ANIMA WG S. Fries
Internet-Draft H. Brockhaus
Intended status: Standards Track Siemens
Expires: December 16, 2021 E. Lear
Cisco Systems
T. Werner
Siemens
June 14, 2021
Support of asynchronous Enrollment in BRSKI (BRSKI-AE)
draft-ietf-anima-brski-async-enroll-02
Abstract
This document describes enhancements of bootstrapping a remote secure
key infrastructure (BRSKI, [RFC8995] ) to also operate in domains
featuring no or only timely limited connectivity between involved
components. Further enhancements are provided to perform the BRSKI
approach in environments, in which the role of the pledge changes
from a client to a server . This changes the interaction model from a
pledge-initiator-mode to a pledge-responder-mode. To support both
use cases, BRSKI-AE relies on the exchange of authenticated self-
contained objects (signature-wrapped objects) also for requesting and
distributing of domain specific device certificates. The defined
approach is agnostic regarding the utilized enrollment protocol
allowing the application of existing and potentially new certificate
management protocols.
Status of This Memo
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This Internet-Draft will expire on December 16, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Scope of solution . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Supported environment . . . . . . . . . . . . . . . . . . 7
3.2. Application Examples . . . . . . . . . . . . . . . . . . 7
3.2.1. Rolling stock . . . . . . . . . . . . . . . . . . . . 7
3.2.2. Building automation . . . . . . . . . . . . . . . . . 8
3.2.3. Substation automation . . . . . . . . . . . . . . . . 8
3.2.4. Electric vehicle charging infrastructure . . . . . . 9
3.2.5. Infrastructure isolation policy . . . . . . . . . . . 9
3.2.6. Less operational security in the target domain . . . 9
4. Requirement discussion and mapping to solution elements . . . 10
5. Architectural Overview and Communication Exchanges . . . . . 12
5.1. Use Case 1 (pledge-initiator-mode): Support of off-site
PKI service . . . . . . . . . . . . . . . . . . . . . . . 13
5.1.1. Behavior of a pledge . . . . . . . . . . . . . . . . 16
5.1.2. Pledge - Registrar discovery and voucher exchange . . 16
5.1.3. Registrar - MASA voucher exchange . . . . . . . . . . 16
5.1.4. Pledge - Registrar - RA/CA certificate enrollment . . 16
5.1.5. Addressing Scheme Enhancements . . . . . . . . . . . 19
5.2. Use Case 2 (pledge-responder-mode): Registrar-agent
communication with Pledges . . . . . . . . . . . . . . . 19
5.2.1. Behavior of a pledge in pledge-responder-mode . . . . 23
5.2.2. Behavior of a registrar-agent . . . . . . . . . . . . 23
5.2.3. Bootstrapping objects and corresponding exchanges . . 25
5.3. Domain registrar support of different enrollment options 46
6. YANG Extensions to Voucher Request . . . . . . . . . . . . . 47
7. Example for signature-wrapping using existing enrollment
protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.1. EST Handling . . . . . . . . . . . . . . . . . . . . . . 50
7.2. CMP Handling . . . . . . . . . . . . . . . . . . . . . . 51
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8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 52
10. Security Considerations . . . . . . . . . . . . . . . . . . . 52
10.1. Exhaustion attack on pledge . . . . . . . . . . . . . . 52
10.2. Misuse of acquired voucher and enrollment responses . . 52
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 53
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
12.1. Normative References . . . . . . . . . . . . . . . . . . 53
12.2. Informative References . . . . . . . . . . . . . . . . . 54
Appendix A. History of changes [RFC Editor: please delete] . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 59
1. Introduction
BRSKI as defined in [RFC8995] specifies a solution for secure zero-
touch (automated) bootstrapping of devices (pledges) in a (customer)
site domain. This includes the discovery of network elements in the
target domain, time synchronization, and the exchange of security
information necessary to establish trust between a pledge and the
domain. Security information about the target domain, specifically
the target domain certificate, is exchanged utilizing voucher objects
as defined in [RFC8366]. These vouchers are authenticated self-
contained (signed) objects, which may be provided online
(synchronous) or offline (asynchronous) via the domain registrar to
the pledge and originate from a Manufacturer's Authorized Signing
Authority (MASA).
For the enrollment of devices BRSKI relies on EST [RFC7030] to
request and distribute target domain specific device certificates.
EST in turn relies on a binding of the certification request to an
underlying TLS connection between the EST client and the EST server.
According to BRSKI the domain registrar acts as EST server and is
also acting as registration authority (RA) or local registration
authority (LRA). The binding to TLS is used to protect the exchange
of a certification request (for a LDevID EE certificate) and to
provide data origin authentication (client identity information), to
support the authorization decision for processing the certification
request. The TLS connection is mutually authenticated and the
client-side authentication utilizes the pledge's manufacturer issued
device certificate (IDevID certificate). This approach requires an
on-site availability of a local asset or inventory management system
performing the authorization decision based on tuple of the
certification request and the pledge authentication using the IDevID
certificate, to issue a domain specific certificate to the pledge.
The EST server (the domain registrar) terminates the security
association with the pledge and thus the binding between the
certification request and the authentication of the pledge via TLS.
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This type of enrollment utilizing an online connection to the PKI is
considered as synchronous enrollment.
For certain use cases on-site support of a RA/CA component and/or an
asset management is not available and rather provided by an
operator's backend and may be provided timely limited or completely
through offline interactions. This may be due to higher security
requirements for operating the certification authority or for
optimization of operation for smaller deployments to avoid the always
on-site operation. The authorization of a certification request
based on an asset management in this case will not / can not be
performed on-site at enrollment time. Enrollment, which cannot be
performed in a (timely) consistent fashion is considered as
asynchronous enrollment in this document. It requires the support of
a store and forward functionality of certification request together
with the requester authentication (and identity) information. This
enables processing of the request at a later point in time. A
similar situation may occur through network segmentation, which is
utilized in industrial systems to separate domains with different
security needs. Here, a similar requirement arises if the
communication channel carrying the requester authentication is
terminated before the RA/CA authorization handling of the
certification request. If a second communication channel is opened
to forward the certification request to the issuing RA/ CA, the
requester authentication information needs to be retained and ideally
bound to the certification request. This uses case is independent
from timely limitations of the first use case. For both cases, it is
assumed that the requester authentication information is utilized in
the process of authorization of a certification request. There are
different options to perform store and forward of certification
requests including the requester authentication information:
o Providing a trusted component (e.g., an LRA) in the target domain,
which stores the certification request combined with the requester
authentication information (based on the IDevID) and potentially
the information about a successful proof of possession (of the
corresponding private key) in a way prohibiting changes to the
combined information. Note that the assumption is that the
information elements may not be cryptographically bound together.
Once connectivity to the backend is available, the trusted
component forwards the certification request together with the
requester information (authentication and proof of possession) to
the off-site PKI for further processing. It is assumed that the
off-site PKI in this case relies on the local pledge
authentication result and thus performs the authorization and
issues the requested certificate. In BRSKI the trusted component
may be the EST server residing co-located with the registrar in
the target domain.
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o Utilization of authenticated self-contained objects for the
enrollment, binding the certification request and the requester
authentication in a cryptographic way. This approach reduces the
necessary trust in a domain component to storage and delivery.
Unauthorized modifications of the requester information (request
and authentication) can be detected during the verification of the
authenticated self-contained object.
Focus of this document the support of handling authenticated self-
contained objects for bootstrapping. As it is intended to enhance
BRSKI it is named BRSKI-AE, where AE stands for asynchronous
enrollment. As BRSKI, BRSKI-AE results in the pledge storing an
X.509 domain certificate and sufficient information for verifying the
domain registrar / proxy identity (LDevID CA Certificate) as well as
domain specific X.509 device certificates (LDevID EE certificate).
Based on the proposed approach, a second set of scenarios can be
addressed, in which the pledge has either no direct communication
path to the domain registrar, e.g., due to missing network
connectivity or a different technology stack. In such scenarios the
pledge is expected to act as a server rather than a client. The
pledge will be triggered to generate request objects to be onboarded
in the registrar's domain. For this, an additional component is
introduced acting as an agent for the domain registrar (registrar-
agent) towards the pledge. This could be a functionality of a
commissioning tool or it may be even co-located with the registrar.
In contrast to BRSKI the registrar-agent performs the object exchange
with the pledge and provides/retrieves data objects to/from the
domain registrar. For the interaction with the domain registrar the
registrar agent will use existing BRSKI endpoints.
The goal is to enhance BRSKI to be applicable to the additional use
cases. This is addressed by
o enhancing the well-known URI approach with an additional path for
the utilized enrollment protocol.
o defining a certificate waiting indication and handling, if the
certifying component is (temporarily) not available.
o allowing to utilize credentials different from the pledge's IDevID
to establish a TLS connection to the domain registrar, which is
necessary in case of using a registrar-agent.
o defining the interaction (dta exchange and data objects) between a
pledge acting as server an a registrar-agent and the domain
registrar.
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Note that in contrast to BRSKI, BRSKI-AE assumes support of multiple
enrollment protocols on the infrastructure side, allowing the pledge
manufacturer to select the most appropriate. Thus, BRSKI-AE can be
applied for both, asynchronous and synchronous enrollment.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here. This document relies on the terminology defined in [RFC8995].
The following terms are defined additionally:
CA: Certification authority, issues certificates.
RA: Registration authority, an optional system component to which a
CA delegates certificate management functions such as
authorization checks.
LRA: Local registration authority, an optional RA system component
with proximity to end entities.
IED: Intelligent Electronic Device (in essence a pledge).
on-site: Describes a component or service or functionality available
in the target deployment domain.
off-site: Describes a component or service or functionality
available in an operator domain different from the target
deployment domain. This may be a central site or a cloud service,
to which only a temporary connection is available, or which is in
a different administrative domain.
asynchronous communication: Describes a timely interrupted
communication between an end entity and a PKI component.
synchronous communication: Describes a timely uninterrupted
communication between an end entity and a PKI component.
authenticated self-contained object: Describes an object, which is
cryptographically bound to the EE certificate (IDevID certificate
or LDEVID certificate) of a pledge. The binding is assumed to be
provided through a digital signature of the actual object using
the corresponding private key of the EE certificate.
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3. Scope of solution
3.1. Supported environment
This solution is intended to be used in domains with limited support
of on-site PKI services and comprises use cases in which:
o there is no registration authority available in the target domain.
The connectivity to an off-site RA in an operator's network may
only be available temporarily. A local store and forward device
is used for the communication with the off-site services.
o authoritative actions of a LRA are limited and may not comprise
authorization of certification requests of pledges. Final
authorization is done at the RA residing in the operator domain.
o the target deployment domain already has an established
certificate management approach that shall be reused to (e.g., in
brownfield installations).
In addition, the solution is intended to be applicable in domains in
which pledges have no direct connection to the domain registrar, but
are expected to be managed by the registrar. This can be motivated
by pledges featuring a different technology stack or by pledges
without an existing connection to the domain registrar during
bootstrapping. These pledges are likely to act in a server role.
Therefore, the pledge has to offer endpoints on which it can be
triggered for the generation of voucher-request objects and
certification objects as well as to provide the response objects to
the pledge.
