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Versions: (draft-moskowitz-tmrid-crowd-sourced-rid) 00 01 02 03 04

DRIP                                                        R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: November 21, 2020                               A. Wiethuechter
                                                           AX Enterprize
                                                                 S. Zhao
                                                                 Tencent
                                                             H. Birkholz
                                                          Fraunhofer SIT
                                                            May 20, 2020


                        Crowd Sourced Remote ID
               draft-moskowitz-drip-crowd-sourced-rid-04

Abstract

   This document describes using the ASTM Broadcast Remote ID (B-RID)
   specification in a "crowd sourced" smart phone environment to provide
   much of the FAA mandated Network Remote ID (N-RID) functionality.
   This crowd sourced B-RID data will use multilateration to add a level
   of reliability in the location data on the Unmanned Aircraft (UA).
   The crowd sourced environment will also provide a monitoring coverage
   map to authorized observers.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on November 21, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Draft Status  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   4
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Space . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Meeting the needs of Network ID . . . . . . . . . . . . .   6
     3.2.  Advantages of Broadcast Remote ID . . . . . . . . . . . .   6
     3.3.  Trustworthiness of Proxied Data . . . . . . . . . . . . .   7
     3.4.  Defense against fraudulent RID Messages . . . . . . . . .   7
   4.  The Finder - SDSP Security Relationship . . . . . . . . . . .   7
     4.1.  The Finder Map  . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Managing Finders  . . . . . . . . . . . . . . . . . . . .   8
   5.  The CS-RID Messages . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  CS-RID MESSAGE TYPE . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  CDDL description for CS-RID message type  . . . . . .   9
     5.2.  The CS-RID B-RID Proxy Message  . . . . . . . . . . . . .  11
       5.2.1.  CS-RID ID . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.2.  CDDL description for CS-RID B-RID Proxy Message . . .  12
     5.3.  CS-RID Finder Registration  . . . . . . . . . . . . . . .  13
       5.3.1.  CDDL description for Finder Registration  . . . . . .  14
     5.4.  CS-RID SDSP Response  . . . . . . . . . . . . . . . . . .  14
       5.4.1.  CDDL description for SDSP Response  . . . . . . . . .  15
     5.5.  CS-RID Location Update  . . . . . . . . . . . . . . . . .  15
       5.5.1.  CDDL description for Location Update  . . . . . . . .  16
   6.  The Full CS-RID CDDL specification  . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     8.1.  Privacy Concerns  . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Using LIDAR for UA location  . . . . . . . . . . . .  21
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21




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1.  Introduction

   This document defines a mechanism to capture the ASTM Broadcast
   Remote ID messages (B-RID) [F3411-19] on any Internet connected
   device that receives them and can forward them to the SDSP(s)
   responsible for the geographic area the UA and receivers are in.
   This will create a ecosystem that will meet most if not all data
   collection requirements that CAAs are placing on Network Remote ID
   (N-RID).

   These Internet connected devices are herein called "Finders", as they
   find UAs by listening for B-RID messages.  The Finders are B-RID
   forwarding proxies.  Their potentially limited spacial view of RID
   messages could result in bad decisions on what messages to send to
   the SDSP and which to drop.  The SDSP will make any filtering
   decisions in what it forwards to the UTM(s).

   Finders can be smartphones, tablets, connected cars, or any computing
   platform with Internet connectivity that can meet the requirements
   defined in this document.  It is not expected, nor necessary, that
   Finders have any information about a UAS beyond the content in the
   B-RID messages.

   Finders MAY only need a loose association with the SDSP(s).  They may
   only have the SDSP's Public Key and FQDN.  It would use these, along
   with the Finder's Public Key to use ECIES, or other security methods,
   to send the messages in a secure manner to the SDSP.  The SDSP MAY
   require a stronger relationship to the Finders.  This may range from
   the Finder's Public Key being registered to the SDSP with other
   information so that the SDSP has some level of trust in the Finders
   to requiring transmissions be sent over long-lived transport
   connections like ESP or DTLS.

