BRSKI with Pledge in Responder Mode (BRSKI-PRM)
draft-ietf-anima-brski-prm-04
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| Last updated | 2022-07-08 | ||
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draft-ietf-anima-brski-prm-04
ANIMA WG S. Fries
Internet-Draft T. Werner
Intended status: Standards Track Siemens
Expires: 9 January 2023 E. Lear
Cisco Systems
M. Richardson
Sandelman Software Works
8 July 2022
BRSKI with Pledge in Responder Mode (BRSKI-PRM)
draft-ietf-anima-brski-prm-04
Abstract
This document defines enhancements to bootstrapping a remote secure
key infrastructure (BRSKI, [RFC8995]) to facilitate bootstrapping in
domains featuring no or only timely limited connectivity between a
pledge and the domain registrar. It specifically targets situations,
in which the interaction model changes from a pledge-initiator-mode,
as used in BRSKI, to a pledge-responder-mode as described in this
document. To support both, BRSKI-PRM introduces a new registrar-
agent component, which facilitates the communication between pledge
and registrar during the bootstrapping phase. For the establishment
of a trust relation between pledge and domain registrar, BRSKI-PRM
relies on the exchange of authenticated self-contained objects
(signature-wrapped objects). The defined approach is agnostic
regarding the utilized enrollment protocol, deployed by the domain
registrar to communicate with the Domain CA.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 9 January 2023.
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scope of Solution . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Supported Environments and Use Case Examples . . . . . . 6
3.1.1. Building Automation . . . . . . . . . . . . . . . . . 7
3.1.2. Infrastructure Isolation Policy . . . . . . . . . . . 7
3.1.3. Less Operational Security in the Target-Domain . . . 7
3.2. Limitations . . . . . . . . . . . . . . . . . . . . . . . 8
4. Requirements Discussion and Mapping to Solution-Elements . . 8
5. Architectural Overview and Communication Exchanges . . . . . 9
5.1. Pledge-responder-mode (PRM): Registrar-agent Communication
with Pledges . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Agent-Proximity Assertion . . . . . . . . . . . . . . . . 13
5.3. Behavior of Pledge in Pledge-Responder-Mode . . . . . . . 14
5.4. Behavior of Registrar-Agent . . . . . . . . . . . . . . . 15
5.4.1. Discovery of Registrar by Registrar-Agent . . . . . . 16
5.4.2. Discovery of Pledge by Registrar-Agent . . . . . . . 16
5.5. Bootstrapping Objects and Corresponding Exchanges . . . . 17
5.5.1. Request Objects Acquisition by Registrar-Agent from
Pledge . . . . . . . . . . . . . . . . . . . . . . . 20
5.5.2. Request Processing by the Registrar-Agent . . . . . . 28
5.5.3. Response Object Supply by Registrar-Agent to
Pledge . . . . . . . . . . . . . . . . . . . . . . . 39
5.5.4. Telemetry status handling (registrar-agent - domain
registrar) . . . . . . . . . . . . . . . . . . . . . 43
6. Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.1. Voucher Request Artifact . . . . . . . . . . . . . . . . 45
6.1.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . 46
6.1.2. YANG Module . . . . . . . . . . . . . . . . . . . . . 46
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50
7.1. BRSKI .well-known Registry . . . . . . . . . . . . . . . 50
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 50
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9. Security Considerations . . . . . . . . . . . . . . . . . . . 50
9.1. Exhaustion Attack on Pledge . . . . . . . . . . . . . . . 50
9.2. Misuse of acquired Voucher and Enrollment objects by
Registrar-Agent . . . . . . . . . . . . . . . . . . . . . 50
9.3. Misuse of Registrar-Agent Credentials . . . . . . . . . . 51
9.4. YANG Module Security Considerations . . . . . . . . . . . 51
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 51
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
11.1. Normative References . . . . . . . . . . . . . . . . . . 52
11.2. Informative References . . . . . . . . . . . . . . . . . 53
Appendix A. History of Changes [RFC Editor: please delete] . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61
1. Introduction
BRSKI as defined in [RFC8995] specifies a solution for secure zero-
touch (automated) bootstrapping of devices (pledges) in a (customer)
site domain. This includes the discovery of network elements in the
customer site/domain and the exchange of security information
necessary to establish trust between a pledge and the domain.
Security information about the customer site/domain, specifically the
customer site/domain certificate, is exchanged utilizing voucher
objects as defined in [RFC8366]. These vouchers are signed objects,
provided via the domain registrar to the pledge and originate from a
Manufacturer's Authorized Signing Authority (MASA).
BRSKI addresses scenarios in which the pledge acts as client for the
bootstrapping and is the initiator of the bootstrapping (this
document refers to the approach as pledge-initiator-mode). In
industrial environments the pledge may behave as a server and thus
does not initiate the bootstrapping with the domain registrar. In
this scenarios it is expected that the pledge will be triggered to
generate request objects to be bootstrapped in the customer site/
domain (this document refers to the approach as pledge-responder-
mode). For this, an additional component is introduced acting as an
agent for the domain registrar (registrar-agent) towards the pledge.
This may be a functionality of a commissioning or configuration tool
or it may be even co-located with the registrar.
In contrast to BRSKI the registrar-agent facilitates 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 [RFC8995] endpoints.
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The term endpoint used in the context of this document is similar to
resources in CoAP [RFC7252] and also in HTTP [RFC9110]. It is not
used to describe a device. Endpoints are accessible via .well-known
URIs.
The goal is to enhance BRSKI to support pledges in responder mode.
This is addressed by
* introducing the registrar-agent as new component to facilitate the
communication between the pledge and the registrar, if the pledge
is in responder mode (acting as server).
* handling the security on application layer only to enable
application of arbitrary transport means between the pledge and
the domain registrar, by keeping the registrar-agent in the
communication path. Examples may be connectivity via IP based
networks (wired or wireless) but also connectivity via Bluetooth
or NFC between the pledge and the registrar-agent.
* 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.
* defining the interaction (data exchange and data objects) between
a pledge acting as server and a registrar-agent and the domain
registrar.
For the enrollment of devices BRSKI relies on EST [RFC7030] to
request and distribute customer site/domain specific device
certificates. EST in turn relies on a binding of the certification
request to an underlying TLS connection between the EST client and
the EST server. According to BRSKI the domain registrar acts as EST
server and is also acting as registration authority (RA) for its
domain. To utilize the EST server endpoints on the domain-registrar,
the registrar-agent defined in this document will act as client
towards the domain registrar. The registrar-agent will also act as
client when communicating with the pledge in responder mode. Here,
TLS with server-side, certificate-based authentication is not
directly applicable, as the pledge only possesses an IDevID
certificate, which does not contain a subject alternative name (SAN)
for the customer site/domain and does also not contain a TLS server
flag. This is one reason for relying on higher layer security by
using signature wrapped objects for the exchange between the pledge
and the registrar agent. A further reason is the application on
different transports, for which TLS may not be available, like
Bluetooth or NFC. Instead of using TLS to provide secure transport
between the pledge and the registrar-agent, BRSKI-PRM will rely on an
additional wrapping signature of the enrollment request by the
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pledge. For EST [RFC7030] the registrar then needs to do additional
pre-processing by verifying this signature, which is not present in
EST.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document relies on the terminology defined in [RFC8995], section
1.2. The following terms are defined additionally:
authenticated self-contained object: Describes an object, which is
cryptographically bound to the end entity (EE) certificate (IDevID
certificate or LDEVID certificate). The binding is assumed to be
provided through a digital signature of the actual object using
the corresponding private key of the EE certificate.
CA: Certification authority, issues certificates.
Commissioning tool: Tool to interact with devices to provide
configuration data
EE: End entity
mTLS: Mutual authenticated Transport Layer Security.
on-site: Describes a component or service or functionality available
in the customer site/domain.
off-site: Describes a component or service or functionality not
available in the customer site/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.
PER: Pledge-enrollment-request is an enrollment object signed by the
pledge that requests to enroll in a domain
POP: Proof of possession (of a private key)
POI: Proof of identity
PVR: Pledge-voucher-request is a voucher request object signed by
the pledge that requests to be part of a domain
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RA: Registration authority, an optional system component to which a
CA delegates certificate management functions such as
authorization checks.
RER: Registrar-enrollment-request is a request object related to the
PER send to the CA by the registrar
RVR: Registrar-voucher-request is a request object containing the
PVR sent to the MASA
3. Scope of Solution
3.1. Supported Environments and Use Case Examples
BRSKI-PRM is applicable to environments where pledges may have
different behavior: pledge-responder-mode, or pledges may have no
direct connection to the domain registrar. Either way pledges are
expected to be managed by the same registrar. This can be motivated
by pledges deployed in environments not yet connected to the
operational customer site/domain network, e.g., at construction time.
Another environment relates to the assembly of cabinets, which are
prepared in advance to be installed on a customer site/domain. As
there is no direct connection to the registrar available in these
environments the solution specified allows the pledges to act in a
server role so they can be triggered for bootstrapping e.g., by a
commissioning tool. As BRSKI focuses on the pledge in a client role,
initiating the bootstrapping (pledge-initiator-mode), BRSKI-PRM
defines pledges acting as a server (pledge-responder-mode) responding
to requests for PVR and PER objects and consumption of the result
objects.
The following examples motivate support of BRSKI-PRM to support
pledges acting as server as well as pledges with limited connectivity
to the registrar.
While BRSKI-PRM defines support for pledges in responder mode, there
may be pledges, which can act in both modes, initiator and responder.
In these cases BRSKI-PRM can be combined with BRSKI as defined in
[RFC8995] or BRSKI-AE [I-D.ietf-anima-brski-ae] to allow for more
bootstrapping flexibility.
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3.1.1. Building Automation
In building automation a typical use case exists where a detached
building (or a cabinet) or the basement of a building is equipped
with sensors, actuators and controllers, but with only limited or no
connection to the central building management system. This limited
connectivity may exist during installation time or also during
operation time. During the installation in the basement, a service
technician collects the device specific information from the basement
network and provides them to the central building management system,
e.g., using a laptop or a mobile device to transport the information.
A domain registrar may be part of the central building management
system and already be operational in the installation network. The
central building management system can then provide operational
parameters for the specific devices in the basement. This
operational parameters may comprise values and settings required in
the operational phase of the sensors/actuators, among them a
certificate issued by the operator to authenticate against other
components and services. These operational parameters are then
provided to the devices in the basement facilitated by the service
technician's laptop.
3.1.2. Infrastructure Isolation Policy
This refers to any case in which the network infrastructure is
normally isolated from the Internet as a matter of policy, most
likely for security reasons. In such a case, limited access to a
domain registrar may be allowed in carefully controlled short periods
of time, for example when a batch of new devices are deployed, but
prohibited at other times.
