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ANIMA WG M. Pritikin
Internet-Draft Cisco
Intended status: Standards Track M. Richardson
Expires: January 4, 2018 SSW
M. Behringer
S. Bjarnason
Cisco
K. Watsen
Juniper Networks
July 3, 2017
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
draft-ietf-anima-bootstrapping-keyinfra-07
Abstract
This document specifies automated bootstrapping of a remote secure
key infrastructure (BRSKI) using vendor installed X.509 certificate,
in combination with a vendor's authorizing service, both online and
offline. Bootstrapping a new device can occur using a routable
address and a cloud service, or using only link-local connectivity,
or on limited/disconnected networks. Support for lower security
models, including devices with minimal identity, is described for
legacy reasons but not encouraged. Bootstrapping is complete when
the cryptographic identity of the new key infrastructure is
successfully deployed to the device but the established secure
connection can be used to deploy a locally issued certificate to the
device as well.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 4, 2018.
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Copyright Notice
Copyright (c) 2017 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Other Bootstrapping Approaches . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Scope of solution . . . . . . . . . . . . . . . . . . . . 7
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 9
2.1. Secure Imprinting using Vouchers . . . . . . . . . . . . 10
2.2. Initial Device Identifier . . . . . . . . . . . . . . . . 10
2.3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 12
2.4. Lack of realtime clock . . . . . . . . . . . . . . . . . 14
2.5. Cloud Registrar . . . . . . . . . . . . . . . . . . . . . 15
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 15
3.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1.1. Proxy Discovery Protocol Details . . . . . . . . . . 18
3.1.2. Registrar Discovery Protocol Details . . . . . . . . 18
3.2. Request Voucher from the Registrar . . . . . . . . . . . 19
3.3. Request Voucher from MASA . . . . . . . . . . . . . . . . 20
3.4. Voucher Response . . . . . . . . . . . . . . . . . . . . 23
3.4.1. Completing authentication of Provisional TLS
connection . . . . . . . . . . . . . . . . . . . . . 24
3.5. Voucher Status Telemetry . . . . . . . . . . . . . . . . 25
3.6. MASA authorization log Request . . . . . . . . . . . . . 26
3.7. MASA authorization log Response . . . . . . . . . . . . . 26
3.8. EST Integration for PKI bootstrapping . . . . . . . . . . 27
3.8.1. EST Distribution of CA Certificates . . . . . . . . . 28
3.8.2. EST CSR Attributes . . . . . . . . . . . . . . . . . 28
3.8.3. EST Client Certificate Request . . . . . . . . . . . 29
3.8.4. Enrollment Status Telemetry . . . . . . . . . . . . . 29
3.8.5. EST over CoAP . . . . . . . . . . . . . . . . . . . . 30
4. Reduced security operational modes . . . . . . . . . . . . . 30
4.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 30
4.2. Pledge security reductions . . . . . . . . . . . . . . . 31
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4.3. Registrar security reductions . . . . . . . . . . . . . . 32
4.4. MASA security reductions . . . . . . . . . . . . . . . . 33
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
5.1. PKIX Registry . . . . . . . . . . . . . . . . . . . . . . 34
6. Security Considerations . . . . . . . . . . . . . . . . . . . 34
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
8.1. Normative References . . . . . . . . . . . . . . . . . . 36
8.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. IPv4 operations . . . . . . . . . . . . . . . . . . 39
A.1. IPv4 Link Local addresses . . . . . . . . . . . . . . . . 39
A.2. Use of DHCPv4 . . . . . . . . . . . . . . . . . . . . . . 39
Appendix B. mDNS / DNSSD proxy discovery options . . . . . . . . 39
Appendix C. IPIP Join Proxy mechanism . . . . . . . . . . . . . 40
C.1. Multiple Join networks on the Join Proxy side . . . . . . 41
C.2. Automatic configuration of tunnels on Registrar . . . . . 41
C.3. Proxy Neighbor Discovery by Join Proxy . . . . . . . . . 42
C.4. Use of connected sockets; or IP_PKTINFO for CoAP on
Registrar . . . . . . . . . . . . . . . . . . . . . . . . 42
C.5. Use of socket extension rather than virtual interface . . 42
Appendix D. To be deprecated: Consolidation remnants . . . . . . 43
D.1. Functional Overview . . . . . . . . . . . . . . . . . . . 43
D.1.1. Behavior of a Pledge . . . . . . . . . . . . . . . . 46
D.1.2. Behavior of a Join Proxy . . . . . . . . . . . . . . 52
D.1.3. Behavior of the Registrar . . . . . . . . . . . . . . 53
D.1.4. Behavior of the MASA Service . . . . . . . . . . . . 57
D.1.5. Leveraging the new key infrastructure / next steps . 58
D.1.6. Interactions with Network Access Control . . . . . . 58
D.2. Domain Operator Activities . . . . . . . . . . . . . . . 58
D.2.1. Instantiating the Domain Certification Authority . . 59
D.2.2. Instantiating the Registrar . . . . . . . . . . . . . 59
D.2.3. Accepting New Entities . . . . . . . . . . . . . . . 59
D.2.4. Automatic Enrollment of Devices . . . . . . . . . . . 60
D.2.5. Secure Network Operations . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61
1. Introduction
BRSKI provides a foundation to securely answer the following
questions between an element of the network domain called the
"Registrar" and an unconfigured and untouched device called a
"Pledge":
o Registrar authenticating the Pledge: "Who is this device? What is
its identity?"
o Registrar authorization the Pledge: "Is it mine? Do I want it?
What are the chances it has been compromised?"
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o Pledge authenticating the Registrar/Domain: "What is this domain's
identity?"
o Pledge authorization the Registrar: "Should I join it?"
This document details protocols and messages to the endpoints to
answer the above questions. The Registrar actions derive from Pledge
identity, third party cloud service communications, and local access
control lists. The Pledge actions derive from a cryptographically
protected "voucher" message delivered through the Registrar.
The syntactic details of vouchers are described in detail in
[I-D.ietf-anima-voucher]. This document details automated protocol
mechanisms to obtain vouchers.
BRSKI results in the Pledge storing an X.509 root certificate
sufficient for verifying the Registrar identity. In the process a
TLS connection is established which can be directly used for
Enrollment over Secure Transport (EST). The Pledge can use these
credentials to secure additional protocol exchanges.
BRSKI is agile enough to support bootstrapping alternative key
infrastructures, such as a symmetric key solutions, but no such
system is described in this document.
1.1. Other Bootstrapping Approaches
To literally "pull yourself up by the bootstraps" is an impossible
action. Similarly the secure establishment of a key infrastructure
without external help is also an impossibility. Today it is commonly
accepted that the initial connections between nodes are insecure,
until key distribution is complete, or that domain-specific keying
material is pre-provisioned on each new device in a costly and non-
scalable manner. Existing mechanisms are known as non-secured 'Trust
on First Use' (TOFU) [RFC7435], 'resurrecting duckling'
[Stajano99theresurrecting] or 'pre-staging'.
Another approach is to try and minimize user actions during
bootstrapping. The enrollment protocol EST [RFC7030] details a set
of non-autonomic bootstrapping methods in this vein:
o using the Implicit Trust Anchor database (not an autonomic
solution because the URL must be securely distributed),
o engaging a human user to authorize the CA certificate using out-
of-band data (not an autonomic solution because the human user is
involved),
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o using a configured Explicit TA database (not an autonomic solution
because the distribution of an explicit TA database is not
autonomic),
o and using a Certificate-Less TLS mutual authentication method (not
an autonomic solution because the distribution of symmetric key
material is not autonomic).
These "touch" methods do not meet the requirements for zero-touch.
There are "call home" technologies where the Pledge first establishes
a connection to a well known vendor service using a common client-
server authentication model. After mutual authentication appropriate
credentials to authenticate the target domain are transfered to the
Pledge. This creates serveral problems and limitations:
o the pledge requires realtime connectivity to the vendor service,
o the domain identity is exposed to the vendor service (this is a
privacy concern),
o the vendor is responsible for making the authorization decisions
(this is a liability concern),
BRSKI addresses these issues by defining extensions to the EST
protocol for the automated distribution of vouchers.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The following terms are defined for clarity:
DomainID: The domain identity is the 160-bit SHA-1 hash of the BIT
STRING of the subjectPublicKey of the domain trust anchor that is
stored by the Domain CA. This is consistent with the
Certification Authority subject key identifier (Section 4.2.1.2
[RFC5280]) of the Domain CA's self signed root certificate. (A
string value bound to the Domain CA's self signed root certificate
subject and issuer fields is often colloquially used as a
humanized identity value but during protocol discussions the more
exact term as defined here is used).
drop ship: The physical distribution of equipment containing the
"factory default" configuration to a final destination. In zero-
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touch scenarios there is no staging or pre-configuration during
drop-ship.
imprint: The process where a device obtains the cryptographic key
material to identify and trust future interactions with a network.
This term is taken from Konrad Lorenz's work in biology with new
ducklings: during a critical period, the duckling would assume
that anything that looks like a mother duck is in fact their
mother. An equivalent for a device is to obtain the fingerprint
of the network's root certification authority certificate. A
device that imprints on an attacker suffers a similar fate to a
duckling that imprints on a hungry wolf. Securely imprinting is a
primary focus of this document.[imprinting]. The analogy to
Lorenz's work was first noted in [Stajano99theresurrecting].
enrollment: The process where a device presents key material to a
network and acquires a network specific identity. For example
when a certificate signing request is presented to a certification
authority and a certificate is obtained in response.
Pledge: The prospective device, which has an identity installed by a
third-party (e.g., vendor, manufacturer or integrator).
Voucher A signed statement from the MASA service that indicates to a
Pledge the cryptographic identity of the Registrar it should
trust. There are different types of vouchers depending on how
that trust asserted. Multiple voucher types are defined in
[I-D.ietf-anima-voucher]
Domain: The set of entities that trust a common key infrastructure
trust anchor. This includes the Proxy, Registrar, Domain
Certificate Authority, Management components and any existing
entity that is already a member of the domain.
Domain CA: The domain Certification Authority (CA) provides
certification functionalities to the domain. At a minimum it
provides certification functionalities to a Registrar and stores
the trust anchor that defines the domain. Optionally, it
certifies all elements.
Join Registrar (and Coordinator): A representative of the domain
that is configured, perhaps autonomically, to decide whether a new
device is allowed to join the domain. The administrator of the
domain interfaces with a Join Registrar (and Coordinator) to
control this process. Typically a Join Registrar is "inside" its
domain. For simplicity this document often refers to this as just
"Registrar". The term JRC is used in common with other bootstrap
mechanisms.
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Join Proxy: A domain entity that helps the pledge join the domain.
A Proxy facilitates communication for devices that find themselves
in an environment where they are not provided connectivity until
after they are validated as members of the domain. The pledge is
unaware that they are communicating with a proxy rather than
directly with a Registrar.
MASA Service: A third-party Manufacturer Authorized Signing
Authority (MASA) service on the global Internet. The MASA signs
vouchers. It also provides a repository for audit log information
of privacy protected bootstrapping events. It does not track
ownership.
Ownership Tracker: An Ownership Tracker service on the global
internet. The Ownership Tracker uses business processes to
accurately track ownership of all devices shipped against domains
that have purchased them. Although optional this component allows
vendors to provide additional value in cases where their sales and
distribution channels allow for accurately tracking of such
ownership. Ownership tracking information is indicated in
vouchers as described in [I-D.ietf-anima-voucher]
IDevID: An Initial Device Identity X.509 certificate installed by
the vendor on new equipment.
