One document matched: draft-ietf-anima-bootstrapping-keyinfra-03.xml
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<front>
<title abbrev="BRewSKI">
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
</title>
<author fullname="Max Pritikin" initials="M." surname="Pritikin">
<organization>Cisco</organization>
<address>
<email>pritikin@cisco.com</email>
</address>
</author>
<author fullname="Michael C. Richardson" initials="M."
surname="Richardson">
<organization abbrev="SSW">Sandelman Software Works</organization>
<address>
<postal>
<street>470 Dawson Avenue</street>
<city>Ottawa</city>
<region>ON</region>
<code>K1Z 5V7</code>
<country>CA</country>
</postal>
<email>mcr+ietf@sandelman.ca</email>
<uri>http://www.sandelman.ca/</uri>
</address>
</author>
<author fullname="Michael H. Behringer" initials="M.H."
surname="Behringer">
<organization>Cisco</organization>
<address>
<email>mbehring@cisco.com</email>
</address>
</author>
<author fullname="Steinthor Bjarnason" initials="S." surname="Bjarnason">
<organization>Cisco</organization>
<address>
<email>sbjarnas@cisco.com</email>
</address>
</author>
<date year="2016" />
<area>Operations and Management</area>
<workgroup>ANIMA WG</workgroup>
<abstract>
<t>This document specifies automated bootstrapping of a remote secure
key infrastructure (BRSKI) using vendor installed IEEE 802.1AR
manufacturing installed certificates, in combination with a vendor based
service on the Internet. Before being authenticated, a new device has
only link-local connectivity, and does not require a routable address.
When a vendor provides an Internet based service devices can be
redirected to a local service. In limited/disconnected networks or
legacy environments we describe a variety of options that allow
bootstrapping to proceed. Support for lower security models, including
devices with minimal identity, is described for legacy reasons but not
encouraged.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<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 accepted
that the initial connections between nodes are insecure, until key
distribution is complete, or that domain-specific keying material is
pre-provisioned on each new device in a costly and non-scalable manner.
This document describes a zero-touch approach to bootstrapping an entity
by securing the initial distribution of key material using third-party
generic keying material, such as a manufacturer installed IEEE 802.1AR
certificate <xref target="IDevID"></xref>, and a corresponding
third-party service on the Internet.</t>
<t>The two sides of an association being bootstrapped authenticate each
other and then determine appropriate authorization. This process is
described as four distinct steps between the existing domain and the new
entity being added:</t>
<t><list style="symbols">
<t>New entity authentication: "Who is this? What is its
identity?"</t>
<t>New entity authorization: "Is it mine? Do I want it? What are the
chances it has been compromised?"</t>
<t>Domain authentication: "What is this domain's claimed
identity?"</t>
<t>Domain authorization: "Should I join it?"</t>
</list></t>
<t>A precise answer to these questions can not be obtained without
leveraging some established key infrastructure(s). A complexity that
this protocol deals with are dealing with devices from a variety of
vendors, and a network infrastructure (the domain) that is operated by
parties that do not have any priviledged relationship with the device
vendors. The domain's decisions are based on the new entity's
authenticated identity, as established by verification of previously
installed credentials such as a manufacturer installed IEEE 802.1AR
certificate, and verified back-end information such as a configured list
of purchased devices or communication with a (unidirectionally) trusted
third-party. The new entity's decisions are made according to verified
communication with a trusted third-party or in a strictly auditable
fashion.</t>
<t>Optimal security is achieved with IEEE 802.1AR certificates on each
new entity, accompanied by a third-party Internet based service for
verification. Bootstrapping concepts run to completion with less
requirements, but are then less secure. A domain can choose to accept
lower levels of security when a trusted third-party is not available so
that bootstrapping proceeds even at the risk of reduced security. Only
the domain can make these decisions based on administrative input and
known behavior of the new entity.</t>
<t>The result of bootstrapping is that a domain specific key
infrastructure is deployed. Since IEEE 802.1AR PKI certificates are used
for identifying the new entity, and the public key of the domain
identity is leveraged during communications with an Internet based
service, which is itself authenticated using HTTPS, bootstrapping of a
domain specific Public Key Infrastructure (PKI) is described. Sufficient
agility to support bootstrapping alternative key infrastructures (such
as symmetric key solutions) is considered although no such alternate key
infrastructure is described.</t>
<section title="Terminology">
<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
<xref target="RFC2119"></xref>.</t>
<t>The following terms are defined for clarity:</t>
<t><list style="hanging">
<t hangText="DomainID:">The domain identity is the 160-bit SHA-1
hash of the BIT STRING of the subjectPublicKey of the domain trust
anchor that is stored by the Domain CA. This is consistent with
the RFC5280 Certification Authority subject key identifier of the
Domain CA's self signed root certificate. (A string value bound to
the Domain CA's self signed root certificate subject and issuer
fields is often colloquially used as a humanized identity value
but during protocol discussions the more exact term as defined
here is used).</t>
<t hangText="drop ship:">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.</t>
<t hangText="imprint:">the process where a device obtains the
cryptographic key material to identity 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"></xref>.</t>
<t hangText="enrollment:">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.</t>
<t hangText="pledge:">the prospective device, which has the
identity provided to at the factory. Neither the device nor the
network knows if the device yet knows if this device belongs with
this network. This is definition 6, according to <xref
target="pledge"></xref></t>
<t hangText="Audit Token:">A signed token from the manufacturer
authorized signing authority indicating that the bootstrapping
event has been successfully logged. This has been referred to as
an "authorization token" indicating that it authorizes
bootstrapping to proceed.</t>
<t hangText="Ownership Voucher:">A signed voucher from the vendor
vouching that a specific domain "owns" the new entity as defined
in <xref target="I-D.ietf-netconf-zerotouch"></xref>.</t>
</list></t>
</section>
<section title="Scope of solution">
<t>Questions have been posed as to whether this solution is suitable
in general for Internet of Things (IoT) networks. In general the
answer is no, but the terminology of <xref target="RFC7228"></xref> is
best used to describe the boundaries.</t>
<t>The entire solution described in this document is aimed in general
at non-constrained (i.e. class 2+) devices operating on a
non-Challenged network. The entire solution described here is not
intended to be useable as-is by constrained devices operating on
challenged networks (such as 802.15.4 LLNs).</t>
<t>In many target applications, the systems involved are large router
platforms with multi-gigabit inter-connections, mounted in controlled
access data centers. But this solution is not exclusive to the large,
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 the 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 bootstraping process can take minutes to complete depending on
the network infrastructure and device processing speed. The network
communication itself is not "chatty" but there can be delays for
privacy reasons. This protocol is not intended for low latency
handoffs. </t>
<t>Specifically, there are protocol aspects described here which 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).</t>
<t>Some aspects are in scope for constrained devices on challenged
networks: the certificate contents, and the process by which the four
questions above are resolved is in scope. It is simply the actual
on-the-wire imprint protocol which is likely inappropriate.</t>
</section>
<section title="Trust bootstrap">
<t>The imprint protocol results in a secure relationship between the
domain registrar and the new device. If the new device is sufficiently
constrained that the ACE protocol should be leveraged for operation,
(see <xref target="I-D.ietf-ace-actors"></xref>), and the domain
registrar is also the Client Authorization Server or the Authorization
Server, then it may be appropriate to use this secure channel to
exchange ACE tokens.</t>
</section>
</section>
<section title="Architectural Overview">
<t>The logical elements of the bootstrapping framework are described in
this section. Figure 1 provides a simplified overview of the components.
Each component is logical and may be combined with other components as
necessary.</t>
<t></t>
<figure>
<artwork><![CDATA[ .
.+------------------------+
+--------------Drop Ship-------------->.| Vendor Service |
| .+------------------------+
| .| M anufacturer| |
| .| A uthorized |Ownership|
| .| S igning |Tracker |
| .| A uthority | |
| .+--------------+---------+
| .............. ^
V |
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
| | . | | | <-------+ .
| | . | Proxy | | Registrar | .
| <--------> <-------> | .
| New | . | | | | .
| Entity| . +------------+ +-----+-----+ .
| | . | .
| | . +-----------------+----------+ .
| | . | Domain Certification | .
| | . | Authority | .
+-------+ . | Management and etc | .
. +----------------------------+ .
. .
................................................
