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Versions: (draft-pritikin-anima-bootstrapping-keyinfra)
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ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Informational M. Richardson
Expires: September 18, 2016 SSW
M. Behringer
S. Bjarnason
Cisco
March 17, 2016
Bootstrapping Key Infrastructures
draft-ietf-anima-bootstrapping-keyinfra-02
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 18, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Scope of solution . . . . . . . . . . . . . . . . . . . . 5
1.3. Trust bootstrap . . . . . . . . . . . . . . . . . . . . . 6
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 6
3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 9
3.1. Behavior of a New Entity . . . . . . . . . . . . . . . . 10
3.1.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 12
3.1.2. Identity . . . . . . . . . . . . . . . . . . . . . . 13
3.1.3. Request Join . . . . . . . . . . . . . . . . . . . . 14
3.1.4. Imprint . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.5. Enrollment . . . . . . . . . . . . . . . . . . . . . 15
3.1.6. Being Managed . . . . . . . . . . . . . . . . . . . . 16
3.2. Behavior of a Proxy . . . . . . . . . . . . . . . . . . . 16
3.2.1. CoAP connection to Registrar . . . . . . . . . . . . 16
3.2.2. HTTPS proxy connection to Registrar . . . . . . . . . 17
3.3. Behavior of the Registrar (Bootstrap Server) . . . . . . 18
3.3.1. Entity Authentication . . . . . . . . . . . . . . . . 19
3.3.2. Entity Authorization . . . . . . . . . . . . . . . . 19
3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 20
3.3.4. Log Verification . . . . . . . . . . . . . . . . . . 20
3.3.5. Forwarding Audit Token plus Configuration . . . . . . 21
3.4. Behavior of the MASA Service . . . . . . . . . . . . . . 21
3.4.1. Issue Authorization Token and Log the event . . . . . 21
3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 22
3.5. Leveraging the new key infrastructure / next steps . . . 22
3.5.1. Network boundaries . . . . . . . . . . . . . . . . . 22
3.6. Interactions with Network Access Control . . . . . . . . 22
4. Domain Operator Activities . . . . . . . . . . . . . . . . . 23
4.1. Instantiating the Domain Certification Authority . . . . 23
4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 23
4.3. Accepting New Entities . . . . . . . . . . . . . . . . . 23
4.4. Automatic Enrollment of Devices . . . . . . . . . . . . . 24
4.5. Secure Network Operations . . . . . . . . . . . . . . . . 24
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 25
5.1. IEEE 802.1AR as client identity . . . . . . . . . . . . . 27
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5.2. EST over CoAP . . . . . . . . . . . . . . . . . . . . . . 28
5.3. Request Audit Token . . . . . . . . . . . . . . . . . . . 28
5.4. Request Audit Token from MASA . . . . . . . . . . . . . . 29
5.5. Basic Configuration Information Package . . . . . . . . . 30
5.6. Request MASA authorization log . . . . . . . . . . . . . 31
6. Reduced security operational modes . . . . . . . . . . . . . 32
6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 32
6.2. New Entity security reductions . . . . . . . . . . . . . 33
6.3. Registrar security reductions . . . . . . . . . . . . . . 33
6.4. MASA security reductions . . . . . . . . . . . . . . . . 34
7. Security Considerations . . . . . . . . . . . . . . . . . . . 34
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.1. Normative References . . . . . . . . . . . . . . . . . . 36
9.2. Informative References . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction
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 [IDevID], and a
corresponding third-party service on the Internet.
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:
o New entity authentication: "Who is this? What is its identity?"
o New entity authorization: "Is it mine? Do I want it? What are
the chances it has been compromised?"
o Domain authentication: "What is this domain's claimed identity?"
o Domain authorization: "Should I join it?"
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
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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.
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.
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.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The following terms are defined for clarity:
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).
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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.
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.[imprinting].
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.
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 [pledge]
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.
Ownership Voucher: A signed voucher from the vendor vouching that a
specific domain "owns" the new entity as defined in
[I-D.ietf-netconf-zerotouch].
1.2. Scope of solution
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 [RFC7228] is best used to describe the
boundaries.
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).
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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.
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.
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).
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.
1.3. Trust bootstrap
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 [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.
2. Architectural Overview
The logical elements of the bootstrapping framework are described in
this section. Figure 1 provides a simplified overview of the
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components. Each component is logical and may be combined with other
components as necessary.
