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dtbootstrap-anima-keyinfra-ALL.xml
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<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent" [
<!ENTITY RFC2119 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml">
<!ENTITY RFC7030 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7030.xml">
<!ENTITY RFC5280 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml">
<!ENTITY RFC5652 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5652.xml">
<!ENTITY RFC7575 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7575.xml">
<!ENTITY RFC7950 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7950.xml">
<!ENTITY RFC7951 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7951.xml">
<!ENTITY RFC3748 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3748.xml">
]>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-anima-bootstrapping-keyinfra-42" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" symRefs="true" sortRefs="true" version="3">
<!-- xml2rfc v2v3 conversion 2.23.1 -->
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<front>
<title abbrev="BRSKI">Bootstrapping Remote Secure Key Infrastructures
(BRSKI)</title>
<seriesInfo name="Internet-Draft" value="draft-ietf-anima-bootstrapping-keyinfra-42"/>
<author fullname="Max Pritikin" initials="M." surname="Pritikin">
<organization>Cisco</organization>
<address>
<email>[email protected]</email>
</address>
</author>
<author fullname="Michael C. Richardson" initials="M." surname="Richardson">
<organization abbrev="Sandelman">Sandelman Software Works</organization>
<address>
<email>[email protected]</email>
<uri>http://www.sandelman.ca/</uri>
</address>
</author>
<author fullname="Toerless Eckert" initials="T.T.E." surname="Eckert">
<organization abbrev="Futurewei USA">
Futurewei Technologies Inc. USA</organization>
<address>
<postal>
<street>2330 Central Expy</street>
<city>Santa Clara</city>
<region>CA</region>
<code>95050</code>
<country>USA</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Michael H. Behringer" initials="M.H." surname="Behringer">
<address>
<email>[email protected]</email>
</address>
</author>
<author fullname="Kent Watsen" initials="K.W." surname="Watsen">
<organization>Watsen Networks</organization>
<address>
<email>[email protected]</email>
</address>
</author>
<date year="2020"/>
<area>Operations and Management</area>
<workgroup>ANIMA WG</workgroup>
<abstract>
<t>
This document specifies automated bootstrapping of an Autonomic
Control Plane. To do this a Secure Key Infrastructure is
bootstrapped. This is done using manufacturer-installed
X.509 certificates, in combination with a manufacturer's authorizing
service, both online and offline. We call this process the
Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol.
Bootstrapping a new device can occur using a routable address and a
cloud service, or using only link-local connectivity, or on
limited/disconnected networks. Support for deployment models
with less stringent security requirements is included.
Bootstrapping is complete when the cryptographic identity of the new
key infrastructure is successfully deployed to the device. The
established secure connection can be used to deploy a locally issued
certificate to the device as well.
</t>
</abstract>
</front>
<middle>
<section numbered="true" toc="default">
<name>Introduction</name>
<t>
The Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol
provides a solution for secure zero-touch (automated) bootstrap of
new (unconfigured) devices that are called pledges in this
document. Pledges have an IDevID installed in them at the factory.
</t>
<t>
"BRSKI" is pronounced like "brewski", a colloquial term for beer in
Canada and parts of the US-midwest. <xref target="brewski" format="default"/>
</t>
<t>
This document primarily provides for the needs of
the ISP and Enterprise focused ANIMA
<xref target="I-D.ietf-anima-autonomic-control-plane" format="default">Autonomic
Control Plane (ACP)</xref>. This bootstrap process satisfies
the <xref target="RFC7575" format="default"/> requirements of section 3.3 of making all operations
secure by default. Other users of the BRSKI protocol
will need to provide separate applicability statements that
include privacy and security considerations appropriate to that
deployment. <xref target="acpapplicability" format="default"/> explains the detailed
applicability for this the ACP usage.
</t>
<t>
The BRSKI protocol requires a significant amount of communication
between manufacturer and owner: in its default modes it provides a
cryptographic transfer of control to the initial owner. In its
strongest modes, it leverages sales channel information to identify
the owner in advance. Resale of devices is possible, provided that
the manufacturer is willing to authorize the transfer. Mechanisms
to enable transfers of ownership without manufacturer authorization
are not included in this version of the protocol, but could be
designed into future versions.
</t>
<t>
This document describes how pledges discover (or are discovered by) an
element of the network domain to which the pledge belongs that will perform
the bootstrap. This element (device) is called the
registrar. Before any other operation, pledge and registrar need to
establish mutual trust:
</t>
<ol spacing="normal" type="1">
<li>Registrar authenticating the pledge: "Who is this device? What is
its identity?"</li>
<li>Registrar authorizing the pledge: "Is it mine? Do I want it?
What are the chances it has been compromised?"</li>
<li>Pledge authenticating the registrar: "What is this
registrar's identity?"</li>
<li>Pledge authorizing the registrar: "Should I join this network?"</li>
</ol>
<t>
This document details protocols and messages to answer the above questions.
