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ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Informational M. Richardson
Expires: May 4, 2017 SSW
M. Behringer
S. Bjarnason
Cisco
K. Watsen
Juniper Networks
October 31, 2016
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
draft-ietf-anima-bootstrapping-keyinfra-04
Abstract
This document specifies automated bootstrapping of a remote secure
key infrastructure (BRSKI) using vendor installed X.509 certificate,
in combination with a vendor authorized service on the Internet.
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 May 4, 2017.
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Copyright Notice
Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Scope of solution . . . . . . . . . . . . . . . . . . . . 7
1.3. Trust bootstrap . . . . . . . . . . . . . . . . . . . . . 8
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 8
3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 10
3.1. Behavior of a Pledge . . . . . . . . . . . . . . . . . . 11
3.1.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 13
3.1.2. Identity . . . . . . . . . . . . . . . . . . . . . . 14
3.1.3. Request Join . . . . . . . . . . . . . . . . . . . . 15
3.1.4. Imprint . . . . . . . . . . . . . . . . . . . . . . . 15
3.1.5. Lack of realtime clock . . . . . . . . . . . . . . . 16
3.1.6. Enrollment . . . . . . . . . . . . . . . . . . . . . 17
3.1.7. Being Managed . . . . . . . . . . . . . . . . . . . . 18
3.2. Behavior of a Proxy . . . . . . . . . . . . . . . . . . . 18
3.2.1. CoAP connection to Registrar . . . . . . . . . . . . 19
3.2.2. HTTPS proxy connection to Registrar . . . . . . . . . 19
3.3. Behavior of the Registrar . . . . . . . . . . . . . . . . 20
3.3.1. Pledge Authentication . . . . . . . . . . . . . . . . 21
3.3.2. Pledge Authorization . . . . . . . . . . . . . . . . 22
3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 23
3.3.4. Log Verification . . . . . . . . . . . . . . . . . . 23
3.4. Behavior of the MASA Service . . . . . . . . . . . . . . 24
3.4.1. Issue Audit Voucher and Log the event . . . . . . . . 24
3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 24
3.5. Leveraging the new key infrastructure / next steps . . . 25
3.5.1. Network boundaries . . . . . . . . . . . . . . . . . 25
3.6. Interactions with Network Access Control . . . . . . . . 25
4. Domain Operator Activities . . . . . . . . . . . . . . . . . 25
4.1. Instantiating the Domain Certification Authority . . . . 26
4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 26
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4.3. Accepting New Entities . . . . . . . . . . . . . . . . . 26
4.4. Automatic Enrollment of Devices . . . . . . . . . . . . . 27
4.5. Secure Network Operations . . . . . . . . . . . . . . . . 27
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 28
5.1. Request Voucher from the Registrar . . . . . . . . . . . 30
5.2. Request Voucher from MASA . . . . . . . . . . . . . . . . 32
5.3. Audit Voucher Response . . . . . . . . . . . . . . . . . 33
5.3.1. Completing authentication of Provisional TLS
connection . . . . . . . . . . . . . . . . . . . . . 34
5.4. Voucher Status Telemetry . . . . . . . . . . . . . . . . 35
5.5. MASA authorization log Request . . . . . . . . . . . . . 36
5.6. MASA authorization log Response . . . . . . . . . . . . . 36
5.7. EST Integration for PKI bootstrapping . . . . . . . . . . 37
5.7.1. EST Distribution of CA Certificates . . . . . . . . . 37
5.7.2. EST CSR Attributes . . . . . . . . . . . . . . . . . 37
5.7.3. EST Client Certificate Request . . . . . . . . . . . 38
5.7.4. Enrollment Status Telemetry . . . . . . . . . . . . . 38
5.7.5. EST over CoAP . . . . . . . . . . . . . . . . . . . . 39
6. Reduced security operational modes . . . . . . . . . . . . . 39
6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 40
6.2. New Entity security reductions . . . . . . . . . . . . . 40
6.3. Registrar security reductions . . . . . . . . . . . . . . 41
6.4. MASA security reductions . . . . . . . . . . . . . . . . 42
7. Security Considerations . . . . . . . . . . . . . . . . . . . 42
7.1. Security concerns with discovery process . . . . . . . . 44
7.1.1. Discovery of Registrar by Proxy . . . . . . . . . . . 44
7.1.2. Discovery of Proxy by New Entity . . . . . . . . . . 44
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
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 issued X.509 certificates and
cryptographically signed "vouchers" issued by a new form of cloud
service.
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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
device, or "pledge", being added:
o Pledge authentication: "Who is this? What is its identity?"
o Pledge 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 pledge's
decisions are made according to verified communication with a trusted
third-party. The domain's decisions are made by comparing the
pledge's authenticated identity against domain information such as a
configured list of purchased devices supplimented by information
provided by a trusted third-party. The third-party is not required
to provide sales channel ownership tracking nor is it required to
authenticate the domain.
Optimal security is achieved with X.509 certificates on each Pledge,
accompanied by a third-party (e.g., vendor, manufacturer or
integrator) Internet based service for verification. Bootstrapping
concepts run to completion with less requirements, but are then less
secure. A domain can choose to accept lower levels of security when
a trusted third-party is not available so that bootstrapping proceeds
even at the risk of reduced security. Only the domain can make these
decisions based on administrative input and known behavior of the
pledge.
The result of bootstrapping is that a domain specific key
infrastructure is deployed. Since X.509 PKI certificates are used
for identifying the pledge, and the public key of the domain identity
is leveraged during communications with an Internet based service,
which is itself authenticated using HTTPS, bootstrapping of a domain
specific Public Key Infrastructure (PKI) is described. Sufficient
agility to support bootstrapping alternative key infrastructures
(such as symmetric key solutions) is considered although no such
alternate key infrastructure is described.
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The following terms are defined for clarity:
DomainID: The domain identity is the 160-bit SHA-1 hash of the BIT
STRING of the subjectPublicKey of the domain trust anchor that is
stored by the Domain CA. This is consistent with the
Certification Authority subject key identifier (Section 4.2.1.2
[RFC5280]) 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 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 by a
third-party (e.g., vendor, manufacturer or integrator).
Voucher A signed statement from the MASA service 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 verified.
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Audit Voucher: A voucher from the MASA service that indicates that
the bootstrapping event has been successfully logged. The
Registrar is primarily responsible for verifying the logs and
ensuring domain network security.
Ownership Voucher: A voucher from the MASA service that indicates
the explicit owner identity. The MASA is primarily responsible
for tracking ownership using out-of-band sales channel integration
(the definition of which is out-of-scope of this document). It is
defined in [I-D.ietf-netconf-zerotouch].
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.
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.
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
provides a repository for audit log information concerning 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
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.
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IDevID An Initial Device Identity X.509 certificate installed by the
vendor on new equipment. The [IDevID] certificate format is the
primary example. In particular the X.509 certificate needs to
contain the device's serial number in a well known location in
order to perform white list operations and in order to extract it
for inclusion in messages to the MASA service. The subject
field's DN encoding MUST include the "serialNumber" attribute with
the device's unique serial number.
1.2. 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 entire solution described in this document is aimed in general at
non-constrained (i.e. class 2+) devices operating on a non-Challenged
network. The entire solution described here is not intended to be
useable as-is by constrained devices operating on challenged networks
(such as 802.15.4 LLNs).
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 bootstraping process can take minutes to complete depending on
the network infrastructure and device processing speed. The network
communication itself is not optimized for speed; the discovery
process allows for the Pledge to avoid broadcasting for privacy
reasons. This protocol is not intended for low latency handoffs.
Specifically, there are protocol aspects described here which might
result in congestion collapse or energy-exhaustion of intermediate
battery powered routers in an LLN. Those types of networks SHOULD
NOT use this solution. These limitations are predominately related
to the large credential and key sizes required for device
authentication. Defining symmetric key techniques that meet the
operational requirements is out-of-scope but the underlying protocol
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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 use of an IDevID that is consistant with [IDevID] allows for
alignment with 802.1X network access control methods which could need
to complete before bootstrapping can be initiated. This document
presumes that network access control has either already occured, 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.