.
.+------------------------+
+--------------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
Figure 1
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.
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.
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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.
New Entity: A new device or virtual machine or software component
that is not yet part of the domain.
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.
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.
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.
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.
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.
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3. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically bootstrap into a key infrastructure delineating the
autonomic domain. See [I-D.irtf-nmrg-autonomic-network-definitions]
for more information.
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.
A representative flow is shown in Figure 2:
+--------+ +-------+ +------------+ +------------+
| 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 | |
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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. | | |
| | | |
| | | |
| | | |
Figure 2
3.1. Behavior of a New Entity
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.
States of a New Entity are as follows:
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+--------------+
| 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
Figure 3
State descriptions for the New Entity are as follows:
1. Discover a communication channel to the "closest" Registrar.
2. 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).
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3. 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.
4. 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)
5. 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) [RFC7030].
6. 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.
The following sections describe each of these steps in more detail.
3.1.1. Discovery
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.
To discover the Domain Bootstrap Server the New Entity performs the
following actions in this order:
a. MUST: Obtains a local address using either IPv4 or IPv6 methods
as described in [RFC4862] IPv6 Stateless Address
AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4
Link-Local Addresses.
b. MAY: Performs DNS-based Service Discovery [RFC6763] over
Multicast DNS [RFC6762] searching for the service
"_bootstrapks._tcp.local."
c. SHOULD: Listen for an unsolicited broadcast response as described
in [RFC6762]. This allows devices to avoid announcing their
presence via mDNS broadcasts and instead silently join a network
by watching for periodic unsolicited broadcast responses.
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d. 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".
e. 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".
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 Section 5. 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.
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.
[[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.]]
3.1.2. Identity
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.
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".
All security associations established are between the new device and
the Bootstrapping server regardless of proxy operations.
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3.1.3. Request Join
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.
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.
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.
3.1.4. Imprint
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.
The enrollment protocol EST [RFC7030] details a set of non-autonomic
bootstrapping methods such as:
o using the Implicit Trust Anchor database (not an autonomic
solution because the URL must be securely distributed),
o engaging a human user to authorize the CA certificate using out-
of-band data (not an autonomic solution because the human user is
involved),
o using a configured Explicit TA database (not an autonomic solution
because the distribution of an explicit TA database is not
autonomic),
o and using a Certificate-Less TLS mutual authentication method (not
an autonomic solution because the distribution of symmetric key
material is not autonomic).
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This document describes additional autonomic methods:
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.
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 [I-D.ietf-netconf-zerotouch].
Since client authentication occurs during the TLS handshake the
bootstrapping server has sufficient information to apply appropriate
policy concerning which method to use.
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.
If the autonomic methods fail the New Entity returns to discovery
state and attempts bootstrapping with the next available discovered
Registrar.
3.1.5. Enrollment
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.
Enrollment proceeds as described in Enrollment over Secure Transport
(EST) [RFC7030]. The New Entity contacts the Registrar using EST as
indicated:
o The New Entity is authenticated using the IEEE 802.1AR
credentials.
o The EST section 4.1.3 CA Certificates Response is verified using
either the Audit Token which provided the domain identity -or-
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o 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.
3.1.6. Being Managed
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.
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.
See Section 3.5.
3.2. Behavior of a Proxy
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.
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.
The document [I-D.richardson-anima-state-for-joinrouter] provides a
more extensive analysis of the alternative proxy methods.
3.2.1. CoAP connection to Registrar
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
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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.]]
As a result of the Proxy Discovery process in section Section 3.1.1,
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.
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.
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.
3.2.2. HTTPS proxy connection to Registrar
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.
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.]]
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.
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
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[RFC3542] for UDP use, and requires a form of connection latching
(see section 4.1 of [RFC5386] and all of [RFC5660], except that a
simple IPIP tunnel is used rather than an IPsec tunnel).
3.3. Behavior of the Registrar (Bootstrap Server)
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.
Registrar behavior is as follows:
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 | | |
+------------------+ +------------+
Figure 4
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3.3.1. Entity Authentication
The applicable authentication methods detailed in EST [RFC7030] are:
o the use of an IEEE 802.1AR IDevID credential,
o 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).
3.3.2. Entity Authorization
In a fully automated network all devices must be securely identified
and authorized to join the domain.