3.1.3. Less Operational Security in the Target-Domain
The registration authority (RA) performing the authorization of a
certificate request is a critical PKI component and therefore
requires higher operational security than other components utilizing
the issued certificates . CAs may also require higher security in the
registration procedures. Especially the CA/Browser [CABF] forum
increases the security requirements in the certificate issuance
procedures for publicly trusted certificates. There may be
situations in which the customer site/domain does not offer enough
security to operate a RA/CA and therefore this service is transferred
to a backend that offers a higher level of operational security.
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3.2. Limitations
The mechanism described in this document presume the availability of
the pledge to communicate with the registrar-agent.
This may not be possible in constrained environments where, in
particular, power must be conserved.
In these situations, it is anticipated that the transceiver will be
powered down most of the time.
This presents a rendezvous problem: the pledge is unavailable for
certain periods of time, and the registrar-agent is similarly
presumed to be unavailable for certain periods of time.
4. Requirements Discussion and Mapping to Solution-Elements
Based on the intended target environment described in Section 3.1 and
the application examples described in Section 3.1 the following
requirements are derived to support bootstrapping of pledges in
responder mode (acting as server).
* To facilitate the communication between a pledge in responder mode
and registrar, additional functionality is needed either on the
registrar (if the registrar needs to interact with pledge in
responder mode directly) or as a stand-alone component. This
component acts as an agent of the registrar to trigger the pledge
to generate request objects for voucher and enrollment. These
voucher an enrollment request objects are than to be provided by
the so called registrar-agent to the registrar. This requires the
definition of endpoints on the pledge.
* The communication between the registrar-agent and the pledge MUST
not rely on transport layer security (TLS) to support also other
technology stacks (e.g., BTLE). Therefore authenticated self-
contained objects are required.
* The registrar-agent must be authenticated by the registrar as a
component, acting on behalf of the registrar. In addition the
registrar must be able to verify, which registrar-agent was in
direct contact with the pledge.
* The pledge cannot get the assertion with value "proximity" in the
voucher, as it was not in direct contact with the registrar for
bootstrapping. Therefore the "agent-proximity" assertion value is
necessary for distinguishing assertions the MASA can state.
At least the following properties are required for the voucher and
enrollment objects:
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* Proof of Identity (POI): provides data-origin authentication of a
data object, e.g., a voucher request or an enrollment request,
utilizing an existing IDevID. Certificate updates may utilize the
certificate that is to be updated.
* Proof of Possession (POP): proves that an entity possesses and
controls the private key corresponding to the public key contained
in the certification request, typically by adding a signature
using the private key to the enrollment request object.
Solution examples based on existing technology are provided with the
focus on existing IETF RFCs:
* Voucher request and response objects as used in [RFC8995] already
provide both, POP and POI, through a digital signature to protect
the integrity of the voucher object, while the corresponding
signing certificate contains the identity of the signer.
* Certification request objects: Certification requests are data
structures containing the information from a requester for a CA to
create a certificate. The certification request format in BRSKI
is PKCS#10 [RFC2986]. In PKCS#10, the structure is signed to
ensure integrity protection and proof of possession of the private
key of the requester that corresponds to the contained public key.
In the application examples, this POP alone is not sufficient.
POI is also required for the certification request object and
therefore needs to be additionally bound to the existing
credential of the pledge (IDevID). This binding supports the
authorization decision for the certification request through a
proof of identity (POI). The binding of data origin
authentication or POI to the certification request may be provided
directly by the certification request object. While BRSKI uses
the binding to TLS, BRSKI-PRM aims at an additional signature of
the PCKS#10 object using existing credentials on the pledge
(IDevID). This ensures independence of the selected transport.
5. Architectural Overview and Communication Exchanges
For BRSKI with pledge in responder mode, the base system architecture
defined in BRSKI [RFC8995] is enhanced to facilitate the new use
cases. The pledge-responder-mode allows delegated bootstrapping
using a registrar-agent instead of a direct connection between the
pledge and the domain registrar. The communication model between
registrar-agent and pledge in this document assumes that the pledge
is acting as server and responds to requests.
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Necessary enhancements to support authenticated self-contained
objects for certificate enrollment are kept at a minimum to enable
reuse of already defined architecture elements and interactions.
For the authenticated self-contained objects used for the
certification request, BRSKI-PRM relies on the defined message
wrapping mechanisms of the enrollment protocols stated in Section 4
above.
The security used within the document for bootstrapping objects
produced or consumed by the pledge bases on JOSE [RFC7515]. In
constraint environments it may provided based on COSE [RFC8152].
An abstract overview of the BRSKI-PRM protocol can be found in
[BRSKI-PRM-abstract].
5.1. Pledge-responder-mode (PRM): Registrar-agent Communication with
Pledges
To support mutual trust establishment between the domain registrar
and pledges not directly connected to the customer site/domain, this
document specifies the exchange of authenticated self-contained
objects (the voucher request/response objects as known from BRSKI and
the enrollment request/response objects as introduced by BRSKI-PRM)
with the help of a registrar-agent. This allows independence from
protection provided by the utilized transport protocol.
The registrar-agent may be implemented as an integrated functionality
of a commissioning tool or be co-located with the registrar itself.
This leads to extensions of the logical components in the BRSKI
architecture as shown in Figure 1. Note that the Join Proxy is
neglected in the figure as not needed by the registrar-agent. The
registrar-agent interacts with the pledge to transfer the required
data objects for bootstrapping, which are then also exchanged between
the registrar-agent and the domain registrar. The addition of the
registrar-agent influences the sequences of the data exchange between
the pledge and the domain registrar as described in [RFC8995]. To
enable reuse of BRSKI defined functionality as much as possible,
BRSKI-PRM * uses existing endpoints were the required functionality
is provided * enhances existing with new supported media types, e.g.,
for JWS voucher * defines new endpoints were additional functionality
is required, e.g., for wrapped certification request.
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+------------------------+
+---- Drop Ship ---------| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| | BRSKI-
| BRSKI-PRM | MASA
| .............................|.........
V . | .
+-------+ . +-----------+ +-----v-----+ .
| | . | | | | .
|Pledge | . | Registrar | | Domain | .
| | . | Agent | | Registrar | .
| <-------->...........<-------> (PKI RA) | .
| | . | LDevID | | | .
| | . +-----------+ +-----+-----+ .
|IDevID | . | .
| | . +------------------+-----+ .
+-------+ . | Key Infrastructure | .
. | (e.g., PKI Certificate | .
. | Authority) | .
. +------------------------+ .
.......................................
"Domain" components
Figure 1: Architecture overview using registrar-agent
For authentication to the domain registrar, the registrar-agent uses
its LDevID(RegAgt). The provisioning of the registrar-agent LDevID
is out of scope for this document, but may be done in advance using a
separate BRSKI run or by other means like configuration.
It is recommended to use short lived registrar-agent LDevIDs in the
range of days or weeks as outlined in Section 9.3.
If a registrar detects a request that originates from a registrar-
agent it is able to switch the operational mode from BRSKI to BRSKI-
PRM. This may be supported by a specific naming in the SAN (subject
alternative name) component of the LDevID(RegAgt) certificate.
Alternatively, the domain may feature an own issuing CA for
registrar-agent LDevID certificates. This allows the registrar to
detect registrar-agents based on the issuing CA.
The following list describes the components in a (customer) site
domain:
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* Pledge: The pledge is expected to respond with the necessary data
objects for bootstrapping to the registrar-agent. The protocol
used between the pledge and the registrar-agent is assumed to be
HTTP in the context of this document. Other protocols may be used
like CoAP, Bluetooth, or NFC, but are out of scope of this
document. A pledge acting as a server during bootstrapping leads
to some differences to BRSKI:
- Discovery of the pledge by the registrar-agent must be
possible.
- As the registrar-agent must be able to request data objects for
bootstrapping of the pledge, the pledge must offer
corresponding endpoints.
- The registrar-agent may provide additional data to the pledge
in the context of the voucher triggering request, to make
itself visible to the domain registrar.
- Order of exchanges in the call flow may be different as the
registrar-agent collects both objects, PVR objects and PER
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).
* Registrar-agent: provides a communication path to exchange data
objects between the pledge and the domain registrar. The
registrar-agent brokers in situations, in which the domain
registrar is not directly reachable by the pledge, either due to a
different technology stack or due to missing connectivity. The
registrar-agent triggers a pledge to create bootstrapping
artifacts such as voucher-request objects and enrollment-request
objects on one or multiple pledges and performs a (bulk)
bootstrapping based on the collected data. The registrar-agent is
expected to possess information of the domain registrar (i.e.,
LDevID(Reg) certificate, LDevID(CA) certificate, address), either
by configuration or by using the discovery mechanism defined in
[RFC8995]. There is no trust assumption between the pledge and
the registrar-agent as only authenticated self-contained objects
are used, which are transported via the registrar-agent and
provided either by the pledge or the registrar. The trust
assumption between the registrar-agent and the registrar is based
on the LDevID of the registrar-agent, provided by the PKI
responsible for the domain.
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This allows the registrar-agent to authenticate towards the
registrar, e.g., in a TLS handshake. Based on this, the registrar
is able to distinguish a pledge from a registrar-agent during the
session establishment and also to verify that the registrar-agent
is authorized to perform the bootstrapping of the distinct pledge.
* Join Proxy (not shown): same functionality as described in
[RFC8995] if needed. Note that a registrar-agent may use a join
proxy to facilitate the TLS connection to the registrar, in the
same way that a BRSKI pledge would use a join proxy. This is
useful in cases where the registrar-agent does not have full IP
connectivity via the domain network, or cases where it has no
other means to locate the registrar on the network.
* Domain Registrar: In general the domain registrar fulfills the
same functionality regarding the bootstrapping of the pledge in a
(customer) site domain by facilitating the communication of the
pledge with the MASA service and the domain PKI service. In
contrast to [RFC8995], the domain registrar does not interact with
a pledge directly but through the registrar-agent. The registrar
detects if the bootstrapping is performed by the pledge directly
or by the registrar-agent. The manufacturer provided components/
services (MASA and Ownership tracker) are used as defined in
[RFC8995]. For issuing a voucher, the MASA may perform additional
checks on voucher-request objects, to issue a voucher indicating
agent-proximity instead of (registrar-)proximity.
5.2. Agent-Proximity Assertion
"Agent-proximity" is a weaker assertion then "proximity". It is
defined as additional assertion type in [I-D.ietf-anima-rfc8366bis]
"agent-proximity" is a statement, that the proximity registrar
certificate was provided via the registrar-agent as defined in
Section 5.5 and not directly to the pledge. This can be verified by
the registrar and also by the MASA during the voucher-request
processing. Note that at the time of creating the voucher-request,
the pledge cannot verify the registrar's LDevID(Reg) certificate and
has no proof-of-possession of the corresponding private key for the
certificate. The pledge therefore accepts the LDevID(Reg)
provisionally until it receives the voucher as described in
Section 5.5.3.