Further integration is not in scope.
Some aspects are in scope for constrained devices on challenged
networks: the certificate contents, and the process by which the four
questions above are resolved is in scope. It is simply the actual
on-the-wire imprint protocol which is likely inappropriate.
1.3. Trust bootstrap
The imprint protocol results in a secure relationship between a
domain Registrar and the Pledge. If the new device is sufficiently
constrained that the ACE protocol should be leveraged for operation,
(see [I-D.ietf-ace-actors]), and the domain registrar is also the
Client Authorization Server or the Authorization Server, then it may
be appropriate to use this secure channel to exchange ACE tokens.
2. Architectural Overview
The logical elements of the bootstrapping framework are described in
this section. Figure 1 provides a simplified overview of the
components. Each component is logical and may be combined with other
components as necessary.
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.
.+------------------------+
+--------------Drop Ship-------------->.| Vendor Service |
| .+------------------------+
| .| M anufacturer| |
| .| A uthorized |Ownership|
| .| S igning |Tracker |
| .| A uthority | |
| .+--------------+---------+
| .............. ^
V |
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
| | . | | | <-------+ .
| | . | Proxy | | Registrar | .
| <--------> <-------> | .
| New | . | | | | .
| Entity| . +------------+ +-----+-----+ .
| | . | .
| | . +-----------------+----------+ .
| | . | Domain Certification | .
| | . | Authority | .
+-------+ . | Management and etc | .
. +----------------------------+ .
. .
................................................
"Domain" components
Figure 1
We assume a multi-vendor network. In such an environment there could
be a MASA or Ownership Tracker for each vendor that supports devices
following this document's specification, or an integrator could
provide a MASA service for all devices. It is unlikely that an
integrator could provide Ownership Tracking services for multiple
vendors.
This document describes a secure zero-touch approach to bootstrapping
a key infrastructure; if certain devices in a network do not support
this approach, they can still be bootstrapped manually. Although
manual deployment is not scalable and is not a focus of this document
the necessary mechanisms are called out in this document to ensure
such edge conditions are covered by the architectural and protocol
models.
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3. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically bootstrap into a key infrastructure delineating the
autonomic domain. See [RFC7575] for more information.
This section details the state machine and operational flow for each
of the main three entities. The pledge, the domain (primarily a
Registrar) and the MASA service.
A representative flow is shown in Figure 2:
+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
| | | |
|<-RFC3927 IPv4 adr | | |
or|<-RFC4862 IPv6 adr | | |
| | | |
|-------------------->| | |
| optional: mDNS query| | |
| RFC6763/RFC6762 | | |
| | | |
|<--------------------| | |
| mDNS broadcast | | |
| response or periodic| | |
| | | |
|<------------------->C<----------------->| |
| TLS via the Circuit Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---X.509 client authentication---------->| |
P | | |
P---Request Voucher (include nonce)------>| |
P | | |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--Pledge ID-------->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | | | |
P | optional: | [update audit log]
P | |can | |
P | |occur | |
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P | |in | |
P | |advance | |
P | | | |
P | | |<-device audit log--|
P | | |<- voucher ---------|
P | \----> | |
P | | |
P | [verify audit log and voucher] |
P | | |
P<------voucher---------------------------| |
[verify voucher ] | | |
[verify provisional cert ]| | |
| | | |
|---------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
| | | |
| | | |
| | | |
Figure 2
3.1. Behavior of a Pledge
A pledge that has not yet been bootstrapped attempts to find a local
domain and join it. A pledge MUST NOT automatically initiate
bootstrapping if it has already been configured or is in the process
of being configured.
States of a pledge are as follows:
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+--------------+
| Start |
| |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input
| Bad Vendor +------+-------+
| response |
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Being |
^------------+ Managed |
Factory +--------------+
reset
Figure 3
State descriptions for the pledge are as follows:
1. Discover a communication channel to a Registrar.
2. Identify itself. This is done by presenting an IDevID X.509
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. Requests to Join the discovered Registrar. A unique nonce is
included ensuring that any responses can be associated with this
particular bootstrapping attempt.
4. Imprint on the Registrar. This requires verification of the
vendor service provided "Audit" or "Ownership" Voucher. Either
of these responses contains sufficient information for the pledge
to complete authentication of a Registrar. (The pledge can now
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.
The following sections describe each of these steps in more detail.
3.1.1. Discovery
The result of discovery is a logical communication with a Registrar,
through a Proxy. The Proxy is transparent to the Pledge but is
always assumed to exist.
To discover the Registrar the Pledge performs the following actions:
a. MUST: Obtains a local address using either IPv4 or IPv6 methods
as described in [RFC4862] IPv6 Stateless Address
AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4
Link-Local Addresses. The Plege MAY obtain an IP address via
DHCP [RFC2131]. The DHCP provided parameters for the Domain Name
System can be used to perform step (d) DNS operations if all
local discovery attempts fail (see below).
b. MUST: Performs DNS-based Service Discovery [RFC6763] over
Multicast DNS [RFC6762] searching for the service
"_bootstrapks._tcp.local.". To prevent unaccceptable levels of
network traffic the congestion avoidance mechanisms specified in
[RFC6762] section 7 MUST be followed. The Pledge SHOULD listen
for an unsolicited broadcast response as described in [RFC6762].
This allows devices to avoid announcing their presence via mDNS
broadcasts and instead silently join a network by watching for
periodic unsolicited broadcast responses.
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c. MAY: Performs DNS-based Service Discovery [RFC6763] over normal
DNS operations. The service searched for is
"_bootstrapks._tcp.example.com". In this case the domain
"example.com" is discovered as described in [RFC6763] section 11.
d. MAY: If no local bootstrapks service is located using the DNS-
based Service Discovery methods the Pledge contacts a well known
vendor provided bootstrapping server by performing a DNS lookup
using a well known URI such as "bootstrapks.vendor-example.com".
The details of the URI are vendor specific. Vendors that
leverage this method on the Pledge are responsible for providing
the bootstrapks service.
DNS-based service discovery communicates the local proxy IPv4 or IPv6
address and port to the Pledge. Once a proxy is discovered the
Pledge communicates with a Registrar through the proxy using the
bootstrapping protocol defined in Section 5. The current DNS
services returned during each query is maintained until bootstrapping
is completed. If bootstrapping fails and the Pledge returns to the
Discovery state it picks up where it left off and continues
attempting bootstrapping. For example if the first Multicast DNS
_bootstrapks._tcp.local response doesn't work then the second and
third responses are tried. If these fail the Pledge moves on to
normal DNS-based Service Discovery.
Each discovery method attempted SHOULD exponentially back-off
attempts (to a maximum of one hour) to avoid overloading the network
infrastructure with discovery. The back-off timer for each method
MUST be independent of other methods. Methods SHOULD be run in
parallel to avoid head of queue problems. Once a connection to a
Registrar is established (e.g. establishment of a TLS session key)
there are expectations of more timely responses, see Section 5.1.
Once all discovered services are attempted the device SHOULD return
to Multicast DNS. It should periodically retry the vendor specific
mechanisms. The Pledge may prioritize selection order as appropriate
for the anticipated environment.
3.1.2. Identity
The Pledge identifies itself during the communication protocol
handshake. If the client identity is rejected the Pledge repeats the
Discovery process using the next proxy or discovery method available.
The bootstrapping protocol server is not initially authenticated.
Thus the connection is provisional and all data received is untrusted
until sufficiently validated even though it is over a TLS connection.
This is aligned with the existing provisional mode of EST [RFC7030]
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during s4.1.1 "Bootstrap Distribution of CA Certificates". See
Section 5.3 for more information about when the TLS connection
authenticated is completed.
All security associations established are between the new device and
the Bootstrapping server regardless of proxy operations.
3.1.3. Request Join
The Pledge POSTs a request to join the domain to the Bootstrapping
server. This request contains a Pledge generated nonce and informs
the Bootstrapping server which imprint methods the Pledge will
accept.