   This document has minimal information about the actions of SDSPs.  In
   general the SDSP is out of scope of this document.  That said, the
   SDSPs should not simply proxy B-RID messages to the UTM(s).  They
   should perform some minimal level of filtering and content checking
   before forwarding those messages that pass these tests in a secure
   manner to the UTM(s).

   The SDSPs are also capable of maintaining a monitoring map, based on
   location of active Finders.  UTMs may use this information to notify
   authorized observers of where this is and there is not monitoring
   coverage.  They may also use this information of where to place pro-
   active monitoring coverage.

   An SDSP SHOULD only forward Authenticated B-RID messages like those
   defined in [tmrid-auth] to the UTM(s).  Further, the SDSP SHOULD



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   validate the Remote ID (RID) and the Authentication signature before
   forwarding anything from the UA.

   When 3 or more Finders are reporting to an SDSP on a specific UA, the
   SDSP is in a unique position to perform multilateration on these
   messages and compute the Finder's view of the UA location to compare
   with the UA Location/Vector messages.  This check against the UA's
   location claims is both a validation on the UA's reliability as well
   as the trustworthiness of the Finders.  Other than providing data to
   allow for multilateration, this SDSP feature is out of scope of this
   document.

1.1.  Draft Status

   This draft is still incomplete.  New features are being added as
   capabilities are researched.  The actual message formats also still
   need work.

2.  Terms and Definitions

2.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  Definitions

   B-RID:
      Broadcast Remote ID.  A method of sending RID messages as 1-way
      transmissions from the UA to any Observers within radio range.

   CAA:
      Civil Aeronautics Administration.  An example is the Federal
      Aviation Administration (FAA) in the United States of America.

   DAA:
      Detect and Avoid.  The process of a UA detecting obstacles, like
      other UAs and taking the necessary evasive action.

   ECIES:
      Elliptic Curve Integrated Encryption Scheme.  A hybrid encryption
      scheme which provides semantic security against an adversary who
      is allowed to use chosen-plaintext and chosen-ciphertext attacks.

   GCS:



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      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.

   Finder:
      In Internet connected device that can receive B-RID messages and
      forward them to a UTM.

   Observer:
      Referred to in other UAS documents as a "user", but there are also
      other classes of RID users, so we prefer "observer" to denote an
      individual who has observed an UA and wishes to know something
      about it, starting with its RID.

   Multilateration:
      Multilateration (more completely, pseudo range multilateration) is
      a navigation and surveillance technique based on measurement of
      the times of arrival (TOAs) of energy waves (radio, acoustic,
      seismic, etc.) having a known propagation speed.

   NETSP:
      Network RID Service Provider.  USS receiving Network RID messages
      from UAS (UA or GCS), storing for a short specified time, making
      available to NETDP.

   NETDP:
      Network RID Display Provider.  Entity (might be USS) aggregating
      data from multiple NETSPs to answer query from observer (or other
      party) desiring Situational Awareness of UAS operating in a
      specific airspace volume.

   N-RID:
      Network Remote ID.  A method of sending RID messages via the
      Internet connection of the UAS directly to the UTM.

   RID:
      Remote ID.  A unique identifier found on all UA to be used in
      communication and in regulation of UA operation.

   SDSP:
      Supplemental Data Service Provider.  Entity providing information
      that is allowed, but not required to be present in the UTM system.

   UA:
      Unmanned Aircraft.  In this document UA's are typically though of
      as drones of commercial or military variety.  This is a very




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      strict definition which can be relaxed to include any and all
      aircraft that are unmanned.

   UAS:
      Unmanned Aircraft System.  Composed of Unmanned Aircraft and 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
      the control station.

   UTM:
      UAS Traffic Management.  A "traffic management" ecosystem for
      uncontrolled operations that is separate from, but complementary
      to, the FAA's Air Traffic Management (ATM) system.