It uses a TLS connection and an PKIX-shaped (X.509v3) certificate (an IEEE
802.1AR <xref target="IDevID" format="default"/> IDevID) of the pledge to answer
points 1 and 2.
It uses a new artifact called a "voucher" that the registrar
receives from a "Manufacturer Authorized Signing Authority" (MASA) and
passes to the pledge to answer points 3 and 4.
</t>
<t>
A proxy provides very limited connectivity between the pledge and
the registrar.
</t>
<t>The syntactic details of vouchers are described in detail in <xref target="RFC8366" format="default"/>. This document details automated
protocol mechanisms to obtain vouchers, including the definition
of a 'voucher-request' message that is a minor extension
to the voucher format (see <xref target="voucher-request" format="default"/>) defined
by <xref target="RFC8366" format="default"/>.</t>
<t>BRSKI results in the pledge storing an X.509 root
certificate sufficient for verifying the registrar identity. In the
process a TLS connection is established that can be directly used for
Enrollment over Secure Transport (EST). In effect BRSKI provides
an automated mechanism for the "Bootstrap Distribution of CA Certificates"
described in <xref target="RFC7030" format="default"/> Section 4.1.1 wherein
the pledge "MUST [...] engage a human user to authorize the CA certificate using
out-of-band" information. With BRSKI the pledge now can automate
this process using the voucher. Integration with a complete EST
enrollment is optional but trivial.</t>
<t>BRSKI is agile enough to support
bootstrapping alternative key infrastructures, such as a symmetric key
solutions, but no such system is described in this document.</t>
<section numbered="true" toc="default">
<name>Prior Bootstrapping Approaches</name>
<t>To literally "pull yourself up by the bootstraps" is an impossible
action. Similarly the secure establishment of a key infrastructure
without external help is also an impossibility. Today it is commonly
accepted that the initial connections between nodes are insecure, until
key distribution is complete, or that domain-specific keying material
(often pre-shared keys, including mechanisms like SIM cards)
is pre-provisioned on each new device in a costly and non-scalable
manner. Existing automated mechanisms are known as non-secured 'Trust on
First Use' (TOFU) <xref target="RFC7435" format="default"/>, 'resurrecting duckling'
<xref target="Stajano99theresurrecting" format="default"/> or 'pre-staging'.</t>
<t>Another prior approach has been to try and
minimize user actions during bootstrapping, but not eliminate all
user-actions.
The original EST protocol <xref target="RFC7030" format="default"/> does reduce user actions during bootstrap
but does not provide solutions for how the following protocol steps
can be made autonomic (not involving user actions):
</t>
<ul spacing="normal">
<li>using the Implicit Trust Anchor <xref target="RFC7030" format="default"/> database to authenticate
an owner specific service (not an autonomic solution because
the URL must be securely distributed),</li>
<li>engaging a human user to authorize the CA certificate using
out-of-band data (not an autonomic solution because the human user
is involved),</li>
<li>using a configured Explicit TA database (not an autonomic
solution because the distribution of an explicit TA database is
not autonomic),</li>
<li>and using a Certificate-Less TLS mutual authentication method
(not an autonomic solution because the distribution of symmetric
key material is not autonomic).
</li>
</ul>
<t>
These "touch" methods do not meet the requirements for
zero-touch.
</t>
<t>There are "call home" technologies where the pledge first
establishes a connection to a well known manufacturer service using a common
client-server authentication model. After mutual authentication,
appropriate credentials to authenticate the target domain are
transferred to the pledge. This creates several problems and
limitations:</t>
<ul spacing="normal">
<li>the pledge requires realtime connectivity to the manufacturer
service,</li>
<li>the domain identity is exposed to the manufacturer service (this is a
privacy concern),</li>
<li>the manufacturer is responsible for making the authorization
decisions (this is a liability concern),</li>
</ul>
<t>BRSKI addresses these issues by defining extensions to the EST protocol
for the automated distribution of vouchers.
</t>
</section>
<section numbered="true" toc="default">
<name>Terminology</name>
<t>
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 <xref target="RFC2119" format="default"/>
<xref target="RFC8174" format="default"/> when, and only when, they
appear in all capitals, as shown here.
</t>
<t>The following terms are defined for clarity:</t>
<dl newline="false" spacing="normal">
<dt>ANI:</dt>
<dd>The Autonomic Network Infrastructure as
defined by <xref target="I-D.ietf-anima-reference-model" format="default"/>.