"Domain" components
]]></artwork>
<postamble>Figure 1</postamble>
</figure>
<t><list style="hanging">
<t hangText="Domain:">The set of entities that trust a common key
infrastructure trust anchor. This includes the Proxy, Registrar,
Domain Certificate Authority, Management components and any existing
entity that is already a member of the domain.</t>
<t hangText="Domain CA:">The domain Certification Authority (CA)
provides certification functionalities to the domain. At a minimum
it provides certification functionalities to the Registrar and
stores the trust anchor that defines the domain. Optionally, it
certifies all elements.</t>
<t hangText="Registrar:">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 Registrar to control this process. Typically a
Registrar is "inside" its domain.</t>
<t hangText="New Entity:">A new device or virtual machine or
software component that is not yet part of the domain.</t>
<t hangText="Proxy:">A domain entity that helps the New Entity join
the domain. A 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. The New Entity is unaware that they are communicating with a
proxy rather than directly with the Registrar.</t>
<t hangText="MASA Service:">A Manufacturer Authorized Signing
Authority (MASA) service on the global Internet. The MASA provides a
repository for audit log information concerning privacy protected
bootstrapping events.</t>
<t hangText="Ownership Tracker">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 accurately tracking of such
ownership.</t>
</list></t>
<t>We assume a multi-vendor network. In such an environment there could
be a MASA or Ownership Tracker for each vendor that supports devices
following this document's specification, or an integrator could provide
a MASA service for all devices. It is unlikely that an integrator could
provide Ownership Tracking services for multiple vendors.</t>
<t>This document describes a secure zero-touch approach to bootstrapping
a key infrastructure; if certain devices in a network do not support
this approach, they can still be bootstrapped manually. Although manual
deployment is not scalable and is not a focus of this document the
necessary mechanisms are called out in this document to ensure such edge
conditions are covered by the architectural and protocol models.</t>
</section>
<section title="Functional Overview">
<t>Entities behave in an autonomic fashion. They discover each other and
autonomically bootstrap into a key infrastructure delineating the
autonomic domain. See <xref
target="I-D.irtf-nmrg-autonomic-network-definitions"></xref> for more
information.</t>
<t>This section details the state machine and operational flow for each
of the main three entities. The New Entity, the Domain (primarily the
Registrar) and the MASA service.</t>
<t>A representative flow is shown in Figure 2:</t>
<figure>
<artwork><![CDATA[
+--------+ +---------+ +------------+ +------------+
| New | | Circuit | | Domain | | Vendor |
| Entity | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
| | | |
|<-RFC3927 IPv4 adr | | |
or|<-RFC4862 IPv6 adr | | |
| | | |
|-------------------->| | |
| optional: mDNS query| | |
| RFC6763/RFC6762 | | |
| | | |
|<--------------------| | |
| mDNS broadcast | | |
| response or periodic| | |
| | | |
|<------------------->C<----------------->| |
| TLS via the Circuit Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---IEEE 802.1AR client authentication--->| |
P | | |
P---Request Audit Token (include nonce)-->| |
P | | |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--New Entity ID---->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | | | |
P | optional: | [update audit log]
P | |can | |
P | |occur | optional: is |
P | |in | an ownership |
P | |advance | voucher available?
P | | | |
P | | |<-device audit log--|
P | | | |
P | | | choice: |
P | | |<-audit token-------|
P | | |<-or: ownership-----|
P | \----> | voucher |
P | | |
P | [verify audit log or voucher] |
P | | |
P<--Audit token and/or ownership voucher--| |
[verify response ]| | |
[verify provisional cert ]| | |
| | | |
|---------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
| | | |
| | | |
| | | |
]]></artwork>
<postamble>Figure 2</postamble>
</figure>
<t></t>
<section title="Behavior of a New Entity">
<t>A New Entity that has not yet been bootstrapped attempts to find a
local domain and join it. A New Entity MUST NOT automatically initiate
bootstrapping if it has already been configured.</t>
<t>States of a New Entity are as follows:</t>
<t></t>
<figure>
<artwork><![CDATA[
+--------------+
| Start |
| |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input
| Bad Vendor +------+-------+
| response |
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Being |
^------------+ Managed |
Factory +--------------+
reset
]]></artwork>
<postamble>Figure 3</postamble>
</figure>
<t></t>
<t>State descriptions for the New Entity are as follows:</t>
<t><list style="numbers">
<t>Discover a communication channel to the "closest"
Registrar.</t>
<t>Identify itself. This is done by presenting an IEEE 802.1AR
credentials to the discovered Registrar (via the Proxy) in a TLS
handshake. (Although the Registrar is also authenticated these
credentials are only provisionally accepted at this time).</t>
<t>Requests to Join the discovered Registrar. A unique nonce is
included ensuring that any responses can be associated with this
particular bootstrapping attempt.</t>
<t>Imprint on the Registrar. This requires verification of the
vendor service "Audit Token" or the validation of the vendor
service "Ownership Voucher". Either of these responses contains
sufficient information for the New Entity to complete
authentication of the Registrar. (The New Entity can now finish
authentication of the Registrar TLS server certificate)</t>
<t>Enroll by accepting the domain specific information from the
Registrar, and by obtaining a domain certificate from the
Registrar using a standard enrollment protocol, e.g. Enrollment
over Secure Transport (EST) <xref target="RFC7030"></xref>.</t>
<t>The New Entity 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>
</list>The following sections describe each of these steps in more
detail.</t>
<section anchor="ProxyDiscovery" title="Discovery">
<t>The result of discovery is logically communication with a Proxy
instead of a Domain Registrar but in such a case the proxy
facilitates communication with the actual Domain Registrar in a
manner that is transparent to the New Entity. Therefore or clarity a
Proxy is always assumed.</t>
<t>To discover the Domain Bootstrap Server the New Entity performs
the following actions:</t>
<t><list style="letters">
<t>MUST: Obtains a local address using either IPv4 or IPv6
methods as described in <xref target="RFC4862"></xref> IPv6
Stateless Address AutoConfiguration or <xref
target="RFC3927"></xref> Dynamic Configuration of IPv4
Link-Local Addresses.</t>
<t>MUST: Performs DNS-based Service Discovery <xref
target="RFC6763"></xref> over Multicast DNS <xref
target="RFC6762"></xref> searching for the service
"_bootstrapks._tcp.local.". To prevent unaccceptable levels of
network traffic the congestion avoidance mechanisms specified in
<xref target="RFC6762"></xref> section 7 MUST be followed. The
New Entity SHOULD listen for an unsolicited broadcast response
as described in <xref target="RFC6762"></xref>. This allows
devices to avoid announcing their presence via mDNS broadcasts
and instead silently join a network by watching for periodic
unsolicited broadcast responses.</t>
<t>MAY: Performs DNS-based Service Discovery [RFC6763] over
normal DNS operations. The service searched for is
"_bootstrapks._tcp.example.net". In this case the domain
"example.net" is discovered as described in <xref
target="RFC6763"></xref> section 11. </t>
<t>MAY: If no local bootstrapks service is located using the
DNS-based Service Discovery methods the New Entity contacts a
well known vendor provided bootstrapping server by performing a
DNS lookup using a well known URI such as
"bootstrapks.vendor-example.com". The details of the URI are
vendor specific. Vendors that leverage this method SHOULD
provision appropriately. </t>
</list>DNS-based service discovery communicates the local proxy
IPv4 or IPv6 address and port to the New Entity. Once a proxy is
discovered the New Entity communicates with the Registrar through
the proxy using the bootstrapping protocol defined in <xref
target="ProtocolDetails"></xref>. The current DNS services returned
during each query is maintained until bootstrapping is completed. If
bootstrapping fails and the New Entity returns to the Discovery
state it picks up where it left off and continues attempting
bootstrapping. For example if the first Multicast DNS
_bootstrapks._tcp.local response doesn't work then the second and
third responses are tried. If these fail the New Entity moves on to
normal DNS-based Service Discovery.</t>
<t>Each discovery method attempted SHOULD exponentially back-off
attempts (to a maximum of one hour) to avoid overloading that
discovery methods network infrastructure. The back-off timer for
each method MUST be independent of other methods. Methods SHOULD be
run in parallel to avoid head of queue problems. Once a connection
to a Registrar is established (e.g. establishment of a TLS session
key) there are expectations of more timely responses, see <xref
target="RequestAuditTokenFromRegistrar"></xref>.</t>
<t>Once all discovered services are attempted the device SHOULD
return to Multicast DNS. It should periodically retry the vendor
specific mechanisms. The New Entity may prioritize selection order
as appropriate for the anticipated environment.</t>
</section>
<section anchor="identity" title="Identity">
<t>The New Entity identifies itself during the communication
protocol handshake. If the client identity is rejected the New
Entity repeats the Discovery process using the next proxy or
discovery method available.</t>
<t>The bootstrapping protocol server is not initially authenticated.
