OPS Area Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Informational J. Latour
Expires: 7 September 2020 CIRA Labs
H. Habibi Gharakheili
UNSW Sydney
6 March 2020

Loading MUD URLs from QR codes
draft-richardson-opsawg-securehomegateway-mud-03

Abstract

This informational document details the mechanism used by the CIRA
Secure Home Gateway (SHG) to load MUD definitions for devices which
have no integrated MUD (RFC8520) support.

The document describes extensions to the WiFi Alliance DPP QR code to
support the use of MUD URLs.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://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 7 September 2020.

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

Richardson, et al. Expires 7 September 2020 [Page 1]

Internet-Draft SHG-MUD March 2020

extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Generic URL or Version Specific URL . . . . . . . . . . . . . 4
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8

1. Introduction

The Manufacturer Usage Description (MUD) [RFC8520] defines a YANG
data model to express what sort of access a device requires to
operate correctly. The document additionally defines three ways for
the device to communicate the URL of the resulting JSON [RFC8259]
format file to a network enforcement point: DHCP, within an X.509
certificate extension, and via LLDP.

Each of the above mechanism conveys the MUD URL inband, and requires
modifications to the device firmware. Most small IoT devices do not
have LLDP, and have very restricted DHCP clients. Adding the LLDP or
DHCP options requires at least some minimal configuration change, and
possibly entire new subsystems. The X.509 certificateion extension
only makes sense to deploy as part of a larger IDevID based
[ieee802-1AR] system such as [I-D.ietf-anima-bootstrapping-keyinfra].

In all cases these mechanisms can only be implemented by persons with
access to modify and update the firmware of the device. The MUD
system was designed to be implemented by Manufacturers afterall!

In the meantime there is a chicken or egg problem ([chickenegg]): no
manufacturers include MUD URLs in their products as there are no
gateways that use them. No gateways include code that processes MUD
URLs as no products produce them.

The mechanism described here allows any person with physical access
to the device to affix a reference to a MUD URL that can later be
scanned by an end user. This can be done by the (marketing

Richardson, et al. Expires 7 September 2020 [Page 2]

Internet-Draft SHG-MUD March 2020

department) of the Manufacturer, by an outsourced assembler plant, by
value added resellers, by a company importing the product (possibly
to comply with a local regulation), by a network administrator
(perhaps before sending devices home with employees), or even by a
retailer as a value added service.

The mechanism uses the QRcode, which is informally described in
[qrcode]. QR code generators are available as web services
([qrcodewebservice]), or as programs such as [qrencode]. They are
formally defined in [isoiec18004].

This document details how the CIRALabs Secure Home Gateway encode MUD
URLs as QR codes.

Section {#genericfirmware} addresses the question of whether and when
the MUD file should be specific to a specific version of the device
firmware.

The third issue is that an intermediary (ISP, or third-party security
service) may want to extend or amend a MUD file received from a
manufacturer. In order to maintain an audit trail of changes, a way
to encode the previous MUD URL and signature file (and status) is
provided. (FOR DISCUSSION)

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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. Protocol

The [dpp] specification from the Wi-Fi Alliance has created a base
for a QRcode based enrollment system. This specification extends it
to include a MUD URL.

The QR code is as specified in section 5.2.1 of [dpp] is repeated
here:

dpp-qr = â€œDPP:â€ [channel-list â€œ;â€] [mac â€œ;â€]
[information â€œ;â€] public-key â€œ;;â€

This is amended as follows:

Richardson, et al. Expires 7 September 2020 [Page 3]

Internet-Draft SHG-MUD March 2020

dpp-qr = â€œDPP:â€ [channel-list â€œ;â€] [channel-list â€œ;â€]
[mac â€œ;â€] [information â€œ;â€] public-key
[";" mudurl ] â€œ;;â€
mudurl = "D:" *(%x20-3A / %x3C-7E) ; semicolon not allowed

While the ABNF defined in the [dpp] document assumes a specific order
(C:, M:, I:, K:), this specification relaxes this so that the tags
can come in any order. However, in order to make interoperation with
future DPP-only clients as seamless as possible, the MUD extension
suggested here are placed after those defined in [dpp].

This document establishes an IANA registry for DPP attributes.

The syntax of the QR code definition given above does not permit a
semicolon to be included. Semicolons (";") would otherwise be
permitted in MUD URLs. This restriction on the content the URL is
not considered a concern as it is uncommon to use them in a URL.

The URL provided MUST NOT have a query (?) portion present.

An IANA registry is created for the attributes below.

4. Generic URL or Version Specific URL

MUD URLs which are communicated inband by the device, and which are
programmed into the device's firmware may provide a firmware specific
version of the MUD URL. This has the advantage that the resulting
ACLs implemented are specific to the needs of that version of the
firmware.

If the device evolves, requiring new entries then a failure to use
the correct version may result in the device cause false positives in
the enforcement point audit trail. This can be a serious problem, as
repeated false positives train users/owners to ignore reports.

If an older firmware device is described by a newer MUD file, then
the possibility is that the device may have permissions that it can
never use. Unless those permissions result in the device being open
to an attacker, this is not a problem. If the new MUD file has
removed or changed permissions (such as because the name of an
external resource has changed), then the older device will not be
able to access the resource under the old name.