<xref target="acpapplicability" format="default"/> details specific requirements for pledges,
proxies and registrars when they are part of an ANI.</dd>
<dt>Circuit Proxy:</dt>
<dd>A stateful implementation
of the join proxy. This is the assumed type of proxy.</dd>
<dt>drop-ship:</dt>
<dd>The physical distribution of equipment
containing the "factory default" configuration to a final
destination. In zero-touch scenarios there is no staging or
pre-configuration during drop-ship.</dd>
<dt>Domain:</dt>
<dd>The set of entities that share a common local
trust anchor. This includes the proxy, registrar,
Domain Certificate Authority, Management components and any
existing entity that is already a member of the domain.</dd>
<dt>domainID:</dt>
<dd>The domain IDentity is a unique value
based upon the Registrar CA's certificate.
<xref target="domainID" format="default"/> specifies how it is calculated.
</dd>
<dt>Domain CA:</dt>
<dd>The domain Certification Authority (CA)
provides certification functionalities to the domain. At a minimum
it provides certification functionalities to a registrar and
manages the private key that defines the domain. Optionally, it
certifies all elements.</dd>
<dt>enrollment:</dt>
<dd>The process where a device presents key
material to a network and acquires a network-specific identity.
For example when a certificate signing request is presented to a
certification authority and a certificate is obtained in
response.</dd>
<dt>imprint:</dt>
<dd>The process where a device obtains the
cryptographic key material to identify and trust future
interactions with a network. This term is taken from Konrad
Lorenz's work in biology with new ducklings: during a critical
period, the duckling would assume that anything that looks like a
mother duck is in fact their mother. An equivalent for a device is
to obtain the fingerprint of the network's root certification
authority certificate. A device that imprints on an attacker
suffers a similar fate to a duckling that imprints on a hungry
wolf. Securely imprinting is a primary focus of this
document <xref target="imprinting" format="default"/>. The analogy to
Lorenz's work was first noted in <xref target="Stajano99theresurrecting" format="default"/>.</dd>
<dt>IDevID:</dt>
<dd>An Initial Device Identity X.509 certificate
installed by the vendor on new equipment. This is a term from
802.1AR <xref target="IDevID" format="default"/></dd>
<dt>IPIP Proxy:</dt>
<dd>A stateless proxy alternative.</dd>
<dt>Join Proxy:</dt>
<dd>A domain entity that helps the pledge join
the domain. A join proxy facilitates communication for devices that
find themselves in an environment where they are not provided
connectivity until after they are validated as members of the
domain. For simplicity this document sometimes uses the
term of 'proxy' to indicate the join proxy. The pledge
is unaware that they are communicating with a
proxy rather than directly with a registrar.</dd>
<dt>Join Registrar (and Coordinator):</dt>
<dd>A representative of the domain that is
configured, perhaps autonomically, to decide whether a new device
is allowed to join the domain. The administrator of the domain
interfaces with a "join registrar (and coordinator)" to control this process. Typically a
join registrar is "inside" its domain. For simplicity this document
often refers to this as just "registrar". Within <xref target="I-D.ietf-anima-reference-model" format="default"/> this is
referred to as the "join registrar autonomic service agent".
Other communities use the abbreviation "JRC".
</dd>
<dt>LDevID:</dt>
<dd>A Local Device Identity X.509 certificate
installed by the owner of the equipment. This is a term from
802.1AR <xref target="IDevID" format="default"/></dd>
<dt>manufacturer:</dt>
<dd>the term manufacturer is used
throughout this document to be the entity that created the
device. This is typically the "original equipment manufacturer"
or OEM, but in more complex situations it could be a "value added
retailer" (VAR), or possibly even a systems integrator. In
general, it a goal of BRSKI to eliminate small distinctions
between different sales channels. The reason for this is
that it permits a single device, with a uniform firmware load, to
be shipped directly to all customers. This eliminates costs
for the manufacturer. This also reduces the number of products
supported in the field increasing the chance that firmware will
be more up to date.
</dd>
<dt>MASA Audit-Log:</dt>
<dd>An anonymized list of previous owners
maintained by the MASA on a per device (per pledge)
basis. Described in <xref target="MASAauditlog" format="default"/>.
</dd>
<dt>MASA Service:</dt>
<dd>A third-party Manufacturer Authorized
Signing Authority (MASA) service on the global Internet. The MASA
signs vouchers. It also provides a repository for audit-log
information of privacy protected bootstrapping events. It does
not track ownership. </dd>
<dt>nonced:</dt>
<dd>a voucher (or request) that contains a nonce (the normal
case).</dd>
<dt>nonceless:</dt>
<dd>a voucher (or request) that does not
contain a nonce, relying upon accurate clocks for expiration, or
which does not expire.</dd>
<dt>offline:</dt>
<dd>When an architectural component cannot
perform realtime communications with a peer, either due to
network connectivity or because the peer is turned off, the
operation is said to be occurring offline.</dd>
<dt>Ownership Tracker:</dt>
<dd>An Ownership Tracker service on
the global Internet. The Ownership Tracker uses business processes
to accurately track ownership of all devices shipped against
domains that have purchased them. Although optional, this component
allows vendors to provide additional value in cases where their
sales and distribution channels allow for accurate tracking of
such ownership. Ownership tracking information is indicated in
vouchers as described in <xref target="RFC8366" format="default"/></dd>
<dt>Pledge:</dt>
<dd>The prospective (unconfigured) device, which has an
identity installed at the factory.</dd>
<dt>(Public) Key Infrastructure:</dt>
<dd> The collection of systems and
processes that sustain the activities of a public key system.
