BRSKI with Pledge in Responder Mode (BRSKI-PRM)
draft-ietf-anima-brski-prm-02
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| Authors | Steffen Fries , Thomas Werner , Eliot Lear , Michael Richardson | ||
| Last updated | 2022-03-04 (Latest revision 2022-02-11) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-anima-brski-prm-02
ANIMA WG S. Fries
Internet-Draft T. Werner
Intended status: Standards Track Siemens
Expires: 5 September 2022 E. Lear
Cisco Systems
M. Richardson
Sandelman Software Works
4 March 2022
BRSKI with Pledge in Responder Mode (BRSKI-PRM)
draft-ietf-anima-brski-prm-02
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.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2022.
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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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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scope of Solution . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Supported Environment . . . . . . . . . . . . . . . . . . 6
3.2. Application Examples . . . . . . . . . . . . . . . . . . 6
3.2.1. Building Automation . . . . . . . . . . . . . . . . . 6
3.2.2. Infrastructure Isolation Policy . . . . . . . . . . . 7
3.2.3. Less Operational Security in the Target-Domain . . . 7
3.3. Limitations . . . . . . . . . . . . . . . . . . . . . . . 7
4. Requirements Discussion and Mapping to Solution-Elements . . 7
5. Architectural Overview and Communication Exchanges . . . . . 8
5.1. Pledge-responder-mode (PRM): Registrar-agent Communication
with Pledges . . . . . . . . . . . . . . . . . . . . . . 9
5.1.1. Agent-Proximity . . . . . . . . . . . . . . . . . . . 12
5.1.2. Behavior of Pledge in Pledge-Responder-Mode . . . . . 13
5.1.3. Behavior of Registrar-Agent . . . . . . . . . . . . . 14
5.1.4. Bootstrapping Objects and Corresponding Exchanges . . 16
6. Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.1. Voucher Request Artifact . . . . . . . . . . . . . . . . 42
6.1.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . 42
6.1.2. YANG Module . . . . . . . . . . . . . . . . . . . . . 43
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 47
9. Security Considerations . . . . . . . . . . . . . . . . . . . 47
9.1. Exhaustion Attack on Pledge . . . . . . . . . . . . . . . 48
9.2. Misuse of acquired Voucher and Enrollment responses by
Registrar-Agent . . . . . . . . . . . . . . . . . . . . . 48
9.3. Misuse of Registrar-Agent Credentials . . . . . . . . . . 48
9.4. YANG Module Security Considerations . . . . . . . . . . . 48
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 49
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 49
11.1. Normative References . . . . . . . . . . . . . . . . . . 49
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11.2. Informative References . . . . . . . . . . . . . . . . . 50
Appendix A. History of Changes [RFC Editor: please delete] . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
BRSKI as defined in [RFC8995] specifies a solution for secure zero-
touch (automated) bootstrapping of devices (pledges) in a (customer)
site domain. This includes the discovery of network elements in the
target domain, time synchronization, and the exchange of security
information necessary to establish trust between a pledge and the
domain. Security information about the target domain, specifically
the target domain certificate, is exchanged utilizing voucher objects
as defined in [RFC8366]. These vouchers are 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 registrar's 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 tool or it may be even co-
located with the registrar. In contrast to BRSKI the registrar-agent
performs the object exchange with the pledge and provides/retrieves
data objects to/from the domain registrar. For the interaction with
the domain registrar the registrar-agent will use existing BRSKI
[RFC8995] endpoints.
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, when 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.
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* 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 target domain specific device certificates.
EST in turn relies on a binding of the certification request to an
underlying TLS connection between the EST client and the EST server.
According to BRSKI the domain registrar acts as EST server and is
also acting as registration authority (RA) 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 target
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. As the
described solution will rely on additional wrapping signature it will
require pre-processing specifically for EST, as it currently uses
PKCS#10 requests only.
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]. The
following terms are defined additionally:
asynchronous communication: Describes a timely interrupted
communication between an end entity and a PKI component.
authenticated self-contained object: Describes an object, which is
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cryptographically bound to the EE certificate (IDevID certificate
or LDEVID certificate) of a pledge. The binding is assumed to be
provided through a digital signature of the actual object using
the corresponding private key of the EE certificate.
CA: Certification authority, issues certificates.
EE: End entity
on-site: Describes a component or service or functionality available
in the target deployment domain.
off-site: Describes a component or service or functionality
available in an operator domain different from the target
deployment domain. This may be a central site or a cloud service,
to which only a temporary connection is available, or which is in
a different administrative domain.
PER: Pledge-enrollment-request
POP: Prove of possession (of a private key)
POI: Prove of identity
PVR: Pledge-voucher-request
IED: Intelligent Electronic Device (in essence a pledge).
RA: Registration authority, an optional system component to which a
CA delegates certificate management functions such as
authorization checks.
RER: Registrar-enrollment-request
RVR: Registrar-voucher-request
synchronous communication: Describes a timely uninterrupted
communication between an end entity and a PKI component.
3. Scope of Solution
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3.1. Supported Environment
The described solution is applicable in domains in which pledges have
no direct connection to the domain registrar, but are expected to be
managed by this registrar. This can be motivated by pledges
featuring a different technology stack or by pledges without an
existing connection to the domain registrar during bootstrapping.
These pledges are likely to act in a server role. Therefore, the
pledge has to offer endpoints on which it can be triggered for the
generation of pledge-voucher-request objects and certification
objects as well as to provide the response objects to the pledge.
3.2. Application Examples
The following examples are intended to motivate the support of
additional bootstrapping approaches in general by introducing
industrial applications cases, which could leverage BRSKI as such but
also require support a pledge acting as server and only answers
requests as well as scenarios with limited connectivity to the
registrar.
3.2.1. Building Automation
In building automation, a use case can be described by a detached
building (or a cabinet) or the basement of a building equipped with
sensor, actuators, and controllers connected, but with only limited
or no connection to the centralized building management system. This
limited connectivity may be during the installation time but also
during operation time. During the installation in the basement, a
service technician collects the 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, beyond 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.
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3.2.2. Infrastructure Isolation Policy
This refers to any case in which network infrastructure is normally
isolated from the Internet as a matter of policy, most likely for
security reasons. In such a case, limited access to a domain
registrar may be allowed in carefully controlled short periods of
time, for example when a batch of new devices are deployed, but
impossible at other times.
