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dtbootstrap-anima-keyinfra-11.txt
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ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Standards Track M. Richardson
Expires: August 24, 2018 SSW
M. Behringer
S. Bjarnason
Arbor Networks
K. Watsen
Juniper Networks
February 20, 2018
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
draft-ietf-anima-bootstrapping-keyinfra-11
Abstract
This document specifies automated bootstrapping of a remote secure
key infrastructure (BRSKI) using manufacturer installed X.509
certificate, in combination with a manufacturer's authorizing
service, both online and offline. Bootstrapping a new device can
occur using a routable address and a cloud service, or using only
link-local connectivity, or on limited/disconnected networks.
Support for lower security models, including devices with minimal
identity, is described for legacy reasons but not encouraged.
Bootstrapping is complete when the cryptographic identity of the new
key infrastructure is successfully deployed to the device but the
established secure connection can be used to deploy a locally issued
certificate to the device as well.
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 August 24, 2018.
Pritikin, et al. Expires August 24, 2018 [Page 1]
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Copyright Notice
Copyright (c) 2018 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Other Bootstrapping Approaches . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Scope of solution . . . . . . . . . . . . . . . . . . . . 8
1.4. Leveraging the new key infrastructure / next steps . . . 10
1.5. Requirements for Autonomic Network Infrastructure (ANI)
devices . . . . . . . . . . . . . . . . . . . . . . . . . 10
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 11
2.1. Behavior of a Pledge . . . . . . . . . . . . . . . . . . 12
2.2. Secure Imprinting using Vouchers . . . . . . . . . . . . 14
2.3. Initial Device Identifier . . . . . . . . . . . . . . . . 15
2.4. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 16
2.4.1. Architectural component: Pledge . . . . . . . . . . . 18
2.4.2. Architectural component: Circuit Proxy . . . . . . . 18
2.4.3. Architectural component: Domain Registrar . . . . . . 18
2.4.4. Architectural component: Manufacturer Service . . . . 18
2.5. Lack of realtime clock . . . . . . . . . . . . . . . . . 18
2.6. Cloud Registrar . . . . . . . . . . . . . . . . . . . . . 19
2.7. Determining the MASA to contact . . . . . . . . . . . . . 20
3. Voucher-Request artifact . . . . . . . . . . . . . . . . . . 20
3.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 20
3.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 23
4. Proxy details . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1. Pledge discovery of Proxy . . . . . . . . . . . . . . . . 27
4.1.1. Proxy GRASP announcements . . . . . . . . . . . . . . 28
4.2. CoAP connection to Registrar . . . . . . . . . . . . . . 28
4.3. HTTPS Proxy connection to Registrar . . . . . . . . . . . 28
4.4. Proxy discovery of Registrar . . . . . . . . . . . . . . 29
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 30
5.1. BRSKI-EST TLS establishment details . . . . . . . . . . . 32
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5.2. Pledge Requests Voucher from the Registrar . . . . . . . 32
5.3. BRSKI-MASA TLS establishment details . . . . . . . . . . 34
5.4. Registrar Requests Voucher from MASA . . . . . . . . . . 34
5.5. Voucher Response . . . . . . . . . . . . . . . . . . . . 37
5.5.1. Completing authentication of Provisional TLS
connection . . . . . . . . . . . . . . . . . . . . . 38
5.6. Voucher Status Telemetry . . . . . . . . . . . . . . . . 39
5.7. MASA authorization log Request . . . . . . . . . . . . . 40
5.7.1. MASA authorization log Response . . . . . . . . . . . 41
5.8. EST Integration for PKI bootstrapping . . . . . . . . . . 42