Trust handover to the domain is established via the "pinned-domain-
certificate" in the voucher.
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.
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The provisionally accepted LDevID(Reg) certificate can be verified
after the voucher has been processed by the pledge. As the returned
voucher includes an additional signature by the registrar, the pledge
can also verify that the registrar possesses the corresponding
private key.
5.3. Behavior of Pledge in Pledge-Responder-Mode
In contrast to BRSKI the pledge acts as server. It is triggered by
the registrar-agent for the generation of the PVR and PER 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 4. To enable interaction with the registrar-agent, the pledge
provides endpoints using the BRSKI defined endpoints based on the
"/.well-known/brski" URI tree.
The following endpoints are defined for the _pledge_ in this
document. The URI path begins with "http://www.example.com/.well-
known/brski" followed by a path-suffix that indicates the intended
operation.
Operations and their corresponding URIs:
+------------------------+----------------------------+---------+
| Operation |Operation path | Details |
+========================+============================+=========+
| Trigger pledge-voucher-| /pledge-voucher-request | Section |
| request creation | | 5.5.1 |
| Returns PVR | | |
+------------------------+----------------------------+---------+
| Trigger pledge- | /pledge-enrollment-request | Section |
| enrollment-request | | 5.5.1 |
| Returns PER | | |
+------------------------+----------------------------+---------+
| Provide voucher to | /pledge-voucher | Section |
| pledge | | 5.5.3 |
| Returns | | |
| pledge-voucher-status | | |
+------------------------+----------------------------+---------+
| Provide enrollment | /pledge-enrollment | Section |
| response to pledge | | 5.5.3 |
| Returns pledge- | | |
| enrollment-status | | |
+------------------------+----------------------------+---------+
| Provide CA certs to | /pledge-CACerts | Section |
| pledge | | 5.5.3 |
+------------------------+----------------------------+---------+
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Figure 2: Endpoints on the pledge
5.4. Behavior of 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 with the pledge the
registrar-agent utilizes communication endpoints provided by the
pledge. The transport in this specification is based on HTTP but may
also be done using other transport mechanisms. This new component
changes the general interaction between the pledge and the domain
registrar as shown in Figure 1.
The registrar-agent is expected to already possess an LDevID(RegAgt)
to authenticate to the domain registrar. The registrar-agent will
use this LDevID(RegAgt) when establishing the TLS session with the
domain registrar for TLS client authentication. The LDevID(RegAgt)
certificate MUST include a SubjectKeyIdentifier (SKID), which is used
as reference in the context of an agent-signed-data object as defined
in Section 5.5.1. Note that this is an additional requirement for
issuing the certificate, as [IEEE-802.1AR] only requires the SKID to
be included for intermediate CA certificates. In BRSKI-PRM, the SKID
is used in favor of a certificate fingerprint to avoid additional
computations.
Using an LDevID for TLS client 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-PRM 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
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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. For instance, [RFC9238] describes scanning of a QR
code, the product-serial-number would be initialized from the 12N
B005 Product Serial Number.
According to [RFC8995] section 5.3, the domain registrar performs the
pledge authorization for bootstrapping within his domain based on the
pledge voucher-request object.
The following information must therefore be available at the
registrar-agent:
* LDevID(RegAgt): own operational key pair.
* LDevID(reg) certificate: certificate of the domain registrar.
* Serial-number(s): product-serial-number(s) of pledge(s) to be
bootstrapped.
5.4.1. Discovery of Registrar by Registrar-Agent
The discovery of the domain registrar may be done as specified in
[RFC8995] with the deviation that it is done between the registrar-
agent and the domain registrar. Alternatively, the registrar-agent
may be configured with the address of the domain registrar and the
certificate of the domain registrar.
5.4.2. Discovery of Pledge by Registrar-Agent
The discovery of the pledge by registrar-agent should be done by
using DNS-based Service Discovery [RFC6763] over Multicast DNS
[RFC6762] to discover the pledge. The pledge constructs a local host
name based on device local information (product-serial-number), which
results in "product-serial-number._brski-pledge._tcp.local".
The registrar-agent MAY use
* "product-serial-number._brski-pledge._tcp.local", to discover a
specific pledge, e.g., when connected to a local network.
* "_brski-pledge._tcp.local" to get a list of pledges to be
bootstrapped.
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To be able to detect the pledge using mDNS, network connectivity is
required. For Ethernet it is provided by simply connecting the
network cable. For WIFI networks, connectivity can be provided by
using a pre-agreed SSID for bootstrapping. The same approach can be
used by 6LoWPAN/mesh using a pre-agreed PAN ID. How to gain network
connectivity is out of scope of this document.
5.5. 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. These transport means may differ from, and
are independent from, the ones used between the registrar-agent and
the registrar. 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) certificate) to the pledge to be included into the
"agent-provided-proximity-registrar-certificate" leaf of the PVR
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, when verifying
the PVR. Optionally the registrar-agent may provide its
LDevID(RegAgt) certificate (and optionally also the issuing CA
certificate) to the pledge to be used in the "agent-sign-cert"
component of the PVR. If contained, the LDevID(RegAgt) certificate
MUST be the first certificate in the array. Note, this may be
omitted in constraint environments to save bandwidth between the
registrar-agent and the pledge. If not contained, the registrar MUST
fetch the LDevID(RegAgt) certificate based on the
SubjectKeyIdentifier (SKID) in the header of the agent-signed-data of
the PVR. The registrar includes the LDevID(RegAgt) certificate
information into the RVR if the PVRs contains the assertion of
"agent-proximity".
The MASA in turn verifies the LDevID(Reg) certificate is included in
the PVR (prior-signed-voucher-request) in the "agent-provided-
proximity-registrar-certificate" leaf and may assert in the voucher
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"verified" or "logged" instead of "proximity", as there is no direct
connection between the pledge and the registrar. In addition, the
MASA can provide the assertion "agent-proximity" as following. If
the LDevID(RegAgt) certificate information is contained in the
"agent-sign-cert" component of the RVR, the MASA can verify the
signature of the agent-signed-data contained 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". Depending on the MASA verification policy,
it may also respond with a suitable 4xx or 5xx error HTTP response
code as described in section 5.6 of [RFC8995].
The voucher can then be supplied via the registrar to the registrar-
agent.
Figure 3 provides an overview of the exchanges detailed in the
following sub sections.
+--------+ +-----------+ +-----------+ +--------+ +---------+
| Pledge | | Registrar | | Domain | | Domain | | Vendor |
| | | Agent | | Registrar | | CA | | Service |
| | | (RegAgt) | | (JRC) | | | | (MASA) |
+--------+ +-----------+ +-----------+ +--------+ +---------+
| | | | Internet |
/* discover pledge */
| mDNS query | | | |
|<-------------| | | |
|------------->| | | |
| | | | |
/* trigger PVR and PER generation */
|<- vTrigger --| | | |
|-Voucher-Req->| | | |
| | | | |
|<- eTrigger --| | | |
|- Enroll-Req->| | | |
~ ~ ~ ~ ~
/* provide PVR to infrastructure */
| |<------ TLS ----->| | |
| | [Reg-Agt authenticated | |
| | and authorized?] | |
| |-- Voucher-Req -->| | |
| | [Reg-Agt authorized?] | |
| | [accept device?] | |
| | [contact vendor] | |
| | |------- Voucher-Req ------>|
| | | [extract DomainID]
| | | [update audit log]
| | |<-------- Voucher ---------|
| |<---- Voucher ----| | |
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| | | | |
/* provide PER to infrastructure */
| |-- Enroll-Req --->| | |
| | |- Cert-Req -->| |
| | |<-Certificate-| |
| |<-- Enroll-Resp --| | |
| | | | |
/* query cACerts from infrastructure */
| |-- cACerts-Req -->| | |
| |<- cACerts-Resp --| | |
~ ~ ~ ~ ~
/* provide voucher and certificate and collect status info */
|<-- Voucher --| | | |
|-- vStatus -->| | | |
|<-- cACerts --| | | |
|<-Enroll-Resp-| | | |
|-- eStatus -->| | | |
~ ~ ~ ~ ~
/* provide voucher status and enroll status to registrar */
| |<------ TLS ----->| | |
| |---- vStatus --->| | |
| | |-- req. device audit log ->|
| | |<---- device audit log ----|
| | [verify audit log]
| | | | |
| |---- eStatus --->| | |
| | | | |
Figure 3: Overview pledge-responder-mode exchanges
The following sub sections split the interactions between the
different components into:
* Section 5.5.1 describes objects exchanged between the registrar-
agent and the pledge.
* Section 5.5.2 describes objects exchanged between the registrar-
agent and the registrar and also the interaction of the registrar
with the MASA and the domain CA.
* Section 5.5.3 describes objects exchanged between the registrar-
agent and the pledge including the status objects.
* Section 5.5.4 describes the status handling addresses the
exchanges between the registrar-agent and the registrar.
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5.5.1. Request Objects Acquisition by Registrar-Agent from Pledge
The following description assumes that the registrar-agent already
discovered the pledge. This may be done as described in
Section 5.4.2 based on mDNS.
The focus is on the exchange of signature-wrapped objects using
endpoints defined for the pledge in Section 5.3.
Preconditions:
* Pledge: possesses IDevID
* Registrar-agent: possesses/trusts IDevID CA certificate and an own
LDevID(RegAgt) EE credential for the registrar domain. In
addition, the registrar-agent MUST know the product-serial-
number(s) of the pledge(s) to be bootstrapped. The registrar-
agent MAY be provided with the product-serial-number in different
ways:
- configured, e.g., as a list of pledges to be bootstrapped via
QR code scanning
- discovered by using standard approaches like mDNS as described
in Section 5.4.2
- discovered by using a vendor specific approach, e.g., RF
beacons
* Registrar: possesses/trusts IDevID CA certificate and an own
LDevID(Reg) credential.
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+--------+ +-----------+
| 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 PVR
| |
|<----- trigger enrollment request ------|
| (empty) |
| |
|------ pledge-enrollment-request ------>|-store (PER)
| |
Figure 4: Request collection (registrar-agent - pledge)
Note that the registrar-agent may trigger the pledge for the PVR or
the PER or both. It is expected that this will be aligned with a
service technician workflow doing the pledge installation.
Triggering the pledge to create the PVR is done using HTTP POST on
the defined pledge endpoint "/.well-known/brski/pledge-voucher-
request".
The registrar-agent PVR Content-Type header is: application/json. It
defines a JSON document to provide three parameter:
* agent-provided-proximity-registrar-cert: base64-encoded
LDevID(Reg) TLS certificate.
* agent-signed-data: base64-encoded JWS-object.
* agent-sign-cert: array of base64-encoded certificate data
(optional).