Thus the connection is provisional and all data received is
untrusted until sufficiently validated even though it is over a TLS
connection. This is aligned with the existing provisional mode of
EST [RFC7030] during s4.1.1 "Bootstrap Distribution of CA
Certificates". See <xref target="AuditTokenResponse"></xref> for
more information about when the TLS connection authenticated is
completed.</t>
<t>All security associations established are between the new device
and the Bootstrapping server regardless of proxy operations.</t>
</section>
<section title="Request Join">
<t>The New Entity POSTs a request to join the domain to the
Bootstrapping server. This request contains a New Entity generated
nonce and informs the Bootstrapping server which imprint methods the
New Entity will accept.</t>
<t>As indicated in EST [RFC7030] the bootstrapping server MAY
redirect the client to an alternate server. This is most useful in
the case where the New Entity has resorted to a well known vendor
URI and is communicating with the vendor's Registrar directly. In
this case the New Entity has authenticated the Registrar using the
local Implicit Trust Anchor database and can therefore treat the
redirect URI as a trusted URI which can also be validated using the
Implicit Trust Anchor database. Since client authentication occurs
during the TLS handshake the bootstrapping server has sufficient
information to apply appropriate policy concerning which server to
redirect to.</t>
<t>The nonce ensures the New Entity can verify that responses are
specific to this bootstrapping attempt. This minimizes the use of
global time and provides a substantial benefit for devices without a
valid clock.</t>
</section>
<section anchor="AcceptDomain" title="Imprint">
<t>The domain trust anchor is received by the New Entity during the
bootstrapping protocol methods in the form of either an Audit Token
containing the domain CA cert or an explicit ownership voucher. The
goal of the imprint state is to securely obtain a copy of this trust
anchor without involving human interaction.</t>
<t>The enrollment protocol EST <xref target="RFC7030"></xref>
details a set of non-autonomic bootstrapping methods such as:</t>
<t><list style="symbols">
<t>using the Implicit Trust Anchor database (not an autonomic
solution because the URL must be securely distributed),</t>
<t>engaging a human user to authorize the CA certificate using
out-of-band data (not an autonomic solution because the human
user is involved),</t>
<t>using a configured Explicit TA database (not an autonomic
solution because the distribution of an explicit TA database is
not autonomic),</t>
<t>and using a Certificate-Less TLS mutual authentication method
(not an autonomic solution because the distribution of symmetric
key material is not autonomic).</t>
</list>This document describes additional autonomic methods:</t>
<t><list style="hanging">
<t hangText="MASA audit token">Audit tokens are obtained by the
Registrar from the MASA service and presented to the New Entity
for validation. These indicate to the New Entity that joining
the domain has been logged by a logging service.</t>
<t hangText="Ownership Voucher">Ownership Vouchers are obtained
by the Registrar from the MASA service and explicitly indicate
the fully qualified domain name of the domain the new entity
currently belongs to. The Ownership Voucher is defined in <xref
target="I-D.ietf-netconf-zerotouch"></xref>.</t>
</list></t>
<t>Since client authentication occurs during the TLS handshake the
bootstrapping server has sufficient information to apply appropriate
policy concerning which method to use.</t>
<t>The audit token contains the domain's public key material as
provided to the MASA service by the Registrar. This provides
sufficient information to the client to complete automated
bootstrapping with the local key infrastructure.</t>
<t>If the autonomic methods fail the New Entity returns to discovery
state and attempts bootstrapping with the next available discovered
Registrar.</t>
</section>
<section anchor="timeunknown" title="Lack of realtime clock">
<t>Many devices when bootstrapping do not have knowledge of the
current time. Mechanisms like Network Time Protocols can not be
secured until bootstrapping is complete. Therefore bootstrapping is
defined in a method that does not require knowledge of the current
time.</t>
<t>Unfortunately there are moments during bootstrapping when
certificates are verified, such as during the TLS handshake, where
validity periods are confirmed. This paradoxical "catch-22" is
resolved by the New Entity maintaining a concept of the current
"window" of presumed time validity that is continually refined
throughout the bootstrapping process as follows:</t>
<t><list style="symbols">
<t>Initially the New Entity does not know the current time. The
nonce included in join attempts provides an alternate mechanism
for the New Entity to ensure responses are associated with a
particular bootstrapping attempt. Nonceless audit tokens from
the MASA server are always valid and thus time is not
needed.</t>
<t>In accordance with IEEE 802.1AR and RFC5280 all manufacturing
installed certificates and trust anchors are assumed to have
infinite lifetimes. All such certificates "SHOULD be assigned
the GeneralizedTime value of 99991231235959Z" [RFC5280]. The New
Entity, Registrar and MASA server MUST ignore any other validity
period information in these credentials and treat the effective
lifetime as 99991231235959Z. This ensures that client
authentication (see <xref target="entityauthentication"></xref>)
and the audit token signature (see <xref
target="AuditTokenResponse"></xref>) can always be verified
during RFC5280 path validation.</t>
<t>Once the audit token is accepted the validity period of the
domainCAcert in the token (see <xref
target="AuditTokenResponse"></xref>) now describes a valid time
window. Any subsequent certificate validity periods checked
during RFC5280 path validation MUST occur within this
window.</t>
<t>When accepting an enrollment certificate the validity period
within the new end entity certificate is assumed to be valid by
the New Entity. The New Entity is now willing to use this
credential for client authentication.</t>
</list></t>
<t>Once in this state the New Entity has a valid trust anchor with
the local domain and has a locally issued credential. These MAY be
used to secure distribution of more accurate time information
although specification of such a protocol is out-of-scope of this
document.</t>
</section>
<section title="Enrollment">
<t>As the final step of bootstrapping a Registrar helps to issue a
domain specific credential to the New Entity. For simplicity in this
document, a Registrar primarily facilitates issuing a credential by
acting as an RFC5280 Registration Authority for the Domain
Certification Authority.</t>
<t>Enrollment proceeds as described in Enrollment over Secure
Transport (EST) [RFC7030]. The New Entity contacts the Registrar
using EST as indicated:</t>
<t><list style="symbols">
<t>The New Entity is authenticated using the IEEE 802.1AR
credentials.</t>
<t>The EST section 4.1.3 CA Certificates Response is verified
using either the Audit Token which provided the domain identity
-or-</t>
<t>The EST server is authenticated by using the Ownership
Voucher indicated fully qualified domain name to build the EST
URI such that EST section 4.1.1 bootstrapping using the New
Entity implicit Trust Anchor database can be used.</t>
</list>Once the Audit Token is received, as specified in this
document, the client has sufficient information to leverage the
existing communication channel with the Registrar to continue an EST
RFC7030 enrollment. Enrollment picks up at RFC7030 section 4.1.1.
bootstrapping where the audit token provides the "out-of-band" CA
certificate fingerprint (in this case the full CA certificate) such
that the client can now complete the TLS server authentication. At
this point the client continues with EST enrollment operations
including "CA Certificates Request", "CSR Attributes" and "Client
Certificate Request" or "Server-Side Key Generation".</t>
</section>
<section title="Being Managed">
<t>Functionality to provide generic "configuration" information is
supported. The parsing of this data and any subsequent use of the
data, for example communications with a Network Management System is
out of scope but is expected to occur after bootstrapping enrollment
is complete. This ensures that all communications with management
systems which can divulge local security information (e.g. network
topology or raw key material) is secured using the local credentials
issued during enrollment.</t>
<t>The New Entity uses bootstrapping to join only one domain.
Management by multiple domains is out-of-scope of bootstrapping.
After the device has successfully joined a domain and is being
managed it is plausible that the domain can insert credentials for
other domains depending on the device capabilities.</t>
<t>See <xref target="PostEnrollment"></xref>.</t>
</section>
</section>
<section anchor="proxybehaviour" title="Behavior of a Proxy">
<t>The role of the Proxy is to facilitate communications. The Proxy
forwards packets between the New Entity and the Registrar that has
been configured on the Proxy. The Proxy does not terminate the TLS
handshake.</t>
<t>In order to permit the proxy functionality to be implemented on the
maximum variety of devices the chosen mechanism SHOULD use the minimum
amount of state on the proxy device. While many devices in the ANIMA
target space will be rather large routers, the proxy function is
likely to be implemented in the control plane CPU such a device, with
available capabilities for the proxy function similar to many class 2
IoT devices.</t>
<t>The document <xref
target="I-D.richardson-anima-state-for-joinrouter"></xref> provides a
more extensive analysis of the alternative proxy methods.</t>
<section anchor="coapconnection" title="CoAP connection to Registrar">
<t>The proxy MUST implement an IPIP (protocol 41) encapsulation
function for CoAP traffic to the configured UDP port on the
registrar. The proxy does not terminate the CoAP DTLS connection.
[[EDNOTE: The choice of CoAP as the mandatory to implement protocol
rather than HTTP maximizes code reuse on the smallest of devices.
Unfortunately this means this document will have to include the EST
over CoAP details as additional sections. The alternative is to make
'HTTPS proxy' method the mandatory to implement and provide a less
friendly environment for the smallest of devices. This is a decision
we'll have to see addressed by the broader team.]]</t>
<t>As a result of the Proxy Discovery process in section <xref
target="ProxyDiscovery"></xref>, the port number exposed by the
proxy does not need to be well known, or require an IANA
allocation.
