Internet DRAFT - draft-richardson-mud-qrcode
draft-richardson-mud-qrcode
Network Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Informational J. Latour
Expires: 22 September 2022 CIRA Labs
H. Habibi Gharakheili
UNSW Sydney
21 March 2022
On loading MUD URLs from QR codes
draft-richardson-mud-qrcode-07
Abstract
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
// https://github.com/mcr/mud-qrcode
Status of This Memo
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This Internet-Draft will expire on 22 September 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 (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
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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. URL Shortening services can change content . . . . . . . 10
8.4. MUD QR code stickers could be confused . . . . . . . . . 11
8.5. QR code can include MAC address . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
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 [RFC8995].
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
regulation),
* 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
product.
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",
"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.
Readers should be familiar with the terminology in [RFC8520],
including: MUD file, MUD URL, Manufacturer and MUD manager and
controller.
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:
<RS><EoT>
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
confusion.
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. MUD files can contain arbitrary UTF8 for
the model-name, while the SQRL files are expected to be 7-bit US-
ASCII.
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
image.
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
understood. The Security Considerations section of [RFC3986]
applies, particularly section 7.1.
Section 8.1 of [SQRL] also has some good advice on longevity concerns
with URLs.
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The URL provided MUST NOT have a query (?) portion present. If one
is present, the query portion MUST be removed before processing.
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
Record.
[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) This
document RECOMMENDS use of upper-case hexadecimal letters.
Parsers that find punctuation (such as colons (":"), dashes ("-"), or
white space) MUST skip over it. Parses MUST tolerate hexadecimal in
both upper, lower and even mixed case. Systems SHOULD canonicalize
it to upper case.
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
all.
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
addresses.
3. The entire file may be replaced, and may also include supply
chain information, such as Software Bill of Materials (SBOM).
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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.
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
benign.
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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.
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
field.
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
operation.
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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.
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 (even though such
trust is not justified based on that evidence.) 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. URL Shortening services can change content
If a URL shorterning service is used, it is possible that the MUD
Controller is redirected to another MUD file with different content.
The use of MUD signatures can detect attacks on the integrity of the
file. To do this, the MUD controller needs to be able to verify the
signature on the file.
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If a Trust On First Use (TOFU) policy is used for signature trust
anchors, then the URL shortening service can still attack, if it
substitutes content and signature on the first use. MUD controllers
and the people operating them need to be cautious when using TOFU.
8.4. 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!
8.5. 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
interface.
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 (cira.ca).
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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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
[SQRL] Reverse Logistics Association, "SQRL Codes: Standardized
Quick Response for Logistics, Using the 12N Data
Identifier", February 2017,
<https://rla.org/resource/12n-documentation>.
11.2. Informative References
[chickenegg]
Wikipedia, "Chicken or the egg", December 2019,
<https://en.wikipedia.org/wiki/Chicken_or_the_egg>.
[I-D.ietf-opsawg-mud-acceptable-urls]
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,
<https://www.ietf.org/archive/id/draft-ietf-opsawg-mud-
acceptable-urls-04.txt>.
[ieee802-1AR]
IEEE Standard, "IEEE 802.1AR Secure Device Identifier",
2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[isoiec18004]
ISO/IEC, "Information technology - Automatic
identification and data capture techniques - QR Code bar
code symbology specification (ISO/IEC 18004)", February
2015.
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[mh10] "ANSI MH10.8.2 Committee", May 2021,
<https://webstore.ansi.org/Standards/MHIA/ANSIMH102016>.
[MUDfiles] UNSW Sydney, "MUD Profiles", July 2019,
<https://iotanalytics.unsw.edu.au/mud/>.
[MUDgee] Hamza, A., "MUDgee", July 2019,
<https://github.com/ayyoob/mudgee>.
[qrcode] Wikipedia, "QR Code", December 2019,
<https://en.wikipedia.org/wiki/QR_code>.
[qrcodewebservice]
Internet, "QR Code Generators", December 2019,
<https://duckduckgo.com/?q=QR+code+web+generator>.
[qrencode] Fukuchi, K., "QR encode", December 2019,
<https://fukuchi.org/works/qrencode/index.html.en>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[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>.
[RFC8995] 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>.
[URLshorten]
Wikipedia, "URL shortening", May 2021,
<https://en.wikipedia.org/wiki/URL_shortening>.
Authors' Addresses
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Jacques Latour
CIRA Labs
Email: Jacques.Latour@cira.ca
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Hassan Habibi Gharakheili
UNSW Sydney
Email: h.habibi@unsw.edu.au
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