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On loading MUD URLs from QR codes

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9238.
Authors Michael Richardson , Jacques Latour , Hassan Habibi Gharakheili
Last updated 2022-02-15 (Latest revision 2022-02-11)
Replaces draft-richardson-opsawg-securehomegateway-mud
RFC stream Independent Submission
IETF conflict review conflict-review-richardson-mud-qrcode, conflict-review-richardson-mud-qrcode, conflict-review-richardson-mud-qrcode, conflict-review-richardson-mud-qrcode, conflict-review-richardson-mud-qrcode, conflict-review-richardson-mud-qrcode
Stream ISE state In IESG Review
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Document shepherd Eliot Lear
Shepherd write-up Show Last changed 2022-02-12
IESG IESG state Became RFC 9238 (Informational)
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IANA IANA review state IANA OK - No Actions Needed
Network Working Group                                      M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Informational                                 J. Latour
Expires: 15 August 2022                                        CIRA Labs
                                                   H. Habibi Gharakheili
                                                             UNSW Sydney
                                                        11 February 2022

                   On loading MUD URLs from QR codes


   This informational document details a protocol to load MUD
   definitions for devices which have no integrated Manufacturer Usage
   Description (MUD) as described in RFC8520.

   This document is published to inform the Internet community of this
   mechanism to allow interoperability and to serve as a basis of other
   standards work if there is interest.

   // RFC-EDITOR-please-remove: This work is tracked at

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

   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 15 August 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  The SQRL Protocol . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Manufacturer Usage Descriptions in SQRL . . . . . . . . .   5
       3.2.1.  B000 Company Name . . . . . . . . . . . . . . . . . .   6
       3.2.2.  B001 Product Name . . . . . . . . . . . . . . . . . .   6
       3.2.3.  B002 Model Number . . . . . . . . . . . . . . . . . .   6
       3.2.4.  MUD URL Data Record . . . . . . . . . . . . . . . . .   6
       3.2.5.  Device MAC Address  . . . . . . . . . . . . . . . . .   7
   4.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Generic URL or Version Specific URL . . . . . . . . . . . . .   8
   6.  Crowd Supply of MUD Files . . . . . . . . . . . . . . . . . .   8
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     8.1.  QR codes are not assurances . . . . . . . . . . . . . . .   9
     8.2.  MUD files can have signatures . . . . . . . . . . . . . .  10
     8.3.  MUD QR code stickers could be confused  . . . . . . . . .  10
     8.4.  QR code can include MAC address . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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.  That document additionally defines three ways for
   the device to to communicate to a network enforcement point the MUD
   URL, i.e., the URL of the resulting MUD file in JSON [RFC8259]: DHCP,
   within an X.509 certificate extension, and via LLDP.

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   Each of the above mechanism conveys the MUD URL in-band, and requires
   modifications to the device firmware.  Most small IoT devices do not
   have LLDP, and often have very restricted DHCP clients.  Adding the
   LLDP or DHCP options requires at least some minimal configuration
   change, and possibly entire new subsystems.  Meanwhile, use of the
   PKIX certification extension only makes sense as part of a larger
   IDevID based [ieee802-1AR] deployment such as

   In the above cases these mechanisms can only be implemented by
   persons with access to modify and update the firmware of the device.

   In the meantime there is a chicken or egg problem ([chickenegg]):
   manufacturers are not motivated to (and thus likely do not) include
   MUD URLs in their products, as they believe that there are no
   gateways using those URLs.  At the same time, gateways have little
   incentive to (and thus likely do not) include code that processes MUD
   URLs, as it is believed that no products have and disseminate them.

   The protocol described in this document 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.

   The QR-based protocol is presented as a convenient alternative when
   the mechanisms from RFC 8520 are not available to use, on the device
   or the gateway.

   Affixing a sticker can be done by

   *  the marketing department of the Manufacturer,

   *  an outsourced assembler plant,

   *  value added resellers (perhaps in response to a local RFP),

   *  a company importing the product (possibly to comply with a local

   *  a network administrator (perhaps before sending devices home with
      employees, or to remote sites),

   *  a retailer as a value added service.

   QRcodes are informally described in [qrcode] and formally defined in
   [isoiec18004].  The protocol described in this document uses a QRcode
   to encode the MUD URL.  Specifically, the protocol leverages the data
   format from the Reverse Logistics Association's Standardized Quick
   Response for Logistics [SQRL].

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   SQRL codes are being put on devices via sticker or via laser etching
   into the case in order to deal with many situations, but specifically
   for end-of-life processing for the device.  An important idea behind
   the effort is that clearly identifying a product permits appropriate
   disposal, refurbishment or recycling of the components of the

   There are also use cases for SQRL described in which the codes are
   used as part of regular maintenance for a product.