3.2.3. 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
implicates higher operational security than other components
utilizing the issued certificates . CAs may also demand higher
security in the registration procedures. Especially the CA/Browser
forum currently increases the security requirements in the
certificate issuance procedures for publicly trusted certificates.
There may be the situation in which the target domain does not offer
enough security to operate a RA/CA and therefore this service is
transferred to a backend that offers a higher level of operational
security.
3.3. Limitations
The mechanisms in this draft 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 motivated application examples described in Section 3.2 the
following base requirements are derived to support the communication
between a pledge and a registrar via a registrar-agent.
At least the following properties are required by the voucher
handling and the enrollment:
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* 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.
* Proof of Identity (POI): provides data-origin authentication of a
data object, e.g., a certificate request, utilizing an existing
IDevID. Certificate updates may utilize the certificate that is
to be updated.
Solution examples based on existing technology are provided with the
focus on existing IETF documents:
* 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
utilizes PKCS#10 [RFC2986]. Here, 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
delegated to the protocol used for certificate management or it
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 the existing
credential on the pledge (IDevID). This supports independence
from 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
case. 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. In constraint
environments it may provided based on COSE.
5.1. Pledge-responder-mode (PRM): Registrar-agent Communication with
Pledges
To support mutual trust establishment of pledges, not directly
connected to the domain registrar, this document relies on the
exchange of authenticated self-contained objects (the voucher
request/response objects as known from BRSKI and the enrollment
request/response objects as introduced by BRSKI-PRM) with the help of
a registrar-agent. This allows independence from protection provided
by the utilized transport protocol.
The registrar-agent may be an integrated functionality of a
commissioning tool or be co-located with the registrar itself. This
leads to enhancements of the logical elements in the BRSKI
architecture as shown in Figure 1. The registrar-agent interacts
with the pledge to acquire and to supply the required data objects
for bootstrapping, which are also exchanged between the registrar-
agent and the domain registrar. Moreover, the addition of the
registrar-agent influences the sequences of the data exchange between
the pledge and the domain registrar described in [RFC8995]. A
general goal for the registrar-agent application is the reuse of
already defined endpoints of the domain registrar side. The
functionality of the already existing registrar endpoints may need
small enhancements to cope with the additional signatures.
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+------------------------+
+--------------Drop Ship---------------| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| | BRSKI-
V BRSKI-PRM | MASA
+-------+ +---------+ .............................|.........
| | | | . | .
| | | | . +-----------+ +-----v-----+ .
| | |Registrar| . | | | | .
|Pledge | |Agent | . | Join | | Domain | .
| | | | . | Proxy | | Registrar | .
| <----->.........<------>...........<-------> (PKI RA) | .
| | | | . | | | | .
| | | | . | | +-----+-----+ .
|IDevID | | LDevID | . +-----------+ | .
| | | | . +------------------+-----+ .
+-------+ +---------+ . | Key Infrastructure | .
. | (e.g., PKI Certificate | .
. | Authority) | .
. +------------------------+ .
.......................................
"Domain" components
Figure 1: Architecture overview using registrar-agent
For authentication towards the domain registrar, the registrar-agent
uses its LDevID. The provisioning of the registrar-agent LDevID may
be done by a separate BRSKI run or other means in advance. It is
recommended to use short lived registrar-agent LDevIDs in the range
of days or weeks.
If a registrar detects a request 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 LDeID(RegAgt) certificate. Alternatively, the
domain may feature an own issuing CA for registrar agent LDevID
certificates.
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In addition, the domain registrar may authenticate the user operating
the registrar-agent to perform additional authorization of a pledge
bootstrapping action. Examples for such user level authentication
may be HTTP authentication or the usage of authorization tokens or
other. This is out of scope of this document.
The following list describes the components in a (customer) site
domain:
* Pledge: The pledge is expected to respond with the necessary data
objects for bootstrapping to the registrar-agent. The transport
protocol used between the pledge and the registrar-agent is
assumed to be HTTP in the context of this document. Other
transport protocols may be used 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 domain registrar by the pledge is not needed
as the pledge will be triggered by the registrar-agent.
- Discovery of the pledge by the registrar-agent must be
possible.
- As the registrar-agent must be able to request data objects for
bootstrapping of the pledge, the pledge must offer
corresponding endpoints.
- The registrar-agent may provide additional data to the pledge,
in the context of the triggering request, 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, pledge-voucher-request
objects and pledge-enrollment-request objects, at once and
provides them to the registrar. This approach may also be used
to perform a bulk bootstrapping of several devices.
- The data objects utilized for the data exchange between the
pledge and the registrar are self-contained authenticated
objects (signature-wrapped objects).
* Registrar-agent: provides a communication path to exchange data
objects between the pledge and the domain registrar. The
registrar-agent facilitates situations, in which the domain
registrar is not directly reachable by the pledge, either due to a
different technology stack or due to missing connectivity. The
registrar-agent triggers a pledge to create bootstrapping
information such as voucher-request objects and enrollment-request
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objects on one or multiple pledges at performs may perform a bulk
bootstrapping based on the collected data. The registrar-agent is
expected to possess information of the domain registrar, either by
configuration or by using the discovery mechanism defined in
[RFC8995]. There is no trust assumption between the pledge and
the registrar-agent as only authenticated self-contained objects
are applied, which are transported via the registrar-agent and
provided either by the pledge or the registrar. The trust
assumption between the registrar-agent and the registrar bases on
the LDevID of the registrar-agent, provided by the PKI responsible
for the domain. This allows the registrar-agent to authenticate
towards the registrar, e.g., in a TLS handshake. Based on this,
the registrar is able to distinguish a pledge from a registrar-
agent during the session establishment.
* Join Proxy: same functionality as described in [RFC8995]. Note
that it may be used by the registrar-agent instead of the pledge
to find the registrar, if not configured.
* 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.
5.1.1. Agent-Proximity
"Agent-proximity" is a weaker assertion then "proximity". It is
defined as additional assertion type in
[I-D.richardson-anima-rfc8366bis] In case of "agent-proximity" it is
a statement, that the proximity-registrar-certificate was provided
via the registrar-agent 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) EE
certificate and has no proof-of-possession of the corresponding
private key for the certificate.
Trust handover to the domain is established via the "pinned-domain-
certificate" in the voucher.
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In contrast, "proximity" provides a statement, that the pledge was in
direct contact with the registrar and was able to verify proof-of-
possession of the private key in the context of the TLS handshake.
