DRIP                                                        S. Card, Ed.
Internet-Draft                                           A. Wiethuechter
Intended status: Informational                             AX Enterprize
Expires: 26 February 2021                                   R. Moskowitz
                                                          HTT Consulting
                                                               A. Gurtov
                                                    Linköping University
                                                          25 August 2020

        Drone Remote Identification Protocol (DRIP) Requirements


   This document defines the requirements for Drone Remote
   Identification Protocol (DRIP) Working Group protocols to support
   Unmanned Aircraft System Remote Identification and tracking (UAS RID)
   for security, safety and other purposes.  Complementing external
   technical standards as regulator-accepted means of compliance with
   UAS RID regulations, DRIP will:

      facilitate use of existing Internet resources to support UAS RID
      and to enable enhanced related services;

      enable online and offline verification that UAS RID information is

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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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 26 February 2021.

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Copyright Notice

   Copyright (c) 2020 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/
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Table of Contents

   1.  Introduction (Informative)  . . . . . . . . . . . . . . . . .   2
     1.1.  Overall Context . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Intended Use  . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  DRIP Scope  . . . . . . . . . . . . . . . . . . . . . . .   7
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   8
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  UAS RID Problem Space . . . . . . . . . . . . . . . . . . . .  15
     3.1.  Network RID . . . . . . . . . . . . . . . . . . . . . . .  16
     3.2.  Broadcast RID . . . . . . . . . . . . . . . . . . . . . .  17
     3.3.  DRIP Focus  . . . . . . . . . . . . . . . . . . . . . . .  18
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  19
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  19
     4.2.  Identifier  . . . . . . . . . . . . . . . . . . . . . . .  21
     4.3.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . .  22
     4.4.  Registries  . . . . . . . . . . . . . . . . . . . . . . .  23
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   7.  Privacy and Transparency Considerations . . . . . . . . . . .  24
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  25
   Appendix A.  Discussion and Limitations . . . . . . . . . . . . .  28
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction (Informative)

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1.1.  Overall Context

   Many considerations (especially safety and security) dictate that UAS
   be remotely identifiable.  Any Observer with responsibilities
   involving aircraft inherently must classify Unmanned Aircraft (UA)
   situationally according to basic considerations, as illustrated
   notionally in Figure 1 below.  An Observer who classifies an UAS: as
   Taskable, can ask it to do something useful; as Low Concern, can
   reasonably assume it is not malicious, and would cooperate with
   requests to modify its flight plans for safety reasons; as High
   Concern or Unidentified, is worth focused surveillance.

                        xxxxxxx        +--------------+
                       x       x  No   |              |
                      x   ID?   x+---->| UNIDENTIFIED |
                       x       x       |              |
                        xxxxxxx        +--------------+
                           | Yes
                       x       x
           +---------+x  TYPE?  x+----------+
           |           x       x            |
           |            xxxxxxx             |
           |               +                |
           v               v                v
   +--------------+ +--------------+ +--------------+
   |              | |              | |              |
   |              | |              | |              |
   +--------------+ +--------------+ +--------------+

                  Figure 1: "Notional UAS Classification"

   Civil Aviation Authorities (CAAs) worldwide are mandating Unmanned
   Aircraft System Remote Identification and tracking (UAS RID).  The
   European Union Aviation Safety Agency (EASA) has published
   [Delegated] and [Implementing] Regulations.  The United States (US)
   Federal Aviation Administration (FAA) has published a Notice of
   Proposed Rule Making [NPRM] and has described the key role that UAS
   RID plays in UAS Traffic Management (UTM) in [FAACONOPS] (especially
   Section 2.6).  CAAs currently (2020) promulgate performance-based
   regulations that do not specify techniques, but rather cite industry
   consensus technical standards as acceptable means of compliance.

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   ASTM International, Technical Committee F38 (UAS), Subcommittee
   F38.02 (Aircraft Operations), Work Item WK65041, developed ASTM
   F3411-19 [F3411-19] Standard Specification for Remote ID and Tracking
   (early drafts are freely available as [OpenDroneID] specifications).
   It defines two means of UAS RID:

      Network RID defines a set of information for UAS to make available
      globally indirectly via the Internet, through servers that can be
      queried by Observers.

      Broadcast RID defines a set of messages for UA to transmit locally
      directly one-way over Bluetooth or Wi-Fi, to be received in real
      time by local Observers.

   The same information must be provided via both means.  The
   presentation may differ, as Network RID defines a data dictionary,
   whereas Broadcast RID defines message formats (which carry items from
   that same data dictionary).  The frequency with which it is sent may
   differ, as Network RID can accommodate Observer queries asynchronous
   to UAS updates (which generally need be sent only when information,
   such as GCS location, changes), whereas Broadcast RID depends upon
   Observers receiving UA messages at the time they are transmitted.
   Network RID depends upon Internet connectivity in several segments
   from the UAS to each Observer.  Broadcast RID should need Internet
   (or other Wide Area Network) connectivity only for UAS registry
   information lookup using the directly locally received UAS Identifier
   (UAS ID) as a key.  Broadcast RID does not assume IP connectivity of
   UAS; messages are encapsulated by the UA without IP, directly in
   Bluetooth or WiFi link layer frames.

   [F3411-19] specifies three UAS ID types:

   TYPE-1  A static, manufacturer assigned, hardware serial number per
           ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers"

   TYPE-2  A CAA assigned (presumably static) ID.

   TYPE-3  A UTM system assigned UUID [RFC4122], which can but need not
           be dynamic.

   The EU allows only Type 1.  The US allows Types 1 and 3, but requires
   Type 3 IDs (if used) each to be used only once (for a single UAS
   flight, which in the context of UTM is called an "operation").  The
   EU also requires an operator registration number (an additional
   identifier distinct from the UAS ID) that can be carried in an
   [F3411-19] optional Operator ID message.  As yet apparently there are
   no CAA proposals to use Type 2.

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   [F3411-19] Broadcast RID transmits all information as cleartext
   (ASCII or binary), so static IDs enable trivial correlation of
   patterns of use, unacceptable in many applications, e.g., package
   delivery routes of competitors.

   [Opinion1] and [WG105] cite the Direct Remote Identification
   previously required and specified, explicitly stating that whereas
   Direct RID is primarily for security purposes, "Electronic
   Identification" (or the "Network Identification Service" in the
   context of U-Space) is primarily for safety purposes (e.g. air
   traffic management, especially hazards deconfliction) and also is
   allowed to be used for other purposes such as support of efficient
   operations.  These emerging standards allow the security and safety
   oriented systems to be separate or merged.  In addition to mandating
   both Broadcast and Network one-way to Observers, they will use V2V to
   other UAS (also likely to and/or from some manned aircraft).

