BRSKI Cloud Registrar
draft-ietf-anima-brski-cloud-06
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Owen Friel , Rifaat Shekh-Yusef , Michael Richardson | ||
| Last updated | 2023-05-17 (Latest revision 2022-11-13) | ||
| Replaces | draft-friel-anima-brski-cloud | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Sheng Jiang | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | jiangsheng@huawei.com |
draft-ietf-anima-brski-cloud-06
Network Working Group O. Friel
Internet-Draft Cisco
Intended status: Standards Track R. Shekh-Yusef
Expires: 18 November 2023 Auth0
M. Richardson
Sandelman Software Works
17 May 2023
BRSKI Cloud Registrar
draft-ietf-anima-brski-cloud-06
Abstract
Bootstrapping Remote Secure Key Infrastructures defines how to
onboard a device securely into an operator maintained infrastructure.
It assumes that there is local network infrastructure for the device
to discover and to help the device. This document extends the new
device behaviour so that if no local infrastructure is available,
such as in a home or remote office, that the device can use a well
defined "call-home" mechanism to find the operator maintained
infrastructure.
To this, this document defines how to contact a well-known cloud
registrar, and two ways in which the new device may be redirected
towards the operator maintained infrastructure.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-anima-brski-cloud/.
Discussion of this document takes place on the anima Working Group
mailing list (mailto:anima@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/anima/.
Source for this draft and an issue tracker can be found at
https://github.com/anima-wg/brski-cloud.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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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 18 November 2023.
Copyright Notice
Copyright (c) 2023 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Target Use Cases . . . . . . . . . . . . . . . . . . . . 4
1.2.1. Owner Registrar Discovery . . . . . . . . . . . . . . 4
1.2.2. Bootstrapping with no Owner Registrar . . . . . . . . 5
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Network Connectivity . . . . . . . . . . . . . . . . . . 7
2.2. Pledge Certificate Identity Considerations . . . . . . . 7
3. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 8
3.1. Pledge Requests Voucher from Cloud Registrar . . . . . . 8
3.1.1. Cloud Registrar Discovery . . . . . . . . . . . . . . 8
3.1.2. Pledge - Cloud Registrar TLS Establishment Details . 8
3.1.3. Pledge Issues Voucher Request . . . . . . . . . . . . 9
3.2. Cloud Registrar Handles Voucher Request . . . . . . . . . 9
3.2.1. Pledge Ownership Lookup . . . . . . . . . . . . . . . 9
3.2.2. Cloud Registrar Redirects to Owner Registrar . . . . 10
3.2.3. Cloud Registrar Issues Voucher . . . . . . . . . . . 10
3.3. Pledge Handles Cloud Registrar Response . . . . . . . . . 10
3.3.1. Redirect Response . . . . . . . . . . . . . . . . . . 10
3.3.2. Voucher Response . . . . . . . . . . . . . . . . . . 11
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4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Voucher Request Redirected to Local Domain Registrar . . 11
4.2. Voucher Request Handled by Cloud Registrar . . . . . . . 13
5. YANG extension for Voucher based redirect . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7.1. Issues with Security of HTTP Redirect . . . . . . . . . . 16
7.2. Security Updates for the Pledge . . . . . . . . . . . . . 17
7.3. Trust Anchors for Cloud Registrar . . . . . . . . . . . . 17
7.4. Issues with Redirect via Voucher . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Bootstrapping Remote Secure Key Infrastructures [BRSKI] and [RFC8994]
specifies automated network onboarding of devices, referred to as
pledges, within an Autonomic Control Plane or other managed network
infrastructure. BRSKI Section 2.7 describes how a pledge "MAY
contact a well-known URI of a cloud registrar if a local registrar
cannot be discovered or if the pledge's target use cases do not
include a local registrar".
This document further specifies use of a BRSKI cloud registrar and
clarifies operations that are not sufficiently specified in BRSKI.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the terms Pledge, Registrar, MASA, and Voucher
from [BRSKI] and [RFC8366].
Local Domain: The domain where the pledge is physically located and
bootstrapping from. This may be different to the pledge owner's
domain.
Owner Domain: The domain that the pledge needs to discover and
bootstrap with.
Cloud Registrar: The default Registrar that is deployed at a URI
that is well known to the pledge.