The provisionally accepted LDevID(Reg) EE certificate can be verified
after the voucher has been processed by the pledge through a
verification of an additional signature of the returned voucher by
the registrar if contained (optional feature).
5.1.2. Behavior of Pledge in Pledge-Responder-Mode
In contrast to BRSKI the pledge acts as a server component. It is
triggered by the registrar-agent for the generation of pledge-
voucher-request and pledge-enrollment-request objects as well as for
the processing of the response objects and the generation of status
information. Due to the use of the registrar-agent, the interaction
with the domain registrar is changed as shown in Figure 4. To enable
interaction with the registrar-agent, the pledge provides endpoints
using the BRSKI interface based on the "/.well-known/brski" URI tree.
The following endpoints are defined for the _pledge_ in this
document. The URI path begins with "http://www.example.com/.well-
known/brski" followed by a path-suffix that indicates the intended
operation.
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Operations and their corresponding URIs:
+------------------------+----------------------------+---------+
| Operation |Operation path | Details |
+========================+============================+=========+
| Trigger pledge-voucher-| /pledge-voucher-request | Section |
| request creation | | 5.1.4.1 |
| Returns | | |
| pledge-voucher-request | | |
++------------------------+----------------------------+---------+
| Trigger pledge- | /pledge-enrollment-request | Section |
| enrollment-request | | 5.1.4.1 |
| Returns pledge- | | |
| enrollment-request | | |
+------------------------+----------------------------+---------+
| Provide voucher to | /pledge-voucher | Section |
| pledge | | 5.1.4.3 |
| Returns | | |
| pledge-voucher-status | | |
+------------------------+----------------------------+---------+
| Provide enrollment | /pledge-enrollment | Section |
| response to pledge | | 5.1.4.3 |
| Returns pledge- | | |
| enrollment-status | | |
+------------------------+----------------------------+---------+
| Provide CA certs to | /pledge-CACerts | |
| pledge (OPTIONAL) | | |
+------------------------+----------------------------+---------+
Figure 2: Endpoints on the pledge
5.1.3. 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 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 10.
The registrar-agent is expected to already possess an LDevID(RegAgt)
to authenticate towards the domain registrar. The registrar-agent
will use this LDevID(RegAgt) when establishing the TLS session with
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the domain registrar in the context of for TLS client-side
authentication. The LDevID(RegAgt) EE certificate MUST include a
SubjectKeyIdentifier (SKID), which is used as reference in the
context of an agent-signed-data object as defined in Section 5.1.4.1.
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-side authentication is a deviation
from [RFC8995], in which the pledge's IDevID credential is used to
perform TLS client authentication. The use of the LDevID(RegAgt)
allows the domain registrar to distinguish, if bootstrapping is
initiated from a pledge or from a registrar-agent and adopt the
internal handling accordingly. As BRSKI-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
In addition to the LDevID(RegAgt), the registrar-agent is provided
with the product-serial-numbers of the pledges to be bootstrapped.
This is necessary to allow the discovery of pledges by the registrar-
agent using mDNS. The list may be provided by administrative means
or the registrar agent may get the information via an interaction
with the pledge, like scanning of product-serial-number information
using a QR code or similar.
According to [RFC8995] section 5.3, the domain registrar performs the
pledge authorization for bootstrapping within his domain based on the
pledge voucher-request object.
The following information 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.
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5.1.3.1. 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.
5.1.3.2. 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 at "product-serial-number.brski-
pledge._tcp.local." The pledge constructs a local host name based on
device local information (product-serial-number), which results in
"product-serial-number.brski-pledge._tcp.local." It can then be
discovered by the registrar-agent via mDNS. Note that other
mechanisms for discovery may be used.
The registrar-agent is able to build the same information based on
the provided list of product-serial-number.
5.1.4. Bootstrapping Objects and Corresponding Exchanges
The interaction of the pledge with the registrar-agent may be
accomplished using different transport means (protocols and or
network technologies). For this document the usage of HTTP is
targeted as in BRSKI. Alternatives may be CoAP, Bluetooth Low Energy
(BLE), or Nearfield Communication (NFC). This requires independence
of the exchanged data objects between the pledge and the registrar
from transport security. Therefore, authenticated self-contained
objects (here: signature-wrapped objects) are applied in the data
exchange between the pledge and the registrar.
The registrar-agent provides the domain-registrar certificate
(LDevID(Reg) EE certificate) to the pledge to be included into the
"agent-provided-proximity-registrar-certificate" leaf of the pledge-
voucher-request object. This enables the registrar to verify, that
it is the target registrar for handling the request. The registrar
certificate may be configured at the registrar-agent or may be
fetched by the registrar-agent based on a prior TLS connection
establishment with the domain registrar. In addition, the registrar-
agent provides agent-signed-data containing the product-serial-number
in the body, signed with the LDevID(RegAgt). This enables the
registrar to verify and log, which registrar-agent was in contact
with the pledge, when verifying the pledge-voucher-request.
Optionally the registrar-agent may provide its LDevID(RegAgt) EE
certificate (and optionally also the issuing CA certificate) to the
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pledge to be used in the "agent-sign-cert" component of the pledge-
voucher-request. If contained, the LDevID(RegAgt) EE certificate
MUST be the first certificate in the array. Note, this may be
omitted in constraint environments to safe bandwidth between the
registrar-agent and the pledge. If not contained, the registrar-
agent MUST fetch the LDevID(RegAgt) EE certificate based on the
SubjectKeyIdentifier (SKID) in the header of the agent-signed-data of
the pledge-voucher-request. The registrar includes the
LDevID(RegAgt) EE certificate information into the registrar-voucher-
request if the pledge-voucher-requests requests the assertion of
"agent-proximity".
The MASA in turn verifies the LDevID(Reg) EE certificate is included
in the pledge-voucher-request (prior-signed-voucher-request) in the
"agent-provided-proximity-registrar-certificate" leaf and may assert
in the voucher "verified" or "logged" instead of "proximity", as
there is no direct connection between the pledge and the registrar.