   Security oriented UAS RID regulations essentially have two goals:
   enable the general public to obtain and record an opaque ID for any
   observed UA, which they can then report to authorities; enable
   authorities, from such an ID, to look up information about the UAS
   and its operator, especially location.  Safety oriented UAS RID has
   stronger requirements.  Aviation community SDOs set a higher bar for
   safety than for security, especially with respect to reliability.

1.2.  Intended Use

   An ID is not an end in itself; it exists to enable lookups and
   provision of services complementing mere identification.

   Minimal specified information must be made available to the public;
   access to other data, e.g., UAS operator Personally Identifiable
   Information (PII), must be limited to strongly authenticated
   personnel, properly authorized per policy.  The balance between
   privacy and transparency remains a subject for public debate and
   regulatory action; DRIP can only offer tools to expand the achievable
   trade space and enable trade-offs within that space.  [F3411-19]
   specifies only how to get the UAS ID to the Observer; how the
   Observer can perform these lookups, and how the registries first can
   be populated with information, is unspecified.

   Using UAS RID to facilitate vehicular (V2X) communications and
   applications such as Detect And Avoid (DAA), which would impose
   tighter latency bounds than RID itself, is an obvious possibility,
   explicitly contemplated in the FAA NPRM.  However, applications of
   RID beyond RID itself have been omitted from [F3411-19]; DAA has been
   explicitly declared out of scope in ASTM working group discussions,
   based on a distinction between RID as a security standard vs DAA as a

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   safety application.  Although dynamic establishment of secure
   communications between the Observer and the UAS pilot seems to have
   been contemplated by the FAA UAS ID and Tracking Aviation Rulemaking
   Committee (ARC) in their [Recommendations], it is not addressed in
   any of the subsequent proposed regulations or technical

   The need for near-universal deployment of UAS RID is pressing.  This
   implies the need to support use by Observers of already ubiquitous
   mobile devices (typically smartphones and tablets).  Anticipating
   likely CAA requirements to support legacy devices, especially in
   light of [Recommendations], [F3411-19] specifies that any UAS sending
   Broadcast RID over Bluetooth must do so over Bluetooth 4, regardless
   of whether it also does so over newer versions; as UAS sender devices
   and Observer receiver devices are unpaired, this implies extremely
   short "advertisement" (beacon) frames.

   UA onboard RID devices are severely constrained in Cost ($), Size,
   Weight and Power ($SWaP).  Cost is a significant impediment to the
   necessary near-universal adoption of UAS send and Observer receive
   RID capabilities. $SWaP is a burden not only on the designers of new
   UA for production and sale, but also on owners of existing UA that
   must be retrofit.  Radio Controlled (RC) aircraft modelers, "hams"
   who use licensed amateur radio frequencies to control UAS, drone
   hobbyists and others who custom build UAS all need means of
   participating in UAS RID, sensitive to both generic $SWaP and
   application-specific considerations.

   To accommodate the most severely constrained cases, all these
   conspire to motivate system design decisions, especially for the
   Broadcast RID data link, which complicate the protocol design
   problem: one-way links; extremely short packets; and Internet-
   disconnected operation of UA onboard devices.  Internet-disconnected
   operation of Observer devices has been deemed by ASTM F38.02 too
   infrequent to address, but for some users is important and presents
   further challenges.

   Despite work by regulators and Standards Development Organizations
   (SDOs), there are substantial gaps in UAS standards generally and UAS
   RID specifically.  [Roadmap] catalogs UAS related standards, ongoing
   standardization activities and gaps (as of early 2020); Section 7.8
   catalogs those related specifically to UAS RID.

   Given not only packet payload length and bandwidth, but also
   processing and storage within the $SWaP constraints of very small
   (e.g. consumer toy) UA, heavyweight cryptographic security protocols
   are infeasible, yet trustworthiness of UAS RID information is
   essential.  Under [F3411-19], even the most basic datum, the UAS ID

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   string (typically number) itself can be merely an unsubstantiated
   claim.  Observer devices being ubiquitous, thus popular targets for
   malware or other compromise, cannot be generally trusted (although
   the user of each device is compelled to trust that device, to some
   extent); a "fair witness" functionality (inspired by [Stranger]) is

1.3.  DRIP Scope

   DRIP's initial goal is to make RID immediately actionable, in both
   Internet and local-only connected scenarios (especially emergencies),
   in severely constrained UAS environments, balancing legitimate (e.g.,
   public safety) authorities' Need To Know trustworthy information with
   UAS operators' privacy.  By "immediately actionable" is meant
   information of sufficient precision, accuracy, timeliness, etc. for
   an Observer to use it as the basis for immediate decisive action,
   whether that be to trigger a defensive counter-UAS system, to attempt
   to initiate communications with the UAS operator, to accept the
   presence of the UAS in the airspace where/when observed as not
   requiring further action, or whatever, with potentially severe
   consequences of any action or inaction chosen based on that
   information.  For further explanation of the concept of immediate
   actionability, see [ENISACSIRT].  Note that UAS RID must achieve near
   universal adoption, but DRIP can add value even if only selectively
   deployed, as those with jurisdiction over more sensitive airspace
   volumes may set a higher than generally mandated RID bar for flight
   in those volumes.  Potential follow-on goals may extend beyond
   providing timely and trustworthy identification data, to using it to
   enable identity-oriented networking of UAS.

   DRIP (originally Trustworthy Multipurpose Remote Identification, TM-
   RID) potentially could be applied to verifiably identify other types
   of registered things reported to be in specified physical locations,
   but the urgent motivation and clear initial focus is UAS.  Existing
   Internet resources (protocol standards, services, infrastructure, and
   business models) should be leveraged.  A natural Internet based
   architecture for UAS RID conforming to proposed regulations and
   external technical standards is described in a companion architecture
   document [drip-architecture] and elaborated in other DRIP documents;
   this document describes only relevant requirements and defines
   terminology for the set of DRIP documents.