   SQRL is an application of the 12N Data Identifier system specified by
   the ANSI MH10.8.2 Committee [mh10] in a format appropriate for
   QRcodes as well as other things like NFCs transmissions.

   QRcode generators are available as web services [qrcodewebservice],
   or as programs such as [qrencode].

   Section 5 summarizes the considerations contained in
   [I-D.ietf-opsawg-mud-acceptable-urls] section 6.1 ("Updating MUD URLs
   vs Updating MUD files").  Due to the immutable nature of the QRcode,
   MUD URLs in this document will need to be non-firmware specific.

2.  Terminology

   Although this document is not an IETF Standards Track publication, it
   adopts the conventions for normative language to provide clarity of
   instructions to the implementer.  The key words "MUST", "MUST NOT",
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown

   Readers should be familiar with the terminology in [RFC8520],
   including: MUD file, MUD URL, Manufacturer and MUD manager and

3.  Protocol

   This QRcode protocol builds upon the work by [SQRL].  That protocol
   is very briefly described in Section 3.1.  Then the list of needed
   Data Records to be filled in is explained.

3.1.  The SQRL Protocol

   [SQRL] documents an octet protocol that can be efficiently encoded
   into QRcodes using a sequence of ASCII bytes, plus six control codes
   (see section 3.1 of [SQRL]):

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   *  <RS> Record Separator (ASCII 30)

   *  <EoT> End of Transmission (ASCII 4)

   *  <FS> Field Separator (ASCII 28)

   *  <GS> Group Separator (ASCII 29)

   *  <US> Unit Separator (ASCII 31),

   *  Concatenation Operator (ASCII 43: "+").

   Section 7.2 of [SQRL] gives the details, which can be summarized as:

   1.  The QR code header starts with:

   "[)>" <RS> "06" <GS> "12N"

   1.  Include one or more Data Records.  This consists of a four letter
       Field Identifiers followed by ASCII characters terminated with a
       <Unit Separator>.

   2.  End with:


   There are additionally optional flags that may be present in every
   Data Record as described in section 7.4 of [SQRL].  These flags have
   no bearing on MUD processing.  A parser which is only collecting MUD
   URLs will not need to parse those flags.  A general purpose SQRL
   parser will need more complexity.

   Field Separator characters are used in SQRL to signify the beginning
   of a new unit of data.  A MUD specific parser that encounters a Field
   Separator and has not yet collected the right MUD information MUST
   ignore the characters collected so far and then restart.

   Environment records, as described in [SQRL] section 7.4, look and act
   exactly as fields, with a special Field Identifier.  They serve no
   purpose when looking for MUD information, and MAY be ignored.

3.2.  Manufacturer Usage Descriptions in SQRL

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3.2.1.  B000 Company Name

   The B000 Data Record is mandatory in [SQRL].  It MUST be in ASCII
   representation.  It should be a representation of the company or
   brand name.  It SHOULD match the ietf-mud/mud/mfg-name in the MUD
   file, however the MUD file can contain arbitrary UTF8 for this name,
   while the SQRL files are expected to be 7-bit US-ASCII.

3.2.2.  B001 Product Name

   The B001 Data Record is optional in [SQRL].  It is the Product Name
   in ASCII.  Its presence is RECOMMENDED.  Some third parties that
   create QRcode stickers might not know the product name with 100%
   certainty, and MAY prefer to omit this rather than create further

3.2.3.  B002 Model Number

   The B002 Data Record is optional in [SQRL], but is MANDATORY in this
   profile.  It is the Model Name in ASCII.  It SHOULD match the
   optional ietf-mud/mud/model-name in the MUD file if that entry is
   present in the MUD file.

   If a third party that is creating QRcodes can not locate an official
   model number when creating their MUD file and QRcode, then the third
   party SHOULD make one up.

3.2.4.  MUD URL Data Record

   A new Field Identifier has been assigned by the Reverse Logistics
   Association (RLA), which is "M180" This record MUST be filled with
   the MUD URL.

   Short URLs are easier to encode into QRcode because they require
   fewer pixels of QRcode.  More content in the QRcode requires a bigger

   Use of URL shortening services (see [URLshorten]) can be useful
   provided that the service is stable throughout the lifetime of the
   device and QRcode, and that the privacy stance of the service is well

   Section 8.1 of [SQRL] also has some good advice on longevity concerns
   with URLs.

