Bootstrapping Remote Secure Key Infrastructures (BRSKI)
draft-ietf-anima-bootstrapping-keyinfra-03
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (anima WG) | |
|---|---|---|---|
| Authors | Max Pritikin , Michael Richardson , Michael H. Behringer , Steinthor Bjarnason | ||
| Last updated | 2016-06-30 | ||
| Replaces | draft-pritikin-anima-bootstrapping-keyinfra | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Reviews |
GENART Telechat review
(of
-28)
Ready with Issues
SECDIR Telechat review
(of
-28)
Has Nits
SECDIR Last Call review
(of
-20)
Has Nits
IOTDIR Telechat review
(of
-17)
Not Ready
GENART Last Call review
(of
-16)
Not Ready
SECDIR Last Call review
(of
-16)
Has Issues
|
||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-anima-bootstrapping-keyinfra-03
ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Informational M. Richardson
Expires: January 1, 2017 SSW
M. Behringer
S. Bjarnason
Cisco
June 30, 2016
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
draft-ietf-anima-bootstrapping-keyinfra-03
Abstract
This document specifies automated bootstrapping of a remote secure
key infrastructure (BRSKI) using vendor installed IEEE 802.1AR
manufacturing installed certificates, in combination with a vendor
based service on the Internet. Before being authenticated, a new
device has only link-local connectivity, and does not require a
routable address. When a vendor provides an Internet based service
devices can be redirected to a local service. In limited/
disconnected networks or legacy environments we describe a variety of
options that allow bootstrapping to proceed. Support for lower
security models, including devices with minimal identity, is
described for legacy reasons but not encouraged.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 1, 2017.
Pritikin, et al. Expires January 1, 2017 [Page 1]
Internet-Draft BRewSKI June 2016
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 . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Scope of solution . . . . . . . . . . . . . . . . . . . . 6
1.3. Trust bootstrap . . . . . . . . . . . . . . . . . . . . . 7
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 7
3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 9
3.1. Behavior of a New Entity . . . . . . . . . . . . . . . . 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 (Bootstrap Server) . . . . . . 20
3.3.1. Entity Authentication . . . . . . . . . . . . . . . . 21
3.3.2. Entity Authorization . . . . . . . . . . . . . . . . 21
3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 22
3.3.4. Log Verification . . . . . . . . . . . . . . . . . . 23
3.4. Behavior of the MASA Service . . . . . . . . . . . . . . 24
3.4.1. Issue Authorization Token and Log the event . . . . . 24
3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 24
3.5. Leveraging the new key infrastructure / next steps . . . 24
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 . . . . 25
4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 25
Pritikin, et al. Expires January 1, 2017 [Page 2]
Internet-Draft BRewSKI June 2016
4.3. Accepting New Entities . . . . . . . . . . . . . . . . . 26
4.4. Automatic Enrollment of Devices . . . . . . . . . . . . . 27
4.5. Secure Network Operations . . . . . . . . . . . . . . . . 27
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 27
5.1. Request Audit Token from the Registrar . . . . . . . . . 30
5.2. Request Audit Token from MASA . . . . . . . . . . . . . . 32
5.3. Audit Token Response . . . . . . . . . . . . . . . . . . 33
5.3.1. Completing authentication of Provisional TLS
connection . . . . . . . . . . . . . . . . . . . . . 34
5.4. Audit Token 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 . . . . . . . . . . . . . . . . . 38
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 . . . . . . . . . . . . . 40
6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 40
6.2. New Entity security reductions . . . . . . . . . . . . . 41
6.3. Registrar security reductions . . . . . . . . . . . . . . 41
6.4. MASA security reductions . . . . . . . . . . . . . . . . 42
7. Security Considerations . . . . . . . . . . . . . . . . . . . 42
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction
To literally "pull yourself up by the bootstraps" is an impossible
action. Similarly the secure establishment of a key infrastructure
without external help is also an impossibility. Today it is accepted
that the initial connections between nodes are insecure, until key
distribution is complete, or that domain-specific keying material is
pre-provisioned on each new device in a costly and non-scalable
manner. This document describes a zero-touch approach to
bootstrapping an entity by securing the initial distribution of key
material using third-party generic keying material, such as a
manufacturer installed IEEE 802.1AR certificate [IDevID], and a
corresponding third-party service on the Internet.
The two sides of an association being bootstrapped authenticate each
other and then determine appropriate authorization. This process is
described as four distinct steps between the existing domain and the
new entity being added:
Pritikin, et al. Expires January 1, 2017 [Page 3]
Internet-Draft BRewSKI June 2016
o New entity authentication: "Who is this? What is its identity?"
o New entity authorization: "Is it mine? Do I want it? What are
the chances it has been compromised?"
o Domain authentication: "What is this domain's claimed identity?"
o Domain authorization: "Should I join it?"
A precise answer to these questions can not be obtained without
leveraging some established key infrastructure(s). A complexity that
this protocol deals with are dealing with devices from a variety of
vendors, and a network infrastructure (the domain) that is operated
by parties that do not have any priviledged relationship with the
device vendors. The domain's decisions are based on the new entity's
authenticated identity, as established by verification of previously
installed credentials such as a manufacturer installed IEEE 802.1AR
certificate, and verified back-end information such as a configured
list of purchased devices or communication with a (unidirectionally)
trusted third-party. The new entity's decisions are made according
to verified communication with a trusted third-party or in a strictly
auditable fashion.
Optimal security is achieved with IEEE 802.1AR certificates on each
new entity, accompanied by a third-party Internet based service for
verification. Bootstrapping concepts run to completion with less
requirements, but are then less secure. A domain can choose to
accept lower levels of security when a trusted third-party is not
available so that bootstrapping proceeds even at the risk of reduced
security. Only the domain can make these decisions based on
administrative input and known behavior of the new entity.
The result of bootstrapping is that a domain specific key
infrastructure is deployed. Since IEEE 802.1AR PKI certificates are
used for identifying the new entity, and the public key of the domain
identity is leveraged during communications with an Internet based
service, which is itself authenticated using HTTPS, bootstrapping of
a domain specific Public Key Infrastructure (PKI) is described.