2.  Terms and Definitions

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2.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

2.2.  Definitions

   This section defines a set of terms expected to be used in DRIP
   documents.  This list is meant to be the DRIP terminology reference.
   Some of the terms listed below are not used in this document.
   [RFC4949] provides a glossary of Internet security terms that should
   be used where applicable.  In the UAS community, the plural form of
   acronyms generally is the same as the singular form, e.g.  Unmanned
   Aircraft System (singular) and Unmanned Aircraft Systems (plural) are
   both represented as UAS.  On this and other terminological issues, to
   encourage comprehension necessary for adoption of DRIP by the
   intended user community, that community's norms are respected herein,
   and definitions are quoted in cases where they have been found in
   that community's documents.  Most of the listed terms are from that
   community (even if specific source documents are not cited); any that
   are DRIP-specific or invented by the authors of this document are
   marked "(DRIP)".

      Cost, Size, Weight and Power.  (DRIP)

      Attestation, Authentication, Authorization, Access Control,
      Accounting, Attribution, Audit, or any subset thereof (uses differ
      by application, author and context).  (DRIP)

      AirBorne DAA.  Accomplished using systems onboard the aircraft
      involved.  Also known as "self-separation".

      Automatic Dependent Surveillance - Broadcast.  "ADS-B Out"
      equipment obtains aircraft position from other on-board systems
      (typically GNSS) and periodically broadcasts it to "ADS-B In"
      equipped entities, including other aircraft, ground stations and
      satellite based monitoring systems.

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      Above Ground Level.  Relative altitude, above the variously
      defined local ground level, typically of an UA, measured in feet
      or meters.  Should be explicitly specified as either barometric
      (pressure) or geodetic (GNSS).

      Air Traffic Control.  Explicit flight direction to pilots from
      ground controllers.  Contrast with ATM.

      Air Traffic Management.  A broader functional and geographic scope
      and/or a higher layer of abstraction than ATC.  "The dynamic,
      integrated management of air traffic and airspace including air
      traffic services, airspace management and air traffic flow
      management - safely, economically and efficiently - through the
      provision of facilities and seamless services in collaboration
      with all parties and involving airborne and ground-based
      functions."  [ICAOATM]

   Authentication Message
      [F3411-19] Message Type 2.  Provides framing for authentication
      data, only.  Optional per [F3411-19] but may be required by

   Basic ID Message
      [F3411-19] Message Type 0.  Provides UA Type, UAS ID Type and UAS
      ID, only.  Mandatory per [F3411-19].

      Beyond Line Of Sight (LOS).  Term to be avoided due to ambiguity.
      See LOS.

      Beyond Visual Line Of Sight (V-LOS).  See V-LOS.

      Civil Aviation Authority.  Two examples are the United States
      Federal Aviation Administration (FAA) and the European Union
      Aviation Safety Agency (EASA).

      Command and Control.  A set of organizational and technical
      attributes and processes that employs human, physical, and
      information resources to solve problems and accomplish missions.
      Previously primarily used in military contexts.  In the UAS
      context, typically refers to the link between GCS and UA over
      which the former controls the latter.

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      Detect And Avoid, formerly Sense And Avoid (SAA).  A means of
      keeping aircraft "well clear" of each other for safety.

   Direct RID
      Direct Remote Identification.  Per [Delegated], "a system that
      ensures the local broadcast of information about a UA in
      operation, including the marking of the UA, so that this
      information can be obtained without physical access to the UA".
      Requirement could be met with ASTM Broadcast RID: Basic ID message
      with UAS ID Type 1; Location/Vector message; Operator ID message;
      System Message.  Corresponds roughly to the Broadcast RID portion
      of FAA NPRM Standard RID.

      Discovery and Synchronization Service.  Formerly Inter-USS.  The
      UTM system overlay network backbone.  Most importantly, it enables
      one USS to learn which other USS have UAS operating in a given 4-D
      airspace volume, for deconfliction and surveillance; but it also
      supports other functions.

      End to End.

      European Organisation for Civil Aviation Equipment.  Aviation SDO,
      originally European, now with broader membership.  Cooperates
      extensively with RTCA.

      Ground Based DAA.  Accomplished with the aid of ground based

      Ground Control Station.  The part of the UAS that the remote pilot
      uses to exercise C2 over the UA, whether by remotely exercising UA
      flight controls to fly the UA, by setting GPS waypoints, or
      otherwise directing its flight.

      Global Navigation Satellite System.  Satellite based timing and/or
      positioning with global coverage, often used to support

      Global Positioning System.  A specific GNSS, but in this context,
      the term is typically misused in place of the more generic term

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      Global Resilient Aviation Interoperable Network.  ICAO managed
      IPv6 overlay internetwork per IATF, dedicated to aviation (but not
      just aircraft).  Currently in design.

      International Aviation Trust Framework.  ICAO effort to develop a
      resilient and secure by design framework for networking in support
      of all aspects of aviation.

      International Civil Aviation Organization.  A United Nations
      specialized agency that develops and harmonizes international
      standards relating to aviation.

      Low Altitude Authorization and Notification Capability.  Supports
      ATC authorization requirements for UAS operations: remote pilots
      can apply to receive a near real-time authorization for operations
      under 400 feet in controlled airspace near airports.  US partial
      stopgap until UTM comes.

   Limited RID
      Per the FAA NPRM, a mode of operation that must use Network RID,
      must not use Broadcast RID, and must provide pilot/GCS location
      only (not UA location).  This mode is only allowed for UA that
      neither require (due to e.g. size) nor are equipped for Standard
      RID, operated within V-LOS and within 400 feet of the pilot, below
      400 feet AGL, etc.

   Location/Vector Message
      [F3411-19] Message Type 1.  Provides UA location, altitude,
      heading and speed, only.  Mandatory per [F3411-19].

      Line Of Sight.  An adjectival phrase describing any information
      transfer that travels in a nearly straight line (e.g.
      electromagnetic energy, whether in the visual light, RF or other
      frequency range) and is subject to blockage.  A term to be avoided
      due to ambiguity, in this context, between RF-LOS and V-LOS.

      Mean Sea Level.  Relative altitude, above the variously defined
      mean sea level, typically of an UA (but in FAA NPRM also for a
      GCS), measured in or meters.  Should be explicitly specified as
      either barometric (pressure) or geodetic (GNSS).

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   Net-RID DP
      Network RID Display Provider.  Logical entity that aggregates data
      from Net-RID SPs as needed in response to user queries regarding
      UAS operating within specified airspace volumes, to enable display
      by a user application on a user device.  Potentially could provide
      not only information sent via UAS RID but also information
      retrieved from UAS RID registries, or information beyond UAS RID,
      regarding subscribed USS.  Under the FAA NPRM, not recognized as a
      distinct entity, but a service provided by USS, including Public
      Safety USS that may exist primarily for this purpose rather than
      to manage any subscribed UAS.

