ANIMA WG M. Pritikin
Internet-Draft M. Behringer
Intended status: Informational S. Bjarnason
Expires: August 17, 2015 Cisco
February 13, 2015
Bootstrapping Key Infrastructures
draft-pritikin-anima-bootstrapping-keyinfra-01
Abstract
This document specifies automated bootstrapping of an key
infrastructure 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 for constrained environments
we describe a variety of options that allow bootstrapping to proceed.
Status of This Memo
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on August 17, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
3. Operational Overview . . . . . . . . . . . . . . . . . . . . 7
3.1. Instantiating the Domain Certification Authority . . . . 7
3.2. Instantiating the Registrar . . . . . . . . . . . . . . . 7
3.3. Accepting New Entities . . . . . . . . . . . . . . . . . 8
3.4. Automatic Enrolment of Devices . . . . . . . . . . . . . 9
3.5. Operating the Network . . . . . . . . . . . . . . . . . . 9
4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 9
4.1. Behavior of a new entity . . . . . . . . . . . . . . . . 10
4.1.1. Proxy Discovery . . . . . . . . . . . . . . . . . . . 11
4.1.2. Receiving and accepting the Domain Identity . . . . . 12
4.1.3. Enrollment . . . . . . . . . . . . . . . . . . . . . 13
4.1.4. After Enrollment . . . . . . . . . . . . . . . . . . 13
4.2. Behavior of a proxy . . . . . . . . . . . . . . . . . . . 13
4.3. Behavior of the Registrar . . . . . . . . . . . . . . . . 14
4.3.1. Authenticating the Device . . . . . . . . . . . . . . 14
4.3.2. Accepting the Entity . . . . . . . . . . . . . . . . 14
4.3.3. Claiming the new entity . . . . . . . . . . . . . . . 15
4.4. Behavior of the MASA Service . . . . . . . . . . . . . . 15
4.4.1. Issue Authorization Token and Log the event . . . . . 16
4.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 16
4.5. Leveraging the new key infrastructure / next steps . . . 16
4.5.1. Network boundaries . . . . . . . . . . . . . . . . . 16
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 17
5.1. EAP-EST . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2. Request bootstrap token . . . . . . . . . . . . . . . . . 18
5.3. Request MASA authorization token . . . . . . . . . . . . 18
5.4. Request MASA authorization log . . . . . . . . . . . . . 19
6. Reduced security operational modes . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 22
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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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 an established key infrastructure(s). 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 trusted third-party. The new entity's
decisions are made according to verified communication with a trusted
third-party or in a strictly auditable fasion.
Optimal security is achieved with IEEE 802.1AR certificates on each
new entity, accompanied by a third-party Internet based service for
verification. The concept also works with less requirements, but is
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.
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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 communiciations with an Internet based
service, which is itself authenticated using HTTPS, bootstrapping of
a domain specific Public Key Infrastructure (PKI) is fully described.
Sufficient agility to support bootstrapping alternative key
infrastructures (such as symmetric key solutions) is considered
although no such 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:
2. Architectural Overview
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.
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Factory components
.
. +------------+
. | Factory CA |
. +------------+
. |
. +------------+
. | |
+--------------(provides)---------------------------| Factory |
| +---------->| |
| | . +------------+
| V .
| +---------------+ . +------------+
| | Orchestrator | . | MASA |
V +---------------+ . | Service |
+-------+ | . | |
| New | +------------+ +-----------+ . +------------+
| Entity|<--L2-->| Proxy |<----->| | ....... ^
| | +------------+ | | |
| | | Registrar | |
| | | | |
| |<--DHCP-->(L3 bootstrap) | | |
| | | | |
| |<-----L3---------------------( registrar )-----------+
| | ( may proxy ) |
+-------+ +-----------+
|
+----------------------------+
^ | Domain Certification | ^
. | Authority | .
. +----------------------------+ .
. .
.........................................
|
"domain" components
Figure 1
Domain: The set of entities that trust a common key infrastructure
trust anchor.
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
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the trust anchor that defines the domain. Optionally, it
certifies all elements.
Domain Identity: 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).
Orchestrator: Although bootstrapping of an individual device is
automated and requires zero administrative involvement
(particularly on the New Entity) the orchestrator drives general
operations of the domain. This can be an automated process or a
human administrator, see Section 3.3 for more details.
Factory: This instantiates the New Entity. For physical devices
this can be representative of third-party vendor manufacturing,
ordering and shipping process(es) that results in a physical
hardware device with an IEEE 802.1AR identity being drop shipped
to a destination domain for physical installation. In a virtual
machine environment this can be the virtual machine hypervisor
control software that initiates a virtual machine instance, in
which case the factory is a "virtual factory" and might be managed
by the domain itself.