Sufficient agility to support bootstrapping alternative key
infrastructures (such as symmetric key solutions) is considered
although no such alternate key infrastructure is described.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
Pritikin, et al. Expires January 1, 2017 [Page 4]
Internet-Draft BRewSKI June 2016
The following terms are defined for clarity:
DomainID: The domain identity is the 160-bit SHA-1 hash of the BIT
STRING of the subjectPublicKey of the domain trust anchor that is
stored by the Domain CA. This is consistent with the RFC5280
Certification Authority subject key identifier of the Domain CA's
self signed root certificate. (A string value bound to the Domain
CA's self signed root certificate subject and issuer fields is
often colloquially used as a humanized identity value but during
protocol discussions the more exact term as defined here is used).
drop ship: The physical distribution of equipment containing the
"factory default" configuration to a final destination. In zero-
touch scenarios there is no staging or pre-configuration during
drop-ship.
imprint: the process where a device obtains the cryptographic key
material to identity and trust future interactions with a network.
This term is taken from Konrad Lorenz's work in biology with new
ducklings: during a critical period, the duckling would assume
that anything that looks like a mother duck is in fact their
mother. An equivalent for a device is to obtain the fingerprint
of the network's root certification authority certificate. A
device that imprints on an attacker suffers a similar fate to a
duckling that imprints on a hungry wolf. Securely imprinting is a
primary focus of this document.[imprinting].
enrollment: the process where a device presents key material to a
network and acquires a network specific identity. For example
when a certificate signing request is presented to a certification
authority and a certificate is obtained in response.
pledge: the prospective device, which has the identity provided to
at the factory. Neither the device nor the network knows if the
device yet knows if this device belongs with this network. This
is definition 6, according to [pledge]
Audit Token: A signed token from the manufacturer authorized signing
authority indicating that the bootstrapping event has been
successfully logged. This has been referred to as an
"authorization token" indicating that it authorizes bootstrapping
to proceed.
Ownership Voucher: A signed voucher from the vendor vouching that a
specific domain "owns" the new entity as defined in
[I-D.ietf-netconf-zerotouch].
Pritikin, et al. Expires January 1, 2017 [Page 5]
Internet-Draft BRewSKI June 2016
1.2. Scope of solution
Questions have been posed as to whether this solution is suitable in
general for Internet of Things (IoT) networks. In general the answer
is no, but the terminology of [RFC7228] is best used to describe the
boundaries.
The entire solution described in this document is aimed in general at
non-constrained (i.e. class 2+) devices operating on a non-Challenged
network. The entire solution described here is not intended to be
useable as-is by constrained devices operating on challenged networks
(such as 802.15.4 LLNs).
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 "chatty" but there can be delays 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
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).
Pritikin, et al. Expires January 1, 2017 [Page 6]
Internet-Draft BRewSKI June 2016
Some aspects are in scope for constrained devices on challenged
networks: the certificate contents, and the process by which the four
questions above are resolved is in scope. It is simply the actual
on-the-wire imprint protocol which is likely inappropriate.
1.3. Trust bootstrap
The imprint protocol results in a secure relationship between the
domain registrar and the new device. If the new device is
sufficiently constrained that the ACE protocol should be leveraged
for operation, (see [I-D.ietf-ace-actors]), and the domain registrar
is also the Client Authorization Server or the Authorization Server,
then it may be appropriate to use this secure channel to exchange ACE
tokens.
2. Architectural Overview
The logical elements of the bootstrapping framework are described in
this section. Figure 1 provides a simplified overview of the
components. Each component is logical and may be combined with other
components as necessary.
Pritikin, et al. Expires January 1, 2017 [Page 7]
Internet-Draft BRewSKI June 2016
.
.+------------------------+
+--------------Drop Ship-------------->.| Vendor Service |
| .+------------------------+
| .| M anufacturer| |
| .| A uthorized |Ownership|
| .| S igning |Tracker |
| .| A uthority | |
| .+--------------+---------+
| .............. ^
V |
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
| | . | | | <-------+ .
| | . | Proxy | | Registrar | .
| <--------> <-------> | .
| New | . | | | | .
| Entity| . +------------+ +-----+-----+ .
| | . | .
| | . +-----------------+----------+ .
| | . | Domain Certification | .
| | . | Authority | .
+-------+ . | Management and etc | .
. +----------------------------+ .
. .
................................................
"Domain" components
Figure 1
Domain: The set of entities that trust a common key infrastructure
trust anchor. This includes the Proxy, Registrar, Domain
Certificate Authority, Management components and any existing
entity that is already a member of the domain.
Domain CA: The domain Certification Authority (CA) provides
certification functionalities to the domain. At a minimum it
provides certification functionalities to the Registrar and stores
the trust anchor that defines the domain. Optionally, it
certifies all elements.
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
Pritikin, et al. Expires January 1, 2017 [Page 8]
Internet-Draft BRewSKI June 2016
with a Registrar to control this process. Typically a Registrar
is "inside" its domain.
New Entity: A new device or virtual machine or software component
that is not yet part of the domain.
Proxy: A domain entity that helps the New Entity join the domain. A
Proxy facilitates communication for devices that find themselves
in an environment where they are not provided connectivity until
after they are validated as members of the domain. The New Entity
is unaware that they are communicating with a proxy rather than
directly with the Registrar.
MASA Service: A Manufacturer Authorized Signing Authority (MASA)
service on the global Internet. The MASA provides a repository
for audit log information concerning privacy protected
bootstrapping events.
Ownership Tracker An Ownership Tracker service on the global
internet. The Ownership Tracker uses business processes to
accurately track ownership of all devices shipped against domains
that have purchased them. Although optional this component allows
vendors to provide additional value in cases where their sales and
distribution channels allow for accurately tracking of such
ownership.
We assume a multi-vendor network. In such an environment there could
be a MASA or Ownership Tracker for each vendor that supports devices
following this document's specification, or an integrator could
provide a MASA service for all devices. It is unlikely that an
integrator could provide Ownership Tracking services for multiple
vendors.
This document describes a secure zero-touch approach to bootstrapping
a key infrastructure; if certain devices in a network do not support
this approach, they can still be bootstrapped manually. Although
manual deployment is not scalable and is not a focus of this document
the necessary mechanisms are called out in this document to ensure
such edge conditions are covered by the architectural and protocol
models.
3. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically bootstrap into a key infrastructure delineating the
autonomic domain. See [I-D.irtf-nmrg-autonomic-network-definitions]
for more information.
Pritikin, et al. Expires January 1, 2017 [Page 9]
Internet-Draft BRewSKI June 2016
This section details the state machine and operational flow for each
of the main three entities. The New Entity, the Domain (primarily
the Registrar) and the MASA service.
A representative flow is shown in Figure 2:
+--------+ +---------+ +------------+ +------------+
| New | | Circuit | | Domain | | Vendor |
| Entity | | 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---IEEE 802.1AR client authentication--->| |
P | | |
P---Request Audit Token (include nonce)-->| |
P | | |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--New Entity ID---->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | | | |
P | optional: | [update audit log]
P | |can | |
P | |occur | optional: is |
P | |in | an ownership |
P | |advance | voucher available?