The the trigger for the pledge to create a PVR is depicted in the
following figure:
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{
"agent-provided-proximity-registrar-cert": "base64encodedvalue==",
"agent-signed-data": "base64encodedvalue==",
"agent-sign-cert": ["base64encodedvalue==", "base64encodedvalue==", "..."]
}
Figure 5: Representation of trigger to create PVR
The pledge provisionally accepts the agent-provided-proximity-
registrar-cert and can verify it once it has received the voucher.
If the optionally agent-sign-cert data is included the pledge MAY
verify at least the signature of the agent-signed-data using the
first contained certificate, which is the LDevID(RegAgt) certificate.
If further certificates are contained in the agent-sign-cert, they
enable also the certificate chain validation. The pledge may not
verify the agent-sign-cert itself as the domain trust has not been
established at this point of the communication. It can be done,
after the voucher has been received.
The agent-signed-data is a JOSE object and contains the following
information:
The header of the agent-signed-data contains:
* alg: algorithm used for creating the object signature.
* kid: MUST contain the base64-encoded bytes of the
SubjectKeyIdentifier (the "KeyIdentifier" OCTET STRING value),
excluding the ASN.1 encoding of "OCTET STRING" of the
LDevID(RegAgt) certificate.
The body of the agent-signed-data contains an ietf-voucher-request-
prm:agent-signed-data element (defined in Section 6.1):
* created-on: MUST contain the creation date and time in yang:date-
and-time format.
* serial-number: MUST contain the product-serial-number as type
string as defined in [RFC8995], section 2.3.1. The serial-number
corresponds with the product-serial-number contained in the
X520SerialNumber field of the IDevID certificate of the pledge.
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{
"payload": {
"ietf-voucher-request-prm:agent-signed-data": {
"created-on": "2021-04-16T00:00:01.000Z",
"serial-number": "callee4711"
},
"signatures": [
{
"protected": {
"alg": "ES256",
"kid": "base64encodedvalue=="
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 6: Representation of agent-signed-data
Upon receiving the voucher-request trigger, the pledge SHALL
construct the body of the PVR object as defined in [RFC8995]. It
will contain additional information provided by the registrar-agent
as specified in the following. This object becomes a JSON-in-JWS
object as defined in [I-D.ietf-anima-jws-voucher]. If the pledge is
unable to construct the PVR it SHOULD respond with HTTP 406 error
code to the registrar-agent to indicate that it is not able to create
the PVR.
The header of the PVR SHALL contain the following parameters as
defined in [RFC7515]:
* alg: algorithm used for creating the object signature.
* x5c: contains the base64-encoded pledge IDevID certificate. It
may optionally contain the certificate chain for this certificate.
The payload of the PVR object MUST contain the following parameters
as part of the ietf-voucher-request-prm:voucher as defined in
[RFC8995]:
* created-on: SHALL contain the current date and time in yang:date-
and-time format.
* nonce: SHALL contain a cryptographically strong random or pseudo-
random number.
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* serial-number: SHALL contain the pledge product-serial-number as
X520SerialNumber.
* assertion: SHALL contain the requested voucher assertion "agent-
proximity".
The ietf-voucher-request:voucher is enhanced with additional
parameters:
* agent-provided-proximity-registrar-cert: MUST be included and
contains the base64-encoded LDevID(Reg) certificate (provided as
trigger parameter by the registrar-agent).
* agent-signed-data: MUST contain the base64-encoded agent-signed-
data (as defined in Figure 6) and provided as trigger parameter.
* agent-sign-cert: MAY contain the certificate or certificate chain
of the registrar-agent as array of base64encoded certificate
information. It starts from the base64-encoded LDevID(RegAgt)
certificate optionally followed by the issuing CA certificate and
potential further certificates. If supported, it MUST at least
contain the LDevID(RegAgt) certificate provided as trigger
parameter.
The enhancements of the YANG module for the ietf-voucher-request with
these new leafs are defined in Section 6.1.
The object is signed using the pledge's IDevID credential contained
as x5c parameter of the JOSE header.
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{
"payload": {
"ietf-voucher-request-prm:voucher": {
"created-on": "2021-04-16T00:00:02.000Z",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"serial-number": "callee4711",
"assertion": "agent-proximity",
"agent-provided-proximity-registrar-cert": "base64encodedvalue==",
"agent-signed-data": "base64encodedvalue==",
"agent-sign-cert": [
"base64encodedvalue==",
"base64encodedvalue==",
"..."
]
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 7: Representation of PVR
The PVR Content-Type is defined in [I-D.ietf-anima-jws-voucher] as
application/voucher-jws+json.
The pledge SHOULD include this Content-Type header field indicating
the included media type for the voucher response. Note that this is
also an indication regarding the acceptable format of the voucher
response. This format is included by the registrar as described in
Section 5.5.2.
Once the registrar-agent has received the PVR it can trigger the
pledge to generate an enrollment-request object. As in BRSKI the
enrollment request object is a PKCS#10, but additionally signed using
the pledge's IDevID. Note, as the initial enrollment aims to request
a generic certificate, no certificate attributes are provided to the
pledge.
Triggering the pledge to create the enrollment-request is done using
HTTP POST on the defined pledge endpoint "/.well-known/brski/pledge-
enrollment-request".
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The registrar-agent PER Content-Type header is: application/json with
an empty body. Note that using HTTP POST allows for an empty body,
but also to provide additional data, like CSR attributes or
information about the enroll type: "enroll-generic-cert" or
"reenroll-generic-cert". The "enroll-generic-cert" case is shown in
Figure 8.
{
"enroll-type" = "enroll-generic-cert"
}
Figure 8: Example of trigger to create a PER
In the following the enrollment is described as initial enrollment
with an empty body.
Upon receiving the enrollment-trigger, the pledge SHALL construct the
PER as authenticated self-contained object. The CSR already assures
proof of possession of the private key corresponding to the contained
public key. In addition, based on the additional signature using the
IDevID, proof of identity is provided. Here, a JOSE object is being
created in which the body utilizes the YANG module ietf-ztp-types
with the grouping for csr-grouping for the CSR as defined in
[I-D.ietf-netconf-sztp-csr].
Depending on the capability of the pledge, it constructs the
enrollment request as plain PKCS#10. Note that the focus in this use
case is placed on PKCS#10 as PKCS#10 can be transmitted in different
enrollment protocols in the infrastructure like EST, CMP, CMS, and
SCEP. If the pledge 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 certification request objects such as CMP or
CMC.
The pledge SHOULD construct the PER as PKCS#10 object. In BRSKI-PRM
it MUST sign it additionally with its IDevID credential to provide
proof-of-identity bound to the PKCS#10 as described below.
If the pledge is unable to construct the enrollment-request it SHOULD
respond with HTTP 406 error code to the registrar-agent to indicate
that it is not able to create the enrollment-request.
A successful enrollment will result in a generic LDevID certificate
for the pledge in the new domain, which can be used to request
further (application specific) LDevID certificates if necessary for
its operation. The registrar-agent SHALL use the endpoints specified
in this document.
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[I-D.ietf-netconf-sztp-csr] considers PKCS#10 but also CMP and CMC as
certification request format. Note that the wrapping signature is
only necessary for plain PKCS#10 as other request formats like CMP
and CMS support the signature wrapping as part of their own
certificate request format.
The registrar-agent enrollment-request Content-Type header for a
wrapped PKCS#10 is: application/jose+json
The header of the pledge enrollment-request SHALL contain the
following parameter as defined in [RFC7515]:
* alg: algorithm used for creating the object signature.
* x5c: contains the base64-encoded pledge IDevID certificate. It
may optionally contain the certificate chain for this certificate.
The body of the pledge enrollment-request object SHOULD contain a P10
parameter (for PKCS#10) as defined for ietf-ztp-types:p10-csr in
[I-D.ietf-netconf-sztp-csr]:
* P10: contains the base64-encoded PKCS#10 of the pledge.
The JOSE object is signed using the pledge's IDevID credential, which
corresponds to the certificate signaled in the JOSE header.
{
"payload": {
"ietf-ztp-types": {
"p10-csr": "base64encodedvalue=="
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 9: Representation of PER
With the collected PVR object and the PER object, the registrar-agent
starts the interaction with the domain registrar.
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As the registrar-agent is intended to facilitate communication
between the pledge and the domain registrar, a collection of requests
from more than one pledge is possible, allowing a bulk bootstrapping
of multiple pledges using the same connection between the registrar-
agent and the domain registrar.
5.5.2. Request Processing by the Registrar-Agent
The BRSKI-PRM bootstrapping exchanges between registrar-agent and
domain registrar resemble the BRSKI exchanges between pledge and
domain registrar (pledge-initiator-mode) with some deviations.
Preconditions:
* Registrar-agent: possesses it's own LDevID(RegAgt) credentials of
the site domain. In addition, it may possess the IDevID CA
certificate of the pledge vendor/manufacturer to verify the pledge
certificate in the received request messages. It has the address
of the domain registrar through configuration or by discovery,
e.g., mDNS/DNSSD. The registrar-agent has acquired PVR and PER
objects(s).
* Registrar: possesses the IDevID CA certificate of the pledge
vendor/manufacturer and an it's own LDevID(Reg) credentials of the
site domain.
* MASA: possesses it's own vendor/manufacturer credentials (voucher
signing key, TLS server certificate) related to pledges IDevID and
the site-specific LDevID CA certificate.
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+-----------+ +-----------+ +--------+ +---------+
| Registrar-| | Domain | | Domain | | Vendor |
| agent | | Registrar | | CA | | Service |
| (RegAgt) | | (JRC) | | | | (MASA) |
+-----------+ +-----------+ +--------+ +---------+
| | | Internet |
[voucher + enrollment] | | |
[objects available. ] | | |
| | | |
|<----- mTLS ----->| | |
| [Reg-Agt authenticated | |
| and authorized?] | |
| | | |
|-- Voucher-Req -->| | |
| (PVR) | | |
| [Reg-Agt authorized?] | |
| [accept device?] | |
| [contact vendor] |
| |----------- mTLS --------->|
| |-- Voucher-Req ----------->|
| | (RVR) |
| | [extract DomainID]
| | [update audit log]
| |<-------- Voucher ---------|
|<---- Voucher ----| |
| | |
|--- Enroll-Req -->| | |
| (PER) | | |
| |--- mTLS ---->| |
| |- Enroll-Req->| |
| | (RER) | |
| |<-Enroll-Resp-| |
|<-- Enroll-Resp---| | |
| | | |
|--- caCerts-Req ->| | |
|<-- caCerts-Res --| | |
| | | |
Figure 10: 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.
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In contrast to [RFC8995] TLS client authentication to the registrar
is achieved by using registrar-agent LDevID(RegAgt) credentials
instead of pledge IDevID credentials. Consequently BRSKI (pledge-
initiator-mode) is distinguishable from BRSKI-PRM (pledge-responder-
mode) by the registrar. The registrar SHOULD verify that the
registrar-agent is authorized to establish a connection to the
registrar by TLS client authentication using LDevID(RegAgt)
credentials. If the connection form registrar-agent to registrar is
established, the authorization SHALL be verified again based on the
agent-signed-data contained in the PVR. This ensures that the pledge
has been triggered by an authorized registrar-agent.