As indicated in EST [RFC7030] the bootstrapping server MAY redirect
the client to an alternate server. This is most useful in the case
where the Pledge has resorted to a well known vendor URI and is
communicating with the vendor's Registrar directly. In this case the
Pledge has authenticated the Registrar using the local Implicit Trust
Anchor database and can therefore treat the redirect URI as a trusted
URI which can also be validated using the Implicit Trust Anchor
database. Since client authentication occurs during the TLS
handshake the bootstrapping server has sufficient information to
apply appropriate policy concerning which server to redirect to.
The nonce ensures the Pledge can verify that responses are specific
to this bootstrapping attempt. This minimizes the use of global time
and provides a substantial benefit for devices without a valid clock.
3.1.4. Imprint
The domain trust anchor is received by the Pledge during the
bootstrapping protocol methods in the form of a voucher. The goal of
the imprint state is to securely obtain a copy of this trust anchor
without involving human interaction.
The enrollment protocol EST [RFC7030] details a set of non-autonomic
bootstrapping methods such as:
o using the Implicit Trust Anchor database (not an autonomic
solution because the URL must be securely distributed),
o engaging a human user to authorize the CA certificate using out-
of-band data (not an autonomic solution because the human user is
involved),
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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).
This document describes autonomic methods that MUST be supported by
the Pledge:
Audit Voucher Audit Vouchers are obtained by a Registrar from the
MASA service and presented to the Pledge for validation. These
indicate to the Pledge that joining the domain has been logged by
a logging service.
Ownership Voucher Ownership Vouchers are obtained by a Registrar
from the MASA service and explicitly indicate the owner of the
Pledge. The Ownership Voucher is defined in
[I-D.ietf-netconf-zerotouch].
Since client authentication occurs during the TLS handshake the
bootstrapping server has sufficient information to apply appropriate
policy concerning which method to use.
The Audit Voucher contains the domain's public key material as
provided to the MASA service by a Registrar. This provides
sufficient information to the client to complete automated
bootstrapping with the local key infrastructure. The Ownership
Voucher contains the Owner Certificate which the Pledge uses to
authenticate the TLS connection.
If the autonomic methods fail the Pledge returns to discovery state
and attempts bootstrapping with the next available discovered
Registrar.
3.1.5. Lack of realtime clock
Many devices when bootstrapping do not have knowledge of the current
time. Mechanisms like Network Time Protocols can not 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"
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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
be used by the Registrar. This bullet expands on a closely
related issue regarding Pledge lifetimes. RFC5280 indicates that
long lived Pledge certifiates "SHOULD be assigned the
GeneralizedTime value of 99991231235959Z" [RFC5280] so the
Registrar MUST support such lifetimes and SHOULD support ignoring
Pledge lifetimes if they did not follow the RFC5280
recommendations.
o Once the Audit Voucher is accepted the validity period of the
domainCAcert in the voucher (see Section 5.3) now describes a
valid time window. Any subsequent certificate validity periods
checked during RFC5280 path validation MUST occur within this
window.
o When accepting an enrollment certificate the validity period
within the new certificate is assumed to be valid by the Pledge.
The Pledge is now willing to use this credential for client
authentication.
Once in this state the Pledge has a valid trust anchor with the local
domain and has a locally issued credential. These MAY be used to
secure distribution of more accurate time information although
specification of such a protocol is out-of-scope of this document.
The nonce included in join attempts provides an alternate mechanism
for the Pledge to ensure Audit Voucher responses are associated with
a particular bootstrapping attempt. Nonceless Audit Vouchers from
the MASA server are always valid and thus time is not needed.
Ownership Vouchers include time information and MUST be validated
using a realtime clock.
3.1.6. Enrollment
As the final step of bootstrapping a Registrar helps to issue a
domain specific credential to the Pledge. For simplicity in this
document, a Registrar primarily facilitates issuing a credential by
acting as an RFC5280 Registration Authority for the Domain
Certification Authority.
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Enrollment proceeds as described in [RFC7030]. Authentication of the
EST server is done using the Voucher rather than the methods defined
in EST.
Once the Audit or Ownership Voucher is received, as specified in this
document, the client has sufficient information to leverage the
existing communication channel with a Registrar to continue an EST
RFC7030 enrollment. Enrollment picks up at RFC7030 section 4.1.1.
bootstrapping where the Audit Voucher provides the "out-of-band" CA
certificate fingerprint (in this case the full CA certificate) such
that the client can now complete the TLS server authentication. At
this point the client continues with EST enrollment operations
including "CA Certificates Request", "CSR Attributes" and "Client
Certificate Request" or "Server-Side Key Generation".
3.1.7. Being Managed
Functionality to provide generic "configuration" information is
supported. The parsing of this data and any subsequent use of the
data, for example communications with a Network Management System is
out of scope but is expected to occur after bootstrapping enrollment
is complete. This ensures that all communications with management
systems which can divulge local security information (e.g. network
topology or raw key material) is secured using the local credentials
issued during enrollment.
The Pledge uses bootstrapping to join only one domain. Management by
multiple domains is out-of-scope of bootstrapping. After the device
has successfully joined a domain and is being managed it is plausible
that the domain can insert credentials for other domains depending on
the device capabilities.
See Section 3.5.
3.2. Behavior of a Proxy
The role of the Proxy is to facilitate communications. The Proxy
forwards packets between the Pledge and a Registrar that has been
configured on the Proxy. The Proxy does not terminate the TLS
handshake. A Proxy is always assumed even if directly integrated
into a Registrar.
As a result of the Proxy Discovery process in section Section 3.1.1,
the port number exposed by the proxy does not need to be well known,
or require an IANA allocation.
If the Proxy joins an Autonomic Control Plane
([I-D.ietf-anima-autonomic-control-plane]) it SHOULD use Autonomic
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Control Plane secured GRASP ([I-D.ietf-anima-grasp]) to discovery the
Registrar address and port. For the IPIP encapsulation methods, the
port announced by the Proxy MUST be the same as on the registrar in
order for the proxy to remain stateless.
In order to permit the proxy functionality to be implemented on the
maximum variety of devices the chosen mechanism SHOULD use the
minimum amount of state on the proxy device. While many devices in
the ANIMA target space will be rather large routers, the proxy
function is likely to be implemented in the control plane CPU such a
device, with available capabilities for the proxy function similar to
many class 2 IoT devices.
The document [I-D.richardson-anima-state-for-joinrouter] provides a
more extensive analysis of the alternative proxy methods.
3.2.1. CoAP connection to Registrar
The proxy MUST implement an IPIP (protocol 41) encapsulation function
for CoAP traffic to the configured UDP port on the registrar. The
proxy does not terminate the CoAP DTLS connection. [[EDNOTE: The
choice of CoAP as the mandatory to implement protocol rather than
HTTP maximizes code reuse on the smallest of devices. Unfortunately
this means this document will have to include the EST over CoAP
details as additional sections. The alternative is to make 'HTTPS
proxy' method the mandatory to implement and provide a less friendly
environment for the smallest of devices. This is a decision we'll
have to see addressed by the broader team.]]
The IPIP encapsulation allows the proxy to forward traffic which is
otherwise not to be forwarded, as the traffic between New Node and
Proxy use IPv6 Link Local addresses.
If the Proxy device has more than one interface on which it offers
the proxy function, then it must select a unique (ACP) IP address per
interface in order so that the proxy can stateless return the (link-
local) reply packets to the correct link.
3.2.2. HTTPS proxy connection to Registrar
The proxy SHOULD also provide one of: an IPIP encapsulation of HTTP
traffic on TCP port TBD to the registrar, or a TCP circuit proxy that
connects the Pledge to a Registrar.
When the Proxy provides a circuit proxy to a Registrar the Registrar
MUST accept HTTPS connections.
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When the Proxy provides a stateless IPIP encapsulation to a
Registrar, then the Registrar will have to perform IPIP
decapsulation, remembering the originating outer IPIP source address
in order to qualify the inner link-local address. This is a kind of
encapsulation and processing which is similar in many ways to how
mobile IP works.
Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link-
local address with an encapsulated IPIP header requires API
extensions beyond [RFC3542] for UDP use, and requires a form of
connection latching (see section 4.1 of [RFC5386] and all of
[RFC5660], except that a simple IPIP tunnel is used rather than an
IPsec tunnel).
3.3. Behavior of the Registrar
A Registrar listens for Pledges and determines if they can join the
domain. A Registrar obtains a Voucher from the MASA service and
delivers them to the Pledge as well as facilitating enrollment with
the domain PKI.
A Registrar is typically configured manually. If the Registrar joins
an Autonomic Control Plane ([I-D.ietf-anima-autonomic-control-plane])
it MUST use Autonomic Control Plane secured GRASP
([I-D.ietf-anima-grasp]) to broadcast the Registrar's address and
port to potential Proxies.
Registrar behavior is as follows:
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Contacted by Pledge
+
|
+-------v----------+
| Entity | fail?
| Authentication +---------+
+-------+----------+ |
| |
+-------v----------+ |
| Entity | fail? |
| Authorization +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Claiming the | fail? |
| Entity +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Log Verification | fail? |
| +--------->
+-------+----------+ |
| |
+-------v----------+ +----v-------+
| Forward | | |
| Audit | | Reject |
| voucher + config | | Device |
| to the Entity | | |
+------------------+ +------------+
Figure 4
3.3.1. Pledge Authentication
The applicable authentication methods detailed in EST [RFC7030] are:
o the use of an IDevID X.509 credential during the TLS client
authentication,
o or the use of a secret that is transmitted out of band between the
Pledge and a Registrar (this use case is not autonomic).
In order to validate the IDevID X.509 credential a Registrar
maintains a database of vendor trust anchors (e.g. vendor root
certificates or keyIdentifiers for vendor root public keys). For
user interface purposes this database can be mapped to colloquial
vendor names. Registrars can be shipped with the trust anchors of a
significant number of third-party vendors within the target market.
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3.3.2. Pledge Authorization
In a fully automated network all devices must be securely identified
and authorized to join the domain.
A Registrar accepts or declines a request to join the domain, based
on the authenticated identity presented. Automated acceptance
criteria include:
o allow any device of a specific type (as determined by the X.509
IDevID),
o allow any device from a specific vendor (as determined by the
X.509 IDevID),
o allow a specific device from a vendor (as determined by the X.509
IDevID) against a domain white list. (The mechanism for checking
a shared white list potentiatlly used by multiple Registrars is
out of scope).
To look the Pledge up in a domain white list a consistent method for
extracting device identity from the X.509 certificate is required.
RFC6125 describes Domain-Based Application Service identity but here
we require Vendor Device-Based identity. The subject field's DN
encoding MUST include the "serialNumber" attribute with the device's
unique serial number. In the language of RFC6125 this provides for a
SERIALNUM-ID category of identifier that can be included in a
certificate and therefore that can also be used for matching
purposes. The SERIALNUM-ID whitelist is collated according to vendor
trust anchor since serial numbers are not globally unique.
Since all Pledges accept Audit Vouchers a Registrar MUST use the
vendor provided MASA service to verify that the device's history log
does not include unexpected Registrars. If a device had previously
registered with another domain, a Registrar of that domain would show
in the log.
If a Pledge is accepted into the domain, it is expected to request a
domain certificate through a certificate enrollment process. The
result is a common trust anchor and device certificates for all
autonomic devices in a domain (these certificates can be used for
other methods, for example boundary detection, auto-securing
protocols, etc.). The authorization performed during this phase is
used for EST enrollment requests.
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3.3.3. Claiming the New Entity
Claiming an entity establishes an audit log at the MASA server and
provides a Registrar with proof, in the form of a MASA Audit Voucher,
that the log entry has been inserted. As indicated in Section 3.1.4
a Pledge will only proceed with bootstrapping if a validated MASA
Audit Voucher has been received. The Pledge therefore enforces that
bootstrapping only occurs if the claim has been logged. There is no
requirement for the vendor to definitively know that the device is
owned by the Registrar.
Registrar's obtain the Vendor URI via static configuration or by
extracting it from the X.509 IDevID credential. The imprint method
supported by the Pledge is known from the X.509 IDevID credential.
[[EDNOTE: An appropriate extension for indicating the Vendor URI and
imprint method could be defined using the methods described in
[I-D.lear-mud-framework]]].
During initial bootstrapping the Pledge provides a nonce specific to
the particular bootstrapping attempt. The Registrar SHOULD include
this nonce when claiming the Pledge from the MASA service. Claims
from an unauthenticated Registrar are only serviced by the MASA
resource if a nonce is provided.
The Registrar can claim a Pledge that is not online by forming the
request using the entities unique identifier and not including a
nonce in the claim request. Audit Voucher 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
although no requirement is implied that the MASA associates this
authentication with ownership.
An Ownership Voucher requires the vendor to definitively know that a
device is owned by a specific domain. The method used to "claim"
this are out-of-scope. A MASA ignores or reports failures when an
attempt is made to claim a device that has a an Ownership Voucher.
3.3.4. Log Verification
A Registrar requests the log information for the Pledge from the MASA
service. The log is verified to confirm that the following is true
to the satisfaction of a Registrar's configured policy:
o Any nonceless entries in the log are associated with domainIDs
recognized by the registrar.
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o Any nonce'd entries are older than when the domain is known to
have physical possession of the Pledge or that the domainIDs are
recognized by the registrar.
If any of these criteria are unacceptable to a Registrar the entity
is rejected. A Registrar MAY be configured to ignore the history of
the device but it is RECOMMENDED that this only be configured if
hardware assisted NEA [RFC5209] is supported.
This document specifies a simple log format as provided by the MASA
service to the registar. This format could be improved by
distributed consensus technologies that integrate the Audit Voucher
with a current technologies such as block-chain or hash trees or the
like. Doing so is out of the scope of this document but are
anticipated improvements for future work.
3.4. Behavior of the MASA Service
The MASA service is provided by the Factory provider on the global
Internet. The URI of this service is well known. The URI SHOULD
also be provided as an X.509 IDevID extension (a "MASA Audit Voucher
Distribution Point" extension).
The MASA service provides the following functionalities to
Registrars:
3.4.1. Issue Audit Voucher and Log the event
A Registrar POSTs a claim message optionally containing the bootstrap
nonce to the MASA server.
If a nonce is provided the MASA service responds to all requests.
The MASA service verifies the Registrar is representative of the
domain and generates a privacy protected log entry before responding
with the Audit Voucher. For the simple log format defined in this
document using the DomainID is considered sufficient privacy. Future
work to improve the logging mechanism could include additional
privacy protections.
If a nonce is not provided then the MASA service MUST authenticate
the Registrar as a valid customer. This prevents denial of service
attacks.
3.4.2. Retrieve Audit Entries from Log
When determining if a Pledge 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
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previously claimed the device. Included in the list is an indication
of the time the entry was made and if the nonce was included.
3.5. Leveraging the new key infrastructure / next steps
As the devices have a common trust anchor, device identity can be
securely established, making it possible to automatically deploy
services across the domain in a secure manner.
Examples of services:
o Device management.
o Routing authentication.
o Service discovery.
3.5.1. Network boundaries
When a device has joined the domain, it can validate the domain
membership of other devices. This makes it possible to create trust
boundaries where domain members have higher level of trusted than
external devices. Using the autonomic User Interface, specific
devices can be grouped into to sub domains and specific trust levels
can be implemented between those.
3.6. Interactions with Network Access Control
The assumption is that Network Access Control (NAC) completes using
the Pledge 's X.509 IDevID credentials and results in the device
having sufficient connectivity to discovery and communicate with the
proxy. Any additional connectivity or quarantine behavior by the NAC
infrastructure is out-of-scope. After the devices has completed
bootstrapping the mechanism to trigger NAC to re-authenticate the
device and provide updated network privileges is also out-of-scope.
This achieves the goal of a bootstrap architecture that can integrate
with NAC but does not require NAC within the network where it wasn't
previously required. Future optimizations can be achieved by
integrating the bootstrapping protocol directly into an initial EAP
exchange.
