Detecting Unwanted Location Trackers
draft-detecting-unwanted-location-trackers-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Brent Ledvina , Zachary Eddinger , Ben Detwiler , Siddika Parlak Polatkan | ||
| Last updated | 2023-05-05 (Latest revision 2023-05-02) | ||
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draft-detecting-unwanted-location-trackers-00
Network Working Group B. Ledvina
Internet-Draft Apple
Intended status: Informational Z. Eddinger
Expires: 3 November 2023 Google
B. Detwiler
Apple
S. P. Polatkan
Google
2 May 2023
Detecting Unwanted Location Trackers
draft-detecting-unwanted-location-trackers-00
Abstract
This document lists a set of best practices and protocols for
accessory manufacturers whose products have built-in location-
tracking capabilities. By following these requirements and
recommendations, a location-tracking accessory will be compatible
with unwanted tracking detection and alerts on mobile platforms.
This is an important capability for improving the privacy and safety
of individuals in the circumstance that those accessories are used to
track their location without their knowledge or consent.
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-detecting-unwanted-location-
trackers/.
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
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 3 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Bluetooth Low Energy . . . . . . . . . . . . . . . . . . 6
3.2.1. Advertising . . . . . . . . . . . . . . . . . . . . . 6
3.2.2. Connection . . . . . . . . . . . . . . . . . . . . . 6
3.3. Location Tracking . . . . . . . . . . . . . . . . . . . . 6
3.4. Location-enabled Bluetooth LE Advertisement Payload . . . 7
3.4.1. Overview . . . . . . . . . . . . . . . . . . . . . . 7
3.4.2. Location-enabled advertisement payload format . . . . 7
3.4.3. Duration of advertising location-enabled advertisement
payload . . . . . . . . . . . . . . . . . . . . . . . 8
3.4.4. Maximum duration after physical separation from owner
to transition into separated mode . . . . . . . . . . 8
3.4.5. Maximum duration after reunification with owner to
transition into near-owner mode . . . . . . . . . . . 9
3.5. Resolvable and private address . . . . . . . . . . . . . 9
3.5.1. Rotation policy . . . . . . . . . . . . . . . . . . . 9
3.6. Service data TLV . . . . . . . . . . . . . . . . . . . . 10
3.7. Protocol ID . . . . . . . . . . . . . . . . . . . . . . . 10
3.8. Near-owner bit . . . . . . . . . . . . . . . . . . . . . 10
3.9. Bluetooth LE advertising interval . . . . . . . . . . . . 10
3.10. Accessory Connections . . . . . . . . . . . . . . . . . . 11
3.10.1. Byte transmission order . . . . . . . . . . . . . . 11
3.11. Accessory Information . . . . . . . . . . . . . . . . . . 11
3.11.1. Opcodes . . . . . . . . . . . . . . . . . . . . . . 11
3.12. Non-Owner Finding . . . . . . . . . . . . . . . . . . . . 15
3.12.1. Hardware . . . . . . . . . . . . . . . . . . . . . . 15
3.12.2. Motion detector . . . . . . . . . . . . . . . . . . 15
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3.12.3. Sound maker . . . . . . . . . . . . . . . . . . . . 16
3.12.4. Non-owner controls . . . . . . . . . . . . . . . . . 17
3.12.5. Alternate finding hardware . . . . . . . . . . . . . 20
3.12.6. Recommended Finding Options . . . . . . . . . . . . 20
3.12.7. Future hardware . . . . . . . . . . . . . . . . . . 20
3.13. Disablement . . . . . . . . . . . . . . . . . . . . . . . 20
3.13.1. Disablement instructions . . . . . . . . . . . . . . 20
3.13.2. Retrieval . . . . . . . . . . . . . . . . . . . . . 21
3.14. Serial Number Identification . . . . . . . . . . . . . . 21
3.14.1. Serial number retrieval capability . . . . . . . . . 21
3.14.2. Serial number retrieval over Bluetooth LE . . . . . 21
3.14.3. Serial number retrieval from a server . . . . . . . 21
3.14.4. Serial number over NFC . . . . . . . . . . . . . . . 22
3.15. Pairing registry . . . . . . . . . . . . . . . . . . . . 22
3.15.1. Obfuscated owner information . . . . . . . . . . . . 22
3.15.2. Persistence . . . . . . . . . . . . . . . . . . . . 23
3.15.3. Availability for law enforcement . . . . . . . . . . 23
4. Accessory Category Value . . . . . . . . . . . . . . . . . . 23
5. Firmware Updates . . . . . . . . . . . . . . . . . . . . . . 25
6. Platform Support for Unwanted Tracking . . . . . . . . . . . 25
6.1. Paired Accessory Identification . . . . . . . . . . . . . 25
6.1.1. Implementation . . . . . . . . . . . . . . . . . . . 25
6.1.2. Platform Software Extension . . . . . . . . . . . . . 25
6.1.3. Network Access . . . . . . . . . . . . . . . . . . . 26
6.1.4. Removal . . . . . . . . . . . . . . . . . . . . . . . 26
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
7.1. Serial number look-up . . . . . . . . . . . . . . . . . . 26
7.1.1. Design of encrypted serial number look-up . . . . . . 27
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 27
8.1. Obfuscated owner information . . . . . . . . . . . . . . 27
8.2. Serial number look-up . . . . . . . . . . . . . . . . . . 28
8.3. Location-enabled payload . . . . . . . . . . . . . . . . 28
8.3.1. Stable identifiers . . . . . . . . . . . . . . . . . 28
8.3.2. Proprietary company payload data . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
9.1. Manufacturer Protocol ID Registry . . . . . . . . . . . . 28
9.2. Product Data Registry . . . . . . . . . . . . . . . . . . 29
10. Normative References . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
This document’s goal is to, in part, help protect the privacy of
individuals from unwanted tracking by location-tracking accessories.