</t>
<t>
The address and port of the Registrar to which the packets will be
forwarded will be discovered by the GRASP protocol inside the
ACP. For the IPIP encapsulation methods, the port announced by
the Proxy MUST be the same as on the registrar in order for the
proxy to remain stateless.</t>
<t>The IPIP encapsulation allows the proxy to forward traffic which
is otherwise not to be forwarded, as the traffic between New Node
and Proxy use IPv6 Link Local addresses.</t>
<t>If the Proxy device has more than one interface on which it
offers the proxy function, then it must select a unique (ACP) IP
address per interface in order so that the proxy can stateless return the
reply packets to the correct link.</t>
</section>
<section title="HTTPS proxy connection to Registrar">
<t>The proxy SHOULD also provide one of: an IPIP encapsulation of
HTTP traffic on TCP port TBD to the registrar, or a TCP circuit proxy that
connects the New Node to the Registrar.</t>
<t>When the Proxy provides a circuit proxy to the Registrar the
Registrar MUST accept HTTPS connections.</t>
<t>When the Proxy provides a stateless IPIP encapsulation to the
Registrar, then the Registrar will have to perform IPIP
decapsulation, remembering the originating outer IPIP source address
in order to qualify the inner link-local address. This is a kind
of encapsulation and processing which is similar in many ways to
how mobile IP works.
</t>
<t>
Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link-local address
with an encapsulated IPIP header requires API extensions beyond
<xref target="RFC3542"></xref> for UDP use, and requires a form of
connection latching (see section 4.1 of <xref
target="RFC5386"></xref> and all of <xref target="RFC5660"></xref>,
except that a simple IPIP tunnel is used rather than an IPsec
tunnel).
</t>
</section>
</section>
<section title="Behavior of the Registrar (Bootstrap Server)">
<t>Once a Registrar is established it listens for new entities and
determines if they can join the domain. The registrar delivers any
necessary authorization information to the new device and facilitates
enrollment with the domain PKI.</t>
<t>Registrar behavior is as follows:</t>
<t></t>
<figure>
<artwork><![CDATA[Contacted by New Entity
+
|
+-------v----------+
| Entity | fail?
| Authentication +---------+
+-------+----------+ |
| |
+-------v----------+ |
| Entity | fail? |
| Authorization +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Claiming the | fail? |
| Entity +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Log Verification | fail? |
| +--------->
+-------+----------+ |
| |
+-------v----------+ +----v-------+
| Forward | | |
| Audit | | Reject |
| token + config | | Device |
| to the Entity | | |
+------------------+ +------------+]]></artwork>
<postamble>Figure 4</postamble>
</figure>
<section anchor="entityauthentication" title="Entity Authentication">
<t>The applicable authentication methods detailed in EST [RFC7030]
are:</t>
<t><list style="symbols">
<t>the use of an IEEE 802.1AR IDevID credential during the TLS
client authentication,</t>
<t>or the use of a secret that is transmitted out of band
between the New Entity and the Registrar (this use case is not
autonomic).</t>
</list></t>
</section>
<section anchor="AcceptingTheEntity" title="Entity Authorization">
<t>In a fully automated network all devices must be securely
identified and authorized to join the domain.</t>
<t>A Registrar accepts or declines a request to join the domain,
based on the authenticated identity presented. Automated acceptance
criteria include:</t>
<t><list style="symbols">
<t>allow any device of a specific type (as determined by the
IEEE 802.1AR device identity),</t>
<t>allow any device from a specific vendor (as determined by the
IEEE 802.1AR identity),</t>
<t>allow a specific device from a vendor (as determined by the
IEEE 802.1AR identity)</t>
</list>Since all New Entities accept Audit Tokens the Registrar
MUST use the vendor provided MASA service to verify that the
device's history log does not include unexpected Registrars. If a
device had previously registered with another domain, the Registrar
of that domain would show in the log.</t>
<t>In order to validate the IEEE 802.1AR device identity the
Registrar maintains a database of vendor trust anchors (e.g. vendor
root certificates or keyIdentifiers for vendor root public keys).
For user interface purposes this database can be mapped to
colloquial vendor names. Registrars can be shipped with the trust
anchors of a significant number of third-party vendors within the
target market.</t>
<t>If a device is accepted into the domain, it is expected request a
domain certificate through a certificate enrollment process. The
result is a common trust anchor and device certificates for all
autonomic devices in a domain (these certificates can subsequently
be used to determine the boundaries of the homenet, to authenticate
other domain nodes, and to autonomically enable services on the
homenet). The authorization performed during this phase MAY be
cached for the TLS session and applied to subsequent EST enrollment
requests so long as the session lasts.</t>
</section>
<section title="Claiming the New Entity">
<t>Claiming an entity establishes an audit log at the MASA server
and provides the Registrar with proof, in the form of a MASA
authorization token, that the log entry has been inserted. As
indicated in <xref target="AcceptDomain"></xref> a New Entity will
only proceed with bootstrapping if a validated MASA authorization
token has been received. The New Entity therefore enforces that
bootstrapping only occurs if the claim has been logged. There is no
requirement for the vendor to definitively know that the device is
owned by the Registrar.</t>
<t>Registrar's obtain the Vendor URI via static configuration or by
extracting it from the IEEE 802.1AR credential. The imprint method
supported by the New Entity is known from the IEEE 802.1AR
credential. [[EDNOTE: An appropriate extension for indicating the
Vendor URI and imprint method could be defined using the methods
described in <xref target="I-D.lear-mud-framework"></xref>]].</t>
<t>During initial bootstrapping the New Entity provides a nonce
specific to the particular bootstrapping attempt. The Registrar
SHOULD include this nonce when claiming the New Entity from the MASA
service. Claims from an unauthenticated Registrar are only serviced
by the MASA resource if a nonce is provided.</t>
<t>The Registrar can claim a New Entity that is not online by
forming the request using the entities unique identifier and not
including a nonce in the claim request. Audit Tokens obtained in
this way do not have a lifetime and they provide a permanent method
for the domain to claim the device. Evidence of such a claim is
provided in the audit log entries available to any future Registrar.
Such claims reduce the ability for future domains to secure
bootstrapping and therefore the Registrar MUST be authenticated by
the MASA service.</t>
<t>An ownership voucher requires the vendor to definitively know
that a device is owned by a specific domain. The method used to
"claim" this are out-of-scope. The Registrar simply requests an
ownership validation token and the New Entity trusts the
response.</t>
</section>
<section title="Log Verification">
<t>The Registrar requests the log information for the new entity
from the MASA service. The log is verified to confirm that the
following is true to the satisfaction of the Registrar's configured
policy:</t>
<t><list style="symbols">
<t>Any nonceless entries in the log are associated with
domainIDs recognized by the registrar.</t>
<t>Any nonce'd entries are older than when the domain is known
to have physical possession of the new entity or that the
domainIDs are recognized by the registrar.</t>
</list>If any of these criteria are unacceptable to the registrar
the entity is rejected. The Registrar MAY be configured to ignore
the history of the device but it is RECOMMENDED that this only be
configured if hardware assisted NEA [RFC5209] is supported.</t>
<t>This document specifies a simple log format as provided by the
MASA service to the registar. This format could be improved by
distributed consensus technologies that integrate the audit token
with a current technologies such as block-chain or hash trees or the
like. Doing so is out of the scope of this document but are
anticipated improvements for future work.</t>
</section>
</section>
<section title="Behavior of the MASA Service">
<t>The MASA service is provided by the Factory provider on the global
Internet. The URI of this service is well known. The URI SHOULD also
be provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA Audit
Token Distribution Point" extension).</t>
<t>The MASA service provides the following functionalities to
Registrars:</t>
<section title="Issue Authorization Token and Log the event">
<t>A Registrar POSTs a claim message optionally containing the
bootstrap nonce to the MASA server.</t>
<t>If a nonce is provided the MASA service responds to all requests.
The MASA service verifies the Registrar is representative of the
domain and generates a privacy protected log entry before responding
with the Audit Token.</t>
<t>If a nonce is not provided then the MASA service MUST
authenticate the Registrar as a valid customer. This prevents denial
of service attacks.</t>
</section>
<section title="Retrieve Audit Entries from Log">
<t>When determining if a New Entity should be accepted into a domain
the Registrar retrieves a copy of the audit log from the MASA
service. This contains a list of privacy protected domain identities
that have previously claimed the device. Included in the list is an
indication of the time the entry was made and if the nonce was
included.</t>
</section>
</section>
<section anchor="PostEnrollment"
title="Leveraging the new key infrastructure / next steps">
<t>As the devices have a common trust anchor, device identity can be
securely established, making it possible to automatically deploy
services across the domain in a secure manner.</t>
<t>Examples of services:<list style="symbols">
<t>Device management.</t>
<t>Routing authentication.</t>
<t>Service discovery.</t>
</list></t>
<section anchor="boundary" title="Network boundaries">
<t>When a device has joined the domain, it can validate the domain
membership of other devices. This makes it possible to create trust
boundaries where domain members have higher level of trusted than
external devices. Using the autonomic User Interface, specific
devices can be grouped into to sub domains and specific trust levels
can be implemented between those.</t>
</section>
</section>
<section title="Interactions with Network Access Control">
<t>The assumption is that Network Access Control (NAC) completes using
the New Entity 802.1AR credentials and results in the device having
sufficient connectivity to discovery and communicate with the proxy.