4. Domain Operator Activities
This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.
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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 Pledge 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 a 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 a 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
belong to the network. This list can be extracted from an
inventory database, or sales records. If a device is detected
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that is not on the list of known devices, it can still be
manually accepted using the per device acceptance methods.
4. Automated Whitelist: an automated process that builds the
necessary whitelists and inserts them into the larger network
domain infrastructure is plausible. Once set up, no human
intervention is required in this process. Defining the exact
mechanisms for this is out of scope although the registrar
authorization checks is identified as the logical integration
point of any future work in this area.
None of these approaches require the network to have permanent
Internet connectivity. Even when the Internet based MASA service is
used, it is possible to pre-fetch the required information from the
MASA a priori, for example at time of purchase such that devices can
enroll later. This supports use cases where the domain network may
be entirely isolated during device deployment.
Additional policy can be stored for future authorization decisions.
For example an expected deployment time window or that a certain
Proxy must be used.
4.4. Automatic Enrollment of Devices
The approach outlined in this document provides a secure zero-touch
method to enroll new devices without any pre-staged configuration.
New devices communicate with already enrolled devices of the domain,
which proxy between the new device and a Registrar. As a result of
this completely automatic operation, all devices obtain a domain
based certificate.
4.5. Secure Network Operations
The certificate installed in the previous step can be used for all
subsequent operations. For example, to determine the boundaries of
the domain: If a neighbor has a certificate from the same trust
anchor it can be assumed "inside" the same organization; if not, as
outside. See also Section 3.5.1. The certificate can also be used
to securely establish a connection between devices and central
control functions. Also autonomic transactions can use the domain
certificates to authenticate and/or encrypt direct interactions
between devices. The usage of the domain certificates is outside
scope for this document.
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5. Protocol Details
A bootstrapping protocol could be implemented as an independent
protocol from EST, but for simplicity and to reduce the number of TLS
connections and crypto operations required on the Pledge, it is
described specifically as extensions to EST. These extensions MUST
be supported by the Registrar EST server within the same .well-known
URI tree as the existing EST URIs as described in [RFC7030] section
3.2.2.
The Pledge establishes a TLS connection with the Registrar through
the circuit proxy (see Section 3.2) but the TLS connection is with
the Registar; so for this section the "Pledge" is the TLS client and
the "Registrar" is the TLS server.
Establishment of the TLS connection for bootstrapping is as specified
for EST [RFC7030]. In particular server identity and client identity
are as described in EST [RFC7030] section 3.3. In EST [RFC7030]
provisional server authentication for bootstrapping is described in
section 4.1.1 wherein EST clients can "engage a human user to
authorize the CA certificate using out-of-band data such as a CA
certificate" or wherein a human user configures the URI of the EST
server for Implicit TA based authentication. As described in this
document, Section 5.3.1, a new method of bootstrapping now provides a
completely automating method of bootstrapping PKI.
The extensions for the Pledge client are as follows:
o The Pledge provisionally accept the EST server certificate during
the TLS handshake as detailed in Section 5.3.1.
o The Pledge requests and validates the Audit Voucher as described
below. At this point the Pledge has sufficient information to
validate domain credentials.
o The Pledge calls the EST defined /cacerts method to obtain the
current CA certificate. These are validated using the Audit
Voucher.
o The Pledge completes bootstrapping as detailed in EST section
4.1.1.
In order to obtain a validated Audit Voucher and Audit Log a
Registrar contacts the MASA service Service using REST calls:
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+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
+---------------C---------------> |
| | | |
HTTP REST | POST /requestvoucher | |
Data +--------------------nonce------> |
| . | /requestvoucher|
| . +---------------->
| <----------------+
| | /requestlog |
| +---------------->
| voucher <----------------+
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 5
In some use cases the Registrar may need to contact the Vendor in
advanced, for example when the target network is air-gapped. The
nonceless request format is provided for this and the resulting flow
is slightly different. The security differences associated with not
knowing the nonce are discussed below:
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+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| | | /requestvoucher|
| | (nonce +---------------->
| | unknown) <----------------+
| | | /requestlog |
| | +---------------->
| | <----------------+
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
| | | |
HTTP REST | POST /requestvoucher | |
Data +----------------------nonce----> (discard |
| voucher | nonce) |
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 6
The extensions for a Registrar server are as follows:
o The Registrar requests and validates the Audit Voucher from the
vendor authorized MASA service.
o The Registrar forwards the Audit Voucher to the Pledge when
requested.
o The Registar performs log verifications in addition to local
authorization checks before accepting the Pledge device.
5.1. Request Voucher from the Registrar
When the Pledge bootstraps it makes a request for a Voucher from a
Registrar.
This is done with an HTTPS POST using the operation path value of
"/requestvoucher".
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The request format is JSON object containing a 64bit nonce generated
by the client for each request. This nonce MUST be a
cryptographically strong random or pseudo-random number that can not
be easily predicted. The nonce MUST NOT be reused for multiple
attempts to join a network domain. The nonce assures the Pledge that
the Audit Voucher response is associated with this bootstrapping
attempt and is not a replay.
Request media type: application/auditnonce
Request format: a JSON file with the following:
{
"version":"1",
"nonce":"<64bit nonce value>",
}
[[EDNOTE: Even if the nonce was signed it would provide no defense
against rogue registrars; although it would assure the MASA that a
certified Pledge exists. To protect against rogue registrars a nonce
component generated by the MASA (a new round trip) would be
required). Instead this is addressed by requiring MASA & Registrar
authentications but it is worth exploring additional protections.
This to be explored more at IETF96.]]
The Registrar validates the client identity as described in EST
[RFC7030] section 3.3.2. The registrar performs authorization as
detailed in Section 3.3.2. If authorization is successful the
Registrar obtains an Voucher from the MASA service (see Section 5.2).
The received Voucher is forwarded to the Pledge.
As indicated in EST [RFC7030] the bootstrapping server can redirect
the client to an alternate server. If the Pledge authenticated a
Registrar using the well known URI method then the Pledge MUST follow
the redirect automatically and authenticate the new Registrar against
the redirect URI provided. If the Pledge had not yet authenticated a
Registrar because it was discovered and was not a known-to-be-valid
URI then the new Registrar must be authenticated using one of the two
autonomic methods described in this document. Similarly the Registar
MAY respond with an HTTP 202 ("the request has been accepted for
processing, but the processing has not been completed") as described
in EST [RFC7030] section 4.2.3.
Recall that during this communication with the Registar the TLS
authentication is only provisional. The Pledge client MUST handle
all data from the Registrar with upmost care. In particular the
Pledge MUST only allow a single redirection and MUST only support a
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delay of five seconds before declaring the Registrar a failure and
moving on to the next discovered Registrar. As detailed in
Section 3.1.1 if no suitable Registrar is found the Pledge restarts
the state machine and tries again. So a Registrar that is unable to
complete the transaction the first time will have future chances.
5.2. Request Voucher from MASA
A Registrar requests a Voucher from the MASA service using a REST
interface. For simplicity this is defined as an optional EST message
between a Registrar and an EST server running on the MASA service
although the Registrar is not required to make use of any other EST
functionality when communicating with the MASA service. (The MASA
service MUST properly reject any EST functionality requests it does
not wish to service; a requirement that holds for any REST
interface).
This is done with an HTTP POST using the operation path value of
"/requestvoucher".
The request format is a JSON object optionally containing the nonce
value (as obtained from the bootstrap request) and the X.509 IDevID
extracted serial number (the full certificate is not needed and no
proof-of-possession information for the device identity is included).