P | | | |
P | | |<-device audit log--|
P | | | |
P | | | choice: |
Pritikin, et al. Expires January 1, 2017 [Page 10]
Internet-Draft BRewSKI June 2016
P | | |<-audit token-------|
P | | |<-or: ownership-----|
P | \----> | voucher |
P | | |
P | [verify audit log or voucher] |
P | | |
P<--Audit token and/or ownership voucher--| |
[verify response ]| | |
[verify provisional cert ]| | |
| | | |
|---------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
| | | |
| | | |
| | | |
Figure 2
3.1. Behavior of a New Entity
A New Entity that has not yet been bootstrapped attempts to find a
local domain and join it. A New Entity MUST NOT automatically
initiate bootstrapping if it has already been configured.
States of a New Entity are as follows:
Pritikin, et al. Expires January 1, 2017 [Page 11]
Internet-Draft BRewSKI June 2016
+--------------+
| Start |
| |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input
| Bad Vendor +------+-------+
| response |
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Being |
^------------+ Managed |
Factory +--------------+
reset
Figure 3
State descriptions for the New Entity are as follows:
1. Discover a communication channel to the "closest" Registrar.
2. Identify itself. This is done by presenting an IEEE 802.1AR
credentials to the discovered Registrar (via the Proxy) in a TLS
handshake. (Although the Registrar is also authenticated these
credentials are only provisionally accepted at this time).
Pritikin, et al. Expires January 1, 2017 [Page 12]
Internet-Draft BRewSKI June 2016
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 "Audit Token" or the validation of the vendor
service "Ownership Voucher". Either of these responses contains
sufficient information for the New Entity to complete
authentication of the Registrar. (The New Entity can now finish
authentication of the Registrar TLS server certificate)
5. Enroll by accepting the domain specific information from the
Registrar, and by obtaining a domain certificate from the
Registrar using a standard enrollment protocol, e.g. Enrollment
over Secure Transport (EST) [RFC7030].
6. The New Entity is now a member of, and can be managed by, the
domain and will only repeat the discovery aspects of
bootstrapping if it is returned to factory default settings.
The following sections describe each of these steps in more detail.
3.1.1. Discovery
The result of discovery is logically communication with a Proxy
instead of a Domain Registrar but in such a case the proxy
facilitates communication with the actual Domain Registrar in a
manner that is transparent to the New Entity. Therefore or clarity a
Proxy is always assumed.
To discover the Domain Bootstrap Server the New Entity performs the
following actions:
a. MUST: Obtains a local address using either IPv4 or IPv6 methods
as described in [RFC4862] IPv6 Stateless Address
AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4
Link-Local Addresses.
b. 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 New Entity 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.
Pritikin, et al. Expires January 1, 2017 [Page 13]
Internet-Draft BRewSKI June 2016
c. MAY: Performs DNS-based Service Discovery [RFC6763] over normal
DNS operations. The service searched for is
"_bootstrapks._tcp.example.net". In this case the domain
"example.net" 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 New Entity contacts a well
known vendor provided bootstrapping server by performing a DNS
lookup using a well known URI such as "bootstrapks.vendor-
example.com". The details of the URI are vendor specific.
Vendors that leverage this method SHOULD provision appropriately.
DNS-based service discovery communicates the local proxy IPv4 or IPv6
address and port to the New Entity. Once a proxy is discovered the
New Entity communicates with the 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 New Entity returns to
the Discovery state it picks up where it left off and continues
attempting bootstrapping. For example if the first Multicast DNS
_bootstrapks._tcp.local response doesn't work then the second and
third responses are tried. If these fail the New Entity moves on to
normal DNS-based Service Discovery.
Each discovery method attempted SHOULD exponentially back-off
attempts (to a maximum of one hour) to avoid overloading that
discovery methods network infrastructure. 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 New Entity may prioritize selection order as
appropriate for the anticipated environment.
3.1.2. Identity
The New Entity identifies itself during the communication protocol
handshake. If the client identity is rejected the New Entity repeats
the Discovery process using the next proxy or discovery method
available.
The bootstrapping protocol server is not initially authenticated.
Thus the connection is provisional and all data received is untrusted
until sufficiently validated even though it is over a TLS connection.
Pritikin, et al. Expires January 1, 2017 [Page 14]
Internet-Draft BRewSKI June 2016
This is aligned with the existing provisional mode of EST [RFC7030]
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 New Entity POSTs a request to join the domain to the
Bootstrapping server. This request contains a New Entity generated
nonce and informs the Bootstrapping server which imprint methods the
New Entity will accept.
As indicated in EST [RFC7030] the bootstrapping server MAY redirect
the client to an alternate server. This is most useful in the case
where the New Entity has resorted to a well known vendor URI and is
communicating with the vendor's Registrar directly. In this case the
New Entity has authenticated the Registrar using the local Implicit
Trust Anchor database and can therefore treat the redirect URI as a
trusted URI which can also be validated using the Implicit Trust
Anchor database. Since client authentication occurs during the TLS
handshake the bootstrapping server has sufficient information to
apply appropriate policy concerning which server to redirect to.
The nonce ensures the New Entity can verify that responses are
specific to this bootstrapping attempt. This minimizes the use of
global time and provides a substantial benefit for devices without a
valid clock.
3.1.4. Imprint
The domain trust anchor is received by the New Entity during the
bootstrapping protocol methods in the form of either an Audit Token
containing the domain CA cert or an explicit ownership voucher. The
goal of the imprint state is to securely obtain a copy of this trust
anchor without involving human interaction.
The enrollment protocol EST [RFC7030] details a set of non-autonomic
bootstrapping methods such as:
o using the Implicit Trust Anchor database (not an autonomic
solution because the URL must be securely distributed),
o engaging a human user to authorize the CA certificate using out-
of-band data (not an autonomic solution because the human user is
involved),
Pritikin, et al. Expires January 1, 2017 [Page 15]
Internet-Draft BRewSKI June 2016
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 additional autonomic methods:
MASA audit token Audit tokens are obtained by the Registrar from the
MASA service and presented to the New Entity for validation.
These indicate to the New Entity that joining the domain has been
logged by a logging service.
Ownership Voucher Ownership Vouchers are obtained by the Registrar
from the MASA service and explicitly indicate the fully qualified
domain name of the domain the new entity currently belongs to.
The Ownership Voucher is defined in [I-D.ietf-netconf-zerotouch].
