},{
    "protected":"eyJ4NWMiOlsiTUlJQjRqQ0NBWWlnQXdJQkFnSUdBWFk3MmJiWk1\
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2In0",
    "signature":"N4oXV48V6umsHMKkhdSSmJYFtVb6agjD32uXpIlGx6qVE7Dh0-b\
qhRRyjnxp80IV_Fy1RAOXIIzs3Q8CnMgBgg"
  }]
}
Figure 26: Example Voucher Response from MASA, with additional Registrar signature

Appendix B. History of Changes [RFC Editor: please delete]

Proof of Concept Code available

From IETF draft 04 -> IETF draft 05:

  • Restructured document to have a distinct section for the object flow and handling and shortened introduction, issue #72
  • Added security considerations for using mDNS without a specific product-serial-number, issue #75
  • Clarified pledge-status responses are cumulative, issue #73
  • Removed agent-sign-cert from trigger data to save bandwidth and remove complexity through options, issue #70
  • Changed terminology for LDevID(Reg) certificate to registrar EE certificate, as it does not need to be an LDevID, issue #66
  • Added new protected header parameter (created-on) in PER to support freshness validation, issue #63
  • Removed reference to CAB Forum as not needed for BRSKI-PRM specifically, issue #65
  • Enhanced error codes in section 5.5.1, issue #39, #64
  • Enhanced security considerations and privacy considerations, issue #59
  • Issue #50 addressed by referring to the utilized enrollment protocol
  • Issue #47 MASA verification of LDevID(RegAgt) to the same registrar EE certificate domain CA
  • Reworked terminology of "enrollment object", "certification object", "enrollment request object", etc., issue #27
  • Reworked all message representations to align with encoding
  • Added explanation of MASA requiring domain CA cert in section 5.5.1 and section 5.5.2, issue #36
  • Defined new endpoint for pledge bootstrapping status inquiry, issue #35 in section Section 6.4, IANA considerations and section Section 5.3
  • Included examples for several objects in section Appendix A including message example sizes, issue #33
  • PoP for private key to registrar certificate included as mandatory, issues #32 and #49
  • Issue #31, clarified that combined pledge may act as client/server for further (re)enrollment
  • Issue #42, clarified that Registrar needs to verify the status responses with and ensure that they match the audit log response from the MASA, otherwise it needs drop the pledge and revoke the certificate
  • Issue #43, clarified that the pledge shall use the create time from the trigger message if the time has not been synchronized, yet.
  • Several editorial changes and enhancements to increasing readability.

From IETF draft 03 -> IETF draft 04:

  • In deep Review by Esko Dijk lead to issues #22-#61, which are bein stepwise integrated
  • Simplified YANG definition by augmenting the voucher request from RFC 8995 instead of redefining it.
  • Added explanation for terminology "endpoint" used in this document, issue #16
  • Added clarification that registrar-agent may collect PVR or PER or both in one run, issue #17
  • Added a statement that nonceless voucher may be accepted, issue #18
  • Simplified structure in section Section 3.1, issue #19
  • Removed join proxy in Figure 1 and added explanatory text, issue #20
  • Added description of pledge-CAcerts endpoint plus further handling of providing a wrapped CA certs response to the pledge in section Section 6.3; also added new required registrar endpoint (section Section 6.2 and IANA considerations) for the registrar to provide a wrapped CA certs response, issue #21
  • utilized defined abbreviations in the document consistently, issue #22
  • Reworked text on discovery according to issue #23 to clarify scope and handling
  • Added several clarifications based on review comments

From IETF draft 02 -> IETF draft 03:

  • Updated examples to state "base64encodedvalue==" for x5c occurrences
  • Include link to SVG graphic as general overview
  • Restructuring of section 5 to flatten hierarchy
  • Enhanced requirements and motivation in Section 4
  • Several editorial improvements based on review comments

From IETF draft 01 -> IETF draft 02:

  • Issue #15 included additional signature on voucher from registrar in section Section 6.2 and section Section 5.2 The verification of multiple signatures is described in section Section 6.3
  • Included representation for General JWS JSON Serialization for examples
  • Included error responses from pledge if it is not able to create a pledge-voucher request or an enrollment request in section Section 6.1
  • Removed open issue regarding handling of multiple CSRs and enrollment responses during the bootstrapping as the initial target it the provisioning of a generic LDevID certificate. The defined endpoint on the pledge may also be used for management of further certificates.