TOFU: Trust on First Use. Used similarly to [RFC7435]. This is
where a Pledge device makes no security decisions but rather
simply trusts the first Registrar it is contacted by. This is
also known as the "resurrecting duckling" model.
1.3. Scope of solution
Questions have been posed as to whether this solution is suitable in
general for Internet of Things (IoT) networks. This depends on the
capabilities of the devices in question. The terminology of
[RFC7228] is best used to describe the boundaries.
The solution described in this document is aimed in general at non-
constrained (i.e. class 2+) devices operating on a non-Challenged
network. The entire solution as described here is not intended to be
useable as-is by constrained devices operating on challenged networks
(such as 802.15.4 LLNs).
In many target applications, the systems involved are large router
platforms with multi-gigabit inter-connections, mounted in controlled
access data centers. But this solution is not exclusive to the
large, it is intended to scale to thousands of devices located in
hostile environments, such as ISP provided CPE devices which are
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drop-shipped to the end user. The situation where an order is
fulfilled from distributed warehouse from a common stock and shipped
directly to the target location at the request of the domain owner is
explicitly supported. That stock ("SKU") could be provided to a
number of potential domain owners, and the eventual domain owner will
not know a-priori which device will go to which location.
The bootstrapping process can take minutes to complete depending on
the network infrastructure and device processing speed. The network
communication itself is not optimized for speed; for privacy reasons,
the discovery process allows for the Pledge to avoid announcing it's
presence through broadcasting.
This protocol is not intended for low latency handoffs. In networks
requiring such things, the pledge SHOULD already have been enrolled.
Specifically, there are protocol aspects described here 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).
The certificate contents, and the process by which the four questions
above are resolved do apply to constrained devices. It is simply the
actual on-the-wire imprint protocol which could be inappropriate.
This document presumes that network access control has either already
occurred, is not required, or is integrated by the proxy and
registrar in such a way that the device itself does not need to be
aware of the details. Although the use of an X.509 Initial Device
Identity is consistant with IEEE 802.1AR [IDevID], and allows for
alignment with 802.1X network access control methods, its use here is
for Pledge authentication rather than network access control.
Integrating this protocol with network access control, perhaps as an
Extensible Authentication Protocol (EAP) method (see [RFC3748]), is
out-of-scope.
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2. Architectural Overview
The logical elements of the bootstrapping framework are described in
this section. Figure 1 provides a simplified overview of the
components. Each component is logical and may be combined with other
components as necessary.
.
.+------------------------+
+--------------Drop Ship-------------->.| Vendor Service |
| .+------------------------+
| .| M anufacturer| |
| .| A uthorized |Ownership|
| .| S igning |Tracker |
| .| A uthority | |
| .+--------------+---------+
| .............. ^
V |
+-------+ ............................................|...
| | . | .
| | . +------------+ +-----------+ | .
| | . | | | | | .
|Pledge | . | Circuit | | Domain <-------+ .
| | . | Proxy | | Registrar | .
| <--------> <-------> | .
| | . | | | | .
|X.509 | . +------------+ +-----+-----+ .
|IDevID | . | .
| | . +-----------------+----------+ .
| | . | Key Infrastructure | .
| | . | (e.g. PKI Certificate | .
+-------+ . | Authority) | .
. +----------------------------+ .
. .
................................................
"Domain" components
Figure 1
We assume a multi-vendor network. In such an environment there could
be a Vendor Service for each vendor that supports devices following
this document's specification, or an integrator could provide a
generic service authorized by multiple vendors. It is unlikely that
an integrator could provide Ownership Tracking services for multiple
vendors due to the required sales channel integrations necessary to
track ownership.
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The domain is the managed network infrastructure with a Key
Infrastructure the Pledge is joining. The a domain provides initial
device connectivity sufficient for bootstrapping with a Circuit
Proxy. The Domain registrar authenticates the Pledge, makes
authorization decisions, and distributes vouchers obtained from the
Vendor Service. Optionally the Registrar also acts as a PKI
Registration Authority.
2.1. Secure Imprinting using Vouchers
A voucher is a cryptographically protected statement to the Pledge
device authorizing a zero-touch imprint on the Registrar domain.
The format and cryptographic mechanism of vouchers is described in
detail in [I-D.ietf-anima-voucher].
Vouchers provide a flexible mechanism to secure imprinting: the
Pledge device only imprints when a voucher can be validated. At the
lowest security levels the MASA server can indiscriminately issue
vouchers. At the highest security levels issuance of vouchers can be
integrated with complex sales channel integrations that are beyond
the scope of this document. This provides the flexibility for a
number of use cases via a single common protocol mechanism on the
Pledge and Registrar devices that are to be widely deployed in the
field. The MASA vendor services have the flexibility to leverage
either the currently defined claim mechanisms or to experiment with
higher or lower security levels.
Vouchers provide a signed but non-encrypted communication channel
between the Pledge, the MASA, and the Registrar. The Registrar
maintains control over the transport and policy decisions allowing
the local security policy of the domain network to be enforced.
2.2. Initial Device Identifier
Pledge authentication is via an X.509 certificate installed during
the manufacturing process. This Initial Device Identifier provides a
basis for authenticating the Pledge during subsequent protocol
exchanges and informing the Registrar of the MASA URI. There is no
requirement for a common root PKI hierarchy. Each device vendor can
generate their own root certificate.
The following previously defined fields are in the X.509 IDevID
certificate:
o The subject field's DN encoding MUST include the "serialNumber"
attribute with the device's unique serial number.
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o The subject-alt field's encoding SHOULD include a non-critical
version of the RFC4108 defined HardwareModuleName.
In order to build the voucher "serial-number" field these IDevID
fields need to be converted into a serial-number of "type string".
The following methods is used depending on the first available IDevID
certificate field (attempted in this order):
o An RFC4514 String Representation of the Distinguished Name
"serialNumber" attribute.
o The HardwareModuleName hwSerialNum OCTET STRING base64 encoded.
o The RFC4514 String Representation of the Distinguished Name
"common name" attribute.
The following newly defined field SHOULD be in the X.509 IDevID
certificate: An X.509 non-critical certificate extension that
contains a single Uniform Resource Identifier (URI) that points to an
on-line Manufacturer Authorized Signing Authority. The URI is
represented as described in Section 7.4 of [RFC5280].
Any Internationalized Resource Identifiers (IRIs) MUST be mapped to
URIs as specified in Section 3.1 of [RFC3987] before they are placed
in the certificate extension. The URI provides the authority
information. The BRSKI .well-known tree is described in Section 3
The new extension is identified as follows:
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<CODE BEGINS>
MASAURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-MASAURLExtn2016(TBD) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL --
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
id-pe
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
MASACertExtensions EXTENSION ::= { ext-MASAURL, ... }
ext-MASAURL EXTENSION ::= { SYNTAX MASAURLSyntax
IDENTIFIED BY id-pe-masa-url }
id-pe-masa-url OBJECT IDENTIFIER ::= { id-pe TBD }
MASAURLSyntax ::= IA5String
END
<CODE ENDS>
The choice of id-pe is based on guidance found in Section 4.2.2 of
[RFC5280], "These extensions may be used to direct applications to
on-line information about the issuer or the subject". The MASA URL
is precisely that: online information about the particular subject.
2.3. Protocol Flow
A representative flow is shown in Figure 2:
+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
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| | | |
|<-RFC3927 IPv4 adr | Appendix A | |
or|<-RFC4862 IPv6 adr | | |
| | | |
|-------------------->| | |
| optional: mDNS query| Appendix B | |
| RFC6763/RFC6762 | | |
| | | |
|<--------------------| | |
| GRASP M_FLOOD | | |
| periodic broadcast| | |
| | | |
|<------------------->C<----------------->| |
| TLS via the Circuit Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---X.509 client authentication---------->| |
P | | |
P---Request Voucher (include nonce)------>| |
P | | |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--Pledge ID-------->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | | | |
P | optional: | [update audit log]
P | |can | |
P | |occur | |
P | |in | |
P | |advance | |
P | | | |
P | | |<-device audit log--|
P | | |<- voucher ---------|
P | \----> | |
P | | |
P | [verify audit log and voucher] |
P | | |
P<------voucher---------------------------| |
[verify voucher ] | | |
[verify provisional cert| | |
| | | |
|<--------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
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| | | |
| | | |
| | | |
Figure 2
2.4. Lack of realtime clock
Many devices when bootstrapping do not have knowledge of the current
time. Mechanisms like Network Time Protocols can not be secured
until bootstrapping is complete. Therefore bootstrapping is defined
in a method that does not require knowledge of the current time.
Unfortunately there are moments during bootstrapping when
certificates are verified, such as during the TLS handshake, where
validity periods are confirmed. This paradoxical "catch-22" is
resolved by the Pledge maintaining a concept of the current "window"
of presumed time validity that is continually refined throughout the
bootstrapping process as follows:
o Initially the Pledge does not know the current time.
o During Pledge authentiation by the Registrar a realtime clock can
be used by the Registrar. This bullet expands on a closely
related issue regarding Pledge lifetimes. RFC5280 indicates that
long lived Pledge certifiates "SHOULD be assigned the
GeneralizedTime value of 99991231235959Z" [RFC7030] so the
Registrar MUST support such lifetimes and SHOULD support ignoring
Pledge lifetimes if they did not follow the RFC5280
recommendations.
o The Pledge authenticates the voucher presented to it. During this
authentication the Pledge ignores certificate lifetimes (by
necessity because it does not have a realtime clock).
o If the voucher contains a nonce then the Pledge MUST confirm the
nonce matches the original voucher request. This ensures the
voucher is fresh. See / (Section 3.2).
o Once the voucher is accepted the validity period of the
domainCAcert in the voucher (see Section 3.4) now serves as a
valid time window. Any subsequent certificate validity periods
checked during RFC5280 path validation MUST occur within this
window.
o When accepting an enrollment certificate the validity period
within the new certificate is assumed to be valid by the Pledge.
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The Pledge is now willing to use this credential for client
authentication.
2.5. Cloud Registrar
The Pledge MAY contact a well known URI of a cloud Registrar if a
local Registrar can not be discovered or if the Pledge's target use
cases do not include a local Registrar.
If the Pledge uses a well known URI for contacting a cloud Registrar
an Implicit Trust Anchor database (see [RFC7030]) MUST be used to
authenticate service as described in RFC6125. This is consistent
with the human user configuration of an EST server URI in [RFC7030]
which also depends on RFC6125.
3. Protocol Details
The Pledge MUST initiate BRSKI after boot if it is unconfigured. The
Pledge MUST NOT automatically initiate BRSKI if it has been
configured or is in the process of being configured.
BRSKI is described as extensions to EST [RFC7030] to reduce the
number of TLS connections and crypto operations required on the
Pledge. The Registrar implements the BRSKI REST interface within the
same .well-known URI tree as the existing EST URIs as described in
EST [RFC7030] section 3.2.2. A MASA URI is therefore "https://
authority "./well-known/est".
