One document matched: draft-ietf-anima-bootstrapping-keyinfra-02.xml
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<front>
<title>Bootstrapping Key Infrastructures</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 key
infrastructure (BSKI) 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 forced to join
only specific domains but in limited/disconnected networks or legacy
environments we describe a variety of options that allow bootstrapping
to proceed.</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"/>.</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" /> 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>
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" />), 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
trusted 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 | | Proxy | | Domain | | Vendor |
| Entity | | | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +-------+ +------------+ +------------+
| | | |
|<-RFC3927 IPv4 adr | | |
or|<-RFC4862 IPv6 adr | | |
| | | |
|-------------------->| | |
| optional: mDNS query| | |
| RFC6763/RFC6762 | | |
| | | |
|<--------------------| | |
| mDNS broadcast | | |
| response or periodic| | |
| | | |
|<------------------->|<----------------->| |
| (d)TLS via the 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 | | |<-audit token-------|
P | | | |
P | | |<-optional: --------|
P | \----> | ownership 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 (d)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. The acceptable
imprint methods are indicated along with a nonce 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 (d)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 in this order:</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>MAY: Performs DNS-based Service Discovery <xref target="RFC6763"></xref> over
Multicast DNS <xref target="RFC6762"></xref> searching for the service
"_bootstrapks._tcp.local."</t>
<t>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. In this case the domain is known so the
service searched for is "_bootstrapks._tcp.example.com".</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".</t>
</list>Once a Registrar is discovered (technically a
communication channel through a Proxy) the New
Entity communicates with the Registrar 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>Once all discovered services are attempted the device SHOULD
return to Multicast DNS and keep trying. The New Entity may
prioritize selection order as appropriate for the anticipated
environment.</t>
<t>[[EDNOTE: An appropriate backoff or rate limiting strategy should
be defined here such that the device doesn't flood the local network
with queries. If the device were to eventually give up -- or at
least have too long between attempts -- a power cycle would restart
the backoff mechanism.]]</t>
</section>
<section 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 authenticated. Thus
this connection is provisional and all data received is untrusted
until sufficiently validated even though it is over a (D)TLS
connection. This is aligned with the existing provisional mode of
EST [RFC7030] during s4.1.1 "Bootstrap Distribution of CA
Certificates".</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 domainID 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 trusted logging server.</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"/>.</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>An arbitrary basic configuration information package that is
signed by the domain can be delivered alongside the Audit Token or
ownership validation. This information is signed by the domain
private keys and is a one time delivery containing information such
as which enrollment server to communicate with and which management
system to communicate with. It is intended as a limited basic
configuration for these purposes and is not intended to deliver
entire final configuration to the device.</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 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>
</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 (d)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" /> 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. The address and port of the Registrar 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.
</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 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, an HTTP proxy which
accepts URLs that reach the Registrar, or a TCP circuit proxy that
connects the New Node to the Registrar.
</t>
<t>
In order to make the HTTP choice above transparent to the New Node,
the New Node will always initiate an HTTP connection, and will
always send an appropriate CONNECT message to initiate an HTTPS
connection to the registrar. [[EDNOTE: The CONNECT syntax
is that the New Entity specifies the Registrar server
in the CONNECT line. See RFC7231 s4.3.6. We wish the Proxy
to override any value with the locally known-to-the-proxy
Registrar address.]]
</t>
<t>
When the Proxy provides a circuit proxy to the Registrar the Registrar
MUST accept HTTP connections,
and be willing to perform an HTTP proxy (CONNECT) operation to
itself, and then initiate HTTPS.
</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.