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Owner Registrar: The Registrar that is operated by the Owner, or the
Owner's delegate. There may not be an Owner Registrar in all
deployment scenarios.
Local Domain Registrar: The Registrar discovered on the Local
Domain. There may not be a Local Domain Registrar in all
deployment scenarios.
EST: Enrollment over Secure Transport [RFC7030]
VAR: Value Added Reseller
1.2. Target Use Cases
Two high level use cases are documented here. There are more details
provided in sections Section 4.1 and Section 4.2. While both use
cases aid with incremental deployment of BRSKI infrastructure, for
many smaller sites (such as teleworkers) no further infrastructure is
expected.
The pledge is not expected to know which of these two situations it
is in. The pledge determines this based upon signals that it
receives from the Cloud Registrar. The Cloud Registrar is expected
to make the determination based upon the identity presented by the
pledge.
A Cloud Registrar will typically handle all the devices of a
particular product line from a particular manufacturer. This
document places no restrictions on how many different deployments or
owner sites the Cloud Registrar can handle, or how many devices per
site that the Cloud Registrar can handle. It is also entirely
possible that all devices sold by through a particular Value Added
Reseller (VAR) might be preloaded with a configuration that changes
the Cloud Registrar URL to point to a VAR. Such an effort would
require unboxing each device in a controlled environment, but the
provisioning could occur using a regular BRSKI or SZTP [RFC8572]
process.
1.2.1. Owner Registrar Discovery
A pledge is bootstrapping from a remote location with no local domain
registrar (specifically: with no local infrastructure to provide for
automated discovery), and needs to discover its owner registrar. The
cloud registrar is used by the pledge to discover the owner
registrar. The cloud registrar redirects the pledge to the owner
registrar, and the pledge completes bootstrap against the owner
registrar.
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A typical example is an enduser deploying a pledge in a home or small
branch office, where the pledge belongs to the enduser's employer.
There is no local domain registrar, and the pledge needs to discover
and bootstrap with the employer's registrar which is deployed in
headquarters. For example, an enduser is deploying an IP phone in a
home office and the phone needs to register to an IP PBX deployed in
their employer's office.
1.2.2. Bootstrapping with no Owner Registrar
A pledge is bootstrapping where the owner organization does not yet
have an owner registrar deployed. The cloud registrar issues a
voucher, and the pledge completes trust bootstrap using the cloud
registrar. The voucher issued by the cloud includes domain
information for the owner's Enrollment over Secure Transport (EST)
[RFC7030] service the pledge should use for certificate enrollment.
In one use case, an organization has an EST service deployed, but
does not have yet a BRSKI capable Registrar service deployed. The
pledge is deployed in the organization's domain, but does not
discover a local domain registrar or owner registrar. The pledge
uses the cloud registrar to bootstrap, and the cloud registrar
provides a voucher that includes instructions on finding the
organization's EST service.
2. Architecture
The high level architecture is illustrated in Figure 1.
The pledge connects to the cloud registrar during bootstrap.
The cloud registrar may redirect the pledge to an owner registrar in
order to complete bootstrap against the owner registrar.
If the cloud registrar issues a voucher itself without redirecting
the pledge to an owner registrar, the cloud registrar will inform the
pledge what domain to use for accessing EST services in the voucher
response.
Finally, when bootstrapping against an owner registrar, this
registrar may interact with a backend CA to assist in issuing
certificates to the pledge. The mechanisms and protocols by which
the registrar interacts with the CA are transparent to the pledge and
are out-of-scope of this document.
The architecture shows the cloud registrar and MASA as being
logically separate entities. The two functions could of course be
integrated into a single service.
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There are two different mechanisms for a cloud registrar to handle
voucher requests. It can redirect the request to Owner Registrar for
handling, or it can return a voucher that pins the actual Owner
Register. When returning a voucher, additional bootstrapping
information embedded in the voucher. Both mechanisms are described
in detail later in this document.
|<--------------OWNER--------------------------->| MANUFACTURER
On-site Cloud
+--------+ +-----------+
| Pledge |----------------------------------------->| Cloud |
+--------+ | Registrar |
| +-----+-----+
| |
| +-----------+ +-----+-----+
+---------------->| Owner |---------------->| MASA |
| VR-sign(N) | Registrar |sign(VR-sign(N)) +-----------+
| +-----------+
| | +-----------+
| +--->| CA |
| +-----------+
|
| +-----------+
+---------------->| Services |
+-----------+
Figure 1: High Level Architecture
As depicted in Figure 1, there are a number of parties involve in the
process. The Manufacturer, or Original Equipment Maker (OEM) builds
the device, but also is expected to run the MASA, or arrange for it
to exist.