A Registrar accepts or declines a request to join the domain, based
on the authenticated identity presented. Automated acceptance
criteria include:
o allow any device of a specific type (as determined by the IEEE
802.1AR device identity),
o allow any device from a specific vendor (as determined by the IEEE
802.1AR identity),
o allow a specific device from a vendor (as determined by the IEEE
802.1AR identity)
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.
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.
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
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cached for the TLS session and applied to subsequent EST enrollment
requests so long as the session lasts.
3.3.3. Claiming the New Entity
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 Section 3.1.4 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.
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 [I-D.lear-mud-framework]]].
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.
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.
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.
3.3.4. Log Verification
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:
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o Any nonceless entries in the log are associated with domainIDs
recognized by the registrar.
o 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.
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.
3.3.5. Forwarding Audit Token plus Configuration
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.
[[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)]]
3.4. Behavior of the MASA Service
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).
The MASA service provides the following functionalities to
Registrars:
3.4.1. Issue Authorization Token and Log the event
A Registrar POSTs a claim message optionally containing the bootstrap
nonce to the MASA server.
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.
If a nonce is not provided then the MASA service MUST authenticate
the Registrar as a valid customer. This prevents denial of service
attacks.
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3.4.2. Retrieve Audit Entries from Log
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.
3.5. Leveraging the new key infrastructure / next steps
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.
Examples of services:
o Device management.
o Routing authentication.
o Service discovery.
3.5.1. Network boundaries
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.
3.6. Interactions with Network Access Control
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.
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.
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4. Domain Operator Activities
This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.
4.1. Instantiating the Domain Certification Authority
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.
4.2. Instantiating the Registrar
This is a one time step by the domain administrator. One or more
devices in the domain are configured take on a Registrar function.
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.
4.3. Accepting New Entities
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:
1. 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.
2. 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 [I-D.behringer-homenet-trust-bootstrap] for
how the approach could work in a homenet.
3. Whitelist acceptance: In larger networks, neither of the previous
approaches is acceptable. Default acceptance is not secure, and
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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.
4. 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.
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.
Additional policy can be stored for future authorization decisions.
For example an expected deployment time window or that a certain
Proxy must be used.
4.4. Automatic Enrollment of Devices
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.
4.5. Secure Network Operations
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 Section 3.5.1. 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.
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5. Protocol Details
For simplicity the bootstrapping protocol is described as extensions
to EST [RFC7030].
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).
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.
The "New Entity" is the EST client and the "Registrar" is the EST
server.
The extensions for the client are as follows:
o 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").
o The Registrar requests and validates the Audit Token from the
vendor authorized MASA service.
o 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.
o The New Entity calls the EST defined /cacerts method to obtain the
current CA certificate. These are validated using the Audit
Token.
o The New Entity completes bootstrapping as detailed in EST section
4.1.1.
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.
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In order to obtain a validated Audit Token and Audit Log the
Registrar contacts the MASA service Service using REST calls:
+-----------+ +----------+ +-----------+ +----------+
| 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) | |
| . | |
| . | |
Figure 5
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:
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+-----------+ +----------+ +-----------+ +----------+
| 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) | |
| . | |
| . | |
Figure 6
5.1. IEEE 802.1AR as client identity
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.
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
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as the authority key identifier is also maintained and checked to
ensure that no two vendors collide in their use of serialNumber's).
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.
[[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.]]
5.2. EST over CoAP
[[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].]]
5.3. Request Audit Token
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.
This is done with an HTTPS POST using the operation path value of
"/requestaudittoken".
The request format is JSON object containing a nonce.
Request media type: application/auditnonce
Request format: a JSON file with the following:
{"nonce":"<64bit nonce value>", "OwnershipValidation":boolean}
[[EDNOTE: exact format TBD. There is an advantage to having the
client sign the nonce (similar to a PKI Certification Signing
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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.]]
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).
The received MASA authorization token is returned to the New Entity.
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.
5.4. Request Audit Token from MASA
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).
This is done with an HTTP POST using the operation path value of
"/requestaudittoken".
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:
{"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
subjectaltname serial number>"}
The Registrar MAY exclude the nonce from the request. Doing so
allows the Registrar to request an authorization token when the New
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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 Section 3.3.2. If authorization is successful the
Registrar obtains an Audit Token from the MASA service (see
Section 5.4).
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.
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.