3.2. Application Examples
The following examples are intended to motivate the support of
different enrollment approaches in general and asynchronous
enrollment specifically, by introducing industrial applications
cases, which could leverage BRSKI as such but also require support of
asynchronous operation as intended with BRSKI-AE.
3.2.1. Rolling stock
Rolling stock or railroad cars contain a variety of sensors,
actuators, and controllers, which communicate within the railroad car
but also exchange information between railroad cars building a train,
or with a backend. These devices are typically unaware of backend
connectivity. Managing certificates may be done during maintenance
cycles of the railroad car, but can already be prepared during
operation. The preparation may comprise the generation of
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certification requests by the components which are collected and
forwarded for processing, once the railroad car is connected to the
operator backend. The authorization of the certification request is
then done based on the operator's asset/inventory information in the
backend.
3.2.2. Building automation
In building automation, a use case can be described by a detached
building or the basement of a building equipped with sensor,
actuators, and controllers connected, but with only limited or no
connection to the centralized building management system. This
limited connectivity may be during the installation time but also
during operation time. During the installation in the basement, a
service technician collects the necessary information from the
basement network and provides them to the central building management
system, e.g., using a laptop or even a mobile phone to transport the
information. This information may comprise parameters and settings
required in the operational phase of the sensors/actuators, like a
certificate issued by the operator to authenticate against other
components and services.
The collected information may be provided by a domain registrar
already existing in the installation network. In this case
connectivity to the backend PKI may be facilitated by the service
technician's laptop. Contrary, the information can also be collected
from the pledges directly and provided to a domain registrar deployed
in a different network. In this cases connectivity to the domain
registrar may be facilitated by the service technician's laptop.
3.2.3. Substation automation
In electrical substation automation a control center typically hosts
PKI services to issue certificates for Intelligent Electronic Devices
(IED)s operated in a substation. Communication between the
substation and control center is done through a proxy/gateway/DMZ,
which terminates protocol flows. Note that [NERC-CIP-005-5] requires
inspection of protocols at the boundary of a security perimeter (the
substation in this case). In addition, security management in
substation automation assumes central support of different enrollment
protocols to facilitate the capabilities of IEDs from different
vendors. The IEC standard IEC62351-9 [IEC-62351-9] specifies the
mandatory support of two enrollment protocols, SCEP [RFC8894] and EST
[RFC7030] for the infrastructure side, while the IED must only
support one of the two.
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3.2.4. Electric vehicle charging infrastructure
For the electric vehicle charging infrastructure protocols have been
defined for the interaction between the electric vehicle (EV) and the
charging point (e.g., ISO 15118-2 [ISO-IEC-15118-2]) as well as
between the charging point and the charging point operator (e.g.
OCPP [OCPP]). Depending on the authentication model, unilateral or
mutual authentication is required. In both cases the charging point
uses an X.509 certificate to authenticate itself in the context of a
TLS connection between the EV and the charging point. The management
of this certificate depends (beyond others) on the selected backend
connectivity protocol. Specifically, in case of OCPP it is intended
as single communication protocol between the charging point and the
backend carrying all information to control the charging operations
and maintain the charging point itself. This means that the
certificate management is intended to be handled in-band of OCPP.
This requires to be able to encapsulate the certificate management
exchanges in a transport independent way. Authenticated self-
containment will ease this by allowing the transport without a
separate enrollment protocol. This provides a binding of the
exchanges to the identity of the communicating endpoints.
3.2.5. Infrastructure isolation policy
This refers to any case in which 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 external PKI
resources will be allowed in carefully controlled short periods of
time, for example when a batch of new devices are deployed, but
impossible at other times.
3.2.6. Less operational security in the target domain
The registration point performing the authorization of a certificate
request is a critical PKI component and therefore implicates higher
operational security than other components utilizing the issued
certificates for their security features. CAs may also demand higher
security in the registration procedures. Especially the CA/Browser
forum currently increases the security requirements in the
certificate issuance procedures for publicly trusted certificates.
There may be the situation that the target domain does not offer
enough security to operate a registration point and therefore wants
to transfer this service to a backend that offers a higher level of
operational security.
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4. Requirement discussion and mapping to solution elements
For the requirements discussion it is assumed that the domain
registrar receiving a certification request as authenticated self-
contained object is not the authorization point for this
certification request. If the domain registrar is the authorization
point and the pledge has a direct connection to the registrar, BRSKI
can be used directly. Note that BRSKI-AE could also be used in this
case.
Based on the intended target environment described in Section 3.1 and
the motivated application examples described in Section 3.2 the
following base requirements are derived to support authenticated
self-contained objects as container carrying the certification
request and further information to support asynchronous operation.
At least the following properties are required:
o Proof of Possession: proves to possess and control the private key
corresponding to the public key contained in the certification
request, typically by adding a signature using the private key.
o Proof of Identity: provides data-origin authentication of a data
object, e.g., a certificate request, utilizing an existing IDevID.
Certificate updates may utilize the certificate that is to be
updated.
Solution examples (not complete) based on existing technology are
provided with the focus on existing IETF documents:
o Certification request objects: Certification requests are
structures protecting only the integrity of the contained data
providing a proof-of-private-key-possession for locally generated
key pairs. Examples for certification requests are:
* PKCS#10 [RFC2986]: Defines a structure for a certification
request. The structure is signed to ensure integrity
protection and proof of possession of the private key of the
requester that corresponds to the contained public key.
* CRMF [RFC4211]: Defines a structure for the certification
request message. The structure supports integrity protection
and proof of possession, through a signature generated over
parts of the structure by using the private key corresponding
to the contained public key. CRMF also supports further proof-
of-possession methods for key pairs not capable to be used for
signing.
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Note that the integrity of the certification request is bound to
the public key contained in the certification request by
performing the signature operation with the corresponding private
key. In the considered application examples, this is not
sufficient to provide data origin authentication and needs to be
bound to the existing credential of the pledge (IDevID)
additionally. This binding supports the authorization decision
for the certification request through the provisioning of a proof
of identity. The binding of data origin authentication to the
certification request may be delegated to the protocol used for
certificate management.
o Proof of Identity options: The certification request should be
bound to an existing credential (here IDevID) to enable a proof of
identity and based on it an authorization of the certification
request. The binding may be realized through security options in
an underlying transport protocol if the authorization of the
certification request is done at the next communication hop.
Alternatively, this binding can be done by a wrapping signature
employing an existing credential (initial: IDevID, renewal:
LDevID). This requirement is addressed by existing enrollment
protocols in different ways, for instance:
* EST [RFC7030]: Utilizes PKCS#10 to encode the certification
request. The Certificate Signing Request (CSR) may contain a
binding to the underlying TLS by including the tls-unique value
in the self-signed CSR structure. The tls-unique value is one
result of the TLS handshake. As the TLS handshake is performed
mutually authenticated and the pledge utilized its IDevID for
it, the proof of identity can be provided by the binding to the
TLS session. This is supported in EST using the simpleenroll
endpoint. To avoid the binding to the underlying
authentication in the transport layer, EST offers the support
of a wrapping the CSR with an existing certificate by using
Full PKI Request messages.
* SCEP [RFC8894]: Provides the option to utilize either an
existing secret (password) or an existing certificate to
protect the CSR based on SCEP Secure Message Objects using CMS
wrapping ([RFC5652]). Note that the wrapping using an existing
IDevID credential in SCEP is referred to as renewal. SCEP
therefore does not rely on the security of an underlying
transport.
* CMP [RFC4210] Provides the option to utilize either an existing
secret (password) or an existing certificate to protect the
PKIMessage containing the certification request. The
certification request is encoded utilizing CRMF. PKCS#10 is
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optionally supported. The proof of identity of the PKIMessage
containing the certification request can be achieved by using
IDevID credentials to a PKIProtection carrying the actual
signature value. CMP therefore does not rely on the security
of an underlying transport protocol.
* CMC [RFC5272] Provides the option to utilize either an existing
secret (password) or an existing certificate to protect the
certification request (either in CRMF or PKCS#10) based on CMS
[RFC5652]). Here a FullCMCRequest can be used, which allows
signing with an existing IDevID credential to provide a proof
of identity. CMC therefore does not rely on the security of an
underlying transport.
Note that besides the already existing enrollment protocols there is
ongoing work in the ACE WG to define an encapsulation of EST messages
in OSCORE to result in a TLS independent way of protecting EST. This
approach [I-D.selander-ace-coap-est-oscore] may be considered as
further variant.
5. Architectural Overview and Communication Exchanges
To support asynchronous enrollment, the base system architecture
defined in BRSKI [RFC8995] is enhanced to facilitate the two target
use cases.
o Use case 1 (Pledge-initiator-mode): the pledge requests
certificates from a PKI operated off-site via the domain
registrar. The communication model follows the BRSKI model in
which the pledge initiates the communication.
o Use case 2 (Pledge-responder-mode): allows delegated bootstrapping
using a registrar-agent instead a direct connection from the
pledge to the domain registrar. The communication model between
registrar-agent and pledge assumes that the pledge is acting as
server and responds to requests.
Both use cases are described in the next subsections. They utilize
the existing BRSKI architecture elements as much as possible.
Necessary enhancements to support authenticated self-contained
objects for certificate enrollment are kept on a minimum to ensure
reuse of already defined architecture elements and interactions.
For the authenticated self-contained objects used for the
certification request, BRSKI-AE relies on the defined message
wrapping mechanisms of the enrollment protocols stated in Section 4
above.
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5.1. Use Case 1 (pledge-initiator-mode): Support of off-site PKI
service
One assumption of BRSKI-AE is that the authorization of a
certification request is performed based on an authenticated self-
contained object, binding the certification request to the
authentication using the IDevID. This supports interaction with off-
site or off-line PKI (RA/CA) components. In addition, the
authorization of the certification request may not be done by the
domain registrar but by a PKI residing in the backend of the domain
operator (off-site) as described in Section 3.1. Also, the
certification request may be piggybacked by another protocol. This
leads to changes in the placement or enhancements of the logical
elements as shown in Figure 1.
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+------------------------+
+--------------Drop Ship--------------->| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| |
V |
+--------+ ......................................... |
| | . . | BRSKI-
| | . +------------+ +------------+ . | MASA
| Pledge | . | Join | | Domain <-----+
| | . | Proxy | | Registrar/ | .
| <-------->............<-------> Enrollment | .
| | . | BRSKI-AE | Proxy | .
| IDevID | . | | +------^-----+ .
| | . +------------+ | .
| | . | .
+--------+ ...............................|.........
"on-site domain" components |
|e.g., RFC 7030,
| RFC 4210, ...
.............................................|.....................
. +---------------------------+ +--------v------------------+ .
. | Public Key Infrastructure |<----+ PKI RA | .
. | PKI CA |---->+ | .
. +---------------------------+ +---------------------------+ .
...................................................................
"off-site domain" components
Figure 1: Architecture overview using off-site PKI components
The architecture overview in Figure 1 utilizes the same logical
elements as BRSKI but with a different placement in the deployment
architecture for some of the elements. The main difference is the
placement of the PKI RA/CA component, which is performing the
authorization decision for the certification request message. It is
placed in the off-site domain of the operator (not the deployment
site directly), which may have no or only temporary connectivity to
the deployment or on-site domain of the pledge. This is to underline
the authorization decision for the certification request in the
backend rather than on-site. The following list describes the
components in the target domain:
o Join Proxy: same functionality as described in BRSKI.