The network operator or enterprise is the intended owner of the new
device: the pledge. This could be the enterprise itself, or in many
cases there is some outsourced IT department that might be involved.
They operator the Registrar or EST Server. They may operate the CA,
or they may contract those services from another entity.
Unlike in [BRSKI] there is a potential additional party involved, the
network integrator, who may operate the Cloud Registrar. This is
typically a value added reseller who works with the OEM to ship
products with the right configuration to the owner. For example, SIP
telephones or other conferencing systems may be installed by this
VAR, often shipped directly from a warehouse to the customer's remote
office location. The network integrator and manufacturer are aware
of which devices have been shipped to the integrator through sales
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channel integrations, and so the manufacturer's Cloud Registrar is
able to redirect the pledge through a chain of Cloud Registrars, as
explained in Section 3.3.1.
2.1. Network Connectivity
The assumption is that the pledge already has network connectivity
prior to connecting to the cloud registrar. The pledge must have an
IP address that is able to make DNS queries, and be able to send HTTP
requests to the cloud registrar. There are many ways to accomplish
this, from routeable IPv4 or IPv6 addresses, to use of NAT44, to
using HTTP or SOCKS proxies. There are are DHCP options that a
network operator can configure to accomplish any of these options.
The pledge operator has already connected the pledge to the network,
and the mechanism by which this has happened is out of scope of this
document. For many telephony applications, this is typically going
to be a wired connection. For wireless use cases, some kind of
existing WiFi onboarding mechanism such as WPS. Similarly, what
address space the IP address belongs to, whether it is an IPv4 or
IPv6 address, or if there are firewalls or proxies deployed between
the pledge and the cloud registar are all out of scope of this
document.
2.2. Pledge Certificate Identity Considerations
BRSKI section 5.9.2 specifies that the pledge MUST send an EST
[RFC7030] CSR Attributes request to the registrar. The registrar MAY
use this mechanism to instruct the pledge about the identities it
should include in the CSR request it sends as part of enrollment.
The registrar may use this mechanism to tell the pledge what Subject
or Subject Alternative Name identity information to include in its
CSR request. This can be useful if the Subject must have a specific
value in order to complete enrollment with the CA.
EST [RFC7030] is not clear on how the CSR Attributes response should
be structured, and in particular is not clear on how a server can
instruct a client to include specific attribute values in its CSR.
[I-D.ietf-lamps-rfc7030-csrattrs] clarifies how a server can use CSR
Attributes response to specify specific values for attributes that
the client should include in its CSR.
For example, the pledge may only be aware of its IDevID Subject which
includes a manufacturer serial number, but must include a specific
fully qualified domain name in the CSR in order to complete domain
ownership proofs required by the CA.
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As another example, the registrar may deem the manufacturer serial
number in an IDevID as personally identifiable information, and may
want to specify a new random opaque identifier that the pledge should
use in its CSR.
3. Protocol Operation
3.1. Pledge Requests Voucher from Cloud Registrar
3.1.1. Cloud Registrar Discovery
BRSKI defines how a pledge MAY contact a well-known URI of a cloud
registrar if a local domain registrar cannot be discovered.
Additionally, certain pledge types might never attempt to discover a
local domain registrar and might automatically bootstrap against a
cloud registrar.
The details of the URI are manufacturer specific, with BRSKI giving
the example "brski-registrar.manufacturer.example.com".
The Pledge SHOULD be provided with the entire URL of the Cloud
Registrar, including the path component, which is typically "/.well-
known/brski/requestvoucher", but may be another value.
3.1.2. Pledge - Cloud Registrar TLS Establishment Details
The pledge MUST use an Implicit Trust Anchor database (see EST
[RFC7030]) to authenticate the cloud registrar service. In order to
make use of a Cloud Registrar, the Pledge MUST be manufactured with
pre-loaded trust-anchors that are used to validate the TLS
connection. The TLS connection can be validated using a public Web
PKI trust anchors using [RFC6125] DNS-ID mechanisms, a pinned
certification authority, or even a pinned raw public key. This is a
local implementation decision.