The registrar can receive request objects in different formats as
defined in [RFC8995]. Specifically, the registrar will receive JSON-
in-JWS objects generated by the pledge for voucher-request and
enrollment-request (instead of BRSKI voucher-request as CMS-signed
JSON and enrollment-request as PKCS#10 objects).
The registrar-agent SHALL send the PVR by HTTP POST to the registrar
endpoint: "/.well-known/brski/requestvoucher"
The Content-Type header field for JSON-in-JWS PVR is: application/
voucher-jws+json (see Figure 7 for the content definition), as
defined in [I-D.ietf-anima-jws-voucher].
The registrar-agent SHOULD set the Accept field in the request-header
indicating the acceptable Content-Type for the voucher-response. The
voucher-response Content-Type header field SHOULD be set to
application/voucher-jws+json as defined in
[I-D.ietf-anima-jws-voucher].
After receiving the PVR from registrar-agent, the registrar SHALL
perform the verification as defined in section 5.3 of [RFC8995]. In
addition, the registrar shall verify the following parameters from
the PVR:
* agent-provided-proximity-registrar-cert: MUST contain registrar's
own LDevID(Reg) certificate to ensure the registrar in proximity
of the registrar-agent is the destination for this PVR.
* agent-signed-data: The registrar MUST verify that the agent
provided data has been signed with the LDevID(RegAgt) credential
indicated in the "kid" JOSE header parameter. If the certificate
is not included in the agent-sign-cert properties of the PVR, it
must be fetched out-of-band by the registrar if "agent-proximity"
assertion is requested.
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* agent-sign-cert: MAY contain an array of base64-encoded
certificate data starting with the LDevID(RegAgt) certificate. If
contained the registrar MUST verify that the LDevID(ReAgt)
certificate, used to sign the data, is still valid. If the
certificate is already expired, the registrar SHALL reject the
request. Validity of used signing certificates during
bootstrapping is necessary as no trusted timestamp is available,
see also Section 9.3.
If the agent-signed-cert is not provided, the registrar MUST fetch
the LDevID(RegAgt) certificate, based on the provided
SubjectKeyIdentifier (SKID) contained in the kid header of the
agent-signed-data, and perform this verification. This requires,
that the registrar can fetch the LDevID(RegAgt) certificate data
(including intermediate CA certificates if existent) based on the
SKID.
If the validation fails the registrar SHOULD respond with HTTP 404
error code to the registrar-agent. HTTP 406 error code SHOULD be
used if the format of PVR is unknown.
If the validation succeeds, the registrar SHOULD accept the PVR to
join the domain as defined in section 5.3 of [RFC8995]. The
registrar then establishes a TLS connection to MASA as described in
section 5.4 of [RFC8995] to obtain a voucher for the pledge.
The registrar SHALL construct the payload of the RVR object as
defined in [RFC8995]. The RVR object encoding SHALL be JSON-in-JWS
as defined in [I-D.ietf-anima-jws-voucher].
The header of the RVR SHALL contain the following parameter as
defined in [RFC7515]:
* alg: algorithm used to create the object signature.
* x5c: contains the base64-encoded registrar LDevID certificate(s).
It may optionally contain the certificate chain for this
certificate.
The payload of the RVR object MUST contain the following parameter as
part of the voucher request as defined in [RFC8995]:
* created-on: contains the current date and time in yang:date-and-
time format for the RVR creation time.
* nonce: copied form the PVR
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* serial-number: contains the pledge product-serial-number. The
registrar MUST verify that the IDevID certificate subject
serialNumber of the pledge (X520SerialNumber) matches the serial-
number value in the PVR. In addition, it MUST be equal to the
serial-number value contained in the agent-signed data of PVR.
* assertion: contains the voucher assertion requested by the pledge
(agent-proximity). The registrar provides this information to
assure successful verification of agent proximity based on the
agent-signed-data.
* prior-signed-voucher-request: contains the PVR provided by the
registrar-agent.
The RVR can be enhanced optionally with the following parameter as
defined in Section 6.1:
* agent-sign-cert: contains the LDevID(RegAgt) certificate or the
LDevID(RegAgt) certificate including the certificate chain. In
the context of this document it is a JSON array of base64encoded
certificate information and handled in the same way as x5c header
objects.
If only a single object is contained in the x5c it MUST be the
base64-encoded LDevID(RegAgt) certificate. If multiple certificates
are included in the x5c, the first MUST be the base64-encoded
LDevID(RegAgt) certificate.
The MASA uses this information for verification that the registrar-
agent is in proximity to the registrar to state the corresponding
assertion "agent-proximity". Note that the agent-sign-cert may also
be contained in the "prior-signed-voucher-request" carrying the PVR
if the pledge included it.
The object is signed using the registrar LDevID(Reg) credential,
which corresponds to the certificate signaled in the JOSE header.
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{
"payload": {
"ietf-voucher-request-prm:voucher": {
"created-on": "2022-01-04T02:37:39.235Z",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"serial-number": "callee4711",
"assertion": "agent-proximity",
"prior-signed-voucher-request": "base64encodedvalue==",
"agent-sign-cert": [
"base64encodedvalue==",
"base64encodedvalue==",
"..."
]
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 11: Representation of RVR
The registrar SHALL send the RVR to the MASA endpoint by HTTP POST:
"/.well-known/brski/requestvoucher"
The RVR Content-Type header field is defined in
[I-D.ietf-anima-jws-voucher] as: application/voucher-jws+json
The RVR SHOULD set the Accept header indicating the desired media
type for the voucher-response. The media type is application/
voucher-jws+json as defined in [I-D.ietf-anima-jws-voucher].
Once the MASA receives the RVR it SHALL perform the verification as
described in section 5.5 in [RFC8995].
In addition, the following processing SHALL be performed for PVR data
contained in RVR "prior-signed-voucher-request" field:
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* agent-provided-proximity-registrar-cert: The MASA MAY verify that
this field contains the LDevID(Reg) certificate. If so, it MUST
correspond to the LDevID(Reg) certificate used to sign the RVR.
Note: Correspond here relates to the case that a single
LDevID(Reg) certificate is used or that different LDevID(Reg)
certificates are used, which are issued by the same CA.
* agent-signed-data: The MASA MAY verify this field to issue "agent-
proximity" assertion. If so, the agent-signed-data MUST contain
the pledge product-serial-number, contained in the "serial-number"
field of the PVR (from "prior-signed-voucher-request" field) and
also in "serial-number" field of the RVR. The LDevID(RegAgt)
certificate used to generate the signature is identified by the
"kid" parameter of the JOSE header (agent-signed-data). If the
assertion "agent-proximity" is requested, the RVR MUST contain the
corresponding LDevID(RegAgt) certificate data in the "agent-sign-
cert" field of either the LDevID(RegAgt) certificate of RVR or of
PVR from "prior-signed-voucher-request" field. It MUST be
verified by the MASA that it can be verified to the same domain CA
as the LDevID(Reg) certificate.
If the "agent-sign-cert" field is not provided, the MASA MAY state
a lower level assertion value, e.g.: "logged" or "verified" Note:
Sub-CA certificate(s) MUST also be carried by "agent-sign-cert",
in case the LDevID(RegAgt) certificate is issued by a sub-CA and
not the domain CA known to the MASA. As the "agent-sign-cert"
field is defined as array (x5c), it can handle multiple
certificates.
If validation fails, the MASA SHOULD respond with an HTTP error code
to the registrar. The HTTP error codes are kept the same as defined
in section 5.6 of [RFC8995], and comprise the codes: 403, 404, 406,
and 415.
The expected voucher-response format for the pledge-responder-mode
the application/voucher-jws+json as defined in
[I-D.ietf-anima-jws-voucher] is applied. The voucher syntax is
described in detail by [RFC8366]. Figure 12 shows an example of the
contents of a voucher.
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{
"payload": {
"ietf-voucher:voucher": {
"assertion": "agent-proximity",
"serial-number": "callee4711",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"created-on": "2022-01-04T00:00:02.000Z",
"pinned-domain-cert": "MIIBpDCCA...w=="
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 12: Representation of MASA issued voucher
The MASA returns the voucher-response object to the registrar.
After receiving the voucher the registrar SHOULD evaluate it for
transparency and logging purposes as outlined in section 5.6 of
[RFC8995]. The registrar MUST add an additional signature to the
voucher-response object, by signing it using its registrar
credentials (LDevID(Reg)). This signature is done over the same
content as the MASA signature of the voucher and provides a proof of
possession of the private key corresponding to the LDevID(Reg) the
pledge received in the trigger for the PVR (see Figure 5). The
registrar MUST use the same LDevID(Reg) credential that is used for
authentication in the TLS handshake to authenticate towards the
registrar-agent. This ensures that the same LDevID(Reg) certificate
can be used to verify the signature as transmitted in the voucher
request as is transferred in the PVR in the agent-provided-proximity-
registrar-cert component. Figure Figure 13 below provides an example
of the voucher with two signatures.
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{
"payload": {
"ietf-voucher:voucher": {
"assertion": "agent-proximity",
"serial-number": "callee4711",
"nonce": "eDs++/FuDHGUnRxN3E14CQ==",
"created-on": "2022-01-04T00:00:02.000Z",
"pinned-domain-cert": "MIIBpDCCA...w=="
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
},
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 13: Representation of MASA issued voucher with additional
registrar signature
Depending on the security policy of the operator, this signature can
also be interpreted by the pledge explicit authorization of the
registrar to install the contained trust anchor. The registrar sends
the voucher to the registrar-agent.
After receiving the voucher, the registrar-agent sends the PER to the
registrar. Deviating from BRSKI the PER is not a raw PKCS#10 object.
As the registrar-agent is involved in the exchange, the PKCS#10 is
wrapped in a JWS object by the pledge and signed with pledge's IDevID
to ensure proof-of-identity as outlined in Figure 9.
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[RFC7030] EST standard endpoints (/simpleenroll, /simplereenroll,
/serverkeygen, /cacerts) on the registrar cannot be used for BRSKI-
PRM. This is caused by the utilization of signature wrapped-objects
in BRSKI-PRM. As EST requires to sent a raw PKCS#10 request to the
/simpleenroll endpoint, this document makes an enhancement by
utilizing EST but with the exception to transport a signature wrapped
PKCS#10 request. Therefore a new endpoint for BRSKI-PRM on the
registrar is defined as "/.well-known/brski/requestenroll"
The Content-Type header of PER is: application/jose+json.