The AuthorityKeyIdentifier value from the certificate is included to
ensure a statistically unique identity. The Pledge's serial number
is extracted from the X.509 IDevID subject name id-at-serialNumber or
it is the base64 encoded RFC4108 hardwareModuleName hwSerialNum:
{
"version":"1",
"nonce":"<64bit nonce value>",
"IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier">,
"DevIDSerialNumber":"<id-at-serialNumber or base64 encoded
hardwareModuleName hwSerialNum>",
}
A Registrar MAY exclude the nonce from the request. Doing so allows
the Registrar to request a Voucher when the Pledge is not online, or
when the target bootstrapping environment is not on the same network
as the MASA server (this requires the Registrar to learn the
appropriate DevIDSerialNumber field from the physical device labeling
or from the sales channel -- how this occurs is out-of-scope of this
document). If a nonce is not provided the MASA server MUST
authenticate the client as described in EST [RFC7030] section 3.3.2
to reduce the risk of DDoS attacks. A Registrar performs
authorization as detailed in Section 3.3.2. If authorization is
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successful the Registrar obtains an Voucher from the MASA service
(see Section 5.2).
The JSON message information is encapsulated in a [RFC5652] Signed-
data that is signed by the Registrar. The entire certificate chain,
up to and including the Domain CA, MUST be included in the
CertificateSet structure. The MASA service checks the internal
consistency of the CMS but does not authenticate the domain identity
information. The domain is not know to the MASA server in advance
and a shared trust anchor is not implied. The MASA server MUST
verify that the CMS is signed by a Registrar certificate (by checking
for the cmc-idRA field) that was issued by a the root certificate
included in the CMS. This ensures that the Registrar making the
claim is an authorized Registrar of the unauthenticated domain. The
EST style client authentication (TLS and HTTP) is used to provide a
DDoS prevention strategy.
The root certificate is extracted and used to populate the Audit
Voucher. The domain ID (e.g. hash of the public key of the domain)
is extracted from the root certificate and is used to update the
audit log.
5.3. Audit Voucher Response
The voucher response to requests from the device and requests from a
Registrar are in the same format. A Registrar either caches prior
MASA responses or dynamically requests a new Voucher based on local
policy.
If the the join operation is successful, the server response MUST
contain an HTTP 200 response code with a content-type of
"application/authorizationvoucher". The server MUST answer with a
suitable 4xx or 5xx HTTP [RFC2616] error code when a problem occurs.
The response data from the MASA server MUST be a plaintext human-
readable error message containing explanatory information describing
why the request was rejected.
The Audit Voucher consists of the nonce, if supplied, the serial
number information identifying the device and the domain CA
certificate extracted from the request:
{
"version":"1",
"nonce":"<64bit nonce value>",
"IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier>",
"DevIDSerialNumber":"<id-at-serialNumber>",
"domainCAcert":"<the base64 encoded domain CA's certificate>"
}
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The Audit Voucher response is encapsulated in a [RFC5652] Signed-data
that is signed by the MASA server. The Pledge verifies this signed
message using the manufacturer installed trust anchor assocaited with
the X.509 IDevID. [[EDNOTE: As detailed in netconf-zerotouch this
might be a distinct trust anchor rather than re-using the trust
anchor for the IDevID. This concept will need to be detailed in this
document as well.]]
[[EDNOTE: Using CMS is consistent with the alignment of this
bootstrapping document with EST, a PKIX enrollment protocol that
includes Certificate Management over CMS. An alternative format
would be the RFC7515 JSON Web Signature (JWS), which would allow
clients that do not use fullCMC messages to avoid CMS entirely. Use
of JWS would likely include a discussion of CBOR in order ensure the
base64 expansions of the certs and signatures within the JWS message
are of minimal size -- it is not yet clear to this author how that
would work out]]
The 'domainCAcert' element of this message contains the domain CA's
public key. This is specific to bootstrapping a public key
infrastructure. To support bootstrapping other key infrastructures
additional domain identity types might be defined in the future.
Clients MUST be prepared to ignore additional fields they do not
recognize. Clients MUST be prepared to parse and fail gracefully
from an Audit Voucher response that does not contain a 'domainCAcert'
field at all.
To minimize the size of the Audit Voucher response message the
domainCAcert is not a complete distribution of the EST section 4.1.3
CA Certificate Response.
The Pledge installs the domainCAcert trust anchor. As indicated in
Section 3.1.2 the newly installed trust anchor is used as an EST
RFC7030 Explicit Trust Anchor. The Pledge MUST use the domainCAcert
trust anchor to immediately validate the currently provisional TLS
connection to a Registrar.
5.3.1. Completing authentication of Provisional TLS connection
If a Registrar's credential can not be verified using the
domainCAcert trust anchor the TLS connection is immediately discarded
and the Pledge abandons attempts to bootstrap with this discovered
registrar.
The following behaviors on a Registrar and Pledge are in addition to
normal PKIX operations:
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o The EST server MUST use a certificate that chains to the
domainCAcert. This means that when the EST server obtains renewed
credentials the credentials included in the Section 5.2 request
match the chain used in the current provisional TLS connection.
o The Pledge PKIX path validation of a Registrar validity period
information is as described in Section 3.1.5.
Because the domainCAcert trust anchor is installed as an Explicit
Trust Anchor it can be used to authenticate any dynamically
discovered EST server that contain the id-kp-cmcRA extended key usage
extension as detailed in EST RFC7030 section 3.6.1; but to reduce
system complexity the Pledge SHOULD avoid additional discovery
operations. Instead the Pledge SHOULD communicate directly with the
Registrar as the EST server to complete PKI local certificate
enrollment. Additionally the Pledge SHOULD use the existing TLS
connection to proceed with EST enrollment, thus reducing the total
amount of cryptographic and round trip operations required during
bootstrapping. [[EDNOTE: It is reasonable to mandate that the
existing TLS connection be re-used? e.g. MUST >> SHOULD?]]
5.4. Voucher Status Telemetry
For automated bootstrapping of devices the adminstrative elements
providing bootstrapping also provide indications to the system
administrators concerning device lifecycle status. To facilitate
this those elements need telemetry information concerning the
device's status.
To indicate Pledge status regarding the Audit Voucher the client
SHOULD post a status message.
The client HTTP POSTs the following to the server at the EST well
known URI /voucher_status. The Status field indicates if the Voucher
was acceptable. If it was not acceptable the Reason string indicates
why. In the failure case this message is being sent to an
unauthenticated, potentially malicious Registrar and therefore the
Reason string SHOULD NOT provide information beneficial to an
attacker. The operational benefit of this telemetry information is
balanced against the operational costs of not recording that an
Voucher was ignored by a client the registar expected to continue
joining the domain.
{
"version":"1",
"Status":FALSE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
}
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The server SHOULD respond with an HTTP 200 but MAY simply fail with
an HTTP 404 error. The client ignores any response. Within the
server logs the server SHOULD capture this telemetry information.
5.5. MASA authorization log Request
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
"/requestauditlog".
The client HTTP POSTs the same Voucher Request as for requesting an
audit token but now posts it to the /requestauditlog URI instead.
The IDevIDAuthorityKeyIdentifier and DevIDSerialNumber informs the
MASA server which log is requested so the appropriate log can be
prepared for the response.
5.6. MASA authorization log Response
A log data file is returned consisting of all log entries. For
example:
{
"version":"1",
"events":[
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit voucher request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
},
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit voucher request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
}
]
}
Distribution of a large log is less than ideal. This structure can
be optimized as follows: All nonce-less entries for the same domainID
MAY be condensed into the single most recent nonceless entry.
A Registrar uses this log information to make an informed decision
regarding the continued bootstrapping of the Pledge. For example if
the log includes unexpected domainIDs this is indicative of
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problematic imprints by the Pledge. If the log includes nonce-less
entries this is indicative of the permanent ability for the indicated
domain to trigger a reset of the device and take over management of
it. Equipment that is purchased pre-owned can be expected to have an
extensive history.
Log entries containing the Domain's ID can be compared against local
history logs in search of discrepancies.
5.7. EST Integration for PKI bootstrapping
The prior sections describe EST extensions necessary to enable fully
automated bootstrapping. Although the Audit Voucher request/response
structure members IDevIDAuthorityKeyIdentifier and DevIDSerialNumber
are specific to PKI bootstrapping these are the only PKI specific
aspects of the extensions and future work might replace them with
non-PKI structures.