Establishment of the TLS connection for bootstrapping is as specified
in EST [RFC7030] section 4.1.1 "Bootstrap Distribution of CA
Certificates" [RFC7030] with the following extensions for automation:
Automation extensions for the Pledge (equivalent to EST client) are:
o The Pledge provisionally accepts the Registrar certificate during
the TLS handshake as detailed in EST.
o If the Registrar responds with a redirection to other web origins
the Pledge MUST follow only a single redirection. (EST supports
redirection but does not allow redirections to other web origins
without user input).
o 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 wherein
the client "MUST wait at least the specified 'retry-after' time
before repeating the same request". The Pledge is RECOMMENDED to
provide local feed (blinked LED etc) during this wait cycle if
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mechanisms for this are available. To prevent an attacker
Registrar from significantly delaying bootstrapping the Pledge
MUST limit the 'retry-after' time to 60 seconds. To avoid waiting
on a single erroneous Registrar the Pledge MUST drop the
connection after 5 seconds and proceed to other discovered
Registrars. Ideally the Pledge could keep track of the
appropriate retry-after value for any number of outstanding
Registrars but this would involve a large state table on the
Pledge. Instead the Pledge MAY ignore the exact retry-after value
in favor of a single hard coded value that takes effect between
discovery (Appendix D.1.1.1) attempts. A Registrar that is unable
to complete the transaction the first time due to timing reasons
will have future chances.
o The Pledge requests and validates a voucher using the new REST
calls described below.
o If necessary the Pledge calls the EST defined /cacerts method to
obtain the current CA certificate. These are validated using the
Voucher.
o The Pledge completes authentication of the server certificate as
detailed in Section 3.4.1. This moves the TLS connection out of
the provisional state. Optionally the TLS connection can now be
used for EST enrollment.
The Pledge establishes the TLS connection with the Registrar through
the circuit proxy (see Appendix D.1.2) but the TLS connection is with
the Registar; so in the above section the "Pledge" is the TLS client
and the "Registrar" is the TLS server. All security associations
established are between the new device and the Registrar regardless
of proxy operations.
The extensions for a Registrar (equivalent to EST server) are:
o Client authentication is automated using Initial Device Identity.
The subject field's DN encoding MUST include the "serialNumber"
attribute with the device's unique serial number. In the language
of RFC6125 this provides for a SERIALNUM-ID category of identifier
that can be included in a certificate and therefore that can also
be used for matching purposes. The SERIALNUM-ID whitelist is
collated according to vendor trust anchor since serial numbers are
not globally unique.
o The Registrar requests and validates the Voucher from the vendor
authorized MASA service.
o The Registrar forwards the Voucher to the Pledge when requested.
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o The Registar performs log verifications in addition to local
authorization checks before accepting optional Pledge device
enrollment requests.
3.1. Discovery
The result of discovery is a logical communication with a Registrar,
through a Proxy. The Proxy is transparent to the Pledge but is
always assumed to exist.
To discover the Registrar the Pledge performs the following actions:
a. MUST: Obtains a local address using IPv6 methods as described in
[RFC4862] IPv6 Stateless Address AutoConfiguration. [RFC7217] is
encouraged. Pledges will generally prefer use of IPv6 Link-Local
addresses, and discovery of Proxy will be by Link-Local
mechanisms. IPv4 methods are described in Appendix A
b. MUST: Listen for GRASP M_FLOOD ([I-D.ietf-anima-grasp])
announcements of the objective: "ACP+Proxy". See section
Section 3.1.1 for the details of the the objective. The Pledge
may listen concurrently for other sources of information, see
Appendix B.
Once a proxy is discovered the Pledge communicates with a Registrar
through the proxy using the bootstrapping protocol defined in
Section 3.
Each discovery method attempted SHOULD exponentially back-off
attempts (to a maximum of one hour) to avoid overloading the network
infrastructure with discovery. The back-off timer for each method
MUST be independent of other methods.
Methods SHOULD be run in parallel to avoid head of queue problems
wherein an attacker running a fake proxy or registrar can operate
protocol actions intentionally slowly.
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 3.2.
Once all discovered services are attempted the device SHOULD return
to listening for GRASP M_FLOOD. It should periodically retry the
vendor specific mechanisms. The Pledge MAY prioritize selection
order as appropriate for the anticipated environment.
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3.1.1. Proxy Discovery Protocol Details
The proxy uses the GRASP M_FLOOD mechanism to announce itself. This
announcement is done with the same message as the ACP announcement
detailed in [I-D.ietf-anima-autonomic-control-plane].
proxy-objective = ["Proxy", [ O_IPv6_LOCATOR, ipv6-address,
transport-proto, port-number ] ]
ipv6-address - the v6 LL of the proxy
transport-proto - 6, for TCP 17 for UDP
port-number - the TCP or UDP port number to find the proxy
Figure 5
3.1.2. Registrar Discovery Protocol Details
A Registrar is typically configured manually. When the Registrar
joins an Autonomic Control Plane
([I-D.ietf-anima-autonomic-control-plane]) it MUST respond to GRASP
([I-D.ietf-anima-grasp]) M_NEG_SYN message.
The registrar responds to discovery messages from the proxy (or GRASP
caches between them) as follows: (XXX changed from M_DISCOVERY)
objective = ["AN_registrar", F_DISC, 255 ]
discovery-message = [M_NEG_SYN, session-id, initiator, objective]
Figure 6: Registrar Discovery
The response from the registrar (or cache) will be a M_RESPONSE with
the following parameters:
response-message = [M_RESPONSE, session-id, initiator, ttl,
(+locator-option // divert-option), ?objective)]
initiator = ACP address of Registrar
locator1 = [O_IPv6_LOCATOR, fd45:1345::6789, 6, 443]
locator2 = [O_IPv6_LOCATOR, fd45:1345::6789, 17, 5683]
locator3 = [O_IPv6_LOCATOR, fe80::1234, 41, nil]
Figure 7: Registrar Response
The set of locators is to be interpreted as follows. A protocol of 6
indicates that TCP proxying on the indicated port is desired. A
protocol of 17 indicates that UDP proxying on the indicated port is
desired. In each case, the traffic SHOULD be proxied to the same
port at the ULA address provided.
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A protocol of 41 indicates that packets may be IPIP proxy'ed. In the
case of that IPIP proxying is used, then the provided link-local
address MUST be advertised on the local link using proxy neighbour
discovery. The Join Proxy MAY limit forwarded traffic to the
protocol (6 and 17) and port numbers indicated by locator1 and
locator2. The address to which the IPIP traffic should be sent is
the initiator address (an ACP address of the Registrar), not the
address given in the locator.
Registrars MUST accept TCP / UDP traffic on the ports given at the
ACP address of the Registrar. If the Registrar supports IPIP
tunnelling, it MUST also accept traffic encapsulated with IPIP.
Registrars MUST accept HTTPS/EST traffic on the TCP ports indicated.
Registrars MAY accept DTLS/CoAP/EST traffic on the UDP in addition to
TCP traffic.
3.2. Request Voucher from the Registrar
When the Pledge bootstraps it makes a request for a Voucher from a
Registrar.
This is done with an HTTPS POST using the operation path value of
"/requestvoucher".
The request media types are:
application/voucherrequest The request is a "YANG-defined JSON
document that has been signed using a PKCS#7 structure" as
described in [I-D.ietf-anima-voucher] using the JSON encoded
described in [RFC7951]. Signing the request is RECOMMENDED if the
Pledge has sufficient processing to perform the crypto operations.
Doing so allows the Registrar to forward the Pledge's signed
'proximity' assertion to the MASA as discussed in the security
considerations.
application/unsignedvoucherrequest The request is the "YANG-defined
JSON document" but has not been signed. It is the inner JSON
structure protected only by the TLS client authentication. This
reduces the cryptographic requirements on the Pledge.
For simplicity the term 'voucher request' is used to refer to either
of these media types. Registrar impementations SHOULD anticipate
future media types but of course will simply fail the request if
those types are not yet known.
The Pledge populates the voucher request fields as follows:
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created-on: Pledges that have a realtime clock are RECOMMENDED to
populate this field. This provides additional information to the
MASA.
nonce: The voucher request MUST contain a cryptographically strong
random or pseudo-random number nonce. Doing so ensures
Section 2.4 functionality. The nonce MUST NOT be reused for
multiple bootstrapping attempts.
assertion: The voucher request MAY contain an assertion of
"proximity".
pinned-domain-cert: In a Pledge voucher request this is the
Registrar certificate as extracted from the TLS handshake (for
example the first certificate in the TLS 'certificate_list'
sequence (see [RFC5246]). This MUST be populated in a Pledge's
voucher request if the "proximity" assertion is populated.
All other fields MAY be ommitted in the voucher request.
An example JSON payload of a voucher request from a Pledge:
{
"ietf-voucher:voucher": {
"nonce": "62a2e7693d82fcda2624de58fb6722e5",
"created-on": "2017-01-01T00:00:00.000Z",
"assertion": "proximity",
"pinned-domain-cert": "<base64 encoded certificate>"
}
}
The Registrar validates the client identity as described in EST
[RFC7030] section 3.3.2. If the request is signed the Registrar
confirms the 'proximity' asserion and associated 'pinned-domain-cert'
are correct. The registrar performs authorization as detailed in
[[EDNOTE: UNRESOLVED. See Appendix D "Pledge Authorization"]]. If
these validations fail the Registrar SHOULD respond with an
appropriate HTTP error code.
If authorization is successful the Registrar obtains a voucher from
the MASA service (see Section 3.3) and returns that MASA signed
voucher to the pledge as described in Section 3.4.
3.3. Request Voucher from MASA
when a Registrar recieves a voucher request from a Pledge it in turn
requests a voucher from the MASA service. For simplicity this is
defined as an optional EST message between a Registrar and an EST
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server running on the MASA service although the Registrar is not
required to make use of any other EST functionality when
communicating with the MASA service. (The MASA service MUST properly
reject any EST functionality requests it does not wish to service; a
requirement that holds for any REST interface).
This is done with an HTTP POST using the operation path value of
"/requestvoucher".
The request media type is:
application/voucherrequest The request is a "YANG-defined JSON
document that has been signed using a PKCS#7 structure" as
described in [I-D.ietf-anima-voucher] using the JSON encoded
described in [RFC7951]. The Registrar MUST sign the request. The
entire Registrar certificate chain, up to and including the Domain
CA, MUST be included in the PKCS#7 structure.
For simplicity the term 'voucher request' is used. MASA
impementations SHOULD anticipate future media types but of course
will simply fail the request if those types are not yet known.
The Registrar populates the voucher request fields as follows:
created-on: Registrars are RECOMMENDED to populate this field. This
provides additional information to the MASA.
nonce: The optional nonce value from the Pledge request if desired
(see below).
serial-number: The serial number of the Pledge the Registrar would
like a voucher for.
idevid-issuer: The idevid-issuer value from the pledge certificate
is included to ensure a statistically unique identity. The
Pledge's serial number is extracted from the X.509 IDevID. See
Section 2.2.
prior-signed-voucher: If the Pledge provided a signed voucher
request then it SHOULD be included in the voucher request built by
the Registrar.
All other fields MAY be ommitted in the voucher request.
An example JSON payload of a voucher request from a Registrar:
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{
"ietf-voucher:voucher": {
"nonce": "62a2e7693d82fcda2624de58fb6722e5",
"created-on": "2017-01-01T00:00:00.000Z",
"assertion": "proximity"
"idevid-issuer": "<base64 encoded Authority Key Identifier>"
"serial-number": "JADA123456789"
"prior-signed-voucher": "<base64 encode prior voucher request>"
}
}
A Registrar MAY exclude the nonce from the voucher request it submits
to the MASA. Doing so allows the Registrar to request a Voucher when
the Pledge is offline, or when the Registrar is expected to be
offline when the Pledge is being deployed. These use cases require
the Registrar to learn the appropriate IDevID SerialNumber field from
the physical device labeling or from the sales channel (out-of-scope
of this document). If a nonce is not provided the MASA server MUST
authenticate the Registrar as described in EST [RFC7030] section
3.3.2 to reduce the risk of DDoS attacks and to provide an
authenticated identity as an input to sales channel integration and
authorizations (also out-of-scope of this document).