Any additional connectivity or quarantine behavior by the NAC
infrastructure is out-of-scope. After the devices has completed
bootstrapping the mechanism to trigger NAC to re-authenticate the
device and provide updated network privileges is also
out-of-scope.</t>
<t>This achieves the goal of a bootstrap architecture that can
integrate with NAC but does not require NAC within the network where
it wasn't previously required. Future optimizations can be achieved by
integrating the bootstrapping protocol directly into an initial EAP
exchange.</t>
</section>
</section>
<section title="Domain Operator Activities">
<t>This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.</t>
<section title="Instantiating the Domain Certification Authority">
<t>This is a one time step by the domain administrator. This is an
"off the shelf" CA with the exception that it is designed to work as
an integrated part of the security solution. This precludes the use of
3rd party certification authority services that do not provide support
for delegation of certificate issuance decisions to a domain managed
Registration Authority.</t>
</section>
<section title="Instantiating the Registrar">
<t>This is a one time step by the domain administrator. One or more
devices in the domain are configured take on a Registrar function.</t>
<t>A device can be configured to act as a Registrar or a device can
auto-select itself to take on this function, using a detection
mechanism to resolve potential conflicts and setup communication with
the Domain Certification Authority. Automated Registrar selection is
outside scope for this document.</t>
</section>
<section anchor="accepting" title="Accepting New Entities">
<t>For each New Entity the Registrar is informed of the unique
identifier (e.g. serial number) along with the manufacturer's
identifying information (e.g. manufacturer root certificate). This can
happen in different ways:</t>
<t><list style="numbers">
<t>Default acceptance: In the simplest case, the new device
asserts its unique identity to the registrar. The registrar
accepts all devices without authorization checks. This mode does
not provide security against intruders and is not recommended.</t>
<t>Per device acceptance: The new device asserts its unique
identity to the registrar. A non-technical human validates the
identity, for example by comparing the identity displayed by the
registrar (for example using a smartphone app) with the identity
shown on the packaging of the device. Acceptance may be triggered
by a click on a smartphone app "accept this device", or by other
forms of pairing. See also <xref
target="I-D.behringer-homenet-trust-bootstrap"></xref> for how the
approach could work in a homenet.</t>
<t>Whitelist acceptance: In larger networks, neither of the
previous approaches is acceptable. Default acceptance is not
secure, and a manual per device methods do not scale. Here, the
registrar is provided a priori with a list of identifiers of
devices that belong to the network. This list can be extracted
from an inventory database, or sales records. If a device is
detected that is not on the list of known devices, it can still be
manually accepted using the per device acceptance methods.</t>
<t>Automated Whitelist: an automated process that builds the
necessary whitelists and inserts them into the larger network
domain infrastructure is plausible. Once set up, no human
intervention is required in this process. Defining the exact
mechanisms for this is out of scope although the registrar
authorization checks is identified as the logical integration
point of any future work in this area.</t>
</list></t>
<t>None of these approaches require the network to have permanent
Internet connectivity. Even when the Internet based MASA service is
used, it is possible to pre-fetch the required information from the
MASA a priori, for example at time of purchase such that devices can
enroll later. This supports use cases where the domain network may be
entirely isolated during device deployment.</t>
<t>Additional policy can be stored for future authorization decisions.
For example an expected deployment time window or that a certain Proxy
must be used.</t>
</section>
<section title="Automatic Enrollment of Devices">
<t>The approach outlined in this document provides a secure zero-touch
method to enroll new devices without any pre-staged configuration. New
devices communicate with already enrolled devices of the domain, which
proxy between the new device and a Registrar. As a result of this
completely automatic operation, all devices obtain a domain based
certificate.</t>
</section>
<section title="Secure Network Operations">
<t>The certificate installed in the previous step can be used for all
subsequent operations. For example, to determine the boundaries of the
domain: If a neighbor has a certificate from the same trust anchor it
can be assumed "inside" the same organization; if not, as outside. See
also <xref target="boundary"></xref>. The certificate can also be used
to securely establish a connection between devices and central control
functions. Also autonomic transactions can use the domain certificates
to authenticate and/or encrypt direct interactions between devices.
The usage of the domain certificates is outside scope for this
document.</t>
</section>
</section>
<section anchor="ProtocolDetails" title="Protocol Details">
<t>A bootstrapping protocol could be implemented as an independent
protocol from EST, but for simplicity and to reduce the number of TLS
connections and crypto operations required on the New Entity, it is
described specifically as extensions to EST. These extensions MUST be
supported by the Registrar EST server within the same .well-known URI
tree as the existing EST URIs as described in [RFC7030] section
3.2.2.</t>
<t>The new entity establishes a TLS connection with the Registrar
through the circuit proxy (see <xref target="proxybehaviour"></xref>)
but the TLS connection is with the Registar; so for this section the
"New Entity" is the TLS client and the "Registrar" is the TLS
server.</t>
<t>Establishment of the TLS connection for bootstrapping is as specified
for EST [RFC7030]. In particular server identity and client identity are
as described in EST [RFC7030] section 3.3. In EST [RFC7030] provisional
server authentication for bootstrapping is described in section 4.1.1
wherein EST clients can "engage a human user to authorize the CA
certificate using out-of-band data such as a CA certificate" or wherein
a human user configures the URI of the EST server for Implicit TA based
authentication. As described in this document, <xref
target="CompletingAuthenticationBootstrapping"></xref>, a new method of
bootstrapping now provides a completely automating method of
bootstrapping PKI.</t>
<t>The extensions for the New Entity client are as follows:</t>
<t><list style="symbols">
<t>The New Entity provisionally accept the EST server certificate
during the TLS handshake as detailed in <xref
target="CompletingAuthenticationBootstrapping"></xref>.</t>
<t>The New Entity requests and validates the Audit Token as
described below. At this point the New Entity has sufficient
information to validate domain credentials.</t>
<t>The New Entity calls the EST defined /cacerts method to obtain
the current CA certificate. These are validated using the Audit
Token.</t>
<t>The New Entity completes bootstrapping as detailed in EST section
4.1.1.</t>
</list></t>
<t>In order to obtain a validated Audit Token and Audit Log the
Registrar contacts the MASA service Service using REST calls:</t>
<figure>
<artwork><![CDATA[ +-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
+---------------C---------------> |
| | | |
HTTP REST | POST /requestaudittoken | |
Data +--------------------nonce------> |
| . | /requestaudittoken
| . +---------------->
| <----------------+
| | /requestauditlog
| +---------------->
| audit token or owner voucher <----------------+
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |]]></artwork>
<postamble>Figure 5</postamble>
</figure>
<t>In some use cases the Registrar may need to contact the Vendor in
advanced, for example when the target network is air-gapped. The
nonceless request format is provided for this and the resulting flow is
slightly different. The security differences associated with not knowing
the nonce are discussed below:</t>
<figure>
<artwork><![CDATA[ +-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| | | /requestaudittoken
| | (nonce +---------------->
| | unknown) <----------------+
| | | /requestauditlog
| | +---------------->
| | <----------------+
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
| | | |
HTTP REST | POST /requestaudittoken | |
Data +----------------------nonce----> (discard |
| audit token or owner Voucher | nonce) |
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |]]></artwork>
<postamble>Figure 6</postamble>
</figure>
<t></t>
<t>The extensions for the Registrar server are as follows:</t>
<t><list style="symbols">
<t>The Registrar requests and validates the Audit Token from the
vendor authorized MASA service.</t>
<t>The Registrar forwards the Audit Token to the New Entity when
requested.</t>
<t>The Registar performs log verifications in addition to local
authorization checks before accepting the New Entity device.</t>
</list></t>
<section anchor="RequestAuditTokenFromRegistrar"
title="Request Audit Token from the Registrar">
<t>When the New Entity reaches the EST section 4.1.1 "Bootstrap
Distribution of CA Certificates" state but wishes to proceed in a
fully automated fashion it makes a request for a MASA authorization
token from the Registrar.</t>
<t>This is done with an HTTPS POST using the operation path value of
"/requestaudittoken".</t>
<t>The request format is JSON object containing a 64bit nonce
generated by the client for each request. This nonce MUST be a
cryptographically strong random or pseudo-random number that can not
be easily predicted. The nonce MUST NOT be reused for multiple
attempts to join a network domain. The nonce assures the New Entity
that the audit token response is associated with this bootstrapping
attempt and is not a replay.</t>
<t>Request media type: application/auditnonce</t>
<t>Request format: a JSON file with the following:</t>
<figure>
<artwork><![CDATA[{
"version":"1",
"nonce":"<64bit nonce value>",
}]]></artwork>
</figure>
<t></t>
<t>[[EDNOTE: Even if the nonce was signed it would provide no defense
against rogue registrars; although it would assure the MASA that a
certified new entity exists. To protect against rogue registrars a
nonce component generated by the MASA (a new round trip) would be
required). Instead this is addressed by requiring MASA & Registrar
authentications but it is worth exploring additional protections. This
to be explored more at IETF96.]] </t>
<t>The Registrar validates the client identity as described in EST
[RFC7030] section 3.3.2. The registrar performs authorization as
detailed in Section 3.3.2. If authorization is successful the
Registrar obtains an Audit Token from the MASA service (see Section
5.2).</t>
<t>The received MASA authorization token is returned to the New
Entity.</t>
<t>As indicated in EST [RFC7030] the bootstrapping server can redirect
the client to an alternate server. If the New Entity authenticated the
Registrar using the well known URI method then the New Entity MUST
follow the redirect automatically and authenticate the new Registrar
against the redirect URI provided. If the New Entity had not yet
authenticated the Registrar because it was discovered and was not a
known-to-be-valid URI then the new Registrar must be authenticated
using one of the two autonomic methods described in this document.