Location-tracking accessories provide numerous benefits to consumers,
but, as with all technology, it is possible for them to be misused.
Misuse of location-tracking accessories can result in unwanted
tracking of individuals or items for nefarious purposes such as
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stalking, harassment, and theft. Formalizing a set of best practices
for manufacturers will allow for scalable compatibility with unwanted
tracking detection technologies on various smartphone platforms and
improve privacy and security for individuals.
Unwanted tracking detection can both detect and alert individuals
that a location tracker separated from the owner's device is
traveling with them, as well as provide means to find and disable the
tracker. This document outlines technical best practices for
location tracker manufacturers, which will allow for their
compatibility with unwanted tracking detection and alerting
technology on platforms.
1.1. Conventions and Definitions
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.
1.2. Terminology
Throughout this document, these terms have specific meanings:
* The term platform is used to refer to mobile device hardware and
associated operating system. Examples of mobile devices are
phones, tablets, laptops, etc.
* The term accessory is used to refer to any product intended to
interface with a platform through the means described in this
specification.
* The term owner device is a device that is paired to the accessory
and can retrieve the accessory's location.
* The term non-owner device refers to a device that may connect to
an accessory but is not an owner device of that accessory.
* The term location-tracking accessory refers to any accessory that
has location-tracking capabilities, including, but not limited to,
crowd-sourced location, GPS/GNSS location, WiFi location, cell
location, etc., and provides the location information back to the
owner of the accessory via the internet, cellular connection, etc.
* The term location-enabled state refers to the state an accessory
in where its location can be remotely viewed by its owner
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* The term location-enabled advertisement payload refers to the
Bluetooth (BT) advertisement payload that is advertised when an
accessory has recently, is currently, or will in the future
provide location updates to its owner
* The term unwanted tracking (UT) refers to undesired tracking of a
person, their property, or their belongings by a location-enabled
accessory.
* The term unwanted tracking detection refers to the algorithms that
detect the presence of an unknown accessory traveling with a
person over time.
* The term unwanted tracking alert refers to notifying the user of
the presence of an unrecognized accessory that may be traveling
with them over time and allows them to take various actions,
including playing a sound on the accessory if it's in Bluetooth
Low Energy (LE) range.
* The term platform-compatible method refers to a method of
communication between the platform and the accessory/accessory
manufacturers to exchange information, including, but not limited
to, BT GATT protocol, BT advertisement, HTTP, etc.
2. Background
2.1. Applicability
These best practices are REQUIRED for location-enabled accessories
that are small and not easily discoverable. For large accessories,
such as a bicycle, these best practices are RECOMMENDED.
Accessories are considered easily discoverable if they meet one of
the following criteria:
- The item is larger than 30 cm in at least one dimension.
- The item is larger than 18 cm x 13 cm in two of its dimensions.
- The item is larger than 250 cm^3 in three-dimensional space.
3. Requirements
3.1. Overview
This section details requirements and recommendations for best
practices for location-enabled accessory manufacturers to allow
unwanted tracking detection by platform makers.
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3.2. Bluetooth Low Energy
The accessory SHALL use Bluetooth Low Energy (LE) as the transport
protocol. This enables platforms to detect and connect to
accessories.
3.2.1. Advertising
The accessory SHALL advertise using Bluetooth LE.
3.2.2. Connection
The accessory MUST support at least one non-owner unencrypted
connection in a peripheral role. The connection interval of the
Bluetooth LE link between the device and accessory MAY depend on the
type of user interaction. Non-owner connections to the accessory
SHALL be implemented using a platform-compatible method, e.g., BT
GATT service.
3.3. Location Tracking
The location-enabled accessory has location capabilities via
Bluetooth crowd-sourcing, GPS/GNSS location, WiFi location, cellular
location, or by some other means. Furthermore, the accessory has a
way to communicate its location to its owner via a network (e.g.,
cell network, crowd-sourced location via Bluetooth, etc.).
The accessory SHALL maintain an internal state that determines when
its location is, or has been, available to the owner via a network.
This state is called the location-enabled state.
Misuse of location-enabled accessories can occur when the owner’s
device is not physically with the accessory. Thereby, the accessory
SHOULD maintain a second internal state, denoted the near-owner
state, which indicates if the accessory is connected to or nearby one
or more of the owner’s devices. Near-owner state can take on two
values, either near-owner mode or separated mode. Near-owner mode is
denoted as the opposite of separated mode.
Figure 1 details the requirements and recommendations for advertising
the location-enabled payload based on the location-enabled state and
separated state.
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+---------------------+
| Location |
| Currently Enabled |
| OR |
| Enabled in Past 24 |
| Hours |
+--------------------+---------------------|
| near-owner | SHOULD NOT |
| mode | advertise location- |
| Near- | enabled payload |
| Owner +---------------------|
| State separated | MUST advertise |
| mode | location-enabled |
| | payload |
+--------------------+---------------------+
Figure 1: Requirements & Recommendations For Advertising
Location-Enabled Payload
It is RECOMMENDED that the location-enabled payload is only
advertised when the accessory is in the separated state. The
reasoning behind this recommendation is that unwanted tracking
detection relies on the Bluetooth LE advertisements emitted while in
the location-enabled state to determine if an unknown accessory is
traveling with someone who is not the owner. If the location-enabled
payload is advertised only in the separated state, that minimizes
false-positive UT alerts.
As a point of clarity, if the accessory maker chooses to continue
advertising the location-enabled payload while in near-owner mode,
setting the near-owner bit (Section 3.8) compensates for this.