Factory CA: This Certification Authority is leveraged by the Factory
to issue IEEE 802.1AR identities to each New Entity. For a
virtual factory it may be reasonable to assume the domain
certification authority is directly used but in a complex
environment it is assumed the Factory does not have direct access
to the Domain Certification Authority.
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
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in an environment where they are not provided L3 connectivity
until after they are validated as members of the domain.
MASA Service: A Manufacturer Authorized Signing Authority (MASA)
service on the global Internet. At a minimum the MASA provides a
trusted repository for audit information concerning privacy
protected bootstrapping events. As a service offering the MASA
can incorporate many of the bootstrapping elements (such as the
Registrar and the Domain CA) into the overall service. The MASA
is not a mandatory component, but it enables the new device to
validate which domain it is joining. This allows for a completely
secure zero-touch bootstrap of domain certificates with mutual
authentication (device <-> domain).
We assume a multi-vendor network. In such an environment, there
could a MASA for each vendor that supports devices following this
document's specification, or an integrator could provide a MASA
service for all devices which he supplies. Note again that the MASA
is not mandatory. Also, this approach 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.
3. Operational Overview
This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.
3.1. 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.
3.2. 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.
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3.3. Accepting New Entities
For each New Entity the Registrar is informed 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 itself
provides its identity to the registrar, which then accepts any
device blindly, without validating its identity. This mode does
not provide any security against intruders and is not
recommended.
2. Per device acceptance: Also here the device provides its identity
directly to the registrar during enrollment. 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 approach: In larger networks, neither of the previous
approaches is acceptable. Default acceptance is not secure, and
a manual real-time acceptance per device does 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 for example
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 or declined.
4. Automated Orchestrator: an automated process that queries the
MASA service or an inventory database either a priori for all
devices, or in real time for each new device. It feeds this
information into the Registrar. Once set up, no human
intervention is required in this process.
None of the approaches requires 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. In this case devices
can enrol later even in a completely isolated network.
Additional policy can be stored for future authorization decisions.
For example an expected deployment time window or that a certain
Proxy must be used.
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3.4. Automatic Enrolment of Devices
The approach outlined in this document provides a secure zero-touch
method to enrol 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.
3.5. Operating the Network
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 4.5.1. 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.
4. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically establish a key infrastructure deliminating the
autonomic domain. See [I-D.irtf-nmrg-autonomic-network-definitions]
for more information.
The overall flow is shown in Figure 2:
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+---------+ +----------+ +-----------+
| New | | | | MASA |
| Entity | | Domain | | Service |
| | | | | (Internet)|
+---------+ +----------+ +-----------+
| | |
|<-------discovery--------->| |
|---802.1AR credential----->| |
| | |
| [ accept device? ] |
| | |
| |---802.1AR identity-------->|
| |---Domain ID--------------->|
| | |
| | [device belongs]
| | [to domain? ]
| | |
| | [update audit log]
| | |
| |<---device history log------|
| |<-- authorization token-----|
| | |
| [ still accept device?] |
| | |
|<----authorization token---| |
|<----domain information----| |
| | |
[auth token valid?] | |
| | |
|----domain enrolment------>| |
|<----domain certificate----| |
| |
Figure 1
4.1. Behavior of a new entity
A New Entity that has not yet been bootstrapped attempts to find a
local domain and join it. A number of methods are attempted for
establishing communications with the domain in a specified order.
Client behavior is as follows:
1. Discover a communication channel to the "closest" Registrar by
trying the following steps in this order:
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A. Search for a Proxy on the local link using a link local
discovery protocol (no routable addresses are required for
this approach). If multiple local proxies are discovered
attempt communications with each before widening the search
to other options. The proxy relays information to the
registrar. If this fails:
B. Obtain an IP address using existing methods, such as SLAAC or
DHCPv6, and search for a local registrar using DNS service
discovery. If this fails:
C. Obtain an IP address (as above), and search for the domain
registrar using a pre-defined Factory provided Internet based
re-direct service. Various methods could be used, such as
DNS or RESTful APIs.
2. Present IEEE 802.1AR credentials to the discovered Registrar (via
a Proxy if necessary). Included is a generated nonce that is
specific to this attempt.
3. Verify the MASA service generated authorization token as provided
by the contacted Registrar. The authorization token contains the
valid domain(s) for this device and is signed by the MASA
service. The device uses a pre-installed certificate of the MASA
service to validate the signature of the MASA. The nonce
information previously provided is also checked, if it was not
removed by the Registrar.