   Net-RID SP
      Network RID Service Provider.  Logical entity that collects RID
      messages from UAS and responds to NetRID-DP queries for
      information on UAS of which it is aware.  Under the FAA NPRM, the
      USS to which the UAS is subscribed ("Remote ID USS").

   Network Identification Service
      EU regulatory requirement for Network RID.  Requirement could be
      met with ASTM Network RID: Basic ID message with UAS ID Type 1;
      Location/Vector message; Operator ID message; System Message.
      Corresponds roughly to the Network RID portion of FAA NPRM
      Standard RID.

      An entity (typically but not necessarily an individual human) who
      has directly or indirectly observed an UA and wishes to know
      something about it, starting with its ID.  An observer typically
      is on the ground and local (within V-LOS of an observed UA), but
      could be remote (observing via Network RID or other surveillance),
      operating another UA, aboard another aircraft, etc.  (DRIP)

      A flight, or series of flights of the same mission, by the same
      UAS, in the same airspace volume, separated by at most brief
      ground intervals.

      "A person, organization or enterprise engaged in or offering to
      engage in an aircraft operation."  [ICAOUTM]

   Operator ID Message
      [F3411-19] Message Type 5.  Provides CAA issued Operator ID, only.
      Operator ID is distinct from UAS ID.  Optional per [F3411-19] but
      may be required by regulations.

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      Pilot In Command.  "The pilot designated by the operator, or in
      the case of general aviation, the owner, as being in command and
      charged with the safe conduct of a flight."  [ICAOATM]

      Personally Identifiable Information.  In this context, typically
      of the UAS Operator, Pilot In Command (PIC) or Remote Pilot, but
      possibly of an Observer or other party.

   Remote Pilot
      A pilot using a GCS to exercise proximate control of an UA.
      Either the PIC or under the supervision of the PIC.

      RF LOS.  Typically used in describing operation of a direct radio
      link between a GCS and the UA under its control, potentially
      subject to blockage by foliage, structures, terrain or other
      vehicles, but less so than V-LOS.

      Radio Technical Commission for Aeronautics.  US aviation SDO.
      Cooperates extensively with EUROCAE.

   Self-ID Message
      [F3411-19] Message Type 3.  Provides a 1 byte descriptor and 23
      byte ASCII free text field, only.  Expected to be used to provide
      context on the operation, e.g. mission intent.  Optional unless
      required by the cognizant CAA.  Optional per [F3411-19] but may be
      required by regulations.

   Standard RID
      Per the FAA NPRM, a mode of operation that must use both Network
      RID (if Internet connectivity is available at the time in the
      operating area) and Broadcast RID (always and everywhere), and
      must provide both pilot/GCS location and UA location.  This mode
      is required for UAS that exceed the allowed envelope (e.g. size,
      range) of Limited RID and for all UAS equipped for Standard RID
      (even if operated within parameters that would otherwise permit
      Limited RID).  The Broadcast RID portion corresponds roughly to EU
      Direct RID; the Network RID portion corresponds roughly to EU
      Network Identification Service.

      Standards Development Organization.  ASTM, IETF, et al.

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      Supplemental Data Service Provider.  An entity that participates
      in the UTM system, but provides services beyond those specified as
      basic UTM system functions.  E.g., provides weather data.

   System Message
      [F3411-19] Message Type 4.  Provides general UAS information,
      including remote pilot location, multiple UA group operational
      area, etc.  Optional per [F3411-19] but may be required by

      EU concept and emerging framework for integration of UAS into all
      classes of airspace, specifically including high density urban
      areas, sharing airspace with manned aircraft.

      Unmanned Aircraft.  An aircraft which is intended to operate with
      no pilot on board.  In popular parlance, "drone".

      Unmanned Aircraft System.  Composed of UA, all required on-board
      subsystems, payload, control station, other required off-board
      subsystems, any required launch and recovery equipment, all
      required crew members, and C2 links between UA and control

      UAS identifier.  Although called "UAS ID", unique to the UA:
      neither to the operator (as previous registration numbers have
      been assigned), nor to the combination of GCS and UA that comprise
      the UAS.  Per [F3411-19]: maximum length of 20 bytes; see
      Section 1.1, Paragraph 7 for currently defined values.

   UAS ID Type
      Identifier type index.  Per [F3411-19], 4 bits, values 0-3 already

      UAS Remote Identification.  System for identifying UA during
      flight by other parties.

   UAS RID Verification Service
      System component designed to handle the authentication
      requirements of RID by offloading verification to a web hosted

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      UAS Service Supplier.  "A USS is an entity that assists UAS
      Operators with meeting UTM operational requirements that enable
      safe and efficient use of airspace" and "... provide services to
      support the UAS community, to connect Operators and other entities
      to enable information flow across the USS Network, and to promote
      shared situational awareness among UTM participants" per

      UAS Traffic Management.  Per ICAO, "A specific aspect of air
      traffic management which manages UAS operations safely,
      economically and efficiently through the provision of facilities
      and a seamless set of services in collaboration with all parties
      and involving airborne and ground-based functions."  In the US,
      per FAA, a "traffic management" ecosystem for "uncontrolled" low
      altitude UAS operations, separate from, but complementary to, the
      FAA's ATC system for "controlled" operations of manned aircraft.

      Vehicle-to-Vehicle.  Originally communications between
      automobiles, now extended to apply to communications between
      vehicles generally.  Often, together with Vehicle-to-
      Infrastructure (V2I) etc., generalized to V2X.

      Visual LOS.  Typically used in describing operation of an UA by a
      "remote" pilot who can clearly directly (without video cameras or
      any other aids other than glasses or under some rules binoculars)
      see the UA and its immediate flight environment.  Potentially
      subject to blockage by foliage, structures, terrain or other
      vehicles, more so than RF-LOS.