3.4. Location-enabled Bluetooth LE Advertisement Payload
3.4.1. Overview
When in location-enabled state, the accessory SHALL advertise a
Bluetooth LE format, denoted the location-enabled Bluetooth
advertisement payload, that is recognizable to the platforms.
3.4.2. Location-enabled advertisement payload format
The payload format is defined in Table 1
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+=======+=========================================+=============+
| Bytes | Description | Requirement |
+=======+=========================================+=============+
| 0-5 | MAC address | REQUIRED |
+-------+-----------------------------------------+-------------+
| 6-8 | Flags TLV; length = 1 byte, type = 1 | OPTIONAL |
| | byte, value = 1 byte | |
+-------+-----------------------------------------+-------------+
| 9-12 | Service data TLV; length = 1 byte, type | REQUIRED |
| | = 1 byte, value = 2 bytes (TBD value) | |
+-------+-----------------------------------------+-------------+
| 13 | Protocol ID (TBD value) | REQUIRED |
+-------+-----------------------------------------+-------------+
| 14 | Near-owner bit (1 bit) + reserved (7 | REQUIRED |
| | bits) | |
+-------+-----------------------------------------+-------------+
| 15-36 | Proprietary company payload data | OPTIONAL |
+-------+-----------------------------------------+-------------+
Table 1: Location-Enabled Payload Format
When Flags TLV are not added, the MAC address type needs to be set to
random. This implies that if Bluetooth LE pairing is supported, the
accessory SHALL NOT use its public address as its public identity
when exchanging pairing keys at phase 3 (see Vol.3, Part H,
Section 2.1 of the [BTCore5.4]) and it SHALL only use a static random
address. Additionally, the LE advertisement needs to be connectable
to allow for non-owner unencrypted connections to the accessory.
Further details are discussed in Section 3.10.
Proprietary company payload data is both OPTIONAL and variable
length.
3.4.3. Duration of advertising location-enabled advertisement payload
The accessory SHALL broadcast the location-enabled advertisement
payload if location is available to the owner or was available any
time within the past 24 hours. This allows unwanted tracking
detection to operate both between and beyond the specific moments an
accessory's location is made available to the owner.
3.4.4. Maximum duration after physical separation from owner to
transition into separated mode
The accessory SHALL transition from near-owner mode to separated mode
if it has physically separated from the owner device for a duration
no longer than 30 minutes.
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3.4.5. Maximum duration after reunification with owner to transition
into near-owner mode
The accessory SHALL transition from separated to near-owner mode if
it has reunited with the owner device for a duration no longer than
30 minutes.
3.5. Resolvable and private address
The Bluetooth LE advertisement payload SHALL contain a resolvable and
private address for the accessory which is the 6-byte Bluetooth LE
MAC address.
The address MUST be private and it MUST rotate periodically and be
unlinkable; otherwise, if the same address is used for long periods
of time, an adversary may be able to track a legitimate person from
carrying the accessory.
The rotation policy (Section 3.5.1) defined below aims to reduce this
risk.
Lastly, the address MUST be resolvable so owner devices can identify
their paired accessories. Further details are described in Paired
Accessory Identification (Section 6.1).
A general approach to generate addresses meeting this requirement is
to construct them using a Pseudo-Random Function (PRF) taking as
input a key established during the pairing of the accessory and
either a counter or coarse notion of time. The counter or coarse
notion of time allows for the address to change periodically. The
key allows the owner devices to predict the sequence of addresses for
the purposes of recognizing its paired accessories.
3.5.1. Rotation policy
An accessory SHALL rotate its resolvable and private address on any
transition from near-owner state to separated state as well as any
transition from separated state to near-owner state.
When in near-owner state, the accessory SHALL rotate its resolvable
and private address every 15 minutes. This is a privacy
consideration to deter tracking of the accessory by non-owners when
it is in physical proximity to the owner.
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When in a separated state, the accessory SHALL rotate its resolvable
and private address every 24 hours. This duration allows a
platform's unwanted tracking algorithms to detect that the same
accessory is in proximity for some period of time, when the owner is
not in physical proximity.
3.6. Service data TLV
The Service data TLV with a 2-byte UUID value of TODO provides a way
for platforms to easily scan for and detect the location-enabled
Bluetooth advertisement.
3.7. Protocol ID
The 1-byte Protocol ID SHALL be set based on a registered value for
the manufacturer, as defined in Manufacturer Protocol ID Registry
(Section 9.1).
3.8. Near-owner bit
It is important to prevent unwanted tracking alerts from occurring
when the owner of the accessory is in physical proximity of the
accessory, i.e., it is in near-owner mode. In order to allow
suppression of unwanted tracking alerts for an accessory advertising
the location-enabled advertisement with the owner nearby, the
accessory MUST set the near-owner bit to be 1 when the near-owner
state is in near-owner mode, otherwise the bit is set to 0. Table 2
specifies the values of this bit.
+======================+==================+
| Near-owner Bit Value | Near-owner state |
+======================+==================+
| 0 | Near-owner mode |
+----------------------+------------------+
| 1 | Separated mode |
+----------------------+------------------+
Table 2: Near-Owner Bit
3.9. Bluetooth LE advertising interval
The Bluetooth LE advertising interval SHALL be as described in
Table 3
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+====================+===================================+
| | Bluetooth LE Advertising Interval |
+====================+===================================+
| Advertising policy | 0.5 - 2 seconds |
+--------------------+-----------------------------------+
Table 3: Advertising Policy
3.10. Accessory Connections
The accessory non-owner service UUID SHALL be TODO. This service
SHALL use GATT over LE. The non-owner accessory service SHALL be
instantiated as a primary service. The accessory non-owner
characteristic UUID SHALL be TODO.