If the LDevID(RegAgt) EE certificate information is contained in the
"agent-sign-cert" component of the registrar-voucher-request, 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". 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 |
[discovery of pledge]
| mDNS query | | | |
|<-------------| | | |
|------------->| | | |
| | | | |
[trigger pledge-voucher-request and
pledge-enrollment-request generation]
|<- vTrigger --| | | |
|-Voucher-Req->| | | |
| | | | |
|<- eTrigger --| | | |
|- Enroll-Req->| | | |
~ ~ ~ ~ ~
[provide pledge-voucher-request to infrastructure]
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| |<------ TLS ----->| | |
| | [Reg-Agt auth+authz?] | |
| |-- Voucher-Req -->| | |
| | [Reg-Agt authorized?] | |
| | [accept device?] | |
| | [contact vendor] | |
| | |------- Voucher-Req ------>|
| | | [extract DomainID]
| | | [update audit log]
| | |<-------- Voucher ---------|
| |<---- Voucher ----| | |
| | | | |
[provide pledge enrollment request to infrastructure]
| |-- Enroll-Req --->| | |
| | |- Cert-Req -->| |
| | |<-Certificate-| |
| |<-- Enroll-Resp --| | |
~ ~ ~ ~ ~
[provide voucher and certificate
to pledge and collect status info]
|<-- Voucher --| | | |
|-- vStatus -->| | | |
|<-Enroll-Resp-| | | |
|-- eStatus -->| | | |
~ ~ ~ ~ ~
[provide voucher-status and enrollment status to registrar]
| |<------ TLS ----->| | |
| |---- vStatus --->| | |
| | |-- req. device audit log ->|
| | |<---- device audit log ----|
| | [verify audit log]
| | | | |
| |---- eStatus --->| | |
| | | | |
Figure 3: Overview pledge-responder-mode exchanges
The following sub sections split the interactions between the
different components into:
* Request objects acquisition targets exchanges and objects between
the registrar-agent and the pledge.
* Request handling targets exchanges and objects between the
registrar-agent and the registrar and also the interaction of the
registrar with the MASA and the domain CA.
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* Response object supply targets the exchanges and objects between
the registrar-agent and the pledge including the status objects.
* Status handling addresses the exchanges between the registrar-
agent and the registrar.
5.1.4.1. 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 5.1.3.2 based on mDNS.
The focus is on the exchange of signature-wrapped objects using
endpoints defined for the pledge in Section 5.1.2.
Preconditions:
* Pledge: possesses IDevID
* Registrar-agent: possesses IDevID CA certificate and an own
LDevID(RegAgt) EE credential for the registrar domain. In
addition, the registrar-agent can be configured with the product-
serial-number(s) of the pledge(s) to be bootstrapped. Note that
the product-serial-number may have been used during the pledge
discovery already.
* Registrar: possesses IDevID CA certificate and an own LDevID(Reg)
credential.
* MASA: possesses own credentials (voucher signing key, TLS server
certificate) as well as IDevID CA certificate of pledge vendor /
manufacturer and site-specific LDevID CA certificate.
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+--------+ +-----------+
| Pledge | | Registrar |
| | | Agent |
| | | (RegAgt) |
+--------+ +-----------+
| |-create
| | agent-signed-data
|<--- trigger pledge-voucher-request ----|
|-agent-provided-proximity-registrar-cert|
|-agent-signed-data |
|-agent-sign-cert (optional) |
| |
|----- pledge-voucher-request ---------->|-store
| | pledge-voucher-request
|<----- trigger enrollment request ------|
| (empty) |
| |
|------ pledge-enrollment-request ------>|-store
| | pledge-enrollment-req.
Figure 4: Request collection (registrar-agent - pledge)
Triggering the pledge to create the pledge-voucher-request is done
using HTTP POST on the defined pledge endpoint "/.well-known/brski/
pledge-voucher-request".
The registrar-agent pledge-voucher-request 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 EE 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 pledge-voucher-request is
depicted in the following figure:
{
"agent-provided-proximity-registrar-cert": "base64encodedvalue==",
"agent-signed-data": "base64encodedvalue==",
"agent-sign-cert": ["base64encodedvalue==", "base64encodedvalue==", "..."]
}
Figure 5: Representation of trigger to create pledge-voucher-request
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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) EE
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: contains the base64-encoded SubjectKeyIdentifier 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 SHOULD
construct the body of the pledge-voucher-request 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 pledge-voucher-request it
SHOULD respond with HTTP 406 error code to the registrar-agent to
indicate that it is not able to create the pledge-voucher-request.
The header of the pledge-voucher-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 payload of the pledge-voucher-request (PVR) object MUST contain
the following parameter as part of the ietf-voucher-request-
prm:voucher as defined in [RFC8995]:
* created-on: contains the current date and time in yang:date-and-
time format.
* nonce: contains a cryptographically strong random or pseudo-random
number.
* serial-number: contains the pledge product-serial-number.
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* assertion: contains the requested voucher assertion.
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) EE certificate (provided
as trigger parameter by the registrar-agent).
* agent-signed-data: MUST contain the base64-encoded agent-signed-
data (as defined in Figure 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) EE
certificate optionally followed by the issuing CA certificate and
potential further certificates. If supported, it MUST at least
contain the LDevID(RegAgt) EE 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 pledge-voucher-request
The pledge-voucher-request 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 5.1.4.2.
Once the registrar-agent has received the pledge-voucher-request it
can trigger the pledge to generate an enrollment-request object. As
in BRSKI the enrollment request object is a PKCS#10, 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.
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Triggering the pledge to create the enrollment-request is done using
HTTP POST on the defined pledge endpoint "/.well-known/brski/pledge-
enrollment-request".
The registrar-agent pledge-enrollment-request 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: initial or re-
enroll as shown in Figure 8.
{
"enroll-type" = "intial"
}
Figure 8: Example of trigger to create a pledge-enrollment-request
In the following the enrollment is described as initial enrollment
with an empty body.
Upon receiving the enrollment-trigger, the pledge SHALL construct the
pledge-enrollment-request as authenticated self-contained object.
The CSR already assures proof of possession of the private key
corresponding to the contained public key. In addition, based on the
additional signature using the IDevID, proof of identity is provided.
Here, a JOSE object is being created in which the body utilizes the
YANG module 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 pledge-enrollment-request 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.
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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 may use the endpoints specified
in this document.
[I-D.ietf-netconf-sztp-csr] considers PKCS#10 but also CMP and CMC as
certification request format. Note that the wrapping signature is
only necessary for plain PKCS#10 as other request formats like CMP
and CMS support the signature wrapping as part of their own
certificate request format.