The MASA verifies that the voucher request is internally consistent
but does not authenticate the domain identity information since the
domain is not know to the MASA server in advance. The MASA
validation checks before issuing a voucher are as follows:
Renew for expired voucher: As described in [I-D.ietf-anima-voucher]
vouchers are normally short lived to avoid revocation issues. If
the request is for a previous (expired) voucher using the same
Registrar (as determined by the Registrar pinned-domain-cert) and
the MASA has not been informed that the claim is invalid then the
request for a renewed voucher SHOULD be automatically authorized.
Voucher signature consistency: The MASA MUST verify that the voucher
request is signed by a Registrar. This is confirmed by verifying
that the id-kp-cmcRA extended key usage extension field (as
detailed in EST RFC7030 section 3.6.1) exists in the certificate
of the entity that signed the voucher request. This verification
is only a consistency check that the unauthenticated domain CA
intended this to be a Registrar. Performing this check provides
value to domain PKI by assuring the domain administrator that the
MASA service will only respect claims from authorized Registration
Authorities of the domain. (The requirement for the Registrar to
include the Domain CA certificate in the signature structure was
stated above).
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Registrar revocation consistency: The MASA SHOULD check for
revocation of the Registrar certificate. The maximum lifetime of
the voucher issued SHOULD NOT exceed the lifetime of the
Registrar's revocation validation (for example if the Registrar
revocation status is indicated in a CRL that is valid for two
weeks then that is an appropriate lifetime for the voucher).
Because the Registar certificate authority is unknown to the MASA
in advance this is only an extended consistency check and is not
required. The maximum lifetime of the voucher issued SHOULD NOT
exceed the lifetime of the Registrar's revocation validation (for
example if the Registrar revocation status is indicated in a CRL
that is valid for two weeks then that is an appropriate lifetime
for the voucher).
Pledge proximity assertion: The MASA server MAY verify that the
Registrar signed voucher includes the 'prior-signed-voucher' field
populated with a Pledge signed voucher that includes a pinned-
domain-cert that is consistent with the Registrar certificate
chain. The MASA server is aware of which Pledge's support signing
of their voucher requests and can use this information to confirm
proximity of the Pledge with the Registrar.
The root certificate is extracted from the signature method and used
to populate the "pinned-domain-cert" of the Voucher being issued.
The domain ID (e.g. hash of the public key of the domain) is
extracted from the root certificate and is used to update the audit
log.
3.4. Voucher Response
The voucher response to requests from the Pledge and requests from a
Registrar are in the same format. A Registrar either caches prior
MASA responses or dynamically requests a new Voucher based on local
policy.
If the the join operation is successful, the server response MUST
contain an HTTP 200 response code. 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 (ASCII, english) error message containing explanatory
information describing why the request was rejected.
Response media type: application/voucher+cms
The syntactic details of vouchers are described in detail in
[I-D.ietf-anima-voucher]. For example, the voucher consists of:
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{
"ietf-voucher:voucher": {
"nonce": "62a2e7693d82fcda2624de58fb6722e5",
"assertion": "logging"
"pinned-domain-cert": "<base64 encoded certificate>"
"serial-number": "JADA123456789"
}
}
The Pledge verifies the signed voucher using the manufacturer
installed trust anchor associated with the vendor's selected
Manufacturer Authorized Signing Authority.
The 'pinned-domain-cert' element of the voucher contains the domain
CA's public key. The Pledge MUST use the 'pinned-domain-cert' trust
anchor to immediately complete authentication of the provisional TLS
connection.
The Pledge MUST be prepared to parse and fail gracefully from an
Voucher response that does not contain a 'pinned-domain-cert' field.
The Pledge MUST be prepared to ignore additional fields it does not
recognize.
3.4.1. Completing authentication of Provisional TLS connection
If a Registrar's credentials can not be verified using the pinned-
domain-cert trust anchor from the voucher then the TLS connection is
immediately discarded and the Pledge abandons attempts to bootstrap
with this discovered registrar. The pledge SHOULD send voucher
status telemetry (described below) before closing the TLS connection.
The pledge MUST attempt to enroll using any other proxies it has
found. It SHOULD return to the same proxy again after attempting
with other proxies. Attempts should be attempted in the exponential
backoff described earlier. Attempts SHOULD be repeated as failure
may be the result of a temporary inconsistently (an inconsistently
rolled Registrar key, or some other mis-configuration). The
inconsistently could also be the result an active MITM attack on the
EST connection.
The Registrar MUST use a certificate that chains to the pinned-
domain-cert as its TLS server certificate.
The Pledge's PKIX path validation of a Registrar certificate's
validity period information is as described in Section 2.4. Once the
PKIX path validation is successful the TLS connection is no longer
provisional.
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The pinned-domain-cert is installed as an Explicit Trust Anchor for
future operations. It can therefore can be used to authenticate any
dynamically discovered EST server that contain the id-kp-cmcRA
extended key usage extension as detailed in EST RFC7030 section
3.6.1; but to reduce system complexity the Pledge SHOULD avoid
additional discovery operations. Instead the Pledge SHOULD
communicate directly with the Registrar as the EST server. The '
pinned-domain-cert' is not a complete distribution of the EST section
4.1.3 CA Certificate Response which is an additional justification
for the recommendation to proceed with EST key management operations.
Once a full CA Certificate Response is obtained it is more
authoritative for the domain than the limited 'pinned-domain-cert'
response.'
3.5. Voucher Status Telemetry
The domain is expected to provide indications to the system
administrators concerning device lifecycle status. To facilitate
this it needs telemetry information concerning the device's status.
To indicate Pledge status regarding the Voucher the client SHOULD
post a status message.
The posted data media type: application/json
The client HTTP POSTs the following to the server at the EST well
known URI /voucher_status. The Status field indicates if the Voucher
was acceptable. If it was not acceptable the Reason string indicates
why. In the failure case this message is being sent to an
unauthenticated, potentially malicious Registrar and therefore the
Reason string SHOULD NOT provide information beneficial to an
attacker. The operational benefit of this telemetry information is
balanced against the operational costs of not recording that an
Voucher was ignored by a client the registar expected to continue
joining the domain.
{
"version":"1",
"Status":FALSE /* TRUE=Success, FALSE=Fail"
"Reason":"Informative human readable message"
}
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.
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3.6. MASA authorization log Request
A registrar requests the MASA authorization log from the MASA service
using this EST extension. If a device had previously registered with
another domain, a Registrar of that domain would show in the log.
This is done with an HTTP GET using the operation path value of
"/requestauditlog".
The registrar MUST HTTP POSTs the same Voucher Request as when
requesting a Voucher. It is posted to the /requestauditlog URI
instead. The "idevid-issuer" and "serial-number" informs the MASA
server which log is requested so the appropriate log can be prepared
for the response. Using the same media type and message minimizes
cryptographic and message operations although it results in
additional network traffic. The relying MASA server implementation
MAY leverage internal state to associate this request with the
original, and by now already validated, voucher request so as to
avoid an extra crypto validation.
Request media type: application/voucherrequest+cms
3.7. MASA authorization log Response
A log data file is returned consisting of all log entries. For
example:
{
"version":"1",
"events":[
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit voucher request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
},
{
"date":"<date/time of the entry>",
"domainID":"<domainID as extracted from the domain CA certificate
within the CMS of the audit voucher request>",
"nonce":"<any nonce if supplied (or the exact string 'NULL')>"
}
]
}
Distribution of a large log is less than ideal. This structure can
be optimized as follows: All nonce-less entries for the same domainID
MAY be condensed into the single most recent nonceless entry.
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A Registrar SHOULD use this log information to make an informed
decision regarding the continued bootstrapping of the Pledge. For
example if the log includes unexpected domainIDs this is indicative
of problematic imprints by the Pledge. If the log includes nonce-
less entries this is indicative of the permanent ability for the
indicated domain to trigger a reset of the device and take over
management of it. Equipment that is purchased pre-owned can be
expected to have an extensive history. A Registrar MAY request logs
at future times. A Registrar MAY be configured to ignore the history
of the device but it is RECOMMENDED that this only be configured if
hardware assisted NEA [RFC5209] is supported.
Log entries containing the Domain's ID can be compared against local
history logs in search of discrepancies.
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 vouchers with a
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. As such, the Registrar client SHOULD anticipate new
kinds of responses, and SHOULD provide operator controls to indicate
how to process unknown responses.
3.8. EST Integration for PKI bootstrapping
This section describes EST extensions necessary to enable fully
automated bootstrapping. Although the Voucher request/response
structure members "idevid-issuer" and "pinned-domain-cert" are
specific to PKI bootstrapping these are the only PKI specific aspects
of the extensions and future voucher definitions might replace them
with non-PKI fields.
Once the Voucher is received, as specified in this document, the
client has sufficient information to leverage the existing
communication channel with a Registrar to continue an EST RFC7030
enrollment. The voucher provides an automated mechanism for the
"Bootstrap Distribution of CA Certificates" described in [RFC7030]
section 4.1.1 wherein the Pledge "MUST [...]. engage a human user to
authorize the CA certificate using out-of-band" information".
Instead the Pledge now can automate this process using the voucher
provided "pinned-domain-cert".
The Pledge SHOULD use the existing current TLS connection to proceed
with EST enrollment, thus reducing the total amount of cryptographic
and round trip operations required during bootstrapping. After
voucher verification the Pledge continues with EST enrollment
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operations including "CA Certificates Request", "CSR Attributes" and
"Client Certificate Request" or "Server-Side Key Generation" etc.
The Pledge is RECOMMENDED to implement the following EST automation
extensions. They supplement the RFC7030 EST to better support
automated devices that do not have an end user.
3.8.1. EST Distribution of CA Certificates
The Pledge MUST request the full EST Distribution of CA Certificates
message. See RFC7030, section 4.1.
This ensures that the Pledge has the complete set of current CA
certificates beyond the domainCAcert (see Section 3.4 for a
discussion of the limitations). Although these restrictions are
acceptable for a Registrar integrated with initial bootstrapping they
are not appropriate for ongoing PKIX end entity certificate
validation.
3.8.2. EST CSR Attributes
Automated bootstrapping occurs without local administrative
configuration of the Pledge. In some deployments its plausible that
the Pledge generates a certificate request containing only identity
information known to the Pledge (essentially the X.509 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. Even with all
standardized protocols used, it could operationally be problematic to
expect that service specific certificate fields can be created by a
CA that is likely operated by a group that has no insight into
different network services/protocols used. For example, the CA could
even be outsourced.
To alleviate these operational difficulties, the Pledge MUST request
the EST "CSR Attributes" from the EST server and the EST server needs
to be able to reply with the attributes necessary for use of the
certificate in its intended protocols/services. This approach allows
for minimal CA integrations and instead the local infrastructure (EST
server) informs the Pledge of the proper fields to include in the
generated CSR. This approach is beneficial to automated boostrapping
in the widest number of environments.