This is a deviation from the Content-Type header values used in
[RFC7030] and results in additional processing at the domain
registrar (as EST server). Note, the registrar is already aware that
the bootstrapping is performed in a pledge-responder-mode due to the
use of the LDevID(RegAgt) certificate in the TLS establishment and
the provided PVR as JSON-in-JWS object.
* If the registrar receives a PER with Content-Type header:
application/jose+json, it MUST verify the wrapping signature using
the certificate indicated in the JOSE header.
* The registrar verifies that the pledge's certificate (here
IDevID), carried in "x5c" header field, is accepted to join the
domain after successful validation of the PVR.
* If both succeed, the registrar utilizes the PKCS#10 request
contained in the JWS object body as "P10" parameter of "ietf-sztp-
csr:csr" for further processing of the enrollment request with the
corresponding domain CA. It creates a registrar-enrollment-
request (RER) by utilizing the protocol expected by the domain CA.
The domain registrar may either directly forward the provided
PKCS#10 request to the CA or provide additional information about
attributes to be included by the CA into the requested LDevID
certificate. The approach of sending this information to the CA
depends on the utilized certificate management protocol between
the RA and the CA and is out of scope for this document.
The registrar-agent SHALL send the PER to the registrar by HTTP POST
to the endpoint: "/.well-known/brski/requestenroll"
The registrar SHOULD respond with an HTTP 200 in the success case or
fail with HTTP 4xx/5xx codes as defined by the HTTP standard.
A successful interaction with the domain CA will result in a pledge
LDevID certificate, which is then forwarded by the registrar to the
registrar-agent using the Content-Type header: application/
pkcs7-mime.
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As the pledge will verify it own certificate LDevID certificate when
received, it also needs the corresponding CA certificates. This is
done in EST using the /cacerts endpoint, which provides the CA
certificates over a TLS protected connection. BRSKI-PRM requires a
signature wrapped CA certificate response, to avoid that the pledge
can be provided with arbitrary CA certificates in an authorized way.
The additional signature of the registrar will allow the pledge to
verify the authorization to install CA certificates. As the CA
certificates are provided to the pledge after the voucher, the pledge
has the necessary information to validate the provisioning object.
To allow the registrar-agent to request a signature wrapped CA
certificate object, a new endpoint for BRSKI-PRM on the registrar is
defined as "/.well-known/brski/wrappedcacerts"
The registrar-agent SHALL requests the EST CA trust anchor database
information (in form of CA certificates) with an HTTPS GET message.
The Content-Type header of the response SHALL be: application/
jose+json.
This is a deviation from the Content-Type header values used in
[RFC7030] and results in additional processing at the domain
registrar (as EST server). The additional processing is the
signature of the CA certificate information using the LDevID(Reg)
credential resulting in a signed JSON object. The CA certificates
are provided as base64 encoded x5b.
{
"payload": {
"x5b": [ "base64encodedvalue==" ],
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 14: Representation of CA certificates data with additional
registrar signature
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The registrar-agent has now finished the exchanges with the domain
registrar and can supply the voucher-response (from MASA via
Registrar), the CA certificates, and the enrollment-response (LDevID
certificate, from CA via Registrar) 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 by the
voucher [RFC8366] and the certificate [RFC5280].
5.5.3. Response Object Supply by Registrar-Agent to 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 5.4.2 or use
stored information from the first contact with the pledge.
Preconditions in addition to Section 5.5.2:
* Registrar-agent: possesses voucher and LDevID certificate and
optionally CA certificates.
+--------+ +-----------+
| Pledge | | Registrar-|
| | | Agent |
| | | (RegAgt) |
+--------+ +-----------+
| [voucher and enrollment]
| [responses available]
| |
|<------- supply voucher -----------|
| |
|--------- voucher status --------->| - store
| | pledge voucher status
|<----- supply CA certificates ----|
| |
|<--- supply enrollment response ---|
| |
|--------- enroll status ---------->| - store
| | pledge enroll status
|<--- supply CAcerts (optional) ----|
| |
Figure 15: Response and status handling between pledge and
registrar-agent
The registrar-agent provides the information via distinct pledge
endpoints as following.
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The registrar-agent SHALL send the voucher-response to the pledge by
HTTP POST to the endpoint: "/.well-known/brski/pledge-voucher".
The registrar-agent voucher-response Content-Type header is
application/voucher-jws+json and contains the voucher as provided by
the MASA. An example if given in Figure 12 for a MASA only signed
voucher and in Figure Figure 13 for multiple signatures.
If a single signature is contained, the pledge receives the voucher
and verifies it as described in section 5.6.1 in [RFC8995].
A nonceless voucher may be accepted as in [RFC8995] and may be
allowed by a manufactures pledge implementation. It requires to
perform the validation that the pledge is connected to an authorized
registrar-agent by other means, as the registrar would be able to
verify it using the agent-signed-data in the PER.
If multiple signatures are contained in the voucher, the pledge SHALL
perform the signature verification in the following order:
1. Validate MASA signature as described in section 5.6.1 in
[RFC8995] successfully.
2. Install contained trust anchor provisionally.
3. Verify registrar signature as described in section 5.6.1 in
[RFC8995] successfully, but take the registrar certificate
instead of the MASA certificate for verification.
4. Validate the registrar certificate received in the agent-
provided-proximity-registrar-cert in the pledge-voucher-request
trigger request (in the field "agent-provided-proximity-
registrar-cert") successfully, including validity and
authorization to bootstrap the particular pledge.
If all verification steps stated above have been performed
successfully, the pledge SHALL end the provisional accept state for
the domain trust anchor and the LDevID(Reg). If multiple signatures
are contained in the voucher-response, the pledge MUST verify all
successfully.
If an error occurs during the verification it SHALL be signaled in
the reason field of the pledge voucher status object.
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After verification the pledge MUST reply with a status telemetry
message as defined in section 5.7 of [RFC8995].
The pledge generates the voucher status object and provides it as
JOSE object with the wrapping signature in the response message to
the registrar-agent.
The response has the Content-Type application/jose+json and is signed
using the IDevID of the pledge as shown in Figure 16. As the reason
field is optional (see [RFC8995]), it MAY be omitted in case of
success.
{
"payload": {
"version": 1,
"status": true,
"reason": "Informative human readable message",
"reason-context": {
"additional": "JSON"
}
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
Figure 16: Representation of pledge voucher status telemetry
The registrar-agent SHALL provide the set of CA certificates
requested from the registrar to the pledge by HTTP POST to the
endpoint: "/.well-known/brski/pledge-CAcerts".
As the CA certificate provisioning is crucial from a security
perspective, this provisioning SHALL only be done, if the voucher-
response has been provided to the pledge.
The supply CA certificates message has the Content-Type application/
jose+json and is signed using the LDevID(Reg) of the registrar pledge
as shown in Figure 14.
The CA certificates are provided as base64 encoded x5b. The pledge
SHALL install the received CA certificates in its trust anchor
database after successful verification of the registrar's signature.
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If validation of the wrapping signature fails, the pledge SHOULD
respond with the HTTP 403 error code. The HTTP 406 error code SHOULD
be used, if the response is in an unknown format.
The registrar-agent SHALL send the enroll-response to the pledge by
HTTP POST to the endpoint: "/.well-known/brski/pledge-enrollment".
The registrar-agent enroll-response Content-Type header, when using
EST [RFC7030] as enrollment protocol between the registrar-agent and
the infrastructure, is application/pkcs7-mime. Note that it only
contains the LDevID certificate for the pledge, not the certificate
chain.
Upon reception, the pledge SHALL verify the received LDevID
certificate. The pledge SHALL generate the enroll status object and
provide it in the response message to the registrar-agent. If the
verification of the LDevID certificate succeeds, the status SHALL be
set to true, otherwise to FALSE.
The pledge MUST reply with a status telemetry message as defined in
section 5.9.4 of [RFC8995]. As for the other objects, the enrollment
status object is provided with an additional signature using JOSE.
If the pledge verified the received LDevID certificate successfully
it SHALL sign the response using the LDevID of the pledge as shown in
Figure 17. In the failure case, the pledge SHALL use the available
IdevID credentials. As the reason field is optional, it MAY be
omitted in case of success.
The response has the Content-Type application/jose+json.
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{
"payload": {
"version": 1,
"status": true,
"reason": "Informative human readable message",
"reason-context": {
"additional": "JSON"
}
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "base64encodedvalue==" ]
},
"signature": "base64encodedvalue=="
}
]
}
Figure 17: Representation of pledge enroll status telemetry
Once the registrar-agent has collected the information, it can
connect to the registrar-agent to provide the status responses to the
registrar.
5.5.4. Telemetry status handling (registrar-agent - domain registrar)
The following description requires that the registrar-agent has
collected the status objects from the pledge. It SHALL provide the
status objects to the registrar for further processing.
Preconditions in addition to Section 5.5.2:
* 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 |
[voucher + enroll ] | | |
[status objects avail.]| | |
| | | |
|<----- mTLS ----->| | |
| | | |
|--Voucher Status->| | |
| |-- req- device audit log ->|
| |<---- device audit log ----|
| [verify audit log ]
| | | |
|--Enroll Status-->| | |
| | | |
| | | |
Figure 18: Bootstrapping status handling
The registrar-agent MUST provide the collected pledge voucher status
object to the registrar. This status indicates if the pledge could
process the voucher successfully or not.
If the TLS connection to the registrar was closed, the registrar-
agent establishes a TLS connection with the registrar as stated in
Section 5.5.2.
The registrar-agent sends the pledge voucher status object without
modification to the registrar with an HTTP-over-TLS POST using the
registrar endpoint "/.well-known/brski/voucher_status". The Content-
Type header is kept as application/jose+json as described in
Figure 15 and depicted in the example in Figure 16.
The registrar SHALL verify the signature of the pledge voucher status
object 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 in the success case or fail with HTTP 4xx/5xx codes as
defined by the HTTP standard. The registrar-agent may use the
response to signal success / failure to the service technician
operating the registrar agent. Within the server logs the server
SHOULD capture this telemetry information.
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The registrar SHOULD proceed with collecting and logging status
information by requesting the MASA audit-log from the MASA service as
described in section 5.8 of [RFC8995].
The registrar-agent MUST provide the pledge's enroll status 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 HTTP-over-TLS POST using the
registrar endpoint "/.well-known/brski/enrollstatus". The Content-
Type header is kept as application/jose+json as described in
Figure 15 and depicted in the example in Figure 17.
The registrar MUST verify the signature of the pledge enroll status
object. Also, the registrar SHALL validate that the pledge belongs
to an accepted device in his domain based on the contained product-
serial-number in the LDevID certificate referenced in the header of
the enroll status object. The registrar SHOULD log this event. In
case the enroll status object indicates a failure, the pledge was
unable to verify the received LDevID certificate and therefore signed
the enroll status objects with its IDevID credential. Note that the
verification of a signature of the object is a deviation from 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 in the success case or fail with HTTP 4xx/5xx codes
as defined by the HTTP standard. Based on the failure case the
registrar MAY decide that for security reasons the pledge is not
allowed to reside in the domain. In this case the registrar MUST
revoke the certificate. The registrar-agent may use the response to
signal success / failure to the service technician operating the
registrar agent. Within the server log the registrar SHOULD capture
this telemetry information.
