Loading MUD URLs from QR codes

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Table of Contents

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 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.¶

A issue addressed by this document is 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 = “DPP:” [channel-list “;”] [mac “;”]
                    [information “;”] public-key “;;”

This is amended as follows:¶

    dpp-qr = “DPP:” [channel-list “;”] [channel-list “;”]
             [mac “;”] [information “;”] public-key
             [";" mudurl ] “;;”
    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. Privacy Considerations

TBD.¶

5. 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.¶

6. 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:¶

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

7. Acknowledgements

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

Authors' Addresses