BRSKI with Pledge in Responder Mode (BRSKI-PRM)

BRSKI with Pledge in Responder Mode (BRSKI-PRM) Siemens AG

Otto-Hahn-Ring 6 Munich 81739 Germany steffen.fries@siemens.com https://www.siemens.com/

Siemens AG

Otto-Hahn-Ring 6 Munich 81739 Germany thomas-werner@siemens.com https://www.siemens.com/

Cisco Systems

Richtistrasse 7 Wallisellen 8304 Switzerland +41 44 878 9200 lear@cisco.com

Sandelman Software Works

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

Operations and Management ANIMA WG This document defines enhancements to Bootstrapping a Remote Secure Key Infrastructure (BRSKI, RFC8995) to enable bootstrapping in domains featuring no or only limited connectivity between a pledge and the domain registrar. It specifically changes the interaction model from a pledge-initiated mode, as used in BRSKI, to a pledge-responding mode, where the pledge is in server role. For this, BRSKI with Pledge in Responder Mode (BRSKI-PRM) introduces new endpoints for the Domain Registrar and pledge, and a new component, the Registrar-Agent, which facilitates the communication between pledge and registrar during the bootstrapping phase. To establish the trust relation between pledge and registrar, BRSKI-PRM relies on object security rather than transport security. The approach defined here is agnostic to the enrollment protocol that connects the domain registrar to the Key Infrastructure (e.g., domain CA). About This Document Status information for this document may be found at . Source for this draft and an issue tracker can be found at .

Introduction BRSKI as defined in specifies a solution for secure zero-touch (automated) bootstrapping of devices (pledges) in a customer domain, which may be associated with a specific installation location. This includes the discovery of the BRSKI registrar in the customer domain and the exchange of security information necessary to establish trust between a pledge and the domain. Security information about the customer domain, specifically the customer domain certificate, are exchanged and authenticated utilizing signed data objects, the voucher artifacts as defined in . In response to a voucher-request, the Manufacturer Authorized Signing Authority (MASA) issues the voucher and provides it via the domain registrar to the pledge. specifies the format of the voucher artifacts, including the voucher-request artifact. For the certificate enrollment of devices, BRSKI relies on EST to request and distribute customer domain specific device certificates. EST in turn relies for the authentication and authorization of the certification request on the credentials used by the underlying TLS between the EST client and the EST server. BRSKI addresses scenarios in which the pledge initiates the bootstrapping acting as client (referred to as initiator mode by this document). BRSKI with Pledge in Responder Mode (BRSKI-PRM) defined in this document allows the pledge to act as server, so that it can be triggered externally and at a specific time to generate bootstrapping requests in the customer domain. For this approach, this document:

defines additional endpoints for the domain registrar and new endpoints for the pledge to enable responder mode.
introduces the Registrar-Agent as new component to facilitate the communication between the pledge and the domain registrar. The Registrar-Agent may be implemented as an integrated functionality of a commissioning tool or be co-located with the domain registrar itself. BRSKI-PRM supports the identification of the Registrar-Agent that was performing the bootstrapping allowing for accountability of the pledges installation, when the Registrar-Agent is a component used by an installer and not co-located with the domain registrar.
specifies additional artifacts for the exchanges between a pledge acting as server, the Registrar-Agent acting as client, and the domain registrar acting as server toward the Registrar-Agent.
allows the application of Registrar-Agent credentials to establish TLS connections to the domain registrar; these are different from the pledge IDevID credentials.
also enables the usage of alternative transports, both IP-based and non-IP, between the pledge and the domain registrar via the Registrar-Agent; security is addressed at the application layer through object security with an additional signature wrapping the exchanged artifacts.

The term endpoint used in the context of this document is equivalent to resource in HTTP and CoAP ; it is not used to describe a device. Endpoints are accessible via Well-Known URIs . To utilize EST for enrollment, the domain registrar performs pre-processing of the wrapping signature before actually using EST as defined in . There may be pledges that can support both modes, initiator and responder mode. In these cases BRSKI-PRM can be combined with BRSKI as defined in or BRSKI-AE to allow for more bootstrapping flexibility.

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 when, and only when, they appear in all capitals, as shown here. This document relies on the terminology defined in . The following terms are defined in addition:

authenticated self-contained object:: Describes a data object, which is cryptographically bound to the end entity (EE) certificate. The binding is assumed to be provided through a digital signature of the actual object using the corresponding private key of the certificate.
CA:: Certification Authority, issues certificates.
Commissioning tool:: Tool to interact with devices to provide configuration data.
CSR:: Certificate Signing Request.
EE:: End entity, as defined in . Typically, a device or service that owns a public-private key pair for which it manages a public key certificate.
EE certificate:: the certificate of the EE signed by its owner (e.g., CA). For domain components, the EE certificate is signed by the domain owner. For the pledge, the EE certificate is either the IDevID certificate signed by the manufacturer or the LDevID certificate signed by the domain owner or an application-specific EE certificate signed by the domain owner.
endpoint:: Term equivalent to resource in HTTP and CoAP . Endpoints are accessible via Well-Known URIs .
IDevID:: An Initial Device Identifier X.509 certificate installed by the vendor on new equipment. This is a term from 802.1AR .
LDevID:: A Local Device Identifier X.509 certificate installed by the owner of the equipment. This is a term from 802.1AR .
mTLS:: mutual Transport Layer Security.
PER:: Pledge Enroll-Request is a signature-wrapped CSR, signed by the pledge that requests enrollment to a domain via the Registrar-Agent.
POI:: Proof-of-Identity, as defined in .
POP:: Proof-of-Possession (of a private key), as defined in .
PVR:: Pledge Voucher-Request is a signature-wrapped voucher-request, signed by the pledge that sends it to the domain registrar via the Registrar-Agent.
RA:: Registration Authority, an optional system component to which a CA delegates certificate management functions such as authorization checks. In BRSKI-PRM, this is a functionality of the domain registrar, as in BRSKI .
Registrar_Agent:: Component facilitating the data exchange between a pledge in responder mode and a domain registrar.
RVR:: Registrar Voucher-Request is a signature-wrapped voucher-request, signed by the domain registrar that sends it to the MASA. For BRSKI-PRM, it contains a copy of the original PVR received from the pledge.

This document uses the following encoding notations in the given JWS-signed artifact examples:

BASE64(OCTETS):: Denotes the base64 encoding of an octet sequence using the character set defined in and without the inclusion of any line breaks, whitespace, or other additional characters. Note that the base64 encoding of the empty octet sequence is the empty string.
BASE64URL(OCTETS):: Denotes the base64url encoding of an octet sequence, per .
UTF8(STRING):: Denotes the octet sequence of the UTF-8 representation of STRING, per .

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 those examples short, they use the token base64encodedvalue== as a placeholder for base64 data. The full base64 data is included in the appendices of this document.

Scope of Solution

Supported Environments and Use Case Examples BRSKI-PRM is applicable to scenarios where pledges may have no direct connection to the domain registrar, may have no continuous connection, or require coordination of the pledge requests to be provided to a domain registrar. This can be motivated by pledges deployed in environments not yet connected to the operational customer domain network, e.g., at a building construction site, or environments intentionally disconnected from the Internet, e.g., critical industrial facilities. Another example is the assembly of electrical cabinets, which are prepared in advance before the installation at a customer domain.

Building Automation In building automation a typical use case exists where a detached building or the basement 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, 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 successively collect device-specific information in different parts of the building before connecting to the domain registrar for bulk bootstrapping. 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 or other detached areas. These 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. The Registrar-Agent, defined in this document, may be run on the technician's laptop to interact with pledges.

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.

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 domain does not offer enough physical security to operate an RA/CA and therefore this service is transferred to a backend that offers a higher level of operational security.

Potential Limitations The mechanism described in this document presumes the ability of the pledge and the Registrar-Agent to communicate with one another. 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. To overcome this situation, the pledges may need to be powered on, either manually or by sending a trigger signal.

Requirements Discussion and Mapping to Solution-Elements Based on the intended target environment described in , 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 the 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 then provided by the Registrar-Agent to the registrar. This requires the definition of pledge endpoints to allow interaction with the Registrar-Agent.
The security of communication between the Registrar-Agent and the pledge must not rely on Transport Layer Security (TLS) to enable application of BRSKI-PRM in environments, in which the communication between the Registrar-Agent and the pledge is done over other technologies like BTLE or NFC, which may not support TLS protected communication. In addition, the pledge does not have a certificate that can easily be verified by methods.
The use of authenticated self-contained objects addresses 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 the assertion type proximity in the voucher, as the pledge was not in direct contact with the registrar for bootstrapping. Therefore, a new assertion type is necessary for distinguishing assertions the MASA can state.

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

POI: provides data-origin authentication of an artifact, e.g., a voucher-request or an Enroll-Request, utilizing an existing IDevID. Certificate updates may utilize the certificate that is to be updated.
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 computed 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 Vouchers as used in 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.
Enroll-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 . In PKCS#10, the structure is signed to ensure integrity protection and POP 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 the certification request needs to be additionally bound to the existing pledge IDevID credential. This binding supports the authorization decision for the certification request and 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.

Solution Architecture

Overview For BRSKI with Pledge in Responder Mode (BRSKI-PRM), the base system architecture defined in BRSKI is enhanced to facilitate new use cases in which the pledge acts as server. The 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. The format of the bootstrapping objects produced or consumed by the pledge is usually based on JSON Web Signature (JWS) and further specified in to address the requirements stated in above. In constrained environments, it may be based on COSE . An abstract overview of the BRSKI-PRM protocol can be found on slide 8 of . To support mutual trust establishment between the domain registrar and pledges not directly connected to the customer domain, this document specifies the exchange of authenticated self-contained objects with the help of the Registrar-Agent. This leads to extensions of the logical components in the BRSKI architecture as shown in . Note that the Join Proxy is not shown in the figure. In certain situations the Join Proxy may still be present and could be used by the Registrar-Agent to connect to the Registrar. For example, a Registrar-Agent application on a smartphone often can connect to local Wi-Fi without giving up their cellular network connection , but only can make link-local connections. 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 described in . To enable reuse of BRSKI defined functionality as much as possible, BRSKI-PRM:

uses existing endpoints where the required functionality is provided.
enhances existing endpoints with new supported media types, e.g., for JWS voucher.
defines new endpoints where additional functionality is required, e.g., for wrapped certification request, wrapped CA certificates, and new status information.

BRSKI-PRM architecture overview using Registrar-Agent | |<------>| | . | | . | EE cert. | | EE cert. | . | | . +------------+ +-----+-----+ . | IDevID | . | . | | . +------------------+-----+ . +--------+ . | Key Infrastructure | . . | (e.g., PKI CA) | . . +------------------------+ . ......................................... Customer Domain ]]> shows the relations between the following main components:

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(S) in the context of this document. Any other protocol can be used as long as it supports the exchange of the necessary artifacts. This includes CoAP or protocols to be used over Bluetooth or NFC connections. A pledge acting as server leads to the following differences compared to BRSKI :
- The pledge no longer initiates bootstrapping, but is discovered and triggered by the Registrar-Agent as defined in .
- The pledge offers additional endpoints as defined in , so that the Registrar-Agent can request data required for bootstrapping the pledge.
- The pledge includes additional data in the PVR, which is provided and signed by the Registrar-Agent as defined in . This allows the registrar to identify with which Registrar-Agent the pledge was in contact (see ).
- The artifacts exchanged between the pledge and the registrar via the Registrar-Agent are authenticated self-contained objects (i.e., signature-wrapped artifacts).
Registrar-Agent: Is a new component defined in that provides a store and forward communication path to exchange data objects between the pledge and the domain registrar. This is for situations in which the domain registrar is not directly reachable by the pledge, which may be due to a different technology stacks or due to missing connectivity. A Registrar-Agent acting as client leads to the following new aspects:
- The order of exchanges in the BRSKI-PRM call flow is different from that in BRSKI , as the Registrar-Agent can trigger one or more pledges and collects the PVR and PER artifacts simultaneously as defined in . This enables bulk bootstrapping of several devices.
- 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 domain registrar.
- The trust assumption between the Registrar-Agent and the domain registrar may be based on EE certificates that are both signed by the domain owner.
- The Registrar-Agent may be realized as stand-alone component supporting nomadic activities of a service technician moving between different installation sites.
- Alternatively, the Registrar-Agent may also be realized as co-located functionality for a registrar, to support pledges in responder mode.
Join Proxy (not shown): Has the same functionality as described in 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 fulfills the same functionality regarding the bootstrapping of the pledge in a customer domain by facilitating the communication of the pledge with the MASA service and the domain key infrastructure (PKI). However, there are also differences compared to BRSKI :
- A BRSKI-PRM domain registrar does not interact with a pledge directly, but through the Registrar-Agent as defined in .
- A BRSKI-PRM domain registrar offers additional endpoints as defined in to support the signature-wrapped artifacts used by BRSKI-PRM.
Vendor services: Encompass MASA and Ownership Tracker and are used as defined in . A MASA responsible for pledges that implement BRSKI-PRM is expected to support BRSKI-PRM extensions:
- The default format for voucher artifacts (incl. voucher-request) is JWS-signed JSON as defined in .
- The Agent Proximity Assertion (see ) requires additional validation steps as defined in .

Nomadic Connectivity In one example instance of the PRM architecture as shown in , there is no connectivity between the location in which the pledge is installed and the location of the domain registrar. This is often the case in the aforementioned building automation use case ().

Registrar-Agent nomadic connectivity example : Agent : . | . +--------+ L2 or L3 :-.-.-.-.-.-.-: . | BRSKI- . connectivity ^ . | MASA ..........................!............. | Pledge Installation ! | Location ! Nomadic | ! connectivity | ! | ...........!....................|......... . v v . . .-.-.-.-.-.-.-. BRSKI- +-----------+ . . : Registrar- : PRM | Domain | . . : Agent :<------>| Registrar | . . :-.-.-.-.-.-.-: +-----+-----+ . . | . . +-------------------+-----+ . . | Key Infrastructure | . . | (e.g., PKI CA) | . . +-------------------------+ . .......................................... Customer Domain ]]> PRM enables support of this case through nomadic connectivity of the Registrar-Agent. To perform enrollment in this setup, multiple round trips of the Registrar-Agent between the pledge installation location and the domain registrar are required.

Connectivity to domain registrar: preparation tasks for pledge bootstrapping not part of the BRSKI-PRM protocol definition, like retrieval of list of pledges to enroll.
Connectivity to pledge installation location: retrieve information about available pledges (IDevID), collect request objects (i.e., Pledge Voucher-Requests and Pledge Enroll-Requests using the BRSKI-PRM approach described in and ).
Connectivity to domain registrar, submit collected request information of pledges, retrieve response objects (i.e., Voucher and Enroll-Response) using the BRSKI-PRM approach described in and .
Connectivity to pledge installation location, provide retrieved objects to the pledges to enroll pledges and collect status using the BRSKI-PRM approach described in , , and .
Connectivity to domain registrar, submit Voucher Status and Enrollment Status using the BRSKI-PRM approach described in and .