Since client authentication occurs during the TLS handshake the
bootstrapping server has sufficient information to apply appropriate
policy concerning which method to use.
The audit token contains the domain's public key material as provided
to the MASA service by the Registrar. This provides sufficient
information to the client to complete automated bootstrapping with
the local key infrastructure.
If the autonomic methods fail the New Entity 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 New Entity maintaining a concept of the current
"window" of presumed time validity that is continually refined
throughout the bootstrapping process as follows:
Pritikin, et al. Expires January 1, 2017 [Page 16]
Internet-Draft BRewSKI June 2016
o Initially the New Entity does not know the current time. The
nonce included in join attempts provides an alternate mechanism
for the New Entity to ensure responses are associated with a
particular bootstrapping attempt. Nonceless audit tokens from the
MASA server are always valid and thus time is not needed.
o In accordance with IEEE 802.1AR and RFC5280 all manufacturing
installed certificates and trust anchors are assumed to have
infinite lifetimes. All such certificates "SHOULD be assigned the
GeneralizedTime value of 99991231235959Z" [RFC5280]. The New
Entity, Registrar and MASA server MUST ignore any other validity
period information in these credentials and treat the effective
lifetime as 99991231235959Z. This ensures that client
authentication (see Section 3.3.1) and the audit token signature
(see Section 5.3) can always be verified during RFC5280 path
validation.
o Once the audit token is accepted the validity period of the
domainCAcert in the token (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 end entity certificate is assumed to be valid by
the New Entity. The New Entity is now willing to use this
credential for client authentication.
Once in this state the New Entity 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.
3.1.6. Enrollment
As the final step of bootstrapping a Registrar helps to issue a
domain specific credential to the New Entity. For simplicity in this
document, a Registrar primarily facilitates issuing a credential by
acting as an RFC5280 Registration Authority for the Domain
Certification Authority.
Enrollment proceeds as described in Enrollment over Secure Transport
(EST) [RFC7030]. The New Entity contacts the Registrar using EST as
indicated:
o The New Entity is authenticated using the IEEE 802.1AR
credentials.
Pritikin, et al. Expires January 1, 2017 [Page 17]
Internet-Draft BRewSKI June 2016
o The EST section 4.1.3 CA Certificates Response is verified using
either the Audit Token which provided the domain identity -or-
o The EST server is authenticated by using the Ownership Voucher
indicated fully qualified domain name to build the EST URI such
that EST section 4.1.1 bootstrapping using the New Entity implicit
Trust Anchor database can be used.
Once the Audit Token is received, as specified in this document, the
client has sufficient information to leverage the existing
communication channel with the Registrar to continue an EST RFC7030
enrollment. Enrollment picks up at RFC7030 section 4.1.1.
bootstrapping where the audit token 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 New Entity uses bootstrapping to join only one domain.
Management by multiple domains is out-of-scope of bootstrapping.
After the device has successfully joined a domain and is being
managed it is plausible that the domain can insert credentials for
other domains depending on the device capabilities.
See Section 3.5.
3.2. Behavior of a Proxy
The role of the Proxy is to facilitate communications. The Proxy
forwards packets between the New Entity and the Registrar that has
been configured on the Proxy. The Proxy does not terminate the TLS
handshake.
In order to permit the proxy functionality to be implemented on the
maximum variety of devices the chosen mechanism SHOULD use the
minimum amount of state on the proxy device. While many devices in
Pritikin, et al. Expires January 1, 2017 [Page 18]
Internet-Draft BRewSKI June 2016
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.]]
As a result of the Proxy Discovery process in section Section 3.1.1,
the port number exposed by the proxy does not need to be well known,
or require an IANA allocation.
The address and port of the Registrar to which the packets will be
forwarded will be discovered by the GRASP protocol inside the ACP.
For the IPIP encapsulation methods, the port announced by the Proxy
MUST be the same as on the registrar in order for the proxy to remain
stateless.
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 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 New Node to the Registrar.
When the Proxy provides a circuit proxy to the Registrar the
Registrar MUST accept HTTPS connections.
Pritikin, et al. Expires January 1, 2017 [Page 19]
Internet-Draft BRewSKI June 2016
When the Proxy provides a stateless IPIP encapsulation to the
Registrar, then the Registrar will have to perform IPIP
decapsulation, remembering the originating outer IPIP source address
in order to qualify the inner link-local address. 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 (Bootstrap Server)
Once a Registrar is established it listens for new entities and
determines if they can join the domain. The registrar delivers any
necessary authorization information to the new device and facilitates
enrollment with the domain PKI.
Registrar behavior is as follows:
Pritikin, et al. Expires January 1, 2017 [Page 20]
Internet-Draft BRewSKI June 2016
Contacted by New Entity
+
|
+-------v----------+
| Entity | fail?
| Authentication +---------+
+-------+----------+ |
| |
+-------v----------+ |
| Entity | fail? |
| Authorization +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Claiming the | fail? |
| Entity +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Log Verification | fail? |
| +--------->
+-------+----------+ |
| |
+-------v----------+ +----v-------+
| Forward | | |
| Audit | | Reject |
| token + config | | Device |
| to the Entity | | |
+------------------+ +------------+
Figure 4
3.3.1. Entity Authentication
The applicable authentication methods detailed in EST [RFC7030] are:
o the use of an IEEE 802.1AR IDevID credential during the TLS client
authentication,
o or the use of a secret that is transmitted out of band between the
New Entity and the Registrar (this use case is not autonomic).
3.3.2. Entity Authorization
In a fully automated network all devices must be securely identified
and authorized to join the domain.
Pritikin, et al. Expires January 1, 2017 [Page 21]
Internet-Draft BRewSKI June 2016
A Registrar accepts or declines a request to join the domain, based
on the authenticated identity presented. Automated acceptance
criteria include:
o allow any device of a specific type (as determined by the IEEE
802.1AR device identity),
o allow any device from a specific vendor (as determined by the IEEE
802.1AR identity),
o allow a specific device from a vendor (as determined by the IEEE
802.1AR identity)
Since all New Entities accept Audit Tokens the Registrar MUST use the
vendor provided MASA service to verify that the device's history log
does not include unexpected Registrars. If a device had previously
registered with another domain, the Registrar of that domain would
show in the log.
In order to validate the IEEE 802.1AR device identity the Registrar
maintains a database of vendor trust anchors (e.g. vendor root
certificates or keyIdentifiers for vendor root public keys). For
user interface purposes this database can be mapped to colloquial
vendor names. Registrars can be shipped with the trust anchors of a
significant number of third-party vendors within the target market.