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" /> for UDP use, and
requires a form of connection latching (see section 4.1 of
<xref target="RFC5386"/> and all of <xref target="RFC5660" />,
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 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,</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"/>]]. </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>
</section>
<section title="Forwarding Audit Token plus Configuration">
<t>The Registrar forwards the received Audit Token to the New
Entity. To simplify the message flows an initial configuration
package can be delivered at this time which is signed by a
representative of the domain.</t>
<t>[[EDNOTE: format TBD. The configuration package signature data
must contain the full certificate path sufficient for the new entity
to use the domainID information (as a trust anchor) to accept and
validate the configuration)]]</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>For simplicity the bootstrapping protocol is described as extensions
to EST [RFC7030].</t>
<t>EST provides a bootstrapping mechanism for new entities that are
configured with the URI of the EST server such that the Implicit TA
database can be used to authenticate the EST server. Alternatively EST
clients can "engage a human user to authorize the CA certificate using
out-of-band data such as a CA certificate". EST does not provide a
completely automated method of bootstrapping the PKI as both of these
methods require some user input (either of the URI or authorizing the CA
certificate).</t>
<t>This section details additional EST functionality that support
automated bootstrapping of the public key infrastructure. These
additions provide for fully automated bootstrapping. These additions are
to be optionally supported by the EST server within the same .well-known
URI tree as the existing EST URIs.</t>
<t>The "New Entity" is the EST client and the "Registrar" is the EST
server.</t>
<t>The extensions for the 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 EST section 4.1.1
("Bootstrap Distribution of CA Certificates").</t>
<t>The Registrar requests and validates the Audit Token from the
vendor authorized MASA service. </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>These extensions could be implemented as an independent protocol from
EST but since the overlap with basic enrollment is extensive,
particularly with respect to client authorization, they are presented
here as additions to EST.</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 | | | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| (D)TLS hello | | |
Establish +---------------> (D)TLS hello | |
(D)TLS | |---------------> |
connection | (forwarding) | |
| Server Cert <---------------+ |
<---------------+ | |
| Client Cert | | |
+-------------------------------> |
| | | |
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 | | | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| | | /requestaudittoken
| | (nonce +---------------->
| | unknown) <----------------+
| | | /requestauditlog
| | +---------------->
| | <----------------+
| (D)TLS hello | | |
Establish +---------------> (D)TLS hello | |
(D)TLS | |---------------> |
connection | (forwarding) | |
| SerVer Cert <---------------+ |
<---------------+ | |
| 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>
<section title="IEEE 802.1AR as client identity">
<t>The Registrar authenticates the client and performs authorization checks to ensure this client is expected to join the domain. This require a common procedure for representing and verifying the identity of the client. The methods
detailed in [RFC6125] such as matching DNS Domain Name or Application
Service Type are not directly applicable.</t>
<t>Clients presents an IEEE 802.AR certificate complete with subject field
identifying the device uniquely in the Distinguished Name serialNumber subfield.
The subjectAltName MAY contain a hardwareModuleName as specified in RFC4108.
The Registrar extracts this
information and compares against a per vendor access control list. (This can
be implemented with a single database table so long as the authority key
identifier is also maintained and checked to ensure that no two vendors
collide in their use of serialNumber's).</t>
<t>When enrollment is complete and a local certificate is issued to the new device
the local CA has complete control over the namespace. If this credential
is intended for RFC6125 style TLS connections where servers are identified by a
server's DNS-ID identity the CA is likely to ensure the dNSName field is populated.
For Anima purposes the IEEE 802.1AR serialNumber and hardwareModuleName fields
MUST be propagated to the issued certificate.</t>
<t>[[EDNOTE: the above authority key identifier trick works for database lookups
and here the inclusion of the DNS name would serve the same purpose.
Alternatively an Anima specified domain specific identifier must be indicated.]]</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]
so this section is anticipated to be relatively straightforward.
A complexity is that the large message sizes necessary
for bootstrapping will require support for [draft-ietf-core-block].]]