5.8.1. EST Distribution of CA Certificates . . . . . . . . . 43
5.8.2. EST CSR Attributes . . . . . . . . . . . . . . . . . 43
5.8.3. EST Client Certificate Request . . . . . . . . . . . 44
5.8.4. Enrollment Status Telemetry . . . . . . . . . . . . . 44
5.8.5. EST over CoAP . . . . . . . . . . . . . . . . . . . . 45
6. Reduced security operational modes . . . . . . . . . . . . . 45
6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 45
6.2. Pledge security reductions . . . . . . . . . . . . . . . 46
6.3. Registrar security reductions . . . . . . . . . . . . . . 47
6.4. MASA security reductions . . . . . . . . . . . . . . . . 48
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
7.1. PKIX Registry . . . . . . . . . . . . . . . . . . . . . . 49
7.2. Voucher Status Telemetry . . . . . . . . . . . . . . . . 49
8. Security Considerations . . . . . . . . . . . . . . . . . . . 49
8.1. Freshness in Voucher-Requests . . . . . . . . . . . . . . 51
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 52
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
10.1. Normative References . . . . . . . . . . . . . . . . . . 52
10.2. Informative References . . . . . . . . . . . . . . . . . 55
Appendix A. IPv4 operations . . . . . . . . . . . . . . . . . . 56
A.1. IPv4 Link Local addresses . . . . . . . . . . . . . . . . 57
A.2. Use of DHCPv4 . . . . . . . . . . . . . . . . . . . . . . 57
Appendix B. mDNS / DNSSD proxy discovery options . . . . . . . . 57
Appendix C. IPIP Join Proxy mechanism . . . . . . . . . . . . . 58
C.1. Multiple Join networks on the Join Proxy side . . . . . . 58
C.2. Automatic configuration of tunnels on Registrar . . . . . 59
C.3. Proxy Neighbor Discovery by Join Proxy . . . . . . . . . 59
C.4. Use of connected sockets; or IP_PKTINFO for CoAP on
Registrar . . . . . . . . . . . . . . . . . . . . . . . . 60
C.5. Use of socket extension rather than virtual interface . . 60
Appendix D. MUD Extension . . . . . . . . . . . . . . . . . . . 60
Appendix E. Example Vouchers . . . . . . . . . . . . . . . . . . 62
E.1. Keys involved . . . . . . . . . . . . . . . . . . . . . . 62
E.1.1. MASA key pair for voucher signatures . . . . . . . . 62
E.1.2. Manufacturer key pair for IDevID signatures . . . . . 62
E.1.3. Registrar key pair . . . . . . . . . . . . . . . . . 63
E.1.4. Pledge key pair . . . . . . . . . . . . . . . . . . . 65
E.2. Example process . . . . . . . . . . . . . . . . . . . . . 66
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E.2.1. Pledge to Registrar . . . . . . . . . . . . . . . . . 66
E.2.2. Registrar to MASA . . . . . . . . . . . . . . . . . . 72
E.2.3. MASA to Registrar . . . . . . . . . . . . . . . . . . 78
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 83
1. Introduction
BRSKI provides a foundation to securely answer the following
questions between an element of the network domain called the
"Registrar" and an unconfigured and untouched device called a
"Pledge":
o Registrar authenticating the Pledge: "Who is this device? What is
its identity?"
o Registrar authoring the Pledge: "Is it mine? Do I want it? What
are the chances it has been compromised?"
o Pledge authenticating the Registrar/Domain: "What is this domain's
identity?"
o Pledge authorizing the Registrar: "Should I join it?"
This document details protocols and messages to the endpoints to
answer the above questions. The Registrar actions derive from Pledge
identity, third party cloud service communications, and local access
control lists. The Pledge actions derive from a cryptographically
protected "voucher" message delivered through the Registrar but
originating at a Manufacturer Authorized Signing Authority.
The syntactic details of vouchers are described in detail in
[I-D.ietf-anima-voucher]. This document details automated protocol
mechanisms to obtain vouchers, including the definition of a
'voucher-request' message that is a minor extension to the voucher
format (see Section 3) defined by [I-D.ietf-anima-voucher].