The prior sections provide functionality for the Pledge to obtain a
trust anchor representative of the Domain. The following section
describe using EST to obtain a locally issued PKI certificate. The
Pledge SHOULD leverage the discovered Registrar to proceed with
certificate enrollment and, if they do, MUST implement the EST
options described in this section. The Pledge MAY perform
alternative enrollment methods including discovering an alternate EST
server, or proceed to use its IDevID credential indefinitely.
5.7.1. EST Distribution of CA Certificates
The Pledge MUST request the full EST Distribution of CA Certificates
message. See RFC7030, section 4.1.
This ensures that the Pledge has the complete set of current CA
certificates beyond the domainCAcert (see Section 5.3 for a
discussion of the limitations). Although these restrictions are
acceptable for a Registrar integrated with initial bootstrapping they
are not appropriate for ongoing PKIX end entity certificate
validation.
5.7.2. EST CSR Attributes
Automated bootstrapping occurs without local administrative
configuration of the Pledge. In some deployments its plausible that
the Pledge generates a certificate request containing only identity
information known to the Pledge (essentially the IDevID information)
and ultimately receives a certificate containing domain specific
identity information. Conceptually the CA has complete control over
all fields issued in the end entity certificate. Realistically this
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is operationally difficult with the current status of PKI certificate
authority deployments where the CSR is submitted to the CA via a
number of non-standard protocols.
To alleviate operational difficulty the Pledge MUST request the EST
"CSR Attributes" from the EST server. This allows the local
infrastructure to inform the Pledge of the proper fields to include
in the generated CSR.
[[EDNOTE: The following is specific to anima purposes and should be
moved to an appropriate anima document so as to keep bootstrapping as
generic as possible: What we want are a 'domain name' stored in [TBD]
and an 'ACP IPv6 address' stored in the iPAddress field as specified
in RFC5208 s4.2.1.6. ref ACP draft where certificate verification
[TBD]. These should go into the subjectaltname in the [TBD]
fields.]]. If the hardwareModuleName in the IDevID is populated then
it SHOULD by default be propagated to the LDevID along with the
hwSerialNum. The registar SHOULD support local policy concerning
this functionality. [[EDNOTE: extensive use of EST CSR Attributes
might need an new OID definition]].]]
The Registar MUST also confirm the resulting CSR is formatted as
indicated before forwarding the request to a CA. If the Registar is
communicating with the CA using a protocol like full CMC which
provides mechanisms to override the CSR attributes, then these
mechanisms MAY be used even if the client ignores CSR Attribute
guidance.
5.7.3. EST Client Certificate Request
The Pledge MUST request a new client certificate. See RFC7030,
section 4.2.
5.7.4. Enrollment Status Telemetry
For automated bootstrapping of devices the adminstrative elements
providing bootstrapping also provide indications to the system
administrators concerning device lifecycle status. This might
include information concerning attempted bootstrapping messages seen
by the client, MASA provides logs and status of credential
enrollment. The EST protocol assumes an end user and therefore does
not include a final success indication back to the server. This is
insufficient for automated use cases.
To indicate successful enrollment the client SHOULD re-negotiate the
EST TLS session using the newly obtained credentials. This occurs by
the client initiating a new TLS ClientHello message on the existing
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TLS connection. The client MAY simply close the old TLS session and
start a new one. The server MUST support either model.
In the case of a failure the Reason string indicates why the most
recent enrollment failed. The SubjectKeyIdentifier field MUST be
included if the enrollment attempt was for a keypair that is locally
known to the client. If EST /serverkeygen was used and failed then
the this field is ommited from the status telemetry.
The client HTTP POSTs the following to the server at the new EST well
known URI /enrollstatus.
{
"version":"1",
"Status":TRUE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
"SubjectKeyIdentifier":"<base64 encoded subjectkeyidentifier for the
enrollment that failed>"
}
The server SHOULD respond with an HTTP 200 but MAY simply fail with
an HTTP 404 error.
Within the server logs the server MUST capture if this message was
recieved over an TLS session with a matching client certificate.
This allows for clients that wish to minimize their crypto operations
to simpy POST this response without renegotiating the TLS session -
at the cost of the server not being able to accurately verify that
enrollment was truly successful.
5.7.5. EST over CoAP
[[EDNOTE: In order to support smaller devices the above section on
Proxy behavior introduces mandatory to implement support for CoAP
support by the Proxy. This implies similar support by the Pledge and
Registrar and means that the EST protocol operation encapsulation
into CoAP needs to be described. EST is HTTP based and "CoaP is
designed to easily interface with HTTP for integration" [RFC7252].
Use of CoAP implies Datagram TLS (DTLS) wherever this document
describes TLS handshake specifics. A complexity is that the large
message sizes necessary for bootstrapping will require support for
[draft-ietf-core-block].]]
6. Reduced security operational modes
A common requirement of bootstrapping is to support less secure
operational modes for support specific use cases. The following
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sections detail specific ways that the Pledge, Registrar and MASA can
be configured to run in a less secure mode for the indicated reasons.
6.1. Trust Model
+--------+ +---------+ +------------+ +------------+
| New | | Circuit | | Domain | | Vendor |
| Entity | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
Figure 7
Pledge: The Pledge could be compromised and providing an attack
vector for malware. The entity is trusted to only imprint using
secure methods described in this document. Additional endpoint
assessment techniques are RECOMMENDED but are out-of-scope of this
document.
Proxy: Provides proxy functionalities but is not involved in
security considerations.
Registrar: When interacting with a MASA server a Registrar makes all
decisions. When Ownership Vouchers are involved a Registrar is
only a conduit and all security decisions are made on the vendor
service.
Vendor Service, MASA: This form of vendor service is trusted to
accurately log all claim attempts and to provide authoritative log
information to Registrars. The MASA does not know which devices
are associated with which domains. These claims could be
strengthened by using cryptographic log techniques to provide
append only, cryptographic assured, publicly auditable logs.
Current text provides only for a trusted vendor.
Vendor Service, Ownership Validation: This form of vendor service is
trusted to accurately know which device is owned by which domain.
6.2. New Entity security reductions
The Pledge MAY support "trust on first use" on physical interfaces
but MUST NOT support "trust on first use" on network interfaces.
This is because "trust on first use" permanently degrades the
security for all other use cases.
The Pledge MAY have an operational mode where it skips Voucher
validation one time. For example if a physical button is depressed
during the bootstrapping operation. This can be useful if the vendor
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service is unavailable. This behavior SHOULD be available via local
configuration or physical presence methods to ensure new entities can
always be deployed even when autonomic methods fail. This allows for
unsecured imprint.
It is RECOMMENDED that this only be available if hardware assisted
NEA [RFC5209] is supported.
6.3. Registrar security reductions
A Registrar can choose to accept devices using less secure methods.
These methods are acceptable when low security models are needed, as
the security decisions are being made by the local administrator, but
they MUST NOT be the default behavior:
1. A registrar MAY choose to accept all devices, or all devices of a
particular type, at the administrator's discretion. This could
occur when informing all Registrars of unique identifiers of new
entities might be operationally difficult.
2. A registrar MAY choose to accept devices that claim a unique
identity without the benefit of authenticating that claimed
identity. This could occur when the Pledge does not include an
X.509 IDevID factory installed credential. New Entities without
an IDevID credential MAY form the Section 5.1 request using the
Section 5.2 format to ensure the Pledge's serial number
information is provided to the Registar (this includes the
IDevIDAuthorityKeyIdentifier value which would be statically
configured on the Pledge). The Pledge MAY refused to provide a
TLS client certificate (as one is not available). The Pledge
SHOULD support HTTP-based or certificate-less TLS authentication
as described in EST RFC7030 section 3.3.2. A Registrar MUST NOT
accept unauthenticated New Entities unless it has been configured
to do so by an administrator that has verified that only expected
new entities can communicate with a Registrar (presumably via a
physically secured perimeter).
3. A Registrar MAY request nonce-less Audit Vouchers from the MASA
service (by not including a nonce in the request). These Audit
Vouchers can then be transmitted to the Registrar and stored
until they are needed during bootstrapping operations. This is
for use cases where target network is protected by an air gap and
therefore can not contact the MASA service during Pledge
deployment.