From IETF draft 00 -> IETF draft 01:

  • Issue #15 lead to the inclusion of an option for an additional signature of the registrar on the voucher received from the MASA before forwarding to the registrar-agent to support verification of POP of the registrars private key in section Section 6.2 and Section 6.3.
  • Based on issue #11, a new endpoint was defined for the registrar to enable delivery of the wrapped enrollment request from the pledge (in contrast to plain PKCS#10 in simple enroll).
  • Decision on issue #8 to not provide an additional signature on the enrollment-response object by the registrar. As the enrollment response will only contain the generic LDevID certificate. This credential builds the base for further configuration outside the initial enrollment.
  • Decision on issue #7 to not support multiple CSRs during the bootstrapping, as based on the generic LDevID certificate the pledge may enroll for further certificates.
  • Closed open issue #5 regarding verification of ietf-ztp-types usage as verified via a proof-of-concept in section {#exchanges_uc2_1}.
  • Housekeeping: Removed already addressed open issues stated in the draft directly.
  • Reworked text in from introduction to section pledge-responder-mode
  • Fixed "serial-number" encoding in PVR/RVR
  • Added prior-signed-voucher-request in the parameter description of the registrar-voucher-request in Section 6.2.
  • Note added in Section 6.2 if sub-CAs are used, that the corresponding information is to be provided to the MASA.
  • Inclusion of limitation section (pledge sleeps and needs to be waked up. Pledge is awake but registrar-agent is not available) (Issue #10).
  • Assertion-type aligned with voucher in RFC8366bis, deleted related open issues. (Issue #4)
  • Included table for endpoints in Section 5.3 for better readability.
  • Included registrar authorization check for registrar-agent during TLS handshake in section Section 6.2. Also enhanced figure Figure 9 with the authorization step on TLS level.
  • Enhanced description of registrar authorization check for registrar-agent based on the agent-signed-data in section Section 6.2. Also enhanced figure Figure 9 with the authorization step on pledge-voucher-request level.
  • Changed agent-signed-cert to an array to allow for providing further certificate information like the issuing CA cert for the LDevID(RegAgt) certificate in case the registrar and the registrar-agent have different issuing CAs in Figure 9 (issue #12). This also required changes in the YANG module in Section 7.1.2
  • Addressed YANG warning (issue #1)
  • Inclusion of examples for a trigger to create a pledge-voucher-request and an enrollment-request.

From IETF draft-ietf-anima-brski-async-enroll-03 -> IETF anima-brski-prm-00:

  • Moved UC2 related parts defining the pledge in responder mode from draft-ietf-anima-brski-async-enroll-03 to this document This required changes and adaptations in several sections to remove the description and references to UC1.
  • Addressed feedback for voucher-request enhancements from YANG doctor early review in Section 7.1 as well as in the security considerations (formerly named ietf-async-voucher-request).
  • Renamed ietf-async-voucher-request to IETF-voucher-request-prm to to allow better listing of voucher related extensions; aligned with constraint voucher (#20)
  • Utilized ietf-voucher-request-async instead of ietf-voucher-request in voucher exchanges to utilize the enhanced voucher-request.
  • Included changes from draft-ietf-netconf-sztp-csr-06 regarding the YANG definition of csr-types into the enrollment request exchange.

From IETF draft 02 -> IETF draft 03:

  • Housekeeping, deleted open issue regarding YANG voucher-request in Section 6.1 as voucher-request was enhanced with additional leaf.
  • Included open issues in YANG model in Section 5.1 regarding assertion value agent-proximity and csr encapsulation using SZTP sub module).