3.  UAS RID Problem Space

   UA may be fixed wing Short Take-Off and Landing (STOL), rotary wing
   (e.g., helicopter) Vertical Take-Off and Landing (VTOL), or hybrid.
   They may be single- or multi-engine.  The most common today are
   multicopters: rotary wing, multi engine.  The explosion in UAS was
   enabled by hobbyist development, for multicopters, of advanced flight
   stability algorithms, enabling even inexperienced pilots to take off,
   fly to a location of interest, hover, and return to the take-off
   location or land at a distance.  UAS can be remotely piloted by a
   human (e.g., with a joystick) or programmed to proceed from GNSS
   waypoint to waypoint in a weak form of autonomy; stronger autonomy is
   coming.  UA are "low observable": they typically have small radar
   cross sections; they make noise quite noticeable at short range but
   difficult to detect at distances they can quickly close (500 meters

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   in under 17 seconds at 60 knots); they typically fly at low altitudes
   (for the small UAS to which RID applies in the US, under 400 feet
   AGL); they are highly maneuverable so can fly under trees and between

   UA can carry payloads including sensors, cyber and kinetic weapons,
   or can be used themselves as weapons by flying them into targets.
   They can be flown by clueless, careless or criminal operators.  Thus
   the most basic function of UAS RID is "Identification Friend or Foe"
   (IFF) to mitigate the significant threat they present.  Numerous
   other applications can be enabled or facilitated by RID: consider the
   importance of identifiers in many Internet protocols and services.

   Network RID from the UA itself (rather than from its GCS) and
   Broadcast RID require one or more wireless data links from the UA,
   but such communications are challenging due to $SWaP constraints and
   low altitude flight amidst structures and foliage over terrain.

   Disambiguation of multiple UA flying in close proximity may be very
   challenging, even if each is reporting its identity, position and
   velocity as accurately as it can.

3.1.  Network RID

   Network RID is essentially publish-subscribe-query.  First the UAS
   operator pushes an operation plan to the USS that will serve that UAS
   for that operation, for deconfliction with other operations; assuming
   the plan receives approval and the operation commences, that UAS
   periodically pushes location/status updates to that USS (call it
   USS#1), which serves as the Network RID Service Provider (Net-RID SP)
   for that operation.  If users of any other USS (whether they be other
   UAS operators or Observers) develop an interest in any 4-D airspace
   volume containing that UAS operation, their USS learns, via the UTM
   Discovery and Synchronization Service (DSS), that USS#1 has such
   operations.  Observers or other interested parties can then
   subscribe, via their USS, which serves as a Network RID Display
   Provider (Net-RID DP) for that surveillance session.  The Net-RID SP
   (USS#1) will then publish updates of the UAS position/status to all
   subscribed Net-RID DP, which in turn will deliver the surveillance
   information to their users via unspecified (but expected to be web
   browser based) means.

   Network RID has several variants.  The UA may have persistent onboard
   Internet connectivity, in which case it can consistently source RID
   information directly over the Internet.  The UA may have intermittent
   onboard Internet connectivity, in which case the GCS must source RID
   information whenever the UA itself is offline.  The UA may not have
   Internet connectivity of its own, but have instead some other form of

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   communications to another node that can relay RID information to the
   Internet; this would typically be the GCS (which to perform its
   function must know where the UA is, although C2 link outages do

   The UA may have no means of sourcing RID information, in which case
   the GCS must source it; this is typical under FAA NPRM Limited RID
   proposed rules, which require providing the location of the GCS (not
   that of the UA).  In the extreme case, this could be the pilot using
   a web browser/application to designate, to an UAS Service Supplier
   (USS) or other UTM entity, a time-bounded airspace volume in which an
   operation will be conducted; this may impede disambiguation of ID if
   multiple UAS operate in the same or overlapping spatio-temporal

   In most cases in the near term, if the RID information is fed to the
   Internet directly by the UA or GCS, the first hop data links will be
   cellular Long Term Evolution (LTE) or Wi-Fi, but provided the data
   link can support at least UDP/IP and ideally also TCP/IP, its type is
   generally immaterial to the higher layer protocols.  An UAS as the
   ultimate source of Network RID information feeds an USS acting as a
   Network RID Service Provider (Net-RID SP), which essentially proxies
   for that and other sources; an observer or other ultimate consumer of
   Network RID information obtains it from a Network RID Display
   Provider (Net-RID DP), which aggregates information from multiple
   Net-RID SPs to offer coverage of an airspace volume of interest.
   Network RID Service and Display providers are expected to be
   implemented as servers in well-connected infrastructure, accessible
   via typical means such as web APIs/browsers.

   Network RID is the more flexible and less constrained of the defined
   UAS RID means, but is only partially specified in [F3411-19].  It is
   presumed that IETF efforts supporting Broadcast RID (see next
   section) can be easily generalized for Network RID.

3.2.  Broadcast RID

   [F3411-19] specifies three Broadcast RID data links: Bluetooth 4.X;
   Bluetooth 5.X Long Range; and Wi-Fi with Neighbor Awareness
   Networking (NAN).  For compliance with [F3411-19], an UA must
   broadcast (using advertisement mechanisms where no other option
   supports broadcast) on at least one of these; if broadcasting on
   Bluetooth 5.x, it is also required concurrently to do so on 4.x
   (referred to in [F3411-19] as Bluetooth Legacy).

   The selection of the Broadcast media was driven by research into what
   is commonly available on 'ground' units (smartphones and tablets) and
   what was found as prevalent or 'affordable' in UA.  Further, there

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   must be an Application Programming Interface (API) for the observer's
   receiving application to have access to these messages.  As yet only
   Bluetooth 4.X support is readily available, thus the current focus is
   on working within the 26 byte limit of the Bluetooth 4.X "Broadcast
   Frame" transmitted on beacon channels.  After nominal overheads, this
   limits the UAS ID string to a maximum length of 20 bytes, and
   precludes the same frame carrying position, velocity and other
   information that should be bound to the UAS ID, much less strong
   authentication data.  This requires segmentation ("paging") of longer
   messages or message bundles ("Message Pack"), and/or correlation of
   short messages (anticipated by ASTM to be done on the basis of
   Bluetooth 4 MAC address, which is weak and unverifiable).

3.3.  DRIP Focus

   DRIP will focus on making information obtained via UAS RID
   immediately usable:

   1.  by making it trustworthy (despite the severe constraints of
       Broadcast RID);

   2.  by enabling verification that an UAS is registered, and if so, in
       which registry (for classification of trusted operators on the
       basis of known registry vetting, even by observers lacking
       Internet connectivity at observation time);

   3.  by facilitating independent reports of UA's aeronautical data
       (location, velocity, etc.) to confirm or refute the operator
       self-reports upon which UAS RID and UTM tracking are based;

   4.  by enabling instant establishment, by authorized parties, of
       secure communications with the remote pilot.

   Any UA can assert any ID using the [F3411-19] required Basic ID
   message, which lacks any provisions for verification.  The Position/
   Vector message likewise lacks provisions for verification, and does
   not contain the ID, so must be correlated somehow with a Basic ID
   message: the developers of [F3411-19] have suggested using the MAC
   addresses, but these may be randomized by the operating system stack
   to avoid the adversarial correlation problems of static identifiers.