4. A registrar MAY ignore unrecognized nonce-less Audit Log entries.
This could occur when used equipment is purchased with a valid
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history being deployed in air gap networks that required
permanent Audit Vouchers.
These modes are not available for devices that require a vendor
Ownership Voucher. The methods vendors use to determine which
devices are owned by which domains is out-of-scope.
6.4. MASA security reductions
Lower security modes chosen by the MASA service effect all device
deployments unless bound to the specific device identities. In which
case these modes can be provided as additional features for specific
customers. The MASA service can choose to run in less secure modes
by:
1. Not enforcing that a Nonce is in the Audit Voucher. This results
in distribution of Audit Voucher that never expire and in effect
makes the Domain an always trusted entity to the Pledge during
any subsequent bootstrapping attempts. That this occurred is
captured in the log information so that the Domain registrar can
make appropriate security decisions when a Pledge joins the
Domain. This is useful to support use cases where Registrars
might not be online during actual device deployment. Because
this results in long lived Audit Voucher and do not require the
proof that the device is online this is only accepted when the
Registrar is authenticated by the MASA server and authorized to
provide this functionality. The MASA server is RECOMMENDED to
use this functionality only in concert with Ownership Validation
tracking.
2. Not verifying ownership before responding with an Audit Voucher.
This is expected to be a common operational model because doing
so relieves the vendor providing MASA services from having to
tracking ownership during shipping and supply chain and allows
for a very low overhead MASA service. A Registrar uses the audit
log information as a defense in depth strategy to ensure that
this does not occur unexpectedly (for example when purchasing new
equipment the Registrar would throw an error if any audit log
information is reported).
7. Security Considerations
In order to support a wide variety of use cases, devices can be
claimed by a registrar without proving possession of the device in
question. This would result in a nonceless, and thus always valid,
claim. Or would result in an invalid nonce being associated with a
claim. The MASA service is required to authenticate such Registrars
but no programmatic method is provided to ensure good behavior by the
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MASA service. Nonceless entries into the audit log therefore
permanently reduce the value of a device because future Registrars,
during future bootstrap attempts, would now have to be configured
with policy to ignore previously (and potentially unknown) domains.
Future registrars are recommended to take the audit history of a
device into account when deciding to join such devices into their
network. If the MASA server were to have allowed a significantly
large number of claims this might become onerous to the MASA server
which must maintain all the extra log entries. Ensuring a Registrar
is representative of a valid customer domain even without validating
ownership helps to mitigate this.
It is possible for an attacker to send an authorization request to
the MASA service directly after the real Registrar obtains an
authorization log. If the attacker could also force the
bootstrapping protocol to reset there is a theoretical opportunity
for the attacker to use the Audit Voucher to take control of the
Pledge but then proceed to enroll with the target domain. Possible
prevention mechanisms include:
o Per device rate limits on the MASA service ensure such timing
attacks are difficult.
o In the advent of an unexpectedly lost bootstrapping connection the
Registrar repeats the request for audit log information.
To facilitate logging and administrative oversight the Pledge reports
on Audit Voucher parsing status to the Registrar. In the case of a
failure this information is informative to a potentially malicious
Registar but this is RECOMMENDED anyway because of the operational
benefits of an informed administrator in cases where the failure is
indicative of a problem.
As indicated in EST [RFC7030] the connection is provisional and
untrusted until the server is successfully authorized. If the server
provides a redirect response the client MUST follow the redirect but
the connection remains provisional. If the client uses a well known
URI for contacting a well known Registrar the EST Implicit Trust
Anchor database is used as is described in RFC6125 to authenticate
the well known URI. In this case the connection is not provisional
and RFC6125 methods can be used for each subsequent redirection.
To facilitate truely limited clients EST RFC7030 section 3.3.2
requirements that the client MUST support a client authentication
model have been reduced in Section 6 to a statement that clients only
"SHOULD" support such a model. This reflects current (not great)
practices but is NOT RECOMMENDED.
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The MASA service could lock a claim and refuse to issue a new voucher
or the MASA service could go offline (for example if a vendor went
out of business). This functionality provides benefits such as theft
resistance, but it also implies an operational risk to the Domain
that Vendor behavior could limit future bootstrapping of the device
by the Domain. This can be mitigated by Registrars that request
nonce-less Audit Vouchers.
7.1. Security concerns with discovery process
7.1.1. Discovery of Registrar by Proxy
As described in section Section 3.2, the RECOMMENDED mechanism is for
the proxy to discover the address of the registrar via GRASP
[I-D.ietf-anima-grasp]
GRASP is intended to run over a secured, and private Autonomic
Control Plan [I-D.ietf-anima-autonomic-control-plane]. This
discovery is between the already registered Registrar, and the
already registered Proxy. There are no GRASP security issues with
this part, as both entities will have already joined the secured ACP.
7.1.2. Discovery of Proxy by New Entity
[[EDNOTE: To be discussed]]
8. Acknowledgements
We would like to thank the various reviewers for their input, in
particular Markus Stenberg, Brian Carpenter, Fuyu Eleven, Toerless
Eckert, Eliot Lear and Sergey Kasatkin.
9. References
9.1. Normative References
[IDevID] IEEE Standard, , "IEEE 802.1AR Secure Device Identifier",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
Pritikin, et al. Expires May 4, 2017 [Page 44]
Internet-Draft BRewSKI October 2016
[RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003,
<http://www.rfc-editor.org/info/rfc3542>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<http://www.rfc-editor.org/info/rfc3927>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
Security: An Unauthenticated Mode of IPsec", RFC 5386,
DOI 10.17487/RFC5386, November 2008,
<http://www.rfc-editor.org/info/rfc5386>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>.
[RFC5660] Williams, N., "IPsec Channels: Connection Latching",
RFC 5660, DOI 10.17487/RFC5660, October 2009,
<http://www.rfc-editor.org/info/rfc5660>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
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[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
9.2. Informative References
[I-D.behringer-homenet-trust-bootstrap]
Behringer, M., Pritikin, M., and S. Bjarnason,
"Bootstrapping Trust on a Homenet", draft-behringer-
homenet-trust-bootstrap-02 (work in progress), February
2014.
[I-D.ietf-ace-actors]
Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
architecture for authorization in constrained
environments", draft-ietf-ace-actors-04 (work in
progress), September 2016.
[I-D.ietf-anima-autonomic-control-plane]
Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
Control Plane", draft-ietf-anima-autonomic-control-
plane-03 (work in progress), July 2016.
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-08 (work in progress), October 2016.
[I-D.ietf-netconf-zerotouch]
Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
for NETCONF or RESTCONF based Management", draft-ietf-
netconf-zerotouch-09 (work in progress), July 2016.
[I-D.lear-mud-framework]
Lear, E., "Manufacturer Usage Description Framework",
draft-lear-mud-framework-00 (work in progress), January
2016.
[I-D.richardson-anima-state-for-joinrouter]
Richardson, M., "Considerations for stateful vs stateless
join router in ANIMA bootstrap", draft-richardson-anima-
state-for-joinrouter-01 (work in progress), July 2016.
[imprinting]
Wikipedia, , "Wikipedia article: Imprinting", July 2015,
<https://en.wikipedia.org/wiki/Imprinting_(psychology)>.
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[pledge] Dictionary.com, , "Dictionary.com Unabridged", July 2015,
<http://dictionary.reference.com/browse/pledge>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<http://www.rfc-editor.org/info/rfc7575>.
[Stajano99theresurrecting]
Stajano, F. and R. Anderson, "The resurrecting duckling:
security issues for ad-hoc wireless networks", 1999,
<https://www.cl.cam.ac.uk/~fms27/papers/1999-StajanoAnd-
duckling.pdf>.
Authors' Addresses
Max Pritikin
Cisco
Email: pritikin@cisco.com
Michael C. Richardson
Sandelman Software Works
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
Kent Watsen
Juniper Networks
Email: kwatsen@juniper.net
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