   USS:
      UAS Service Supplier.  Provide UTM 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.  (From FAA UTM
      ConOps V1, May 2018).

3.  Problem Space

3.1.  Meeting the needs of Network ID

   The Federal (US) Aviation Authority (FAA), in the December 31, 2019
   Remote ID Notice of Proposed Rulemaking [FAA-NPRM], is requiring
   "Standard" and "Limited" Remote ID.  Standard is when the UAS
   provides both Network and Broadcast RID.  Limited is when the UAS
   provides only Network RID.  The FAA has dropped their previous
   position on allowing for only Broadcast RID.  We can guess as to
   their reasons; they are not spelled out in the NPRM.  It may be that
   just B-RID does not meet the FAA's statutory UA tracking
   responsibility.

   The UAS vendors have commented that N-RID places considerable demands
   on currently used UAS.  For some UAS like RC planes, meaningful N-RID
   (via the Pilot's smartphone) are of limited value.  A mechanism that
   can augment B-RID to provide N-RID would help all members of the UAS
   environment to provide safe operation and allow for new applications.

3.2.  Advantages of Broadcast Remote ID

   B-RID has its advantages over N-RID.






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   o  B-RID can more readily be implemented directly in the UA.  N-RID
      will more frequently be provided by the GCS or a pilot's Internet
      connected device.

      *  If Command and Control (C2) is bi-directional over a direct
         radio connection, B-RID could be a straight-forward addition.

      *  Small IoT devices can be mounted on UA to provide B-RID.

   o  B-RID can also be used by the UA to assist in Detect and Avoid
      (DAA).

   o  B-RID is available to observers even in situations with no
      Internet like natural disaster situations.

3.3.  Trustworthiness of Proxied Data

   When a proxy is introduced in any communication protocol, there is a
   risk of corrupted data and DOS attacks.

   The Finders, in their role as proxies for B-RID, are authenticated to
   the SDSP (see Section 4).  The SDSP can compare the information from
   multiple Finders to isolate a Finder sending fraudulent information.
   SDSPs can additionally verify authenticated messages that follow
   [tmrid-auth].

   The SPDP can manage the number of Finders in an area (see
   Section 4.2) to limit DOS attacks from a group of clustered Finders.

3.4.  Defense against fraudulent RID Messages

   The strongest defense against fraudulent RID messages is to focus on
   [tmrid-auth] conforming messages.  Unless this behavior is mandated,
   SPDPs will have to use assorted algorithms to isolate messages of
   questionable content.

4.  The Finder - SDSP Security Relationship

   The SDSP(s) and Finders SHOULD use EDDSA [RFC8032] keys as their
   trusted Identities.  The public keys SHOULD be registered
   Hierarchical HITS, [hierarchical-hit] and [hhit-registries].

   The SDSP uses some process (out of scope here) to register the
   Finders and their EDDSA Public Key.  During this registration, the
   Finder gets the SDSP's EDDSA Public Key.  These Public Keys allow for
   the following options for authenticated messaging from the Finder to
   the SDSP.




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   1.  ECIES can be used with a unique nonce to authenticate each
       message sent from a Finder to the SDSP.

   2.  ECIES can be used at the start of some period (e.g. day) to
       establish a shared secret that is then used to authenticate each
       message sent from a Finder to the SDSP sent during that period.

   3.  HIPv2 [RFC7401] can be used to establish a session secret that is
       then used with ESP [RFC4303] to authenticate each message sent
       from a Finder to the SDSP.

   4.  DTLS [RFC5238] can be used to establish a secure connection that
       is then used to authenticate each message sent from a Finder to
       the SDSP.

4.1.  The Finder Map

   The Finders are regularly providing their SDSP with their location.
   This is through the B-RID Proxy Messages and Finder Location Update
   Messages.  With this information, the SDSP can maintain a monitoring
   map.  That is a map of where there Finder coverage.