BRSKI results in the Pledge storing an X.509 root certificate
sufficient for verifying the Registrar identity. In the process a
TLS connection is established that can be directly used for
Enrollment over Secure Transport (EST). In effect BRSKI provides an
automated mechanism for the "Bootstrap Distribution of CA
Certificates" described in [RFC7030] Section 4.1.1 wherein the Pledge
"MUST [...] engage a human user to authorize the CA certificate using
out-of-band" information". With BRSKI the Pledge now can automate
this process using the voucher. Integration with a complete EST
enrollment is optional but trivial.
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BRSKI is agile enough to support bootstrapping alternative key
infrastructures, such as a symmetric key solutions, but no such
system is described in this document.
1.1. Other Bootstrapping Approaches
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 commonly
accepted that the initial connections between nodes are insecure,
until key distribution is complete, or that domain-specific keying
material (often pre-shared keys, including mechanisms like SIM cards)
is pre-provisioned on each new device in a costly and non-scalable
manner. Existing mechanisms are known as non-secured 'Trust on First
Use' (TOFU) [RFC7435], 'resurrecting duckling'
[Stajano99theresurrecting] or 'pre-staging'.
Another approach is to try and minimize user actions during
bootstrapping. The enrollment protocol EST [RFC7030] details a set
of non-autonomic bootstrapping methods in this vein:
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).
These "touch" methods do not meet the requirements for zero-touch.
There are "call home" technologies where the Pledge first establishes
a connection to a well known manufacturer service using a common
client-server authentication model. After mutual authentication,
appropriate credentials to authenticate the target domain are
transfered to the Pledge. This creates serveral problems and
limitations:
o the Pledge requires realtime connectivity to the manufacturer
service,
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o the domain identity is exposed to the manufacturer service (this
is a privacy concern),
o the manufacturer is responsible for making the authorization
decisions (this is a liability concern),
BRSKI addresses these issues by defining extensions to the EST
protocol for the automated distribution of vouchers.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The following terms are defined for clarity:
domainID: The domain IDentity is the 160-bit SHA-1 hash of the BIT
STRING of the subjectPublicKey of the root certificate for the
Registrars in the domain. This is consistent with the subject key
identifier (Section 4.2.1.2 [RFC5280]).
drop ship: The physical distribution of equipment containing the
"factory default" configuration to a final destination. In zero-
touch scenarios there is no staging or pre-configuration during
drop-ship.
imprint: The process where a device obtains the cryptographic key
material to identify and trust future interactions with a network.
This term is taken from Konrad Lorenz's work in biology with new
ducklings: during a critical period, the duckling would assume
that anything that looks like a mother duck is in fact their
mother. An equivalent for a device is to obtain the fingerprint
of the network's root certification authority certificate. A
device that imprints on an attacker suffers a similar fate to a
duckling that imprints on a hungry wolf. Securely imprinting is a
primary focus of this document [imprinting]. The analogy to
Lorenz's work was first noted in [Stajano99theresurrecting].
enrollment: The process where a device presents key material to a
network and acquires a network specific identity. For example
when a certificate signing request is presented to a certification
authority and a certificate is obtained in response.
Pledge: The prospective device, which has an identity installed at
the factory.
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Voucher: A signed artifact from the MASA that indicates to a Pledge
the cryptographic identity of the Registrar it should trust.
There are different types of vouchers depending on how that trust
is asserted. Multiple voucher types are defined in
[I-D.ietf-anima-voucher]
Domain: The set of entities that trust a common key infrastructure
trust anchor. This includes the Proxy, Registrar, Domain
Certificate Authority, Management components and any existing
entity that is already a member of the domain.
Domain CA: The domain Certification Authority (CA) provides
certification functionalities to the domain. At a minimum it
provides certification functionalities to a Registrar and stores
the trust anchor that defines the domain. Optionally, it
certifies all elements.
Join Registrar (and Coordinator): 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 Join Registrar (and Coordinator) to
control this process. Typically a Join Registrar is "inside" its
domain. For simplicity this document often refers to this as just
"Registrar". The term JRC is used in common with other bootstrap
mechanisms.