3.10.1. Byte transmission order
The characteristic used within this service SHALL be transmitted with
the least significant octet first (that is, little endian).
3.11. Accessory Information
The following accessory information MUST be persistent through the
lifetime of the accessory: Product data (Section 3.11.1.1),
Manufacturer name (Section 3.11.1.2), Model name (Section 3.11.1.3),
Accessory category (Section 3.11.1.4), and Accessory capabilities
(Section 3.11.1.5).
3.11.1. Opcodes
The opcodes for accessory information are defined in Table 4.
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+===================================+======+============+============+
| Opcode |Opcode| Operands | GATT |
| |value | |subprocedure|
+===================================+======+============+============+
| Get_Product_Data |0x306 | None | Write; To |
| | | | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Product_Data_Response |0x311 |Product Data|Indications;|
| | | (Section | From |
| | | 3.11.1.1) | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Manufacturer_Name |0x307 | None | Write; To |
| | | | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Manufacturer_Name_Response |0x312 |Manufacturer|Indications;|
| | | Name | From |
| | | (Section | Accessory |
| | | 3.11.1.2) | |
+-----------------------------------+------+------------+------------+
| Get_Model_Name |0x308 | None | Write; To |
| | | | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Model_Name_Response |0x313 | Model Name |Indications;|
| | | (Section | From |
| | | 3.11.1.3) | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Accessory_Category |0x309 | None | Write; To |
| | | | Accessory |
+-----------------------------------+------+------------+------------+
| Get_Accessory_Category_Response |0x314 | Accessory |Indications;|
| | | Category | From |
| | | (Section | Accessory |
| | | 3.11.1.4) | |
+-----------------------------------+------+------------+------------+
| Get_Accessory_Capabilities |0x30A | None | Write; To |
| | | | Accessory |
+-----------------------------------+------+------------+------------+
|Get_Accessory_Capabilities_Response|0x315 | Accessory |Indications;|
| | |Capabilities| From |
| | | (Section | Accessory |
| | | 3.11.1.5) | |
+-----------------------------------+------+------------+------------+
Table 4: Accessory Information Opcodes
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3.11.1.1. Product data
The Product Data operand represents an 8-byte value that is intended
to serve as a unique identifier for the accessory make and model.
This value SHALL be available in a public registry as defined in
Section 9.2.
The Product Data operand is 8 bytes, composed of two 8-character hex
strings (lowercase zero padded), each of which is 4 bytes.
For example, the Product Data value of 0xdfeceff1e1ff54db, the value
converted to binary would be
0xdfeceff1 11011111 11101100 11101111 11110001
0xe1ff54db 11100001 11111111 01010100 11011011
+==============+===========+===============+====================+
| Operand name | Data type | Size (octets) | Description |
+==============+===========+===============+====================+
| Product Data | Uint8 | 8 | See Product data |
| | | | (Section 3.11.1.1) |
+--------------+-----------+---------------+--------------------+
Table 5: Product Data Operand
3.11.1.2. Manufacturer name
The Manufacturer Name operand contains the name of the company whose
brand will appear on the accessory, e.g., ”Acme”.
+===================+===========+===============+===================+
| Operand name | Data type | Size (octets) | Description |
+===================+===========+===============+===================+
| Manufacturer Name | UTF-8 | 64 | Manufacturer |
| | | | name |
+-------------------+-----------+---------------+-------------------+
Table 6: Manufacturer Name Operand
3.11.1.3. Model name
The Model Name operand contains the manufacturer specific model of
the accessory.
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+==============+===========+===============+=============+
| Operand name | Data type | Size (octets) | Description |
+==============+===========+===============+=============+
| Model Name | UTF-8 | 64 | Model name |
+--------------+-----------+---------------+-------------+
Table 7: Model Name Operand
3.11.1.4. Accessory category
The Accessory Category operand describes the category the accessory
most closely resembles.
+===========+=======+==========+==================================+
| Operand | Data | Size | Description |
| name | type | (octets) | |
+===========+=======+==========+==================================+
| Accessory | Uint8 | 8 | Byte 0: Uint8 value of Accessory |
| Category | | | Category Value (Section 4) |
| | | | Byte 1-7: Reserved |
+-----------+-------+----------+----------------------------------+
Table 8: Accessory Category Operand
3.11.1.5. Accessory capabilities
The Accessory Capabilities operand enumerates the various
capabilities supported on the accessory as defined in Table 9.
+==============+========+==========+=============================+
| Operand name | Data | Size | Description |
| | type | (octets) | |
+==============+========+==========+=============================+
| Accessory | Uint32 | 4 | Bit 0 : Supports play sound |
| Capabilities | | | Bit 1 : Supports motion |
| | | | detector UT |
| | | | Bit 2 : Supports serial |
| | | | number lookup by NFC |
| | | | Bit 3 : Supports serial |
| | | | number lookup by BLE |
+--------------+--------+----------+-----------------------------+
Table 9: Accessory Capabilities Operand
For example, an accessory supporting play sound, motion detector UT,
and serial number look-up over BT will have the value set as 1011 in
binary and 11 as Uint32.
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3.12. Non-Owner Finding
Once a user has been notified of an unknown accessory traveling with
them, it is REQUIRED they have the means to physically locate the
accessory. This is called non-owner finding of the accessory.
3.12.1. Hardware
This is a description of the REQUIRED and RECOMMENDED hardware to be
incorporated into the accessory to enable non-owner finding.
3.12.2. Motion detector
The accessory SHOULD include a motion detector that can detect
accessory motion reliably (for example, an accelerometer). If the
accessory includes an accelerometer, it MUST be configured to detect
an orientation change of ±10° along any two axes of the accessory.