The pledge MUST NOT establish a provisional TLS connection (see BRSKI
section 5.1) with the cloud registrar.
The cloud registrar MUST validate the identity of the pledge by
sending a TLS CertificateRequest message to the pledge during TLS
session establishment. The cloud registrar MAY include a
certificate_authorities field in the message to specify the set of
allowed IDevID issuing CAs that pledges may use when establishing
connections with the cloud registrar.
The cloud registrar MAY only allow connections from pledges that have
an IDevID that is signed by one of a specific set of CAs, e.g.
IDevIDs issued by certain manufacturers.
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The cloud registrar MAY allow pledges to connect using self-signed
identity certificates or using Raw Public Key [RFC7250] certificates.
3.1.3. Pledge Issues Voucher Request
After the pledge has established a full TLS connection with the cloud
registrar and has verified the cloud registrar PKI identity, the
pledge generates a voucher request message as outlined in BRSKI
section 5.2, and sends the voucher request message to the cloud
registrar.
3.2. Cloud Registrar Handles Voucher Request
The cloud registrar must determine pledge ownership. if the registrar
is unwilling or unable to handle the voucher request, for example it
is unable to determine ownership, then the cloud registrar MUST
return a suitable 4xx or 5xx error response to the pledge.
If the cloud registrar successfully determines ownership, then the
registrar MUST take one of the following actions:
* return a suitable 4xx or 5xx error response to the pledge if the
registrar is unwilling or unable to handle the voucher request for
any reason
* redirect the pledge to an owner register via 307 response code
* issue a voucher and return a 200 response code
3.2.1. Pledge Ownership Lookup
The cloud registrar needs some suitable mechanism for knowing the
correct owner of a connecting pledge based on the presented identity
certificate. For example, if the pledge establishes TLS using an
IDevID that is signed by a known manufacturing CA, the registrar
could extract the serial number from the IDevID and use this to
lookup a database of pledge IDevID serial numbers to owners.
Alternatively, if the cloud registrar allows pledges to connect using
self-signed certificates, the registrar could use the thumbprint of
the self-signed certificate to lookup a database of pledge self-
signed certificate thumbprints to owners.
The mechanism by which the cloud registrar determines pledge
ownership is out-of-scope of this document.
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3.2.2. Cloud Registrar Redirects to Owner Registrar
Once the cloud registrar has determined pledge ownership, the cloud
registrar MAY redirect the pledge to the owner registrar in order to
complete bootstrap. Ownership registration will require the owner to
register their local domain. The mechanism by which pledge owners
register their domain with the cloud registrar is out-of-scope of
this document.
The cloud registrar replies to the voucher request with a suitable
HTTP 307 response code, including the owner's local domain in the
HTTP Location header.
3.2.3. Cloud Registrar Issues Voucher
If the cloud registrar issues a voucher, it returns the voucher in a
HTTP response with a 200 response code.
The cloud registrar MAY issue a 202 response code if it is willing to
issue a voucher, but will take some time to prepare the voucher.
The voucher MUST include the "est-domain" field as defined below.
This tells the pledge where the domain of the EST service to use for
completing certificate enrollment.
The voucher MAY include the "additional-configuration" field. This
points the pledge to a URI where application specific additional
configuration information may be retrieved. Pledge and Registrar
behavior for handling and specifying the "additional-configuration"
field is out-of-scope of this document.
3.3. Pledge Handles Cloud Registrar Response
3.3.1. Redirect Response
The cloud registrar returned a 307 response to the voucher request.
The pledge SHOULD restart the process using a new voucher request
using the location provided in the HTTP redirect. Note if the pledge
is able to validate the new server using a trust anchor found in its
Implicit Trust Anchor database, then it MAY accept additional 307
redirects.redirect. The pledge MUST never visit a location that it
has already been to. If that happens then the pledge MUST fail the
onboarding attempt and go back to the beginning, which includes
listening to other sources of onboarding information as specified in
[BRSKI] section 4.1 and 5.0.
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The pledge SHOULD establish a provisional TLS connection with
specified local domain registrar. The pledge SHOULD NOT use its
Implicit Trust Anchor database for validating the local domain
registrar identity. The pledge SHOULD send a voucher request message
via the local domain registrar. When the pledge downloads a voucher,
it can validate the TLS connection to the local domain registrar and
continue with enrollment and bootstrap as per standard BRSKI
operation.