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o Domain Registrar / Enrollment Proxy: In general the domain
registrar proxy has a similar functionality regarding the
imprinting of the pledge in the deployment domain to facilitate
the communication of the pledge with the MASA and the PKI.
Different is the authorization of the certification request.
BRSKI-AE allows to perform this in the operator's backend (off-
site), and not directly at the domain registrar.
* Voucher exchange: The voucher exchange with the MASA via the
domain registrar is performed as described in BRSKI [RFC8995] .
* Certificate enrollment: For the pledge enrollment the domain
registrar in the deployment domain supports the adoption of the
pledge in the domain based on the voucher request.
Nevertheless, it may not have sufficient information for
authorizing the certification request. If the authorization of
the certification request is done in the off-site domain, the
domain registrar forwards the certification request to the RA
to perform the authorization. Note that this requires, that
the certification request object is enhanced with a proof-of-
identity to allow the authorization based on the bound identity
information of the pledge. As stated above, this can be done
by an additional signature using the IDevID. The domain
registrar here acts as an enrollment proxy or local
registration authority. It is also able to handle the case
having no connection temporarily to an off-site PKI, by storing
the authenticated certification request and forwarding it to
the RA upon reestablished connectivity. As authenticated self-
contained objects are used, it requires an enhancement of the
domain registrar. This is done by supporting alternative
enrollment approaches (protocol options, protocols, encoding)
by enhancing the addressing scheme to communicate with the
domain registrar (see Section 5.1.5).
The following list describes the vendor related components/service
outside the deployment domain:
o MASA: general functionality as described in [RFC8995]. Assumption
is that the interaction with the MASA may be synchronous (voucher
request with nonce) or asynchronous (voucher request without
nonce).
o Ownership tracker: as defined in [RFC8995].
The following list describes the operator related components/service
operated in the backend:
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o PKI RA: Performs certificate management functions (validation of
certification requests, interaction with inventory/asset
management for authorization of certification requests, etc.) for
issuing, updating, and revoking certificates for a domain as a
centralized infrastructure for the domain operator. The inventory
(asset) management may be a separate component or integrated into
the RA directly.
o PKI CA: Performs certificate generation by signing the certificate
structure provided in the certification request.
Based on BRSKI and the architectural changes the original protocol
flow is divided into three phases showing commonalities and
differences to the original approach as depicted in the following.
o Discovery phase (same as BRSKI)
o Voucher exchange with deployment domain registrar (same as BRSKI).
o Enrollment phase (changed to support the application of
authenticated self-contained objects).
5.1.1. Behavior of a pledge
The behavior of a pledge as described in [RFC8995] is kept with one
exception. After finishing the imprinting phase (4) the enrollment
phase (5) is performed with a method supporting authenticated self-
contained objects. Using EST with simple-enroll cannot be applied
here, as it binds the pledge authentication with the existing IDevID
to the transport channel (TLS) rather than to the certification
request object directly. This authentication in the transport layer
is not visible / verifiable at the authorization point in the off-
site domain. Section 7 discusses potential enrollment protocols and
options applicable.
5.1.2. Pledge - Registrar discovery and voucher exchange
The discovery phase is applied as specified in [RFC8995].
5.1.3. Registrar - MASA voucher exchange
The voucher exchange is performed as specified in [RFC8995].
5.1.4. Pledge - Registrar - RA/CA certificate enrollment
As stated in Section 4 the enrollment shall be performed using an
authenticated self-contained object providing proof of possession and
proof of identity.
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+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Operator |
| | | Join | | Registrar | | RA/CA |
| | | Proxy | | (JRC) | | (OPKI) |
+--------+ +---------+ +------------+ +------------+
/--> | |
[Request of CA Certificates] | |
|---------- CA Certs Request ------------>| |
| [if connection to operator domain is available] |
| |-Request CA Certs ->|
| |<- CA Certs Response|
|<-------- CA Certs Response--------------| |
/--> | |
[Request of Certificate Attributes to be included] |
|---------- Attribute Request ----------->| |
| [if connection to operator domain is available] |
| |Attribute Request ->|
| |<-Attribute Response|
|<--------- Attribute Response -----------| |
/--> | |
[Certification request] | |
|-------------- Cert Request ------------>| |
| [if connection to operator domain is available] |
| |--- Cert Request -->|
| | |
[Optional Certificate waiting indication] | |
/--> | |
|<----- Cert Response (with Waiting) -----| |
|-- Cert Polling (with orig request ID) ->| |
| | |
/--> | |
| |<-- Cert Response --|
| | |
|<-- Cert Response (with Certificate) ----| |
/--> | |
[Certificate confirmation] | |
|-------------- Cert Confirm ------------>| |
| /--> |
| |[optional] |
| |--- Cert Confirm -->|
| |<-- PKI Confirm ----|
|<------------- PKI/Registrar Confirm ----| |
Figure 2: Certificate enrollment
The following list provides an abstract description of the flow
depicted in Figure 2.
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o CA Cert Request: The pledge SHOULD request the full distribution
of CA Certificates. This ensures that the pledge has the complete
set of current CA certificates beyond the pinned-domain-cert
(which may be the domain registrar certificate contained in the
voucher).
o CA Cert Response: Contains at least one CA certificate of the
issuing CA.
o Attribute Request: Typically, the automated bootstrapping occurs
without local administrative configuration of the pledge.
Nevertheless, there are cases, in which the pledge may also
include additional attributes specific to the deployment domain
into the certification request. To get these attributes in
advance, the attribute request SHOULD be used.
o Attribute Response: Contains the attributes to be included in the
certification request message.
o Cert Request: Depending on the utilized enrollment protocol, this
certification request contains the authenticated self-contained
object ensuring both, proof-of-possession of the corresponding
private key and proof-of-identity of the requester.
o Cert Response: certification response message containing the
requested certificate and potentially further information like
certificates of intermediary CAs on the certification path.
o Cert Waiting: waiting indication for the pledge to retry after a
given time. For this a request identifier is necessary. This
request identifier may be either part of the enrollment protocol
or build based on the certification request.
o Cert Polling: querying the registrar, if the certificate request
was already processed; can be answered either with another Cert
Waiting, or a Cert Response.
o Cert Confirm: confirmation message from pledge after receiving and
verifying the certificate.
o PKI/Registrar Confirm: confirmation message from PKI/registrar
about reception of the pledge's certificate confirmation.
The generic messages described above can implemented using various
protocols implementing authenticated self-contained objects, as
described in Section 4. Examples are available in Section 7.
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5.1.5. Addressing Scheme Enhancements
BRSKI-AE provides enhancements to the addressing scheme defined in
[RFC8995] to accommodate the additional handling of authenticated
self-contained objects for the certification request. As this is
supported by different enrollment protocols, they can be directly
employed (see also Section 7).
The addressing scheme in BRSKI for client certificate request and CA
certificate distribution function during the enrollment uses the
definition from EST [RFC7030], here on the example on simple enroll:
"/.well-known/est/simpleenroll" This approach is generalized to the
following notation: "/.well-known/enrollment-protocol/request" in
which enrollment-protocol may be an already existing protocol or a
newly defined approach. Note that enrollment is considered here as a
sequence of at least a certification request and a certification
response. In case of existing enrollment protocols the following
notation is used proving compatibility to BRSKI:
o enrollment-protocol: references either EST [RFC7030] as in BRSKI
or CMP, CMC, SCEP, or newly defined approaches as alternatives.
Note: additional endpoints (well-known URI) at the registrar may
need to be defined by the utilized enrollment protocol.
o request: depending on the utilized enrollment protocol, the
request describes the required operation at the registrar side.
Enrollment protocols are expected to define the request endpoints
as done by existing protocols (see also Section 7).
5.2. Use Case 2 (pledge-responder-mode): Registrar-agent communication
with Pledges
To support mutual trust establishment of pledges, not directly
connected to the domain registrar. It relies on the exchange of
authenticated self-contained objects (the voucher request/response
objects as known from BRSKI and the enrollment request/response
objects as introduced by BRSKI-AE). This approach has also been
applied also for the use case 1. This allows independence of a
potential protection provided by the used transport protocol.
In contrast to BRSKI, the object exchanges performed with the help of
a registrar-agent component, supporting the interaction of the pledge
with the domain registrar. It may be an integrated functionality of
a commissioning tool. This leads to enhancements of the logical
elements in the BRSKI architecture as shown in Figure 3. The
registrar-agent interacts with the pledge to acquire and to supply
the required data objects for bootstrapping, which are also exchanged
between the registrar-agent and the domain registrar. Moreover, the
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addition of the registrar-agent also influences the sequences for the
data exchange between the pledge and the domain registrar described
in [RFC8995]. The general goal for the registrar-agent application
is the reuse of already defined endpoints of the domain registrar
side. The functionality of the already existing registrar endpoints
may need small enhancements.
+------------------------+
+--------------Drop Ship---------------| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| | BRSKI-
V | MASA
+-------+ +---------+ .............................|.........
| | | | . | .
| | | | . +-----------+ +-----v-----+ .
| | |Registrar| . | | | | .
|Pledge | |Agent | . | Join | | Domain | .
| | | | . | Proxy | | Registrar | .
| <----->.........<------>...........<-------> (PKI RA) | .
| | | | . | BRSKI-AE | | .
| | | | . | | +-----+-----+ .
|IDevID | | LDevID | . +-----------+ | .
| | | | . +------------------+-----+ .
+-------+ +---------+ . | Key Infrastructure | .
. | (e.g., PKI Certificate | .
. | Authority) | .
. +------------------------+ .
.......................................
"Domain" components
Figure 3: Architecture overview using registrar-agent
The architecture overview in Figure 3 utilizes the same logical
components as BRSKI with the registrar-agent component in addition.
For authentication towards the domain registrar, the registrar-agent
uses its LDevID. The provisioning of the registrar-agent LDevID may
be done by a separate BRSKI run or other means in advance. It is
recommended to use short lived registrar-agent LDevIDs in the range
of days or weeks.
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If a registrar detects a request originates from a registrar-agent it
is able to switch the operational mode from BRSKI to BRSKI-AE.
In addition, the domain registrar may authenticate the user operating
the registrar-agent to perform additional authorization of a pledge
enrollment action. Examples for such user level authentication are
the application of HTTP authentication or the usage of authorization
tokens or other. This is out of scope of this document.
The following list describes the components in a (customer) site
domain:
o Pledge: The pledge is expected to respond with the necessary data
objects for bootstrapping to the registrar-agent. The transport
protocol used between the pledge and the registrar-agent is
assumed to be HTTP in the context of this document. Other
transport protocols may be used but are out of scope of this
document. As the pledge is acting as a server during
bootstrapping it leads to some differences to BRSKI:
* Discovery of the domain registrar by the pledge is not needed
as the pledge will be triggered by the registrar-agent.
* Discovery of the pledge by the registrar-agent must be
possible.
* As the registrar-agent must be able to request data objects for
bootstrapping of the pledge, the pledge must offer
corresponding endpoints.
* The registrar-agent may provide additional data to the pledge,
in the context of the triggering request.