4. If and only if step three is successful: Join Domain, by
accepting the domain specific information from the registrar, and
by enrolling a domain certificate from the registrar.
5. The New Entity is now a member of 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.
4.1.1. Proxy Discovery
Existing protocols provide the appropriate functionality for both
discovering the Proxy and facilitating communication through the
Proxy:
IEEE 802.1X Where the New Entity can be cast as the "supplicant" and
the Proxy is the "authenticator". The bootstrapping protocol
messages are encapsulated as EAP methods. The "authenticator"
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reencapsulates the EAPOL frames and forwards them to the
"Authentication Server", which provides Registrar functionalities.
PANA [RFC5191] [[EDNOTE: TBD]]
ND [RFC2461] / [RFC4861] [[EDNOTE: TBD]] NOTE: Neighbor Discovery
protocols do not describe a mechanism for forwarding messages.
Each provides a method for the New Entity to discover and initiate
communication with a local neighbor. In each protocol methods are
available to support encapsulation of the bootstrapping protocol
messages described elsewhere in this document. Other protocols for
transporting bootstrapping messages can be added in future
references.
All security assocaitions established are between the new device and
the Registrar regardless of proxy operations.
If multiple proxies are available the New Entity tries each until a
successful bootstrapping occurs. The New Entity may prioritize
proxies selection order as appropriate for the anticipated
environment.
If Proxy discovery fails the New Entity moves on to discovering a
Registrar directly.
4.1.2. Receiving and accepting the Domain Identity
The domain trust anchor is received by the New Entity during the
boostrapping protocol exchange.
An enrollment protocol such as 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 an additional autonomic method:
MASA authorization token Authorization tokens are obtained by the
Registrar from the MASA service and presented to the New Entity
for validation.
If the autonomic methods fails the New Entity returns to discovery
state and attempts bootstrapping with the next available discovered
Registrar.
4.1.3. 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. (EST support for .
o The EST section 4.1.3 CA Certificates Response is verified using
the MASA authorization token provided domain identity.
4.1.4. After Enrollment
Functionality to provide generic "configuration" 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.
See Section 4.5.
4.2. Behavior of a proxy
The role of the Proxy is to facilitate communications. The Proxy
forwards messages between the New Entity and a Registrar. Where
existing protocols, as detailed in Section 4.1.1, already provide
this functionality nothing additional is defined.
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4.3. Behavior of the Registrar
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:
4.3.1. Authenticating the Device
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).
4.3.2. Accepting the Entity
In a fully automated network all devices must be securely identified.
A Registrar accepts or declines a request to join the domain, based
on the authenticated identity presented and other policy defined
criteria such as Proxy identity. 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 Factory (as determined by the
IEEE 802.1AR identity),
o allow a specific device from a Factory (as determined by the IEEE
802.1AR identity)
In all cases a Registrar must use the globally available MASA service
to verify that the device's history log does not include unexpected
Registrars. Because if a device had previously registered with
another domain, the registrar of that domain would show in the log.
If a device is accepted into the domain, it is then invited to
request a domain certificate through a certificate enrolment 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.
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For each entity that will be accepted a Registrar maintains the
Factory CA identity and the entity's unique identifier. The Factory
CA identity could be implemented as the Factory CA root certificate
keyIdentifier (the 160-bit SHA-1 hash of the value of the BIT STRING
subjectPublicKey). For user interface purposes the keyIdentifier
information can be mapped to a colloquial Factory name (Registrars
can be shipped with the keyIdentifier of a significant number of
third-party manufacturers).
4.3.3. Claiming the new entity
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 Internet
based MASA service. If a nonce is provided by the Registrar, then
claims from an unauthenticated Registrar are serviced by the MASA
resource.
The Registrar can claim a New Entity that is not online by forming
the request using the entities unique identifier but not including a
nonce in the claim request. MASA authorization 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.
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 4.1.2 a New Entity will only proceed with
bootstrapping if a validated MASA authorization token has been
recieved. The New Entity therefore enforces that bootstrapping only
occurs if the claim has been logged.
4.4. 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 be
provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA
authorization token Distribution Point" extension).
The MASA service provides the following functionalities to
Registrars:
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4.4.1. 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 authorization 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. The specific level of authentication provided by the
customer is not defined here. An MASA Practice Statement (MPS)
similar to the Certification Authority CPS, as defined in RFC5280, is
provided by the Factory such that Registrar's can determine the level
of trust they have in the Factory.
4.4.2. 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.
4.5. 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.
4.5.1. 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.
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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 New Entity request and validates a "bootstrap 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 "bootstrap
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.
In order to obtain a validated bootstrap token and history logs the
Registrar contacts the MASA service Service using REST calls.