3.3.2. Voucher Response
The cloud registrar returned a voucher to the pledge. The pledge
SHOULD perform voucher verification as per standard BRSKI operation.
The pledge SHOULD verify the voucher signature using the
manufacturer-installed trust anchor(s), SHOULD verify the serial
number in the voucher, and SHOULD verify any nonce information in the
voucher.
The pledge SHOULD extract the "est-domain" field from the voucher,
and SHOULD continue with EST enrollment as per standard BRSKI
operation.
4. Protocol Details
4.1. Voucher Request Redirected to Local Domain Registrar
This flow illustrates the Owner Registrar Discovery flow. A pledge
is bootstrapping in a remote location with no local domain registrar.
The assumption is that the owner registrar domain is accessible and
the pledge can establish a network connection with the owner
registrar. This may require that the owner network firewall exposes
the registrar on the public internet.
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+--------+ +----------+
| Pledge | | Cloud RA |
| | | |
+--------+ +----------+
| |
| 1. Mutual-authenticated TLS |
|<----------------------------------------------->|
| |
| 2. Voucher Request |
|------------------------------------------------>|
| |
| 3. 307 Location: owner-ra.example.com |
|<------------------------------------------------|
|
| +-----------+ +---------+
| | Owner | | MASA |
| | Registrar | | |
| +-----------+ +---------+
| 4. Provisional TLS | |
|<-------------------->| |
| | |
| 5. Voucher Request | |
|--------------------->| 6. Voucher Request |
| |------------------------->|
| | |
| | 7. Voucher Response |
| |<-------------------------|
| 8. Voucher Response | |
|<---------------------| |
| | |
| 9. Validate TLS | |
|<-------------------->| |
| | |
| 10. etc. | |
|--------------------->| |
The process starts, in step 1, when the Pledge establishes a Mutual
TLS channel with the Cloud RA using artifacts created during the
manufacturing process of the Pledge.
In step 2, the Pledge sends a voucher request to the Cloud RA.
The Cloud RA completes pledge ownership lookup as outlined in
Section 3.2.1, and determines the owner registrar domain. In step 3,
the Cloud RA redirects the pledge to the owner registrar domain.
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Steps 4 and onwards follow the standard BRSKI flow. The pledge
establishes a provisional TLS connection with the owner registrar,
and sends a voucher request to the owner registrar. The registrar
forwards the voucher request to the MASA. Assuming the MASA issues a
voucher, then the pledge validates the TLS connection with the
registrar using the pinned-domain-cert from the voucher and completes
the BRSKI flow.
4.2. Voucher Request Handled by Cloud Registrar
The Voucher includes the EST domain to use for EST enroll. It is
assumed services are accessed at that domain too. As trust is
already established via the Voucher, the pledge does a full TLS
handshake against the local RA indicated by the voucher response.
The returned voucher contains an attribute, "est-domain", defined in
Section 5 below. The pledge is directed to continue enrollment using
the EST server found at that URI. The pledge uses the pinned-domain-
cert from the voucher to authenticate the EST server.
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+--------+ +----------+
| Pledge | | Cloud RA |
| | | / MASA |
+--------+ +----------+
| |
| 1. Mutual TLS |
|<----------------------------------------------->|
| |
| 2. Voucher Request |
|------------------------------------------------>|
| |
| 3. Voucher Response {est-domain:fqdn} |
|<------------------------------------------------|
| |
| +----------+ |
| | RFC7030 | |
| | EST | |
| | Server | |
| +----------+ |
| | |
| 4. Full TLS | |
|<-------------------->| |
| |
| 3a. /voucher_status POST success |
|------------------------------------------------>|
| ON FAILURE 3b. /voucher_status POST |
| |
| 5. EST Enrol | |
|--------------------->| |
| | |
| 6. Certificate | |
|<---------------------| |
| | |
| 7. /enrollstatus | |
|--------------------->| |
The process starts, in step 1, when the Pledge establishes a Mutual
TLS channel with the Cloud RA/MASA using artifacts created during the
manufacturing process of the Pledge. In step 2, the Pledge sends a
voucher request to the Cloud RA/MASA, and in response the Pledge
receives an [RFC8366] format voucher from the Cloud RA/MASA that
includes its assigned EST domain in the est-domain attribute.