From IETF draft 01 -> IETF draft 02:

  • Defined call flow and objects for interactions in UC2. Object format based on draft for JOSE signed voucher artifacts and aligned the remaining objects with this approach in Section 6 .
  • Terminology change: issue #2 pledge-agent -> registrar-agent to better underline agent relation.
  • Terminology change: issue #3 PULL/PUSH -> pledge-initiator-mode and pledge-responder-mode to better address the pledge operation.
  • Communication approach between pledge and registrar-agent changed by removing TLS-PSK (former section TLS establishment) and associated references to other drafts in favor of relying on higher layer exchange of signed data objects. These data objects are included also in the pledge-voucher-request and lead to an extension of the YANG module for the voucher-request (issue #12).
  • Details on trust relationship between registrar-agent and registrar (issue #4, #5, #9) included in Section 5.1.
  • Recommendation regarding short-lived certificates for registrar-agent authentication towards registrar (issue #7) in the security considerations.
  • Introduction of reference to agent signing certificate using SKID in agent signed data (issue #37).
  • Enhanced objects in exchanges between pledge and registrar-agent to allow the registrar to verify agent-proximity to the pledge (issue #1) in Section 6.
  • Details on trust relationship between registrar-agent and pledge (issue #5) included in Section 5.1.
  • Split of use case 2 call flow into sub sections in Section 6.

From IETF draft 00 -> IETF draft 01:

  • Update of scope in Section 3.1 to include in which the pledge acts as a server. This is one main motivation for use case 2.
  • Rework of use case 2 in Section 5.1 to consider the transport between the pledge and the pledge-agent. Addressed is the TLS channel establishment between the pledge-agent and the pledge as well as the endpoint definition on the pledge.
  • First description of exchanged object types (needs more work)
  • Clarification in discovery options for enrollment endpoints at the domain registrar based on well-known endpoints do not result in additional /.well-known URIs. Update of the illustrative example. Note that the change to /brski for the voucher related endpoints has been taken over in the BRSKI main document.
  • Updated references.
  • Included Thomas Werner as additional author for the document.

From individual version 03 -> IETF draft 00:

  • Inclusion of discovery options of enrollment endpoints at the domain registrar based on well-known endpoints in new section as replacement of section 5.1.3 in the individual draft. This is intended to support both use cases in the document. An illustrative example is provided.
  • Missing details provided for the description and call flow in pledge-agent use case Section 5.1, e.g. to accommodate distribution of CA certificates.
  • Updated CMP example in to use lightweight CMP instead of CMP, as the draft already provides the necessary /.well-known endpoints.
  • Requirements discussion moved to separate section in Section 4. Shortened description of proof of identity binding and mapping to existing protocols.
  • Removal of copied call flows for voucher exchange and registrar discovery flow from [RFC8995] in UC1 to avoid doubling or text or inconsistencies.
  • Reworked abstract and introduction to be more crisp regarding the targeted solution. Several structural changes in the document to have a better distinction between requirements, use case description, and solution description as separate sections. History moved to appendix.

From individual version 02 -> 03:

  • Update of terminology from self-contained to authenticated self-contained object to be consistent in the wording and to underline the protection of the object with an existing credential. Note that the naming of this object may be discussed. An alternative name may be attestation object.
  • Simplification of the architecture approach for the initial use case having an offsite PKI.
  • Introduction of a new use case utilizing authenticated self-contain objects to onboard a pledge using a commissioning tool containing a pledge-agent. This requires additional changes in the BRSKI call flow sequence and led to changes in the introduction, the application example,and also in the related BRSKI-PRM call flow.

From individual version 01 -> 02:

  • Update of introduction text to clearly relate to the usage of IDevID and LDevID.
  • Update of description of architecture elements and changes to BRSKI in Section 5.
  • Enhanced consideration of existing enrollment protocols in the context of mapping the requirements to existing solutions in Section 4.

From individual version 00 -> 01:

  • Update of examples, specifically for building automation as well as two new application use cases in Section 3.1.
  • Deletion of asynchronous interaction with MASA to not complicate the use case. Note that the voucher exchange can already be handled in an asynchronous manner and is therefore not considered further. This resulted in removal of the alternative path the MASA in Figure 1 and the associated description in Section 5.
  • Enhancement of description of architecture elements and changes to BRSKI in Section 5.
  • Consideration of existing enrollment protocols in the context of mapping the requirements to existing solutions in Section 4.
  • New section starting with the mapping to existing enrollment protocols by collecting boundary conditions.

Contributors

Esko Dijk
IoTconsultancy.nl

Authors' Addresses

Steffen Fries
Siemens AG
Otto-Hahn-Ring 6
81739 Munich
Germany
Thomas Werner
Siemens AG
Otto-Hahn-Ring 6
81739 Munich
Germany
Eliot Lear
Cisco Systems
Richtistrasse 7
CH-8304 Wallisellen
Switzerland
Michael C. Richardson
Sandelman Software Works