* Order of exchanges in the call flow may be different as the
registrar-agent collects both objects, pledge-voucher-request
objects and pledge-enrollment-request objects, at once and
provides them to the registrar. This approach may also be used
to perform a bulk bootstrapping of several devices.
* The data objects utilized for the data exchange between the
pledge and the registrar are self-contained authenticated
objects (signature-wrapped objects) as in use case 1
Section 5.1.
o Registrar-agent: provides a communication path to exchange data
objects between the pledge and the domain registrar. The
registrar-agent facilitates situations, in which the domain
registrar is not directly reachable by the pledge, either due to a
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different technology stack or due to missing connectivity. The
registrar-agent triggers the pledge to create bootstrapping
information such as voucher request objects and enrollment request
objects from one or multiple pledges at once and performs a bulk
bootstrapping based on the collected data. The registrar-agent is
expected to possess information of the domain registrar, either by
configuration or by using the discovery mechanism defined in
[RFC8995]. There is no trust assumption between the pledge and
the registrar-agent as only authenticated self-contained objects
are applied, which are transported via the registrar-agent and
provided either by the pledge or the registrar. The trust
assumption between the registrar-agent and the registrar bases on
an own LDevID of the registrar-agent, acting as registrar
component. This allows the registrar-agent to authenticate
towards the registrar. The registrar can utilize this
authentication to distinguish communication with a pledge from a
registrar-agent based on the exchanged objects.
o Join Proxy: same functionality as described in [RFC8995]. Note
that it may be used by the registrar-agent instead of the pledge
to find the registrar, if not configured.
o Domain Registrar: In general the domain registrar fulfills the
same functionality regarding the bootstrapping of the pledge in a
(customer) site domain by facilitating the communication of the
pledge with the MASA service and the domain PKI service. In
contrast to [RFC8995], the domain registrar does not interact with
a pledge directly but through the registrar-agent. The registrar
detects if the bootstrapping is performed by the pledge directly
or by the registrar-agent.
The manufacturer provided components/services (MASA and Ownership
tracker) are used as defined in [RFC8995]. For issuing a voucher,
the MASA may perform additional checks on voucher-request objects, to
issue a voucher indicating agent-proximity instead of registrar-
proximity.
"Agent-proximity" is a weaker assertion then "proximity". In case of
"agent-proximity" it is a statement, that the proximity-registrar-
certificate was provided via the registrar-agent and not directly.
This can be verified by the registrar and also by the MASA through
voucher-request processing. Note that at the time of creating the
voucher-request, the pledge cannot verify the LDevID(Reg) EE
certificate and has no proof-of-possession of the corresponding
private key for the certificate. Trust handover to the domain is
established via the "pinned-domain-certificate" in the voucher.
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In contrast, "proximity" provides a statement, that the pledge was in
direct contact with the registrar and was able to verify proof-of-
possession of the private key in the context of the TLS handshake.
The provisionally accepted LDevID(Reg) EE certificate can be verified
after the voucher has been processed by the pledge.
5.2.1. Behavior of a pledge in pledge-responder-mode
In contrast to use case 1 Section 5.1 the pledge acts as a server
component if data is triggered by the registrar-agent for the
generation of pledge-voucher-request and pledge-enrollment-request
objects as well as for the processing of the response objects and the
generation of status information. Due to the use of the registrar-
agent, the interaction with the domain registrar is changed as shown
in Figure 5. To enable interaction with the registrar-agent, the
pledge provides endpoints using the BRSKI interface based on the
"/.well-known/brski" URI tree. The following endpoints are defined
for the pledge in this document:
o /.well-known/brski/pledge-voucher-request: trigger pledge to
create voucher request. It returns the pledge-voucher-request.
o /.well-known/brski/pledge-enrollment-request: trigger pledge to
create enrollment request. it returns the pledge-enrollment-
request.
o /.well-known/brski/pledge-voucher: supply MASA provided voucher to
pledge. It returns the pledge-voucher-status.
o /.well-known/brski/pledge-enrollment: supply enroll response
(certificate) to pledge. It returns the pledge-enrollment-status.
o /.well-known/brski/pledge-CACerts: supply CACerts to pledge
(optional).
5.2.2. Behavior of a registrar-agent
The registrar-agent is a new component in the BRSKI context. It
provides connectivity between the pledge and the domain registrar and
reuses the endpoints of the domain registrar side already specified
in [RFC8995]. It facilitates the exchange of data objects between
the pledge and the domain registrar, which are the voucher request/
response objects, the enrollment request/response objects, as well as
related status objects. For the communication the registrar-agent
utilizes communication endpoints provided by the pledge. The
transport in this specification is based on HTTP but may also be done
using other transport mechanisms. This new component changes the
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general interaction between the pledge and the domain registrar as
shown in Figure 9.
The registrar-agent is expected to already possess an LDevID(RegAgt)
to authenticate towards the domain registrar. The registrar-agent
will use this LDevID(RegAgt) when establishing the TLS session with
the domain registrar in the context of for TLS client-side
authentication. The LDevID(RegAgt) certificate MUST include a
SubjectKeyIdentifier (SKID), which is used as reference in the
context of an agent-signed-data object. Note that this is an
additional requirement for issuing the certificate, as [IEEE-802.1AR]
only requires the SKID to be included for intermediate CA
certificates. In the specific application of BRSKI-AE, it is used in
favor of a certificate fingerprint to avoid additional computations.
Using an LDevID for TLS client-side authentication is a deviation
from [RFC8995], in which the pledge's IDevID credential is used to
perform TLS client authentication. The use of the LDevID(RegAgt)
allows the domain registrar to distinguish, if bootstrapping is
initiated from a pledge or from a registrar-agent and adopt the
internal handling accordingly. As BRSKI-AE uses authenticated self-
contained data objects between the pledge and the domain registrar,
the binding of the pledge identity to the request object is provided
by the data object signature employing the pledge's IDevID. The
objects exchanged between the pledge and the domain registrar used in
the context of this specifications are JOSE objects
In addition to the LDevID(RegAgt), the registrar-agent is provided
with the product-serial-numbers of the pledges to be bootstrapped.
This is necessary to allow the discovery of pledges by the registrar-
agent using mDNS. The list may be provided by administrative means
or the registrar agent may get the information via an interaction
with the pledge, like scanning of product-serial-number information
using a QR code or similar.
According to [RFC8995] section 5.3, the domain registrar performs the
pledge authorization for bootstrapping within his domain based on the
pledge voucher-request object.
The following information is therefore available at the registrar-
agent:
o LDevID(RegAgt): own operational key pair.
o LDevID(reg) certificate: certificate of the domain registrar.
o Serial-number(s): product-serial-number(s) of pledge(s) to be
bootstrapped.
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5.2.2.1. Registrar discovery by the registrar-agent
The discovery of the domain registrar may be done as specified in
[RFC8995] with the deviation that it is done between the registrar-
agent and the domain registrar. Alternatively, the registrar-agent
may be configured with the address of the domain registrar and the
certificate of the domain registrar.
5.2.2.2. Pledge discovery by the registrar-agent
The discovery of the pledge by registrar-agent should be done by
using DNS-based Service Discovery [RFC6763] over Multicast DNS
[RFC6762] to discover the pledge at "product-serial-number.brski-
pledge._tcp.local." The pledge constructs a local host name based on
device local information (product-serial-number), which results in
"product-serial-number.brski-pledge._tcp.local.". It can then be
discovered by the registrar-agent via mDNS. Note that other
mechanisms for discovery may be used.
The registrar-agent is able to build the same information based on
the provided list of product-serial-number.
5.2.3. Bootstrapping objects and corresponding exchanges
The interaction of the pledge with the registrar-agent may be
accomplished using different transport means (protocols and or
network technologies). For this document the usage of HTTP is
targeted as in BRSKI. Alternatives may be CoAP, Bluetooth Low Energy
(BLE), or Nearfield Communication (NFC). This requires independence
of the exchanged data objects between the pledge and the registrar
from transport security. Therefore, authenticated self-contained
objects (here: signature-wrapped objects) are applied in the data
exchange between the pledge and the registrar.
The registrar-agent provides the domain-registrar certificate
(LDevID(Reg) EE certificate) to the pledge to be included into the
"agent-provided-proximity-registrar-certificate" leaf in the pledge-
voucher-request object. This enables the registrar to verify, that
it is the target registrar for handling the request. The registrar
certificate may be configured at the registrar-agent or may be
fetched by the registrar-agent based on a prior TLS connection
establishment with the domain registrar. In addition, the registrar-
agent provides agent-signed-data containing the product-serial-number
in the body, signed with the LDevID(RegAgt). This enables the
registrar to verify and log, which registrar-agent was in contact
with the pledge. Optionally the registrar-agent may provide its
LDevID(RegAgt) certificate to the pledge for inclusion into the
pledge-voucher-request as "agent-sign-cert" leaf. Note that this may
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be omitted in constraint environments to safe bandwidth between the
registrar-agent and the pledge. If not contained, the registrar-
agent MUST fetch the LDevID(RegAgt) certificate based on the
SubjectKeyIdentifier (SKID) in the header of the agent-signed-data.
The registrar may include the LDevID(RegAgt) certificate information
into the registrar-voucher-request.
The MASA in turn verifies the LDevID(Reg) certificate is included in
the pledge-voucher-request (prior-signed-voucher-request) in the
"agent-provided-proximity-registrar-certificate" leaf and may assert
in the voucher "verified" or "logged" instead of "proximity", as
there is no direct connection between the pledge and the registrar.
If the LDevID(RegAgt) certificate is included contained in the
"agent-sign-cert" leave of the registrar-voucher-request, the MASA
can verify the LDevID(RegAgt) certificate and the signature of the
registrar-agent in the agent-signed-data provided in the prior-
signed-voucher-request. If both can be verified successfully, the
MASA can assert "agent-proximity" in the voucher. Otherwise, it may
assert "verified" or "logged". The voucher can then be supplied via
the registrar to the registrar-agent.
Figure 4 provides an overview of the exchanges detailed in the
following sub sections.
+--------+ +-----------+ +-----------+ +--------+ +---------+
| Pledge | | Registrar | | Domain | | Domain | | Vendor |
| | | Agent | | Registrar | | CA | | Service |
| | | (RegAgt) | | (JRC) | | | | (MASA) |
+--------+ +-----------+ +-----------+ +--------+ +---------+
| | | | Internet |
[discovery of pledge]
| mDNS query | | | |
|<-------------| | | |
|------------->| | | |
| | | | |
[trigger pledge-voucher-request and
pledge-enrollment-request generation]
|<- vTrigger --| | | |
|-Voucher-Req->| | | |
| | | | |
|<- eTrigger --| | | |
|- Enroll-Req->| | | |
~ ~ ~ ~ ~
[provide pledge-voucher-request to infrastructure]
| |<------ TLS ----->| | |
| |-- Voucher-Req -->| | |
| | [accept device?] | |
| | [contact vendor] | |
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| | |------- Voucher-Req ------>|
| | | [extract DomainID]
| | | [update audit log]
| | |<-------- Voucher ---------|
| |<---- Voucher ----| | |
| | | | |
[provide pledge enrollment request to infrastructure]
| |-- Enroll-Req --->| | |
| | |- Cert-Req -->| |
| | |<-Certificate-| |
| |<-- Enroll-Resp --| | |
~ ~ ~ ~ ~
[provide voucher and certificate
to pledge and collect status info]
|<-- Voucher --| | | |
|-- vStatus -->| | | |
|<-Enroll-Resp-| | | |
|-- eStatus -->| | | |
~ ~ ~ ~ ~
[provide voucher-status and enrollment status to registrar]
| |<------ TLS ----->| | |
| |---- vStatus --->| | |
| | |-- req. device audit log ->|
| | |<---- device audit log ----|
| | [verify audit log]
| | | | |
| |---- eStatus --->| | |
| | | | |
Figure 4: Overview pledge-responder-mode exchanges
The following sub sections split the interactions between the
different components into:
o Request objects acquisition targets exchanges and objects between
the registrar-agent and the pledge.
o Request handling targets exchanges and objects between the
registrar-agent and the registrar and also the interaction of the
registrar with the MASA and the domain CA.
o Response object supply targets the exchanges and objects between
the registrar-agent and the pledge including the status objects.
o Status handling addresses the exchanges between the registrar-
agent and the registrar.