Similarly the Registar MAY respond with an HTTP 202 ("the request has
been accepted for processing, but the processing has not been
completed") as described in EST [RFC7030] section 4.2.3.</t>
<t>Recall that during this communication with the Registar the TLS
authentication is only provisional. The New Entity client MUST handle
all data from the Registrar with upmost care. In particular the New
Entity MUST only allow a single redirection and MUST only support a
delay of five seconds before declaring the Registrar a failure and
moving on to the next discovered Registrar. As detailed in <xref
target="ProxyDiscovery"></xref> if no suitable Registrar is found the
New Entity restarts the state machine and tries again. So a Registrar
that is unable to complete the transaction the first time will have
future chances.</t>
</section>
<section anchor="RequestAuditToken"
title="Request Audit Token from MASA">
<t>The Registrar requests the Audit Token from the MASA service using
a REST interface. For simplicity this is defined as an optional EST
message between the Registrar and an EST server running on the MASA
service although the Registrar is not required to make use of any
other EST functionality when communicating with the MASA service. (The
MASA service MUST properly reject any EST functionality requests it
does not wish to service; a requirement that holds for any REST
interface).</t>
<t>This is done with an HTTP POST using the operation path value of
"/requestaudittoken".</t>
<t>The request format is a JSON object optionally containing the nonce
value (as obtained from the bootstrap request) and the IEEE 802.1AR
identity of the device as a serial number (the full certificate is not
needed and no proof-of-possession information for the device identity
is included). The AuthorityKeyIdentifier value from the certificate is
included to ensure a statistically unique identity. The New Entity's
serial number is extracted from the IEEE 802.1AR subject name
id-at-serialNumber or it is the base64 encoded RFC4108
hardwareModuleName hwSerialNum:</t>
<figure>
<artwork><![CDATA[{
"version":"1",
"nonce":"<64bit nonce value>",
"IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier">,
"DevIDSerialNumber":"<id-at-serialNumber or base64 encoded
hardwareModuleName hwSerialNum>",
}]]></artwork>
</figure>
<t></t>
<t>The Registrar MAY exclude the nonce from the request. Doing so
allows the Registrar to request an authorization token when the New
Entity is not online, or when the target bootstrapping environment is
not on the same network as the MASA server (this requires the
Registrar to learn the appropriate DevIDSerialNumber field from the
physical device labeling or from the sales channel -- how this occurs
is out-of-scope of this document). If a nonce is not provided the MASA
server MUST authenticate the client as described in EST [RFC7030]
section 3.3.2 to reduce the risk of DDoS attacks. The registrar
performs authorization as detailed in <xref
target="AcceptingTheEntity"></xref>. If authorization is successful
the Registrar obtains an Audit Token from the MASA service (see <xref
target="RequestAuditToken"></xref>).</t>
<t>The JSON message information is encapsulated in a <xref
target="RFC5652"></xref> Signed-data that is signed by the Registrar.
The entire certificate chain, up to and including the Domain CA, MUST
be included in the CertificateSet structure. The MASA service checks
the internal consistency of the CMS but does not authenticate the
domain identity information. The domain is not know to the MASA server
in advance and a shared trust anchor is not implied. The MASA server
MUST verify that the CMS is signed by a Registrar certificate (by
checking for the cmc-idRA field) that was issued by a the root
certificate included in the CMS. This ensures that the Registrar
making the claim is an authorized Registrar of the unauthenticated
domain. The EST style client authentication (TLS and HTTP) is used to
provide a DDoS prevention strategy.</t>
<t>The domain ID (e.g. hash of the public key of the domain) is
extracted from the root certificate and is used to populate the MASA
authorization token and to update the audit log.</t>
</section>
<section anchor="AuditTokenResponse" title="Audit Token Response">
<t>The authorization token response to requests from the device and
requests from the Registrar are in the same format. The Registrar
either caches prior MASA responses or dynamically requests a new Audit
Token based on local policy.</t>
<t>If the the join operation is successful, the server response MUST
contain an HTTP 200 response code with a content-type of
"application/authorization-token". The server MUST answer with a
suitable 4xx or 5xx HTTP [RFC2616] error code when a problem occurs.
The response data from the MASA server MUST be a plaintext
human-readable error message containing explanatory information
describing why the request was rejected.</t>
<t>The authorization token consists of the nonce, if supplied, the
serial number information identifying the device and the domain CA
certificate extracted from the request:</t>
<figure>
<artwork><![CDATA[{
"version":"1",
"nonce":"<64bit nonce value>",
"IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier>",
"DevIDSerialNumber":"<id-at-serialNumber>",
"domainCAcert":"<the base64 encoded domain CA's certificate>"
}]]></artwork>
</figure>
<t>The audit token response is encapsulated in a <xref
target="RFC5652"></xref> Signed-data that is signed by the MASA
server. The New Entity verifies this signed message using the IEEE
802.1AR manufacturer installed trust anchor. </t>
<t>[[EDNOTE: Using CMS is consistent with the alignment of this
bootstrapping document with EST, a PKIX enrollment protocol that
includes Certificate Management over CMS. An alternative format would
be the RFC7515 JSON Web Signature (JWS), which would allow clients
that do not use fullCMC messages to avoid CMS entirely. Use of JWS
would likely include a discussion of CBOR in order ensure the base64
expansions of the certs and signatures within the JWS message are of
minimal size -- it is not yet clear to this author how that would work
out]]</t>
<t>The 'domainCAcert' element of this message contains the domain CA's
public key. This is specific to bootstrapping a public key
infrastructure. To support bootstrapping other key infrastructures
additional domain identity types might be defined in the future.
Clients MUST be prepared to ignore additional fields they do not
recognize. Clients MUST be prepared to parse and fail gracefully from
an audit token response that does not contain a 'domainCAcert' field
at all.</t>
<t>To minimize the size of the audit token response message the
domainCAcert is not a complete distribution of the EST section 4.1.3
CA Certificate Response.</t>
<t>The New Entity installs the domainCAcert trust anchor. As indicated
in <xref target="identity"></xref> the newly installed trust anchor is
used as an EST RFC7030 Explicit Trust Anchor. The New Entity MUST use
the domainCAcert trust anchor to immediately validate the currently
provisional TLS connection to the Registrar.</t>
<section anchor="CompletingAuthenticationBootstrapping"
title="Completing authentication of Provisional TLS connection">
<t>If the Registrar's credential can not be verified using the
domainCAcert trust anchor the TLS connection is immediately
discarded and the New Entity abandons attempts to bootstrap with
this discovered registrar.</t>
<t>The following behaviors on the Registrar and New Entity are in
addition to normal PKIX operations:</t>
<t><list style="symbols">
<t>The EST server MUST use a certificate that chains to the
domainCAcert. This means that when the EST server obtains
renewed credentials the credentials included in the <xref
target="RequestAuditToken"></xref> request match the chain used
in the current provisional TLS connection.</t>
<t>The New Entity PKIX path validation of the Registrar validity
period information is as described in <xref
target="timeunknown"></xref>.</t>
</list>Because the domainCAcert trust anchor is installed as an
Explicit Trust Anchor it can be used to authenticate any dynamically
discovered EST server that contain the id-kp-cmcRA extended key
usage extension as detailed in EST RFC7030 section 3.6.1; but to
reduce system complexity the New Entity SHOULD avoid additional
discovery operations. Instead the New entity SHOULD communicate
directly with the Registrar as the EST server to complete PKI local
certificate enrollment. Additionally the New Entity SHOULD use the
existing TLS connection to proceed with EST enrollment, thus
reducing the total amount of cryptographic and round trip operations
required during bootstrapping. [[EDNOTE: It is reasonable to mandate
that the existing TLS connection be re-used? e.g. MUST >>
SHOULD?]]</t>
</section>
</section>
<section title="Audit Token Status Telemetry ">
<t>For automated bootstrapping of devices the adminstrative elements
providing bootstrapping also provide indications to the system
administrators concerning device lifecycle status. To facilitate this
those elements need telemetry information concerning the device's
status.</t>
<t>To indicate New Entity status regarding the audit token the client
SHOULD post a status message.</t>
<t>The client HTTP POSTs the following to the server at the EST well
known URI /requestaudittoken_status. The Status field indicates if the
audit token was acceptable. If it was not acceptable the Reason string
indicates why. In the failure case this message is being sent to an
unauthenticated, potentially malicious Registrar and therefore the
Reason string SHOULD NOT provide information beneficial to an
attacker. The operational benefit of this telemetry information is
balanced against the operational costs of not recording that an audit
token was ignored by a client the registar expected to continue
joining the domain.</t>
<t><figure>
<artwork><![CDATA[{
"version":"1",
"Status":FALSE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
}]]></artwork>
</figure>The server SHOULD respond with an HTTP 200 but MAY simply
fail with an HTTP 404 error. The client ignores any response. Within
the server logs the server SHOULD capture this telemetry
information.</t>
</section>
<section title="MASA authorization log Request ">
<t>A registrar requests the MASA authorization log from the MASA
service using this EST extension.</t>
<t>This is done with an HTTP GET using the operation path value of
"/requestMASAlog".</t>
<t>The client HTTP POSTs the same Audit Token Request as for
requesting an audit token but now posts it the /requestMASAlog URI
instead. The IDevIDAuthorityKeyIdentifier and DevIDSerialNumber
informs the MASA server which log is requested so the appropriate log
can be prepared for the response.</t>
</section>
<section title="MASA authorization log Response">
<t>A log data file is returned consisting of all log entries. For
example:</t>
<t><figure>
<artwork><![CDATA[{
"version":"1",
"events":[
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit token request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
},
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit token request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
}
]
}]]></artwork>
</figure></t>
<t>Distribution of a large log is less than ideal. This structure can
be optimized as follows: All nonce-less entries for the same domainID
MAY be condensed into the single most recent nonceless entry.</t>
<t>The Registrar uses this log information to make an informed
decision regarding the continued bootstrapping of the New Entity. For
example if the log includes unexpected domainIDs this is indicative of
problematic imprints by the new entity. If the log includes nonce-less
entries this is indicative of the permanent ability for the indicated
domain to trigger a reset of the device and take over management of
it. Equipment that is purchased pre-owned can be expected to have an
extensive history.</t>
<t>Log entries containing the Domain's ID can be compared against
local history logs in search of discrepancies.</t>
</section>
<section title="EST Integration for PKI bootstrapping">
<t>The prior sections describe EST extensions necessary to enable
fully automated bootstrapping. Although the audit token
request/response structure members IDevIDAuthorityKeyIdentifier and
DevIDSerialNumber are specific to PKI bootstrapping these are the only
PKI specific aspects of the extensions and future work might replace
them with non-PKI structures.</t>
<t>The prior sections provide functionality for the New Entity to
obtain a trust anchor representative of the Domain. The following
section describe using EST to obtain a locally issued PKI certificate.