If the hardwareModuleName in the X.509 IDevID is populated then it
SHOULD by default be propagated to the LDevID along with the
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hwSerialNum. The EST server SHOULD support local policy concerning
this functionality.
In networks using the BRSKI enrolled certificate to authenticate the
ACP (Autonomic Control Plane), the EST attributes MUST include the
"ACP information" field. See
[I-D.ietf-anima-autonomic-control-plane] for more details.
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.
3.8.3. EST Client Certificate Request
The Pledge MUST request a new client certificate. See RFC7030,
section 4.2.
3.8.4. Enrollment Status Telemetry
For automated bootstrapping of devices the adminstrative elements
providing bootstrapping also provide indications to the system
administrators concerning device lifecycle status. This might
include information concerning attempted bootstrapping messages seen
by the client, MASA provides logs and status of credential
enrollment. The EST protocol assumes an end user and therefore does
not include a final success indication back to the server. This is
insufficient for automated use cases.
To indicate successful enrollment the client SHOULD re-negotiate the
EST TLS session using the newly obtained credentials. This occurs by
the client initiating a new TLS ClientHello message on the existing
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 FAIL 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 field
is omitted from the status telemetry.
In the case of a SUCCESS the Reason string is omitted. The
SubjectKeyIdentifier is included so that the server can record the
successful certificate distribution.
Status media type: application/json
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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
received over an TLS session with a matching client certificate.
This allows for clients that wish to minimize their crypto operations
to simply 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.
3.8.5. EST over CoAP
This document describes extensions to EST for the purposes of
bootstrapping of remote key infrastructures. Bootstrapping is
relevant for CoAP enrollment discussions as well. The defintion of
EST and BRSKI over CoAP is not discussed within this document beyond
ensuring proxy support for CoAP operations. Instead it is
anticipated that a definition of CoAP mappings will occur in
subsequent documents such as [I-D.vanderstok-ace-coap-est] and that
CoAP mappings for BRSKI will be discussed either there or in future
work.
4. 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 Pledge, Registrar and MASA can
be configured to run in a less secure mode for the indicated reasons.
4.1. Trust Model
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+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
Figure 10
Pledge: The Pledge could be compromised and providing an attack
vector for malware. The entity is trusted to only imprint using
secure methods described in this document. Additional endpoint
assessment techniques are RECOMMENDED but are out-of-scope of this
document.
Proxy: Provides proxy functionalities but is not involved in
security considerations.
Registrar: When interacting with a MASA server a Registrar makes all
decisions. When Ownership Vouchers are involved a Registrar is
only a conduit and all security decisions are made on the vendor
service.
Vendor Service, MASA: This form of vendor service is trusted to
accurately log all claim attempts and to provide authoritative log
information to Registrars. The MASA does not know which devices
are associated with which domains. These claims could be
strengthened by using cryptographic log techniques to provide
append only, cryptographic assured, publicly auditable logs.
Current text provides only for a trusted vendor.
Vendor Service, Ownership Validation: This form of vendor service is
trusted to accurately know which device is owned by which domain.
4.2. Pledge security reductions
The Pledge can choose to accept vouchers using less secure methods.
These methods enable offline and emergency (touch based) deployment
use cases:
1. The Pledge MUST accept nonceless vouchers. This allows for
offline use cases. Logging and validity periods address the
inherent security considerations of supporting these use cases.
2. The Pledge MAY support "trust on first use" for physical
interfaces such as a local console port or physical user
interface but MUST NOT support "trust on first use" on network
interfaces. This is because "trust on first use" permanently
degrades the security for all use cases.
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3. The Pledge MAY have an operational mode where it skips Voucher
validation one time. For example if a physical button is
depressed during the bootstrapping operation. This can be useful
if the vendor service is unavailable. This behavior SHOULD be
available via local configuration or physical presence methods to
ensure new entities can always be deployed even when autonomic
methods fail. This allows for unsecured imprint.
It is RECOMMENDED that "trust on first use" or skipping voucher
validation only be available if hardware assisted Network Endpoint
Assessment [RFC5209] is supported. This recommendation ensures that
domain network monitoring can detect innappropriate use of offline or
emergency deployment procedures.
4.3. Registrar security reductions
A Registrar can choose to accept devices using less secure methods.
These methods are acceptable when low security models are needed, as
the security decisions are being made by the local administrator, but
they MUST NOT be the default behavior:
1. A registrar MAY choose to accept all devices, or all devices of a
particular type, at the administrator's discretion. This could
occur when informing all Registrars of unique identifiers of new
entities might be operationally difficult.
2. A registrar MAY choose to accept devices that claim a unique
identity without the benefit of authenticating that claimed
identity. This could occur when the Pledge does not include an
X.509 IDevID factory installed credential. New Entities without
an X.509 IDevID credential MAY form the Section 3.2 request using
the Section 3.3 format to ensure the Pledge's serial number
information is provided to the Registar (this includes the IDevID
AuthorityKeyIdentifier value which would be statically configured
on the Pledge). The Pledge MAY refuse to provide a TLS client
certificate (as one is not available). The Pledge SHOULD support
HTTP-based or certificate-less TLS authentication as described in
EST RFC7030 section 3.3.2. A Registrar MUST NOT accept
unauthenticated New Entities unless it has been configured to do
so by an administrator that has verified that only expected new
entities can communicate with a Registrar (presumably via a
physically secured perimeter).
3. A Registrar MAY request nonce-less Vouchers from the MASA service
(by not including a nonce in the request). These Vouchers can
then be transmitted to the Registrar and stored until they are
needed during bootstrapping operations. This is for use cases
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where target network is protected by an air gap and therefore can
not contact the MASA service during Pledge deployment.
4. A registrar MAY ignore unrecognized nonce-less log entries. This
could occur when used equipment is purchased with a valid history
being deployed in air gap networks that required permanent
Vouchers.
4.4. 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 Voucher. This results in
distribution of Voucher that never expires and in effect makes
the Domain an always trusted entity to the Pledge during any
subsequent bootstrapping attempts. That this occurred is
captured in the log information so that the Domain registrar can
make appropriate security decisions when a Pledge joins the
Domain. This is useful to support use cases where Registrars
might not be online during actual device deployment. Because
this results in long lived Voucher and does 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 an enhanced level of
ownership tracking (out-of-scope). If the Pledge device is known
to have a real-time-clock that is set from the factory use of a
voucher validity period is RECOMMENDED.
2. Not verifying ownership before responding with an Voucher. This
is expected to be a common operational model because doing so
relieves the vendor providing MASA services from having to track
ownership during shipping and supply chain and allows for a very
low overhead MASA service. A Registrar uses the audit log
information as a defense in depth strategy to ensure that this
does not occur unexpectedly (for example when purchasing new
equipment the Registrar would throw an error if any audit log
information is reported). The MASA should verify the 'prior-
signed-voucher' information for Pledge's that support that
functionality. This provides a proof-of-proximity check that
reduces the need for ownership verification.
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5. IANA Considerations
5.1. PKIX Registry
This document requests a number for id-mod-MASAURLExtn2016(TBD) from
the pkix(7) id-mod(0) Registry. [[EDNOTE: fix names]]
This document requests a number from the id-pe registry for id-pe-
masa-url. XXX
6. Security Considerations
There are uses cases where the MASA could be unavailable or
uncooperative to the Registrar. They include planned and unplanned
network partitions, changes to MASA policy, or other instances where
MASA policy rejects a claim. These introduce an operational risk to
the Registrar owner that MASA/vendor behavior might limit the ability
to re-boostrap a Pledge device. For example this might be an issue
during disaster recovery. This risk can be mitigated by Registrars
that request and maintain long term copies of "nonceless" Vouchers.
In that way they are guaranteed to be able to repeat bootstrapping
for their devices.
The issuance of nonceless vouchers themselves create a security
concern. If the Registrar of a previous domain can intercept
protocol communications then it can use a previously issued nonceless
voucher to establish management control of a pledge device even after
having sold it. This risk is mitigated by recording the issuance of
such vouchers in the MASA audit log that is verified by the
subsequent Registrar. This reduces the resale value of the equipment
because future owners will detect the lowered security inherent in
the existence of a nonceless voucher that would be trusted by their
Pledge. This reflects a balance between partition resistant recovery
and security of future bootstrapping. Registrars take the Pledge's
audit history into account when applying policy to new devices.
The MASA server is exposed to DoS attacks wherein attackers claim an
unbounded number of devices. Ensuring a Registrar is representative
of a valid vendor customer, even without validating ownership of
specific Pledge devices, helps to mitigate this. Pledge signatures
on the initial voucher request, as forwarded by the Registrar in the
prior-signed-voucher field, significantly reduce this risk by
ensuring the MASA can confirm proximity between the Pledge and the
Registrar making the request. This mechanism is optional to allow
for constrained devices.
It is possible for an attacker to request a voucher from the MASA
service directly after the real Registrar obtains an audit log. If
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the attacker could also force the bootstrapping protocol to reset
there is a theoretical opportunity for the attacker to use their
voucher to take control of the Pledge but then proceed to enroll with
the target domain. Possible prevention mechanisms include:
o Per device rate limits on the MASA service ensure such timing
attacks are difficult.
o The Registrar can repeat the request for audit log information at
some time after bootstrapping is complete.
To facilitate logging and administrative oversight the Pledge reports
on Voucher parsing status to the Registrar. In the case of a failure
this information is informative to a potentially malicious Registar
but this is RECOMMENDED anyway because of the operational benefits of
an informed administrator in cases where the failure is indicative of
a problem.
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 4 to a statement that the
Registrar "MAY" choose to accept devices that fail cryptographic
authentication. This reflects current (poor) practices in shipping
devices without a cryptographic identity that are NOT RECOMMENDED.
During the provisional period of the connection all HTTP header and
content data MUST treated as untrusted data. HTTP libraries are
regularly exposed to non-secured HTTP traffic: mature libraries
should not have any problems.
Pledge's might chose to engage in protocol operations with multiple
discovered Registrars in parallel. As noted above they will only do
so with distinct nonce values, but the end result could be multple
voucher's issued from the MASA if all registrars attempt to claim the
device. This is not a failure and the Pledge choses whichever
voucher to accept based on internal logic. The Registrar's verifying
log information will see multiple entries and take this into account
for their analytics purposes.
7. Acknowledgements
We would like to thank the various reviewers for their input, in
particular Brian Carpenter, Toerless Eckert, Fuyu Eleven, Eliot Lear,
Sergey Kasatkin, Markus Stenberg, and Peter van der Stok
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8. References
8.1. Normative References
[I-D.ietf-anima-autonomic-control-plane]
Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
Control Plane", draft-ietf-anima-autonomic-control-
plane-06 (work in progress), March 2017.
[I-D.ietf-anima-voucher]
Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"Voucher Profile for Bootstrapping Protocols", draft-ietf-
anima-voucher-04 (work in progress), July 2017.
[I-D.vanderstok-ace-coap-est]
Kumar, S., Stok, P., Kampanakis, P., Furuhed, M., and S.
Raza, "EST over secure CoAP (EST-coaps)", draft-
vanderstok-ace-coap-est-02 (work in progress), June 2017.
[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, DOI 10.17487/RFC3542, May 2003,
<http://www.rfc-editor.org/info/rfc3542>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<http://www.rfc-editor.org/info/rfc3748>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<http://www.rfc-editor.org/info/rfc3927>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
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[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
Security: An Unauthenticated Mode of IPsec", RFC 5386,
DOI 10.17487/RFC5386, November 2008,
<http://www.rfc-editor.org/info/rfc5386>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>.