4.2.  Managing Finders

   Finder density will vary over time and space.  For example, sidewalks
   outside an urban train station can be packed with pedestrians at rush
   hour, either coming or going to their commute trains.  An SDSP may
   want to proactively limit the number of active Finders in such
   situations.

   Using the Finder mapping feature, the SDSP can instruct Finders to
   NOT proxy B-RID messages.  These Finders will continue to report
   their location and through that reporting, the SDSP can instruct them
   to again take on the proxying role.  For example a Finder moving
   slowly along with dozens of other slow-moving Finders may be
   instructed to suspend proxying.  Whereas a fast-moving Finder at the
   same location (perhaps a connected car or a pedestrian on a bus)
   would not be asked to suspend proxying as it will soon be out of the
   congested area.

5.  The CS-RID Messages

   The CS-RID messages between the Finders and the SDSPs primarily
   support the proxy role of the Finders in forwarding the B-RID
   messages.  There are also Finder registration and status messages.

   CS-RID information is represented in CBOR [RFC7049].  The CDDL
   [RFC8610] specification is used for CS-RID message description



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   CS-RID MAC and COAP [RFC7252] for the CS-RID protocol.

   The following is a general representation of the content in the CS-
   RID messages.

     (
       CS-RID MESSAGE TYPE,
       CS-RID MESSAGE CONTENT,
       CS-RID MAC
     )

   The CS-RID MESSAGE CONTENT varies by MESSAGE TYPE.

5.1.  CS-RID MESSAGE TYPE

   The CS-RID MESSAGE TYPE is defined in Figure 1:

     Number   CS-RID Message Type
     ------   -----------------
     0        Reserved
     1        B-RID Forwarding
     2        Finder Registration
     3        SDSP Response
     4        Finder Location

                                 Figure 1

5.1.1.  CDDL description for CS-RID message type

   The overall CS-RID CDDL description is structured in Figure 2.





















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   CSRID_Object = {
     application-context,
     info                => info_message,
     proxy_message       => broadcast_rid_proxy_message,
     finder_registration => finder_registration_message,
     sdsp_response       => sdsp_response_message,
     location_update     => location_update_message,
   }

   info_message = {
     common_message_members,
     message_content => tstr,
   }

   common_message_members = (
     message_type  => message_types,
     mac_address   => #6.37(bstr),
   )

   message_types = &(
     Reserved            : 0,
     BRD                 : 1,
     Finder-Registration : 2,
     SDSP-Response       : 3,
     Finder-Location     : 4,
   )

                                 Figure 2

   The application context rule is defined in Figure 3 for CS-RID
   application identification and version negotiation.

   application-context = (
     application => "DRIP-CSRID",
     ? version => uint .size(1..2),
   )

                                 Figure 3

   The predefined CDDL text string labels (author note: for JSON
   currently, will move to CBOR uint keys in upcoming versions) used in
   the specification is listed in Figure 4.









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   application           = "application"
   version               = "version"
   info                  = "message_info"
   proxy_message         = "proxy_message-type"
   finder_registration   = "finder_registration"
   sdsp_response         = "sdsp_response"
   location_update       = "location_update"
   rid                   = "id"
   message_type          = "message_type"
   mac_address           = "mac_address"
   message_content       = "message_content"
   timestamp             = "timestamp"
   gps                   = "gps"
   radio_type            = "radio_type"
   broadcast_mac_address = "broadcast_mac_address"
   broadcast_message     = "broadcast_message"
   sdsp_id               = "sdsp_id"
   proxy_status_type     = "proxy_status_type"
   update_interval       = "update_interval"

                                 Figure 4

5.2.  The CS-RID B-RID Proxy Message

   The Finders add their own information to the B-RID messages,
   permitting the SDSP(s) to gain additional knowledge about the UA(s).
   The RID information is the B-RID message content plus the MAC
   address.  The MAC address is critical, as it is the only field that
   links a UA's B-RID messages together.  Only the ASTM Basic ID Message
   and possibly the Authentication Message contain the UAS ID field.