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5.1. EAP-EST
In order to support Proxy environments EAP-EST is defined.
[[EDNOTE: TBD. EST is TLS with some data. EAP-TLS and other similar
protocols provide an example framework for filling out this section]]
5.2. Request bootstrap 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
"/requestbootstraptoken".
The request format is JSON object containing a nonce.
Request media type: application/masanonce
Request format: a json file with the following:
{"nonce":"<64bit nonce value>"}
[[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.]]
The Registrar validates the client identity as described in EST
[RFC7030] section 3.3.2. The registrar performs authorization as
detailed in Section 4.3.2. If authorization is successful the
Registrar obtains a MASA authorization token from the MASA service
(see Section 5.3).
The recieved MASA authorization token is returned to the New Entity.
5.3. Request MASA authorization token
A registrar requests the MASA authorization token from the MASA
service using a REST interface.
This is done with an HTTP POST using the operation path value of
"/requestMASAauthorization".
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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 subject name :
{"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
subjectaltname serial number>"}
Inclusion of the nonce is optional because the Registar might request
an authorization token when the New Entity is not online, or when the
target bootstrapping environment is not on the same network as the
MASA server.
This 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, is included in the PKCS7.
The MASA service checks the internal consistency of the PKCS7 but is
unable to actually 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 verifies that the PKCS7 is
signed by a Registrar (by checking for the cmc-idRA field in the
Registrar certificate) certificate that was issued by the root
certificate included in the PKCS7.
The domain ID is extracted from the root certificate and is used to
generate the MASA authorization token and to update the audit log.
[[EDNOTE: This assumes the Registrar can extract the serial number
successfullly from the cilent certificate. The RFC4108
hardwareModuleName is likely the best known location.]]
5.4. 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:
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"log":[
{"date":"<date/time of the entry>"},
"domainID":"<domainID as extracted from the root
certificate within the PKCS7 of the
authorization 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
authorization 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: only the most recent nonce'd log entry is
required in the response. 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.
[[EDNOTE: certificate transparency might offer an alternative log
entry method]]
6. Reduced security operational modes
A common requirement of bootstrapping infrastructures is often that
they support less secure operational modes. To support these
operational modes the Registrar can choose to accept devices using
less secure methods. For example:
1. The registrar may choose to accept all devices, or all devices of
a particular type, at the administrator's discretion. This may
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 may occur when: The New Entity does not include
an IEEE 802.1AR factory installed credential.
3. A representative of the Registrar (e.g. the Orchestrator) may
request nonce-less authorization tokens from the MASA service
when network connectivity is available. These tokens can then be
transmitted to the Registrar and stored until they are needed
during bootstrapping operations. This may occur when: The target
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network is protected by an air gap and therefore can not contact
the MASA service during New Entity deployment.
4. The device may have an operational mode where it skips
authorization token validation. For example if a physical button
is depressed during the bootstrapping operation. This may occur
when: A device Factory goes out of business or otherwise fails to
provide a reliable MASA service.
5. The device may not require the MASA service authorization token.
An entity that does not validate the domain identity is
inherently dangerous as it may contain malware. This risk should
be mitigated using attestation and measurement technologies. In
order to support an unsecured imprint the New Entity MUST support
remote attestation technologies such as is defined by the Trusted
Computing Group. [[EDNOTE: How to include remote attestation
into the boostrapping protocol exchange is TBD]]. This may occur
when: The device Factory does not provide a MASA service.
7. Security Considerations
In order to support a 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. 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, must now 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.
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 authorization token to take control of
the New Entity but then proceed to enrol with the target domain. To
prevent this the MASA service is rate limited to only generate
authorization tokens at a rate of 1 per minute. The Registrar
therefore has at least 1 minute to get the response back to the New
Entity. [[EDNOTE: a better solution can likely be found. This text
captures the issue for now.]] Also the Registrar can double check the
log information after enrolling the New Entity.
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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. This can be
mitigated by Registrars that request nonce-less authorization tokens.
7.1. Trust Model
[[EDNOTE: (need to describe that we need to trust the device h/w. To
be completed.)]]
8. Acknowledgements
We would like to thank the various reviewers for their input, in
particular Markus Stenberg, Michael Richardson, 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, March 1997.
[RFC7030] Pritikin, M., Yee, P., and D. Harkins, "Enrollment over
Secure Transport", RFC 7030, October 2013.
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.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-05 (work in progress),
December 2014.
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Authors' Addresses
Max Pritikin
Cisco
Email: pritikin@cisco.com
Michael H. Behringer
Cisco
Email: mbehring@cisco.com
Steinthor Bjarnason
Cisco
Email: sbjarnas@cisco.com
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