At this stage, the Pledge should be able to establish a TLS channel
with the EST server. The connection may involve crossing the
Internet requiring a DNS lookup on the provided name. It may also be
a local address that includes an IP address literal including both
[RFC1918] and IPv6 Unique Local Address. The EST server is validated
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using the pinned-domain-cert value provided in the voucher as
described in [BRSKI] section 5.6.2. This involves treating the
artifact provided in the pinned-domain-cert as a trust anchor, and
attempting to validate the EST server from this anchor only.
There is a case where the pinned-domain-cert is the identical End-
Entity (EE) Certificate as the EST server. It also explicitly
includes the case where the EST server has a self-signed EE
Certificate, but it may also be an EE certificate that is part of a
larger PKI. If the certificate is not a self-signed or EE
certificate, then the Pledge SHOULD apply [RFC6125] DNS-ID validation
on the certificate against the URL provided in the est-domain
attribute. If the est-domain was provided by with an IP address
literal, then it is unlikely that it can be validated, and in that
case, it is expected that either a self-signed certificate or an EE
certificate will be pinned.
The Pledge also has the details it needs to be able to create the CSR
request to send to the RA based on the details provided in the
voucher.
In step 4, the Pledge establishes a TLS channel with the Cloud RA/
MASA, and optionally the pledge should send a request, steps 3.a and
3.b, to the Cloud RA/MASA to inform it that the Pledge was able to
establish a secure TLS channel with the EST server.
The Pledge then follows that, in step 5, with an EST Enroll request
with the CSR and obtains the requested certificate. The Pledge must
validate that the issued certificate has the expected identifier
obtained from the Cloud RA/MASA in step 3.
5. YANG extension for Voucher based redirect
[RFC8366bis] contains the two needed voucher extensions: est-domain
and additional-configuration which are needed when a client is
redirected to a local EST server.
6. IANA Considerations
This document makes no IANA requests.
7. Security Considerations
The Cloud-Registrar described in this document inherits all of the
issues that are described in [BRSKI]. This includes dependency upon
continued operation of the manufacturer provided MASA, as well as
potential complications where a manufacturer might interfere with
resale of a device.
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In addition to the dependency upon the MASA, the successful
enrollment of a device using a Cloud Registrar depends upon the
correct and continued operation of this new service. This internet
accessible service may be operated by the manufacturer and/or by one
or more value-added-resellers. All of the considerations for
operation of the MASA also apply to operation of the Cloud Registrar.
7.1. Issues with Security of HTTP Redirect
If the Redirect to Registrar method is used, as described in
Section 4.1, there may be a series of 307 redirects. An example of
why this might occur is that the manufacturer only knows that it
resold the device to a particular value added reseller (VAR), and
there may be a chain of such VARs. It is important the pledge avoid
being drawn into a loop of redirects. This could happen if a VAR
does not think they are authoritative for a particular device. A
"helpful" programmer might instead decide to redirect back to the
manufacturer in an attempt to restart at the top: perhaps there is
another process that updates the manufacturer's database and this
process is underway. Instead, the VAR MUST return a 404 error if it
cannot process the device. This will force the device to stop,
timeout, and then try all mechanisms again.
There is another case where a connection problem may occur: when the
pledge is behind a captive portal or an intelligent home gateway that
provides access control on all connections. Captive portals that do
not follow the requirements of [RFC8952] section 1 may forcibly
redirect HTTPS connections. While this is a deprecated practice as
it breaks TLS in a way that most users can not deal with, it is still
common in many networks.
On the first connection, the incorrect connection will be discovered
because the Pledge will be unable to validate the connection to its
cloud registrar via DNS-ID. That is, the certificate returned from
the captive portal will not match.
At this point a network operator who controls the captive portal,
noticing the connection to what seems a legitimate destination (the
cloud registrar), may then permit that connection. This enables the
first connection to go through.
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The connection is then redirected to the Registrar, either via 307,
or via est-domain in a voucher. If it is a 307 redirect, then a
provisional TLS connection will be initiated, and it will succeed.
The provisional TLS connection does not do [RFC6125] DNS-ID
validation at the beginning of the connection, so a forced
redirection to a captive portal system will not be detected. The
subsequent BRSKI POST of a voucher will most likely be met by a 404
or 500 HTTP code. As the connection is provisional, the pledge will
be unable to determine this.
