Internet DRAFT - draft-pritikin-anima-bootstrapping-keyinfra
draft-pritikin-anima-bootstrapping-keyinfra
ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Informational M. Richardson
Expires: January 7, 2016 SSW
M. Behringer
S. Bjarnason
Cisco
July 6, 2015
Bootstrapping Key Infrastructures
draft-pritikin-anima-bootstrapping-keyinfra-02
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
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 January 7, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Architectural Overview . . . . . . . . . . . . . . . . . . . . 5
3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 7
3.1. Behavior of a new entity . . . . . . . . . . . . . . . . . 8
3.1.1. Discovery and Identity . . . . . . . . . . . . . . . . 10
3.1.2. Imprint . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.3. Enrollment . . . . . . . . . . . . . . . . . . . . . . 12
3.1.4. Being Managed . . . . . . . . . . . . . . . . . . . . 12
3.2. Behavior of a proxy . . . . . . . . . . . . . . . . . . . 13
3.3. Behavior of the Registrar . . . . . . . . . . . . . . . . 13
3.3.1. Entity Authentication . . . . . . . . . . . . . . . . 14
3.3.2. Entity Authorization . . . . . . . . . . . . . . . . . 14
3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 15
3.3.4. Log Verification . . . . . . . . . . . . . . . . . . . 16
3.3.5. Forwarding Authorization Token plus Configuration . . 16
3.4. Behavior of the MASA Service . . . . . . . . . . . . . . . 16
3.4.1. Issue Authorization Token and Log the event . . . . . 17
3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 17
3.5. Leveraging the new key infrastructure / next steps . . . . 17
3.5.1. Network boundaries . . . . . . . . . . . . . . . . . . 17
4. Domain Operator Activities . . . . . . . . . . . . . . . . . . 18
4.1. Instantiating the Domain Certification Authority . . . . . 18
4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 18
4.3. Accepting New Entities . . . . . . . . . . . . . . . . . . 18
4.4. Automatic Enrolment of Devices . . . . . . . . . . . . . . 19
4.5. Secure Network Operations . . . . . . . . . . . . . . . . 19
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. EAP-EST . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2. Request bootstrap token . . . . . . . . . . . . . . . . . 21
5.3. Request MASA authorization token . . . . . . . . . . . . . 21
5.4. Basic Configuration Information Package . . . . . . . . . 22
5.5. Request MASA authorization log . . . . . . . . . . . . . . 23
6. Reduced security operational modes . . . . . . . . . . . . . . 23
6.1. New Entity security reductions . . . . . . . . . . . . . . 24
6.2. Registrar security reductions . . . . . . . . . . . . . . 24
6.3. MASA security reductions . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 26
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.1. Normative References . . . . . . . . . . . . . . . . . . . 26
9.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Editor notes . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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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.
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
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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:
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).
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 that wishes to join a network
acquires it's domain specific identity. 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. [imprinting]
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]
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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Vendor components
.
.+---------------+
+--------------Drop Ship------------------------.| Manufacturer |
| .+---------------+
| .| M anufacturer |
| .| A uthorized |
| .| S igning |
| .| A uthority |
| .+---------------+
V ...... ^
+-------+ |
| New | +------------+ +-----------+ |
| Entity|<--L2-->| Proxy |<----->| | |
| | +------------+ | | |
| | | Registrar | |
| | | | |
| |<-----L3---------------------( may proxy )---------+
| | +-----------+
| | |
| | +----------------------------+
| |<-----Enroll---->| Domain Certification | ^
| |<-----Config---->| Authority | .
+-------+ . | Management and etc | .
. +----------------------------+ .
. .
.........................................
"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
the trust anchor that defines the domain. Optionally, it
certifies all elements.
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.
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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 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. The MASA is recommended to
provide ownership validation services which allows for fully
secure zero-touch bootstrap of domain certificates with mutual
authentication.
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.
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
all such edge conditions are covered by the architectural and
protocol models.
3. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically bootstrap into a key infrastructure deliminating
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.
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---| |
|<----config information----| |
| | |
[authorization token valid?] | |
[apply config information] | |
| | |
|----domain enrolment------>| |
|<----domain certificate----| |
| | |
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.
States of a New Entity are as follows:
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+--------------+
| Start |
| |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input
| Bad MASA +------+-------+
| response |
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Being |
^------------+ Managed |
Factory +--------------+
reset
Figure 3
State descriptions are as follows:
1. Discover a communication channel to the "closest" Registrar by
trying the following steps in this order:
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:
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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. Identify itself. This is done by presenting an 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. Imprint on the Registrar. This requires verification of 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. Enroll by accepting the domain specific information from the
registrar, and by enrolling a domain certificate from the
registrar using a standard enrollment protocol, e.g. Enrolment
over Secure Transport (EST) [RFC7030].
5. The New Entity is now a member of and Being 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 and Identity
Existing architectures provide the functionality for discovery of the
Domain Registrar. Use of an existing architecture is preferred over
development of a new architecture. Discovering of a Domain Proxy
that facilitates communication through to the Domain Registrar is
simplified as "discovery of the domain". A proxy is included in
Figure 1 although the simplified flow in Figure 2 does not include a
proxy - under the assuption that the proxy forwarding is mostly
transparent to the New Entity. Existing architectures for
investigation include:
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"
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 which is assumed to be a member
of the domain infrastructure. In each protocol methods are available
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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. [[EDNOTE: this is the
simplest and most direct threat model but should be evaluated against
the anima use cases. It may be preferable to engage in secure
communications with the proxy itself?]]
The New Entity is expected to identify itself during one of the
communication protocol exchanges. For example using EAP-TLS. If the
client identity is rejected the New Entity repeats the Discovery
process using the next proxy or discovery method available. 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 using an appropriate L3 protocol mechanisms.