Variations of this setup include cases where the Registrar-Agent uses for example WiFi to connect to the pledge installation network, and mobile network connectivity to connect to the domain registrar. Both connections may also be possible in a single location at the same time, based on installation building conditions.

Co-located Registrar-Agent and Domain Registrar Compared to BRSKI, pledges supporting BRSKI-PRM can be completely passive and only need to react when being requested to react by a Registrar-Agent. In , pledges instead need to continuously request enrollment from a domain registrar, which may result in undesirable communications pattern and possible overload of a domain registrar.

Registrar-Agent integrated into Domain Registrar example |. Agent . Registrar | . +--------+ L2 or L3 |.............. | . connectivity +-------------------+-----+ . . | . . +------------------+-----+ . . | Key Infrastructure | . . +------------------------+ . ......................................... Customer Domain ]]> The benefits of BRSKI-PRM can be achieved even without the operational complexity of stand-alone Registrar-Agents by integrating the necessary functionality of the Registrar-Agent as a module into the domain registrar as shown in so that it can support the BRSKI-PRM communications to the pledge.

Agent Proximity Assertion "Agent proximity" is a statement in the PVR and the voucher that the registrar communicates via the Registrar-Agent as defined in and not directly to the pledge. It is therefore a different assertion than "network proximity", which is defined in . Hence, defines the additional assertion type agent-proximity. This assertion type can be verified by the registrar and MASA during BRSKI-PRM voucher-request processing. In BRSKI, the pledge verifies POP of the registrar end-entity (EE) credentials via the TLS handshake and pins that public key as the proximity-registrar-cert into the voucher request. This allows the MASA to verify the proximity of the pledge and registrar, facilitating a decision to assign the pledge to that domain owner. In BRSKI, the TLS session is considered provisional until the pledge receives the voucher to verify POI. In contrast, in BRSKI-PRM the pledge has no direct connection to the registrar and MUST accept the supplied registrar EE certificate provisionally until it receives the voucher as described in to verify both POP and POI. The provisional registrar EE certificate is used for the object security along the authenticated self-contained objects that in BRSKI-PRM replace the direct TLS connection to the registrar available in BRSKI . See also on "provisional state". For the Agent Proximity Assertion, the Registrar-Agent EE certificate and registrar EE certificate must be signed by the same domain owner, i.e., MUST possess a common domain trust anchor in their certificate chain. Akin to the Network Proximity Assertion in BRSKI , the Agent Proximity Assertion provides pledge proximity evidence to the MASA. But additionally, the Agent Proximity Assertion allows the domain registrar to be sure that the PVR supplied by the Registrar-Agent was in fact collected by the Registrar-Agent to which the registrar is connected by utilizing an agent-signed data object.

System Components

Registrar-Agent The Registrar-Agent is a new component in BRSKI-PRM that provides a store and forward communication path with secure message passing between pledges in responder mode and the domain registrar. It uses its own end-entity (EE) certificate and corresponding credentials (i.e., private key) for TLS client authentication and for signing agent-signed data objects. The Registrar-Agent EE certificate MUST include a SubjectKeyIdentifier as defined in , which is used as a reference within agent-signed data objects as defined in . Note that this is an additional requirement for issuing the Registrar-Agent EE certificate. has a similar requirement for the registrar EE certificate. The SubjectKeyIdentifier is used in favor of providing the complete Registrar-Agent EE certificate in agent-signed data objects to accommodate also constrained environments and reduce bandwidth needed for communication with the pledge. In addition, it follows the recommendation from BRSKI to use SubjectKeyIdentifier in favor of a certificate fingerprint to avoid additional computations. The provisioning of the Registrar-Agent EE certificate is out of scope for this document, but may be done using its own BRSKI run or by other means such as configuration. It is RECOMMENDED to use short lived Registrar-Agent EE certificates in the range of days or weeks as outlined in . Further, the Registrar-Agent requires the registrar EE certificate to provide it to the pledge. It MAY use the certificate verified during server authentication within an initial TLS session with the registrar; in this case, the Registrar-Agent MUST possess the domain trust anchor (i.e., CA certificate) for the registrar EE certificate to verify the certificate chain. Alternatively, the registrar EE certificate MAY be provided via configuration or a repository. The registrar IP address or hostname is provided either by configuration or by using the discovery mechanism defined in (see ). In addition to the certificates, the Registrar-Agent is provided with the product-serial-number(s) of the pledge(s) to be bootstrapped. This is necessary to allow for the discovery of pledges by the Registrar-Agent using DNS-SD with mDNS (see ). The list may be provided by prior administrative means or the Registrar-Agent may get the information via an (out-of-band) interaction with the pledge. For instance, describes scanning of a QR code, where the product-serial-number would be initialized from the 12N B005 Product Serial Number data record. In summary, the following information MUST be available at the Registrar-Agent before the interaction with a pledge:

Registrar-Agent EE certificate and corresponding private key: own operational credentials to authenticate and sign agent-signed data
Registrar EE certificate: certificate of the domain registrar to be provided to the pledge
Serial number(s): product-serial-number(s) of pledge(s) to be bootstrapped; used for discovery

Further, the Registrar-Agent SHOULD have synchronized time. Finally, the Registrar-Agent MAY possess the IDevID (root or issuing) CA certificate of the pledge manufacturer/vendor to validate the IDevID certificate on returned PVR or in case of optional TLS usage for pledge communication (see ). The distribution of IDevID CA certificates to the Registrar-Agent is out of scope of this document and may be done by a manual configuration.

Discovery of the Registrar While the Registrar-Agent requires the IP address of the domain registrar to initiate a TLS session, a separate discovery of the registrar is likely not needed and a configuration of the domain registrar IP address or hostname is assumed. Registrar-Agent and registrar are domain components that already have a trust relation, as a Registrar-Agent acts as representative of the domain registrar towards the pledge or may even be collocated with the domain registrar. Further, other communication (not part of this document) between the Registrar-Agent and the registrar is assumed, e.g., to exchange information about product-serial-number(s) of pledges to be discovered as outlined in . Moreover, the standard discovery described in and the does not support identification of registrars with an enhanced feature set (like the support of BRSKI-PRM), and hence this standard discovery is not applicable. As a more general solution, the BRSKI discovery mechanism can be extended to provide upfront information on the capabilities of registrars, such as the mode of operation (pledge-responder-mode or registrar-responder-mode). Defining discovery extensions is out of scope of this document. For further discussion, see .

Discovery of the Pledge The discovery of the pledge by the Registrar-Agent in the context of this document describes the minimum discovery approach that MUST be supported. A more general discovery mechanism, also supporting GRASP besides DNS-SD with mDNS, is discussed in . Discovery in BRSKI-PRM uses DNS-based Service Discovery over Multicast DNS to discover the pledge. Note that provides support for conflict resolution in situations when a DNS-SD with mDNS responder receives an mDNS response with inconsistent data. Note that does not support conflict resolution of mDNS, which may be a limitation for its application. The pledge constructs a Service Instance Name based on device local information (manufacturer/vendor name and serial number), which results in <product-serial-number>._brski-pledge._tcp.local. The product-serial-number composition is manufacturer dependent and may contain information regarding the manufacturer, the product type, and further information specific to the product instance. To allow distinction of pledges, the product-serial-number therefore needs to be sufficiently unique. Note that this goes against the naming recommendation of . The _brski-pledge._tcp service, however, targets machine-to-machine discovery. In the absence of a more general discovery as defined in the Registrar-Agent MUST 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 DNS-SD with mDNS discovery without its product-serial-number contained. This allows a commissioning tool to discover pledges to be bootstrapped in the domain. The manufacturer supports this functionality as outlined in . Establishing network connectivity of the pledge is out of scope of this document but necessary to apply DNS-SD with mDNS. 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, e.g., as proposed in . 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.

Pledge in Responder Mode In BRSKI-PRM, the pledge is triggered by the Registrar-Agent to create the PVR and PER. It is also triggered for processing of the responses and the generation of status information once the Registrar-Agent has received the responses from the registrar later in the process. To enable interaction as responder with the Registrar-Agent, pledges in responder mode MUST act as servers and MUST provide the endpoints defined in within the BRSKI-defined /.well-known/brski/ URI path, except for the OPTIONAL endpoint "qps". The endpoints are defined with short names to also accommodate for resource-constrained devices. Well-Known Endpoints on a Pledge in Responder Mode

Endpoint	Operation	Exchange and Artifacts
tpvr	Trigger Pledge Voucher-Request
tper	Trigger Pledge Enroll-Request
svr	Supply Voucher to Pledge
scac	Supply CA Certificates to Pledge
ser	Supply Enroll-Response to Pledge
qps	Query Pledge Status

HTTP(S) uses the Host header field (or :authority in HTTP/2) to allow for name-based virtual hosting as explained in . This header field is mandatory, and so a compliant HTTP(S) client is going to insert it, which may be just an IP address. The pledge MUST respond to all requests regardless of the Host header field provided by the client (i.e., ignore it). Note that there is no requirement for the pledge to operate its BRSKI-PRM service on port 80 or port 443, so there is no reason for name-based virtual hosting. For instance, when the Registrar-Agent reaches out to the "tpvr" endpoint on a pledge in responder mode with the full URI http://pledge.example.com/.well-known/brski/tpvr, it sets the Host header field to pledge.example.com and the absolute path /.well-known/brski/tpbr. In practice, however, the pledge is usually known by a .local hostname or only its IP address as returned by a discovery protocol, which will be included in the Host header field. As BRSKI-PRM uses authenticated self-contained objects between the pledge and the domain registrar, the binding of the pledge identity to the voucher-requests is provided by the wrapping signature employing the pledge IDevID credential. Hence, pledges MUST have an Initial Device Identifier (IDevID) installed in them at the factory.

Pledge with Combined Functionality Pledges MAY support both initiator and responder mode. A pledge in initiator mode should listen for announcement messages as described in . Upon discovery of a potential registrar, it initiates the bootstrapping to that registrar. At the same time (so as to avoid the Slowloris-like attack described in ), it SHOULD also respond to the triggers for responder mode described in this document. Once a pledge with combined functionality has been bootstrapped, it MAY act as client for enrollment of further certificates needed, e.g., using the enrollment protocol of choice. If it still acts as server, the defined BRSKI-PRM endpoints to trigger a Pledge Enroll-Request (PER) or to provide an Enroll-Response can be used for further certificates.

Domain Registrar In BRSKI-PRM, the domain registrar provides the endpoints already specified in (derived from EST ) where suitable. In addition, it MUST provide the endpoints defined in within the BRSKI-defined /.well-known/brski/ Well-Known URI path. These endpoints accommodate for the authenticated self-contained objects used by BRSKI-PRM to provide Pledge Enroll-Request (PER) artifacts and signature-wrapped CA certificates via the Registrar-Agent. Additional Well-Known Endpoints on a BRSKI-PRM Registrar

Endpoint	Operation	Exchange and Artifacts
requestenroll	Supply PER to Registrar
wrappedcacerts	Obtain CA Certificates

The registrar possesses its own EE certificate and corresponding private key for authenticating and signing. It MUST use the same certificate/credentials for authentication in the TLS session with a Registrar-Agent and for signing artifacts for that Registrar-Agent and its pledges (see ). Overall, this may have operational implications when the registrar is part of a scalable framework as described in . According to , the domain registrar performs the pledge authorization for bootstrapping within its domain based on the Pledge Voucher-Request. For this, it MUST possess the IDevID trust anchor(s) (i.e., root or issuing CA certificate(s)) of the pledge vendor(s)/manufacturer(s). This behavior is retained in BRSKI-PRM. In its role as EST server , the domain registrar MUST also possess the domain CA certificates as defined in . Finally, the domain registrar MUST possess the Registrar-Agent EE certificate(s) to validate agent-signed data and to provide it to the MASA. The registrar MAY use the certificate verified during client authentication within the TLS sessions with the Registrar-Agent; in this case, the registrar MUST possess the domain trust anchor (i.e., domain CA certificate) for the Registrar-Agent EE certificate to verify the certificate chain. Alternatively, the Registrar-Agent EE certificate(s) MAY be provided via configuration or a repository.

Domain Registrar with Combined Functionality A registrar with combined BRSKI and BRSKI-PRM functionality MAY detect if the bootstrapping is performed by the pledge directly (BRSKI case) or by a Registrar-Agent (BRSKI-PRM case) based on the utilized credentials for client authentication during the TLS session establishment and 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 Registrar-Agent EE certificate, which allows the domain registrar to explicitly detect already in the TLS session establishment that the connecting client is a Registrar-Agent. The registrar MAY be restricted by configuration, if it accepts every Registrar-Agent, which can authenticate with a domain issued certificate or only explicitly authorized ones. Note that using an EE certificate for TLS client authentication of the Registrar-Agent is a deviation from , in which the pledge IDevID certificate is used to perform TLS client authentication.

MASA The Manufacturer Authorized Signing Authority (MASA) is a vendor service that generates and signs voucher artifacts for pledges by the same vendor. When these pledges support BRSKI-PRM, the MASA needs to implement the following functionality in addition to BRSKI . A MASA for pledges in responder mode MUST support the voucher format defined in to parse and process JWS-signed voucher-request artifacts and generate JWS-signed voucher artifacts. Further, a MASA for pledges in responder mode MUST support the Agent Proximity Assertion (see ) through the validation steps defined in based on the Pledge Voucher-Request (PVR) and Registrar Voucher-Request (RVR) artifact fields defined in and , respectively.

Exchanges and Artifacts The interaction of the pledge with the Registrar-Agent may be accomplished using different transports (i.e., protocols and/or network technologies). This specification utilizes HTTP(S) as default transport. Other specifications may define alternative transports such as CoAP, Bluetooth Low Energy (BLE), or Near Field Communication (NFC). These transports may differ from and are independent of the ones used between the Registrar-Agent and the registrar. Transport independence is realized through authenticated self-contained objects that are not bound to a specific transport security and stay the same along the communication path from the pledge via the Registrar-Agent to the registrar. defines CMS-signed JSON structures as format for artifacts representing authenticated self-contained objects. This specification utilizes JWS-signed JSON structures as default format for BRSKI-PRM. Other specifications may define alternative formats for representing authenticated self-contained objects such as COSE-signed CBOR structures. provides an overview of the exchanges detailed in the following subsections.