The New Entity MAY perform alternative enrollment methods or proceed
to use its IDevID credential indefinately, but those that leverage the
discovered Registrar to proceed with certificate enrollment MUST
implement the following EST choices.</t>
<section title="EST Distribution of CA Certificates">
<t>The New Entity MUST request the full EST Distribution of CA
Certificates message. See RFC7030, section 4.1.</t>
<t>This ensures that the New Entity has the complete set of current
CA certificates beyond the domainCAcert (see <xref
target="AuditTokenResponse"></xref> for a discussion of the
limitations). Although these restrictions are acceptable for the
Registrar integrated with initial bootstrapping they are not
appropriate for ongoing PKIX end entity certificate validation.</t>
</section>
<section title="EST CSR Attributes">
<t>Automated bootstrapping occurs without local administrative
configuration of the New Entity. In some deployments its plausible
that the New Entity generates a certificate request containing only
identity information known to the New Entity (essentially the IDevID
information) and ultimately receives a certificate containing domain
specific identity information. Conceptually the CA has complete
control over all fields issued in the end entity certificate.
Realistically this is operationally difficult with the current
status of PKI certificate authority deployments where the CSR is
submitted to the CA via a number of non-standard protocols.</t>
<t>To alleviate operational difficulty the New Entity MUST request
the EST "CSR Attributes" from the EST server. This allows the local
infrastructure to inform the New Entity of the proper fields to
include in the generated CSR.</t>
<t>[[EDNOTE: The following is specific to anima purposes and should
be moved to an appropriate anima document so as to keep
bootstrapping as generic as possible: What we want are a 'domain
name' stored in [TBD] and an 'ACP IPv6 address' stored in the
iPAddress field as specified in RFC5208 s4.2.1.6. ref ACP draft
where certificate verification [TBD]. These should go into the
subjectaltname in the [TBD] fields.]]. If the hardwareModuleName in
the IDevID is populated then it SHOULD by default be propagated to
the LDevID along with the hwSerialNum. The registar SHOULD support
local policy concerning this functionality. [[EDNOTE: extensive use
of EST CSR Attributes might need an new OID definition]].]]</t>
<t>The Registar MUST also confirm the resulting CSR is formatted as
indicated before forwarding the request to a CA. If the Registar is
communicating with the CA using a protocol like full CMC which
provides mechanisms to override the CSR attributes, then these
mechanisms MAY be used even if the client ignores CSR Attribute
guidance.</t>
</section>
<section title="EST Client Certificate Request">
<t>The New Entity MUST request a new client certificate. See
RFC7030, section 4.2.</t>
</section>
<section title="Enrollment Status Telemetry">
<t>For automated bootstrapping of devices the adminstrative elements
providing bootstrapping also provide indications to the system
administrators concerning device lifecycle status. This might
include information concerning attempted bootstrapping messages seen
by the client, MASA provides logs and status of credential
enrollment. The EST protocol assumes an end user and therefore does
not include a final success indication back to the server. This is
insufficient for automated use cases.</t>
<t>To indicate successful enrollment the client SHOULD re-negotiate
the EST TLS session using the newly obtained credentials. This
occurs by the client initiating a new TLS ClientHello message on the
existing TLS connection. The client MAY simply close the old TLS
session and start a new one. The server MUST support either
model.</t>
<t>In the case of a failure the Reason string indicates why the most
recent enrollment failed. The SubjectKeyIdentifier field MUST be
included if the enrollment attempt was for a keypair that is locally
known to the client. If EST /serverkeygen was used and failed then
the this field is ommited from the status telemetry.</t>
<t>The client HTTP POSTs the following to the server at the new EST
well known URI /enrollstatus.</t>
<t><figure>
<artwork><![CDATA[{
"version":"1",
"Status":TRUE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
"SubjectKeyIdentifier":"<base64 encoded subjectkeyidentifier for the
enrollment that failed>"
}]]></artwork>
</figure></t>
<t>The server SHOULD respond with an HTTP 200 but MAY simply fail
with an HTTP 404 error.</t>
<t>Within the server logs the server MUST capture if this message
was recieved over an TLS session with a matching client certificate.
This allows for clients that wish to minimize their crypto
operations to simpy POST this response without renegotiating the TLS
session - at the cost of the server not being able to accurately
verify that enrollment was truly successful.</t>
</section>
<section title="EST over CoAP">
<t>[[EDNOTE: In order to support smaller devices the above section
on Proxy behavior introduces mandatory to implement support for CoAP
support by the Proxy. This implies similar support by the New Entity
and Registrar and means that the EST protocol operation
encapsulation into CoAP needs to be described. EST is HTTP based and
"CoaP is designed to easily interface with HTTP for integration"
[RFC7252]. Use of CoAP implies Datagram TLS (DTLS) wherever this
document describes TLS handshake specifics. A complexity is that the
large message sizes necessary for bootstrapping will require support
for [draft-ietf-core-block].]]</t>
</section>
</section>
</section>
<section anchor="reducedsecuritymodes"
title="Reduced security operational modes">
<t>A common requirement of bootstrapping is to support less secure
operational modes for support specific use cases. The following sections
detail specific ways that the New Entity, Registrar and MASA can be
configured to run in a less secure mode for the indicated reasons.</t>
<section title="Trust Model">
<figure>
<artwork><![CDATA[
+--------+ +---------+ +------------+ +------------+
| New | | Circuit | | Domain | | Vendor |
| Entity | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
]]></artwork>
<postamble>Figure 7</postamble>
</figure>
<t><list style="hanging">
<t hangText="New Entity:">The New Entity could be compromised and
providing an attack vector for malware. The entity is trusted to
only imprint using secure methods described in this document.