The QR code is updated when the device firmware is updated. The URL
given in the QR code SHOULD be a reference to the latest version of
the MUD file, with no firmware version information. A symbolic name
like "/model/latest.json" which is updated by the manufacturer when
revisions to the MUD file are made is most appropriate. The

Richardson, et al. Expires 7 September 2020 [Page 4]

Internet-Draft SHG-MUD March 2020

manufacturer should be careful to never remove important access
rights that older device may need, as the QRcode provided MUD URL is
what a freshly unpacked device will use. Such a device will point to
the latest MUD URL, but having been a in box for some time, will have
an ancient version of the firmware.

5. Privacy Considerations

The presence of the MUD URL in the QR code reveals the manufacturer
of the device, the type or model of the device, and possibly the
firmware version of the device.

If the QR code is printed on a sticker and is affixed to the device
itself, then the QR code does not reveal anything that a human could
not have determined by simply examining the device. (Save perhaps
the firmware version). The QR code however, may be visible my
machine vision systems in the same area. This includes security
systems, robotic vacuum cleaners, anyone taking a picture with a
camera. Such systems may store the picture(s) in such a way that a
future viewer of the image will be able to decode the QR code,
possibly through assembly of multiple pictures. The QR code is not,
however, a certain indicator that the device is present, only that
the QR code sticker that came with the device is present.

6. Security Considerations

The security of the Device Provisioning Protocol is enhanced when the
public key for a device is not available without physical access to
the device. Placement of a QR code for use by a MUD controller has
no such dependancy, and so such QR codes may be affixed in prominant
places on the outside of packaging. This is not a recommended
practice as future versions of the sticker may include full DPP
information.

The QRcode described in this document is identical for all instances
of the device, and the stickers may be mass produced. The situation
is not the same when a full DPP content is present: each sticker is
unique. A manufacturing plant designed to affix MUD URLs may get
confused and not be ready for the full DPP.

It is recommended that the manufacturing process be designed with the
full DPP process -- unique QR codes per device -- initially so that
no changes are necessary when/if DPP is introduced.

Richardson, et al. Expires 7 September 2020 [Page 5]

Internet-Draft SHG-MUD March 2020

7. IANA Considerations

IANA is requested to create a new Registry entitled: "Device
Provisioning Protocol Attributes". New items can be added to using
Specification Required. In order to conserve space, registrations
are expected to be single upper-case ASCII letters, but the Expert
Reviewer MAY make exceptions. No entry may contain a colon. All
entries beginning with "X" are reserved as Private-Use values.

The following items are to be added to the initial table:

+--------+--------------+-----------------+
| Letter | Name | Document |
+========+==============+=================+
| C | channel-list | [dpp] |
+--------+--------------+-----------------+
| M | MAC address | [dpp] |
+--------+--------------+-----------------+
| I | information | [dpp] |
+--------+--------------+-----------------+
| K | public key | [dpp] |
+--------+--------------+-----------------+
| D | MUD URL | [This document] |
+--------+--------------+-----------------+

Table 1

(EDITORIAL NOTE: the authors of the DPP specification have consented
to seeding control to IANA)

8. Acknowledgements

This work was supported by the Canadian Internet Registration
Authority (cira.ca).

9. References

9.1. Normative References

[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>.

[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.

Richardson, et al. Expires 7 September 2020 [Page 6]

Internet-Draft SHG-MUD March 2020

[qrcode] Wikipedia, ., "QR Code", December 2019,
<https://en.wikipedia.org/wiki/QR_code>.

[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>.

9.2. Informative References

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", Work in Progress, Internet-
Draft, draft-ietf-anima-bootstrapping-keyinfra-37, 26
February 2020, <http://www.ietf.org/internet-drafts/draft-
ietf-anima-bootstrapping-keyinfra-37.txt>.

[ieee802-1AR]
IEEE Standard, ., "IEEE 802.1AR Secure Device Identifier",
2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.

[chickenegg]
Wikipedia, ., "Chicken or the egg", December 2019,
<https://en.wikipedia.org/wiki/Chicken_or_the_egg>.

[qrcodewebservice]
Internet, ., "QR Code Generators", December 2019,
<https://duckduckgo.com/?q=QR+code+web+generator>.

[dpp] "Device Provisioning Protocol Specification", April 2018,
<https://www.wi-fi.org/downloads-registered-guest/Device_P
rovisioning_Protocol_Draft_Technical_Specification_Package
_v0_0_23_0.zip/31255>.

[qrencode] Fukuchi, K., "QR encode", December 2019,
<https://fukuchi.org/works/qrencode/index.html.en>.

[isoiec18004]
ISO/IEC, ., "Information technology - Automatic
identification and data capture techniques - QR Code bar
code symbology specification (ISO/IEC 18004)", February
2015.

Richardson, et al. Expires 7 September 2020 [Page 7]

Internet-Draft SHG-MUD March 2020

Authors' Addresses

Michael Richardson
Sandelman Software Works

Email: mcr+ietf@sandelman.ca

Jacques Latour
CIRA Labs

Email: Jacques.Latour@cira.ca

Hassan Habibi Gharakheili
UNSW Sydney

Email: h.habibi@unsw.edu.au

Richardson, et al. Expires 7 September 2020 [Page 8]