6. Artifacts
6.1. Voucher Request Artifact
The following enhancement extends the voucher-request as defined in
[RFC8995] to include additional fields necessary for handling
bootstrapping in the pledge-responder-mode.
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6.1.1. Tree Diagram
The following tree diagram is mostly a duplicate of the contents of
[RFC8995], with the addition of the fields agent-signed-data, the
registrar-proximity-certificate, and agent-signing certificate. The
tree diagram is described in [RFC8340]. Each node in the diagram is
fully described by the YANG module in Section Section 6.1.2.
module: ietf-voucher-request-prm
grouping voucher-request-prm-grouping
+-- voucher
+-- created-on? yang:date-and-time
+-- expires-on? yang:date-and-time
+-- assertion? enumeration
+-- serial-number string
+-- idevid-issuer? binary
+-- pinned-domain-cert? binary
+-- domain-cert-revocation-checks? boolean
+-- nonce? binary
+-- last-renewal-date? yang:date-and-time
+-- prior-signed-voucher-request? binary
+-- proximity-registrar-cert? binary
+-- agent-signed-data? binary
+-- agent-provided-proximity-registrar-cert? binary
+-- agent-sign-cert? binary
6.1.2. YANG Module
The following YANG module extends the [RFC8995] Voucher Request to
include a signed artifact from the registrar-agent (agent-signed-
data) as well as the registrar-proximity-certificate and the agent-
signing certificate.
<CODE BEGINS> file "ietf-voucher-request-prm@2022-07-05.yang"
module ietf-voucher-request-prm {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-voucher-request-prm";
prefix vrprm;
import ietf-restconf {
prefix rc;
description
"This import statement is only present to access
the yang-data extension defined in RFC 8040.";
reference "RFC 8040: RESTCONF Protocol";
}
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import ietf-voucher-request {
prefix vcr;
description
"This module defines the format for a voucher request,
which is produced by a pledge as part of the RFC8995
onboarding process.";
reference
"RFC 8995: Bootstrapping Remote Secure Key Infrastructure";
}
organization
"IETF ANIMA Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/anima/>
WG List: <mailto:anima@ietf.org>
Author: Steffen Fries
<mailto:steffen.fries@siemens.com>
Author: Eliot Lear
<mailto: lear@cisco.com>
Author: Thomas Werner
<mailto: thomas-werner@siemens.com>
Author: Michael Richardson
<mailto: mcr+ietf@sandelman.ca>";
description
"This module defines the format for a voucher-request form the
pledge in responder mode. It bases on the voucher-request
defined in RFC 8995, which is a superset of the voucher itself.
It provides content to the MASA for consideration
during a voucher-request.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
'MAY', and 'OPTIONAL' in this document are to be interpreted as
described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
Copyright (c) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
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This version of this YANG module is part of RFC xxxx; see the
RFC itself for full legal notices.";
revision 2022-07-05 {
description
"Initial version";
reference
"RFC XXXX: BRSKI for Pledge in Responder Mode";
}
// Top-level statement
rc:yang-data voucher-request-prm-artifact {
// YANG data template for a voucher-request.
uses voucher-request-prm-grouping;
}
// Grouping defined for future usage
grouping voucher-request-prm-grouping {
description
"Grouping to allow reuse/extensions in future work.";
uses vcr:voucher-request-grouping {
augment voucher {
description "Base the voucher-request-prm upon the
regular one";
leaf agent-signed-data {
type binary;
description
"The agent-signed-data field contains a JOSE [RFC7515]
object provided by the Registrar-Agent to the Pledge.
This artifact is signed by the Registrar-Agent
and contains a copy of the pledge's serial-number.";
}
leaf agent-provided-proximity-registrar-cert {
type binary;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
The first certificate in the registrar TLS server
certificate_list sequence (the end-entity TLS
certificate; see RFC 8446) presented by the
registrar to the registrar-agent and provided to
the pledge.
This MUST be populated in a pledge's voucher-request
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when an agent-proximity assertion is requested.";
reference
"ITU X.690: Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)
RFC 5280: Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile
RFC 8446: The Transport Layer Security (TLS)
Protocol Version 1.3";
}
leaf-list agent-sign-cert {
type binary;
min-elements 1;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
This certificate can be used by the pledge,
the registrar, and the MASA to verify the signature
of agent-signed-data. It is an optional component
for the pledge-voucher request.
This MUST be populated in a registrar's
voucher-request when an agent-proximity assertion
is requested.
It is defined as list to enable inclusion of further
certificates along the certificate chain if different
issuing CAs have been used for the registrar-agent
and the registrar.";
reference
"ITU X.690: Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)
RFC 5280: Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile";
}
}
}
}
}
<CODE ENDS>
Examples for the PVR are provided in Section 5.5.2.
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7. IANA Considerations
This document requires the following IANA actions.
7.1. BRSKI .well-known Registry
IANA is requested to enhance the Registry entitled: "BRSKI Well-Known
URIs" with the following endpoints:
URI Description Reference
pledge-voucher-request create pledge-voucher-request [THISRFC]
pledge-enrollment-request create pledge-enrollment-request [THISRFC]
pledge-voucher supply voucher response [THISRFC]
pledge-enrollment supply enrollment response [THISRFC]
pledge-cacerts supply CA certificates to pledge [THISRFC]
requestenroll supply PER to registrar [THISRFC]
wrappedcacerts request wrapped CA certificates [THISRFC]
8. 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.
9. Security Considerations
9.1. Exhaustion Attack on Pledge
Exhaustion attack on pledge based on DoS attack (connection
establishment, etc.)
9.2. Misuse of acquired Voucher and Enrollment objects by Registrar-
Agent
A Registrar-agent that uses acquired voucher and enrollment objects
for domain-A in domain-B can be avoided by the PVR processing on the
domain registrar side. This requires the domain registrar to verify
the "proximity-registrar-cert" field in the PVR against his own
LDevID(Reg). In addition, the domain registrar has to verify the
association of the pledge to his domain based on the product-serial-
number contained in the PVR and in the pledge IDevID certificate.
Moreover, the registrar verifies if the registrar-agent is authorized
to interact with the pledge for voucher-requests, based on the
LDevID(RegAgt) certificate information contained in the PVR.
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Misbinding of a pledge by a faked domain registrar is countered as
described in BRSKI security considerations (section 11.4).
9.3. Misuse of Registrar-Agent Credentials
Concerns on opportunities to misuse the registrar-agent with a valid
LDevID, may be addressed by utilizing short-lived certificates (e.g.,
valid for a day) to authenticate the registrar-agent against the
domain registrar. The LDevID(RegAgt) certificate may be acquired by
a prior BRSKI run for the registrar-agent, if IDevID is available on
registrar-agent. Alternatively, the LDevID may be acquired by a
service technician from the domain PKI system.
In addition it is required that the LDevID(RegAgt) certificate is
valid for the complete bootstrapping phase. This avoids a registrar-
agent could be misused to create arbitrary "agent-signed-data"
objects to perform an authorized bootstrapping of a rouge pledge. As
"agent-signed-data" could be dated after the validity time of the
LDevID(RegAgt) certificate, due to missing trusted timestamp in the
registrar-agents signature.
To address this, the registrar SHOULD verify the certificate used to
create the signature on "agent-signed-data". Furthermore the
registrar also verifies the LDevID(RegAgt) certificate used in the
TLS handshake. If both certificates are successfully verified, the
registrar-agents signature can be considered as valid.
9.4. YANG Module Security Considerations
The enhanced voucher-request described in section Section 6.1 is
bases on [RFC8995], but uses a different encoding based on
[I-D.ietf-anima-jws-voucher]. Therefore similar considerations as
described in Section 11.7 (Security Considerations) of [RFC8995]
apply. The YANG module specified in this document defines the schema
for data that is subsequently encapsulated by a JOSE signed-data
Content-type as described in [I-D.ietf-anima-jws-voucher]. As such,
all of the YANG-modeled data is protected against modification. The
use of YANG to define data structures via the "yang-data" statement,
is relatively new and distinct from the traditional use of YANG to
define an API accessed by network management protocols such as
NETCONF [RFC6241] and RESTCONF [RFC8040]. For this reason these
guidelines do not follow the template described by Section 3.7 of
[RFC8407].
10. Acknowledgments
We would like to thank the various reviewers, in particular Brian E.
Carpenter, Oskar Camenzind, and Hendrik Brockhaus for their input and
discussion on use cases and call flows.
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11. References
11.1. Normative References
[I-D.ietf-anima-jws-voucher]
Richardson, M. and T. Werner, "JWS signed Voucher
Artifacts for Bootstrapping Protocols", Work in Progress,
Internet-Draft, draft-ietf-anima-jws-voucher-03, 7 March
2022, <https://www.ietf.org/archive/id/draft-ietf-anima-
jws-voucher-03.txt>.
[I-D.ietf-anima-rfc8366bis]
Watsen, K., Richardson, M. C., Pritikin, M., Eckert, T.,
and Q. Ma, "A Voucher Artifact for Bootstrapping
Protocols", Work in Progress, Internet-Draft, draft-ietf-
anima-rfc8366bis-00, 31 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-anima-
rfc8366bis-00.txt>.
[I-D.ietf-netconf-sztp-csr]
Watsen, K., Housley, R., and S. Turner, "Conveying a
Certificate Signing Request (CSR) in a Secure Zero Touch
Provisioning (SZTP) Bootstrapping Request", Work in
Progress, Internet-Draft, draft-ietf-netconf-sztp-csr-14,
2 March 2022, <https://www.ietf.org/archive/id/draft-ietf-
netconf-sztp-csr-14.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[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,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[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, <https://www.rfc-editor.org/info/rfc8995>.
11.2. Informative References
[BRSKI-PRM-abstract]
"Abstract BRSKI-PRM Protocol Overview", April 2022,
<https://raw.githubusercontent.com/anima-wg/anima-brski-
prm/main/pics/brski_prm_overview.png>.
[CABF] "CA Browser Forum", n.d., <https://cabforum.org/>.
[I-D.ietf-anima-brski-ae]
Oheimb, D. V., Fries, S., Brockhaus, H., and E. Lear,
"BRSKI-AE: Alternative Enrollment Protocols in BRSKI",
Work in Progress, Internet-Draft, draft-ietf-anima-brski-
ae-02, 3 June 2022, <https://www.ietf.org/archive/id/
draft-ietf-anima-brski-ae-02.txt>.