Overview pledge-responder-mode exchanges | | | | | | | | | ~ ~ ~ ~ ~ (1) Trigger Pledge Voucher-Request ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<------tPVR-------| | | | |--------PVR------>| | | | | | | | | ~ ~ ~ ~ ~ (2) Trigger Pledge Enroll-Request ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<------tPER-------| | | | |--------PER------>| | | | | | | | | ~ ~ ~ ~ ~ (3) Supply PVR to Registrar (including MASA interaction) ~ ~ ~ ~ ~ | | | | | | |<-----mTLS------>| | | | | | | | | | [Registrar-Agent | | | | authenticated&authorized?] | | | | | | | | |-------PVR------>| | | | | | | | | | [accept device?] | | | | | | | | | |<------------mTLS------------>| | | |--------------RVR------------>| | | | ~ | | | | [extract DomainID] | | | [update audit-log] | | | ~ | | | |<-----------Voucher-----------| | |<----Voucher''---| | | | | | | | ~ ~ ~ ~ ~ (4) Supply PER to Registrar (including Key Infrastructure interaction) ~ ~ ~ ~ ~ | | | | | | |<---((mTLS))---->| | | | |-------PER------>| | | | | |----[Request]--->| | | | |<--[Certificate]-| | | |<--Enroll-Resp---| | | | | | | | ~ ~ ~ ~ ~ (5) Obtain CA Certificates ~ ~ ~ ~ ~ | | | | | | |<----(mTLS)----->| | | | |<----caCerts-----| | | | | | | | ~ ~ ~ ~ ~ (6) Supply Voucher to Pledge ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<-----Voucher''---| | | | |------vStatus---->| | | | | | | | | ~ ~ ~ ~ ~ (7) Supply CA Certificates to Pledge ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<-----caCerts-----| | | | | | | | | ~ ~ ~ ~ ~ (8) Supply Enroll-Response to Pledge ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<---Enroll-Resp---| | | | |-----eStatus----->| | | | | | | | | ~ ~ ~ ~ ~ (9) Voucher Status Telemetry (including backend interaction) ~ ~ ~ ~ ~ | | | | | | |<----(mTLS)----->| | | | |-----vStatus---->| | | | | |<-----------(mTLS)----------->| | | |-----req device audit-log---->| | | |<------device audit-log-------| | | | | | | | [verify audit-log] | | | | | | | ~ ~ ~ ~ ~ (10) Enroll Status Telemetry ~ ~ ~ ~ ~ | | | | | | |<----(mTLS)----->| | | | |-----eStatus---->| | | | | | | | ~ ~ ~ ~ ~ (11) Query Pledge Status ~ ~ ~ ~ ~ | | | | | |<----opt. TLS---->| | | | |<-----tStatus-----| | | | |------pStatus---->| | | | | | | | | ~ ~ ~ ~ ~ ]]> The following subsections split the interactions shown in between the different components into:

describes the acquisition exchange for the Pledge Voucher-Request initiated by the Registrar-Agent to the pledge.
describes the acquisition exchange for the Pledge Enroll-Request initiated by the Registrar-Agent to the pledge.
describes the issuing exchange for the Voucher initiated by the Registrar-Agent to the registrar, including the interaction of the registrar with the MASA using the RVR , as well as the artifact processing by these entities.
describes the enroll exchange initiated by the Registrar-Agent to the registrar including the interaction of the registrar with the CA using the PER as well as the artifact processing by these entities.
describes the retrieval exchange for the optional CA certificate provisioning to the pledge initiated by the Registrar-Agent to the CA.
describes the Voucher exchange initiated by the Registrar-Agent to the pledge and the returned status information.
describes the CA certificate exchange initiated by the Registrar-Agent to the pledge.
describes the Enroll-Response exchange initiated by the Registrar-Agent to the pledge (containing a new pledge EE certificate) and the returned status information.
describes the Voucher Status telemetry exchange initiated by the Registrar-Agent to the registrar, including the interaction of the registrar with the MASA.
describes the Enroll Status telemetry exchange initiated by the Registrar-Agent to the registrar.
describes the Pledge Status exchange about the general bootstrapping state initiated by the Registrar-Agent to the pledge.

Trigger Pledge Voucher-Request The Registrar-Agent MUST begin the sequence of exchanges by sending the Pledge Voucher-Request Trigger (tPVR). This assumes that the Registrar-Agent has already discovered the pledge, for instance as described in based on DNS-SD or similar. Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the acquisition of the Pledge Voucher-Request (PVR) and the following subsections describe the corresponding artifacts.

PVR acquisition exchange | | | | |<------tPVR-------| | | | |--------PVR------>| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL trigger the pledge to create a PVR via HTTP(S) POST to the pledge endpoint at /.well-known/brski/tpvr. The request body MUST contain the JSON-based Pledge Voucher-Request Trigger (tPVR) artifact as defined in . In the request header, the Content-Type field MUST be set to application/json and the Accept field SHOULD be set to application/voucher-jws+json as defined in . Upon receiving a valid tPVR, the pledge MUST reply with the PVR artifact as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/voucher-jws+json as defined in . Note that the pledge provisionally accepts the registrar EE certificate contained in the tPVR until it receives the voucher (see ). If the pledge is unable to create the PVR, it SHOULD respond with an HTTP error status code to the Registrar-Agent. The following client error status codes SHOULD be used:

400 Bad Request: if the pledge detects an error in the format of the request, e.g., missing field, wrong data types, etc. or if the request is not valid JSON even though the Content-Type request header field was set to application/json
406 Not Acceptable: if the Accept request header field indicates a type that is unknown or unsupported, e.g., a type other than application/voucher-jws+json
415 Unsupported Media Type: if the Content-Type request header field indicates a type that is unknown or unsupported, e.g., a type other than application/json

The pledge MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent.

Request Artifact: Pledge Voucher-Request Trigger (tPVR) The Pledge Voucher-Request Trigger (tPVR) artifact SHALL be an unsigned data object, providing the necessary parameters for generating the Pledge Voucher-Request (PVR) artifact such that the Agent Proximity Assertion can be verified by registrar and MASA: the registrar EE certificate and an agent-signed data object containing the product-serial-number and a timestamp. The artifact is unsigned because at the time of receiving the tPVR, the pledge could not verify any signature. For the JSON-based format used by this specification, the tPVR artifact SHALL be a UTF-8 encoded JSON document that conforms with the CDDL data model defined in :

CDDL for Pledge Voucher-Request Trigger (pledgevoucherrequesttrigger) The agent-provided-proximity-registrar-cert member SHALL contain the base64-encoded registrar EE certificate in X.509 v3 (DER) format. The agent-signed-data member SHALL contain the base64-encoded JWS Agent-Signed Data as defined in . summarizes the serialization the JSON tPVR artifact:

tPVR Representation in JSON

JWS Agent-Signed Data To enable alternative formats, the YANG module in defines the leaf agent-signed-data as binary. For the JWS-signed JSON format used by this specification, the agent-signed-data leaf SHALL be a UTF-8 encoded JWS structure in "General JWS JSON Serialization Syntax" as defined in signing the JSON Agent-Signed Data defined in . summarizes this JWS structure for the agent-signed-data member of the tPVR artifact:

JWS Agent-Signed Data in General JWS JSON Serialization Syntax The JSON Agent-Signed Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON Agent-Signed Data The JSON Agent-Signed Data SHALL be a JSON document that MUST conform with the CDDL data model defined in :

CDDL for JSON Agent-Signed Data (prmasd) The created-on member SHALL contain the current date and time at tPVR creation as standard date/time string as defined in . The serial-number member SHALL contain the product-serial-number of the pledge with which the Registrar-Agent assumes to communicate as string. The format MUST correspond to the X520SerialNumber field of IDevID certificates. below shows an example for the JSON Agent-Signed Data:

JSON Agent-Signed Data Example

JWS Protected Header The JWS Protected Header of the agent-signed-data member MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
kid: SHALL contain the base64-encoded OCTET STRING value of the SubjectKeyIdentifier of the Registrar-Agent EE certificate as described in

below shows an example for this JWS Protected Header:

JWS Protected Header Example for

JWS Signature The Registrar-Agent MUST sign the agent-signed-data member using its EE credentials. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Response Artifact: Pledge Voucher-Request (PVR) The Pledge Voucher-Request (PVR) artifact SHALL be an authenticated self-contained object signed by the pledge, containing an extended Voucher-Request artifact based on . The BRSKI-PRM related enhancements of the ietf-voucher-request YANG module are defined in . For the JWS-signed JSON format used by this specification, the PVR artifact MUST be a JWS Voucher structure as defined in , which MUST contain the JSON PVR Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON PVR artifact:

PVR Representation in General JWS JSON Serialization Syntax

JSON PVR Data The JSON PVR Data MUST contain the following fields of the ietf-voucher-request YANG module as defined in ; note that this makes optional leaves in the YANG definition mandatory for the PVR artifact:

created-on: SHALL contain the current date and time at PVR creation as standard date/time string as defined in ; if the pledge does not have synchronized time, it SHALL use the created-on value from the JSON Agent-Signed Data received with the tPVR artifact and SHOULD advance that value based on its local clock to reflect the PVR creation time
nonce: SHALL contain a cryptographically strong pseudo-random number
serial-number: SHALL contain the product-serial-number in the X520SerialNumber field of the pledge IDevID certificate as string as defined in
assertion: SHALL contain the assertion type agent-proximity to indicate the pledge request (different from BRSKI )
agent-provided-proximity-registrar-cert: SHALL contain the base64-encoded registrar EE certificate provided in the tPVR by the Registrar-Agent; enables the registrar and MASA to verify the Agent Proximity Assertion
agent-signed-data: SHALL contain the same value as the agent-signed-data member in the tPVR provided by the Registrar-Agent; enables the registrar and MASA to verify the Agent Proximity Assertion; also enables the registrar to log which Registrar-Agent was in contact with the pledge

below shows an example for the JSON PVR Data:

JSON PVR Data Example

JWS Protected Header The JWS Protected Header MUST follow the definitions of .

JWS Signature The pledge MUST sign the PVR artifact using its IDevID credential following the definitions of .

Trigger Pledge Enroll-Request Once the Registrar-Agent has received the PVR it can trigger the pledge to generate a Pledge Enroll-Request (PER). Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the acquisition of the PER and the following subsections describe the corresponding artifacts.

PER acquisition exchange | | | | |<------tPER-------| | | | |--------PER------>| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL trigger the pledge to create the PER via HTTP(S) POST to the pledge endpoint at /.well-known/brski/tper. The request body MUST contain the JSON-based Pledge Enroll-Request Trigger (tPER) artifact as defined in . In the request header, the Content-Type field MUST be set to application/json and the Accept field SHOULD be set to application/jose+json. Upon receiving a valid tPER, the pledge MUST reply with the PER artifact as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/jose+json. If the pledge is unable to create the PER, it SHOULD respond with an HTTP error status code to the Registrar-Agent. The following client error status codes MAY be used:

400 Bad Request: if the pledge detects an error in the format of the request
406 Not Acceptable: if the Accept request header field indicates a type that is unknown or unsupported, e.g., a type other than application/jose+json
415 Unsupported Media Type: if the Content-Type request header field indicates a type that is unknown or unsupported, e.g., a type other than application/json

The pledge MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent.

Request Artifact: Pledge Enroll-Request Trigger (tPER) The Pledge Enroll-Request Trigger (tPVR) artifact SHALL be an unsigned data object, providing enrollment parameters. This document specifies only the basic parameter for a generic, device-related LDevID certificate with no CSR attributes provided to the pledge. If specific attributes in the certificate are required, they have to be inserted by the issuing Key Infrastructure. The Pledge Enroll-Request Trigger (tPER) artifact MAY be used to provide additional enrollment parameters such as CSR attributes. How to provide and use such additional data is out of scope for this specification. For the JSON-based format used by this specification, the tPER artifact MUST be a UTF-8 encoded JSON document that conforms with the CDDL data model defined in :

CDDL for Pledge Enroll-Request Trigger (pledgeenrollrequesttrigger) The enroll-type member allows for specifying which type of certificate is to be enrolled. As shown in , BRSKI-PRM only defines the enumeration value enroll-generic-cert for the enrollment of the generic, device-related LDevID certificate. Other specifications using this artifact may define further enum values, e.g., to bootstrap application-related EE certificates with additional CSR attributes.

Response Artifact: Pledge Enroll-Request (PER) The Pledge Enroll-Request (PER) artifact SHALL be an authenticated self-contained object signed by the pledge, containing a PKCS#10 Certificate Signing Request (CSR) . The CSR already assures POP of the private key corresponding to the contained public key. In addition, based on the PER signature using the IDevID of the pledge, POI is provided. For the JWS-signed JSON format used by this specification, the PER artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON CSR Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON PER artifact:

PER Representation in General JWS JSON Serialization Syntax The JSON CSR Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON CSR Data The JSON CSR Data SHALL be a JSON document that MUST conform with the data model described by the csr-grouping of the ietf-ztp-types YANG module defined in and MUST be encoded using the rules defined in . Note that also allows for inclusion of CSRs in different formats used by CMP and CMC. For PKCS#10 CSRs as used in BRSKI and BRSKI-PRM, the p10-csr case of the csr-grouping MUST be used. below shows an example for the JSON CSR Data:

JSON CSR Data Example

JWS Protected Header The JWS Protected Header of the PER artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded pledge EE certificate used to sign the PER artifact; it SHOULD also contain the certificate chain for this certificate; if the certificate chain is not included in the x5c Header Parameter, it MUST be available at the domain registrar for verification
crit: SHALL indicate the extension Header Parameter created-on to ensure that it must be understood and validated by the receiver as defined in

In addition, the JWS Protected Header of the PER artifact MUST contain the following extension Header Parameter:

created-on: SHALL contain the current date and time at PER creation as standard date/time string as defined in ; if the pledge does not have synchronized time, it SHALL use the created-on value from the JSON Agent-Signed Data received with the tPVR artifact and SHOULD advance that value based on its local clock to reflect the PER creation time

The new protected Header Parameter created-on is introduced to reflect freshness of the PER. It allows the registrar to verify the timely correlation between the PER artifact and previous exchanges, i.e., created-on of PER >= created-on of PVR >= created-on of PVR trigger. The registrar MAY consider ignoring any but the newest PER artifact from the same pledge in case the registrar has at any point in time more than one pending PER from the pledge. below shows an example for this JWS Protected Header:

JWS Protected Header Example within PER

JWS Signature The pledge MUST sign the PER artifact using its IDevID credential. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in . While BRSKI-PRM targets the initial enrollment, re-enrollment can be supported similarly. In this case, the pledge MAY use its current, potentially application-related EE credential instead of its IDevID credential to sign the PER artifact. The issuing CA can associate the re-enrollment request with the pledge based on the previously issued and still valid EE certificate. Note that a pledge that does not have synchronized time needs to advance the last known current date and time based on its local clock over a longer period, which also requires persisting the local clock advancements across reboots.