   The URL provided MUST NOT have a query (?) portion present.  If one
   is present, the query portion MUST be removed before processing.

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3.2.5.  Device MAC Address

   If a MAC address is used as a unique device identifier (which is
   RECOMMENDED if possible), then it MUST be included in this Data

   [SQRL] section 9.10 defines the Data Record: "M06C" as the MAC
   address.  No format for the MAC address is provided in that document.

   This document RECOMMENDS 12 (or 16) hex octets are used with no
   spaces or punctuation. (16 octets are used in the IEEE OUI-64 format
   used in 802.15.4, and some next generation Ethernet proposals)

   Parsers that find punctuation (such as colons (":"), dashes ("-"), or
   white space) MUST skip over it.

4.  Applicability

   The use of stickers to convey MUD URLs would appear to have little
   value when the stickers are applied by the end user organization and
   consumed by the same.  This is particularly the case when the QR code
   does not include the device MAC address.  In such a situation the
   installer handling the device would scan the QR code to get the
   appropriate MUD file reference, and have to input the associated MAC
   address as well.

   In such a case, one might wonder why the installer couldn't just
   enter the appropriate MAC address and select the appropriate ACLs for
   the device.  No MUD file or QR code to convey it would be useful at

   The use of a MUD file (or QR code other other way to convey it) has
   the advantage that it offers several layers of indirection:

   1.  The list of ACLs for a given device may be added or removed.

   2.  The ACLs may refer to DNS names, which may map to IPv4 or IPv6

   3.  The entire file may be replaced, and may also include supply
       chain information, such as Software Bill of Materials (SBOM).

   In addition, the mechanism to install a new device (MAC address) to
   MUD file mapping does not need to permit any other network security
   settings to be alterable by the person doing the installation.

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5.  Generic URL or Version Specific URL

   MUD URLs which are communicated in-band 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
   Access Control Lists (ACLs) enforced in the network are specific to
   the needs of that version of the firmware.

   A MUD URL which is affixed to the device with a sticker, or etched
   into the case can not be changed.

   Given the considerations of [I-D.ietf-opsawg-mud-acceptable-urls]
   section 6.1 ("Updating MUD URLs vs Updating MUD files"), it is
   prudent to use a MUD URL which points to a MUD file which will only
   have new features added over time, and never have features removed.
   To recap, if a feature is removed from the firmware, and the MUD file
   still permits it then there is a potential hole that could perhaps be
   exploited.  The opposite situation, where a MUD file wrongly forbids
   something leads to false positives in the security system, and
   evidence is that this results in the entire system being ignored.
   Preventing attacks on core infrastructure may be more important than
   getting the ACL perfect.

   When the firmware eventually receives built-in MUD URL support, then
   a more specific URL may be used.

   Note that in many cases it will be third parties who are generating
   these QRcodes, so the MUD file may be hosted by the third party.

6.  Crowd Supply of MUD Files

   At the time of writing, the IETF MUD is a new IETF Proposed Standard.
   Hence, IoT device manufacturers have not yet provided MUD profiles
   for their devices.  A research group at the University of New South
   Wales (UNSW Sydney) has developed an open-source tool, called MUDgee
   ([MUDgee]), which automatically generates a MUD file (profile) for an
   IoT device from its traffic trace in order to make this process
   faster, easier, and more accurate.  Note that the generated profile
   completeness solely depends on the completeness of the input traffic
   traces.  MUDgee assumes that all the activity seen is intended and

   UNSW researchers have applied MUDgee to about 30 consumer IoT devices
   from their lab testbed, and publicly released their MUD files
   ([MUDfiles]).  MUDgee can assist IoT manufacturers in developing and
   verifying MUD profiles, while also helping adopters of these devices
   to ensure they are compatible with their organisational policies.

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   Similar processes have been done in a number of other public and
   private labs.  One of the strong motivations for this specification
   is to allow for this work to leave the lab, and to be applied in the

7.  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.

   The MAC address of the device will also need to be present, and this
   is potentially Personally Identifiable Information (PII).  Such
   QRcodes should not be placed on the outside of the packaging, and
   only on the device itself, ideally on a non-prominent part of the
   device. (e.g., the bottom).

   The QR code sticker should not be placed on any part of the device
   that might become visible to 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.  Of course, 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.

   The use of URL shorting services discussed in Section 3.2.4 may
   result in trading convenience and efficiency with privacy, since the
   service provider might leverage per-device or per-customer short URLs
   to track and correlate requests.