The registrar-agent enrollment-request Content-Type header for a
wrapped PKCS#10 is: application/jose
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=="
}
]
}
}
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Figure 9: Representation of pledge-enrollment-request
With the collected pledge-voucher-request object and the pledge-
enrollment-request object, the registrar-agent starts the interaction
with the domain registrar.
Once the registrar-agent has collected the pledge-voucher-request and
pledge-enrollment-request objects, it connects to the registrar and
sends the request objects. As the registrar-agent is intended to
work between the pledge and the domain registrar, a collection of
requests from more than one pledge is possible, allowing a bulk
bootstrapping of multiple pledges using the same connection between
the registrar-agent and the domain registrar.
5.1.4.2. Request Handling - Registrar-Agent (Infrastructure)
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 IDevID CA certificate and it's own
LDevID(RegAgt) credentials of site domain. It has the address of
the domain registrar through configuration or by discovery, e.g.,
mDNS/DNSSD. The registrar-agent has acquired pledge-voucher-
request and pledge-enrollment-request objects(s).
* Registrar: possesses IDevID CA certificate of pledge vendor/
manufacturer and an it's own LDevID(Reg) credentials.
* MASA: possesses it's own vendor/manufacturer credentials (voucher
signing key, TLS server certificate) related to pledges IDevID and
site-specific LDevID CA certificate.
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+-----------+ +-----------+ +--------+ +---------+
| Registrar-| | Domain | | Domain | | Vendor |
| agent | | Registrar | | CA | | Service |
| (RegAgt) | | (JRC) | | | | (MASA) |
+-----------+ +-----------+ +--------+ +---------+
| | | Internet |
[exchange between pledge and ] | |
[registrar-agent done. ] | |
| | | |
|<------ TLS ----->| | |
| [Reg-Agt auth+authz?] | |
| | | |
|-- Voucher-Req -->| | |
| (PVR) | | |
| [Reg-Agt authorized?] | |
| [accept device?] | |
| [contact vendor] | |
| |------------ TLS --------->|
| |-- Voucher-Req ----------->|
| | (RVR) |
| | [extract DomainID]
| | [update audit log]
| |<-------- Voucher ---------|
|<---- Voucher ----| |
| | |
[certification request handling registrar-agent] |
[and site infrastructure] |
|--- Enroll-Req -->| | |
| (PER) | | |
| |---- TLS ---->| |
| |- Enroll-Req->| |
| | (RER) | |
| |<-Enroll-Resp-| |
|<-- Enroll-Resp---| | |
| | | |
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 is achieved by
using registrar-agent LDevID(RegAgt) credentials instead of pledge
IDevID credentials. This allows the registrar to distinguish between
BRSKI (pledge-initiator-mode) and BRSKI-PRM (pledge-responder-mode).
The registrar SHOULD verify that the registrar-agent is authorized to
connect to the registrar based on the LDevID(RegAgt). Note, the
authorization will be verified based on the agent-signed-data carried
in the pledge-voucher-request. As short-lived certificates are
recommended for the registrar-agent, the LDevID(RegAgt) EE
certificate used in the TLS handshake may be newer than the one of in
the pledge-voucher-request.
The registrar can received request objects in different forms 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 sends the pledge-voucher-request to the registrar
by HTTP POST to the endpoint: "/.well-known/brski/requestvoucher"
The pledge-voucher-request Content-Type header field used for pledge-
responder-mode is defined in [I-D.ietf-anima-jws-voucher] as:
application/voucher-jws+json (see Figure 7 for the content
definition).
The registrar-agent SHOULD include the Accept request-header field
indicating the pledge acceptable Content-Type for the voucher-
response. The voucher-response Content-Type header field
"application/voucher-jws+json" is defined in
[I-D.ietf-anima-jws-voucher].
Upon reception of the pledge-voucher-request, the registrar SHALL
perform the verification of the voucher-request parameter as defined
in section 5.3 of [RFC8995]. In addition, the registrar shall verify
the following parameters from the pledge-voucher-request:
* agent-provided-proximity-registrar-cert: MUST contain registrars
own LDevID(Reg) EE certificate to ensure the registrar in
proximity is the target registrar for the request.
* 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 pledge-
voucher-request, it must be fetched from a repository 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) EE certificate.
If contained the registrar MUST verify that the credentials
(LDevID(ReAgt) EE certificate and optionally the certificate
chain), used to sign the data, have been valid at signature
creation time and the corresponding registrar-agent was authorized
for involvement in the bootstrapping process. If the agent-
signed-cert is not provided, the registrar MUST fetch the
LDevID(RegAgt) EE certificate and perform this verification, based
on the provided SubjectKeyIdentifier (SKID) contained in the kid
header of the agent-signed-data. This requires, that the
registrar can fetch the LDevID(RegAgt) certificate data (including
intermediate CA certificates if existent) based on the SKID.
If validation fails the registrar SHOULD respond with HTTP 404 error
code to the registrar-agent. HTTP 406 error code is more
appropriate, if the format of pledge-voucher-request is unknown.
If validation succeeds, the registrar will accept the pledge's
request to join the domain as defined in section 5.3 of [RFC8995].
The registrar then establishes a TLS connection with the MASA as
described in section 5.4 of [RFC8995] to obtain a voucher for the
pledge.
The registrar SHALL construct the body of the registrar-voucher-
request object as defined in [RFC8995]. The encoding SHALL be done
as JSON-in-JWS object as defined in [I-D.ietf-anima-jws-voucher].
The header of the registrar-voucher-request 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 registrar-voucher-request (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 registrar-voucher-request creation time.
* nonce: copied form the pledge-voucher-request
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* serial-number: contains the pledge product-serial-number. The
registrar MUST verify that the IDevID EE 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 pledge-voucher-request
provided by the registrar-agent.
The voucher request can be enhanced optionally with the following
additional parameter as defined in Section 6.1:
* agent-sign-cert: contains the certificate or the certificate
including the chain of the registrar-agent. 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 list it MUST be the
base64-encoded LDevID(RegAgt) EE certificate. If multiple
certificates are included, the first MUST be the base64-encoded
LDevID(RegAgt) EE certificate.
The MASA uses this information for the verification of agent
proximity to issue the corresponding assertion "agent-proximity". If
the agent-sign-cert is not contained in the registrar-voucher-
request, it is contained in the prior-signed-voucher from the pledge.