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5.2.3.1. Request objects acquisition (registrar-agent - pledge)
The following description assumes that the registrar-agent already
discovered the pledge. This may be done as described in
Section 5.2.2.2 based on mDNS.
The focus is on the exchange of signature-wrapped objects using
endpoints defined for the pledge in Section 5.2.1.
Preconditions:
o Pledge: possesses IDevID
o Registrar-agent: possesses IDevID CA certificate and an own
LDevID(RegAgt) EE credential for the registrar domain. In
addition, the registrar-agent can be configured with the product-
serial-number(s) of the pledge(s) to be bootstrapped. Note that
the product-serial-number may have been used during the pledge
discovery already.
o Registrar: possesses IDevID CA certificate and an own LDevID/Reg)
credential.
o MASA: possesses own credentials (voucher signing key, TLS server
certificate) as well as IDevID CA certificate of pledge vendor /
manufacturer and site-specific LDevID CA certificate.
+--------+ +-----------+
| Pledge | | Registrar |
| | | Agent |
| | | (RegAgt) |
+--------+ +-----------+
| |-create
| | agent-signed-data
|<--- trigger pledge-voucher-request ----|
|-agent-provided-proximity-registrar-cert|
|-agent-signed-data |
|-agent-sign-cert (optional) |
| |
|----- pledge-voucher-request ---------->|-store
| | pledge-voucher-request
|<----- trigger enrollment request ------|
| (empty) |
| |
|------ pledge-enrollment-request ------>|-store
| | pledge-enrollment-req.
Figure 5: Request collection (registrar-agent - pledge)
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Triggering the pledge to create the pledge-voucher-request is done
using HTTPS POST on the defined pledge endpoint "/.well-known/brski/
pledge-voucher-request".
The registrar-agent pledge-voucher-request Content-Type header is:
application/json: defines a JSON document to provide three parameter:
o agent-provided-proximity-registrar-cert: base64-encoded
LDevID(Reg) TLS EE certificate.
o agent-sign-cert: base64-encoded LDevID(RegAgt) signing certificate
(optional).
o agent-signed-data: base64-encoded JWS-object.
Note that optionally including the agent-sign-cert enables the pledge
to verify at least the signature of the agent-signed-data. It may
not verify the agent-sign-cert itself due to missing issuing CA
information.
The agent-signed-data is JOSE object and contains the following
information:
The header of the agent-signed-data contains:
o alg: algorithm used for creating the object signature.
o kid: contains the base64-encoded SubjectKeyIdentifier of the
LDevID(RegAgt) certificate.
The body of the agent-signed-data contains an ietf-voucher-
request:agent-signed-data element:
[RFC Editor: please delete] /*
Open Issue regarding YANG Definition. Is either definition of ietf-
voucher-request:agent-signed-data as new leaf in the existing or
ietf-voucher-request-trigger:agent-signed-data as new module or or
would it be sufficient to just keep the product-serial-number and the
date?*/
o created-on: MUST contain the creation date and time in yang:date-
and-time format.
o serial-number: MUST contain the product-serial-number as type
string as defined in [RFC8995], section 2.3.1. The serial-number
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corresponds with the product-serial-number contained in the
X520SerialNumber field of the IDevID certificate of the pledge.
{
"alg": "ES256",
"kid": "base64encodedvalue=="
}
{
"ietf-voucher-request-trigger:agent-signed-data": {
"created-on": "2021-04-16T00:00:01.000Z",
"serial-number": "callee4711"
}
}
{
SIGNATURE
}
Figure 6: Example of agent-signed-data
Upon receiving the voucher-request trigger, the pledge SHOULD
construct the body of the pledge-voucher-request object as defined in
[RFC8995]. This object becomes a JSON-in-JWS object as defined in
[I-D.richardson-anima-jose-voucher].
The header of the pledge-voucher-request SHALL contain the following
parameter as defined in [RFC7515]:
o alg: algorithm used for creating the object signature.
o x5c: contains the base64-encoded pledge IDevID certificate.
The body of the pledge-voucher-request object MUST contain the
following parameter as part of the ietf-voucher-request:voucher as
defined in [RFC8995]:
o created-on: contains the current date and time in yang:date-and-
time format.
o nonce: contains a cryptographically strong random or pseudo-random
number.
o serial-number: contains the base64-encoded pledge product-serial-
number.
o assertion: contains the requested voucher assertion.
The ietf-voucher-request:voucher is enhanced with additional
parameters:
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o agent-provided-proximity-registrar-cert: MUST be included and
contains the base64-encoded LDevID(Reg) EE certificate (provided
as trigger parameter by the registrar-agent).
o agent-signed-data: MUST contain the base64-encoded agent-signed-
data (as defined in Figure 6) and provided as trigger parameter.
o agent-sign-cert: May contain the base64-encoded LDevID(RegAgt) EE
certificate if provided as trigger parameter.
The enhancements of the YANG module for the ietf-voucher-request with
these new leafs are defined in Section 6.
The object is signed using the pledges IDevID credential contained as
x5c parameter of the JOSE header.
{
"alg": "ES256",
"x5c": ["MIIB2jCC...dA=="]
}
{
"ietf-voucher-request:voucher": {
"created-on": "2021-04-16T00:00:02.000Z",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"serial-number": "callee4711",
"assertion": "agent-proximity",
"agent-provided-proximity-registrar-cert": "base64encodedvalue==",
"agent-signed-data": "base64encodedvalue==",
"agent-sign-cert": "base64encodedvalue=="
}
}
{
SIGNATURE
}
Figure 7: Example of pledge-voucher-request
The pledge-voucher-request Content-Type is defined in
[I-D.richardson-anima-jose-voucher] as:
application/voucher-jose+json
The pledge SHOULD include an "Accept" header field indicating the
acceptable media type for the voucher response. The media type
"application/voucher-jose+json" is defined in
[I-D.richardson-anima-jose-voucher].
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Once the registrar-agent has received the pledge-voucher-request it
can trigger the pledge to generate an enrollment-request object. As
in BRSKI the enrollment request object is a PKCS#10, additionally
signed by the IDevID. Note, as the initial enrollment aims to
request a general certificate, no certificate attributes are provided
to the pledge.
Triggering the pledge to create the enrollment-request is done using
HTTPS GET on the defined pledge endpoint "/.well-known/brski/pledge-
enrollment-request".
The registrar-agent pledge-enrollment-request Content-Type header is:
application/json:
with an empty body.
Upon receiving the enrollment-trigger, the pledge SHALL construct the
pledge-enrollment-request as authenticated self-contained object.
The CSR already assures proof of possession of the private key
corresponding to the contained public key. In addition, based on the
additional signature using the IDevID, proof of identity is provided.
Here, a JOSE object is being created in which the body utilizes the
YANG module for the CSR as defined in [I-D.ietf-netconf-sztp-csr].
Depending on the capability of the pledge, it MAY construct the
enrollment request as plain PKCS#10. Note that the focus here is
placed on PKCS#10 as PKCS#10 can be transmitted in different
enrollment protocols like EST, CMP, CMS, and SCEP. If the pledge is
already implementing an enrollment protocol, it may leverage that
functionality for the creation of the enrollment request object.
Note also that [I-D.ietf-netconf-sztp-csr] also allows for inclusion
of certificate request objects from CMP or CMC.
The pledge SHOULD construct the pledge-enrollment-request as PKCS#10
object and sign it additionally with its IDevID credential. The
pledge-enrollment-request should be encoded as JOSE object.
[RFC Editor: please delete] /* Open Issues: Depending on target
environment, it may be useful to assume that the pledge may already
"know" its functional scope and therefore the number of certificates
needed during operation. As a result, multiple CSRs may be generated
to provide achieve multiple certificates as a result of the
enrollment. This would need further description and potential
enhancements also in the enrollment-request object to transport
different CSRs. */
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[I-D.ietf-netconf-sztp-csr] considers PKCS#10 but also CMP and CMC as
certificate request format. Note that the wrapping signature is only
necessary for plain PKCS#10 as other request formats like CMP and CMS
support the signature wrapping as part of their own certificate
request format.
The registrar-agent enrollment-request Content-Type header for a
wrapped PKCS#10 is:
application/jose:
The header of the pledge enrollment-request SHALL contain the
following parameter as defined in [RFC7515]:
o alg: algorithm used for creating the object signature.
o x5c: contains the base64-encoded pledge IDevID certificate.
The body of the pledge enrollment-request object SHOULD contain a P10
parameter (for PKCS#10) as defined for ietf-sztp-csr:csr in
[I-D.ietf-netconf-sztp-csr]:
o P10: contains the base64-encoded PKCS#10 of the pledge.
The JOSE object is signed using the pledge's IDevID credential, which
corresponds to the certificate signaled in the JOSE header.
{
"alg": "ES256",
"x5c": ["MIIB2jCC...dA=="]
}
{
"ietf-sztp-csr:csr": {
"p10": "base64encodedvalue=="
}
}
{
SIGNATURE
}
Figure 8: Example of pledge-enrollment-request
With the collected pledge-voucher-request object and the pledge-
enrollment-request object, the registrar-agent starts the interaction
with the domain registrar.
[RFC Editor: please delete] /*
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Open Issues: further description necessary at least for */
o Values to be taken from the IDevID into the PKCS#10 (like product-
serial-number or subjectName, or certificate template)
Once the registrar-agent has collected the pledge-voucher-request and
pledge-enrollment-request objects, it connects to the registrar and
sends the request objects. As the registrar-agent is intended to
work between the pledge and the domain registrar, a collection of
requests from more than one pledges is possible, allowing a bulk
bootstrapping of multiple pledges using the same connection between
the registrar-agent and the domain registrar.
5.2.3.2. Request handling (registrar-agent - infrastructure)
The bootstrapping exchange between the registrar-agent and the domain
registrar resembles the exchanges between the pledge and the domain
registrar from BRSKI in the pledge-initiator-mode with some
deviations.