Supply PVR to Registrar (including MASA interaction) Once the Registrar-Agent has acquired one or more PVR and PER object pairs, it starts the interaction with the domain registrar. Collecting multiple pairs allows bulk bootstrapping of several pledges using the same session with the registrar. The Registrar-Agent MUST establish a TLS session to the registrar with mutual authentication. In contrast to BRSKI , the TLS client authentication uses the Registrar-Agent EE certificate instead of the pledge IDevID certificate. Consequently, the domain registrar can distinguish BRSKI (pledge-initiator-mode) from BRSKI-PRM (pledge-responder-mode). The registrar SHOULD verify the TLS client authentication of the Registrar-Agent, in particular if the TLS session is used to obtain the Registrar-Agent EE certificate (see ). Note that authentication and authorization of the pledge verified during the TLS session based on the signatures inside the PVR artifact. As already stated in , 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. shows the voucher-request processing and the following subsections describe the corresponding artifacts.

Voucher issuing exchange | | | | | | | | | | [Registrar-Agent | | | | authenticated&authorized?] | | | | | | | | |-------PVR------>| | | | | | | | | | [accept device?] | | | | | | | | | |<------------mTLS------------>| | | |--------------RVR------------>| | | | ~ | | | | [extract DomainID] | | | [update audit-log] | | | ~ | | | |<-----------Voucher-----------| | |<----Voucher''---| | | | | | | | ~ ~ ~ ~ ~ ]]> As a first step of the interaction with the domain registrar, the Registrar-Agent SHALL supply the PVR artifact(s) to the registrar via HTTP-over-TLS POST to the registrar endpoint at /.well-known/brski/requestvoucher. Note that this is the same endpoint as for BRSKI described in . The request body MUST contain one previously acquired PVR artifact as defined in . In the request header, the Content-Type field MUST be set to application/voucher-jws+json and the Accept field SHOULD be set to application/voucher-jws+json as defined in . Upon receiving a PVR artifact, the registrar accepts or declines the request to join the domain. For this, it MUST perform pledge authorization as defined in . Due to the Registrar-Agent in the middle, the registrar MUST verify in addition that

the agent-provided-proximity-registrar-cert field of the PVR contains a registrar EE certificate signed by the same domain owner as the registrar EE certificate used to sign the RVR; note that this check allows for installations with multiple domain registrars and for registrar EE certificate renewal between exchanges with the Registrar-Agent (see ); in many installations with a single registrar the contained certificate is identical to the signing certificate
the agent-signed-data field of the PVR is signed with the private key corresponding to the Registrar-Agent EE certificate as known by the registrar (see ); this is done via the SubjectKeyIdentifier of the certificate in the kid Header Parameter of the JWS Protected Header of the agent-signed-data field.
the product-serial-number inside the agent-signed-data is equal to the serial-number field of the PVR as well as the X520SerialNumber field of the pledge IDevID certificate, which is contained in the JWS Protected Header of the PVR.
the Registrar-Agent EE certificate is still valid; this 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 .

If the registrar is unable to process the request or validate the PVR, it MUST respond with an HTTP client error status code to the Registrar-Agent. The following client error status codes SHOULD be used:

400 Bad Request: if the registrar detects an error in the format of the request
403 Forbidden: if the registrar detected that one or more security related fields are not valid or if the pledge-provided information could not be used with automated allowance
406 Not Acceptable: if the Accept request header field indicates a type that is unknown or unsupported
415 Unsupported Media Type: if the Content-Type request header field indicates a type that is unknown or unsupported

Otherwise, the registrar converts the PVR artifact to a Registrar Voucher-Request (RVR) artifact (see ) and starts the backend interaction with the MASA. Optionally, the domain registrar MAY respond with an HTTP 202 Accepted response status code to the Registrar-Agent at this point following , while the rules defined for the pledge also apply to the Registrar-Agent; in this case, the registrar still continues with the MASA interaction to provide the Voucher artifact to the retry request. The registrar MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent.

MASA Interaction The domain registrar MUST establish a TLS session with mutual authentication to the MASA of the pledge according to . It requests the voucher from the MASA according to via HTTP-over-TLS POST to the MASA endpoint at /.well-known/brski/requestvoucher. The request body MUST contain the RVR artifact as defined in . In the request header, the Content-Type field and the Accept field MUST be set to the same media type as the incoming PVR artifact. For the default format used in this specification, this is application/voucher-jws+json as defined in . The assumption is that a pledge typically supports a single artifact format and creates the PVR in the supported format; to ensure that the pledge is able to process the voucher, the registrar requests this format via the HTTP Accept header field when requesting the voucher. Further, the RVR artifact and the PVR artifact inside should also use the same format to limit the number of required format encoders. Note that BRSKI-PRM allows for alternative formats such as CMS-signed JSON as used in BRSKI or COSE-signed CBOR for constrained environments, when defined by other specifications. Overall, a MASA responsible for BRSKI-PRM capable pledges MUST support the same formats as supported by those pledges. Once the MASA receives the RVR artifact, it MUST perform the verification as described in . Depending on policy, the MASA MAY choose the type of assertion to perform. For the Agent Proximity Assertion of BRSKI-PRM (see ), the MASA MUST skip the verification described in and instead MUST verify for the PVR contained in the prior-signed-voucher-request field of the RVR that

the agent-provided-proximity-registrar-cert field contains an EE certificate that is signed by the same domain owner as the EE certificate/credentials used to sign the RVR; note that this check allows for installations with multiple domain registrars and for registrar EE certificate renewal while PVRs are collected by the Registrar-Agent
the registrar EE certificate in the agent-provided-proximity-registrar-cert field and the Registrar-Agent EE certificate in the agent-sign-cert field of the RVR are signed by the same domain owner.
the agent-signed-data field is signed with the credentials corresponding to the Registrar-Agent EE certificate in the agent-sign-cert field of the RVR; this is done via the SubjectKeyIdentifier of the certificate in the kid Header Parameter of the JWS Protected Header in the agent-signed-data field.
the product-serial-number inside the agent-signed-data is equal to the serial-number field of PVR and the serial-number field of the RVR as well as the X520SerialNumber field of the pledge IDevID certificate, which is contained in the JWS Protected Header of the PVR.

If the agent-sign-cert field in the RVR is not set, the MASA MAY state a lower level assertion value instead of failing the verification, e.g., "logged" or "verified". If the verification fails, the MASA SHOULD respond with an HTTP client error status code to the registrar. The client error status codes are kept the same as defined in :

403 Forbidden: if the voucher-request is not signed correctly or is stale or if the pledge has another outstanding voucher that cannot be overridden
404 Not Found: if the request is for a device that is not known to the MASA
406 Not Acceptable: if a voucher of the desired type or that uses the desired algorithms (as indicated by the "Accept" header fields and algorithms used in the signature) cannot be issued as such because the MASA knows the pledge cannot process that type
415 Unsupported Media Type: if the request uses an artifact format or Accept header value that is not supported by the MASA

Otherwise, the MASA creates a Voucher artifact as defined in and updates the audit-log as described in . The Voucher is then supplied to the registrar within the body of an HTTP 200 OK response according to . In the response header, the Content-Type field MUST be set to the media type of the incoming RVR artifact. For the default format used in this specification, this is application/voucher-jws+json as defined in .

Supply Voucher to Registrar-Agent After receiving the Voucher from the MASA, the registrar SHOULD evaluate it for transparency and logging purposes as outlined in . It then countersigns the Voucher for delivery to the pledge via the Registrar-Agent. The registrar MUST reply to the Registrar-Agent with the Registrar-Countersigned Voucher artifact (Voucher') as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to the media type of the incoming PVR artifact. For the default format used in this specification, this is application/voucher-jws+json as defined in . If the domain registrar is unable to return the Voucher, it MUST respond with an HTTP server error status code to the Registrar-Agent. The following server error status codes SHOULD be used:

500 Internal Server Error: if both Registrar-Agent request and MASA response are valid, but the registrar still failed to return the Voucher, e.g., due to missing configuration or a program failure
502 Bad Gateway: if the registrar received an invalid response from the MASA
503 Service Unavailable: if a simple retry of the Registrar-Agent request might lead to a successful response; this error response SHOULD include the Retry-After response header field with an appropriate value
504 Gateway Timeout: if the backend request to the MASA timed out

Request Artifact: Pledge Voucher-Request (PVR) Identical to the PVR artifact received from the pledge as defined in . The Registrar-Agent MUST NOT modify PVRs.

Backend Request Artifact: Registrar Voucher-Request (RVR) The Registrar Voucher-Request (RVR) artifact SHALL be an extended Voucher-Request artifact based on . The BRSKI-PRM related enhancements of the ietf-voucher-request YANG module are defined in . For the JWS-signed JSON format used by this specification, the RVR artifact MUST be a JWS Voucher structure as defined in , which MUST contain the JSON RVR Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON RVR artifact:

RVR Representation in General JWS JSON Serialization Syntax

JSON RVR Data The JSON RVR Data MUST contain the following fields of the ietf-voucher-request YANG module as defined in ; note that this makes optional leaves in the YANG definition mandatory for the RVR artifact:

created-on: SHALL contain the current date and time at RVR creation as standard date/time string as defined in
nonce: SHALL contain a copy of the nonce field from the JSON PVR Data the registrar provides this information to assure successful verification of Registrar-Agent proximity based on the agent-signed-data
serial-number: SHALL contain the product-serial-number of the pledge; note the required verification by the registrar defined in
idevid-issuer: SHALL contain the issuer value from the pledge IDevID certificate obtained from the PVR JWS Protected Header x5c field
prior-signed-voucher-request: SHALL contain the PVR artifact as received from the Registrar-Agent, see

As BRSKI-PRM uses the Agent Proximity Assertion (see ), the JSON RVR Data MUST also contain the following fields:

assertion: SHALL contain the value agent-proximity to indicate successful verification of the Agent Proximity Assertion (see ) by the registrar
agent-sign-cert: SHALL be a JSON array that contains the base64-encoded Registrar-Agent EE certificate as possessed by the registrar (see ) as the first item; subsequent items MUST contain the corresponding certificate chain for verification at the MASA; the field is used for verification of the agent-signed-data field of the contained PVR

Note that the ietf-voucher-request YANG module defines the leaf agent-sign-cert as binary; this specification refines it as a JSON array structure similar to the x5c Header Parameter defined in . below shows an example for the JSON RVR Data:

JSON RVR Data Example

JWS Protected Header The JWS Protected Header MUST follow the definitions of .

JWS Signature The domain registrar MUST sign the RVR artifact using its EE credentials following the definitions of .

Backend Response Artifact: Voucher The Voucher artifact is defined in (cf. "voucher response"). The only difference for BRSKI-PRM is that the assertion field MAY contain the value agent-proximity as defined in , when the Agent-Proximity Assertion (see ) is performed by the MASA. For the JWS-signed JSON format used by this specification, the Voucher artifact MUST be a JWS Voucher structure as defined in . It contains JSON Voucher Data in the JWS Payload, for which an example is given in :

JSON RVR Data Example

Response Artifact: Registrar-Countersigned Voucher The Registrar-Countersigned Voucher (Voucher') artifact SHALL be an extended Voucher artifact based on using the format defined in . For BRSKI-PRM, the domain registrar MUST add an JWS Protected Header and JWS Signature to the MASA-provided Voucher. summarizes the serialization of the JWS-signed JSON Voucher' artifact:

Voucher' Representation in General JWS JSON Serialization Syntax In BRSKI , the registrar proves possession of its credential through the server authentication within the TLS session with the pledge. While the pledge cannot verify the registrar certificate at the time of TLS session establishment, it can verify the TLS server certificate through the certificate in the pinned-domain-cert field upon receiving the Voucher artifact (see ). In BRSKI-PRM with the Registrar-Agent mediating all communication, this second signature provides verification and POP of the private key for the registrar EE certificate provided in the initial tPVR artifact from the Registrar-Agent (see ). Depending on the security policy of the operator, this signature can also be interpreted as explicit authorization of the registrar to install the contained trust anchor (i.e., pinned domain certificate).

JSON Voucher Data As provided by the MASA inside the JWS Payload. The domain registrar MUST NOT modify the JWS Payload.

JWS Protected Header (Registrar) The registrar-added JWS Protected Header (Registrar) MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded registrar EE certificate used to sign the voucher as well as the certificate chain up to (but not including) the pinned domain certificate (the initial domain trust anchor); the pinned domain certificate is already contained in the JSON Voucher Data

Note that for many installations with a single registrar credential, the registrar EE certificate is pinned.

JWS Signature (Registrar) The signature is created by signing the registrar-added JWS Protected Header (Registrar) and the original JWS Payload produced by the MASA as described in . The registrar MUST use its EE credentials to sign. Note that the credentials need to be the same as used for server authentication in the TLS session with the Registrar-Agent receiving this artifact (see ).

Supply PER to Registrar (including Key Infrastructure interaction) After receiving the Voucher artifact, the Registrar-Agent sends the PER to the domain registrar within the same TLS session. In case the TLS session to the registrar is already closed, the Registrar-Agent establishes a new session as described in . The registrar is able to correlate the PVR and PER artifacts based on the signatures and the contained product-serial-number. Note that this also addresses situations in which a nonceless voucher is used and may be pre-provisioned to the pledge. depicts exchanges for the PER-request handling and the following subsections describe the corresponding artifacts. Note that "Request" and "Certificate" do not denote BRSKI-PRM defined artifacts, but are data objects depending on the certificate management protocol used by the domain Key Infrastructure.

Enroll exchange | | | | |-------PER------>| | | | | |----[Request]--->| | | | |<--[Certificate]-| | | |<--Enroll-Resp---| | | | | | | | ~ ~ ~ ~ ~ ]]> As a second step of the interaction with the domain registrar, the Registrar-Agent SHALL supply the PER artifact(s) to the registrar via HTTP-over-TLS POST to the registrar endpoint at /.well-known/brski/requestenroll. The request body MUST contain one previously acquired PER artifact as defined in . In the request header, the Content-Type field MUST be set to application/jose+json and the Accept field SHOULD be set to application/jose+json. Note that this is different from the EST endpoint used in BRSKI, as the PER artifact is signature-wrapped. Hence, upon receiving a PER artifact, the registrar MUST verify that

the PER was signed with the private key corresponding to the pledge EE certificate, which is contained in the JWS Protected Header of the PER.
the pledge identified by its EE certificate is accepted to join the domain after successful validation of the corresponding PVR.