3.12.2.1. Implementation
The details in this section apply to those accessories that include a
motion detector. Values of the variables referenced are specified in
Table 10.
After T_(SEPARATED_UT_TIMEOUT) in separated state, the accessory MUST
enable the motion detector to detect any motion within
T_(SEPARATED_UT_SAMPLING_RATE1).
If motion is not detected within the T_(SEPARATED_UT_SAMPLING_RATE1)
period, the accessory MUST stay in this state until it exits
separated state.
If motion is detected within the T_(SEPARATED_UT_SAMPLING_RATE1) the
accessory MUST play a sound. After first motion is detected, the
movement detection period is decreased to
T_(SEPARATED_UT_SAMPLING_RATE2). The accessory MUST continue to play
a sound for every detected motion. The accessory SHALL disable the
motion detector for T_(SEPARATED_UT_BACKOFF) under either of the
following conditions:
* Motion has been detected for 20 seconds at
T_(SEPARATED_UT_SAMPLING_RATE2) periods.
* Ten sounds are played.
If the accessory is still in separated state at the end of
T_(SEPARATED_UT_BACKOFF), the UT behavior MUST restart.
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A Bluetooth LE connection from a paired device MUST reset the
separated behavior and transition the accessory to connected state.
+=================================+==============+==================+
| Name | Value | Description |
+=================================+==============+==================+
| T_(SEPARATED_UT_SAMPLING_RATE1) | 10 seconds | Sampling rate |
| | | when motion |
| | | detector is |
| | | enabled in |
| | | separated |
| | | state. |
+---------------------------------+--------------+------------------+
| T_(SEPARATED_UT_SAMPLING_RATE2) | 0.5 seconds | Motion detector |
| | | sampling rate |
| | | when movement |
| | | is detected in |
| | | separated |
| | | state. |
+---------------------------------+--------------+------------------+
| T_(SEPARATED_UT_BACKOFF) | 6 hours | Period to |
| | | disable motion |
| | | detector if |
| | | accessory is in |
| | | separated |
| | | state. |
+---------------------------------+--------------+------------------+
| T_(SEPARATED_UT_TIMEOUT) | random value | Time span in |
| | between 8-24 | separated state |
| | hours chosen | before enabling |
| | from a | motion |
| | uniform | detector. |
| | distribution | |
+---------------------------------+--------------+------------------+
Table 10: Motion Detector Time Values
3.12.3. Sound maker
The accessory MUST include a sound maker (for example, a speaker) to
play sound when in separated state, either periodically or when
motion is detected.
It MUST also play sound when a non-owner tries to locate the
accessory by initiating a play sound command from a non-owner device
when the accessory is in range and connectable through Bluetooth LE.
The sound maker MUST emit a sound with minimum 60 Phon peak loudness
as defined by ISO 532-1:2017. The loudness MUST be measured in free
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acoustic space substantially free of obstacles that would affect the
pressure measurement. The loudness MUST be measured by a calibrated
(to the Pascal) free field microphone 25 cm from the accessory
suspended in free space.
3.12.4. Non-owner controls
Non-owner controls SHALL use the same service and characteristic
UUIDs as defined in Accessory Connections (Section 3.10). The non-
owner control point enables a non-owner device to locate the
accessory by playing a sound. The opcodes for the control point are
defined in Table 11.
+============================+========+=============+==============+
| Opcode | Opcode | Operands | GATT |
| | value | | subprocedure |
+============================+========+=============+==============+
| Sound_Start | 0x300 | None | Write; To |
| | | | accessory |
+----------------------------+--------+-------------+--------------+
| Sound_Stop | 0x301 | None | Write; To |
| | | | accessory |
+----------------------------+--------+-------------+--------------+
| Command_Response | 0x302 | Command | Indications; |
| | | Response | From |
| | | (Section | accessory |
| | | 3.12.4.1.1) | |
+----------------------------+--------+-------------+--------------+
| Sound_Completed | 0x303 | None | Indications; |
| | | | From |
| | | | accessory |
+----------------------------+--------+-------------+--------------+
| Get_Serial_Number | 0x404 | None | Write; To |
| | | | accessory |
+----------------------------+--------+-------------+--------------+
| Get_Serial_Number_Response | 0x405 | Serial | Indications; |
| | | Number | From |
| | | Payload | accessory |
| | | (Section | |
| | | 3.12.4.2) | |
+----------------------------+--------+-------------+--------------+
Table 11: Non-Owner Control Point Opcodes
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This control point SHALL be available to the platform only when the
accessory is in separated state. In all other states, the accessory
SHALL return the Invalid_command error as the ResponseStatus in
CommandResponse. See Command Response (Section 3.12.4.1.1) for
details.
3.12.4.1. Play sound
The Sound_Start opcode is used to play sound on the sound maker of
the accessory. The sound maker MUST play sound for a minimum
duration of 5 seconds.
* The accessory SHALL confirm the start of the play sound procedure
by sending a Command_Response (Section 3.12.4.1.1) with the
corresponding CommandOpCode and a ResponseStatus value of Success.
* Once the play sound action is completed, the accessory sends the
Sound_Completed message.
* The Sound_Stop opcode is used to stop an ongoing sound request.
* If the sound event is completed or was not initiated by the
connected non owner device, the accessory responds with the
Invalid_state ResponseStatus code.
* If the accessory does not support the play sound procedure, it
responds with Invalid_command ResponseStatus code.
* If a Sound_Start procedure is initiated when another play sound
action is in progress, it rejects with Invalid_state error code.
* The accessory SHALL confirm the completion of the stop sound
procedure by sending the Sound_Completed message.
