DRIP                                                        R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: 21 September 2020                               A. Wiethuechter
                                                           AX Enterprize
                                                           20 March 2020

                        Crowd Sourced Remote ID


   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 multi-lateration 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
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   This Internet-Draft will expire on 21 September 2020.

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   extracted from this document must include Simplified BSD License text
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     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 . . . . . . . . . . . . . . . . . . .   8
     5.2.  The CS-RID B-RID Proxy Message  . . . . . . . . . . . . .   9
       5.2.1.  CS-RID ID . . . . . . . . . . . . . . . . . . . . . .   9
     5.3.  CS-RID Finder Registration  . . . . . . . . . . . . . . .   9
     5.4.  CS-RID SDSP Response  . . . . . . . . . . . . . . . . . .  10
     5.5.  CS-RID Location Update  . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     7.1.  Privacy Concerns  . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   10. Informative References  . . . . . . . . . . . . . . . . . . .  11
   Appendix A.  Using LIDAR for UA location  . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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 requriments that CAAs are placing on Network Remote ID

   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

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   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 there 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
   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

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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",
   "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

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

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

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

      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.

      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.

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

      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

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      individual who has observed an UA and wishes to know something
      about it, starting with its RID.

      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.

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

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

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

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

      Unmanned Aircraft.  In this document UA's are typically though of
      as drones of commerical or military variety.  This is a very
      strict definition which can be relaxed to include any and all
      aircraft that are unmanned.

      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.

      UAS Traffic Management.  A "traffic management" ecosystem for

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      uncontrolled operations that is separate from, but complementary
      to, the FAA's Air Traffic Management (ATM) system.

      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

   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.

   *  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.

   *  B-RID can also be used by the UA to assist in Detect and Avoid

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

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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

   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 behaviour 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.

   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.

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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

   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].  COSE [RFC8152]
   may be used for CS-RID MAC and COAP [RFC7252] for the CS-RID

   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)




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

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

            (   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.

5.3.  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.

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   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

   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:

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

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.

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.

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

6.  IANA Considerations


7.  Security Considerations


7.1.  Privacy Concerns


8.  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.

9.  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>.

10.  Informative References

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

   [FAA-NPRM] Federal (US) Aviation Authority, "FAA Remote ID Notice of
              Proposed Rule Making", December 2019,

              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HIT Registries", Work in Progress, Internet-

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              Draft, draft-moskowitz-hip-hhit-registries-02, 9 March
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-

              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HITs for HIPv2", Work in Progress, Internet-
              Draft, draft-moskowitz-hip-hierarchical-hit-04, 3 March
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,

   [RFC5238]  Phelan, T., "Datagram Transport Layer Security (DTLS) over
              the Datagram Congestion Control Protocol (DCCP)",
              RFC 5238, DOI 10.17487/RFC5238, May 2008,

   [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,

   [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,

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,

              Wiethuechter, A., Card, S., and R. Moskowitz, "TM-RID
              Authentication Formats", Work in Progress, Internet-Draft,
              draft-wiethuechter-tmrid-auth-05, 18 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

   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

   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?

Authors' Addresses

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

   Email: rgm@labs.htt-consult.com

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

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   United States of America

   Email: stu.card@axenterprize.com

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

   Email: adam.wiethuechter@axenterprize.com

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