If the registrar is unable to process the request or validate the PER, it MUST respond with an HTTP client error status code to the Registrar-Agent. The following client error status codes SHOULD be used:

400 Bad Request: if the registrar detects an error in the format of the request
401 Unauthorized: if the signature of the PER cannot be verified
404 Not Found: if the PER is for a device that is not known to the registrar
406 Not Acceptable: if the Accept request header field indicates a type that is unknown or unsupported, e.g., a type other than application/jose+json
415 Unsupported Media Type: if the PER uses an artifact format that is not supported by the registrar, e.g., a type other than application/jose+json

Otherwise, the registrar extracts the PKCS#10 Certificate Signing Request (CSR) inside the PER (see ) and uses the CSR to request a new pledge EE certificate from the domain Key Infrastructure. The exact interaction and exchanged data objects depends on the certificate management protocol used by the Key Infrastructure, and is out of scope for this document. A successful interaction with the Key Infrastructure will result in a pledge EE certificate signed by the domain owner (e.g., LDevID certificate). The registrar MUST reply to the Registrar-Agent with the Enroll-Response (Enroll-Resp) as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/pkcs7-mime. If the domain registrar is unable to return the Enroll-Resp, it MUST respond with an HTTP server error status code to the Registrar-Agent. The following server error status codes SHOULD be used:

500 Internal Server Error: if the Key Infrastructure response is valid, but the registrar still failed to return the Enroll-Resp, e.g., due to missing configuration or a program failure
502 Bad Gateway: if the registrar received an invalid response from the Key Infrastructure
503 Service Unavailable: if a simple retry of the Registrar-Agent request might lead to a successful response; this error response SHOULD include the Retry-After response header field with an appropriate value
504 Gateway Timeout: if the backend request to the Key Infrastructure timed out

Note that while BRSKI-PRM targets the initial enrollment, re-enrollment may be supported similarly with the exception that the current, potentially application-related pledge EE certificate is used instead of the IDevID certificate to sign the PER artifact (see also ). Hence, there is no verification whether the pledge is accepted to join the domain, as the still valid EE certificate signed by the domain owner identifies the pledge as already accepted component of the domain.

Request Artifact: Pledge Enroll-Request (PER) Identical to the PER artifact defined in . The Registrar-Agent MUST NOT modify PERs received from pledges.

Response Artifact: Registrar Enroll-Response (Enroll-Resp) The Enroll-Response (Enroll-Resp) artifact SHALL be an authenticated self-contained object signed by the domain owner, containing a pledge EE certificate. For this specification, the Enroll-Resp artifact MUST be a certs-only CMC Simple PKI Response (PKCS#7) as defined in (following EST ). Note that it only contains the pledge EE certificate, but not the certificate chain. The chain is provided with the CA certificates.

Obtain CA Certificates The pinned domain certificate in the voucher is only the initial trust anchor for only the domain registrar. To fully trust the domain and also to verify its own EE certificate, the pledge also needs the corresponding domain CA certificate(s). A bag of CA certificates signed by the registrar will allow the pledge to verify the authorization to install the received CA certificate(s) through the pinned domain certificate in the voucher. Note that this is a deviation from EST used in BRSKI . The Registrar-Agent obtains this artifact within the same TLS session. In case the TLS session to the registrar is already closed, the Registrar-Agent establishes a new session as described in . The CA certificates do not need to be correlated to a specific voucher or Enroll-Response; they only need to be fresh. shows the acquisition of the CA certificate(s) and the following subsections describe the corresponding artifact.

CA certificates retrieval exchange | | | | |<----caCerts-----| | | | | | | | ~ ~ ~ ~ ~ ]]> As a third step of the interaction with the domain registrar, the Registrar-Agent SHALL obtain the CA-Certificates artifact from the registrar via HTTP-over-TLS GET to the registrar endpoint at /.well-known/brski/wrappedcacerts. In the request header, the Accept field SHOULD be set to application/jose+json. Upon receiving a GET request at /.well-known/brski/wrappedcacerts, the domain registrar MUST reply with the CA-Certificates artifact as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/jose+json.

Request (no artifact) In this exchange, the request is a result of the HTTP(S) default transport for this specification. There is no artifact provided to the registrar.

Response Artifact: CA-Certificates (caCerts) The CA-Certificates (caCerts) artifact SHALL be an authenticated self-contained object signed by the registrar, containing the domain trust anchors and the certificate chain for the pledge domain EE certificate, i.e., the root CA certificate(s) and possibly intermediate certificate(s) as described in . For the JWS-signed JSON format used by this specification, the caCerts artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON CA Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON caCerts artifact:

Voucher' Representation in General JWS JSON Serialization Syntax The JSON CA Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON CA Data The JSON CA Data SHALL be a JSON document that MUST conform with the CDDL data model defined in :

CDDL for JSON CA Data (cacerts) The x5bag member MUST follow the definition of the x5bag COSE Header Parameter in . It is either a single X.509 v3 certificate or an array of at least two X.509 v3 certificates in DER format. For JSON syntax, the octet-based certificates MUST be base64-encoded. It SHALL contain one or more domain CA (root or issuing) certificates. Note that as per , the domain registrar acts as EST server, and hence is expected to possess the CA certificates applicable for the domain and can thus deliver them to the pledge (see ). below shows an example for the JSON CA Data:

JSON CA Data Example

JWS Protected Header The JWS Protected Header of the caCerts artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded registrar EE certificate used to sign the caCerts artifact as well as the certificate chain up to (but not including) the pinned domain certificate

below shows an example for this JWS Protected Header:

JWS Protected Header Example within PER

JWS Signature The registrar MUST sign the caCerts artifact using its EE credentials. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Supply Voucher to Pledge Once the Registrar-Agent has acquired the following three bootstrapping artifacts, it can supply them to the pledge starting with the Voucher':

Voucher': voucher countersigned by the registrar (from MASA via Registrar)
Enroll-Resp: pledge EE certificate signed by the domain owner (from Key Infrastructure via registrar)
caCerts: domain trust anchors (from Key Infrastructure via Registrar)

Reconnecting to the pledge might require to re-discover the pledge as described in . The Registrar-Agent MAY store information from the first connection with the pledge to optimize. Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the provisioning of the voucher to the pledge and the following subsections describe the corresponding artifacts.

Voucher exchange | | | | |<-----Voucher''---| | | | |------vStatus---->| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL supply the voucher to the pledge via HTTP(S) POST to the pledge endpoint at /.well-known/brski/svr. The request body MUST contain the Registrar-Countersigned Voucher (Voucher') artifact previously acquired from the domain registrar as defined in . In the request header, the Content-Type field MUST be set to application/voucher-jws+json as defined in and the Accept field SHOULD be set to application/jose+json. Upon receiving the voucher, the pledge SHALL perform the signature verification in the following order:

Verify the MASA signature as described in against the pre-installed manufacturer trust anchor (e.g., IDevID).
Provisionally install the initial domain trust anchor contained in the pinned-domain-cert field of the voucher.
Validate the registrar EE certificate received in the agent-provided-proximity-registrar-cert field of the previously received tPVR artifact using the pinned domain certificate; this terminates the "provisional state" for the object security within the authenticated self-contained objects that in BRSKI-PRM replace the direct TLS connection to the registrar in BRSKI (see ).
Verify registrar signature of the Voucher' artifact similar as described in , but using the pinned domain certificate instead of the MASA certificate for the verification.

If all steps above complete successfully, the pledge SHALL terminate the "provisional state" for the initial domain trust anchor (i.e., the pinned domain certificate). A nonceless voucher MAY be accepted as in if allowed by the pledge implementation of the manufacturer. After voucher validation and verification, the pledge needs to reply with a status telemetry message as defined in . The pledge MUST generate the Voucher Status (vStatus) artifact as defined in and MUST provide it to the Registrar-Agent in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/jose+json. If the pledge is unable to validate or verify the voucher, it MUST report the reason in the corresponding field of the Voucher Status. If the pledge did not provide voucher status telemetry information after processing the voucher, the Registrar-Agent MAY query the pledge status explicitly as described in . It MAY resend the voucher depending on the Pledge status following the same procedure.

Request Artifact: Registrar-Countersigned Voucher Identical to the Registrar-Countersigned Voucher (Voucher') artifact received from the registrar as defined in . The Registrar-Agent MUST NOT modify countersigned vouchers.

Response Artifact: Voucher Status (vStatus) The Voucher Status (vStatus) artifact SHALL be an authenticated self-contained object signed by the pledge, containing status telemetry as defined in . For the JWS-signed JSON format used by this specification, the vStatus artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON Voucher Status Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON vStatus artifact:

vStatus Representation in General JWS JSON Serialization Syntax The JSON Status Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON Voucher Status Data The JSON Status Data SHALL be a JSON document that MUST conform with the voucherstatus-post CDDL data model defined in :

version: contains a version number for the format and semantics of the other fields; this specification assumes version 1 just like BRSKI
status: contains the boolean value true in case of success and false in case of failure
reason: contains a human-readable message; SHOULD NOT provide information beneficial to an attacker
reason-context: contains a JSON object that provides additional information specific to a failure; in contrast to , MUST be provided; SHOULD NOT provide information beneficial to an attacker

BRSKI-PRM implementations utilize the reason-context field to provide a distinguishable token, which enables the registrar to detect status artifacts provided to the wrong endpoint. For vStatus artifacts, the JSON object in the reason-context field MUST contain the member pvs-details. below shows an example for the JSON Voucher Status Data in case of success and in case of failure:

JSON Voucher Status Data Success Example

JSON Voucher Status Data Failure Example

JWS Protected Header The JWS Protected Header of the vStatus artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded pledge IDevID certificate used to sign the vStatus artifact; it SHOULD also contain the certificate chain for this certificate; if the certificate chain is not included in the x5c Header Parameter, it MUST be available at the domain registrar for verification

below shows an example for this JWS Protected Header:

JWS Protected Header Example within vStatus

JWS Signature The pledge MUST sign the vStatus artifact using its IDevID credential. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Supply CA Certificates to Pledge Before supplying the pledge EE certificate, the Registrar-Agent supplies the domain CA certificates to the pledge, so the pledge can verify its EE certificate in the next exchange. As the CA certificate provisioning is crucial from a security perspective, this exchange SHOULD only be done, if supplying the voucher in the previous exchange () has been successfully processed by the pledge as reflected in the vStatus artifact. Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the provisioning of the CA certificates to the pledge and the following subsections describe the corresponding artifacts.

Certificate provisioning exchange | | | | |<-----caCerts-----| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL provide the bag of CA certificates requested from and signed by the registrar to the pledge by HTTP(S) POST to the pledge endpoint at /.well-known/brski/scac. The request body MUST contain the caCerts artifact as defined in . In the request header, the Content-Type field MUST be set to application/jose+json. Upon receiving valid caCerts artifact, the pledge MUST first verify the signature of the registrar using the initial trust anchor (pinned domain certificate). In the case of success, the pledge MUST install the contained CA certificates as trust anchors as described in . This includes the verification of all intermediate CA certificates (i.e., not self-signed CA certificates). If the pledge is unable to process the caCerts, it SHOULD respond with an HTTP error status code to the Registrar-Agent. The following client error status codes SHOULD be used:

400 Bad Request: if the pledge detects an error in the format of the request
401 Unauthorized: if the signature of the registrar cannot be verified against the installed initial trust anchor (pinned domain certificate)
403 Forbidden: if one of the intermediate CA certificates cannot be verified against the available trust anchors (e.g., self-signed CA certificates)
415 Unsupported Media Type: if the Content-Type request header field indicates a type that is unknown or unsupported, e.g., a type other than application/jose+json

Otherwise, if processing completes successfully, the pledge SHOULD reply with HTTP 200 OK without a response body. The pledge MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent.

Request Artifact: CA-Certificates (caCerts) Identical to the CA-Certificates (caCerts) artifact received from the registrar as defined in . The Registrar-Agent MUST NOT modify CA-Certificates artifacts.

Response (no artifact) In this exchange, the response is a result of the HTTP(S) default transport for this specification. There is no artifact provided to the Registrar-Agent.

Supply Enroll-Response to Pledge After supplying the CA certificates, the Registrar-Agent supplies the pledge EE certificate to the pledge. Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the provisioning of the domain-owner signed EE certificate to the pledge and the following subsections describe the corresponding artifacts.

Enroll-Response exchange | | | | |<---Enroll-Resp---| | | | |-----eStatus----->| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL send the domain-owner signed EE certificate to the pledge by HTTP(S) POST to the pledge endpoint at /.well-known/brski/ser. The request body MUST contain the Enroll-Response (Enroll-Resp) artifact previously acquired from the domain registrar as defined in . In the request header, the Content-Type field MUST be set to application/pkcs7-mime and the Accept field SHOULD be set to application/jose+json. Upon reception, the pledge SHALL verify the received EE certificate using the installed trust anchors. After Enroll-Resp validation and verification, the pledge needs to reply with a status telemetry message as defined in . The pledge MUST generate the Enroll Status (eStatus) artifact as defined in and MUST provide it to the Registrar-Agent in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/jose+json. If the pledge is unable to validate or verify the Enroll-Response, it MUST report the reason in the corresponding field of the Enroll Status.

Request Artifact: Enroll-Response (Enroll-Resp) Identical to the Enroll-Response (Enroll-Resp) artifact received from the registrar as defined in . The Registrar-Agent MUST NOT modify Enroll-Response artifacts.

Response Artifact: Enroll Status (eStatus) The Enroll Status (eStatus) artifact SHALL be an authenticated self-contained object signed by the pledge, containing status telemetry as defined in . For the JWS-signed JSON format used by this specification, the eStatus artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON Enroll Status Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON eStatus artifact:

eStatus Representation in General JWS JSON Serialization Syntax The JSON Enroll Status Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON Enroll Status Data The JSON Status Data SHALL be a JSON document that MUST conform with the enrollstatus-post CDDL data model defined in . The members are the same as for the JSON Voucher Status Data and follow the same definitions as given in (incl. making reason-context mandatory). BRSKI-PRM implementations again utilize the reason-context field to provide a distinguishable token. For eStatus artifacts, the JSON object in the reason-context field MUST contain the member pes-details. below shows an example for the JSON Enroll Status Data in case of success and in case of failure:

JSON Enroll Status Data Success Example

JSON Enroll Status Data Failure Example

JWS Protected Header The JWS Protected Header of the eStatus artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded pledge EE certificate used to sign the eStatus artifact; it SHOULD also contain the certificate chain for this certificate; if the certificate chain is not included in the x5c Header Parameter, it MUST be available at the domain registrar for verification

below shows an example for this JWS Protected Header:

JWS Protected Header Example within eStatus

JWS Signature If the pledge verified the received EE certificate successfully, it MUST sign the eStatus artifact using its new EE credentials. In failure case, the pledge MUST sign it using its IDevID credentials. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Voucher Status Telemetry (including MASA interaction) Once the Registrar-Agent has collected both status artifacts from one or more pledges, it SHALL provide the status information to the domain registrar for further processing, beginning with the voucher status telemetry. In case the TLS session to the registrar is closed, the Registrar-Agent establishes a new session as described in . shows the provisioning of the voucher status information from the pledge(s) to the registrar and the following subsections describe the corresponding artifact and MASA interaction.