The registrar acts as an
<xref target="RFC5280" format="default"/> and <xref target="RFC5272" format="default"/> (see
section 7) "Registration Authority".</dd>
<dt>TOFU:</dt>
<dd>Trust on First Use. Used similarly to <xref target="RFC7435" format="default"/>. This is where a pledge
device makes no security decisions but rather simply trusts the
first registrar it is contacted by. This is also known as the
"resurrecting duckling" model.</dd>
<dt>Voucher:</dt>
<dd>A signed artifact from the MASA
that indicates to a pledge the cryptographic identity of the
registrar it should trust. There are different types of vouchers
depending on how that trust is asserted. Multiple voucher types are
defined in <xref target="RFC8366" format="default"/></dd>
</dl>
</section>
<section numbered="true" toc="default">
<name>Scope of solution</name>
<section numbered="true" toc="default">
<name>Support environment</name>
<t>
This solution (BRSKI) can support large router
platforms with multi-gigabit inter-connections, mounted in controlled
access data centers. But this solution is not exclusive to large equipment:
it is intended to scale to thousands of devices located in hostile
environments, such as ISP provided CPE devices which are drop-shipped
to the end user. The situation where an order is fulfilled from
distributed warehouse from a common stock and shipped directly to the
target location at the request of a domain owner is explicitly
supported. That stock ("SKU") could be provided to a number of
potential domain owners, and the eventual domain owner will not know
a-priori which device will go to which location.
</t>
<t>
The bootstrapping process can take minutes to complete depending on
the network infrastructure and device processing speed. The network
communication itself is not optimized for speed; for privacy reasons,
the discovery process allows for the pledge to avoid announcing its
presence through broadcasting.
</t>
<t>
Nomadic or mobile devices often need to acquire credentials to
access the network at the new location. An example of this is
mobile phone roaming among network operators, or even between
cell towers. This is usually called handoff.
BRSKI does not provide a low-latency handoff which is usually a
requirement in such situations.
For these solutions BRSKI can be used to create a relationship
(an LDevID) with the "home" domain owner. The resulting credentials
are then used to provide credentials more appropriate for a
low-latency handoff.
</t>
</section>
<section numbered="true" toc="default">
<name>Constrained environments</name>
<t>Questions have been posed as to whether this solution is suitable
in general for Internet of Things (IoT) networks. This depends on the
capabilities of the devices in question. The terminology of <xref target="RFC7228" format="default"/> is best used to describe the boundaries.</t>
<t>The solution described in this document is aimed in general at
non-constrained (i.e., class 2+ <xref target="RFC7228" format="default"/>) devices operating on a non-Challenged
network. The entire solution as described here is not intended to be
useable as-is by constrained devices operating on challenged networks
(such as 802.15.4 Low-power Lossy Networks (LLN)s).</t>
<t>Specifically, there are protocol aspects described here that might
result in congestion collapse or energy-exhaustion of intermediate
battery powered routers in an LLN. Those types of networks should not
use this solution. These limitations are predominately related to the
large credential and key sizes required for device authentication.