   The Finders add an SDSP assigned ID, a 64 bit timestamp, GPS
   information, and type of B-RID media to the B-RID message.  Both the
   timestamp and GPS information are for when the B-RID message(s) were
   received, not forwarded to the SDSP.  All this content is MACed using
   a key shared between the Finder and SDSP.

   The following is a representation of the content in the CS-RID
   messages.












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     (
       CS-RID MESSAGE TYPE,
       CS-RID ID,
       RECEIVE TIMESTAMP,
       RECEIVE GPS,
       RECEIVE RADIO TYPE,
       B-RID MAC ADDRESS,
       B-RID MESSAGE,
       CS-RID MAC
     )

5.2.1.  CS-RID ID

   The CS-RID ID is the ID recognized by the SDSP.  This may be an HHIT
   Hierarchical HITs [hierarchical-hit], or any ID used by the SDSP.

5.2.2.  CDDL description for CS-RID B-RID Proxy Message

   The broadcast CS-RID proxy CDDL is defined in Figure 5
































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   broadcast_rid_proxy_message = {
     common_message_members,
     rid                   => tstr,
     timestamp             => tdate,
     gps                   => gps-coordinates,
     radio_type            => radio_types,
     broadcast_mac_address => #6.37(bstr),
     broadcast_message     => #6.37(bstr),
   }

   radio_types = &(
     EFL : 0,
     VLF : 1,
     LF  : 2,
     MF  : 3,
     HF  : 4,
     HF  : 5,
     VHF : 6,
     UHF : 7,
     SHF : 8,
     EHF : 9,
   )

   gps-coordinates = [
     latitude : float,
     longitude: float,
   ]

                                 Figure 5

5.3.  CS-RID Finder Registration

   The CS-RID Finder MAY use HIPv2 [RFC7401] with the SDSP to establish
   a Security Association and a shared secret to use for the CS-RID MAC
   generation.  In this approach, the HIPv2 mobility functionality and
   ESP [RFC4303] support are not used.

   When HIPv2 is used as above, the Finder Registration is a SDSP "wake
   up".  It is sent prior to the Finder sending any proxied B-RID
   messages to ensure that the SDSP is able to receive and process the
   messages.

   In this usage, the CS-RID is the Finder HIT.  If the SDSP has lost
   state with the Finder, it initiates the HIP exchange with the Finder
   to reestablish HIP state and a new shared secret for the CS-RID B-RID
   Proxy Messages.  In this case the Finder Registration Message is:





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     (
       CS-RID MESSAGE TYPE,
       CS-RID ID,
       CS-RID TIMESTAMP,
       CS-RID GPS,
       CS-RID MAC
     )

5.3.1.  CDDL description for Finder Registration

   The CDDL for CS-RID Finder Registration is defined in Figure 6

   finder_registration_message = {
     common_message_members,
     rid       => tstr,
     timestamp => tdate,
     gps       => gps-coordinates,
   }

   gps-coordinates = [
     latitude : float,
     longitude: float,
   ]

                                 Figure 6

5.4.  CS-RID SDSP Response

   The SDSP MAY respond to any Finder messages to instruct the Finder on
   its behavior.

     (
       CS-RID MESSAGE TYPE,
       SDSP ID,
       CS-RID ID,
       CS-RID PROXY STATUS,
       CS-RID UPDATE INTERVAL,
       CS-RID MAC
     )

   The Proxy Status instructs the Finder if it should actively proxy
   B-RID messages, or suspend proxying and only report its location.

   The Update Interval is the frequency that the Finder SHOULD notify
   the SDSP of its current location using the Location Update message.