3.12.4.1.1. Command Response
There are 2 components of the command response operands:
CommandOpCode and ResponseStatus. The CommandOpCode operand
indicates the procedure that the accessory is responding to and
ResponseStatus operand indicates the status of the response. The
accessory SHALL respond to any invalid opcode with Command_Response
and Invalid_command as the ResponseStatus.
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+================+========+==========+==============================+
| Operand | Data | Size | Description |
| | type | (octets) | |
+================+========+==========+==============================+
| CommandOpCode | Uint16 | 2 | The control procedure |
| | | | matching this response |
+----------------+--------+----------+------------------------------+
| ResponseStatus | Uint16 | 2 | 0x0000 Success |
| | | | 0x0001 Invalid_state |
| | | | 0x0002 |
| | | | Invalid_configuration |
| | | | 0x0003 Invalid_length |
| | | | 0x0004 Invalid_param |
| | | | 0xFFFF Invalid_command |
+----------------+--------+----------+------------------------------+
Table 12: Command Response Operands
3.12.4.2. Serial Number Payload
The Get_Serial_Number opcode is used to retrieve serial number lookup
payload over Bluetooth LE. This MUST be enabled for 5 minutes upon
user action on the accessory (for example, press and hold a button
for 10 seconds to initiate serial number read state). When the
accessory is in this mode, it MUST respond with
Get_Serial_Number_Response opcode and Serial Number Payload operand.
+=========+===========+===============+=========================+
| Operand | Data type | Size (octets) | Description |
+=========+===========+===============+=========================+
| p | bytes | defined by | Non-identifiable |
| | | accessory | metadata |
+---------+-----------+---------------+-------------------------+
| e | bytes | defined by | Encrypted serial number |
| | | accessory | when in paired state. |
+---------+-----------+---------------+-------------------------+
Table 13: Serial Number Payload Over Bluetooth
If the accessory is not in serial number read state, it MUST send
Command_Response (Section 3.12.4.1.1) with the Invalid_command as the
ResponseStatus. Further considerations for how these operands should
be implemented are discussed in Design of encrypted serial number
look-up (Section 7.1.1).
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3.12.5. Alternate finding hardware
The accessory SHOULD provide alternate means to help find it, e.g. by
vibrating or flashing lights, via a platform-compatible method.
3.12.6. Recommended Finding Options
Table 14 lists two RECOMMENDED options on the set of technology in an
accessory to make it findable.
+=============+==========+==========+
| | Option A | Option B |
+=============+==========+==========+
| | Good | Better |
+-------------+----------+----------+
| Sound maker | X | X |
+-------------+----------+----------+
| Haptics | | X |
+-------------+----------+----------+
| Lights | | X |
+-------------+----------+----------+
Table 14: Accessory Finding
Hardware Options
3.12.7. Future hardware
Future technologies for finding MAY be considered in revisions of
this document.
3.13. Disablement
The accessory SHALL have a way to disabled such that its future
locations cannot be seen by its owner. Disablement SHALL be done via
some physical action (e.g., button press, gesture, removal of
battery, etc.).
3.13.1. Disablement instructions
The accessory manufacturer SHALL provide both a text description of
how to disable the accessory as well as a visual depiction (e.g.
image, diagram, animation, etc.) that MUST be available when the
platform is online and OPTIONALLY when offline. Disablement
procedure or instructions CAN change with accessory firmware updates.
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3.13.2. Retrieval
A registry which maps Product data (Section 3.11.1.1) to an
affiliated URL supporting retrieval of disablement instructions SHALL
be available for platforms to reference, as defined in Section 9.2.
This URL must return a response which can be rendered by an HTML
view.
3.14. Serial Number Identification
The serial number SHALL be printed and be easily accessible on the
accessory. The serial number MUST be unique for each product ID.
3.14.1. Serial number retrieval capability
The serial number payload SHALL be readable either through NFC tap
(see Serial Number payload over NFC (Section 3.14.4)) or Bluetooth LE
( see Serial Number Payload (Section 3.12.4.2) ).
3.14.2. Serial number retrieval over Bluetooth LE
For privacy reasons, accessories that support serial number retrieval
over Bluetooth LE MUST have a physical mechanism, for example, a
button, that SHALL be required to enable the Get_Serial_Number
opcode, as discussed in Serial Number Payload (Section 3.12.4.2).
The accessory manufacturer SHALL provide both a text description of
how to enable serial number retrieval over Bluetooth LE, as well as a
visual depiction (e.g. image, diagram, animation, etc.) that MUST be
available when the platform is online and OPTIONALLY when offline.
The description and visual depiction CAN change with accessory
firmware updates.
A registry which maps Product Data (Section 3.11.1.1) to an
affiliated URL that will return a text description and visual
depiction of how to enable serial number look-up over Bluetooth LE
SHALL be available for platforms to reference, as defined in
Section 9.2. This URL MUST return a response which can be rendered
by an HTML view.
3.14.3. Serial number retrieval from a server
For security reasons, the serial number payload returned from an
accessory in the paired state SHALL be encrypted.
A registry which maps Product Data (Section 3.11.1.1) to an
affiliated URL which will decrypt the serial number payload and
return the serial number value SHALL be available for platforms to
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reference, as defined in Section 9.2. This URL MUST return a
response which can be rendered by an HTML view. The arguments sent
to this URL SHALL match those that are defined in Table 13. Security
considerations are discussed in Section 7.1.
3.14.4. Serial number over NFC
For those accessories that support serial number retrieval over NFC,
a paired accessory SHALL advertise a URL with parameters in Table 15.
This URL SHALL decrypt the serial number payload and return the
serial number of the accessory in a form that can be rendered in the
platform's HTML view.