Additional endpoint assessment techniques are RECOMMENDED but are
out-of-scope of this document.</t>
<t hangText="Proxy:">Provides proxy functionalities but is not
involved in security considerations.</t>
<t hangText="Registrar:">When interacting with a MASA server the
Registrar makes all decisions. When ownership vouchers are
involved the Registrar is only a conduit and all security
decisions are made on the vendor service.</t>
<t hangText="Vendor Service, MASA:">This form of vendor service is
trusted to accurately log all claim attempts and to provide
authoritative log information to Registrars. The MASA does not
know which devices are associated with which domains. These claims
could be strengthened by using cryptographic log techniques to
provide append only, cryptographic assured, publicly auditable
logs. Current text provides only for a trusted vendor.</t>
<t hangText="Vendor Service, Ownership Validation:">This form of
vendor service is trusted to accurately know which device is owned
by which domain.</t>
</list></t>
</section>
<section title="New Entity security reductions">
<t>Although New Entity can choose to run in less secure modes this is
MUST NOT be the default state because it permanently degrades the
security for all other uses cases.</t>
<t>The device may have an operational mode where it skips Audit Token
or Ownership Voucher validation one time. For example if a physical
button is depressed during the bootstrapping operation. This can be
useful if the vendor service is unavailable. This behavior SHOULD be
available via local configuration or physical presence methods to
ensure new entities can always be deployed even when autonomic methods
fail. This allows for unsecure imprint.</t>
<t>It is RECOMMENDED that this only be available if hardware assisted
NEA [RFC5209] is supported.</t>
</section>
<section title="Registrar security reductions">
<t>The Registrar can choose to accept devices using less secure
methods. These methods are acceptable when low security models are
needed, as the security decisions are being made by the local
administrator, but they MUST NOT be the default behavior:<list
style="numbers">
<t>The registrar MAY choose to accept all devices, or all devices
of a particular type, at the administrator's discretion. This
could occur when informing the Registrar of unique identifiers of
new entities might be operationally difficult.</t>
<t>The registrar MAY choose to accept devices that claim a unique
identity without the benefit of authenticating that claimed
identity. This could occur when the New Entity does not include an
IEEE 802.1AR factory installed credential. New Entities without an
IDevID credential MAY form the <xref
target="RequestAuditTokenFromRegistrar"></xref> request using the
<xref target="RequestAuditToken"></xref> format to ensure the New
Entity's serial number information is provided to the Registar
(this includes the IDevIDAuthorityKeyIdentifier value which would
be statically configured on the New Entity). The New Entity MAY
refused to provide a TLS client certificate (as one is not
available). The New Entity SHOULD support HTTP-based or
certificate-less TLS authentication as described in EST RFC7030
section 3.3.2.</t>
<t>The registrar MAY request nonce-less Audit Tokens from the MASA
service. These tokens can then be transmitted to the Registrar and
stored until they are needed during bootstrapping operations. This
is for use cases where target network is protected by an air gap
and therefore can not contact the MASA service during New Entity
deployment.</t>
<t>The registrar MAY ignore unrecognized nonce-less Audit Log
entries. This could occur when used equipment is purchased with a
valid history being deployed in air gap networks that required
permanent Audit Tokens.</t>
</list></t>
<t>These modes are not available for devices that require a vendor
Ownership Voucher. The methods vendors use to determine which devices
are owned by which domains is out-of-scope.</t>
</section>
<section title="MASA security reductions">
<t>Lower security modes chosen by the MASA service effect all device
deployments unless bound to the specific device identities. In which
case these modes can be provided as additional features for specific
customers. The MASA service can choose to run in less secure modes
by:</t>
<t><list style="numbers">
<t>Not enforcing that a Nonce is in the Audit Token. This results
in distribution of Audit Tokens that never expire and in effect
makes the Domain an always trusted entity to the New Entity during
any subsequent bootstrapping attempts. That this occurred is
captured in the log information so that the Domain registrar can
make appropriate security decisions when a New Entity joins the
Domain. This is useful to support use cases where Registrars might
not be online during actual device deployment. Because this
results in long lived Audit Tokens and do not require the proof
that the device is online this is only accepted when the Registrar
is authenticated by the MASA server and authorized to provide this
functionality. The MASA server is RECOMMENDED to use this
functionality only in concert with Ownership Validation
tracking.</t>
<t>Not verifying ownership before responding with an Audit Token.
This is expected to be a common operational model because doing so
relieves the vendor providing MASA services from having to
tracking ownership during shipping and supply chain and allows for
a very low overhead MASA service. The Registrar uses the audit log
information as a defense in depth strategy to ensure that this
does not occur unexpectedly (for example when purchasing new
equipment the Registrar would throw an error if any audit log
information is reported).</t>
</list></t>
</section>
</section>
<section title="Security Considerations">
<t>In order to support a wide variety of use cases, devices can be
claimed by a registrar without proving possession of the device in
question. This would result in a nonceless, and thus always valid,
claim. Or would result in an invalid nonce being associated with a
claim. The MASA service is required to authenticate such Registrars but
no programmatic method is provided to ensure good behavior by the MASA
service. Nonceless entries into the audit log therefore permanently
reduce the value of a device because future Registrars, during future
bootstrap attempts, would now have to be configured with policy to
ignore previously (and potentially unknown) domains.</t>
<t>Future registrars are recommended to take the audit history of a
device into account when deciding to join such devices into their
network. If the MASA server were to have allowed a significantly large
number of claims this might become onerous to the MASA server which must
maintain all the extra log entries. Ensuring the Registrar is
representative of a valid customer domain even without validating
ownership helps to mitigate this.</t>
<t>It is possible for an attacker to send an authorization request to
the MASA service directly after the real Registrar obtains an
authorization log. If the attacker could also force the bootstrapping
protocol to reset there is a theoretical opportunity for the attacker to
use the Audit Token to take control of the New Entity but then proceed
to enroll with the target domain. Possible prevention mechanisms
include:</t>
<t><list style="symbols">
<t>Per device rate limits on the MASA service ensure such timing
attacks are difficult.</t>
<t>In the advent of an unexpectedly lost bootstrapping connection
the Registrar repeats the request for audit log information.</t>
</list></t>
<t>To facilitate auditing the New Entity reports on audit token parsing
status. In the case of a failure this information is informative to the
potentially malicious Registar but this is included because the
operational benefits are concidered beneficial.</t>
<t>As indicated in EST [RFC7030] the connection is provisional and
untrusted until the server is successfully authorized. If the server
provides a redirect response the client MUST follow the redirect but the
connection remains provisional. If the client uses a well known URI for
contacting a well known Registrar the EST Implicit Trust Anchor database
is used as is described in RFC6125 to authenticate the well known URI.
In this case the connection is not provisional and RFC6125 methods can
be used for each subsequent redirection.</t>
<t>To facilitate truely limited clients EST RFC7030 section 3.3.2
requirements that the client MUST support a client authentication model
have been reduced in <xref target="reducedsecuritymodes"></xref> to a
statement that clients only "SHOULD" support such a model. This reflects
current (not great) practices but is NOT RECOMMENDED.</t>
<t>The MASA service could lock a claim and refuse to issue a new token
or the MASA service could go offline (for example if a vendor went out
of business). This functionality provides benefits such as theft
resistance, but it also implies an operational risk to the Domain that
Vendor behavior could limit future bootstrapping of the device by the
Domain. This can be mitigated by Registrars that request nonce-less
authorization tokens.</t>
</section>
<section title="Acknowledgements">
<t>We would like to thank the various reviewers for their input, in
particular Markus Stenberg, Brian Carpenter, Fuyu Eleven, Toerless
Eckert, Eliot Lear and Sergey Kasatkin.</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC7030;
&RFC5652;
<?rfc include="reference.RFC.3542" ?>
<?rfc include="reference.RFC.5386" ?>
<?rfc include="reference.RFC.5660" ?>
<?rfc include="reference.RFC.7228" ?>
<?rfc include="reference.RFC.6762" ?>
<?rfc include="reference.RFC.6763" ?>
<?rfc include="reference.RFC.3927" ?>
<?rfc include="reference.RFC.4862" ?>
<reference anchor="IDevID"
target="http://standards.ieee.org/findstds/standard/802.1AR-2009.html">
<front>
<title>IEEE 802.1AR Secure Device Identifier</title>
<author surname="IEEE Standard"></author>
<date month="December" year="2009" />
</front>
</reference>
</references>
<references title="Informative References">
&I-D.behringer-autonomic-network-framework;
&I-D.irtf-nmrg-autonomic-network-definitions;
<?rfc include="reference.I-D.ietf-ace-actors" ?>
<?rfc include="reference.I-D.richardson-anima-state-for-joinrouter" ?>
<?rfc include="reference.I-D.lear-mud-framework" ?>
<?rfc include="reference.I-D.ietf-netconf-zerotouch" ?>
<reference anchor="imprinting"
target="https://en.wikipedia.org/wiki/Imprinting_(psychology)">
<front>
<title>Wikipedia article: Imprinting</title>
<author surname="Wikipedia"></author>
<date month="July" year="2015" />
</front>
</reference>
<!-- http://dictionary.reference.com/cite.html?qh=pledge&ia=luna
@article {Dictionary.com2015,
title = {Dictionary.com Unabridged},
month = {Jul},
day = {03},
year = {2015},
url = {http://dictionary.reference.com/browse/pledge},
} -->
<reference anchor="pledge"
target="http://dictionary.reference.com/browse/pledge">
<front>
<title>Dictionary.com Unabridged</title>
<author surname="Dictionary.com"></author>
<date month="July" year="2015" />
</front>
</reference>
</references>
</back>
</rfc>
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