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5.4.1.  CDDL description for SDSP Response

   The CDDL for CS-RID SDSP response is defined in Figure 7

   sdsp_response_message = {
     common_message_members,
     sdsp_id           => tstr,
     rid               => tstr,
     proxy_status_type => proxy_status_types,
     update_interval   => uint,
   }

   gps-coordinates = [
     latitude : float,
     longitude: float,
   ]

   proxy_status_types = &(
     0: "forward",
     1: "reverse",
     2: "bi-directional",
   )

                                 Figure 7

5.5.  CS-RID Location Update

   The Finder SHOULD provide regular location updates to the SDSP.  The
   interval is based on the Update Interval from Section 5.4 plus a
   random slew less than 1 second.  The Location Update message is only
   sent when no other CS-RID messages, containing the Finder's GPS
   location, have been sent since the Update Interval.

   If the Finder has not recieved a SDSP Registration Response, a
   default of 5 minutes is used for the Update Interval.

     (
       CS-RID MESSAGE TYPE,
       CS-RID ID,
       CS-RID TIMESTAMP,
       CS-RID GPS,
       CS-RID MAC
     )








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5.5.1.  CDDL description for Location Update

   The CDDL for CS-RID Location update is defined in Figure 8

   location_update_message = {
     common_message_members,
     rid       => tstr,
     timestamp => tdate,
     gps       => gps-coordinates,
   }

   gps-coordinates = [
     latitude : float,
     longitude: float,
   ]

                                 Figure 8

6.  The Full CS-RID CDDL specification

   <CODE BEGINS>
   ; CDDL specification for Crowd source RID
   ; It specifies a collection of CS message types
   ;

   ;
   ; The CSRID overall data structure

   CSRID_Object = {
       application-context,
       info =>  info_message,
       proxy_message => broadcast_rid_proxy_message,
       finder_registration => finder_registration_message,
       sdsp_response => sdsp_response_message,
       location_update => location_update_message,
   }

   ;
   ; Application context: general information about CSRID message

   application-context = (
       application => "DRIP-CSRID", ; TBD: consider CBOR tag
       ? version => uint .size(1..2),
   )

   ; These members are include in every message
   common_message_members = (
       message_type => message_types,



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       mac_address => #6.37(bstr),
   )

   ;
   ; CSRID message general information

   info_message = {
       common_message_members,
       message_content => tstr,
   }

   broadcast_rid_proxy_message = {
       common_message_members,
       rid => tstr,
       timestamp => tdate,
       gps => gps-coordinates,
       radio_type => radio_types,
       broadcast_mac_address => #6.37(bstr)
       broadcast_message => #6.37(bstr)
   }

   finder_registration_message = {
       common_message_members,
       rid => tstr,
       timestamp => tdate,
       gps => gps-coordinates,
   }

   sdsp_response_message = {
       common_message_members,
       sdsp_id => tstr,
       rid => tstr,
       proxy_status_type => proxy_status_types,
       update_interval => uint,
   }

   location_update_message = {
       common_message_members,
       rid => tstr,
       timestamp => tdate,
       gps => gps-coordinates,
   }

   ;
   ; Common rule definition

   message_types = &(
       Reserved            : 0,



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       BRD                 : 1,
       Finder-Registration : 2,
       SDSP-Response       : 3,
       Finder-Location     : 4,
   )

   gps-coordinates = [
       lat: float,
       long: float,
   ]

   ; Radio types, choose from one of radio_types (required)
   radio_types = &(
       EFL : 0,
       VLF : 1,
       LF  : 2,
       MF  : 3,
       HF  : 4,
       HF  : 5,
       VHF : 6,
       UHF : 7,
       SHF : 8,
       EHF : 9,
   )

   proxy_status_types = &(
       0: "forward",
       1: "reverse",
       2: "bi",
   )

   ;
   ; JSON label names

   application = "application"
   version = "version"
   info = "message_info"
   proxy_message = "proxy_message-type"
   finder_registration = "finder_registration"
   sdsp_response = "sdsp_response"
   location_update = "location_update"
   rid = "id"
   message_type = "message_type"
   mac_address = "mac_address"
   message_content = "message_content"
   timestamp = "timestamp"
   gps = "gps"
   radio_type = "radio_type"