(Public) Key Infrastructure: The collection of systems and processes
that sustain the activities of a public key system. In an ANIMA
Autonomic system, this includes a Domain Certification Authority
(CA), (Join) Registrar which acts as an [RFC5280] Registrar, as
well as appropriate certificate revocation list (CRL) distribution
points and/or OCSP ([RFC6960]) servers.
Join Proxy: A domain entity that helps the Pledge join the domain.
A Proxy facilitates communication for devices that find themselves
in an environment where they are not provided connectivity until
after they are validated as members of the domain. The Pledge is
unaware that they are communicating with a Proxy rather than
directly with a Registrar.
MASA Service: A third-party Manufacturer Authorized Signing
Authority (MASA) service on the global Internet. The MASA signs
vouchers. It also provides a repository for audit log information
of privacy protected bootstrapping events. It does not track
ownership.
Ownership Tracker: An Ownership Tracker service on the global
internet. The Ownership Tracker uses business processes to
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accurately track ownership of all devices shipped against domains
that have purchased them. Although optional, this component
allows vendors to provide additional value in cases where their
sales and distribution channels allow for accurately tracking of
such ownership. Ownership tracking information is indicated in
vouchers as described in [I-D.ietf-anima-voucher]
IDevID: An Initial Device Identity X.509 certificate installed by
the vendor on new equipment.
TOFU: Trust on First Use. Used similarly to [RFC7435]. This is
where a Pledge device makes no security decisions but rather
simply trusts the first Registrar it is contacted by. This is
also known as the "resurrecting duckling" model.
nonced: a voucher (or request) that contains a nonce (the normal
case).
nonceless: a voucher (or request) that does not contain a nonce,
relying upon accurate clocks for expiration, or which does not
expire.
manufacturer: the term manufacturer is used throughout this document
to be the entity that created the device. This is typically the
"original equipment manufacturer" or OEM, but in more complex
situations it could be a "value added retailer" (VAR), or possibly
even a systems integrator. In general, it a goal of BRSKI to
eliminate small distinctions between different sales channels.
The reason for this is that it permits a single device, with a
uniform firmware load, to be shipped directly to all customers.
This eliminates costs for the manufacturer. This also reduces the
number of products supported in the field increasing the chance
that firmware will be more up to date.
ANI: The Autonomic Network Infrastructure as defined by
[I-D.ietf-anima-autonomic-control-plane]. This document details
specific requirements for pledges, proxies and registrars when
they are part of an ANI.
1.3. Scope of solution
Questions have been posed as to whether this solution is suitable in
general for Internet of Things (IoT) networks. This depends on the
capabilities of the devices in question. The terminology of
[RFC7228] is best used to describe the boundaries.
The solution described in this document is aimed in general at non-
constrained (i.e., class 2+) devices operating on a non-Challenged
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network. The entire solution as described here is not intended to be
useable as-is by constrained devices operating on challenged networks
(such as 802.15.4 LLNs).
In many target applications, the systems involved are large router
platforms with multi-gigabit inter-connections, mounted in controlled
access data centers. But this solution is not exclusive to the
large, it is intended to scale to thousands of devices located in
hostile environments, such as ISP provided CPE devices which are
drop-shipped to the end user. The situation where an order is
fulfilled from distributed warehouse from a common stock and shipped
directly to the target location at the request of the domain owner is
explicitly supported. That stock ("SKU") could be provided to a
number of potential domain owners, and the eventual domain owner will
not know a-priori which device will go to which location.
The bootstrapping process can take minutes to complete depending on
the network infrastructure and device processing speed. The network
communication itself is not optimized for speed; for privacy reasons,
the discovery process allows for the Pledge to avoid announcing its
presence through broadcasting.
This protocol is not intended for low latency handoffs. In networks
requiring such things, the Pledge SHOULD already have been enrolled.