[RFC5660] Williams, N., "IPsec Channels: Connection Latching",
RFC 5660, DOI 10.17487/RFC5660, October 2009,
<http://www.rfc-editor.org/info/rfc5660>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
[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>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<http://www.rfc-editor.org/info/rfc7951>.
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8.2. 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-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-13 (work in progress), June 2017.
[I-D.ietf-netconf-zerotouch]
Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
Provisioning for NETCONF or RESTCONF based Management",
draft-ietf-netconf-zerotouch-14 (work in progress), June
2017.
[I-D.lear-mud-framework]
Lear, E., "Manufacturer Usage Description Framework",
draft-lear-mud-framework-00 (work in progress), January
2016.
[I-D.richardson-anima-state-for-joinrouter]
Richardson, M., "Considerations for stateful vs stateless
join router in ANIMA bootstrap", draft-richardson-anima-
state-for-joinrouter-01 (work in progress), July 2016.
[imprinting]
Wikipedia, "Wikipedia article: Imprinting", July 2015,
<https://en.wikipedia.org/wiki/Imprinting_(psychology)>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <http://www.rfc-editor.org/info/rfc2473>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <http://www.rfc-editor.org/info/rfc7435>.
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[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<http://www.rfc-editor.org/info/rfc7575>.
[Stajano99theresurrecting]
Stajano, F. and R. Anderson, "The resurrecting duckling:
security issues for ad-hoc wireless networks", 1999,
<https://www.cl.cam.ac.uk/~fms27/papers/1999-StajanoAnd-
duckling.pdf>.
Appendix A. IPv4 operations
A.1. IPv4 Link Local addresses
Instead of an IPv6 link-local address, an IPv4 address may be
generated using [RFC3927] Dynamic Configuration of IPv4 Link-Local
Addresses.
In the case that an IPv4 Local-Local address is formed, then the
bootstrap process would continue as in the IPv6 case by looking for a
(circuit) proxy.
A.2. Use of DHCPv4
The Plege MAY obtain an IP address via DHCP [RFC2131]. The DHCP
provided parameters for the Domain Name System can be used to perform
DNS operations if all local discovery attempts fail.
Appendix B. mDNS / DNSSD proxy discovery options
The Pledge MAY perform DNS-based Service Discovery [RFC6763] over
Multicast DNS [RFC6762] searching for the service
"_bootstrapks._tcp.local.".
To prevent unaccceptable levels of network traffic the congestion
avoidance mechanisms specified in [RFC6762] section 7 MUST be
followed. The Pledge SHOULD listen for an unsolicited broadcast
response as described in [RFC6762]. This allows devices to avoid
announcing their presence via mDNS broadcasts and instead silently
join a network by watching for periodic unsolicited broadcast
responses.
Performs DNS-based Service Discovery [RFC6763] over normal DNS
operations. The service searched for is
"_bootstrapks._tcp.example.com". In this case the domain
"example.com" is discovered as described in [RFC6763] section 11.
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This method is only available if the host has received a useable IPv4
address via DHCPv4 as suggested in Appendix A.
If no local bootstrapks service is located using the GRASP
mechanisms, or the above mentioned DNS-based Service Discovery
methods the Pledge MAY contact a well known vendor provided
bootstrapping server by performing a DNS lookup using a well known
URI such as "bootstrapks.vendor-example.com". The details of the URI
are vendor specific. Vendors that leverage this method on the Pledge
are responsible for providing the bootstrapks service.
The current DNS services returned during each query is maintained
until bootstrapping is completed. If bootstrapping fails and the
Pledge returns to the Discovery state it picks up where it left off
and continues attempting bootstrapping. For example if the first
Multicast DNS _bootstrapks._tcp.local response doesn't work then the
second and third responses are tried. If these fail the Pledge moves
on to normal DNS-based Service Discovery.
Appendix C. IPIP Join Proxy mechanism
The Circuit Proxy mechanism suffers from requiring a state on the
Join Proxy for each connection that is relayed. The Circuit Proxy
can be considered a kind of Algorithm Gateway [FIND-good-REF].
An alternative to proxying at the TCP layer is to selectively forward
at the IP layer. This moves all per-connection to the Join
Registrar. The IPIP tunnel statelessly forwards packets. This
section provides some explanation of some of the details of the
Registrar discovery procotol which are not important to Circuit
Proxy, and some implementation advice.
The IPIP tunnel is described in [RFC2473]. Each such tunnel is
considered a unidirectional construct, but two tunnels may be
associated to form a bidirectional mechanism. An IPIP tunnel is
setup as follows. The outer addresses are an ACP address of the Join
Proxy, and the ACP address of the Join Registrar. The inner
addresses seen in the tunnel are the link-local addresses of the
network on which the join activity is occuring.
One way to look at this construct is to consider that the Registrar
is extending attaching an interface to the network on which the Join
Proxy is physically present. The Registrar then interacts as if it
were present on that network using link-local (fe80::) addresses.
The Join node is unaware that the traffic is being proxied through a
tunnel, and does not need any special routing.
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There are a number of considerations with this mechanism which
require cause some minor amounts of complexity. Note that due to the
tunnels, the Registrar sees multiple connections to a fe80::/10
network on not just physical interfaces, but on each of the virtual
interfaces represending the tunnels.
C.1. Multiple Join networks on the Join Proxy side
The Join Proxy will in the general case be a routing device with
multiple interfaces. Even a device as simple as a wifi access point
may have wired, and multiple frequencies of wireless interfaces,
potentially with multiple ESSIDs.
Each of these interfaces on the Join Proxy may be seperate L3 routing
domains, and therefore will have a unique set of link-local
addresses. An IPIP packet being returned by the Registrar needs to
be forwarded to the correct interface, so the Join Proxy needs an
additional key to distinguish which network the packet should be
returned to.
The simplest way to get this additional key is to allocate an
additional ACP address; one address for each network on which join
traffic is occuring. The Join Proxy SHOULD do a GRASP M_NEG_SYN for
each interface which they wish to relay traffic, as this allows the
Registrar to do any static tunnel configuration that may be required.
C.2. Automatic configuration of tunnels on Registrar
The Join Proxy is expected to do a GRASP negotiation with the proxy
for each Join Interface that it needs to relay traffic from. This is
to permit Registrars to configure the appropriate virtual interfaces
before join traffic arrives.
A Registrar serving a large number of interfaces may not wish to
allocate resources to every interface at all times, but can instead
dynamically allocate interfaces. It can do this by monitoring IPIP
traffic that arrives on it's ACP interface, and when packets arrive
from new Join Proxys, it can dynamically configure virtual
interfaces.
A more sophisticated Registrar willing to modify the behaviour of
it's TCP and UDP stack could note the IPIP traffic origination in the
socket control block and make information available to the TCP layer
(for HTTPS connections), or to the the application (for CoAP
connections) via a proprietary extension to the socket API.
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C.3. Proxy Neighbor Discovery by Join Proxy
The Join Proxy MUST answer neighbor discovery messages for the
address given by the Registrar as being it's link-local address. The
Join Proxy must also advertise this address as the address to which
to connect to when advertising it's existence.
This proxy neighbor discovery means that the pledge will create TCP
and UDP connections to the correct Registrar address. This matters
as the TCP and UDP pseudo-header checksum includes the destination
address, and for the proxy to remain completely stateless, it must
not be necessary for the checksum to be updated.
C.4. Use of connected sockets; or IP_PKTINFO for CoAP on Registrar
TCP connections on the registrar SHOULD properly capture the ifindex
of the incoming connection into the socket structure. This is normal
IPv6 socket API processing. The outgoing responses will go out on
the same (virtual) interface by ifindex.
When using UDP sockets with CoAP, the application will have to pay
attention to the incoming ifindex on the socket. Access to this
information is available using the IP_PKTINFO auxiliary extension
which is a standard part of the IPv6 sockets API.
A registrar application could, after receipt of an initial CoAP
message from the Pledge, create a connected UDP socket (including the
ifindex information). The kernel would then take care of accurate
demultiplexing upon receive, and subsequent transmission to the
correct interface.
C.5. Use of socket extension rather than virtual interface
Some operating systems on which a Registrar need be implemented may
find need for a virtual interface per Join Proxy to be problematic.
There are other mechanism which can make be done.
If the IPIP decapsulator can mark the (SYN) packet inside the kernel
with the address of the Join Proxy sending the traffic, then an
interface per Join Proxy may not be needed. The outgoing path need
just pay attention to this extra information and add an appropriate
IPIP header on outgoing. A CoAP over UDP mechanism may need to
expose this extra information to the application as the UDP sockets
are often not connected, and the application will need to specify the
outgoing path on each packet send.
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Such an additional socket mechanism has not been standardized.
Terminating L2TP connections over IPsec transport mode suffers from
the same challenges.
Appendix D. To be deprecated: Consolidation remnants
[[EDNOTE: As per working group feedback there were multiple instances
where this document repeated itself. To address this we have moved
all text to this appendix and restored only one copy of each
normative discussion. The next pass will reduce and delete this
appendix to '0'; although some may be maintained in a design
considerations appendix.]]
D.1. Functional Overview
Entities behave in an autonomic fashion. They discover each other
and autonomically bootstrap into a key infrastructure delineating the
autonomic domain. See [RFC7575] for more information.
This section details the state machine and operational flow for each
of the main three entities. The pledge, the domain (primarily a
Registrar) and the MASA service.
A representative flow is shown in Figure 2:
+--------+ +---------+ +------------+ +------------+
| Pledge | | Circuit | | Domain | | Vendor |
| | | Proxy | | Registrar | | Service |
| | | | | | | (Internet |
+--------+ +---------+ +------------+ +------------+
| | | |
|<-RFC3927 IPv4 adr | Appendix A | |
or|<-RFC4862 IPv6 adr | | |
| | | |
|-------------------->| | |
| optional: mDNS query| Appendix B | |
| RFC6763/RFC6762 | | |
| | | |
|<--------------------| | |
| GRASP M_FLOOD | | |
| periodic broadcast| | |
| | | |
|<------------------->C<----------------->| |
| TLS via the Circuit Proxy | |
|<--Registrar TLS server authentication---| |
[PROVISIONAL accept of server cert] | |
P---X.509 client authentication---------->| |
P | | |
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P---Request Voucher (include nonce)------>| |
P | | |
P | /---> | |
P | | [accept device?] |
P | | [contact Vendor] |
P | | |--Pledge ID-------->|
P | | |--Domain ID-------->|
P | | |--optional:nonce--->|
P | | | [extract DomainID]
P | | | |
P | optional: | [update audit log]
P | |can | |
P | |occur | |
P | |in | |
P | |advance | |
P | | | |
P | | |<-device audit log--|
P | | |<- voucher ---------|
P | \----> | |
P | | |
P | [verify audit log and voucher] |
P | | |
P<------voucher---------------------------| |
[verify voucher ] | | |
[verify provisional cert| | |
| | | |
|<--------------------------------------->| |
| Continue with RFC7030 enrollment | |
| using now bidirectionally authenticated | |
| TLS session. | | |
| | | |
| | | |
| | | |
Figure 2
[[UNRESOLVED:need to restore some functional overview section for all
these diagrams]]In order to obtain a Voucher and associated logs a
Registrar contacts the MASA service Service using REST calls:
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+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
+---------------C---------------> |
| | | |
HTTP REST | POST /requestvoucher | |
Data +--------------------nonce------> |
| . | /requestvoucher|
| . +---------------->
| <----------------+
| | /requestlog |
| +---------------->
| voucher <----------------+
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 8
In some use cases the Registrar may need to contact the Vendor in
advanced, for example when the target network is air-gapped. The
nonceless request format is provided for this and the resulting flow
is slightly different. The security differences associated with not
knowing the nonce are discussed below:
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+-----------+ +----------+ +-----------+ +----------+
| New | | Circuit | | | | |
| Entity | | Proxy | | Registrar | | Vendor |
| | | | | | | |
++----------+ +--+-------+ +-----+-----+ +--------+-+
| | | |
| | | |
| | | /requestvoucher|
| | (nonce +---------------->
| | unknown) <----------------+
| | | /requestlog |
| | +---------------->
| | <----------------+
| TLS hello | TLS hello | |
Establish +---------------C---------------> |
TLS | | | |
connection | | Server Cert | |
<---------------C---------------+ |
| Client Cert | | |
| | | |
HTTP REST | POST /requestvoucher | |
Data +----------------------nonce----> (discard |
| voucher | nonce) |
<-------------------------------+ |
| (optional config information) | |
| . | |
| . | |
Figure 9
D.1.1. Behavior of a Pledge
A pledge that has not yet been bootstrapped attempts to find a local
domain and join it. A pledge [[RESOLVED:MUST NOT]] automatically
initiate bootstrapping if it has already been configured or is in the
process of being configured.