If a device is accepted into the domain, it is expected request a
domain certificate through a certificate enrollment process. The
result is a common trust anchor and device certificates for all
autonomic devices in a domain (these certificates can subsequently be
used to determine the boundaries of the homenet, to authenticate
other domain nodes, and to autonomically enable services on the
homenet). The authorization performed during this phase MAY be
cached for the TLS session and applied to subsequent EST enrollment
requests so long as the session lasts.
3.3.3. Claiming the New Entity
Claiming an entity establishes an audit log at the MASA server and
provides the Registrar with proof, in the form of a MASA
authorization token, that the log entry has been inserted. As
indicated in Section 3.1.4 a New Entity will only proceed with
bootstrapping if a validated MASA authorization token has been
received. The New Entity therefore enforces that bootstrapping only
occurs if the claim has been logged. There is no requirement for the
vendor to definitively know that the device is owned by the
Registrar.
Pritikin, et al. Expires January 1, 2017 [Page 22]
Internet-Draft BRewSKI June 2016
Registrar's obtain the Vendor URI via static configuration or by
extracting it from the IEEE 802.1AR credential. The imprint method
supported by the New Entity is known from the IEEE 802.1AR
credential. [[EDNOTE: An appropriate extension for indicating the
Vendor URI and imprint method could be defined using the methods
described in [I-D.lear-mud-framework]]].
During initial bootstrapping the New Entity provides a nonce specific
to the particular bootstrapping attempt. The Registrar SHOULD
include this nonce when claiming the New Entity from the MASA
service. Claims from an unauthenticated Registrar are only serviced
by the MASA resource if a nonce is provided.
The Registrar can claim a New Entity that is not online by forming
the request using the entities unique identifier and not including a
nonce in the claim request. Audit Tokens obtained in this way do not
have a lifetime and they provide a permanent method for the domain to
claim the device. Evidence of such a claim is provided in the audit
log entries available to any future Registrar. Such claims reduce
the ability for future domains to secure bootstrapping and therefore
the Registrar MUST be authenticated by the MASA service.
An ownership voucher requires the vendor to definitively know that a
device is owned by a specific domain. The method used to "claim"
this are out-of-scope. The Registrar simply requests an ownership
validation token and the New Entity trusts the response.
3.3.4. Log Verification
The Registrar requests the log information for the new entity from
the MASA service. The log is verified to confirm that the following
is true to the satisfaction of the Registrar's configured policy:
o Any nonceless entries in the log are associated with domainIDs
recognized by the registrar.
o Any nonce'd entries are older than when the domain is known to
have physical possession of the new entity or that the domainIDs
are recognized by the registrar.
If any of these criteria are unacceptable to the registrar the entity
is rejected. The Registrar MAY be configured to ignore the history
of the device but it is RECOMMENDED that this only be configured if
hardware assisted NEA [RFC5209] is supported.
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 token
Pritikin, et al. Expires January 1, 2017 [Page 23]
Internet-Draft BRewSKI June 2016
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 IEEE 802.1AR IDevID X.509 extension (a "MASA
Audit Token Distribution Point" extension).
The MASA service provides the following functionalities to
Registrars:
3.4.1. Issue Authorization Token and Log the event
A Registrar POSTs a claim message optionally containing the bootstrap
nonce to the MASA server.
If a nonce is provided the MASA service responds to all requests.
The MASA service verifies the Registrar is representative of the
domain and generates a privacy protected log entry before responding
with the Audit Token.
If a nonce is not provided then the MASA service MUST authenticate
the Registrar as a valid customer. This prevents denial of service
attacks.
3.4.2. Retrieve Audit Entries from Log
When determining if a New Entity should be accepted into a domain the
Registrar retrieves a copy of the audit log from the MASA service.
This contains a list of privacy protected domain identities that have
previously claimed the device. Included in the list is an indication
of the time the entry was made and if the nonce was included.
3.5. Leveraging the new key infrastructure / next steps
As the devices have a common trust anchor, device identity can be
securely established, making it possible to automatically deploy
services across the domain in a secure manner.
Examples of services:
o Device management.
o Routing authentication.
Pritikin, et al. Expires January 1, 2017 [Page 24]
Internet-Draft BRewSKI June 2016
o Service discovery.
3.5.1. Network boundaries
When a device has joined the domain, it can validate the domain
membership of other devices. This makes it possible to create trust
boundaries where domain members have higher level of trusted than
external devices. Using the autonomic User Interface, specific
devices can be grouped into to sub domains and specific trust levels
can be implemented between those.
3.6. Interactions with Network Access Control
The assumption is that Network Access Control (NAC) completes using
the New Entity 802.1AR credentials and results in the device having
sufficient connectivity to discovery and communicate with the proxy.
Any additional connectivity or quarantine behavior by the NAC
infrastructure is out-of-scope. After the devices has completed
bootstrapping the mechanism to trigger NAC to re-authenticate the
device and provide updated network privileges is also out-of-scope.
This achieves the goal of a bootstrap architecture that can integrate
with NAC but does not require NAC within the network where it wasn't
previously required. Future optimizations can be achieved by
integrating the bootstrapping protocol directly into an initial EAP
exchange.
4. Domain Operator Activities
This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.
4.1. Instantiating the Domain Certification Authority
This is a one time step by the domain administrator. This is an "off
the shelf" CA with the exception that it is designed to work as an
integrated part of the security solution. This precludes the use of
3rd party certification authority services that do not provide
support for delegation of certificate issuance decisions to a domain
managed Registration Authority.
4.2. Instantiating the Registrar
This is a one time step by the domain administrator. One or more
devices in the domain are configured take on a Registrar function.
A device can be configured to act as a Registrar or a device can
auto-select itself to take on this function, using a detection
Pritikin, et al. Expires January 1, 2017 [Page 25]
Internet-Draft BRewSKI June 2016
mechanism to resolve potential conflicts and setup communication with
the Domain Certification Authority. Automated Registrar selection is
outside scope for this document.
4.3. Accepting New Entities
For each New Entity the Registrar is informed of the unique
identifier (e.g. serial number) along with the manufacturer's
identifying information (e.g. manufacturer root certificate). This
can happen in different ways:
1. Default acceptance: In the simplest case, the new device asserts
its unique identity to the registrar. The registrar accepts all
devices without authorization checks. This mode does not provide
security against intruders and is not recommended.