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   The [F3411-19] optional Authentication Message specifies framing for
   authentication data, but does not specify any authentication method,
   and the maximum length of the specified framing is too short for
   conventional digital signatures and far too short for conventional
   certificates.  The one-way nature of Broadcast RID precludes
   challenge-response security protocols (e.g., observers sending nonces
   to UA, to be returned in signed messages).  An observer would be
   seriously challenged to validate the asserted UAS ID or any other
   information about the UAS or its operator looked up therefrom.

   Further, [F3411-19] provides very limited choices for an observer to
   communicate with the pilot, e.g., to request further information on
   the UAS operation or exit from an airspace volume in an emergency.
   The System Message provides the location of the pilot/GCS, so an
   observer could physically go to the asserted GCS location to look for
   the remote pilot.  An observer with Internet connectivity could look
   up operator PII in a registry, then call a phone number in hopes
   someone who can immediately influence the UAS operation will answer
   promptly during that operation.

   Thus complementing [F3411-19] with protocols enabling strong
   authentication, preserving operator privacy while enabling immediate
   use of information by authorized parties, is critical to achieve
   widespread adoption of a RID system supporting safe and secure
   operation of UAS.

4.  Requirements

4.1.  General

   GEN-1   Provable Ownership: DRIP MUST enable verification that the
           UAS ID asserted in the Basic ID message is that of the actual
           current sender of the message (i.e. the message is not a
           replay attack or other spoof, authenticating e.g. by
           verifying an asymmetric cryptographic signature using a
           sender provided public key from which the asserted ID can be
           at least partially derived), even on an observer device
           lacking Internet connectivity at the time of observation.

   GEN-2   Provable Binding: DRIP MUST enable binding all other
           [F3411-19] messages from the same actual current sender to
           the UAS ID asserted in the Basic ID message.

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   GEN-3   Provable Registration: DRIP MUST enable verification that the
           UAS ID is in a registry and identification of which one, even
           on an observer device lacking Internet connectivity at the
           time of observation; with UAS ID Type 3, the same sender may
           have multiple IDs, potentially in different registries, but
           each ID must clearly indicate in which registry it can be

   GEN-4   Readability: DRIP MUST enable information (regulation
           required elements, whether sent via UAS RID or looked up in
           registries) to be read and utilized by both humans and

   GEN-5   Gateway: DRIP MUST enable Broadcast RID -> Network RID
           application layer gateways to stamp messages with precise
           date/time received and receiver location, then relay them to
           a network service (e.g.  SDSP or distributed ledger), to
           support three objectives: mark up a RID message with where
           and when it was actually received (which may agree or
           disagree with the self-report in the set of messages); defend
           against replay attacks; and support optional SDSP services
           such as multilateration (to complement UAS position self-
           reports with independent measurements).

   GEN-6   Finger: DRIP MUST enable dynamically establishing, with AAA,
           per policy, E2E strongly encrypted communications with the
           UAS RID sender and entities looked up from the UAS ID,
           including at least the remote pilot and USS.

   GEN-7   QoS: DRIP MUST enable policy based specification of
           performance and reliability parameters, such as maximum
           message transmission intervals and delivery latencies.

   GEN-8   Mobility: DRIP MUST support physical and logical mobility of
           UA, GCS and Observers.  DRIP SHOULD support mobility of
           essentially all participating nodes (UA, GCS, Observers, Net-
           RID SP, Net-RID DP, Private Registry, SDSP).

   GEN-9   Multihoming: DRIP MUST support multihoming of UA and GCS, for
           make-before-break smooth handoff and resiliency against path/
           link failure.  DRIP SHOULD support multihoming of essentially
           all participating nodes.

   GEN-10  Multicast: DRIP SHOULD support multicast for efficient and
           flexible publish-subscribe notifications, e.g., of UAS
           reporting positions in designated sensitive airspace volumes.

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   GEN-11  Management: DRIP SHOULD support monitoring of the health and
           coverage of Broadcast and Network RID services.

   Requirements imposed either by regulation or in [F3411-19] are not
   reiterated here, but drive many of the numbered requirements listed
   here.  E.g. the QoS requirement currently would be satisfied
   generally by ensuring information refresh rates of at least 1 Hertz,
   with latencies no greater than 1 second, at least 80% of the time;
   but these numbers may change, so instead the DRIP requirement is that
   they be user policy specifiable.  Note that the "provable binding"
   requirement addresses the MAC address correlation problem of
   [F3411-19] noted above.  Note that the "gateway" requirement is the
   only instance in which DRIP transports [F3411-19] messages; most of
   DRIP pertains to the authentication of such messages and the
   identifier carried within them.

4.2.  Identifier

   ID-1  Length: The DRIP (UAS) entity (remote) identifier must be no
         longer than 20 bytes (per [F3411-19] to fit in a Bluetooth 4
         advertisement payload).

   ID-2  Registry ID: The DRIP identifier MUST be sufficient to identify
         a registry in which the (UAS) entity identified therewith is

   ID-3  Entity ID: The DRIP identifier MUST be sufficient to enable
         lookup of other data associated with the (UAS) entity
         identified therewith in that registry.

   ID-4  Uniqueness: The DRIP identifier MUST be unique within a to-be-
         defined scope.

   ID-5  Non-spoofability: The DRIP identifier MUST be non-spoofable
         within the context of Remote ID broadcast messages (some
         collection of messages provides proof of UA ownership of ID).

   ID-6  Unlinkability: A DRIP UAS ID MUST NOT facilitate adversarial
         correlation over multiple UAS operations; this may be
         accomplished e.g. by limiting each identifier to a single use,
         but if so, the UAS ID MUST support well-defined scalable timely
         registration methods.

   Note that Registry ID and Entity ID are requirements on a single DRIP
   entity Identifier, not separate (types of) ID.  In the most common
   use case, the Entity will be the UA, and the DRIP Identifier will be
   the UAS ID; however, other entities may also benefit from having DRIP
   identifiers, so the Entity type is not prescribed here.

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   Whether a UAS ID is generated by the operator, GCS, UA, USS or
   registry, or some collaboration thereamong, is unspecified; however,
   there must be agreement on the UAS ID among these entities.

4.3.  Privacy

   PRIV-1  Confidential Handling: DRIP MUST enable confidential handling
           of private information (i.e., any and all information
           designated by neither cognizant authority nor the information
           owner as public, e.g., personal data).