Specifically, there are protocol aspects described here that might
result in congestion collapse or energy-exhaustion of intermediate
battery powered routers in an LLN. Those types of networks SHOULD
NOT use this solution. These limitations are predominately related
to the large credential and key sizes required for device
authentication. Defining symmetric key techniques that meet the
operational requirements is out-of-scope but the underlying protocol
operations (TLS handshake and signing structures) have sufficient
algorithm agility to support such techniques when defined.
The imprint protocol described here could, however, be used by non-
energy constrained devices joining a non-constrained network (for
instance, smart light bulbs are usually mains powered, and speak
802.11). It could also be used by non-constrained devices across a
non-energy constrained, but challenged network (such as 802.15.4).
The certificate contents, and the process by which the four questions
above are resolved do apply to constrained devices. It is simply the
actual on-the-wire imprint protocol that could be inappropriate.
This document presumes that network access control has either already
occurred, is not required, or is integrated by the Proxy and
Registrar in such a way that the device itself does not need to be
aware of the details. Although the use of an X.509 Initial Device
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Identity is consistant with IEEE 802.1AR [IDevID], and allows for
alignment with 802.1X network access control methods, its use here is
for Pledge authentication rather than network access control.
Integrating this protocol with network access control, perhaps as an
Extensible Authentication Protocol (EAP) method (see [RFC3748]), is
out-of-scope.
1.4. Leveraging the new key infrastructure / next steps
As a result of the protocol described herein, the bootstrapped
devices have a common trust anchor and a certificate has optionally
been issued from a local PKI. This makes it possible to
automatically deploy services across the domain in a secure manner.
Services that benefit from this:
o Device management.
o Routing authentication.
o Service discovery.
The major beneficiary is that it possible to use the credentials
deployed by this protocol to secure the Autonomic Control Plane (ACP)
([I-D.ietf-anima-autonomic-control-plane]).
1.5. Requirements for Autonomic Network Infrastructure (ANI) devices
The BRSKI protocol can be used in a number of environments. Some of
the flexibility in this document is the result of users out of the
ANI scope. This section defines the base requirements for ANI
devices.
For devices that intend to become part of an Autonomic Network
Infrastructure (ANI) ([I-D.ietf-anima-reference-model]) that includes
an Autonomic Control Plane
([I-D.ietf-anima-autonomic-control-plane]), the following actions are
required and MUST be performed by the Pledge:
o BRSKI: Request Voucher
o EST: CA Certificates Request
o EST: CSR Attributes
o EST: Client Certificate Request
o BRSKI: Enrollment status Telemetry
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The ANI Registrar (JRC) MUST support all the BRSKI and above listed
EST operations.
All ANI devices SHOULD support the BRSKI proxy function, using
circuit proxies. Other proxy methods are optional, and may be
enabled only if the JRC indicates support for them in it's
announcement. (See Section 4.4)
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.
+------------------------+
+--------------Drop Ship--------------->| Vendor Service |
| +------------------------+
| | M anufacturer| |
| | A uthorized |Ownership|
| | S igning |Tracker |
| | A uthority | |
| +--------------+---------+
| ^
| | BRSKI-
V | MASA
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
|Pledge | . | Circuit | | Domain <-------+ .
| | . | Proxy | | Registrar | .
| <-------->............<-------> (PKI RA) | .
| | | BRSKI-EST | | .
| | . | | +-----+-----+ .
|IDevID | . +------------+ | EST RFC7030 .
| | . +-----------------+----------+ .
| | . | Key Infrastructure | .
| | . | (e.g., PKI Certificate | .
+-------+ . | Authority) | .
. +----------------------------+ .
. .
................................................
"Domain" components
Figure 1
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We assume a multi-vendor network. In such an environment there could
be a Manufacturer Service for each manufacturer that supports devices
following this document's specification, or an integrator could
provide a generic service authorized by multiple manufacturers. It
is unlikely that an integrator could provide Ownership Tracking
services for multiple manufacturers due to the required sales channel
integrations necessary to track ownership.