2. Per device acceptance: The new device asserts its unique identity
to the registrar. A non-technical human validates the identity,
for example by comparing the identity displayed by the registrar
(for example using a smartphone app) with the identity shown on
the packaging of the device. Acceptance may be triggered by a
click on a smartphone app "accept this device", or by other forms
of pairing. See also [I-D.behringer-homenet-trust-bootstrap] for
how the approach could work in a homenet.
3. Whitelist acceptance: In larger networks, neither of the previous
approaches is acceptable. Default acceptance is not secure, and
a manual per device methods do not scale. Here, the registrar is
provided a priori with a list of identifiers of devices that
belong to the network. This list can be extracted from an
inventory database, or sales records. If a device is detected
that is not on the list of known devices, it can still be
manually accepted using the per device acceptance methods.
4. Automated Whitelist: an automated process that builds the
necessary whitelists and inserts them into the larger network
domain infrastructure is plausible. Once set up, no human
intervention is required in this process. Defining the exact
mechanisms for this is out of scope although the registrar
authorization checks is identified as the logical integration
point of any future work in this area.
None of these approaches require the network to have permanent
Internet connectivity. Even when the Internet based MASA service is
used, it is possible to pre-fetch the required information from the
MASA a priori, for example at time of purchase such that devices can
enroll later. This supports use cases where the domain network may
be entirely isolated during device deployment.
Pritikin, et al. Expires January 1, 2017 [Page 26]
Internet-Draft BRewSKI June 2016
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.
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 New Entity, 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 new entity 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 "New Entity" 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
Pritikin, et al. Expires January 1, 2017 [Page 27]
Internet-Draft BRewSKI June 2016
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 New Entity client are as follows:
o The New Entity provisionally accept the EST server certificate
during the TLS handshake as detailed in Section 5.3.1.
o The New Entity requests and validates the Audit Token as described
below. At this point the New Entity has sufficient information to
validate domain credentials.
o The New Entity calls the EST defined /cacerts method to obtain the
current CA certificate. These are validated using the Audit
Token.
o The New Entity completes bootstrapping as detailed in EST section
4.1.1.
In order to obtain a validated Audit Token and Audit Log the
Registrar contacts the MASA service Service using REST calls:
Pritikin, et al. Expires January 1, 2017 [Page 28]
Internet-Draft BRewSKI June 2016
+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
+---------------C---------------> |
| | | |
HTTP REST | POST /requestaudittoken | |
Data +--------------------nonce------> |
| . | /requestaudittoken
| . +---------------->
| <----------------+
| | /requestauditlog
| +---------------->
| audit token or owner voucher <----------------+
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 5
In some use cases the Registrar may need to contact the Vendor in
advanced, for example when the target network is air-gapped. The
nonceless request format is provided for this and the resulting flow
is slightly different. The security differences associated with not
knowing the nonce are discussed below:
Pritikin, et al. Expires January 1, 2017 [Page 29]
Internet-Draft BRewSKI June 2016
+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| | | /requestaudittoken
| | (nonce +---------------->
| | unknown) <----------------+
| | | /requestauditlog
| | +---------------->
| | <----------------+
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
| | | |
HTTP REST | POST /requestaudittoken | |
Data +----------------------nonce----> (discard |
| audit token or owner Voucher | nonce) |
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 6
The extensions for the Registrar server are as follows:
o The Registrar requests and validates the Audit Token from the
vendor authorized MASA service.
o The Registrar forwards the Audit Token to the New Entity when
requested.
o The Registar performs log verifications in addition to local
authorization checks before accepting the New Entity device.
5.1. Request Audit Token from the Registrar
When the New Entity reaches the EST section 4.1.1 "Bootstrap
Distribution of CA Certificates" state but wishes to proceed in a
fully automated fashion it makes a request for a MASA authorization
token from the Registrar.
Pritikin, et al. Expires January 1, 2017 [Page 30]
Internet-Draft BRewSKI June 2016
This is done with an HTTPS POST using the operation path value of
"/requestaudittoken".
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 New Entity
that the audit token 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 new entity 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 Audit Token from the MASA service (see
Section 5.2).
The received MASA authorization token is returned to the New Entity.
As indicated in EST [RFC7030] the bootstrapping server can redirect
the client to an alternate server. If the New Entity authenticated
the Registrar using the well known URI method then the New Entity
MUST follow the redirect automatically and authenticate the new
Registrar against the redirect URI provided. If the New Entity had
not yet authenticated the Registrar because it was discovered and was
not a known-to-be-valid URI then the new Registrar must be
authenticated using one of the two autonomic methods described in
this document. 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.
Pritikin, et al. Expires January 1, 2017 [Page 31]
Internet-Draft BRewSKI June 2016
Recall that during this communication with the Registar the TLS
authentication is only provisional. The New Entity client MUST
handle all data from the Registrar with upmost care. In particular
the New Entity MUST only allow a single redirection and MUST only
support a 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 New Entity
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 Audit Token from MASA
The Registrar requests the Audit Token from the MASA service using a
REST interface. For simplicity this is defined as an optional EST
message between the Registrar and an EST server running on the MASA
service although the Registrar is not required to make use of any
other EST functionality when communicating with the MASA service.
(The MASA service MUST properly reject any EST functionality requests
it does not wish to service; a requirement that holds for any REST
interface).
This is done with an HTTP POST using the operation path value of
"/requestaudittoken".
The request format is a JSON object optionally containing the nonce
value (as obtained from the bootstrap request) and the IEEE 802.1AR
identity of the device as a serial number (the full certificate is
not needed and no proof-of-possession information for the device
identity is included). The AuthorityKeyIdentifier value from the
certificate is included to ensure a statistically unique identity.
The New Entity's serial number is extracted from the IEEE 802.1AR
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>",
}
The Registrar MAY exclude the nonce from the request. Doing so
allows the Registrar to request an authorization token when the New
Entity is not online, or when the target bootstrapping environment is
not on the same network as the MASA server (this requires the
Registrar to learn the appropriate DevIDSerialNumber field from the
Pritikin, et al. Expires January 1, 2017 [Page 32]
Internet-Draft BRewSKI June 2016
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. The
registrar performs authorization as detailed in Section 3.3.2. If
authorization is successful the Registrar obtains an Audit Token from
the MASA service (see Section 5.2).
The 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 domain ID (e.g. hash of the public key of the domain) is
extracted from the root certificate and is used to populate the MASA
authorization token and to update the audit log.