Preconditions:
o Registrar-agent: possesses IDevID CA certificate and own
LDevID(RegAgt) EE credential of registrar domain. It knows the
address of the domain registrar through configuration or discovery
by, e.g., mDNS/DNSSD. The registrar-agent has acquired pledge-
voucher-request and pledge-enrollment-request objects(s).
o Registrar: possesses IDevID CA certificate of pledge vendors /
manufacturers and an own LDevID(Reg) EE credential.
o MASA: possesses own credentials (voucher signing key, TLS server
certificate) as well as IDevID CA certificate of pledge vendor /
manufacturer and site-specific LDevID CA certificate.
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+-----------+ +-----------+ +--------+ +---------+
| Registrar | | Domain | | Domain | | Vendor |
| Agent | | Registrar | | CA | | Service |
| (RegAgt) | | (JRC) | | | | (MASA) |
+-----------+ +-----------+ +--------+ +---------+
| | | Internet |
[exchange between pledge and ]
[registrar-agent done. ]
| | | |
|<------ TLS ----->| | |
| | | |
|-- Voucher-Req -->| | |
| [accept device?] | |
| [contact vendor] | |
| |------------ TLS --------->|
| |-- Voucher-Req ----------->|
| | [extract DomainID]
| | [update audit log]
|<---- Voucher ----|<-------- Voucher ---------|
| | | |
[certification request handling registrar-agent]
[and site infrastructure]
|--- Enroll-Req -->| | |
| |---- TLS ---->| |
| |- Enroll-Req->| |
| |<-Enroll-Resp-| |
|<-- Enroll-Resp---| | |
| | | |
Figure 9: Request processing between registrar-agent and
infrastructure bootstrapping services
The registrar-agent establishes a TLS connection with the registrar.
As already stated in [RFC8995], the use of TLS 1.3 (or newer) is
encouraged. TLS 1.2 or newer is REQUIRED on the registrar-agent
side. TLS 1.3 (or newer) SHOULD be available on the registrar, but
TLS 1.2 MAY be used. TLS 1.3 (or newer) SHOULD be available on the
MASA, but TLS 1.2 MAY be used.
In contrast to [RFC8995] client authentication is achieved by using
the LDevID(RegAgt) of the registrar-agent instead of the IDevID of
the pledge. This allows the registrar to distinguish between pledge-
initiator-mode and pledge-responder-mode. In pledge-responder-mode
the registrar has no direct connection to the pledge but via the
registrar-agent. The registrar can receive request objects in
different forms as defined in [RFC8995]. Specifically, the registrar
will receive JOSE objects from the pledge for voucher-request and
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enrollment-request (instead of the objects for voucher-request (CMS-
signed JSON) and enrollment-request (PKCS#10).
The registrar-agent sends the pledge-voucher-request to the registrar
with an HTTPS POST to the endpoint "/.well-known/brski/
requestvoucher".
The pledge-voucher-request Content-Type used in the pledge-responder-
mode is defined in [I-D.richardson-anima-jose-voucher] as:
application/voucher-jose+json (see Figure 7 for the content
definition).
The registrar-agent SHOULD include the "Accept" header field received
during the communication with the pledge, indicating the pledge
acceptable Content-Type for the voucher-response. The voucher-
response Content-Type "application/voucher-jose+json" is defined in
[I-D.richardson-anima-jose-voucher].
Upon reception of the pledge-voucher-request, the registrar SHALL
perform the verification of the voucher-request parameter as defined
in section 5.3 of [RFC8995]. In addition, the registrar shall verify
the following parameters from the pledge-voucher-request:
o agent-provided-proximity-registrar-cert: MUST contain the own
LDevID(Reg) EE certificate to ensure the registrar in proximity is
the target registrar for the request.
o agent-signed-data: The registrar MUST verify that the data has
been signed with the LDevID(RegAgt) credential indicated in the
"kid" JOSE header parameter. If the certificate is not contained
in the agent-sign-cert component of the pledge-voucher-request, it
must fetch the certificate from a repository.
o agent-sign-cert: May contain the base64-encoded LDevID(RegAgt)
certificate. If contained the registrar MUST verify that the
connected credential used to sign the data was valid at signature
creation time and that the corresponding registrar-agent was
authorized to be involved in the bootstrapping.
If validation fails the registrar SHOULD respond with the HTTP 404
error code to the registrar-agent. If the pledge-voucher-request is
in an unknown format, then an HTTP 406 error code is more
appropriate.
If validation succeeds, the registrar will accept the pledge request
to join the domain as defined in section 5.3 of [RFC8995]. The
registrar then establishes a TLS connection with the MASA as
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described in section 5.4 of [RFC8995] to obtain a voucher for the
pledge.
The registrar SHALL construct the body of the registrar-voucher-
request object as defined in [RFC8995]. The encoding SHALL be done
as JOSE object as defined in [I-D.richardson-anima-jose-voucher].
The header of the registrar-voucher-request SHALL contain the
following parameter as defined in [RFC7515]:
o alg: algorithm used for creating the object signature.
o x5c: contains the base64-encoded registrar LDevID certificate.
The body of the registrar-voucher-request object MUST contain the
following parameter as part of the ietf-voucher-request:voucher as
defined in [RFC8995]:
o created-on: contains the current date and time in yang:date-and-
time format for the registrar-voucher-request creation time.
o nonce: copied form the pledge-voucher-request
o serial-number: contains the base64-encoded product-serial-number.
The registrar MUST verify that the product-serial-number contained
in the IDevID certificate of the pledge matches the serial-number
field in the pledge-voucher-request. In addition, it MUST be
equal to the serial-number field contained in the agent-signed
data of pledge-voucher-request.
o assertion: contains the voucher assertion requested the pledge
(agent-proximity). The registrar provides this information to
assure successful verification of agent proximity based on the
agent-signed-data.
The ietf-voucher-request:voucher can be optionally enhanced with the
following additional parameter:
o agent-sign-cert: Contain the base64-encoded LDevID(RegAgt) EE
certificate if MASA verification of agent-proximity is required to
provide the assertion "agent-proximity".
The object is signed using the registrar LDevID(Reg) credential,
which corresponds to the certificate signaled in the JOSE header.
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{
"alg": "ES256",
"x5c": ["MIIB2jCC...dA=="]
}
{
"ietf-voucher-request:voucher": {
"created-on": "2021-04-16T02:37:39.235Z",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"serial-number": "callee4711",
"assertion": "agent-proximity",
"prior-signed-voucher-request": "base64encodedvalue==",
"agent-sign-cert": "base64encodedvalue=="
}
}
{
SIGNATURE
}
Figure 10: Example of registrar-voucher-request
The registrar sends the registrar-voucher-request to the MASA with an
HTTPS POST at the endpoint "/.well-known/brski/requestvoucher".
The registrar-voucher-request Content-Type is defined in
[I-D.richardson-anima-jose-voucher] as:
application/voucher-jose+json
The registrar SHOULD include an "Accept" header field indicating the
acceptable media type for the voucher-response. The media type
"application/voucher-jose+json" is defined in
[I-D.richardson-anima-jose-voucher].
Once the MASA receives the registrar-voucher-request it SHALL perform
the verification of the contained components as described in section
5.5 in [RFC8995]. In addition, the following additional processing
SHALL be done for components contained in the prior-signed-voucher-
request:
o agent-provided-proximity-registrar-cert: The MASA MAY verify that
this field contains the LDevID(Reg) certificate. If so, it MUST
be consistent with the certificate used to sign the registrar-
voucher-request.
o agent-signed-data: The MASA MAY verify this field to be able to
provide an assertion "agent-proximity". If so, the agent-signed-
data MUST contain the product-serial-number of the pledge
contained in the serial-number component of the prior-signed-
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voucher and also in serial-number component of the registrar-
voucher-request. The LDevID(RegAgt) used to generate provide the
signature is identified by the "kid" parameter of the JOSE header
(agent-signed-data). If the assertion "agent-proximity" is
requested, the registrar-voucher-request MUST contain the
corresponding LDevID(RegAgt) EE certificate in the agent-sign-
cert, which can be verified by the MASA as issued by the same
domain CA as the LDevID(Reg) EE certificate. If the agent-sign-
cert is not provided, the MASA MAY provide a lower level assertion
"logged" or "verified"
If validation fails, the MASA SHOULD respond with an HTTP error code
to the registrar. The error codes are kept as defined in section 5.6
of [RFC8995]. and comprise the response codes 403, 404, 406, and
415.
The voucher response format is as indicated in the submitted Accept
header fields or based on the MASA's prior understanding of proper
format for this pledge. Specifically for the pledge-responder-mode
the "application/voucher-jose+json" as defined in
[I-D.richardson-anima-jose-voucher] is applied. The syntactic
details of vouchers are described in detail in [RFC8366]. Figure 11
shows an example of the contents of a voucher.
{
"alg": "ES256",
"x5c": ["MIIBkzCCAT...dA=="]
}
{
"ietf-voucher:voucher": {
"assertion": "agent-proximity",
"serial-number": "callee4711",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"created-on": "2021-04-17T00:00:02.000Z",
"pinned-domain-cert": "MIIBpDCCA...w=="
}
}
{
SIGNATURE
}
Figure 11: Example of MASA issued voucher
The MASA sends the voucher in the indicated form to the registrar.
After receiving the voucher the registrar may evaluate the voucher
for transparency and logging purposes as outlined in section 5.6 of
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[RFC8995]. The registrar forwards the voucher without changes to the
registrar-agent.
After receiving the voucher, the registrar-agent sends the pledge's
enrollment-request to the registrar. Deviating from BRSKI the
enrollment-request is not a raw PKCS#10 request. As the registrar-
agent is involved in the exchange, the PKCS#10 is contained in the
JOSE object. The signature is created using the pledge's IDevID to
provide proof-of-identity as outlined in Figure 8.
When using EST, the registrar-agent sends the enrollment request to
the registrar with an HTTPS POST at the endpoint "/.well-known/est/
simpleenroll".
The enrollment-request Content-Type is:
application/jose
If validation of the wrapping signature fails, the registrar SHOULD
respond with the HTTP 404 error code. If the voucher-request is in
an unknown format, then an HTTP 406 error code is more appropriate.
A situation that could be resolved with administrative action (such
as adding a vendor/manufacturer IDevID CA as trusted party) MAY be
responded with an 403 HTTP error code.
This results in a deviation from the content types used in [RFC7030]
and results in additional processing at the domain registrar as EST
server as following. Note that the registrar is already aware that
the bootstrapping is performed in a pledge-responder-mode due to the
use of the LDevID(RegAgt) certificate in the TLS establishment and
the provided pledge-voucher-request in JOSE object.
o If registrar receives the enrollment-request with the Content Type
application/jose, it MUST verify the signature using the
certificate indicated in the JOSE header.
o The domain registrar verifies that the serial-number contained in
the pledge's IDevID certificate contained in the JOSE header as
being accepted to join the domain, based on the verification of
the pledge-voucher-request.
o If both succeed, the registrar utilizes the PKCS#10 request
contained in the JOSE body as "P10" parameter of "ietf-sztp-
csr:csr" for further processing of the enrollment request with the
domain CA.
[RFC Editor: please delete] /*
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Open Issues:
o The domain registrar may either enhance the PKCS#10 request or
generate a structure containing the attributes to be included by
the CA and sends both (the original PKCS#10 request and the
enhancements) to the domain CA. As enhancing the PKCS#10 request
destroys the initial proof of possession of the corresponding
private key, the CA would need to accept RA-verified requests.