The domain is the managed network infrastructure with a Key
Infrastructure the Pledge is joining. The domain provides initial
device connectivity sufficient for bootstrapping with a Circuit
Proxy. The Domain Registrar authenticates the Pledge, makes
authorization decisions, and distributes vouchers obtained from the
Manufacturer Service. Optionally the Registrar also acts as a PKI
Registration Authority.
2.1. Behavior of a Pledge
The Pledge goes through a series of steps, which are outlined here at
a high level.
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+--------------+
| Factory |
| default |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input (Appendix C)
| Bad MASA +------+-------+
| response | send Voucher Status Telemetry
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Enrolled |
^------------+ |
Factory +--------------+
reset
Figure 2
State descriptions for the Pledge are as follows:
1. Discover a communication channel to a Registrar.
2. Identify itself. This is done by presenting an X.509 IDevID
credential to the discovered Registrar (via the Proxy) in a TLS
handshake. (The Registrar credentials are only provisionally
accepted at this time).
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3. Request to Join the discovered Registrar. A unique nonce can be
included ensuring that any responses can be associated with this
particular bootstrapping attempt.
4. Imprint on the Registrar. This requires verification of the
manufacturer service provided voucher. A voucher contains
sufficient information for the Pledge to complete authentication
of a Registrar. (It enables the Pledge to finish authentication
of the Registrar TLS server certificate).
5. Enroll. By accepting the domain specific information from a
Registrar, and by obtaining a domain certificate from a Registrar
using a standard enrollment protocol, e.g. Enrollment over
Secure Transport (EST) [RFC7030].
6. The Pledge is now a member of, and can be managed by, the domain
and will only repeat the discovery aspects of bootstrapping if it
is returned to factory default settings.
2.2. Secure Imprinting using Vouchers
A voucher is a cryptographically protected artifact (a digital
signature) to the Pledge device authorizing a zero-touch imprint on
the Registrar domain.
The format and cryptographic mechanism of vouchers is described in
detail in [I-D.ietf-anima-voucher].
Vouchers provide a flexible mechanism to secure imprinting: the
Pledge device only imprints when a voucher can be validated. At the
lowest security levels the MASA server can indiscriminately issue
vouchers. At the highest security levels issuance of vouchers can be
integrated with complex sales channel integrations that are beyond
the scope of this document. This provides the flexibility for a
number of use cases via a single common protocol mechanism on the
Pledge and Registrar devices that are to be widely deployed in the
field. The MASA services have the flexibility to leverage either the
currently defined claim mechanisms or to experiment with higher or
lower security levels.
Vouchers provide a signed but non-encrypted communication channel
among the Pledge, the MASA, and the Registrar. The Registrar
maintains control over the transport and policy decisions allowing
the local security policy of the domain network to be enforced.
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2.3. Initial Device Identifier
Pledge authentication and Pledge voucher-request signing is via an
X.509 certificate installed during the manufacturing process. This
Initial Device Identifier provides a basis for authenticating the
Pledge during subsequent protocol exchanges and informing the
Registrar of the MASA URI. There is no requirement for a common root
PKI hierarchy. Each device manufacturer can generate its own root
certificate.
The following previously defined fields are in the X.509 IDevID
certificate:
o The subject field's DN encoding MUST include the "serialNumber"
attribute with the device's unique serial number.
o The subject-alt field's encoding SHOULD include a non-critical
version of the RFC4108 defined HardwareModuleName.
In order to build the voucher "serial-number" field these IDevID
fields need to be converted into a serial-number of "type string".
The following methods are used depending on the first available
IDevID certificate field (attempted in this order):
o An RFC4514 String Representation of the Distinguished Name
"serialNumber" attribute.
o The HardwareModuleName hwSerialNum OCTET STRING base64 encoded.
o The RFC4514 String Representation of the Distinguished Name
"common name" attribute.
The following newly defined field SHOULD be in the X.509 IDevID
certificate: An X.509 non-critical certificate extension that
contains a single Uniform Resource Identifier (URI) that points to an
on-line Manufacturer Authorized Signing Authority. The URI is
represented as described in Section 7.4 of [RFC5280].