[[EDNOTE: it is unclear yet if discovery happens on a per interface
basis or once per device. What is the requirement around joining
multiple domains; is this a bootstrapping requirement or is this a
broader autonomic requirement]]
3.1.2. Imprint
The domain trust anchor is received by the New Entity during the
boostrapping protocol methods in the form of a MASA authorization
token containing the domainID. The goal of the imprint state is to
securely obtain a copy of this trust anchor without involving human
interaction.
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),
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o and using a Certificate-Less TLS mutual authentication method (not
an autonomic solution because the distribution of symmetric key
material is not autonomic).
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.
An arbitrary basic configuration information package that is signed
by the domain can be delivered alongside the authorization token.
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 fails the New Entity returns to discovery
state and attempts bootstrapping with the next available discovered
Registrar.
3.1.3. 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.
o The EST section 4.1.3 CA Certificates Response is verified using
the MASA authorization token provided domain identity.
3.1.4. 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
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issued during enrollment.
See Section 3.5.
3.2. 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 3.1.1, already provide
this functionality nothing additional is defined.
3.3. 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:
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Contacted by New Entity
+
|
+-------v----------+
| Entity | fail?
| Authentication +---------+
+-------+----------+ |
| |
+-------v----------+ |
| Entity | fail? |
| Authorization +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Claiming the | fail? |
| Entity +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Log Verification | fail? |
| +--------->
+-------+----------+ |
| |
+-------v----------+ +----v-------+
| Forward | | |
| Authorization | | Reject |
| token + config | | Device |
| to the Entity | | |
+------------------+ +------------+
Figure 4
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.
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:
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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.
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).
3.3.3. 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
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provides the Registrar with proof, in the form of a MASA
authorization token, that the log entry has been inserted. As
indicated in Section 3.1.2 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.
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 parameters:
o Any nonceless entries in the log are associated with domainIDs
recognized by the registrar. The registar MAY be configured to
ignore the history of the device but it is RECOMMENDED that this
only be configured if the MASA server is known to perform
ownership validation or if Trusted Computing Group secure boot and
remote attestation is available.
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.
3.3.5. Forwarding Authorization Token plus Configuration
The Registrar forwards the received authorization 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 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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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 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.
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.
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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
a manual per device methods do not scale. Here, the registrar is
provided a priori with a list of identifiers of devices that
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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
enrol 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 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.
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 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" [[EDNOTE: out of date xref]] 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 3.3.2. 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".
The request format is a JSON object optionally containing the nonce
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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: The authorization token response format needs to be defined
here. It consists of the nonce, if supplied, the serialnumber and
the trust anchor of the domain. For example:
{"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/
subjectaltname serial number>","domainID":}
]]
[[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. 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 Registar. The New Entity first
verifies the MASA authorization token and, if it is valid, then uses
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the domain's TA to validate the Information Package.
[[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]]
5.5. 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
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 is to support less secure
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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. 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. When configured into lower
security modes by a trusted administrator:
1. 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 or when local staging has pre-
configured the New Entity with a known good Trust Anchor.
2. The device may be configured during staging or requested from the
factory to not require the MASA service authorization token. An
entity that does not validate the domain identity is inherently
dangerous as it may have had malware installed on it by a man-in-
the-middle. 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.
6.2. 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 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. The registrar may request nonce-less authorization 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
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service during New Entity deployment.
6.3. MASA security reductions
Lower security modes chosen by the MASA service effect all device
deployments unless paired with strict device ownership validation, 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 authorization token. This
results in distribution of authorization tokens that never expire
and effectly makes the Domain an always trusted entity to the New
Entity during any subsequent bootstrapping attempts. That this
occured is captured in the log information so that the Domain
registrar can make appropriate security decisions when a new
device joins the domain. This is useful to support use cases
where Registrars might not be online during actual device
deployment.
2. Not verifying ownership before responding with an authorization
token. Doing so relieves the vendor providing MASA services from
having to tracking ownership during shipping and supply chain.
The registrar uses the log information as a defense in depth
strategy to ensure that this does not occur unexpectedly. For
example when purchasing used equipment a MASA response is
necessary for autonomic provisioning but the greatest level of
security is achieved when the MASA server is also performing
ownership validation.
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
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 registar
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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 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. Binding the logs via a ]] Also the
Registrar can double check the log information after enrolling the
New Entity.
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, 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.
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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-07 (work in
progress), March 2015.
[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>.
Appendix A. Editor notes
[[EDNOTE: This section is to capturing rough notes between editors
and Anima Bootstrapping design team members. This entire section to
be removed en masse before finalization]]
Change Discussion:
02 Moved sections for readability, Updated introduction, simplified
functional overview to avoid distractions from optional elements,
addressed updated security considerations, fleshed out state
machines.
The following is a non-prioritized list of work items currently
identified:
o Continue to address gaps/opportunities highlighted by community
work on bootstrappping. Refs: IETF92 "Survey of Security
Bootstrapping", Aana Danping He, behcet Sarikaya. "NETCONF Zero
Touch Update for ANIMA"
https://www.ietf.org/proceedings/92/anima.html and "Bootstrapping
Key Infrastructures", Pritikin, Behringer, Bjarnason
o Intergrate "Ownership Voucher" as a valid optional format for the
MASA response. So long as the issuance of this is logged and
captured in the log response then the basic flow and threat model
is substantially the same.
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o Attempt to re-use existing work as per the charter: Toerless
notes: a) are existing [eap] options? or too complex? or doens't
work? b) our own method (e.g. EAP-ANIMA c) if b then investigate
using signaling protocol).
o
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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