It is RECOMMENDED therefore that the pledge look for [RFC8910]
attributes in DHCP, and if present, use the [RFC8908] API to learn if
it is captive.
7.2. Security Updates for the Pledge
Unlike many other uses of BRSKI, in the Cloud Registrar case it is
assumed that the Pledge has connected to a network on which there is
addressing and connectivity, but there is no other local
configuration available.
There is another advantage to being online: the pledge may be able to
contact the manufacturer before onboarding in order to apply the
latest firmware updates. This may also include updates to the
Implicit list of Trust Anchors. In this way, a Pledge that may have
been in a dusty box in a warehouse for a long time can be updated to
the latest (exploit-free) firmware before attempting onboarding.
7.3. Trust Anchors for Cloud Registrar
The Implicit TA database is used to authenticate the Cloud Registrar.
This list is built-in by the manufacturer along with a DNS name to
which to connect. (The manufacturer could even build in IP addresses
as a last resort)
The Cloud Registrar does not have a certificate that can be validated
using a public (WebPKI) anchor. The pledge may have any kind of
Trust Anchor built in: from full multi-level WebPKI to the single
self-signed certificate used by the Cloud Registrar. There are many
tradeoffs to having more or less of the PKI present in the Pledge,
which is addresses in part in
[I-D.irtf-t2trg-taxonomy-manufacturer-anchors] in sections 3 and 5.
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7.4. Issues with Redirect via Voucher
The second redirect case is handled by returning a special extension
in the voucher. The Cloud Registrar actually does all of the voucher
processing as specified in [BRSKI]. In this case, the Cloud
Registrar may be operated by the same entity as the MASA, and it
might even be combined into a single server. Whether or not this is
the case, it behaves as if it was separate.
It may be the case that one or more 307-Redirects have taken the
Pledge from the built-in Cloud Registrar to one operated by a VAR.
When the Pledge is directed to the Owner's EST [RFC7030] Registrar,
the Pledge validates the TLS connection with this server using the
"pinned-domain-cert" attribute in the voucher. There is no
provisional TLS connection, and therefore there are no risks
associated with being behind a captive portal.
8. References
8.1. Normative References
[BRSKI] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
[I-D.ietf-lamps-rfc7030-csrattrs]
Richardson, M., Friel, O., von Oheimb, D., and D. Harkins,
"Clarification of RFC7030 CSR Attributes definition", Work
in Progress, Internet-Draft, draft-ietf-lamps-rfc7030-
csrattrs-02, 8 April 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
rfc7030-csrattrs-02>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8366bis]
Watsen, K., Richardson, M., Pritikin, M., Eckert, T. T.,
and Q. Ma, "A Voucher Artifact for Bootstrapping
Protocols", Work in Progress, Internet-Draft, draft-ietf-
anima-rfc8366bis-07, 7 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-anima-
rfc8366bis-07>.
8.2. Informative References
[I-D.irtf-t2trg-taxonomy-manufacturer-anchors]
Richardson, M., "A Taxonomy of operational security
considerations for manufacturer installed keys and Trust
Anchors", Work in Progress, Internet-Draft, draft-irtf-
t2trg-taxonomy-manufacturer-anchors-00, 22 January 2023,
<https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-
taxonomy-manufacturer-anchors-00>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
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[RFC8908] Pauly, T., Ed. and D. Thakore, Ed., "Captive Portal API",
RFC 8908, DOI 10.17487/RFC8908, September 2020,
<https://www.rfc-editor.org/info/rfc8908>.
[RFC8910] Kumari, W. and E. Kline, "Captive-Portal Identification in
DHCP and Router Advertisements (RAs)", RFC 8910,
DOI 10.17487/RFC8910, September 2020,
<https://www.rfc-editor.org/info/rfc8910>.
[RFC8952] Larose, K., Dolson, D., and H. Liu, "Captive Portal
Architecture", RFC 8952, DOI 10.17487/RFC8952, November
2020, <https://www.rfc-editor.org/info/rfc8952>.
[RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", RFC 8994,
DOI 10.17487/RFC8994, May 2021,
<https://www.rfc-editor.org/info/rfc8994>.
Authors' Addresses
Owen Friel
Cisco
Email: ofriel@cisco.com
Rifaat Shekh-Yusef
Auth0
Email: rifaat.s.ietf@gmail.com
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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