States of a pledge are as follows:
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+--------------+
| Factory |
| default |
+------+-------+
|
+------v-------+
| Discover |
+------------> |
| +------+-------+
| |
| +------v-------+
| | Identity |
^------------+ |
| rejected +------+-------+
| |
| +------v-------+
| | Request |
| | Join |
| +------+-------+
| |
| +------v-------+
| | Imprint | Optional
^------------+ <--+Manual input (Appendix C)
| Bad Vendor +------+-------+
| response |
| +------v-------+
| | Enroll |
^------------+ |
| Enroll +------+-------+
| Failure |
| +------v-------+
| | Enrolled |
^------------+ |
Factory +--------------+
reset
Figure 3
State descriptions for the pledge are as follows:
1. Discover a communication channel to a Registrar.
2. Identify itself. This is done by presenting an X.509 IDevID
credential to the discovered Registrar (via the Proxy) in a TLS
handshake. (The Registrar credentials are only provisionally
accepted at this time).
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3. Requests to Join the discovered Registrar. A unique nonce
[[RESOLVED:can be]] included ensuring that any responses can be
associated with this particular bootstrapping attempt.
4. Imprint on the Registrar. This requires verification of the
vendor service provided voucher. A voucher contains sufficient
information for the Pledge to complete authentication of a
Registrar. (It enables the Pledge to finish authentication of
the Registrar TLS server certificate).
5. Enroll. By accepting the domain specific information from a
Registrar, and by obtaining a domain certificate from a Registrar
using a standard enrollment protocol, e.g. Enrollment over
Secure Transport (EST) [RFC7030].
6. The Pledge is now a member of, and can be managed by, the domain
and will only repeat the discovery aspects of bootstrapping if it
is returned to factory default settings.
The following sections describe each of these steps in more detail.
D.1.1.1. Discovery
[[RESOLVED:TEXT moved up into above]]
D.1.1.2. Identity
The Pledge identifies itself during the communication protocol
handshake. If the client identity is rejected (that is, the TLS
handshake does not complete) the Pledge repeats the Identity process
using the next proxy or discovery method available.
[[RESOLVED: need normative statement in protocol section]] The
bootstrapping protocol server is not initially authenticated. Thus
the connection is provisional and all data received is untrusted
until sufficiently validated even though it is over a TLS connection.
This is aligned with the existing provisional mode of EST [RFC7030]
during s4.1.1 "Bootstrap Distribution of CA Certificates". See
Section 3.4 for more information about when the TLS connection
authentication is completed.
[[RESOLVED:]]All security associations established are between the
new device and the Bootstrapping server regardless of proxy
operations.
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D.1.1.2.1. Concurrent attempts to join
[[RESOLVED: by dropping this text. the "priority mechanism" is
unspecified thus any discussion is unclear. Not only that once an
initial request is sent to the registrar the question of multiple
MASA interactions has already occurred. Nothing breaks if
implementations do this. I've added text to the security
considerations indicating the end result (MASA entries that might be
ignored by the device but which confuse the end administrator)]] The
Pledge MAY attempt multiple mechanisms concurrently, but if it does
so, it MUST wait in the provisional state until all mechanisms have
either succeeded or failed, and then MUST proceed with the highest
priority mechanism which has succeed. To proceed beyond this point,
specifically, to provide a nonce, could result in the MASA
gratuitously auditing a connection.
D.1.1.3. Request Join
The Pledge POSTs a request to join the domain to the Bootstrapping
server. This request contains a Pledge generated nonce and informs
the Bootstrapping server which imprint methods the Pledge will
accept.
The nonce ensures the Pledge can verify that responses are specific
to this bootstrapping attempt. This minimizes the use of global time
and provides a substantial benefit for devices without a valid clock.
D.1.1.3.1. Redirects during the Join Process
[[RESOVED via current root protocol discussion. reference to
mdnsmethods is dropped]] EST [RFC7030] describes situations where the
bootstrapping server MAY redirect the client to an alternate server
via a 3xx status code. Such redirects MAY be accepted if the pledge
has used the methods described in Appendix B, in combination with an
implicit trust anchor. Redirects during the provisional period are
otherwise unstrusted, and MUST cause a failure.
D.1.1.4. Imprint
The Pledge validates the voucher and accepts the Registrar ID. The
provisional TLS connection is validated using the Registrar ID from
the voucher.
D.1.1.5. Lack of realtime clock APPENDIX
[[RESOVED: entire section promoted back into the main text]]
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Many devices when bootstrapping do not have knowledge of the current
time. Mechanisms like Network Time Protocols can not be secured
until bootstrapping is complete. Therefore bootstrapping is defined
in a method that does not require knowledge of the current time.
Unfortunately there are moments during bootstrapping when
certificates are verified, such as during the TLS handshake, where
validity periods are confirmed. This paradoxical "catch-22" is
resolved by the Pledge maintaining a concept of the current "window"
of presumed time validity that is continually refined throughout the
bootstrapping process as follows:
o Initially the Pledge does not know the current time.
o During Pledge authentiation by the Registrar a realtime clock can
be used by the Registrar. This bullet expands on a closely
related issue regarding Pledge lifetimes. RFC5280 indicates that
long lived Pledge certifiates "SHOULD be assigned the
GeneralizedTime value of 99991231235959Z" [RFC7030] so the
Registrar MUST support such lifetimes and SHOULD support ignoring
Pledge lifetimes if they did not follow the RFC5280
recommendations.
o The Pledge authenticates the voucher presented to it. During this
authentication the Pledge ignores certificate lifetimes (by
necessity because it does not have a clock). The voucher itself
SHOULD contain the nonce included in the original request which
proves the voucher is fresh.
o Once the voucher is accepted the validity period of the
domainCAcert in the voucher (see Section 3.4) now serves as a
valid time window. Any subsequent certificate validity periods
checked during RFC5280 path validation MUST occur within this
window.
o When accepting an enrollment certificate the validity period
within the new certificate is assumed to be valid by the Pledge.
The Pledge is now willing to use this credential for client
authentication.
D.1.1.6. Enrollment
As the final step of bootstrapping a Registrar helps to issue a
domain specific credential to the Pledge. For simplicity in this
document, a Registrar primarily facilitates issuing a credential by
acting as an RFC5280 Registration Authority for the Domain
Certification Authority.
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Enrollment proceeds as described in [RFC7030]. Authentication of the
EST server is done using the Voucher rather than the methods defined
in EST.
[[RESOLVED: moved to protocol discussion]]Once the Voucher is
received, as specified in this document, the client has sufficient
information to leverage the existing communication channel with a
Registrar to continue an EST RFC7030 enrollment. Enrollment picks up
at RFC7030 section 4.1.1. bootstrapping where the Voucher provides
the "out-of-band" CA certificate fingerprint (in this case the full
CA certificate) such that the client can now complete the TLS server
authentication. At this point the client continues with EST
enrollment operations including "CA Certificates Request", "CSR
Attributes" and "Client Certificate Request" or "Server-Side Key
Generation".
[[RESOLVED: included into EST discussion]]For the purposes of
creating the ANIMA Autonomic Control Plane, the contents of the new
certificate MUST be carefully specified.
[I-D.ietf-anima-autonomic-control-plane] section 5.1.1 contains
details. The Registrar MUST provide the the correct ACP information
to populate the subjectAltName / rfc822Name field in the "CSR
Attributes" step.
D.1.1.7. Being Managed
[[RESOLVED: by slight change to introduction text.]] Functionality to
provide generic "configuration" information is supported. The
parsing of this data and any subsequent use of the data, for example
communications with a Network Management System is out of scope but
is expected to occur after bootstrapping enrollment is complete.
This ensures that all communications with management systems which
can divulge local security information (e.g. network topology or raw
key material) is secured using the local credentials issued during
enrollment.
The Pledge uses bootstrapping to join only one domain. Management by
multiple domains is out-of-scope of bootstrapping. After the device
has successfully joined a domain and is being managed it is plausible
that the domain can insert credentials for other domains depending on
the device capabilities.
See Appendix D.1.5.
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D.1.2. Behavior of a Join Proxy
The role of the Proxy is to facilitate communications. The Proxy
forwards packets between the Pledge and a Registrar that has been
configured on the Proxy.
[[UNRESOLVED: since proxy behavior is not visible we can limit
ourselves to discussion of what the protocol does to enable/faciliate
a theoretical proxy]]The Proxy does not terminate the TLS handshake.
[[UNRESOLVED: this is an anima architecture requirement to use BRSKI?
move to there?]] A Proxy is always assumed even if it is directly
integrated into a Registrar. (In a completely autonomic network, the
Registrar MUST provide proxy functionality so that it can be
discovered, and the network can grow concentrically around the
Registrar)
As a result of the Proxy Discovery process in section
Appendix D.1.1.1, the port number exposed by the proxy does not need
to be well known, or require an IANA allocation.
If the Proxy joins an Autonomic Control Plane
([I-D.ietf-anima-autonomic-control-plane]) it SHOULD use Autonomic
Control Plane secured GRASP ([I-D.ietf-anima-grasp]) to discovery the
Registrar address and port. As part of the discovery process, the
proxy mechanism (Circuit Proxy vs IPIP encapsulation) is agreed to
between the Registrar and Join Proxy.
For the IPIP encapsulation methods, the port announced by the Proxy
MUST be the same as on the registrar in order for the proxy to remain
stateless.
In order to permit the proxy functionality to be implemented on the
maximum variety of devices the chosen mechanism SHOULD use the
minimum amount of state on the proxy device. While many devices in
the ANIMA target space will be rather large routers, the proxy
function is likely to be implemented in the control plane CPU of 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.
D.1.2.1. CoAP connection to Registrar
[[RESOLVED:this section thus removed]]The CoAP mechanism was
depreciated.
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D.1.2.2. HTTPS proxy connection to Registrar
The proxy SHOULD also provide one of: an IPIP encapsulation of HTTP
traffic on TCP port TBD to the registrar, or a TCP circuit proxy that
connects the Pledge to a Registrar.