5.3. Audit Token Response
The authorization token response to requests from the device and
requests from the Registrar are in the same format. The Registrar
either caches prior MASA responses or dynamically requests a new
Audit Token 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/authorization-token". 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 authorization token consists of the nonce, if supplied, the
serial number information identifying the device and the domain CA
certificate extracted from the request:
Pritikin, et al. Expires January 1, 2017 [Page 33]
Internet-Draft BRewSKI June 2016
{
"version":"1",
"nonce":"<64bit nonce value>",
"IDevIDAuthorityKeyIdentifier":"<base64 encoded keyIdentifier>",
"DevIDSerialNumber":"<id-at-serialNumber>",
"domainCAcert":"<the base64 encoded domain CA's certificate>"
}
The audit token response is encapsulated in a [RFC5652] Signed-data
that is signed by the MASA server. The New Entity verifies this
signed message using the IEEE 802.1AR manufacturer installed trust
anchor.
[[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 token response that does not contain a 'domainCAcert'
field at all.
To minimize the size of the audit token response message the
domainCAcert is not a complete distribution of the EST section 4.1.3
CA Certificate Response.
The New Entity 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 New Entity MUST use the
domainCAcert trust anchor to immediately validate the currently
provisional TLS connection to the Registrar.
5.3.1. Completing authentication of Provisional TLS connection
If the Registrar's credential can not be verified using the
domainCAcert trust anchor the TLS connection is immediately discarded
and the New Entity abandons attempts to bootstrap with this
discovered registrar.
Pritikin, et al. Expires January 1, 2017 [Page 34]
Internet-Draft BRewSKI June 2016
The following behaviors on the Registrar and New Entity are in
addition to normal PKIX operations:
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 New Entity PKIX path validation of the 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 New Entity SHOULD avoid additional discovery
operations. Instead the New entity SHOULD communicate directly with
the Registrar as the EST server to complete PKI local certificate
enrollment. Additionally the New Entity 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. Audit Token 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 New Entity status regarding the audit token the client
SHOULD post a status message.
The client HTTP POSTs the following to the server at the EST well
known URI /requestaudittoken_status. The Status field indicates if
the audit token 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 audit
token was ignored by a client the registar expected to continue
joining the domain.
Pritikin, et al. Expires January 1, 2017 [Page 35]
Internet-Draft BRewSKI June 2016
{
"version":"1",
"Status":FALSE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
}
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
"/requestMASAlog".
The client HTTP POSTs the same Audit Token Request as for requesting
an audit token but now posts it the /requestMASAlog 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 token 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 token request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
}
]
}
Pritikin, et al. Expires January 1, 2017 [Page 36]
Internet-Draft BRewSKI June 2016
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.
The Registrar uses this log information to make an informed decision
regarding the continued bootstrapping of the New Entity. For example
if the log includes unexpected domainIDs this is indicative of
problematic imprints by the new entity. If 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 token 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 New Entity to obtain
a trust anchor representative of the Domain. The following section
describe using EST to obtain a locally issued PKI certificate. The
New Entity MAY perform alternative enrollment methods or proceed to
use its IDevID credential indefinately, but those that leverage the
discovered Registrar to proceed with certificate enrollment MUST
implement the following EST choices.
5.7.1. EST Distribution of CA Certificates
The New Entity MUST request the full EST Distribution of CA
Certificates message. See RFC7030, section 4.1.
This ensures that the New Entity 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 the Registrar integrated with initial bootstrapping
they are not appropriate for ongoing PKIX end entity certificate
validation.
Pritikin, et al. Expires January 1, 2017 [Page 37]
Internet-Draft BRewSKI June 2016
5.7.2. EST CSR Attributes
Automated bootstrapping occurs without local administrative
configuration of the New Entity. In some deployments its plausible
that the New Entity generates a certificate request containing only
identity information known to the New Entity (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 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 New Entity MUST request the
EST "CSR Attributes" from the EST server. This allows the local
infrastructure to inform the New Entity 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 New Entity 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
Pritikin, et al. Expires January 1, 2017 [Page 38]
Internet-Draft BRewSKI June 2016
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
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 New Entity
and Registrar and means that the EST protocol operation encapsulation
into CoAP needs to be described. EST is HTTP based and "CoaP is
designed to easily interface with HTTP for integration" [RFC7252].
Use of CoAP implies Datagram TLS (DTLS) wherever this document
describes TLS handshake specifics. A complexity is that the large
Pritikin, et al. Expires January 1, 2017 [Page 39]
Internet-Draft BRewSKI June 2016
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
sections detail specific ways that the New Entity, Registrar and MASA
can be configured to run in a less secure mode for the indicated
reasons.
6.1. Trust Model
+--------+ +---------+ +------------+ +------------+
| New | | Circuit | | Domain | | Vendor |
| Entity | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
Figure 7
New Entity: The New Entity could be compromised and providing an
attack vector for malware. The entity is trusted to only imprint
using secure methods described in this document. Additional
endpoint assessment techniques are RECOMMENDED but are out-of-
scope of this document.
Proxy: Provides proxy functionalities but is not involved in
security considerations.
Registrar: When interacting with a MASA server the Registrar makes
all decisions. When ownership vouchers are involved the Registrar
is only a conduit and all security decisions are made on the
vendor service.
Vendor Service, MASA: This form of vendor service is trusted to
accurately log all claim attempts and to provide authoritative log
information to Registrars. The MASA does not know which devices
are associated with which domains. 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.
Pritikin, et al. Expires January 1, 2017 [Page 40]
Internet-Draft BRewSKI June 2016
6.2. New Entity security reductions
Although New Entity can choose to run in less secure modes this is
MUST NOT be the default state because it permanently degrades the
security for all other uses cases.
The device may have an operational mode where it skips Audit Token or
Ownership Voucher validation one time. For example if a physical
button is depressed during the bootstrapping operation. This can be
useful if the vendor service is unavailable. This behavior SHOULD be
available via local configuration or physical presence methods to
ensure new entities can always be deployed even when autonomic
methods fail. This allows for unsecure imprint.
It is RECOMMENDED that this only be available if hardware assisted
NEA [RFC5209] is supported.
6.3. Registrar security reductions
The Registrar can choose to accept devices using less secure methods.
These methods are 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. The registrar MAY choose to accept all devices, or all devices of
a particular type, at the administrator's discretion. This could
occur when informing the Registrar of unique identifiers of new
entities might be operationally difficult.
2. The registrar MAY choose to accept devices that claim a unique
identity without the benefit of authenticating that claimed
identity. This could occur when the New Entity does not include
an IEEE 802.1AR factory installed credential. New Entities
without an IDevID credential MAY form the Section 5.1 request
using the Section 5.2 format to ensure the New Entity's serial
number information is provided to the Registar (this includes the
IDevIDAuthorityKeyIdentifier value which would be statically
configured on the New Entity). The New Entity MAY refused to
provide a TLS client certificate (as one is not available). The
New Entity SHOULD support HTTP-based or certificate-less TLS
authentication as described in EST RFC7030 section 3.3.2.