A successful interaction with the domain CA will result in the pledge
LDevID EE certificate, which is then forwarded by the registrar to
the registrar-agent using the content type "application/pkcs7-mime".
The registrar-agent has now finished the exchanges with the domain
registrar. Now the registrar-agent can supply the voucher-response
(from MASA via Registrar) and the enrollment-response (LDevID EE
certificate) to the pledge. It can close the TLS connection to the
domain registrar and provide the objects to the pledge(s). The
content of the response objects is defined through the voucher
[RFC8366] and the certificate [RFC5280].
5.2.3.3. Response object supply (registrar-agent - pledge)
The following description assumes that the registrar-agent has
obtained the response objects from the domain registrar. It will re-
start the interaction with the pledge. To contact the pledge, it may
either discover the pledge as described in Section 5.2.2.2 or use
stored information from the first contact with the pledge.
Preconditions in addition to Section 5.2.3.2:
o Registrar-agent: possesses voucher and LDevID certificate.
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+--------+ +-----------+
| Pledge | | Registrar |
| | | Agent |
| | | (RegAgt) |
+--------+ +-----------+
| |
|<------- supply voucher -----------|
| |
|--------- voucher-status --------->| - store
| | pledge voucher-status
|<--- supply enrollment response ---|
| |
|--------- enroll-status ---------->| - store
| | pledge enroll-status
Figure 12: Response and status handling between pledge and registrar-
agent
The registrar-agent provides the information via two distinct
endpoints to the pledge as following.
The voucher response is provided with a HTTP POST using the operation
path value of "/.well-known/brski/pledge-voucher".
The registrar-agent voucher-response Content-Type header is
"application/voucher-jose+json and contains the voucher as provided
by the MASA. An example if given in Figure 11.
The pledge verifies the voucher as described in section 5.6.1 in
[RFC8995].
After successful verification the pledge MUST reply with a status
telemetry message as defined in section 5.7 of [RFC8995]. As for the
other objects, the defined object is provided with an additional
signature using JOSE. The pledge generates the voucher-status-object
and provides it in the response message to the registrar-agent.
The response has the Content-Type "application/jose", signed using
the IDevID of the pledge as shown in Figure 13. As the reason field
is optional (see [RFC8995]), it MAY be omitted in case of success.
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{
"alg": "ES256",
"x5c": ["MIIB2jCC...dA=="]
{
"version": 1,
"status":true,
"reason":"Informative human readable message",
"reason-context": { "additional" : "JSON" }
}
{
SIGNATURE
}
Figure 13: Example of pledge voucher-status telemetry
The enrollment response is provided with a HTTP POST using the
operation path value of "/.well-known/brski/pledge-enrollment".
The registrar-agent enroll-response Content-Type header when using
EST [RFC7030] as enrollment protocol, from the registrar-agent to the
infrastructure is:
application/pkcs7-mime: note that it only contains the LDevID
certificate for the pledge, not the certificate chain.
[RFC Editor: please delete] /*
Open Issue: the enrollment response object may also be an
application/jose object with a signature of the domain registrar.
This may be used either to transport additional data which is bound
to the LDevID or it may be considered for enrollment status to ensure
that in an error case the registrar providing the certificate can be
identified. */
After successful verification the pledge MUST reply with a status
telemetry message as defined in section 5.9.4 of [RFC8995]. As for
the other objects, the defined object is provided with an additional
signature using the JOSE. The pledge generates the enrollment status
and provides it in the response message to the registrar-agent.
The response has the Content-Type "application/jose", signed using
the LDevID of the pledge as shown in Figure 14. As the reason field
is optional, it MAY be omitted in case of success.
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{
"alg": "ES256",
"x5c": ["MIIB56uz...dA=="]
{
"version": 1,
"status":true,
"reason":"Informative human readable message",
"reason-context": { "additional" : "JSON" }
}
{
SIGNATURE
}
Figure 14: Example of pledge enroll-status telemetry
Once the registrar-agent has collected the information, it can
connect to the registrar agent to provide the status responses to the
registrar.
5.2.3.4. Telemetry status handling (registrar-agent - domain registrar)
The following description assumes that the registrar-agent has
collected the status objects from the pledge. It will provide the
status objects to the registrar for further processing and audit log
information of voucher-status for MASA.
Preconditions in addition to Section 5.2.3.2:
o Registrar-agent: possesses voucher-status and enroll-status
objects from pledge.
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+-----------+ +-----------+ +--------+ +---------+
| Registrar | | Domain | | Domain | | Vendor |
| Agent | | Registrar | | CA | | Service |
| RegAgt) | | (JRC) | | | | (MASA) |
+-----------+ +-----------+ +--------+ +---------+
| | | Internet |
| | | |
|<------ TLS ----->| | |
| | | |
|--Voucher-Status->| | |
| |<---- device audit log ----|
| [verify audit log ]
| | | |
|--Enroll-Status-->| | |
| | | |
| | | |
Figure 15: Bootstrapping status handling
The registrar-agent MUST provide the collected pledge voucher-status
to the registrar. This status indicates the pledge could process the
voucher successfully or not.
If the TLS connection to the registrar was closed, the registrar-
agent establishes a TLS connection with the registrar as stated in
Section 5.2.3.2.
The registrar-agent sends the pledge voucher-status object without
modification to the registrar with an HTTPS POST using the operation
path value of "/.well-known/brski/voucher_status". The Content-Type
header is kept as "application/jose" as described in Figure 12 and
depicted in the example in Figure 13.
The registrar SHALL verify the signature of the pledge voucher-status
and validate that it belongs to an accepted device in his domain
based on the contained "serial-number" in the IDevID certificate
referenced in the header of the voucher-status object.
According to [RFC8995] section 5.7, the registrar SHOULD respond with
an HTTP 200 but MAY simply fail with an HTTP 404 error. The
registrar-agent may use the response to signal success / failure to
the service technician operating the registrar agent. Within the
server logs the server SHOULD capture this telemetry information.
The registrar SHOULD proceed with the collecting and logging the
status information by requesting the MASA audit-log from the MASA
service as described in section 5.8 of [RFC8995].
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The registrar-agent MUST provide the enroll-status object to the
registrar. The status indicates the pledge could process the enroll-
response object and holds the corresponding private key.
The registrar-agent sends the pledge enroll-status object without
modification to the registrar with an HTTPS POST using the operation
path value of "/.well-known/brski/enrollstatus". The Content-Type
header is kept as "application/jose" as described in Figure 12 and
depicted in the example in Figure 14.
The registrar SHALL verify the signature of the pledge enroll-status
object and validate that it belongs to an accepted device in his
domain based on the contained product-serial-number in the LDevID EE
certificate referenced in the header of the enroll-status object.
Note that the verification of a signature of the object is a
deviation form the described handling in section 5.9.4 of [RFC8995].
According to [RFC8995] section 5.9.4, the registrar SHOULD respond
with an HTTP 200 but MAY simply fail with an HTTP 404 error. The
registrar-agent may use the response to signal success / failure to
the service technician operating the registrar agent. Within the
server log the registrar SHOULD capture this telemetry information.
5.3. Domain registrar support of different enrollment options
Well-known URIs for different endpoints on the domain registrar are
already defined as part of the base BRSKI specification. In
addition, alternative enrollment endpoints may be supported at the
domain registrar. The pledge / registrar-agent will recognize if its
supported enrollment option is supported by the domain registrar by
sending a request to its preferred enrollment endpoint.
The following provides an illustrative example for a domain registrar
supporting different options for EST as well as CMP to be used in
BRSKI-AE. The listing contains the supported endpoints for the
bootstrapping, to which the pledge may connect. This includes the
voucher handling as well as the enrollment endpoints. The CMP
related enrollment endpoints are defined as well-known URI in CMP
Updates [I-D.ietf-lamps-cmp-updates].
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,ct=voucher-cms+json
,ct=json
,ct=json
;ct=pkcs7-mime
;ct=pkcs7-mime
;ct=pkcs7-mime
;ct=pkcs7-mime
;ct= pkcs7-mime
;ct=pkcs7-mime
;ct=pkixcmp
;ct=pkixcmp
;ct=pkixcmp
;ct=pkixcmp
;ct=pkixcmp
;ct=pkixcmp
[RFC Editor: please delete] /*
Open Issues:
o In addition to the current content types, we may specify that the
response provide information about different content types as
multiple values. This would allow to further adopt the encoding
of the objects exchanges (ASN.1, JSON, CBOR, ...). -> dependent
on the utilized protocol.
*/
6. YANG Extensions to Voucher Request
The following modules extends the [RFC8995] Voucher Request to
include a signed artifact from the registrar-agent as well as the
registrar-proximity-certificate and the agent-signing certificate.
module ietf-async-voucher-request {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-async-voucher-request";
prefix "constrained";
import ietf-restconf {
prefix rc;
description
"This import statement is only present to access
the yang-data extension defined in RFC 8040.";
reference "RFC 8040: RESTCONF Protocol";
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}
import ietf-voucher-request {
prefix ivr;
description
"This module defines the format for a voucher request,
which is produced by a pledge as part of the RFC8995
onboarding process.";
reference
"RFC 8995: Bootstrapping Remote Secure Key Infrastructure";
}
organization
"IETF ANIMA Working Group";
contact
"WG Web:
WG List:
Author: Steffen Fries
Author: Hendrik Brockhaus
Author: Eliot Lear
";
Author: Thomas Werner
";
description
"This module defines an extension of the RFC8995 voucher
request to permit a registrar-agent to convey the adjacency
relationship from the registrar-agent to the registrar.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
and 'OPTIONAL' in the module text are to be interpreted as
described in RFC 2119.";
revision "YYYY-MM-DD" {
description
"Initial version";
reference
"RFC XXXX: Voucher Request for Asynchronous Enrollment";
}
rc:yang-data voucher-request-async-artifact {
// YANG data template for a voucher.
uses voucher-request-async-grouping;
}
// Grouping defined for future usage
grouping voucher-request-async-grouping {
description
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"Grouping to allow reuse/extensions in future work.";
uses ivr:voucher-request-grouping {
augment "voucher-request" {
description "Base the constrained voucher-request upon the
regular one";
leaf agent-signed-data {
type binary;
description
"The agent-signed-data field contains a JOSE [RFC7515]
object provided by the Registrar-Agent to the Pledge.
This artifact is signed by the Registrar-Agent
and contains a copy of the pledge's serial-number.";
}
leaf agent-provided-proximity-registrar-cert {
type binary;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
The first certificate in the registrar TLS server
certificate_list sequence (the end-entity TLS
certificate; see RFC 8446) presented by the
registrar to the registrar-agent and provided to
the pledge.
This MUST be populated in a pledge's voucher-request
when an agent-proximity assertion is requested.";
reference
"ITU X.690: Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)
RFC 5280: Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile
RFC 8446: The Transport Layer Security (TLS)
Protocol Version 1.3";
}
leaf agent-sign-cert {
type binary;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
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This certificate can be used by the pledge,
the registrar, and the MASA to verify the signature
of agent-signed-data. It is an optional component
for the pledge-voucher request.