Defining symmetric key techniques that meet the operational
requirements is out-of-scope but the underlying protocol operations
(TLS handshake and signing structures) have sufficient algorithm
agility to support such techniques when defined.</t>
<t>The imprint protocol described here could, however, be used by
non-energy constrained devices joining a non-constrained network (for
instance, smart light bulbs are usually mains powered, and speak
802.11). It could also be used by non-constrained devices across a
non-energy constrained, but challenged network (such as 802.15.4). The
certificate contents, and the process by which the four
questions above are resolved do apply to constrained devices. It is
simply the actual on-the-wire imprint protocol that could be
inappropriate.</t>
</section>
<section numbered="true" toc="default">
<name>Network Access Controls</name>
<t>This document presumes that network access control has either
already occurred, is not required, or is integrated by the proxy
and registrar in such a way that the device itself does not need to
be aware of the details. Although the use of an X.509 Initial
Device Identity is consistent with IEEE 802.1AR <xref target="IDevID" format="default"/>, and allows for alignment with 802.1X
network access control methods, its use here is for pledge
authentication rather than network access control. Integrating
this protocol with network access control, perhaps as an
Extensible Authentication Protocol (EAP) method
(see <xref target="RFC3748" format="default"/>), is out-of-scope.</t>
</section>
<section numbered="true" toc="default">
<name>Bootstrapping is not Booting</name>
<t>This document describes "bootstrapping" as the protocol
used to obtain a local trust anchor. It is expected that this
trust anchor, along with any additional configuration
information subsequently installed, is persisted on the device
across system restarts ("booting"). Bootstrapping occurs only
infrequently such as when a device is transferred to a new
owner or has been reset to factory default settings.</t>
</section>
</section>
<section anchor="PostEnrollment" numbered="true" toc="default">
<name>Leveraging the new key infrastructure / next steps</name>
<t>
As a result of the protocol described herein, the bootstrapped devices
have the Domain CA trust anchor in common. An end entity certificate has
optionally been issued from the Domain CA. This makes it possible
to securely deploy functionalities across the domain, e.g:</t>
<ul spacing="normal">
<li>Device management.</li>
<li>Routing authentication.</li>
<li>Service discovery.</li>
</ul>
<t>
The major intended benefit is that it possible to use the credentials
deployed by this protocol to secure the Autonomic Control Plane
(ACP) (<xref target="I-D.ietf-anima-autonomic-control-plane" format="default"/>).
</t>
</section>
<section anchor="ANIrequirements" numbered="true" toc="default">
<name>Requirements for Autonomic Network Infrastructure (ANI) devices</name>
<t>
The BRSKI protocol can be used in a number of environments. Some of
the options in this document are the result of requirements that
are out of the ANI scope. This section defines the base
requirements for ANI devices.
</t>
<t>
For devices that intend to become part of an Autonomic Network
Infrastructure (ANI)
(<xref target="I-D.ietf-anima-reference-model" format="default"/>) that includes an
Autonomic Control Plane
(<xref target="I-D.ietf-anima-autonomic-control-plane" format="default"/>), the
BRSKI protocol MUST be implemented.
</t>
<t>
The pledge must perform discovery of the proxy as described in
<xref target="discovery" format="default"/> using Generic Autonomic Signaling
Protocol (GRASP)'s DULL <xref target="I-D.ietf-anima-grasp" format="default"/>
M_FLOOD announcements.
</t>
<t>
Upon successfully validating a voucher artifact, a status telemetry
MUST be returned. See <xref target="pledgestatus" format="default"/>.
</t>
<t>
An ANIMA ANI pledge MUST implement the EST automation
extensions described in <xref target="ESTintegration" format="default"/>.
They supplement the <xref target="RFC7030" format="default"/> EST to better
support automated devices that do not have an end user.
</t>
<t>
The ANI Join Registrar Autonomic Service Agent (ASA) MUST support all the BRSKI and above listed
EST operations.
</t>
<t>
All ANI devices SHOULD support the BRSKI proxy function, using
circuit proxies over the ACP. (See <xref target="JRCgrasp" format="default"/>)
</t>
</section>
</section>
<section numbered="true" toc="default">
<name>Architectural Overview</name>
<t>The logical elements of the bootstrapping framework are described in
this section. <xref target="architecturefigure" format="default"/> provides a simplified overview of the components.
</t>
<figure anchor="architecturefigure">
<name>Architecture Overview</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
+------------------------+
+--------------Drop Ship----------------| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| | BRSKI-
V | MASA
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
|Pledge | . | Join | | Domain <-------+ .
| | . | Proxy | | Registrar | .
| <-------->............<-------> (PKI RA) | .
| | | BRSKI-EST | | .
| | . | | +-----+-----+ .
|IDevID | . +------------+ | e.g. RFC7030 .
| | . +-----------------+----------+ .
| | . | Key Infrastructure | .
| | . | (e.g., PKI Certificate | .
+-------+ . | Authority) | .
. +----------------------------+ .
. .
................................................