+=========+===========+===============+=========================+
| Operand | Data type | Size (octets) | Description |
+=========+===========+===============+=========================+
| p | bytes | defined by | Non-identifiable |
| | | accessory | metadata |
+---------+-----------+---------------+-------------------------+
| e | bytes | defined by | Encrypted serial number |
| | | accessory | when in paired state. |
+---------+-----------+---------------+-------------------------+
Table 15: Serial Number Lookup Payload Over NFC
3.15. Pairing registry
Verifiable identity information of the owner of an accessory at time
of pairing SHALL be recorded and associated with the serial number of
the accessory, e.g., phone number, email address.
3.15.1. Obfuscated owner information
A limited amount of obfuscated owner information from the pairing
registry SHALL be made available to the platform along with a
retrieved serial number (serial-number-retrieval). This information
SHALL be part of the response of the serial number retrieval from a
server (serial-number-from-server) which can be rendered in a
platform's HTML view.
This MUST include at least one of the following:
* the last four digits of the owner's telephone number. e.g., (***)
***-5555
* an email address with the first letter of the username and entity
visible, as well as the entire extension. e.g.,
b********@i*****.com
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3.15.2. Persistence
The pairing registry SHOULD be stored for a minimum of 25 days after
an owner has unpaired an accessory. After the elapsed period, the
data SHOULD be deleted.
3.15.3. Availability for law enforcement
The pairing registry SHALL be made available to law enforcement upon
a valid law enforcement request.
4. Accessory Category Value
Accessory manufacturer’s MUST pick an accessory category value that
closest resembles their physical product. If none of the accessory
categories provided in Table 16 match the physical product, Other
MUST be chosen.
+============================+=============+
| Accessory Category Name | Value |
+============================+=============+
| Finder | 1 |
+----------------------------+-------------+
| Other | 128 |
+----------------------------+-------------+
| Luggage | 129 |
+----------------------------+-------------+
| Backpack | 130 |
+----------------------------+-------------+
| Jacket | 131 |
+----------------------------+-------------+
| Coat | 132 |
+----------------------------+-------------+
| Shoes | 133 |
+----------------------------+-------------+
| Bike | 134 |
+----------------------------+-------------+
| Scooter | 135 |
+----------------------------+-------------+
| Stroller | 136 |
+----------------------------+-------------+
| Wheelchair | 137 |
+----------------------------+-------------+
| Boat | 138 |
+----------------------------+-------------+
| Helmet | 139 |
+----------------------------+-------------+
| Skateboard | 140 |
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+----------------------------+-------------+
| Skis | 141 |
+----------------------------+-------------+
| Snowboard | 142 |
+----------------------------+-------------+
| Surfboard | 143 |
+----------------------------+-------------+
| Camera | 144 |
+----------------------------+-------------+
| Laptop | 145 |
+----------------------------+-------------+
| Watch | 146 |
+----------------------------+-------------+
| Flash drive | 147 |
+----------------------------+-------------+
| Drone | 148 |
+----------------------------+-------------+
| Headphones | 149 |
+----------------------------+-------------+
| Earphones | 150 |
+----------------------------+-------------+
| Inhaler | 151 |
+----------------------------+-------------+
| Sunglasses | 152 |
+----------------------------+-------------+
| Handbag | 153 |
+----------------------------+-------------+
| Wallet | 154 |
+----------------------------+-------------+
| Umbrella | 155 |
+----------------------------+-------------+
| Water bottle | 156 |
+----------------------------+-------------+
| Tools or tool box | 157 |
+----------------------------+-------------+
| Keys | 158 |
+----------------------------+-------------+
| Smart case | 159 |
+----------------------------+-------------+
| Remote | 160 |
+----------------------------+-------------+
| Hat | 161 |
+----------------------------+-------------+
| Motorbike | 162 |
+----------------------------+-------------+
| Consumer electronic device | 163 |
+----------------------------+-------------+
| Apparel | 164 |
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+----------------------------+-------------+
| Transportation device | 165 |
+----------------------------+-------------+
| Sports equipment | 166 |
+----------------------------+-------------+
| Personal item | 167 |
+----------------------------+-------------+
| Reserved for future use | 2-127, 167+ |
+----------------------------+-------------+
Table 16: Accessory Category Values
5. Firmware Updates
The accessory SHOULD have firmware that is updatable by the owner.
6. Platform Support for Unwanted Tracking
This section details the requirements and recommendations for
platforms to be compatible with the accessory protocol behavior
described in the document.
6.1. Paired Accessory Identification
Any platform that supports both pairing and unwanted tracking SHOULD
also provide the capability to suppress unwanted tracking alerts
caused by an owner device's paired accessory.
If an unwanted tracking alert occurs for an accessory and the
platform does not already have the installed capability to prevent
this alert for the owner of the accessory, then the platform SHOULD
explain to the user how those capabilities can be acquired.
6.1.1. Implementation
Unwanted tracking SHOULD recognize an accessory paired to that owner
device by matching the MAC address advertised, as defined in Table 1,
against the one(s) expected during that time.
6.1.2. Platform Software Extension
Platforms SHOULD implement the paired accessory identification
capability as a software extension to its unwanted tracking
detection.
Accessory manufacturers SHALL provide this set of MAC addresses to
the platform. This set MUST account for the uncertainty involved
with the resolvable and private address (Section 3.5).
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The protocol ID in the advertisement payload, as specified in
Table 1, SHALL be used to associate an accessory detected with the
manufacturer's software extension.
6.1.3. Network Access
Network access MUST NOT be required in the moment that the platform
performs paired accessory recognition.
6.1.4. Removal
The platform MUST delete any local identifying information associated
with an accessory if the manufacturer's software is removed or if the
platform unpairs from the accessory.