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": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 11: Representation of registrar-voucher-request
The registrar sends the registrar-voucher-request to the MASA by HTTP
POST to the endpoint "/.well-known/brski/requestvoucher".
The registrar-voucher-request Content-Type header field is defined in
[I-D.ietf-anima-jws-voucher] as: application/voucher-jws+json
The registrar SHOULD include an Accept request-header field
indicating the acceptable media type for the voucher-response. The
media type "application/voucher-jws+json" is defined in
[I-D.ietf-anima-jws-voucher].
Once the MASA receives the registrar-voucher-request it SHALL perform
the verification of the contained components as described in section
5.5 in [RFC8995].
In addition, the following processing SHALL be performed for data
contained in the prior-signed-voucher-request:
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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 certificate used to sign the registrar-voucher-
request.
* 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
properties of the prior-signed-voucher and also in serial-number
properties of the registrar-voucher-request. The LDevID(RegAgt)
EE 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 registrar-voucher-
request MUST contain the corresponding LDevID(RegAgt) certificate
data in the agent-sign-cert. Either in the LDevID(RegAgt) EE
certificate of registrar-voucher-request or of the prior-signed-
voucher can be verified by the MASA as issued by the same domain
CA as the LDevID(Reg) EE certificate.
If the agent-sign-cert information is not provided, the MASA MAY
provide a lower level assertion, e.g.: "logged" or "verified"
Note, in case the LDevID(RegAgt) EE certificate is issued by a
sub-CA and not the domain CA known to the MASA, sub-CA
certificate(s) MUST also be presented in the agent-sign-cert. As
this field is defined as array, 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 as defined in
section 5.6 of [RFC8995], and comprise the codes: 403, 404, 406, and
415.
The expected voucher response format is indicated by the Accept
request-header field or based on the MASA's prior understanding of
proper format for this pledge. Specifically 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": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
}
Figure 12: Representation of MASA issued voucher
The MASA responds the voucher 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 MAY provide an additional signature of the
voucher. 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 pledge-voucher-request 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": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
},
{
"protected": {
"alg": "ES256",
"x5c": [ "xURZmcWS...dA==" ]
},
"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 as explicit authorization of the registrar to
install the contained trust anchor.
The registrar forwards the voucher to the registrar-agent.
After receiving the voucher, the registrar-agent sends the pledge-
enrollment-request (PER) to the registrar. Deviating from BRSKI the
pledge-enrollment-request 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. The JWS object is signed with the pledge's IDevID
to ensure proof-of-identity as outlined in Figure 9.
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When using EST, the standard endpoint on the registrar cannot be
used. 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 the registrar is defined as "/.well-
known/brski/requestenroll"
The PER Content-Type header is: application/jose.
This results in a deviation from the content types used in [RFC7030]
and in additional processing at the domain registrar as EST server as
following. Note, the registrar is already aware that the
bootstrapping is performed in a pledge-responder-mode due to the use
of the LDevID(RegAgt) EE certificate in the TLS establishment and the
provided pledge-voucher-request as JWS object.
* If the registrar receives a pledge-enrollment-request with
Content-Type header field "application/jose", it MUST verify the
wrapping signature using the certificate indicated in the JOSE
header.
* The registrar verifies that the pledge's IDevID certificate of the
x5c header field, is accepted to join the domain, based on the
verification of the pledge-voucher-request.
* 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
domain CA. It will construct a registrar-enrollment-request (RER)
by utilizing the enrollment protocol expected by the domain CA.
The domain registrar may either enhance the PKCS#10 request or
generate a structure containing the attributes to be included by
the CA into the requested LDevID EE certificate and sends both
(the original PKCS#10 request and the enhancements) to the domain
CA. As enhancing the PKCS#10 request destroys the initial proof
of possession of the corresponding private key, the CA would need
to accept RA-verified requests. This handling is out of scope for
this document.
The registrar-agent sends the PER to the registrar by HTTP POST to
the endpoint: "/.well-known/brski/requestenroll"
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If validation of the wrapping signature fails, the registrar SHOULD
respond with HTTP 404 error code. HTTP 406 error code is more
appropriate, if the pledge-enrollment-request is in an unknown
format.
A situation that could be resolved with administrative action (such
as adding a vendor/manufacturer IDevID CA as trusted party) MAY be
responded with HTTP 403 error code.
A successful interaction with the domain CA will result in a pledge
LDevID EE certificate, which is then forwarded by the registrar to
the registrar-agent using the Content-Type header: "application/
pkcs7-mime".
The registrar-agent has now finished the exchanges with the domain
registrar and can supply the voucher-response (from MASA via
Registrar) and the enrollment-response (LDevID EE certificate) to the
pledge. It can close the TLS connection to the domain registrar and
provide the objects to the pledge(s). The content of the response
objects is defined through the voucher [RFC8366] and the certificate
[RFC5280].
5.1.4.3. 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 5.1.3.2 or use
stored information from the first contact with the pledge.
Preconditions in addition to Section 5.1.4.2:
* Registrar-agent: possesses voucher and LDevID certificate.
+--------+ +-----------+
| Pledge | | Registrar-|
| | | Agent |
| | | (RegAgt) |
+--------+ +-----------+
| |
|<------- supply voucher -----------|
| |
|--------- voucher-status --------->| - store
| | pledge voucher-status
|<--- supply enrollment response ---|
| |
|--------- enroll-status ---------->| - store
| | pledge enroll-status
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Figure 14: Response and status handling between pledge and
registrar-agent
The registrar-agent provides the information via two distinct
endpoints to the pledge as following.
The voucher response is provided with a HTTP POST using the operation
path value of "/.well-known/brski/pledge-voucher".
The registrar-agent voucher-response Content-Type header is
"application/voucher-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].
If multiple signatures are contained in the voucher, the pledge SHALL
perform the signature verification in the following order:
1. Verify 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. Verify the registrar certificate received in the agent-provided-
proximity-registrar-cert in the voucher request successfully.
When 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). When multiple
signatures are contained in the voucher-response, the pledge MUST
verify all successfully.
When an error occurs during the verification it SHALL be signaled in
the reason field of the pledge voucher-status object.
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.
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The response has the Content-Type "application/jose" and is signed
using the IDevID of the pledge as shown in Figure 15. As the reason
field is optional (see [RFC8995]), it MAY be omitted in case of
success.