"Domain" components
]]></artwork>
</figure>
<t>We assume a multi-vendor network. In such an environment there could
be a Manufacturer Service for each manufacturer that supports devices following this
document's specification, or an integrator could provide a generic
service authorized by multiple manufacturers. It is unlikely that an
integrator could provide Ownership Tracking services for multiple
manufacturers due to the required sales channel integrations necessary to
track ownership.</t>
<t>The domain is the managed network infrastructure with a Key Infrastructure the pledge is
joining. The domain provides initial device connectivity
sufficient for bootstrapping through a proxy. The domain
registrar authenticates the pledge, makes authorization decisions, and distributes
vouchers obtained from the Manufacturer Service. Optionally the registrar
also acts as a PKI Certification Authority.</t>
<section numbered="true" toc="default">
<name>Behavior of a Pledge</name>
<t>The pledge goes through a series of steps, which are outlined here
at a high level.</t>
<figure anchor="pledgestatusfigure">
<name>Pledge State Diagram</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
------------
/ Factory \
\ default /
-----+------
|
+------v-------+
| (1) Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | (2) Identify |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | (3) Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | (4) Imprint |
^------------+ |
| Bad MASA +------+-------+
| response | send Voucher Status Telemetry
| +------v-------+
| | (5) Enroll |<---+ (non-error HTTP codes )
^------------+ |\___/ (e.g. 202 'Retry-After')
| Enroll +------+-------+
| Failure |
| -----v------
| / Enrolled \
^------------+ |
Factory \------------/
reset
]]></artwork>
</figure>
<t>State descriptions for the pledge are as follows:</t>
<ol spacing="normal" type="1">
<li>Discover a communication channel to a registrar.</li>
<li>Identify itself. This is done by presenting an X.509 IDevID
credential to the discovered registrar (via the proxy) in a TLS
handshake. (The registrar credentials are only provisionally
accepted at this time).</li>
<li>Request to join the discovered registrar. A unique nonce is
included ensuring that any responses can be associated with this
particular bootstrapping attempt.</li>
<li>Imprint on the registrar. This requires verification of the
manufacturer-service-provided voucher. A voucher contains sufficient
information for the pledge to complete authentication of a
registrar. This document details this step in depth.
</li>
<li>Enroll. After imprint an authenticated TLS (HTTPS) connection exists
between pledge and registrar.
Enrollment over Secure Transport (EST) <xref target="RFC7030" format="default"/> can then be used to obtain a domain
certificate from a registrar.</li>
</ol>
<t>
The pledge is now a member of, and can be managed by, the
domain and will only repeat the discovery aspects of bootstrapping
if it is returned to factory default settings.
</t>
<t>
This specification details integration with EST enrollment so that pledges can
optionally obtain a locally issued certificate, although any
Representational State Transfer (REST) (see <xref target="REST" format="default"/>)
interface could be integrated in future work.
</t>
</section>
<section numbered="true" toc="default">
<name>Secure Imprinting using Vouchers</name>
<t>A voucher is a cryptographically protected artifact (using a digital signature) to the pledge
device authorizing a zero-touch imprint on the registrar
domain. </t>
<t>The format and cryptographic mechanism of vouchers is described in
detail in <xref target="RFC8366" format="default"/>.</t>
<t>Vouchers provide a flexible mechanism to secure imprinting: the
pledge device only imprints when a voucher can be validated.
At the lowest security levels the MASA can indiscriminately issue
vouchers and log claims of ownership by domains. At the highest security
levels issuance of vouchers can be integrated with complex sales channel
integrations that are beyond the scope of this document. The sales
channel integration would verify actual (legal) ownership of the
pledge by the domain.
This
provides the flexibility for a number of use cases via a single
common protocol mechanism on the pledge and registrar devices that
are to be widely deployed in the field. The MASA services have
the flexibility to leverage either the currently defined claim
mechanisms or to experiment with higher or lower security levels.
</t>
<t>
Vouchers provide a signed but non-encrypted communication channel among
the pledge, the MASA, and the registrar. The registrar maintains
control over the transport and policy decisions, allowing the
local security policy of the domain network to be enforced.
</t>
</section>
<section anchor="IDevIDextension" numbered="true" toc="default">
<name>Initial Device Identifier</name>
<t>
Pledge authentication and pledge voucher-request signing is via
a PKIX-shaped certificate installed
during the manufacturing process. This is the 802.1AR Initial
Device Identifier (IDevID), and it
provides a basis for authenticating the pledge during
the protocol exchanges described here.
There is no requirement for a common root PKI hierarchy.
Each device manufacturer can generate its own root certificate.
Specifically, the IDevID enables:
</t>
<ol spacing="normal" type="1">
<li>
Uniquely identifying the pledge by the Distinguished Name (DN)
and subjectAltName (SAN) parameters in the IDevID. The
unique identification of a pledge in the voucher objects are derived
from those parameters as described below. <xref target="idevidprivacy" format="default"/> discusses privacy implications of the identifier.
</li>
<li>
Provides a cryptographic authentication of the pledge to the
Registrar (see <xref target="pledgeauthorization" format="default"/>).
</li>
<li>
Secure auto-discovery of the pledge's MASA by the registrar
(see <xref target="obtainmasaurl" format="default"/>).
</li>
<li>
Signing of voucher-request by the pledge's IDevID
(see <xref target="voucher-request" format="default"/>).
</li>
<li>
Provides a cryptographic authentication of the pledge to the
MASA (see <xref target="MASAassertion" format="default"/>).
</li>
</ol>
<t>
Section 7.2.13 (2009 edition) and section 8.10.3 (2018 edition) of
<xref target="IDevID" format="default"/> discusses keyUsage and
extendedKeyUsage extensions in the IDevID certificate.