Voucher Status telemetry exchange | | | | |-----vStatus---->| | | | | |<----------((mTLS))---------->| | | |-----req device audit-log---->| | | |<------device audit-log-------| | | | | | | | [verify audit-log] | | | | | | | ~ ~ ~ ~ ~ ]]> First, the Registrar-Agent SHALL supply the voucher status telemetry to the registrar via HTTP-over-TLS POST to the registrar endpoint at /.well-known/brski/voucher_status. The request body MUST contain one previously acquired vStatus artifact as defined in . In the request header, the Content-Type field MUST be set to application/jose+json. Upon receiving a vStatus artifact, the registrar MUST process it as described in . Due to the Registrar-Agent in the middle, the registrar MUST in addition verify the signature of the vStatus and that it belongs to an accepted device of the domain based on the serial-number field of the IDevID certificate contained in the JWS Protected Header of the vStatus. According to , the registrar SHOULD respond with an HTTP 200 OK without a response body in the success case or fail with an HTTP error status code. The registrar MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent. The registrar SHOULD proceed with the audit-log request to the MASA as in BRSKI described in .

Request Artifact: Voucher Status (vStatus) Identical to the Voucher Status (vStatus) artifact received from the pledge as defined in . The Registrar-Agent MUST NOT modify vStatus artifacts.

Response (no artifact) In this exchange, the response is a result of the HTTP(S) default transport for this specification. There is no artifact provided to the Registrar-Agent.

Enroll Status Telemetry The Registrar-Agent SHALL complete the sequence of exchanges for bootstrapping with providing the enroll status telemetry to the domain registrar. This status indicates whether the pledge could process the Enroll-Response (pledge EE certificate signed by the domain owner) and holds the corresponding private key. In case the TLS session to the registrar is already closed, the Registrar-Agent establishes a new session as described in . shows the provisioning of the enroll status information from the pledge(s) to the registrar and the following subsections describe the corresponding artifact.

Enroll Status telemetry exchange | | | | |-----eStatus---->| | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL supply the enroll status telemetry to the registrar via HTTP-over-TLS POST to the registrar endpoint at /.well-known/brski/enrollstatus. The request body MUST contain one previously acquired eStatus artifact as defined in . In the request header, the Content-Type field MUST be set to application/jose+json. Upon receiving an eStatus artifact, the registrar MUST process it as described in . Due to the Registrar-Agent in the middle, instead of the BRSKI TLS session with the pledge, the registrar MUST verify the signature of the eStatus artifact and that it belongs to an accepted device of the domain based on the serial-number field of the EE certificate contained in the JWS Protected Header of the eStatus. Note that if the Enroll Status indicates success, the eStatus artifact is signed with the new pledge EE credentials; if it indicates failure, the pledge was unable to process the supplied EE certificate and therefore signed with its IDevID credentials. According to , the registrar SHOULD respond with an HTTP 200 OK in the success case or MAY fail with an HTTP 404 client error status code. The registrar MAY use the response body to signal success/failure details to the service technician operating the Registrar-Agent. If the eStatus indicates failure, 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 pledge EE certificate. An example case for the registrar revoking the issued certificate is when the pledge was not able to verify the received EE certificate and therefore did not accept it for installation.

Request Artifact: Enroll Status (eStatus) Identical to the Enroll Status (eStatus) artifact received from the pledge as defined in . The Registrar-Agent MUST NOT modify eStatus artifacts.

Response (no artifact) In this exchange, the response is a result of the HTTP(S) default transport for this specification. There is no artifact provided to the Registrar-Agent.

Query Pledge Status The following assumes that a Registrar-Agent MAY need to query the overall status of a pledge. This information can be useful to solve errors, when the pledge was not able to connect to the target domain during bootstrapping. A pledge MAY omit the dedicated endpoint for the Query Pledge Status operation (see ). Optionally, TLS MAY be used to provide privacy for this exchange between the Registrar-Agent and the pledge (see ). shows the query and response for the overall pledge status and the following subsections describe the corresponding artifacts.

Pledge Status exchange | | | | |<-----tStatus-----| | | | |------pStatus---->| | | | | | | | | ~ ~ ~ ~ ~ ]]> The Registrar-Agent SHALL query the pledge via HTTP(S) POST to the pledge endpoint at /.well-known/brski/qps. The request body MUST contain the Status Trigger (tStatus) artifact as defined in . In the request header, the Content-Type field MUST be set to application/jose+json and the Accept field SHOULD be set to application/jose+json. If the pledge implements the Query Pledge Status endpoint, it MUST first verify the signature of the tStatus artifact using its trust anchors. If the pledge does not possess any domain trust anchor yet, it MAY skip the signature verification and choose to reply without it. In the case of success, it MUST reply with the Pledge Status (pStatus) artifact as defined in in the body of an HTTP 200 OK response. In the response header, the Content-Type field MUST be set to application/jose+json. If the pledge is unable to create the pStatus artifact, the pledge SHOULD respond with an HTTP error status code to the Registrar-Agent. The following client error status codes SHOULD be used:

400 Bad Request: if the pledge detects an error in the format of the request
401 Unauthorized: if the signature of the Registrar-Agent cannot be verified using the installed trust anchors
406 Not Acceptable: if the Accept request header field indicates a type that is unknown or unsupported, e.g., a type other than application/jose+json
415 Unsupported Media Type: if the Content-Type request header field indicates a type that is unknown or unsupported, e.g., a type other than application/jose+json

The pledge MAY use the response body to signal failure details to the service technician operating the Registrar-Agent.

Request Artifact: Status Trigger (tStatus) The Status Query (tStatus) artifact SHALL be an authenticated self-contained object signed by the pledge, providing status query parameters. For the JWS-signed JSON format used by this specification, the tStatus artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON Status Trigger Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON PER artifact:

tStatus Representation in General JWS JSON Serialization Syntax The JSON Status Trigger Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON Status Trigger Data The JSON Status Trigger Data SHALL be a JSON document that MUST conform with the CDDL data model defined in :

CDDL for JSON Status Trigger Data (statustrigger) The version member is included to permit significant changes to the pledge status artifacts in the future. The format and semantics in this document follow the status telemetry definitions of . Hence, the version SHALL be set to 1. A pledge (or Registrar-Agent) that receives a version larger than it knows about SHOULD log the contents and alert a human. The serial-number member SHALL contain the product-serial-number corresponding to the X520SerialNumber field of the pledge IDevID certificate; it can be correlated with the product-serial-number in the signing certificate contained in the JWS Protected Header of the Pledge Status response artifact. The created-on member SHALL contain the current date and time at tStatus creation as standard date/time string as defined in ; it can be used as reference time for the corresponding Pledge Status response artifact after correlating via the product-serial-number; note that pledges may not have synchronized time to provide the created-on date and time on their own. The status-type allows for specifying which status information is to be returned. As shown in , BRSKI-PRM defines two enumeration values:

bootstrap to query current status information regarding the bootstrapping status (e.g., voucher processing and enrollment of the pledge into a domain)
operation to query current status information regarding the operational status (e.g., utilization of the bootstrapped EE credentials in communication with other peers)

Other specifications using this artifact may define further enumeration values, e.g., to query application-related status. below shows an example for the JSON Status Trigger Data using the status type bootstrap:

JSON Status Trigger Data Example

JWS Protected Header The JWS Protected Header of the tStatus artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded Registrar-Agent EE certificate used to sign the tStatus artifact as well as the certificate chain

below shows an example for this JWS Protected Header:

JWS Protected Header Example within tStatus

JWS Signature The Registrar-Agent MUST sign the tStatus artifact using its EE credentials. The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Response Artifact: Pledge Status (pStatus) The Pledge Status (pStatus) artifact SHALL be an authenticated self-contained object signed by the pledge, containing status telemetry information. The exact content depends on the Status Trigger parameter status-type. For the JWS-signed JSON format used by this specification, the pStatus artifact MUST use the "General JWS JSON Serialization Syntax" defined in , which MUST contain the JSON Pledge Status Data defined in in the JWS Payload. summarizes the serialization of the JWS-signed JSON PER artifact:

pStatus Representation in General JWS JSON Serialization Syntax The JSON Pledge Status Data MUST be UTF-8 encoded to become the octet-based JWS Payload defined in . The JWS Payload is further base64url-encoded to become the string value of the payload member as described in . The octets of the UTF-8 representation of the JWS Protected Header are base64url-encoded to become the string value of the protected member. The generated JWS Signature is base64url-encoded to become the string value of the signature member.

JSON Pledge Status Data The JSON Pledge Status Data SHALL be a JSON document that MUST conform with the CDDL data model defined in , which has the same members as the voucherstatus-post CDDL defined in and the enrollstatus-post CDDL defined in .

CDDL for JSON Pledge Status Data (pledgestatus) The version member follows the definition in (same as in JSON Status Query Data). The reason and reason-context members follow the definitions in , i.e., in contrast to , reason-context MUST be provided. The new pStatus artifact also utilizes the reason-context field to provide a distinguishable token. For pStatus artifacts, the JSON object in the reason-context field MUST contain either the

pbs-details member for status information corresponding to the status-type bootstrap, or the
pos-details member for status information corresponding to the status-type operation (see )

Other documents may add additional reason-context members correlating to other statustrigger status-types or to include further status information. For the pbs-details member, the following values with the given semantics are defined, while additional information MAY be provided in the top-level reason member:

factory-default: Pledge has not been bootstrapped. The pledge signs the response message using its IDevID certificate/credentials.
voucher-success: Pledge processed the voucher exchange successfully. The pledge signs the response message using its IDevID certificate/credentials.
voucher-error: Pledge voucher processing terminated with error. Additional information may be provided in the reason or reason-context members. The pledge signs the response message using its IDevID certificate/credentials.
enroll-success: Pledge processed the enrollment exchange successfully. Additional information may be provided in the reason or reason-context members. The pledge signs the response message using its domain-owner signed EE certificate/credentials.
enroll-error: Pledge enrollment-response processing terminated with error. Additional information may be provided in the reason or reason-context members. The pledge signs the response message using its IDevID certificate/credentials.

The pbs-details values SHALL be cumulative in the sense that enroll-success and enroll-error imply voucher-success. below provides an example for bootstrap status information in the JSON Pledge Status Data:

status-bootstrap JSON Pledge Status Data Example For the pos-details member, the following values with the given semantics are defined, while additional information MAY be provided in the top-level reason member:

connect-success: Pledge could successfully establish a connection to another peer. The pledge signs the response message using its domain-owner signed EE certificate/credentials.
connect-error: Pledge connection establishment terminated with error. The pledge signs the response message using its domain-owner signed EE certificate/credentials.

below provides an example for operational status information in the JSON Pledge Status Data:

status-operation JSON Pledge Status Data Example

JWS Protected Header The JWS Protected Header of the pStatus artifact MUST contain the following standard Header Parameters as defined in :

alg: SHALL contain the algorithm type used to create the signature, e.g., ES256, as defined in
x5c: SHALL contain the base64-encoded pledge EE certificate used to sign the pStatus artifact; it SHOULD also contain the certificate chain for this certificate; if the certificate chain is not included in the x5c Header Parameter, it MUST be available at the Registrar-Agent for verification

below shows an example for this JWS Protected Header:

JWS Protected Header Example within pStatus

JWS Signature The pledge MUST sign the tStatus artifact using its IDevID or domain-owner signed EE credentials according to its bootstrapping status as defined in . The JWS Signature is generated over the JWS Protected Header and the JWS Payload as described in .

Logging Considerations The registrar SHOULD log certain events to provide an audit trail for the onboarding of pledges into its domain. This audit trail may support the root cause analysis in case of device or system failures. Recommend key events for logging comprise

Communication attempts between the pledge, Registrar-Agent, and registrar.
Protocol handshakes and onboarding steps.
Voucher requests and responses.
Authentication successes or failures.

The logging SHOULD include the identity of the pledge, the identity of the Registrar-Agent that was interacting with the pledge, and relevant artifact fields, in particular telemetry information:

PVR received from Registrar-Agent
Acceptance of a pledge into the domain
Voucher provided to Registrar-Agent
PER received from Registrar-Agent
Pledge EE certificate requested
Pledge EE certificate received from Domain CA
Pledge EE certificate provided to Registrar-Agent
CA Certificates provided to Registrar-Agent
Voucher Status received from Registrar-Agent
Enroll Status received from Registrar-Agent
Pledge Status received from Registrar-Agent
Pledge EE certificate revoked

Furthermore, it is recommended to

support adjustable logging levels (severity) to cater to different operational needs or failure situations.
include meta information to distinguish logs that relate to different BRSKI approaches (e.g., BRSKI, BRSKI-AE, BRSKI-PRM, constraint BRSKI) that are likely supported in the same domain in parallel.
include detailed error codes and diagnostics information as defined throughout the document or stemming from other used components or libraries also in the logging information.
support synchronized time (e.g., via NTP) to include timestamps in logging to enable sequencing and correlation of events.
utilize standard logging formats (e.g., syslog) to allow for easy integration into log analysis tools and SIEM systems.
utilize secure transmission of logs to centralized log servers, particularly in cloud or distributed environments (e.g., in case of syslog, updates the utilized cipher suites for TLS and DTLS).
allow for definition of key operational thresholds (e.g., high latency, failed onboarding attempts) to trigger alerts for proactive issue resolution.
avoid inclusion of sensitive information (see also )

For log analysis the following may be considered:

The registrar knows which Registrar-Agent collected which PVR from the included agent-signed-data object.
The registrar always knows the connecting Registrar-Agent from the TLS client authentication using the Registrar-Agent EE certificate and can log it accordingly.
The telemetry information from the pledge can be correlated to the voucher through the product-serial-number in the EE certificate contained in the JWS Protected Header of the status artifacts and the product-serial-number contained in the voucher. By this it can also be related to the PER.

With this, it can for instance be analyzed if multiple Registrar-Agents are involved in bootstrapping devices. In addition, within the domain it can be analyzed, if the onboarding involved different Registrar-Agents or if different registrars have been used.

Operational Considerations As outlined in BRSKI-PRM introduces an additional component with the Registrar-Agent in the BRSKI architecture in addition to new modes of interaction to facilitate the communication between the pledge and the registrar. This has an influence on the configuration and operation not only of the Registrar-Agent, but also for the registrar and the pledge. As outlined in there are additional configuration items dues to the introduction of the Registrar-Agent. This may increase operational complexity and potential misconfigurations in deploying and managing this entity.