{
"payload": {
"version": 1,
"status": true,
"reason": "Informative human readable message",
"reason-context": {
"additional": "JSON"
}
},
"signatures": [
{
"protected": {
"alg": "ES256",
"x5c": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
Figure 15: Representation of pledge voucher-status telemetry
The enrollment response is provided with a HTTP POST using the
operation path value of "/.well-known/brski/pledge-enrollment".
The registrar-agent enroll-response Content-Type header, when using
EST [RFC7030] as enrollment protocol 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 verifies the LDevID certificate. When an
error occurs during the verification it SHALL be signaled in the
reason field of the pledge enroll-status object.
The pledge MUST reply with a status telemetry message as defined in
section 5.9.4 of [RFC8995]. As for the other objects, the defined
object is provided with an additional signature using JOSE. The
pledge generates the enrollment status and provides it in the
response message to the registrar-agent.
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The response has the Content-Type "application/jose", signed using
the freshly provided LDevID of the pledge as shown in Figure 16. As
the reason field is optional, 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": [ "MIIB2jCC...dA==" ]
},
"signature": "base64encodedvalue=="
}
]
}
Figure 16: Representation of pledge enroll-status telemetry
Once the registrar-agent has collected the information, it can
connect to the registrar agent to provide the status responses to the
registrar.
5.1.4.4. Telemetry status handling (registrar-agent - domain registrar)
The following description assumes that the registrar-agent has
collected the status objects from the pledge. It will provide the
status objects to the registrar for further processing and audit log
information of voucher-status for MASA.
Preconditions in addition to Section 5.1.4.2:
* 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 |
| | | |
|<------ TLS ----->| | |
| | | |
|--Voucher-Status->| | |
| |<---- device audit log ----|
| [verify audit log ]
| | | |
|--Enroll-Status-->| | |
| | | |
| | | |
Figure 17: Bootstrapping status handling
The registrar-agent MUST provide the collected pledge voucher-status
to the registrar. This status indicates if the pledge could process
the voucher successfully or not.
If the TLS connection to the registrar was closed, the registrar-
agent establishes a TLS connection with the registrar as stated in
Section 5.1.4.2.
The registrar-agent sends the pledge voucher-status object without
modification to the registrar with an HTTP-over-TLS POST using the
operation path value of "/.well-known/brski/voucher_status". The
Content-Type header is kept as "application/jose" as described in
Figure 14 and depicted in the example in Figure 15.
The registrar SHALL verify the signature of the pledge voucher-status
and validate that it belongs to an accepted device in his domain
based on the contained "serial-number" in the IDevID certificate
referenced in the header of the voucher-status object.
According to [RFC8995] section 5.7, the registrar SHOULD respond with
an HTTP 200 but MAY simply fail with an HTTP 404 error. The
registrar-agent may use the response to signal success / failure to
the service technician operating the registrar agent. Within the
server logs the server SHOULD capture this telemetry information.
The registrar SHOULD proceed with collecting and logging status
information by requesting the MASA audit-log from the MASA service as
described in section 5.8 of [RFC8995].
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The registrar-agent MUST provide the 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
operation path value of "/.well-known/brski/enrollstatus". The
Content-Type header is kept as "application/jose" as described in
Figure 14 and depicted in the example in Figure 16.
The registrar SHALL verify the signature of the pledge enroll-status
object and validate that it belongs to an accepted device in his
domain based on the contained product-serial-number in the LDevID EE
certificate referenced in the header of the enroll-status object.
Note that the verification of a signature of the object is a
deviation form the described handling in section 5.9.4 of [RFC8995].
According to [RFC8995] section 5.9.4, the registrar SHOULD respond
with an HTTP 200 but MAY simply fail with an HTTP 404 error. The
registrar-agent may use the response to signal success / failure to
the service technician operating the registrar agent. Within the
server log the registrar SHOULD capture this telemetry information.
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.
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.
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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@2021-12-16.yang"
module ietf-voucher-request-prm {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-voucher-request-prm";
prefix vrprm;
import ietf-restconf {
prefix rc;
description
"This import statement is only present to access
the yang-data extension defined in RFC 8040.";
reference "RFC 8040: RESTCONF Protocol";
}
import ietf-voucher-request {
prefix vcr;
description
"This module defines the format for a voucher request,
which is produced by a pledge as part of the RFC8995
onboarding process.";
reference
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"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.
It is a superset of the voucher itself.
It provides content to the MASA for consideration
during a voucher-request.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
'MAY', and 'OPTIONAL' in this document are to be interpreted as
described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
Copyright (c) 2022 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8995; see the
RFC itself for full legal notices.";
revision 2021-12-16 {
description
"Initial version";
reference
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"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 {
refine "voucher/expires-on" {
mandatory false;
description
"An expires-on field is not valid in a
voucher-request, and any occurrence MUST be ignored.";
}
refine "voucher/pinned-domain-cert" {
mandatory false;
description
"A pinned-domain-cert field is not valid in a
voucher-request, and any occurrence MUST be ignored.";
}
refine "voucher/last-renewal-date" {
description
"A last-renewal-date field is not valid in a
voucher-request, and any occurrence MUST be ignored.";
}
refine "voucher/domain-cert-revocation-checks" {
description
"The domain-cert-revocation-checks field is not valid in a
voucher-request, and any occurrence MUST be ignored.";
}
refine "voucher/assertion" {
mandatory false;
description
"Any assertion included in registrar voucher-requests
SHOULD be ignored by the MASA.";
}
augment voucher {
description "Base the voucher-request-prm upon the
regular one";
leaf agent-signed-data {
type binary;
description
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"The agent-signed-data field contains a JOSE [RFC7515]
object provided by the Registrar-Agent to the Pledge.
This artifact is signed by the Registrar-Agent
and contains a copy of the pledge's serial-number.";
}
leaf agent-provided-proximity-registrar-cert {
type binary;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
The first certificate in the registrar TLS server
certificate_list sequence (the end-entity TLS
certificate; see RFC 8446) presented by the
registrar to the registrar-agent and provided to
the pledge.
This MUST be populated in a pledge's voucher-request
when an agent-proximity assertion is requested.";
reference
"ITU X.690: Information Technology - ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)
RFC 5280: Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile
RFC 8446: The Transport Layer Security (TLS)
Protocol Version 1.3";
}
leaf-list agent-sign-cert {
type binary;
min-elements 1;
description
"An X.509 v3 certificate structure, as specified by
RFC 5280, Section 4, encoded using the ASN.1
distinguished encoding rules (DER), as specified
in ITU X.690.