3. The registrar MAY request nonce-less Audit Tokens from the MASA
service. These tokens can then be transmitted to the Registrar
and stored until they are needed during bootstrapping operations.
This is for use cases where target network is protected by an air
gap and therefore can not contact the MASA service during New
Entity deployment.
Pritikin, et al. Expires January 1, 2017 [Page 41]
Internet-Draft BRewSKI June 2016
4. The registrar MAY ignore unrecognized nonce-less Audit Log
entries. This could occur when used equipment is purchased with
a valid history being deployed in air gap networks that required
permanent Audit Tokens.
These modes are not available for devices that require a vendor
Ownership Voucher. The methods vendors use to determine which
devices are owned by which domains is out-of-scope.
6.4. MASA security reductions
Lower security modes chosen by the MASA service effect all device
deployments unless bound to the specific device identities. In which
case these modes can be provided as additional features for specific
customers. The MASA service can choose to run in less secure modes
by:
1. Not enforcing that a Nonce is in the Audit Token. This results
in distribution of Audit Tokens that never expire and in effect
makes the Domain an always trusted entity to the New Entity
during any subsequent bootstrapping attempts. That this occurred
is captured in the log information so that the Domain registrar
can make appropriate security decisions when a New Entity joins
the Domain. This is useful to support use cases where Registrars
might not be online during actual device deployment. Because
this results in long lived Audit Tokens and do not require the
proof that the device is online this is only accepted when the
Registrar is authenticated by the MASA server and authorized to
provide this functionality. The MASA server is RECOMMENDED to
use this functionality only in concert with Ownership Validation
tracking.
2. Not verifying ownership before responding with an Audit Token.
This is expected to be a common operational model because doing
so relieves the vendor providing MASA services from having to
tracking ownership during shipping and supply chain and allows
for a very low overhead MASA service. The Registrar uses the
audit log information as a defense in depth strategy to ensure
that this does not occur unexpectedly (for example when
purchasing new equipment the Registrar would throw an error if
any audit log information is reported).
7. Security Considerations
In order to support a wide variety of use cases, devices can be
claimed by a registrar without proving possession of the device in
question. This would result in a nonceless, and thus always valid,
claim. Or would result in an invalid nonce being associated with a
Pritikin, et al. Expires January 1, 2017 [Page 42]
Internet-Draft BRewSKI June 2016
claim. The MASA service is required to authenticate such Registrars
but no programmatic method is provided to ensure good behavior by the
MASA service. Nonceless entries into the audit log therefore
permanently reduce the value of a device because future Registrars,
during future bootstrap attempts, would now have to be configured
with policy to ignore previously (and potentially unknown) domains.
Future registrars are recommended to take the audit history of a
device into account when deciding to join such devices into their
network. If the MASA server were to have allowed a significantly
large number of claims this might become onerous to the MASA server
which must maintain all the extra log entries. Ensuring the
Registrar is representative of a valid customer domain even without
validating ownership helps to mitigate this.
It is possible for an attacker to send an authorization request to
the MASA service directly after the real Registrar obtains an
authorization log. If the attacker could also force the
bootstrapping protocol to reset there is a theoretical opportunity
for the attacker to use the Audit Token to take control of the New
Entity but then proceed to enroll with the target domain. Possible
prevention mechanisms include:
o Per device rate limits on the MASA service ensure such timing
attacks are difficult.
o In the advent of an unexpectedly lost bootstrapping connection the
Registrar repeats the request for audit log information.
To facilitate auditing the New Entity reports on audit token parsing
status. In the case of a failure this information is informative to
the potentially malicious Registar but this is included because the
operational benefits are concidered beneficial.
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.
Pritikin, et al. Expires January 1, 2017 [Page 43]
Internet-Draft BRewSKI June 2016
The MASA service could lock a claim and refuse to issue a new token
or the MASA service could go offline (for example if a vendor went
out of business). This functionality provides benefits such as theft
resistance, but it also implies an operational risk to the Domain
that Vendor behavior could limit future bootstrapping of the device
by the Domain. This can be mitigated by Registrars that request
nonce-less authorization tokens.
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>.
[RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 3542, May 2003.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
Security: An Unauthenticated Mode of IPsec", RFC 5386,
November 2008.
[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, October 2009.
Pritikin, et al. Expires January 1, 2017 [Page 44]
Internet-Draft BRewSKI June 2016
[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>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
9.2. Informative References
[I-D.behringer-homenet-trust-bootstrap]
Behringer, M., Pritikin, M., and S. Bjarnason,
"Bootstrapping Trust on a Homenet", draft-behringer-
homenet-trust-bootstrap-02 (work in progress), February
2014.
[I-D.ietf-ace-actors]
Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
architecture for authorization in constrained
environments", draft-ietf-ace-actors-03 (work in
progress), March 2016.
[I-D.ietf-netconf-zerotouch]
Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
for NETCONF or RESTCONF based Management", draft-ietf-
netconf-zerotouch-08 (work in progress), April 2016.
[I-D.irtf-nmrg-autonomic-network-definitions]
Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking - Definitions and Design Goals", draft-irtf-
nmrg-autonomic-network-definitions-07 (work in progress),
March 2015.
[I-D.lear-mud-framework]
Lear, E., "Manufacturer Usage Description Framework",
draft-lear-mud-framework-00 (work in progress), January
2016.
Pritikin, et al. Expires January 1, 2017 [Page 45]
Internet-Draft BRewSKI June 2016
[I-D.richardson-anima-state-for-joinrouter]
Richardson, M., "Considerations for stateful vs stateless
join router in ANIMA bootstrap", draft-richardson-anima-
state-for-joinrouter-00 (work in progress), January 2016.
[imprinting]
Wikipedia, , "Wikipedia article: Imprinting", July 2015,
<https://en.wikipedia.org/wiki/Imprinting_(psychology)>.
[pledge] Dictionary.com, , "Dictionary.com Unabridged", July 2015,
<http://dictionary.reference.com/browse/pledge>.
Authors' Addresses
Max Pritikin
Cisco
Email: pritikin@cisco.com
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z 5V7
CA
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Michael H. Behringer
Cisco
Email: mbehring@cisco.com
Steinthor Bjarnason
Cisco
Email: sbjarnas@cisco.com
Pritikin, et al. Expires January 1, 2017 [Page 46]