A Registrar-Agent needs to be provided with a Registrar-Agent EE certificate, the domain registrar EE certificate and the list of pledges. BRSKI-PRM is open regarding the selected provisioning method, which may be automated or by configuration.
Pledges may support either BRSKI-PRM only or combined with other modes of operation.
Registrars may support either BRSKI-PRM only or combined with other BRSKI modes of operation. The distinction of BRSKI and BRSKI-PRM is done based on the provided endpoints of the registrar. An operator deploying pledges with a mixed set of operation need to ensure that the domain registrar supports all necessary options to ensure bootstrapping of pledges depending of the supported operational mode.
In addition, registrars may support a co-located Registrar-Agent, if nomadic operation of the Registrar-Agent is not required. This facilitates situations in which an operator wants to deploy BRSKI pledges acting as clients and BSKI pledges acting as servers.

With the Registrar-Agent enhancement a new component is introduced in the communication path between the pledge and the registrar. This likely increases the latency of the communication between the pledge and the registrar. The increase in latency due to this additional component may be neglected given that the Registrar-Agent operates with nomadic connectivity as outlined in . Besides the above, also consider the existing documents on operational modes for

BRSKI registrars in
BRSKI MASA in

IANA Considerations This document requires the following IANA actions.

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

Path Segment	Description	Reference
requestenroll	Supply PER to registrar	[THISRFC]
wrappedcacerts	Obtain wrapped CA certificates	[THISRFC]
tpvr	Trigger Pledge Voucher-Request	[THISRFC]
tper	Trigger Pledge Enroll-Request	[THISRFC]
svr	Supply voucher to pledge	[THISRFC]
scac	Supply CA certificates to pledge	[THISRFC]
ser	Supply Enroll-Response to pledge	[THISRFC]
qps	Query pledge status	[THISRFC]

DNS Service Names IANA has registered the following service names: Service Name: brski-pledge
Transport Protocol(s): tcp
Assignee: IESG iesg@ietf.org
Contact: IESG iesg@ietf.org
Description: The Bootstrapping Remote Secure Key Infrastructure Pledge
Reference: [THISRFC]

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

the introduction of the additional component Registrar-Agent
potentially no transport layer security between Registrar-Agent and pledge

describes to optionally apply TLS to protect the communication between the Registrar-Agent and the pledge. The following is therefore applicable to the communication without the TLS protection. The credentials 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 EE certificate associated with the commissioning device instead of an EE certificate associated with the service technician operating the device. This avoids revealing potentially included personal information to Registrar and MASA. As logging is recommended to better handle failure situations, it is necessary to avoid capturing sensitive or personal data. Privacy-preserving measures in logs SHOULD be applied, such as: * Avoid logging personally identifiable information unless unavoidable. * Anonymize or pseudonymize data where possible. 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 (an "oppressive observer"). 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 easily be eavesdropped, if the wireless network is not encrypted. Even if the wireless network is encrypted, if it uses a network-wide key, then layer-2 attacks (ARP/ND spoofing) could insert an 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.

Security Considerations In general, the security considerations of 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

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. Because in BRSKI-PRM the pledge responds to requests from real or illicit Registrar-Agents, pledges are more subject to DoS-attacks from Registrar-Agents in BRSKI-PRM than they are from illicit registrars in , where pledges do initiate the connections. A DoS attack with a faked Registrar-Agent may block the bootstrapping of the pledge due changing state on the pledge (the pledge may produce a voucher-request, and refuse to produce another one). One mitigation may be that the pledge does not limit the number of voucher-requests it creates until at least one has finished. An alternative may be that the onboarding state may expire after a certain time, if no further interaction has happened. In addition, the pledge may assume that repeated triggering for PVR are the result of a communication error with the Registrar-Agent. In that case the pledge MAY simply resend the PVR previously sent. Note that in case of re-sending, a contained nonce and also the contained agent-signed-data in the PVR would consequently be reused.

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 pledge IDevID certificate. (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 Registrar-Agent EE certificate data contained in the PVR. Mis-binding of a pledge by a faked domain registrar is countered as described in BRSKI security considerations .

Misuse of Registrar-Agent Concerns of misuse of a Registrar-Agent with a valid Registrar-Agent EE certificate may be addressed by utilizing short-lived certificates (e.g., valid for a day) to authenticate the Registrar-Agent against the domain registrar. The Registrar-Agent EE certificate may have been acquired by a prior BRSKI run for the Registrar-Agent, if an IDevID is available on Registrar-Agent. Alternatively, the Registrar-Agent EE certificate may be acquired by a service technician from the domain PKI system in an authenticated way. In addition, it is required that the Registrar-Agent EE 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 rogue pledge at a later point in time. In this misuse "agent-signed-data" could be dated after the validity time of the Registrar-Agent EE 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 Registrar-Agent EE 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. If the registrar detects a mismatch in the utilized certificates, it may conclude the usage of either an outdated "agent-signed-data" component in the PVR or a man-in-the-middle attack by a potentially unauthorized Registrar-Agent.

Misuse of DNS-SD with mDNS to obtain list of pledges To discover a specific pledge a Registrar-Agent may query the Service Type in combination with the product-serial-number of a specific pledge, e.g., in the Service Instance Name or Service Subtype. The pledge reacts on this if its product-serial-number is part of the query 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 an LDevID or to not support this feature at all, to avoid an enumeration in an operative domain.

YANG Module Security Considerations The enhanced voucher-request described in is based on , but uses a different encoding based on . The security considerations as described in (Security Considerations) apply. The YANG module specified in defines the schema for data that is subsequently encapsulated by a JOSE signed-data Content-type as described in . As such, all of the YANG-modeled data is protected against modification. The use of YANG to define data structures via the "structure" statement, is relatively new and distinct from the common use of YANG to define an API accessed by network management protocols such as NETCONF and RESTCONF . For this reason, these guidelines do not follow the template described by (Security Considerations).

Acknowledgments We would like to thank the various reviewers, in particular Brian E. Carpenter, Charlie Kaufman (Early SECDIR review), Martin Björklund (Early YANGDOCTORS review), Marco Tiloca (Early IOTDIR review), Oskar Camenzind, Hendrik Brockhaus, and Ingo Wenda for their input and discussion on use cases and call flows. Further review input was provided by Jesser Bouzid, Dominik Tacke, Christian Spindler, and Julian Krieger. Special thanks to Esko Dijk for the in deep review and the improving proposals. Another special thanks for the detailed Shepherad review and connected discussions to Matthias Kovatsch. Support in PoC implementations and comments resulting from the implementation was provided by Hong Rui Li and He Peng Jia. Review comments in the context of a formal analysis of BRSKI-PRM have been provided by Marco Calipari.

References Normative References Certificate Management over CMS (CMC) This document defines the base syntax for CMC, a Certificate Management protocol using the Cryptographic Message Syntax (CMS). This protocol addresses two immediate needs within the Internet Public Key Infrastructure (PKI) community: 1. The need for an interface to public key certification products and services based on CMS and PKCS #10 (Public Key Cryptography Standard), and 2. The need for a PKI enrollment protocol for encryption only keys due to algorithm or hardware design. CMC also requires the use of the transport document and the requirements usage document along with this document for a full definition. [STANDARDS-TRACK] Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] Multicast DNS As networked devices become smaller, more portable, and more ubiquitous, the ability to operate with less configured infrastructure is increasingly important. In particular, the ability to look up DNS resource record data types (including, but not limited to, host names) in the absence of a conventional managed DNS server is useful. Multicast DNS (mDNS) provides the ability to perform DNS-like operations on the local link in the absence of any conventional Unicast DNS server. In addition, Multicast DNS designates a portion of the DNS namespace to be free for local use, without the need to pay any annual fee, and without the need to set up delegations or otherwise configure a conventional DNS server to answer for those names. The primary benefits of Multicast DNS names are that (i) they require little or no administration or configuration to set them up, (ii) they work when no infrastructure is present, and (iii) they work during infrastructure failures. DNS-Based Service Discovery This document specifies how DNS resource records are named and structured to facilitate service discovery. Given a type of service that a client is looking for, and a domain in which the client is looking for that service, this mechanism allows clients to discover a list of named instances of that desired service, using standard DNS queries. This mechanism is referred to as DNS-based Service Discovery, or DNS-SD. Enrollment over Secure Transport This document profiles certificate enrollment for clients using Certificate Management over CMS (CMC) messages over a secure transport. This profile, called Enrollment over Secure Transport (EST), describes a simple, yet functional, certificate management protocol targeting Public Key Infrastructure (PKI) clients that need to acquire client certificates and associated Certification Authority (CA) certificates. It also supports client-generated public/private key pairs as well as key pairs generated by the CA. JSON Web Signature (JWS) JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. Well-Known Uniform Resource Identifiers (URIs) This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes. In doing so, it obsoletes RFC 5785 and updates the URI schemes defined in RFC 7230 to reserve that space. It also updates RFC 7595 to track URI schemes that support well-known URIs in their registry. Bootstrapping Remote Secure Key Infrastructure (BRSKI) This document specifies automated bootstrapping of an Autonomic Control Plane. To do this, a Secure Key Infrastructure is bootstrapped. This is done using manufacturer-installed X.509 certificates, in combination with a manufacturer's authorizing service, both online and offline. We call this process the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol. Bootstrapping a new device can occur when using a routable address and a cloud service, only link-local connectivity, or limited/disconnected networks. Support for deployment models with less stringent security requirements is included. Bootstrapping is complete when the cryptographic identity of the new key infrastructure is successfully deployed to the device. The established secure connection can be used to deploy a locally issued certificate to the device as well. CBOR Object Signing and Encryption (COSE): Header Parameters for Carrying and Referencing X.509 Certificates The CBOR Object Signing and Encryption (COSE) message structure uses references to keys in general. For some algorithms, additional properties are defined that carry parameters relating to keys as needed. The COSE Key structure is used for transporting keys outside of COSE messages. This document extends the way that keys can be identified and transported by providing attributes that refer to or contain X.509 certificates. Conveying a Certificate Signing Request (CSR) in a Secure Zero-Touch Provisioning (SZTP) Bootstrapping Request This document extends the input to the "get-bootstrapping-data" RPC defined in RFC 8572 to include an optional certificate signing request (CSR), enabling a bootstrapping device to additionally obtain an identity certificate (e.g., a Local Device Identifier (LDevID) from IEEE 802.1AR) as part of the "onboarding information" response provided in the RPC-reply. JWS signed Voucher Artifacts for Bootstrapping Protocols Siemens AG Sandelman Software Works This document introduces a variant of the RFC8366 voucher artifact in which CMS is replaced by the JSON Object Signing and Encryption (JOSE) mechanism described in RFC7515. This supports deployments in which JOSE is preferred over CMS. In addition to specifying the format, the "application/voucher-jws+json" media type is registered and examples are provided. A Voucher Artifact for Bootstrapping Protocols Watsen Networks Sandelman Software Cisco Systems Futurewei Technologies Inc. Huawei This document defines a strategy to securely assign a pledge to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher". This document defines an artifact format as a YANG-defined JSON or CBOR document that has been signed using a variety of cryptographic systems. The voucher artifact is normally generated by the pledge's manufacturer (i.e., the Manufacturer Authorized Signing Authority (MASA)). This document updates RFC8366, merging a number of extensions into the YANG. The RFC8995 voucher request is also merged into this document. Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The JavaScript Object Notation (JSON) Data Interchange Format JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. Date and Time on the Internet: Timestamps This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar. JSON Encoding of Data Modeled with YANG This document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text. Informative References PKCS #10: Certification Request Syntax Specification Version 1.7 This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community. UTF-8, a transformation format of ISO 10646 ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279. Service Identity in TLS Many application technologies enable secure communication between two entities by means of Transport Layer Security (TLS) with Internet Public Key Infrastructure using X.509 (PKIX) certificates. This document specifies procedures for representing and verifying the identity of application services in such interactions. This document obsoletes RFC 6125. Network Configuration Protocol (NETCONF) The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] The Constrained Application Protocol (CoAP) The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. RESTCONF Protocol This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). Guidelines for Authors and Reviewers of Documents Containing YANG Data Models This memo provides guidelines for authors and reviewers of specifications containing YANG modules. Recommendations and procedures are defined, which are intended to increase interoperability and usability of Network Configuration Protocol (NETCONF) and RESTCONF protocol implementations that utilize YANG modules. This document obsoletes RFC 6087. Handling Long Lines in Content of Internet-Drafts and RFCs This document defines two strategies for handling long lines in width-bounded text content. One strategy, called the "single backslash" strategy, is based on the historical use of a single backslash ('\') character to indicate where line-folding has occurred, with the continuation occurring with the first character that is not a space character (' ') on the next line. The second strategy, called the "double backslash" strategy, extends the first strategy by adding a second backslash character to identify where the continuation begins and is thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content. GeneRic Autonomic Signaling Protocol (GRASP) This document specifies the GeneRic Autonomic Signaling Protocol (GRASP), which enables autonomic nodes and Autonomic Service Agents to dynamically discover peers, to synchronize state with each other, and to negotiate parameter settings with each other. GRASP depends on an external security environment that is described elsewhere. The technical objectives and parameters for specific application scenarios are to be described in separate documents. Appendices briefly discuss requirements for the protocol and existing protocols with comparable features. CBOR Object Signing and Encryption (COSE): Structures and Process Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. HTTP Semantics The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. Loading Manufacturer Usage Description (MUD) URLs from QR Codes This informational document details a protocol to load Manufacturer Usage Description (MUD) definitions from RFC 8520 for devices that do not have them integrated. This document is published to inform the Internet community of this mechanism to allow interoperability and to serve as a basis of other standards work if there is interest. Updates to the Cipher Suites in Secure Syslog RFCs 5425 and 6012 describe using TLS and DTLS to securely transport syslog messages. This document updates the cipher suites required by RFC 5245 (TLS Transport Mapping for Syslog) and RFC 6012 (DTLS Transport Mapping for Syslog). It also updates the protocol recommended by RFC 6012 for secure datagram transport. BRSKI-AE: Alternative Enrollment Protocols in BRSKI Siemens AG Siemens AG Siemens AG This document defines enhancements to the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol, known as BRSKI-AE (Alternative Enrollment). BRSKI-AE extends BRSKI to support certificate enrollment mechanisms instead of the originally specified use of EST. It supports certificate enrollment protocols, such as CMP, that use authenticated self-contained signed objects for certification messages, allowing for flexibility in network device onboarding scenarios. The enhancements address use cases where the existing enrollment mechanism may not be feasible or optimal, providing a framework for integrating suitable alternative enrollment protocols. This document also updates the BRSKI reference architecture to accommodate these alternative methods, ensuring secure and scalable deployment across a range of network environments. EAP defaults for devices that need to onboard FreeRADIUS Sandelman Software Works This document describes a method by which an unconfigured device can use EAP to join a network on which further device onboarding, network attestation or other remediation can be done. While RFC 5216 supports EAP-TLS without a client certificate, that document defines no method by which unauthenticated EAP-TLS can be used. This draft addresses that issue. First, by defining the @eap.arpa domain, and second by showing how it can be used to provide quarantined network access for onboarding unauthenticated devices. Operational Considerations for Voucher infrastructure for BRSKI MASA Sandelman Software Works Huawei Technologies This document describes a number of operational modes that a BRSKI Manufacturer Authorized Signing Authority (MASA) may take on. Each mode is defined, and then each mode is given a relevance within an over applicability of what kind of organization the MASA is deployed into. This document does not change any protocol mechanisms. Operational Considerations for BRSKI Registrar Sandelman Software Works Huawei Technologies This document describes a number of operational modes that a BRSKI Registration Authority (Registrar) may take on. Each mode is defined, and then each mode is given a relevance within an over applicability of what kind of organization the Registrar is deployed into. This document does not change any protocol mechanisms. This document includes operational advice about avoiding unwanted consequences. BRSKI discovery and variations Futurewei USA IoTconsultancy.nl This document specifies how BRSKI entities, such as registrars, proxies, pledges or others that are acting as responders, can be discovered and selected by BRSKI entities acting as initiators, especially in the face of variations in the protocols that can introduce non-interoperability when not equally supported by both responder and initiator. IEEE 802.1AR Secure Device Identifier Institute of Electrical and Electronics Engineers Abstract BRSKI-PRM Protocol Overview can an on-path attacker drop traffic? n.d. Android Developer: Connect devices wirelessly n.d. Security with Network Protocols n.d. Lightweight Certificate Management Protocol (CMP) Profile This document aims at simple, interoperable, and automated PKI management operations covering typical use cases of industrial and Internet of Things (IoT) scenarios. This is achieved by profiling the Certificate Management Protocol (CMP), the related Certificate Request Message Format (CRMF), and transfer based on HTTP or Constrained Application Protocol (CoAP) in a succinct but sufficiently detailed and self-contained way. To make secure certificate management for simple scenarios and constrained devices as lightweight as possible, only the most crucial types of operations and options are specified as mandatory. More specialized or complex use cases are supported with optional features. The Base16, Base32, and Base64 Data Encodings This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK] Bidirectional Forwarding Detection (BFD) for Virtual eXtensible Local Area Network (VXLAN) This document describes the use of the Bidirectional Forwarding Detection (BFD) protocol in point-to-point Virtual eXtensible Local Area Network (VXLAN) tunnels used to form an overlay network. A Taxonomy of operational security considerations for manufacturer installed keys and Trust Anchors Sandelman Software Works This document provides a taxonomy of methods used by manufacturers of silicon and devices to secure private keys and public trust anchors. This deals with two related activities: how trust anchors and private keys are installed into devices during manufacturing, and how the related manufacturer held private keys are secured against disclosure. This document does not evaluate the different mechanisms, but rather just serves to name them in a consistent manner in order to aid in communication. RFCEDITOR: please remove this paragraph. This work is occurring in https://github.com/mcr/idevid-security-considerations