   PRIV-2  Encrypted Transport: DRIP MUST enable selective strong
           encryption of private data in motion in such a manner that
           only authorized actors can recover it.  If transport is via
           IP, then encryption MUST be end-to-end, at or above the IP
           layer.  DRIP MUST NOT encrypt safety critical data to be
           transmitted over Broadcast RID in any situation where it is
           unlikely that local observers authorized to access the
           plaintext will be able to decrypt it or obtain it from a
           service able to decrypt it.  DRIP MUST NOT encrypt data when/
           where doing so would conflict with applicable regulations or
           CAA policies/procedures, i.e. DRIP MUST support configurable
           disabling of encryption.

   PRIV-3  Encrypted Storage: DRIP SHOULD facilitate selective strong
           encryption of private data at rest in such a manner that only
           authorized actors can recover it.

   PRIV-4  Public/Private Designation: DRIP SHOULD facilitate
           designation, by cognizant authorities and information owners,
           which information is public and which private.  By default,
           all information required to be transmitted via Broadcast RID,
           even when actually sent via Network RID, is assumed to be
           public; all other information contained in registries for
           lookup using the UAS ID is assumed to be private.

   PRIV-5  Pseudonymous Rendezvous: DRIP MAY enable mutual discovery of
           and communications among participating UAS operators whose UA
           are in 4-D proximity, using the UAS ID without revealing
           pilot/operator identity or physical location.

   How information is stored on end systems is out of scope for DRIP.
   Encouraging privacy best practices, including end system storage
   encryption, by facilitating it with protocol design reflecting such
   considerations, is in scope.  Similar logic applies to methods for
   designating information as public or private.

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   The privacy requirements above are for DRIP, neither for [F3411-19]
   (which requires obfuscation of location to any Network RID subscriber
   engaging in wide area surveillance, limits data retention periods,
   etc. in the interests of privacy), nor for UAS RID in any specific
   jurisdiction (which may have its own regulatory requirements).  The
   requirements above are also in a sense parameterized: who are the
   "authorized actors", how are they designated, how are they
   authenticated, etc.?

4.4.  Registries

   REG-1  Public Lookup: DRIP MUST enable lookup, from the UAS ID, of
          information designated by cognizant authority as public, and
          MUST NOT restrict access to this information based on identity
          of the party submitting the query.

   REG-2  Private Lookup: DRIP MUST enable lookup of private information
          (i.e., any and all information in a registry, associated with
          the UAS ID, that is designated by neither cognizant authority
          nor the information owner as public), and MUST, per policy,
          enforce AAA, including restriction of access to this
          information based on identity of the party submitting the

   REG-3  Provisioning: DRIP MUST enable provisioning registries with
          static information on the UAS and its operator, dynamic
          information on its current operation within the UTM (including
          means by which the USS under which the UAS is operating may be
          contacted for further, typically even more dynamic,
          information), and Internet direct contact information for
          services related to the foregoing.

   REG-4  AAA Policy: DRIP MUST enable closing the AAA-policy registry
          loop by governing AAA per registered policies and
          administering policies only via AAA.

5.  IANA Considerations

   This document does not make any IANA request.

6.  Security Considerations

   DRIP is all about safety and security, so content pertaining to such
   is not limited to this section.  Potential vulnerabilities of DRIP
   include but are not limited to:

   *  Sybil attacks

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   *  Confusion created by many spoofed unsigned messages

   *  Processing overload induced by attempting to verify many spoofed
      signed messages (where verification will fail but still consume

   *  Malicious or malfunctioning registries

   *  Interception of (e.g.  Man In The Middle attacks on) registration

   *  UA impersonation through private key extraction, improper key
      sharing or carriage of a small (presumably harmless) UA, e.g. as a
      "false flag", by a larger (malicious) UA

7.  Privacy and Transparency Considerations

   Privacy is closely related to but not synonymous with security, and
   conflicts with transparency.  Privacy and transparency are important
   for legal reasons including regulatory consistency.  [EU2018]
   [EU2018] states "harmonised and interoperable national registration
   systems... should comply with the applicable Union and national law
   on privacy and processing of personal data, and the information
   stored in those registration systems should be easily accessible."

   Privacy and transparency (where essential to security or safety) are
   also ethical and moral imperatives.  Even in cases where old
   practices (e.g. automobile registration plates) could be imitated,
   when new applications involving PII (such as UAS RID) are addressed
   and newer technologies could enable improving privacy, such
   opportunities should not be squandered.  Thus it is recommended that
   all DRIP documents give due regard to [RFC6973] and more broadly

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   DRIP information falls into two classes: that which, to achieve the
   purpose, must be published openly as cleartext, for the benefit of
   any Observer (e.g., the basic UAS ID itself); and that which must be
   protected (e.g., PII of pilots) but made available to properly
   authorized parties (e.g., public safety personnel who urgently need
   to contact pilots in emergencies).  How properly authorized parties
   are authorized, authenticated, etc. are questions that extend beyond
   the scope of DRIP, but DRIP may be able to provide support for such
   processes.  Classification of information as public or private must
   be made explicit and reflected with markings, design, etc.
   Classifying the information will be addressed primarily in external
   standards; herein it will be regarded as a matter for CAA, registry
   and operator policies, for which enforcement mechanisms will be
   defined within the scope of DRIP WG and offered.  Details of the
   protection mechanisms will be provided in other DRIP documents.
   Mitigation of adversarial correlation will also be addressed.

8.  References

8.1.  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, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [cpdlc]    Gurtov, A., Polishchuk, T., and M. Wernberg, "Controller-
              Pilot Data Link Communication Security", MDPI
              Sensors 18(5), 1636, 2018,

   [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers",
              September 2019.

              European Union Aviation Safety Agency (EASA), "Commission
              Delegated Regulation (EU) 2019/945 of 12 March 2019 on
              unmanned aircraft systems and on third-country operators
              of unmanned aircraft systems", March 2019.

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              Card, S., Wiethuechter, A., Moskowitz, R., Zhao, S., and
              A. Gurtov, "Drone Remote Identification Protocol (DRIP)
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-drip-arch-03, 13 July 2020,

              European Union Agency for Cybersecurity (ENISA),
              "Actionable information for Security Incident Response",
              November 2014, <https://www.enisa.europa.eu/topics/csirt-

   [EU2018]   European Parliament and Council, "2015/0277 (COD) PE-CONS
              2/18", February 2018.

   [F3411-19] ASTM International, "Standard Specification for Remote ID
              and Tracking", February 2020,

              FAA Office of NextGen, "UTM Concept of Operations v2.0",
              March 2020.