Any Internationalized Resource Identifiers (IRIs) MUST be mapped to
URIs as specified in Section 3.1 of [RFC3987] before they are placed
in the certificate extension. The URI provides the authority
information. The BRSKI "/.well-known" tree ([RFC5785]) is described
in Section 5.
The new extension is identified as follows:
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<CODE BEGINS>
MASAURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-MASAURLExtn2016(TBD) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL --
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
id-pe
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
MASACertExtensions EXTENSION ::= { ext-MASAURL, ... }
ext-MASAURL EXTENSION ::= { SYNTAX MASAURLSyntax
IDENTIFIED BY id-pe-masa-url }
id-pe-masa-url OBJECT IDENTIFIER ::= { id-pe TBD }
MASAURLSyntax ::= IA5String
END
<CODE ENDS>
The choice of id-pe is based on guidance found in Section 4.2.2 of
[RFC5280], "These extensions may be used to direct applications to
on-line information about the issuer or the subject". The MASA URL
is precisely that: online information about the particular subject.
2.4. Protocol Flow
A representative flow is shown in Figure 3:
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+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Proxy | | Registrar | | Service |
| | | | | (JRC) | | (MASA) |
+--------+ +---------+ +------------+ +------------+
| | | Internet |
|<-RFC4862 IPv6 addr | | |
|<-RFC3927 IPv4 addr | Appendix A | Legend |
|-------------------->| | C - circuit |
| optional: mDNS query| Appendix B | proxy |
| RFC6763/RFC6762 | | P - provisional |
|<--------------------| | TLS connection |
| GRASP M_FLOOD | | |
| periodic broadcast| | |
|<------------------->C<----------------->| |
| TLS via the Circuit Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---X.509 client authentication---------->| |
P | | |
P---Voucher Request (include nonce)------>| |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--Pledge ID-------->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | optional: | [update audit log]
P | |can | |
P | |occur | |
P | |in | |
P | |advance | |
P | |if | |
P | |nonceless | |
P | | |<- voucher ---------|
P | \----> | |
P<------voucher---------------------------| |
[verify voucher , [verify provisional cert| | |
|---------------------------------------->| |
| [voucher status telemetry] |<-device audit log--|
| | [verify audit log and voucher] |
|<--------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
Figure 3
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2.4.1. Architectural component: Pledge
The Pledge is the device that is attempting to join. Until the
Pledge completes the enrollment process, it has network connectivity
only to the Proxy.
2.4.2. Architectural component: Circuit Proxy
The (Circuit) Proxy provides HTTPS connectivity between the Pledge
and the Registrar. The Proxy mechanism is described in Section 4,
with an optional stateless mechanism described in Appendix C.
2.4.3. Architectural component: Domain Registrar
The Domain Registrar (having the formal name Join Registrar/
Coordinator (JRC), operates as a CMC Registrar, terminating the EST
and BRSKI connections. The Registrar is manually configured or
distributed with a list of trust anchors necessary to authenticate
any Pledge device expected on the network. The Registrar
communicates with the MASA to establish ownership.
2.4.4. Architectural component: Manufacturer Service
The Manufacturer Service provides two logically seperate functions:
the Manufacturer Authorized Signing Authority (MASA), and an
ownership tracking/auditing function.
2.5. Lack of realtime clock
Many devices when bootstrapping do not have knowledge of the current
time. Mechanisms such as Network Time Protocols cannot be secured
until bootstrapping is complete. Therefore bootstrapping is defined
in a method that does not require knowledge of the current time.
Unfortunately there are moments during bootstrapping when
certificates are verified, such as during the TLS handshake, where
validity periods are confirmed. This paradoxical "catch-22" is
resolved by the Pledge maintaining a concept of the current "window"
of presumed time validity that is continually refined throughout the
bootstrapping process as follows:
o Initially the Pledge does not know the current time.
o During Pledge authentiation by the Registrar a realtime clock can