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:
{"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
subjectaltname serial number>","domainID":}
[[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]]
5.5. Basic Configuration Information Package
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.
[[EDNOTE: The domainID as included in the log and as sent in the
authorization token is only a hash of the domain root certificate.
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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.]]
[[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.]]
5.6. Request MASA authorization log
A registrar requests the MASA authorization log from the MASA service
using this EST extension.
This is done with an HTTP GET using the operation path value of
"/requestMASAlog".
The log data returned is a file consisting of all previous log
entries. For example:
"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)>"},
]
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.
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
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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.
Log entries containing the Domain's ID can be compared against local
history logs in search of discrepancies.
[[EDNOTE: certificate transparency style use of merkle tree hash's
might offer an alternative log entry method]]
6. Reduced security operational modes
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.
6.1. Trust Model
+--------+ +-------+ +------------+ +------------+
| New | | Proxy | | Domain | | Vendor |
| Entity | | | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +-------+ +------------+ +------------+
Figure 7
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.
Proxy: Provides proxy functionalities but is not involved in
security considerations.
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.
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
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provide append only", cryptographic assured, publicly auditable
logs. Current text provides for a fully trusted vendor.]]
Vendor Service, Ownership Validation: This form of vendor service is
trusted to accurately know which device is owned by which domain.
6.2. New Entity security reductions
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.
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.
It is RECOMMENDED that this only be available if hardware assisted
NEA [RFC5209] is supported.
6.3. Registrar security reductions
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:
1. 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.
2. 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.
3. 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.
4. The registrar MAY ignore unrecognized nonce-less Audit Log
entries. This could occur when used equipment is purchased with
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a valid history being deployed in air gap networks that required
permanent Audit Tokens.
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.
6.4. MASA security reductions
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:
1. 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.
2. 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).
7. Security Considerations
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
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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.
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.
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:
o Per device rate limits on the MASA service ensure such timing
attacks are difficult.
o In the advent of an unexpectedly lost bootstrapping connection the
Registrar repeats the request for audit log information.
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.
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.
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8. Acknowledgements
We would like to thank the various reviewers for their input, in
particular Markus Stenberg, Brian Carpenter, Fuyu Eleven.
9. References
9.1. Normative References
[IDevID] IEEE Standard, , "IEEE 802.1AR Secure Device Identifier",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 3542, May 2003.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
Security: An Unauthenticated Mode of IPsec", RFC 5386,
November 2008.
[RFC5660] Williams, N., "IPsec Channels: Connection Latching",
RFC 5660, October 2009.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
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[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
9.2. Informative References
[I-D.behringer-homenet-trust-bootstrap]
Behringer, M., Pritikin, M., and S. Bjarnason,
"Bootstrapping Trust on a Homenet", draft-behringer-
homenet-trust-bootstrap-02 (work in progress), February
2014.
[I-D.ietf-ace-actors]
Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
architecture for authorization in constrained
environments", draft-ietf-ace-actors-03 (work in
progress), March 2016.
[I-D.ietf-netconf-zerotouch]
Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
for NETCONF or RESTCONF based Management", draft-ietf-
netconf-zerotouch-07 (work in progress), March 2016.
[I-D.irtf-nmrg-autonomic-network-definitions]
Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking - Definitions and Design Goals", draft-irtf-
nmrg-autonomic-network-definitions-07 (work in progress),
March 2015.
[I-D.lear-mud-framework]
Lear, E., "Manufacturer Usage Description Framework",
draft-lear-mud-framework-00 (work in progress), January
2016.
[I-D.richardson-anima-state-for-joinrouter]
Richardson, M., "Considerations for stateful vs stateless
join router in ANIMA bootstrap", draft-richardson-anima-
state-for-joinrouter-00 (work in progress), January 2016.
[imprinting]
Wikipedia, , "Wikipedia article: Imprinting", July 2015,
<https://en.wikipedia.org/wiki/Imprinting_(psychology)>.
[pledge] Dictionary.com, , "Dictionary.com Unabridged", July 2015,
<http://dictionary.reference.com/browse/pledge>.
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Authors' Addresses
Max Pritikin
Cisco
Email: pritikin@cisco.com
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z 5V7
CA
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Michael H. Behringer
Cisco
Email: mbehring@cisco.com
Steinthor Bjarnason
Cisco
Email: sbjarnas@cisco.com
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