              Maeurer, N., Graeupl, T., and C. Schmitt, "L-band Digital
              Aeronautical Communications System (LDACS)", Work in
              Progress, Internet-Draft, draft-maeurer-raw-ldacs-05, 14
              August 2020,

   [ICAOATM]  International Civil Aviation Organization, "Doc 4444:
              Procedures for Air Navigation Services: Air Traffic
              Management", November 2016.

   [ICAOUTM]  International Civil Aviation Organization, "Unmanned
              Aircraft Systems Traffic Management (UTM) - A Common
              Framework with Core Principles for Global Harmonization,
              Edition 2", November 2019.

              European Union Aviation Safety Agency (EASA), "Commission
              Implementing Regulation (EU) 2019/947 of 24 May 2019 on
              the rules and procedures for the operation of unmanned
              aircraft", May 2019.

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   [NPRM]     United States Federal Aviation Administration (FAA),
              "Notice of Proposed Rule Making on Remote Identification
              of Unmanned Aircraft Systems", December 2019.

              Intel Corp., "Open Drone ID", March 2019,

   [Opinion1] European Union Aviation Safety Agency (EASA), "Opinion No
              01/2020: High-level regulatory framework for the U-space",
              March 2020.

              FAA UAS Identification and Tracking Aviation Rulemaking
              Committee, "UAS ID and Tracking ARC Recommendations Final
              Report", September 2017.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC8280]  ten Oever, N. and C. Cath, "Research into Human Rights
              Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280,
              October 2017, <https://www.rfc-editor.org/info/rfc8280>.

   [Roadmap]  American National Standards Institute (ANSI) Unmanned
              Aircraft Systems Standardization Collaborative (UASSC),
              "Standardization Roadmap for Unmanned Aircraft Systems
              draft v2.0", April 2020, <https://share.ansi.org/Shared
              Documents/Standards Activities/UASSC/

   [Stranger] Heinlein, R.A., "Stranger in a Strange Land", June 1961.

   [WG105]    EUROCAE, "WG-105 draft Minimum Operational Performance
              Standards (MOPS) for Unmanned Aircraft System (UAS)
              Electronic Identification", June 2020.

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Appendix A.  Discussion and Limitations

   This document is largely based on the process of one SDO, ASTM.
   Therefore, it is tailored to specific needs and data formats of this
   standard.  Other organizations, for example in EU, do not necessary
   follow the same architecture.

   The need for drone ID and operator privacy is an open discussion
   topic.  For instance, in the ground vehicular domain each car carries
   a publicly visible plate number.  In some countries, for nominal cost
   or even for free, anyone can resolve the identity and contact
   information of the owner.  Civil commercial aviation and maritime
   industries also have a tradition of broadcasting plane or ship ID,
   coordinates and even flight plans in plain text.  Community networks
   such as OpenSky and Flightradar use this open information through
   ADS-B to deploy public services of flight tracking.  Many researchers
   also use these data to perform optimization of routes and airport
   operations.  Such ID information should be integrity protected, but
   not necessarily confidential.

   In civil aviation, aircraft identity is broadcast by a device known
   as transponder.  It transmits a four-digit squawk code, which is
   assigned by a traffic controller to an airplane after approving a
   flight plan.  There are several reserved codes such as 7600 which
   indicate radio communication failure.  The codes are unique in each
   traffic area and can be re-assigned when entering another control
   area.  The code is transmitted in plain text by the transponder and
   also used for collision avoidance by a system known as Traffic alert
   and Collision Avoidance System (TCAS).  The system could be used for
   UAS as well initially, but the code space is quite limited and likely
   to be exhausted soon.  The number of UAS far exceeds the number of
   civil airplanes in operation.

   The ADS-B system is utilized in civil aviation for each "ADS-B Out"
   equipped airplane to broadcast its ID, coordinates and altitude for
   other airplanes and ground control stations.  If this system is
   adopted for drone IDs, it has additional benefit with backward
   compatibility with civil aviation infrastructure; then, pilots and
   dispatchers will be able to see UA on their control screens and take
   those into account.  If not, a gateway translation system between the
   proposed drone ID and civil aviation system should be implemented.
   Again, system saturation due to large numbers of UAS is a concern.

   Wi-Fi and Bluetooth are two wireless technologies currently
   recommended by ASTM specifications due to their widespread use and
   broadcast nature.  However, those have limited range (max 100s of
   meters) and may not reliably deliver UAS ID at high altitude or
   distance.  Therefore, a study should be made of alternative

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   technologies from the telecom domain (WiMax, 5G) or sensor networks
   (Sigfox, LORA).  Such transmission technologies can impose additional
   restrictions on packet sizes and frequency of transmissions, but
   could provide better energy efficiency and range.  In civil aviation,
   Controller-Pilot Data Link Communications (CPDLC) is used to transmit
   command and control between the pilots and ATC.  It could be
   considered for UAS as well due to long range and proven use despite
   its lack of security [cpdlc].

   L-band Digital Aeronautical Communications System (LDACS) is being
   standardized by ICAO and IETF for use in future civil aviation
   [I-D.maeurer-raw-ldacs].  It provides secure communication,
   positioning and control for aircraft using a dedicated radio band.
   It should be analyzed as a potential provider for UAS RID as well.
   This will bring the benefit of a global integrated system creating a
   global airspace use awareness.


   The work of the FAA's UAS Identification and Tracking (UAS ID)
   Aviation Rulemaking Committee (ARC) is the foundation of later ASTM
   [F3411-19] and IETF DRIP efforts.  The work of Gabriel Cox, Intel
   Corp. and their Open Drone ID collaborators opened UAS RID to a wider
   community.  The work of ASTM F38.02 in balancing the interests of
   diverse stakeholders is essential to the necessary rapid and
   widespread deployment of UAS RID.  IETF volunteers who have
   extensively reviewed or otherwise contributed to this document
   include Amelia Andersdotter, Carsten Bormann, Mohamed Boucadair,
   Toerless Eckert, Susan Hares, Mika Jarvenpaa, Daniel Migault,
   Alexandre Petrescu, Saulo Da Silva and Shuai Zhao.

Authors' Addresses

   Stuart W. Card (editor)
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America

   Email: stu.card@axenterprize.com

   Adam Wiethuechter
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America

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   Email: adam.wiethuechter@axenterprize.com

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI 48237
   United States of America

   Email: rgm@labs.htt-consult.com

   Andrei Gurtov
   Linköping University
   SE-58183 Linköping

   Email: gurtov@acm.org

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