</t>
</section>
<section title="Request Audit Token">
<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 nonce.</t>
<t>Request media type: application/auditnonce</t>
<t>Request format: a JSON file with the following:</t>
<t>{"nonce":"<64bit nonce value>",
"OwnershipValidation":boolean}</t>
<t>[[EDNOTE: exact format TBD. There is an advantage to having the
client sign the nonce (similar to a PKI Certification Signing Request)
since this allows the MASA service to confirm the actual device
identity. It is not clear that there is a security benefit from this
since its the New Entity that verifies the nonce.]]</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.
</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 New Entity's serial number is extracted from the
IEEE 802.1AR subject name:</t>
<t>{"nonce":"<64bit nonce value>", "serialnumber",
"<subjectname/subjectaltname serial number>"}</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. If a nonce is not provided the MASA server MUST
authenticate the client as described in EST [RFC7030] section 3.3.2. 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 PKCS7 signed data
structure that is signed by the Registrar. The entire certificate
chain, up to and including the Domain CA, MUST be included in the
PKCS7.</t>
<t>The MASA service checks the internal consistency of the PKCS7 but
MAY 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 PKCS7
is signed by a Registrar certificate (by checking for the cmc-idRA field)
that was issued by a the root certificate included in the PKCS7. This
ensures that the Registrar is in fact an authorized Registrar
of the unknown domain. </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. The authorization
token consists of the nonce, if supplied, the serialnumber
and the domain identity:</t>
<t>{"nonce":"<64bit nonce value>", "serialnumber",
"<subjectname/subjectaltname serial number>","domainID":}</t>
<t>[[EDNOTE: There is a strong similarity between this and the
previous section. Both involve requesting the Audit Token from the
upstream element. Because there are differing requirements on the data
submitted and the signing of that data they are specified in distinct
sections. The design team should have a meeting to discuss how to
unify these sections or make the distinctions more clear]]</t>
</section>
<section title="Basic Configuration Information Package">
<t>When the MASA authorization token is returned to the New Entity an
arbitrary information package can be signed and delivered along side
it. This is signed by the Domain Registrar. The New Entity first
verifies the Audit Token and, if it is valid, then uses the domain's
TA to validate the Information Package.</t>
<t>[[EDNOTE: The domainID as included in the log and as sent in the
authorization token is only a hash of the domain root
certificate. This is insufficient for the new entity to
move out of the provisional state as it needs a full
root certificate to validate the TLS certificate chain. This
information package could be used to deliver the full
certificate or the full certificate could be included in the
authorization token. Lacking either the new entity needs
to stay in the provisional state until it performs an
RFC7030 /getcacerts to obtain the full certificate chain.]]</t>
<t>[[EDNOTE: The package format to be specified here. Any signed
format is viable and ideally one can simply be specified from netconf.
The Registar knows the New Entity device type from the 802.1AR
credential and so is able to determine the proper format for the
configuration.]]</t>
</section>
<section title="Request MASA authorization log">
<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 log data returned is a file consisting of all previous log
entries. For example:</t>
<t><figure>
<artwork><![CDATA["log":[
{"date":"<date/time of the entry>"},
"domainID":"<domainID as extracted from the root
certificate within the PKCS7 of the
audit token request>",
"nonce":"<any nonce if supplied (or NULL)>"},
{"date":"<date/time of the entry>"},
"domainID":"<domainID as extracted from the root
certificate within the PKCS7 of the
audit token request>",
"nonce":"<any nonce if supplied (or 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
can 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 unexpected
nonce-less entries exist this is indicative of the permanent
ability for the unknown 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>
<t>[[EDNOTE: certificate transparency style use of merkle tree
hash's might offer an alternative log entry method]]</t>
</section>
</section>
<section 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 | | Proxy | | Domain | | Vendor |
| Entity | | | | 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. [[EDNOTE: these
claims could be strengthened using by using cryptographic
log techniques to provide append only", cryptographic
assured, publicly auditable logs. Current text
provides for a fully 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 RECOMMENDED when low security models are
needed as the security decisions are being made by the local
administrator:<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.</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>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>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.</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC7030;
<?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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