<xref target="IDevID" format="default"/> acknowledges that adding restrictions
in the certificate limits applicability of these long-lived
certificates. This specification emphasizes this point, and
therefore RECOMMENDS that no key usage restrictions be included.
This is consistent with <xref target="RFC5280" format="default"/> section 4.2.1.3,
which does not
require key usage restrictions for end entity certificates.
</t>
<section anchor="PledgeIdentification" numbered="true" toc="default">
<name>Identification of the Pledge</name>
<t>
In the context of BRSKI, pledges have a 1:1 relationship
with a "serial-number".
This serial-number is used both in the "serial-number"
field of voucher or voucher-requests (see <xref target="voucher-request" format="default"/>)
and in local policies on registrar or MASA
(see <xref target="ProtocolDetails" format="default"/>).
</t>
<t>
The serialNumber field is defined in <xref target="RFC5280" format="default"/>.
That specification allows for the field to be omitted if there is
a good technical reason. IDevID certificates for use
with this protocol are REQUIRED to include the "serialNumber" attribute with the device's
unique serial number
(from <xref target="IDevID" format="default"/> section 7.2.8, and
<xref target="RFC5280" format="default"/> section 4.1.2.2's list of standard
attributes).
</t>
<t>
The serialNumber field is used as follows by the pledge to build the
"serial-number" that is placed in the voucher-request.
In order to build it, the fields need to be converted into a
serial-number of "type string".
</t>
<t>
An example of a printable form of the "serialNumber" field
is provided in <xref target="RFC4519" format="default"/> section 2.31 ("WI-3005").
That section further provides equality and syntax attributes.
</t>
<t>
Due to the reality of existing device identity provisioning
processes, some
manufacturers have stored serial-numbers in other
fields. Registrar's SHOULD be configurable, on a per-manufacturer
basis, to look for serial-number equivalents in other fields.
</t>
<t>
As explained in <xref target="RequestVoucherFromMASA" format="default"/> the Registrar MUST extract the
serial-number again itself from the pledge's TLS certificate. It
can consult the serial-number in the pledge-request if there are
any possible confusion about the source of the serial-number.
</t>
</section>
<section anchor="MASAURL" numbered="true" toc="default">
<name>MASA URI extension</name>
<t>
This document defines a new PKIX non-critical certificate
extension to carry the MASA URI.
This extension is intended to be used in the IDevID certificate.
The URI is represented as described in Section 7.4 of <xref target="RFC5280" format="default"/>.
</t>
<t>
The URI provides the authority information.
The BRSKI "/.well-known" tree (<xref target="RFC5785" format="default"/>) is
described in <xref target="ProtocolDetails" format="default"/>.
</t>
<t>
A complete URI MAY be in this extension, including the 'scheme', 'authority', and 'path',
The complete URI will typically be used in diagnostic or
experimental situations.
Typically, (and in consideration to constrained systems), this
SHOULD be reduced to only the 'authority', in which
case a scheme of "https://"
(<xref target="RFC7230" format="default"/> section 2.7.3)
and 'path' of "/.well-known/est" is to be
assumed.
</t>
<t>
The registrar can assume that only the 'authority' is present in
the extension, if there are no slash ("/") characters in the
extension.
</t>
<t>
Section 7.4 of <xref target="RFC5280" format="default"/> calls out various
schemes that MUST be supported, including LDAP, HTTP and FTP.
However, the registrar MUST use HTTPS for the BRSKI-MASA connection.