Examples These examples are folded according to Single Backslash rule.

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: 2973 bytes

Example Pledge-Voucher-Request - PVR

Example Parboiled Registrar Voucher-Request (RVR) - from Registrar to MASA The term parboiled refers to food which is partially cooked. In , 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: 7533 bytes

Example Registrar-Voucher-Request - RVR

Example Voucher - 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

Example Voucher-Response from MASA

Example Voucher, 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: 2994 bytes

Example Voucher-Response from MASA, with additional Registrar signature

HTTP-over-TLS operations between Registrar-Agent and Pledge The use of HTTP-over-TLS between Registrar-Agent and pledge has been identified as an optional mechanism. Provided that the key-agreement in the underlying TLS protocol connection can be properly authenticated, the use of TLS provides privacy for the voucher and enrollment operations between the pledge and the Registrar-Agent. The authenticity of the onboarding and enrollment is not dependent upon the security of the TLS connection. The use of HTTP-over-TLS is not mandated by this document for two main reasons:

A certificate is generally required in order to do TLS. While there are other modes of authentication including PSK, various EAP methods, and raw public key, they do not help as there is no previous relationship between the Registrar-Agent and the pledge.
The pledge can use its IDevID certificate to authenticate itself, but DNS-ID methods do not apply, as the pledge does not have a FQDN, and hence cannot be identified by DNS name. Instead a new mechanism is required, which authenticates the X520SerialNumber DN attribute that must be present in every IDevID.

If the Registrar-Agent has a pre-configured list of which product-serial-number(s), from which manufacturers it expects to see, then it can attempt to match this pledge against a list of potential devices. In many cases only the list of manufacturers is known ahead of time, so at most the Registrar-Agent can show the X520SerialNumber to the (human) operator who may then attempt to confirm that they are standing in front of a device with that product-serial-number. The use of scannable QR codes may help automate this in some cases. The CA used to sign the IDevID will be a manufacturer private PKI as described in . The anchors for this PKI will never be part of the public WebPKI anchors which are distributed with most smartphone operating systems. A Registrar-Agent application will need to use different APIs in order to initiate an HTTPS connection without performing WebPKI verification. The application will then have to do its own certificate chain verification against a store of manufacturer trust anchors. In the Android ecosystem this involves use of a customer TrustManager: many application developers do not create these correctly, and there is significant push to remove this option as it has repeatedly resulted in security failures (see ). Also note that an Extended Key Usage (EKU) for TLS WWW Server authentication cannot be expected in the pledge IDevID certificate. IDevID certificates are intended to be widely usable and EKU does not support that use.

History of Changes [RFC Editor: please delete] Proof of Concept Code available From IETF draft 16 -> IETF draft 17:

updated formatting of key events in
updated reference to corresponding sections for JWS Header and Signature in in and
simplified description for JWS Protected Header aligning with the update in draft-ietf-anima-jws-voucher-15 to always include the certificate chain in and

From IETF draft 15 -> IETF draft 16:

issue #135: corrections from IOTDIR review (clarification regarding minimum supported discovery in , clarification regarding CDDl notation in and editorial nits.
updated references (draft-ietf-netconf-sztp-csr became RFC 9646, included RFC 9662, operational considerations drafts for registrar and MASA)
AD review: included term Registrar-Agent in Terminology section
AD review: enhanced interaction information in and
AD review: included new section on to outline operational considerations
AD review: enhanced with more detailed recommendations on logging
AD review: enhanced with enhanced recommendations concerning logging
AD review: enhanced with more information about misuse of the Registrar-Agent
IOTDIR/OPSDIR/AD review: addressed various nits received throughout the draft

From IETF draft 14 -> IETF draft 15:

issue #134: editorial clarifications on references to in and

From IETF draft 13 -> IETF draft 14:

Update of the examples in to align with the defined prototypes
Changes incorporated based on Shepherd review PR #133:
- Terminology alignment and clarification throughout the document to use terms more consistently
- Restructuring of for protocol steps to align to the general approach: Overview, data description, CDDL description (if necessary), JWS Header an Signature. This lead to some movement of text between existing and new subsections.
- Inclusion of new section on logging hints to give recommendations on which events to be logged for auditing
- Alignment of pledge status response data across , , and .
- Included MASA component in description of affected components in
- Moved host header field handling from to as generally applicable
- Updated status artifacts (vStatus, eStatus, pStatus) to align with BRSKI CDDL definition, but made reason-context mandatory to have distinguishable objects for the registrar-agent
- Correction of terminology of local host name vs. service instance name in
Update of informative references and nits

From IETF draft 12 -> IETF draft 13:

Deleted figure in Section "Request Artifact: Pledge Voucher-Request Trigger (tPVR)" for JSON representation of tPVR, as it has been replaced by CDDL
Updated reason-content description in status response messages (enroll-status, voucher-status, and status-response).
Updated CDDL source code integration to allow for automatic verification
Reordered description in in to better match the order of communication and artifact processing.
Updated CDDL for the request-enroll trigger in according to the outcome of the interim ANIMA WG meeting discussions on April 19, 2024
Included statement in for using the advanced created-on time from the agent-signed-data also for the PER, when the pledge has no synchronized clock

From IETF draft 11 -> IETF draft 12:

Updated acknowledgments to reflect early reviews
Addressed Shepherd review part 2 (Pull Request #132); containing: terminology alignment, structural improvements of the document; deletion of leftovers from previous draft versions; change of definitions to CDDL, when no YANG is available

From IETF draft 10 -> IETF draft 11:

issue #79, clarified that BRSKI discovery in the context of BRSKI-PRM is not needed in .
issue #103, removed step 6 in verification handling for the wrapped CA certificate provisioning as only applicable after enrollment
issue #128: included notation of nomadic operation of the Registrar-Agent in , including proposed text from PR #131
issue #130, introduced DNS service discovery name for brski_pledge to enable discovery by the Registrar-Agent in
removed unused reference RFC 5280
removed site terminology
deleted duplicated text in
clarified registrar discovery and relation to BRSKI-Discovery in
clarified discovery of pledges by the Registrar-Agent in , deleted reference to GRASP as handled in BRSKI-Discovery
addressed comments from SECDIR early review

From IETF draft 09 -> IETF draft 10:

issue #79, clarified discovery in the context of BRSKI-PRM and included information about future discovery enhancements in a separate draft in .
issue #93, included information about conflict resolution in mDNS and GRASP in
issue #103, included verification handling for the wrapped CA certificate provisioning in
issue #106, included additional text to elaborate more the registrar status handling in and
issue #116, enhanced DoS description in
issue #120, included statement regarding pledge host header processing in
issue #122, availability of product-serial-number information on registrar agent clarified in
issue #123, Clarified usage of alternative voucher formats in
issue #124, determination of pinned domain certificate done as in RFC 8995 included in
issue #125, remove strength comparison of voucher assertions in and
issue #130, aligned the usage of site and domain throughout the document
changed naming of registrar certificate from LDevID(RegAgt) to Registrar-Agent EE certificate throughout the document
change x5b to x5bag according to
updated JSON examples -> "signature": BASE64URL(JWS Signature)

From IETF draft 08 -> IETF draft 09:

issue #80, enhanced with clarification on the product-serial-number and the inclusion of GRASP
issue #81, enhanced introduction with motivation for agent_signed_data
issue #82, included optional TLS protection of the communication link between Registrar-Agent and pledge in the introduction , and
issue #83, enhanced and with note to re-enrollment
issue #87, clarified available information at the Registrar-Agent in
issue #88, clarified, that the PVR in and PER in may contain the certificate chain. If not contained it MUST be available at the registrar.
issue #91, clarified that a separate HTTP connection may also be used to provide the PER in
resolved remaining editorial issues discovered after WGLC (responded to on the mailing list in Reply 1 and Reply 2) resulting in more consistent descriptions
issue #92: kept separate endpoint for wrapped CSR on registrar
issue #94: clarified terminology (possess vs. obtained)
issue #95: clarified optional IDevID CA certificates on Registrar-Agent
issue #96: updated exchangesfig_uc2_3 to correct to just one CA certificate provisioning
issue #97: deleted format explanation in exchanges_uc2_3 as it may be misleading
issue #99: motivated verification of second signature on voucher in
issue #100: included negative example in
issue #101: included handling if voucher telemetry information has not been received by the Registrar-Agent
issue #102: relaxed requirements for CA certs provisioning in
issue #105: included negative example in
issue #107: included example for certificate revocation in
issue #108: renamed heading to Pledge-Status Request of
issue #111: included pledge-status response processing for authenticated requests in
issue #112: added "Example key word in pledge-status response in
issue #113: enhanced description of status reply for "factory-default" in
issue #114: Consideration of optional TLS usage in Privacy Considerations
issue #115: Consideration of optional TLS usage in Privacy Considerations to protect potentially privacy related information in the bootstrapping like status information, etc.
issue #116: Enhanced DoS description and mitigation options in security consideration section
updated references

From IETF draft 07 -> IETF draft 08:

resolved editorial issues discovered after WGLC (still open issues remaining)
resolved first comments from the Shepherd review as discussed in PR #85 on the ANIMA github

From IETF draft 06 -> IETF draft 07:

WGLC resulted in a removal of the voucher enhancements completely from this document to RFC 8366bis, containing all enhancements and augmentations of the voucher, including the voucher-request as well as the tree diagrams
smaller editorial corrections

From IETF draft 05 -> IETF draft 06:

Update of list of reviewers
Issue #67, shortened the pledge endpoints to prepare for constraint deployments
Included table for new endpoints on the registrar in the overview of the Registrar-Agent
addressed review comments from SECDIR early review (terminology clarifications, editorial improvements)
addressed review comments from IOTDIR early review (terminology clarifications, editorial improvements)

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 LDevID 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 LDevID 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 , IANA considerations and section
Included examples for several objects in section 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 , issue #19
Removed join proxy in 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 ; also added new required registrar endpoint (section 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
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 and section The verification of multiple signatures is described in section
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
Removed open issue regarding handling of multiple CSRs and Enroll-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 and exchanges_uc2_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 Enroll-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 .
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 .
Note added in 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 for better readability.
Included registrar authorization check for Registrar-Agent during TLS handshake in section . Also enhanced figure with the authorization step on TLS level.
Enhanced description of registrar authorization check for Registrar-Agent based on the agent-signed-data in section . Also enhanced figure 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 (issue #12). This also required changes in the YANG module in
Addressed YANG warning (issue #1)
Inclusion of examples for a trigger to create a Pledge-Voucher-Request and a Pledge Enroll-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, meanwhile moved to 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 as voucher-request was enhanced with additional leaf.
Included open issues in YANG model in 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 .
Terminology change: issue #2 pledge-agent -> Registrar-Agent to better underline Registrar-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 .
Recommendation regarding short-lived certificates for Registrar-Agent authentication towards registrar (issue #7) in the security considerations.
Introduction of reference to Registrar-Agent signing certificate using SubjectKeyIdentifier in Registrar-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 .
Details on trust relationship between Registrar-Agent and pledge (issue #5) included in .
Split of use case 2 call flow into sub sections in .

From IETF draft 00 -> IETF draft 01:

Update of scope in 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 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 , 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 . 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 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 .
Enhanced consideration of existing enrollment protocols in the context of mapping the requirements to existing solutions in .

From individual version 00 -> 01:

Update of examples, specifically for building automation as well as two new application use cases in .
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 .
Enhancement of description of architecture elements and changes to BRSKI in .
Consideration of existing enrollment protocols in the context of mapping the requirements to existing solutions in .
New section starting with the mapping to existing enrollment protocols by collecting boundary conditions.

Contributors IoTconsultancy.nl

esko.dijk@iotconsultancy.nl

Futurewei

tte@cs.fau.de

Siemens Schweiz AG

ietf@kovatsch.net