When the Proxy provides a circuit proxy to a Registrar the Registrar
MUST accept HTTPS connections.
When the Proxy provides a stateless IPIP encapsulation to a
Registrar, then the Registrar will have to perform IPIP
decapsulation, remembering the originating outer IPIP source address
in order to qualify the inner link-local address. This is a kind of
encapsulation and processing which is similar in many ways to how
mobile IP works.
Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link-
local address with an encapsulated IPIP header requires API
extensions beyond [RFC3542] for UDP use, and requires a form of
connection latching (see section 4.1 of [RFC5386] and all of
[RFC5660], except that a simple IPIP tunnel is used rather than an
IPsec tunnel).
D.1.3. Behavior of the Registrar
A Registrar listens for Pledges and determines if they can join the
domain. A Registrar obtains a Voucher from the MASA service and
delivers them to the Pledge as well as facilitating enrollment with
the domain PKI.
[[RESOLVED: moved to discovery discussion]] A Registrar is typically
configured manually. When the Registrar joins an Autonomic Control
Plane ([I-D.ietf-anima-autonomic-control-plane]) it MUST respond to
GRASP ([I-D.ietf-anima-grasp]) M_DISCOVERY message. See
Section 3.1.2
Registrar behavior is as follows:
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Contacted by Pledge
+
|
+-------v----------+
| Entity | fail?
| Authentication +---------+
+-------+----------+ |
| |
+-------v----------+ |
| Entity | fail? |
| Authorization +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Claiming the | fail? |
| Entity +--------->
+-------+----------+ |
| |
+-------v----------+ |
| Log Verification | fail? |
| +--------->
+-------+----------+ |
| |
+-------v----------+ +----v-------+
| Forward | | |
| Voucher | | Reject |
| to the Pledge | | Device |
| | | |
+------------------+ +------------+
Figure 4
D.1.3.1. Pledge Authentication
The applicable authentication methods detailed in EST [RFC7030] are:
o [[RESOLVED:pointed out in protocol details]]the use of an X.509
IDevID credential during the TLS client authentication,
o or the use of a secret that is transmitted out of band between the
Pledge and a Registrar (this use case is not autonomic).
In order to validate the X.509 IDevID credential a Registrar
maintains a database of vendor trust anchors (e.g. vendor root
certificates or keyIdentifiers for vendor root public keys). For
user interface purposes this database can be mapped to colloquial
vendor names. Registrars can be shipped with the trust anchors of a
significant number of third-party vendors within the target market.
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D.1.3.2. Pledge Authorization
[[UNRESOLVED: this is referenced above as how the MASA does
authorization. That is incorrect]]
In a fully automated network all devices must be securely identified
and authorized to join the domain.
A Registrar accepts or declines a request to join the domain, based
on the authenticated identity presented. Automated acceptance
criteria include:
o allow any device of a specific type (as determined by the X.509
IDevID),
o allow any device from a specific vendor (as determined by the
X.509 IDevID),
o allow a specific device from a vendor (as determined by the X.509
IDevID) against a domain white list. (The mechanism for checking
a shared white list potentially used by multiple Registrars is out
of scope).
[[RESOLVED: this looks like good text to include in above]]To look
the Pledge up in a domain white list a consistent method for
extracting device identity from the X.509 certificate is required.
RFC6125 describes Domain-Based Application Service identity but here
we require Vendor Device-Based identity. The subject field's DN
encoding MUST include the "serialNumber" attribute with the device's
unique serial number. In the language of RFC6125 this provides for a
SERIALNUM-ID category of identifier that can be included in a
certificate and therefore that can also be used for matching
purposes. The SERIALNUM-ID whitelist is collated according to vendor
trust anchor since serial numbers are not globally unique.
[[RESOLVED: into log request]]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, a Registrar of that domain would show
in the log.
[[RESOLVED: est integration section used 'SHOULD']]The authorization
performed during BRSKI MAY be used for EST enrollment requests by
proceeding with EST enrollment using the authenticated and authorized
TLS connection. This minimizes the number of cryptographic and
protocol operations necessary to complete bootstrapping of the local
key infrastructure.
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D.1.3.3. Claiming the Pledge
Claiming an pledge establishes an audit log at the MASA server and
provides a Registrar with proof, in the form of the Voucher, that the
log entry has been inserted. As indicated in Appendix D.1.1.4 a
Pledge will only proceed with bootstrapping if a Voucher has been
received. The Pledge therefore enforces that bootstrapping only
occurs if the claim has been logged. There is no requirement for the
vendor to definitively know that the device is owned by the
Registrar.
The Registrar obtains the MASA URI via static configuration or by
extracting it from the X.509 IDevID credential. See Section 2.2.
During initial bootstrapping the Pledge provides a nonce specific to
the particular bootstrapping attempt. [[RESOLVED: to resolve this I
updated many points where vouchers are referenced]]The Registrar
SHOULD include this nonce when claiming the Pledge from the MASA
service. Claims from an unauthenticated Registrar are only serviced
by the MASA resource if a nonce is provided.
The Registrar can claim a Pledge that is offline by forming the
request using the entities unique identifier and not including a
nonce in the claim request. Vouchers obtained in this way do not
have a lifetime and they provide a permanent method for the domain to
claim the device. Evidence of such a claim is provided in the audit
log entries available to any future Registrar. Such claims reduce
the ability for future domains to secure bootstrapping and therefore
the Registrar MUST be authenticated by the MASA service although no
requirement is implied that the MASA associates this authentication
with ownership.
An Ownership Voucher requires the vendor to definitively know that a
device is owned by a specific domain. The method used to "claim"
this are out-of-scope. A MASA ignores or reports failures when an
attempt is made to claim a device that has a an Ownership Voucher.
D.1.3.4. Log Verification
A Registrar requests the log information for the Pledge from the MASA
service. The log is verified to confirm that the following is true
to the satisfaction of a Registrar's configured policy:
o Any nonceless entries in the log are associated with domainIDs
recognized by the registrar.
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o Any nonce'd entries are older than when the domain is known to
have physical possession of the Pledge or that the domainIDs are
recognized by the registrar.
If any of these criteria are unacceptable to a Registrar the entity
is rejected. [[RESOLVED: moved to main body]] A Registrar MAY be
configured to ignore the history of the device but it is RECOMMENDED
that this only be configured if hardware assisted NEA [RFC5209] is
supported.
[[RESOLVED: added to main text]]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 vouchers with a 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.
D.1.4. Behavior of the MASA Service
[[UNRESOLVED: primary value of keeping this discussion is to
distinguish between registrar and masa particularly wrt to the
protocol functions provided. perhaps add statements in each protocol
entry "provided by masa" etc?]]
The Manufacturer Authorized Signing Authority service is directly
provided by the manufacturer, or can be provided by a third party the
manufacturer authorizes. It is a cloud resource. The MASA service
provides the following functionalities to Registrars:
Issue Vouchers: In response to Registrar requests the MASA service
issues vouchers. Depending on the MASA policy the Registrar claim
of device ownership is either accepted or verified using out-of-
scope methods (that are expected to improve over time).
Log Vouchers Issued: When a voucher is issued the act of issuing it
includes updating the certifiable logs. Future work to enhance
and distribute these logs is out-of-scope but expected over time.
Provide Logs: As a baseline implementation of the certified logging
mechanism the MASA is repsonsible for reporting logged
information. The current method involves trusting the MASA.
Other logging methods where the MASA is less trusted are expected
to be developed over time.
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D.1.5. Leveraging the new key infrastructure / next steps
As the devices have a common trust anchor, device identity can be
securely established, making it possible to automatically deploy
services across the domain in a secure manner.
Examples of services:
o Device management.
o Routing authentication.
o Service discovery.
D.1.5.1. 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.
D.1.6. Interactions with Network Access Control
[[RESOLVED: via paragraph in 'scope of solution' discussion.]]
The assumption is that Network Access Control (NAC) completes using
the Pledge 's X.509 IDevID credentials and results in the device
having sufficient connectivity to discovery and communicate with the
proxy. Any additional connectivity or quarantine behavior by the NAC
infrastructure is out-of-scope. After the devices has completed
bootstrapping the mechanism to trigger NAC to re-authenticate the
device and provide updated network privileges is also out-of-scope.
This achieves the goal of a bootstrap architecture that can integrate
with NAC but does not require NAC within the network where it wasn't
previously required. Future optimizations can be achieved by
integrating the bootstrapping protocol directly into an initial EAP
exchange.
D.2. Domain Operator Activities
This section describes how an operator interacts with a domain that
supports the bootstrapping as described in this document.
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D.2.1. 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.
D.2.2. Instantiating the Registrar
This is a one time step by the domain administrator. One or more
devices in the domain are configured take on a Registrar function.
A device can be configured to act as a Registrar or a device can
auto-select itself to take on this function, using a detection
mechanism to resolve potential conflicts and setup communication with
the Domain Certification Authority. Automated Registrar selection is
outside scope for this document.
D.2.3. Accepting New Entities
For each Pledge the Registrar is informed of the unique identifier
(e.g. serial number) along with the manufacturer's identifying
information (e.g. manufacturer root certificate). This can happen in
different ways:
1. Default acceptance: In the simplest case, the new device asserts
its unique identity to a Registrar. The registrar accepts all
devices without authorization checks. This mode does not provide
security against intruders and is not recommended.
2. Per device acceptance: The new device asserts its unique identity
to a Registrar. A non-technical human validates the identity,
for example by comparing the identity displayed by the registrar
(for example using a smartphone app) with the identity shown on
the packaging of the device. Acceptance may be triggered by a
click on a smartphone app "accept this device", or by other forms
of pairing. See also [I-D.behringer-homenet-trust-bootstrap] for
how the approach could work in a homenet.
3. Whitelist acceptance: In larger networks, neither of the previous
approaches is acceptable. Default acceptance is not secure, and
a manual per device methods do not scale. Here, the registrar is
provided a priori with a list of identifiers of devices that
belong to the network. This list can be extracted from an
inventory database, or sales records. If a device is detected
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that is not on the list of known devices, it can still be
manually accepted using the per device acceptance methods.
4. Automated Whitelist: an automated process that builds the
necessary whitelists and inserts them into the larger network
domain infrastructure is plausible. Once set up, no human
intervention is required in this process. Defining the exact
mechanisms for this is out of scope although the registrar
authorization checks is identified as the logical integration
point of any future work in this area.
None of these approaches require the network to have permanent
Internet connectivity. Even when the Internet based MASA service is
used, it is possible to pre-fetch the required information from the
MASA a priori, for example at time of purchase such that devices can
enroll later. This supports use cases where the domain network may
be entirely isolated during device deployment.
Additional policy can be stored for future authorization decisions.
For example an expected deployment time window or that a certain
Proxy must be used.
D.2.4. 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.
D.2.5. 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 Appendix D.1.5.1. The certificate can also be
used to securely establish a connection between devices and central
control functions. Also autonomic transactions can use the domain
certificates to authenticate and/or encrypt direct interactions
between devices. The usage of the domain certificates is outside
scope for this document.
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Authors' Addresses
Max Pritikin
Cisco
Email: pritikin@cisco.com
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Michael H. Behringer
Cisco
Email: mbehring@cisco.com
Steinthor Bjarnason
Cisco
Email: sbjarnas@cisco.com
Kent Watsen
Juniper Networks
Email: kwatsen@juniper.net
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