8.  Security Considerations

8.1.  QR codes are not assurances

   The mere presence of a QRcode on a device does not in itself create
   any security issues on its own.  Neither an attached paper sticker or
   a laser etched code in a plastic case will affect the device

   The QRcode is not active, it is not in general able to communicate on
   nearby networks.  It is conceivable that something more active is
   concealed in the sticker: an NFC or RFID tag for instance.  But, any
   sticker could contain such a thing: on some university campuses
   stickers are often used as part of political campaigns, and can be
   found attached all over the place.

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   Security issues that this protocol create are related to assumptions
   that the presence of the QRcode might imply.  The presence of the
   QRcode may imply to some owners or network operators that the
   behaviour of the device has been vetted by some authority.  It is
   here that some caution is required.

   A possibly bigger risk from application of MUD file stickers to
   devices is that they may begin to convey a sense of safety to users
   of the device.  The presence of the sticker, possibly with the logo
   of the physical establishment in which the device is located could
   convey to occupants of the establishment that this device is an
   official device.  For instance, a university which only deploys
   sensors on the university campus that have been vetted for compliance
   against a MUD definition.

   The risk is then of social engineering: any device with a reasonable
   looking QRcode may be seen as a trusted device.  An attacker that
   wishes to infiltrate their own devices need only suitably camouflage
   the device with an appropriate sticker in order to convey legitimacy.

8.2.  MUD files can have signatures

   The network operator who takes the MUD file designated by the QRcode
   needs to be careful that they are validating the signature on the MUD
   file.  Not only that the file is intact, but that the signer of the
   file is authorized to sign MUD files for that vendor, or that the
   network operator has some trust if the MUD file is a crowd sourced
   definition.  At the time of writing, [RFC8520] does not define any
   infrastructure to authenticate or authorize MUD file signers.

8.3.  MUD QR code stickers could be confused

   Another issue with the stickers is that the wrong sticker could be
   applied to a device by a reseller or other trusted party, either in
   error, or via some physical or socially engineered attack against
   that party.  The network operator now onboards a device, and applies
   what they think is a legitimate network policy for the device in
   their hands, only it is in fact a policy for another kind of device.

   Careful examination of stickers is in order!

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8.4.  QR code can include MAC address

   Inclusion of the device specific MAC address (described in
   Section 3.2.5) in the QRcode makes use of the MUD code much easier as
   it identifies the device specifically.  If the MAC address is not
   included, then a network operator, having the device in their hands,
   has to associate the policy with the device through some other

   Despite the significant advantage of having the MAC address included,
   it is unlikely that third party stickers will include that.
   Including the MAC address requires that a unique sticker with a
   QRcode be created for each device.  This is possible if the sticker
   is applied by a manufacturer: it is already common to have a serial
   number and MAC address on the outside of the device.  In that case,
   if the QRcode is part of that sticker, then the customization problem
   is not that complex.

   For cases where a third party has produced the QRcode, it is likely
   that every device of a particular model will have the same QRcode
   applied, omitting the MAC address.  This increases the possibility
   that the wrong policy will be applied to a device.

9.  IANA Considerations

   This document makes no request for IANA actions.

10.  Acknowledgements

   This work was supported by the Canadian Internet Registration
   Authority (

11.  References

11.1.  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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,

   [SQRL]     Reverse Logistics Association, "SQRL Codes: Standardized
              Quick Response for Logistics, Using the 12N Data
              Identifier", February 2017,

11.2.  Informative References

              Wikipedia, "Chicken or the egg", December 2019,

              Pritikin, M., Richardson, M. C., Eckert, T., Behringer, M.
              H., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", Work in Progress, Internet-Draft,
              draft-ietf-anima-bootstrapping-keyinfra-45, 11 November
              2020, <

              Richardson, M., Pan, W., and E. Lear, "Authorized update
              to MUD URLs", Work in Progress, Internet-Draft, draft-
              ietf-opsawg-mud-acceptable-urls-04, 6 October 2021,

              IEEE Standard, "IEEE 802.1AR Secure Device Identifier",
              2009, <

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

   [mh10]     "ANSI MH10.8.2 Committee", May 2021,

   [MUDfiles] UNSW Sydney, ., "MUD Profiles", July 2019,

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   [MUDgee]   Hamza, A., "MUDgee", July 2019,

   [qrcode]   Wikipedia, "QR Code", December 2019,

              Internet, "QR Code Generators", December 2019,

   [qrencode] Fukuchi, K., "QR encode", December 2019,

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,

              Wikipedia, "URL shortening", May 2021,

Authors' Addresses

   Michael Richardson
   Sandelman Software Works


   Jacques Latour
   CIRA Labs


   Hassan Habibi Gharakheili
   UNSW Sydney


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