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[IEEE-802.1AR]
Institute of Electrical and Electronics Engineers, "IEEE
802.1AR Secure Device Identifier", IEEE 802.1AR, June
2018.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
[RFC9238] Richardson, M., Latour, J., and H. Habibi Gharakheili,
"Loading Manufacturer Usage Description (MUD) URLs from QR
Codes", RFC 9238, DOI 10.17487/RFC9238, May 2022,
<https://www.rfc-editor.org/info/rfc9238>.
Appendix A. History of Changes [RFC Editor: please delete]
From IETF draft 03 -> IETF draft 04:
* Simplified YANG definition by augmenting the voucher request from
RFC 8995 instead of redefining it.
* Added explanation for terminology "endpoint" used in this
document, issue #16
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* Added clarification that registrar-agent may collect PVR or PER or
both in one run, issue #17
* Added a statement that nonceless voucher may be accepted, issue
#18
* Simplified structure in section Section 3.1, issue #19
* Removed join proxy in Figure 1 and added explanatory text, issue
#20
* Added description of pledge-CAcerts endpoint plus further handling
of providing a wrapped CA certs response to the pledge in section
Section 5.5.3; also added new required registrar endpoint (section
Section 5.5.2 and IANA considerations) for the registrar to
provide a wrapped CA certs response, issue #21
* utilized defined abbreviations in the document consistently, issue
#22
* Reworked text on discovery according to issue #23 to clarify scope
and handling
* Added several clarifications based on review comments
From IETF draft 02 -> IETF draft 03:
* Updated examples to state "base64encodedvalue==" for x5c
occurrences
* Include link to SVG graphic as general overview
* Restructuring of section 5 to flatten hierarchy
* Enhanced requirements and motivation in Section 4
* Several editorial improvements based on review comments
From IETF draft 01 -> IETF draft 02:
* Issue #15 included additional signature on voucher from registrar
in section Section 5.5.2 and section Section 5.2 The verification
of multiple signatures is described in section Section 5.5.3
* Included representation for General JWS JSON Serialization for
examples
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* Included error responses from pledge if it is not able to create a
pledge-voucher request or an enrollment request in section
Section 5.5.1
* Removed open issue regarding handling of multiple CSRs and
enrollment responses during the bootstrapping as the initial
target it the provisioning of a generic LDevID certificate. The
defined endpoint on the pledge may also be used for management of
further certificates.
From IETF draft 00 -> IETF draft 01:
* Issue #15 lead to the inclusion of an option for an additional
signature of the registrar on the voucher received from the MASA
before forwarding to the registrar-agent to support verification
of POP of the registrars private key in section Section 5.5.2 and
Section 5.5.3.
* Based on issue #11, a new endpoint was defined for the registrar
to enable delivery of the wrapped enrollment request from the
pledge (in contrast to plain PKCS#10 in simple enroll).
* Decision on issue #8 to not provide an additional signature on the
enrollment-response object by the registrar. As the enrollment
response will only contain the generic LDevID certificate. This
credential builds the base for further configuration outside the
initial enrollment.
* Decision on issue #7 to not support multiple CSRs during the
bootstrapping, as based on the generic LDevID certificate the
pledge may enroll for further certificates.
* Closed open issue #5 regarding verification of ietf-ztp-types
usage as verified via a proof-of-concept in section
{#exchanges_uc2_1}.
* Housekeeping: Removed already addressed open issues stated in the
draft directly.
* Reworked text in from introduction to section pledge-responder-
mode
* Fixed "serial-number" encoding in PVR/RVR
* Added prior-signed-voucher-request in the parameter description of
the registrar-voucher-request in Section 5.5.2.
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* Note added in Section 5.5.2 if sub-CAs are used, that the
corresponding information is to be provided to the MASA.
* Inclusion of limitation section (pledge sleeps and needs to be
waked up. Pledge is awake but registrar-agent is not available)
(Issue #10).
* Assertion-type aligned with voucher in RFC8366bis, deleted related
open issues. (Issue #4)
* Included table for endpoints in Section 5.3 for better
readability.
* Included registrar authorization check for registrar-agent during
TLS handshake in section Section 5.5.2. Also enhanced figure
Figure 10 with the authorization step on TLS level.
* Enhanced description of registrar authorization check for
registrar-agent based on the agent-signed-data in section
Section 5.5.2. Also enhanced figure Figure 10 with the
authorization step on pledge-voucher-request level.
* Changed agent-signed-cert to an array to allow for providing
further certificate information like the issuing CA cert for the
LDevID(RegAgt) certificate in case the registrar and the
registrar-agent have different issuing CAs in Figure 10 (issue
#12). This also required changes in the YANG module in
Section 6.1.2
* Addressed YANG warning (issue #1)
* Inclusion of examples for a trigger to create a pledge-voucher-
request and an enrollment-request.
From IETF draft-ietf-anima-brski-async-enroll-03 -> IETF anima-brski-
prm-00:
* Moved UC2 related parts defining the pledge in responder mode from
draft-ietf-anima-brski-async-enroll-03 to this document This
required changes and adaptations in several sections to remove the
description and references to UC1.
* Addressed feedback for voucher-request enhancements from YANG
doctor early review in Section 6.1 as well as in the security
considerations (formerly named ietf-async-voucher-request).
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* Renamed ietf-async-voucher-request to IETF-voucher-request-prm to
to allow better listing of voucher related extensions; aligned
with constraint voucher (#20)
* Utilized ietf-voucher-request-async instead of ietf-voucher-
request in voucher exchanges to utilize the enhanced voucher-
request.
* Included changes from draft-ietf-netconf-sztp-csr-06 regarding the
YANG definition of csr-types into the enrollment request exchange.
From IETF draft 02 -> IETF draft 03:
* Housekeeping, deleted open issue regarding YANG voucher-request in
Section 5.5.1 as voucher-request was enhanced with additional
leaf.
* Included open issues in YANG model in Section 5.1 regarding
assertion value agent-proximity and csr encapsulation using SZTP
sub module).
From IETF draft 01 -> IETF draft 02:
* Defined call flow and objects for interactions in UC2. Object
format based on draft for JOSE signed voucher artifacts and
aligned the remaining objects with this approach in Section 5.5 .
* Terminology change: issue #2 pledge-agent -> registrar-agent to
better underline agent relation.
* Terminology change: issue #3 PULL/PUSH -> pledge-initiator-mode
and pledge-responder-mode to better address the pledge operation.
* Communication approach between pledge and registrar-agent changed
by removing TLS-PSK (former section TLS establishment) and
associated references to other drafts in favor of relying on
higher layer exchange of signed data objects. These data objects
are included also in the pledge-voucher-request and lead to an
extension of the YANG module for the voucher-request (issue #12).
* Details on trust relationship between registrar-agent and
registrar (issue #4, #5, #9) included in Section 5.1.
* Recommendation regarding short-lived certificates for registrar-
agent authentication towards registrar (issue #7) in the security
considerations.
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* Introduction of reference to agent signing certificate using SKID
in agent signed data (issue #11).
* Enhanced objects in exchanges between pledge and registrar-agent
to allow the registrar to verify agent-proximity to the pledge
(issue #1) in Section 5.5.
* Details on trust relationship between registrar-agent and pledge
(issue #5) included in Section 5.1.
* Split of use case 2 call flow into sub sections in Section 5.5.
From IETF draft 00 -> IETF draft 01:
* Update of scope in Section 3.1 to include in which the pledge acts
as a server. This is one main motivation for use case 2.
* Rework of use case 2 in Section 5.1 to consider the transport
between the pledge and the pledge-agent. Addressed is the TLS
channel establishment between the pledge-agent and the pledge as
well as the endpoint definition on the pledge.
* First description of exchanged object types (needs more work)
* Clarification in discovery options for enrollment endpoints at the
domain registrar based on well-known endpoints do not result in
additional /.well-known URIs. Update of the illustrative example.
Note that the change to /brski for the voucher related endpoints
has been taken over in the BRSKI main document.
* Updated references.
* Included Thomas Werner as additional author for the document.
From individual version 03 -> IETF draft 00:
* Inclusion of discovery options of enrollment endpoints at the
domain registrar based on well-known endpoints in new section as
replacement of section 5.1.3 in the individual draft. This is
intended to support both use cases in the document. An
illustrative example is provided.
* Missing details provided for the description and call flow in
pledge-agent use case Section 5.1, e.g. to accommodate
distribution of CA certificates.
* Updated CMP example in to use lightweight CMP instead of CMP, as
the draft already provides the necessary /.well-known endpoints.
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* Requirements discussion moved to separate section in Section 4.
Shortened description of proof of identity binding and mapping to
existing protocols.
* Removal of copied call flows for voucher exchange and registrar
discovery flow from [RFC8995] in UC1 to avoid doubling or text or
inconsistencies.
* Reworked abstract and introduction to be more crisp regarding the
targeted solution. Several structural changes in the document to
have a better distinction between requirements, use case
description, and solution description as separate sections.
History moved to appendix.
From individual version 02 -> 03:
* Update of terminology from self-contained to authenticated self-
contained object to be consistent in the wording and to underline
the protection of the object with an existing credential. Note
that the naming of this object may be discussed. An alternative
name may be attestation object.
* Simplification of the architecture approach for the initial use
case having an offsite PKI.
* Introduction of a new use case utilizing authenticated self-
contain objects to onboard a pledge using a commissioning tool
containing a pledge-agent. This requires additional changes in
the BRSKI call flow sequence and led to changes in the
introduction, the application example,and also in the related
BRSKI-PRM call flow.
From individual version 01 -> 02:
* Update of introduction text to clearly relate to the usage of
IDevID and LDevID.
* Update of description of architecture elements and changes to
BRSKI in Section 5.
* Enhanced consideration of existing enrollment protocols in the
context of mapping the requirements to existing solutions in
Section 4.
From individual version 00 -> 01:
* Update of examples, specifically for building automation as well
as two new application use cases in Section 3.1.
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* Deletion of asynchronous interaction with MASA to not complicate
the use case. Note that the voucher exchange can already be
handled in an asynchronous manner and is therefore not considered
further. This resulted in removal of the alternative path the
MASA in Figure 1 and the associated description in Section 5.
* Enhancement of description of architecture elements and changes to
BRSKI in Section 5.
* Consideration of existing enrollment protocols in the context of
mapping the requirements to existing solutions in Section 4.
* New section starting with the mapping to existing enrollment
protocols by collecting boundary conditions.
Authors' Addresses
Steffen Fries
Siemens AG
Otto-Hahn-Ring 6
81739 Munich
Germany
Email: steffen.fries@siemens.com
URI: https://www.siemens.com/
Thomas Werner
Siemens AG
Otto-Hahn-Ring 6
81739 Munich
Germany
Email: thomas-werner@siemens.com
URI: https://www.siemens.com/
Eliot Lear
Cisco Systems
Richtistrasse 7
CH-8304 Wallisellen
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
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