This certificate can be used by the pledge,
the registrar, and the MASA to verify the signature
of agent-signed-data. It is an optional component
for the pledge-voucher request.
This MUST be populated in a registrar's
voucher-request when an agent-proximity assertion
is requested.
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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 pledge-voucher-request are provided in
Section 5.1.4.2.
7. IANA Considerations
This document requires the following IANA actions:
IANA is requested to enhance the Registry entitled: "BRSKI well-known
URIs" with the following:
URI document description
pledge-voucher-request [THISRFC] create pledge-voucher-request
pledge-enrollment-request [THISRFC] create pledge-enrollment-request
pledge-voucher [THISRFC] supply voucher response
pledge-enrollment [THISRFC] supply enrollment response
pledge-CACerts [THISRFC] supply CA certs to pledge
requestenroll [THISRFC] supply PER to registrar
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
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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 responses by Registrar-
Agent
A Registrar-agent that uses acquired voucher and enrollment response
for domain 1 in domain 2 can be detected by the pledge-voucher-
request processing on the domain registrar side. This requires the
domain registrar to verify the proximity-registrar-cert leaf in the
pledge-voucher-request 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 pledge-
voucher-request and in the IDevID certificate of the pledge.
Moreover, the registrar verifies the authorization of the registrar
agent to deliver pledge-voucher-requests, based on the LDevID(RegAgt)
EE certificate information contained in this request.
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 have been raised, that there may be opportunities to misuse
the registrar-agent with a valid LDevID. This 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 certificate for the registrar-agent may be provided by a prior
BRSKI execution based on an existing IDevID. Alternatively, the
LDevID may be acquired by a service technician after authentication
against the issuing CA.
9.4. YANG Module Security Considerations
The enhanced voucher-request described in section Section 6.1 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 [I-D.ietf-anima-jws-voucher]. As such,
all of the YANG-modeled data is protected from 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
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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 and Oskar Camenzind, for their input and discussion on use
cases and call flows.
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-02, 4 March
2022, <https://www.ietf.org/archive/id/draft-ietf-anima-
jws-voucher-02.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>.
[I-D.richardson-anima-rfc8366bis]
Watsen, K., Richardson, M. C., Pritikin, M., and T.
Eckert, "A Voucher Artifact for Bootstrapping Protocols",
Work in Progress, Internet-Draft, draft-richardson-anima-
rfc8366bis-04, 1 December 2021,
<https://www.ietf.org/archive/id/draft-richardson-anima-
rfc8366bis-04.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>.
[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>.
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[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[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>.
[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>.
[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
[IEEE-802.1AR]
Institute of Electrical and Electronics Engineers, "IEEE
802.1AR Secure Device Identifier", IEEE 802.1AR, June
2018.
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[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>.
[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>.
Appendix A. History of Changes [RFC Editor: please delete]
From IETF draft 01 -> IETF draft 02:
* Issue #15 included additional signature on voucher from registrar
in section Section 5.1.4.2 and section Section 5.1.1 The
verification of multiple signatures is described in section
Section 5.1.4.3
* Included representation for General JWS JSON Serialization for
examples
* Included error responses from pledge if it is not able to create a
pledge-voucher request or an enrollment request in section
Section 5.1.4.1
* 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 5.1.4.2
and Section 5.1.4.3.
* 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).
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* 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 EE 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 EE 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 5.1.4.2.
* Note added in Section 5.1.4.2 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 5.1.2 for better
readability.
* Included registrar authorization check for registrar-agent during
TLS handshake in section Section 5.1.4.2. 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 5.1.4.2. Also enhanced figure Figure 10 with the
authorization step on pledge-voucher-request level.
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* Changed agent-signed-cert to an array to allow for providing
further certificate information like the issuing CA cert for the
LDevID(RegAgt) EE 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).
* 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 5.1.4.1 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:
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* 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 5.1.4
.
* Terminology change: issue #2 pledge-agent -> registrar-agent to
better underline agent relation.
* Terminology change: issue #3 PULL/PUSH -> pledge-initiator-mode
and pledge-responder-mode to better address the pledge operation.
* Communication approach between pledge and registrar-agent changed
by removing TLS-PSK (former section TLS establishment) and
associated references to other drafts in favor of relying on
higher layer exchange of signed data objects. These data objects
are included also in the pledge-voucher-request and lead to an
extension of the YANG module for the voucher-request (issue #12).
* Details on trust relationship between registrar-agent and
registrar (issue #4, #5, #9) included in Section 5.1.
* Recommendation regarding short-lived certificates for registrar-
agent authentication towards registrar (issue #7) in the security
considerations.
* Introduction of reference to agent signing certificate using SKID
in agent signed data (issue #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 5.1.4.
* 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 5.1.4.
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)
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* Clarification in discovery options for enrollment endpoints at the
domain registrar based on well-known endpoints do not result in
additional /.well-known URIs. Update of the illustrative example.
Note that the change to /brski for the voucher related endpoints
has been taken over in the BRSKI main document.
* Updated references.
* Included Thomas Werner as additional author for the document.
From individual version 03 -> IETF draft 00:
* Inclusion of discovery options of enrollment endpoints at the
domain registrar based on well-known endpoints in new section as
replacement of section 5.1.3 in the individual draft. This is
intended to support both use cases in the document. An
illustrative example is provided.
* Missing details provided for the description and call flow in
pledge-agent use case Section 5.1, e.g. to accommodate
distribution of CA certificates.
* Updated CMP example in to use lightweight CMP instead of CMP, as
the draft already provides the necessary /.well-known endpoints.
* Requirements discussion moved to separate section in Section 4.
Shortened description of proof of identity binding and mapping to
existing protocols.
* Removal of copied call flows for voucher exchange and registrar
discovery flow from [RFC8995] in UC1 to avoid doubling or text or
inconsistencies.
* Reworked abstract and introduction to be more crisp regarding the
targeted solution. Several structural changes in the document to
have a better distinction between requirements, use case
description, and solution description as separate sections.
History moved to appendix.
From individual version 02 -> 03:
* Update of terminology from self-contained to authenticated self-
contained object to be consistent in the wording and to underline
the protection of the object with an existing credential. Note
that the naming of this object may be discussed. An alternative
name may be attestation object.
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* 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 3.2.
* 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
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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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