</t>
<t>The new extension is identified as follows:</t>
<figure anchor="masaurlmodule">
<name>MASAURL ASN.1 Module</name>
<sourcecode name="" type="" markers="true"><![CDATA[
MASAURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-MASAURLExtn2016(TBD) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL --
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
id-pe FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
MASACertExtensions EXTENSION ::= { ext-MASAURL, ... }
ext-MASAURL EXTENSION ::= { SYNTAX MASAURLSyntax
IDENTIFIED BY id-pe-masa-url }
id-pe-masa-url OBJECT IDENTIFIER ::= { id-pe TBD }
MASAURLSyntax ::= IA5String
END
]]></sourcecode>
</figure>
<t>The choice of id-pe is based on guidance found in Section 4.2.2 of
[RFC5280], "These extensions may be used to direct applications to on-line
information about the issuer or the subject". The MASA URL is precisely
that: online information about the particular subject. </t>
</section>
</section>
<section anchor="flow" numbered="true" toc="default">
<name>Protocol Flow</name>
<t>A representative flow is shown in
<xref target="protocoltimesequencefigure" format="default"/></t>
<figure anchor="protocoltimesequencefigure">
<name>Protocol Time Sequence Diagram</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Join | | Registrar | | Service |
| | | Proxy | | (JRC) | | (MASA) |
+--------+ +---------+ +------------+ +------------+
| | | Internet |
[discover] | | |
|<-RFC4862 IPv6 addr | | |
|<-RFC3927 IPv4 addr | Appendix A | Legend |
|-++++++++++++++++++->| | C - circuit |
| optional: mDNS query| Appendix B | join proxy |
| RFC6763/RFC6762 (+) | | P - provisional |
|<-++++++++++++++++++-| | TLS connection |
| GRASP M_FLOOD | | |
| periodic broadcast| | |
[identity] | | |
|<------------------->C<----------------->| |
| TLS via the Join Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---X.509 client authentication---------->| |
[request join] | |
P---Voucher Request(w/nonce for voucher)->| |
P /------------------- | |
P | [accept device?] |
P | [contact Vendor] |
P | |--Pledge ID-------->|
P | |--Domain ID-------->|
P | |--optional:nonce--->|
P optional: | [extract DomainID]
P can occur in advance | [update audit log]
P if nonceleess | |
P | |<- voucher ---------|
P \------------------- | w/nonce if provided|
P<------voucher---------------------------| |
[imprint] | |
|-------voucher status telemetry--------->| |
| |<-device audit log--|
| [verify audit log and voucher] |
|<--------------------------------------->| |
[enroll] | |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | |
[enrolled] | |
]]></artwork>
</figure>
<t>
On initial bootstrap, a new device (the pledge) uses a local service
autodiscovery (GRASP or mDNS) to locate a join proxy. The
join proxy connects the pledge to a local registrar (the JRC).
</t>
<t>
Having found a candidate registrar, the fledgling pledge sends
some information about itself to the registrar, including its
serial number in the form of a voucher request and its device identity
certificate (IDevID) as part of the TLS session.
</t>
<t>
The registrar can determine whether it expected such a device to
appear, and locates a MASA. The location of the MASA is usually found in
an extension in the IDevID. Having determined that the MASA is
suitable, the entire information from the initial voucher request
(including device serial number) is transmitted over the internet in a
TLS protected channel to the manufacturer, along with information about
the registrar/owner.
</t>
<t>
The manufacturer can then apply policy based on the provided
information, as well as other sources of information (such as sales
records), to decide whether
to approve the claim by the registrar to own the device; if the claim
is accepted, a voucher is issued that directs the device to accept its
new owner.
</t>
<t>
The voucher is returned to the registrar, but not immediately to
the device -- the registrar has an opportunity to examine the
voucher, the MASA's audit-logs, and other sources of information to
determine whether the device has been tampered with, and whether
the bootstrap should be accepted.
</t>
<t>
No filtering of information is possible in the signed voucher, so
this is a binary yes-or-no decision. If the registrar accepts
the voucher as a proper one for its device, the voucher is returned
to the pledge for imprinting.
</t>
<t>
The voucher also includes a trust anchor that the pledge uses as
representing the owner. This is used to successfully bootstrap from an environment
where only the manufacturer has built-in trust by the
device into an environment where the owner now has a PKI footprint on the
device.
</t>
<t>
When BRSKI is followed with EST this single footprint is further
leveraged into the full owner's PKI and a LDevID for the
device. Subsequent reporting steps provide flows of information to
indicate success/failure of the process.
</t>
</section>
<section numbered="true" toc="default">
<name>Architectural Components</name>
<section anchor="pledge-overview" numbered="true" toc="default">
<name>Pledge</name>
<t>
The pledge is the device that is attempting to join.
The pledge is assumed to talk to the Join Proxy using link-local network
connectivity. In most cases, the pledge has no other
connectivity until the pledge completes the enrollment process
and receives some kind of network credential.
</t>
</section>
<section anchor="proxy-overview" numbered="true" toc="default">
<name>Join Proxy</name>
<t>
The join proxy provides HTTPS connectivity between the
pledge and the registrar. A circuit proxy mechanism is
described in <xref target="proxydetails" format="default"/>. Additional
mechanisms, including a CoAP mechanism and a stateless
IPIP mechanism are the subject of future work.
</t>
</section>
<section anchor="registrar-overview" numbered="true" toc="default">
<name>Domain Registrar</name>
<t>
The domain's registrar operates as the BRSKI-MASA client when
requesting vouchers from the MASA (see <xref target="brskimasatls" format="default"/>). The registrar
operates as the BRSKI-EST server when pledges request
vouchers (see <xref target="brskiesttls" format="default"/>). The registrar operates as the BRSKI-EST server
"Registration Authority" if the pledge requests an end entity certificate
over the BRSKI-EST connection (see <xref target="ESTintegration" format="default"/>).
</t>
<t>
The registrar uses an Implicit Trust Anchor database for
authenticating the BRSKI-MASA connection's MASA TLS Server Certificate.
Configuration or distribution of trust anchors is out-of-scope
for this specification.
</t>