7. Security Considerations
7.1. Serial number look-up
Serial number look-up is required to display important information to
users who encounter an unwanted tracking notification. It helps them
tie the notification to a specific physical device and recognize the
accessory as belonging to a friend or relative.
However, the serial number is unique and stable, and the partial user
information can further make the accessory identifiable. Therefore,
it SHOULD NOT be made directly available to any requesting devices.
Instead, several security- and privacy-preserving steps SHOULD be
employed.
The serial number look-up SHALL only be available in separated mode
for a paired accessory. When requested through any long range
wireless interface like Bluetooth, a user action MUST be required for
the requesting device to access the serial number. Over NFC, it MAY
be acceptable to consider the close proximity as intent for this
flow.
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To uphold privacy and anti-tracking features like the Bluetooth MAC
address randomization, the accessory MUST only provide non-
identifiable data to non-owner requesting devices. One approach is
for the accessory to provide encrypted and unlinkable information
that only the accessory network service can decrypt. With this
approach, the server can employ techniques such as rate limiting and
anti-fraud to limit access to the serial number. In addition to
being encrypted and unlinkable, the encrypted payload provided by the
accessory SHOULD be authenticated and protected against replay. The
replay protection is to prevent an adversary using a payload captured
once to monitor changes to the partial information associated with
the accessory, while the authentication prevents an adversary from
impersonating any accessory from a single payload.
7.1.1. Design of encrypted serial number look-up
One way to design this encryption is for the accessory to contain a
public key for the accessory network server. For every request
received by a device nearby, the accessory would use the public key
and a public key encryption scheme (ie: RSA-OAEP, ECIES, or HPKE) to
encrypt a set of fields including the serial number, a monotonic
counter or one time token and a signature covering both the serial
number and counter or token. The signature can be either a public
key signature or symmetric signature, leveraging a key trusted by the
network server which MAY be established at manufacturing time or when
the user sets up the accessory. Some additional non-identifiable
metadata MAY be sent along with this encrypted payload, allowing the
requesting device to determine which accessory network service to
connect to for the decryption, and for the service to know which
decryption key and protocol version to use.
8. Privacy Considerations
8.1. Obfuscated owner information
In many circumstances when unwanted tracking occurs, the individual
being tracked knows the owner of the location-tracker. By allowing
the retrieval of an obfuscated email or phone number when in
possession of the accessory, as described in Section 3.15.1, this
provides the potential victim with some level of information on the
owner, while balancing the privacy of accessory owners in the
arbitrary situations where they have separated from those
accessories.
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8.2. Serial number look-up
A serial number both physically on the device, as well as retrievable
over NFC or Bluetooth LE, can aid recourse actions in the case of
unwanted tracking. While retrieval of the serial number over NFC
implies having physical possession of the accessory, the same
conclusion can not be made for Bluetooth given its wireless range.
The procedure required for serial number look-up over Bluetooth LE
intends to strike a balance between the privacy of the owner and
ability to empower potential victims, by requiring both the accessory
to be in separated state as well as a physical action be performed to
enable the serial number retrieval.
8.3. Location-enabled payload
8.3.1. Stable identifiers
Rotating the resolvable and private address of the location-enabled
payload, as described in Section 3.5, balances the risk of nefarious
stable identifier tracking with the need for unwanted tracking
detection. If the address were permanently static, then the
accessory would become infinitely trackable for the life of its power
source. By requiring rotation, this reduces the risk of a malicious
actor having the ability to piece together long stretches of
longitudinal data on the whereabouts of an accessory.
8.3.2. Proprietary company payload data
Accessory manufacturers SHOULD evaluate the contents of the
proprietary company payload data in Table 1 to ensure it does not
introduce additional privacy risk through the broadcast of stable
identifiers or unencrypted sensitive data.
9. IANA Considerations
IANA will create a new registry group called "Unwanted Tracking
Protocols (UTP)". This group includes the "Manufacturer Protocol ID"
and "Product Data" registries described below.
9.1. Manufacturer Protocol ID Registry
New entries are assigned only for values that have received Expert
Review, per Section 4.5 of [RFC8126].
An entry in this registry contains the following fields:
* Manufacturer Name: the name of an organization that is producing a
location-tracker accessory
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* Protocol ID: a 1-byte value specifying the Protocol ID associated
with the Manufacturer Name
9.2. Product Data Registry
New entries are assigned only for values that have received Expert
Review, per Section 4.5 of [RFC8126].
There SHALL NOT be two entries in this registry with the same Product
Data value. Serial Number Look-up Over Bluetooth Instructions field
MAY be left empty if the accessory does not support that capability.
An entry in this registry contains the following fields:
* Product Data: an 8-byte string representing a unique identifier
for a product. See Product Data (Section 3.11.1.1).
* Disablement Instructions: a string representing the URL where
disablement instructions can be retrieved.
* Serial Number Look-up Over Bluetooth Instructions: a string
representing the URL where the text instructions and visual
depictions for enabling serial number look-up over Bluetooth LE
can be retrieved.
* Serial Number Look-up: a string representing the URL where the
serial number and obfuscated owner information can be retrieved.
10. Normative References
[BTCore5.4]
"Bluetooth Core Specification v5.4", 31 January 2023,
<https://www.bluetooth.org/DocMan/handlers/
DownloadDoc.ashx?doc_id=556599>.
[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/rfc/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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/rfc/rfc8174>.
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Authors' Addresses
Brent Ledvina
Apple
Email: bledvina@apple.com
Zach Eddinger
Google
Email: zae@google.com
Ben Detwiler
Apple
Email: bdetwiler@apple.com
Siddika Parlak Polatkan
Google
Email: siddikap@google.com
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