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   broadcast_mac_address = "broadcast_mac_address"
   broadcast_message = "broadcast_message"
   sdsp_id = "sdsp_id"
   proxy_status_type = "proxy_status_type"
   update_interval = "update_interval"

   <CODE ENDS>

7.  IANA Considerations

   TBD

8.  Security Considerations

   TBD

8.1.  Privacy Concerns

   TBD

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

9.2.  Informative References

   [F3411-19]
              ASTM International, "Standard Specification for Remote ID
              and Tracking", February 2020,
              <http://www.astm.org/cgi-bin/resolver.cgi?F3411>.






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   [FAA-NPRM]
              Federal (US) Aviation Authority, "FAA Remote ID Notice of
              Proposed Rule Making", December 2019,
              <https://www.regulations.gov/docket?D=FAA-2019-1100>.

   [hhit-registries]
              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HIT Registries", draft-moskowitz-hip-hhit-
              registries-02 (work in progress), March 2020.

   [hierarchical-hit]
              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HITs for HIPv2", draft-moskowitz-hip-
              hierarchical-hit-05 (work in progress), May 2020.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC5238]  Phelan, T., "Datagram Transport Layer Security (DTLS) over
              the Datagram Congestion Control Protocol (DCCP)",
              RFC 5238, DOI 10.17487/RFC5238, May 2008,
              <https://www.rfc-editor.org/info/rfc5238>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7401]  Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
              Henderson, "Host Identity Protocol Version 2 (HIPv2)",
              RFC 7401, DOI 10.17487/RFC7401, April 2015,
              <https://www.rfc-editor.org/info/rfc7401>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [tmrid-auth]
              Wiethuechter, A., Card, S., and R. Moskowitz, "TM-RID
              Authentication Formats", draft-wiethuechter-tmrid-auth-05
              (work in progress), February 2020.




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Appendix A.  Using LIDAR for UA location

   If the Finder has LIDAR or similar detection equipment (e.g. on a
   connected car) that has full sky coverage, the Finder can use this
   equipment to locate UAs in its airspace.  The Finder would then be
   able to detect non-participating UAs.  A non-participating UA is one
   that the Finder can "see" with the LIDAR, but not "hear" any B-RID
   messages.

   These Finders would then take the LIDAR data, construct appropriate
   B-RID messages, and forward them to the SPDP as any real B-RID
   messages.  There is an open issue as what to use for the actual
   RemoteID and MAC address.

   The SDSP would do the work of linking information on a non-
   participating UA that it has received from multiple Finders with
   LIDAR detection.  In doing so, it would have to select a RemoteID to
   use.

   A seemingly non-participating UA may actually be a UA that is beyond
   range for its B-RID but in the LIDAR range.

   This would provide valuable information to SDSPs to forward to UTMs
   on potential at-risk situations.

   At this time, research on LIDAR and other detection technology is
   needed.  there are full-sky LIDAR for automotive use with ranges
   varying from 20M to 250M.  Would more than UA location information be
   available?  What information can be sent in a CS-RID message for such
   "unmarked" UAs?

Acknowledgments

   The Crowd Sourcing idea in this document came from the Apple "Find My
   Device" presentation at the International Association for
   Cryptographic Research's Real World Crypto 2020 conference.

Authors' Addresses

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI  48237
   USA

   Email: rgm@labs.htt-consult.com






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   Stuart W. Card
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY  13495
   USA

   Email: stu.card@axenterprize.com


   Adam Wiethuechter
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY  13495
   USA

   Email: adam.wiethuechter@axenterprize.com


   Shuai Zhao
   Tencent
   2747 Park Blvd
   Palo Alto, CA  94306
   USA

   Email: shuai.zhao@ieee.org


   Henk Birkholz
   Fraunhofer SIT
   Rheinstrasse 75
   Darmstadt  64295
   Germany

   Email: henk.birkholz@sit.fraunhofer.de

















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