This MUST be populated in a registrar's
voucher-request when an agent-proximity assertion
is requested.";
reference
"ITU X.690: Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)
RFC 5280: Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile";
}
}
}
}
}
7. Example for signature-wrapping using existing enrollment protocols
This section map the requirements to support proof of possession and
proof of identity to selected existing enrollment protocols. Note
that that the work in the ACE WG described in
[I-D.selander-ace-coap-est-oscore] may be considered here as well, as
it also addresses the encapsulation of EST in a way to make it
independent from the underlying TLS using OSCORE resulting in an
authenticated self-contained object.
7.1. EST Handling
When using EST [RFC7030], the following constraints should be
considered:
o Proof of possession is provided by using the specified PKCS#10
structure in the request.
o Proof of identity is achieved by signing the certification request
object, which is only supported when Full PKI Request (the
/fullcmc endpoint) is used. This contains sufficient information
for the RA to make an authorization decision on the received
certification request. Note: EST references CMC [RFC5272] for the
definition of the Full PKI Request. For proof of identity, the
signature of the SignedData of the Full PKI Request would be
calculated using the IDevID credential of the pledge.
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o [RFC Editor: please delete] /* TBD: in this case the binding to
the underlying TLS connection is not be necessary. */
o When the RA is not available, as per [RFC7030] Section 4.2.3, a
202 return code should be returned by the Registrar. The pledge
in this case would retry a simpleenroll with a PKCS#10 request.
Note that if the TLS connection is teared down for the waiting
time, the PKCS#10 request would need to be rebuilt if it contains
the unique identifier (tls_unique) from the underlying TLS
connection for the binding.
o [RFC Editor: please delete] /* TBD: clarification of retry for
fullcmc is necessary as not specified in the context of EST */
7.2. CMP Handling
Instead of using CMP [RFC4210], this specification refers to the
lightweight CMP profile [I-D.ietf-lamps-lightweight-cmp-profile], as
it restricts the full featured CMP to the functionality needed here.
For this, the following constrains should be observed:
o For proof of possession, the defined approach in Lightweight CMP
Profile section 4.1.1 (based on CRMF) and 4.1.5 (based on PCKS#10)
should be supported.
o Proof of identity can be provided by using the signatures to
protect the certificate request message as outlined in section
3.2. of [I-D.ietf-lamps-lightweight-cmp-profile].
o When the RA/CA is not available, a waiting indication should be
returned in the PKIStatus by the Registrar. The pledge in this
case would retry using the PollReqContent with a request
identifier certReqId provided in the initial CertRequest message
as specified in section 5.2.4 of
[I-D.ietf-lamps-lightweight-cmp-profile] with delayed enrollment.
8. IANA Considerations
This document requires the following IANA actions:
IANA is requested to enhance the Registry entitled: "BRSKI well-
known URIs" with the following:
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URI document description
pledge-voucher-request [THISRFC] create pledge-voucher-request
pledge-enrollment-request [THISRFC] create pledge-enrollment-request
pledge-voucher [THISRFC] supply voucher response
pledge-enrollment [THISRFC] supply enrollment response
pledge-CACerts [THISRFC] supply CA certs to pledge
[RFC Editor: please delete] /* to be done: IANA consideration to be
included for the defined namespaces in Section 5.1.5 and Section 5.3
. */
9. Privacy Considerations
The credential used by the registrar-agent to sign the data for the
pledge in case of the pledge-initiator-mode should not contain
personal information. Therefore, it is recommended to use an LDevID
certificate associated with the device instead of a potential service
technician operating the device, to avoid revealing this information
to the MASA.
10. Security Considerations
10.1. Exhaustion attack on pledge
Exhaustion attack on pledge based on DoS attack (connection
establishment, etc.)
10.2. Misuse of acquired voucher and enrollment responses
Registrar-agent that uses acquired voucher and enrollment response
for domain 1 in domain 2: can be detected in Voucher Request
processing on domain registrar side. Requires domain registrar to
verify the proximity-registrar-cert leaf in the pledge-voucher-
request against his own as well as the association of the pledge to
his domain based on the product-serial-number contained in the
voucher.
Misbinding of pledge by a faked domain registrar is countered as
described in BRSKI security considerations (section 11.4).
Misuse of registrar-agent LDevID may be addressed by utilizing short-
lived certificates to be used for authenticating the registrar-agent
against the registrar. The LDevID certificate for the registrar-
agent may be provided by a prior BRSKI execution based on an existing
IDevID. Alternatively, the LDevID may be acquired by a service
technician after authentication against the issuing CA.
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11. Acknowledgments
We would like to thank the various reviewers for their input, in
particular Brian E. Carpenter, Michael Richardson, Giorgio
Romanenghi, Oskar Camenzind, for their input and discussion on use
cases and call flows.
12. References
12.1. Normative References
[I-D.ietf-netconf-sztp-csr]
Watsen, K., Housley, R., and S. Turner, "Conveying a
Certificate Signing Request (CSR) in a Secure Zero Touch
Provisioning (SZTP) Bootstrapping Request", draft-ietf-
netconf-sztp-csr-01 (work in progress), November 2020.
[I-D.richardson-anima-jose-voucher]
Richardson, M. and T. Werner, "JOSE signed Voucher
Artifacts for Bootstrapping Protocols", draft-richardson-
anima-jose-voucher-00 (work in progress), December 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, .
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
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[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, .
12.2. Informative References
[I-D.ietf-lamps-cmp-updates]
Brockhaus, H. and D. V. Oheimb, "Certificate Management
Protocol (CMP) Updates", draft-ietf-lamps-cmp-updates-09
(work in progress), April 2021.
[I-D.ietf-lamps-lightweight-cmp-profile]
Brockhaus, H., Fries, S., and D. V. Oheimb, "Lightweight
Certificate Management Protocol (CMP) Profile", draft-
ietf-lamps-lightweight-cmp-profile-05 (work in progress),
February 2021.
[I-D.selander-ace-coap-est-oscore]
Selander, G., Raza, S., Furuhed, M., Vucinic, M., and T.
Claeys, "Protecting EST Payloads with OSCORE", draft-
selander-ace-coap-est-oscore-04 (work in progress),
November 2020.
[IEC-62351-9]
International Electrotechnical Commission, "IEC 62351 -
Power systems management and associated information
exchange - Data and communications security - Part 9:
Cyber security key management for power system equipment",
IEC 62351-9 , May 2017.
[IEEE-802.1AR]
Institute of Electrical and Electronics Engineers, "IEEE
802.1AR Secure Device Identifier", IEEE 802.1AR , June
2018.
[ISO-IEC-15118-2]
International Standardization Organization / International
Electrotechnical Commission, "ISO/IEC 15118-2 Road
vehicles - Vehicle-to-Grid Communication Interface - Part
2: Network and application protocol requirements", ISO/
IEC 15118-2 , April 2014.
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[NERC-CIP-005-5]
North American Reliability Council, "Cyber Security -
Electronic Security Perimeter", CIP 005-5, December 2013.
[OCPP] Open Charge Alliance, "Open Charge Point Protocol 2.0.1
(Draft)", December 2019.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
.
[RFC8894] Gutmann, P., "Simple Certificate Enrolment Protocol",
RFC 8894, DOI 10.17487/RFC8894, September 2020,
.
Appendix A. History of changes [RFC Editor: please delete]
From IETF draft 01 -> IETF 02:
o Defined call flow and objects for interactions in UC2. Object
format based on draft for JOSE signed voucher artifacts and
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aligned the remaining objects with this approach in Section 5.2.3
.
o Terminology change: issue #2 pledge-agent -> registrar-agent to
better underline agent relation.
o Terminology change: issue #3 PULL/PUSH -> pledge-initiator-mode
and pledge-responder-mode to better address the pledge operation.
o 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).
o Details on trust relationship between registrar-agent and
registrar (issue #4, #5, #9) included in Section 5.2.
o Recommendation regarding short-lived certificates for registrar-
agent authentication towards registrar (issue #7) in the security
considerations.
o Introduction of reference to agent signing certificate using SKID
in agent signed data (issue #11).
o Enhanced objects in exchanges between pledge and registrar-agent
to allow the registrar to verify agent-proximity to the pledge
(issue #1) in Section 5.2.3.
o Details on trust relationship between registrar-agent and pledge
(issue #5) included in Section 5.2.
o Split of use case 2 call flow into sub sections in Section 5.2.3.
From IETF draft 00 -> IETF 01:
o Update of scope in Section 3.1 to include in which the pledge acts
as a server. This is one main motivation for use case 2.
o Rework of use case 2 in Section 5.2 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.
o First description of exchanged object types (needs more work)
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o Clarification in discovery options for enrollment endpoints at the
domain registrar based on well-known endpoints in Section 5.3 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.
o Updated references.
o Included Thomas Werner as additional author for the document.
From individual version 03 -> IETF draft 00:
o Inclusion of discovery options of enrollment endpoints at the
domain registrar based on well-known endpoints in Section 5.3 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.
o Missing details provided for the description and call flow in
pledge-agent use case Section 5.2, e.g. to accommodate
distribution of CA certificates.
o Updated CMP example in Section 7 to use lightweight CMP instead of
CMP, as the draft already provides the necessary /.well-known
endpoints.
o Requirements discussion moved to separate section in Section 4.
Shortened description of proof of identity binding and mapping to
existing protocols.
o Removal of copied call flows for voucher exchange and registrar
discovery flow from [RFC8995] in Section 5.1 to avoid doubling or
text or inconsistencies.
o 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:
o 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.
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o Simplification of the architecture approach for the initial use
case having an offsite PKI.
o 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-AE call flow.
o Update of provided examples of the addressing approach used in
BRSKI to allow for support of multiple enrollment protocols in
Section 5.1.5.
From individual version 01 -> 02:
o Update of introduction text to clearly relate to the usage of
IDevID and LDevID.
o Definition of the addressing approach used in BRSKI to allow for
support of multiple enrollment protocols in Section 5.1.5. This
section also contains a first discussion of an optional discovery
mechanism to address situations in which the registrar supports
more than one enrollment approach. Discovery should avoid that
the pledge performs a trial and error of enrollment protocols.
o Update of description of architecture elements and changes to
BRSKI in Section 5.
o Enhanced consideration of existing enrollment protocols in the
context of mapping the requirements to existing solutions in
Section 4 and in Section 7.
From individual version 00 -> 01:
o Update of examples, specifically for building automation as well
as two new application use cases in Section 3.2.
o Deletion of asynchronous interaction with MASA to not complicate
the use case. Note that the voucher exchange can already be
handled in an asynchronous manner and is therefore not considered
further. This resulted in removal of the alternative path the
MASA in Figure 1 and the associated description in Section 5.
o Enhancement of description of architecture elements and changes to
BRSKI in Section 5.
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o Consideration of existing enrollment protocols in the context of
mapping the requirements to existing solutions in Section 4.
o New section starting Section 7 with the mapping to existing
enrollment protocols by collecting boundary conditions.
Authors' Addresses
Steffen Fries
Siemens AG
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: steffen.fries@siemens.com
URI: https://www.siemens.com/
Hendrik Brockhaus
Siemens AG
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: hendrik.brockhaus@siemens.com
URI: https://www.siemens.com/
Eliot Lear
Cisco Systems
Richtistrasse 7
Wallisellen CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Thomas Werner
Siemens AG
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: thomas-werner@siemens.com
URI: https://www.siemens.com/
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