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DRIP                                                        R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: 12 February 2021                                A. Wiethuechter
                                                           AX Enterprize
                                                               A. Gurtov
                                                    Linköping University
                                                          11 August 2020

                             UAS Remote ID


   This document describes the use of Hierarchical Host Identity Tags
   (HHITs) as a self-asserting and thereby trustable Identifier for use
   as the UAS Remote ID.  HHITs include explicit hierarchy to provide
   Registrar discovery for 3rd-party ID attestation.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 12 February 2021.

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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Hierarchical HITs as Remote ID  . . . . . . . . . . . . . . .   4
     3.1.  Hierarchy in ORCHID Generation  . . . . . . . . . . . . .   4
     3.2.  Hierarchical HIT Registry . . . . . . . . . . . . . . . .   4
     3.3.  Remote ID Authentication using HHITs  . . . . . . . . . .   5
   4.  UAS ID HHIT in DNS  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Other UTM uses of HHITs . . . . . . . . . . . . . . . . . . .   6
   6.  DRIP Requirements addressed . . . . . . . . . . . . . . . . .   6
   7.  ASTM Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
     9.1.  Hierarchical HIT Trust  . . . . . . . . . . . . . . . . .   7
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   7
   11. Informative References  . . . . . . . . . . . . . . . . . . .   8
   Appendix A.  EU U-Space RID Privacy Considerations  . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [drip-requirements] describes a UAS ID as a "unique (ID-4), non-
   spoofable (ID-5), and identify a registry where the ID is listed (ID-
   2)"; all within a 20 character Identifier (ID-1).

   This document describes the use of Hierarchical HITs (HHITs)
   [hierarchical-hit] as self-asserting and thereby a trustable
   Identifier for use as the UAS Remote ID.  HHITs include explicit
   hierarchy to provide Registrar discovery for 3rd-party ID

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   HITs are statistically unique through the cryptographic hash feature
   of second-preimage resistance.  The cryptographically-bound addition
   of the Hierarchy and thus HHIT Registries [hhit-registries] provide
   complete, global HHIT uniqueness.  This is in contrast to general IDs
   (e.g. a UUID or device serial number) as the subject in an X.509

   In a multi-CA PKI, a subject can occur in multiple CAs, possibly
   fraudulently.  CAs within the PKI would need to implement an approach
   to enforce assurance of uniqueness.

   Hierarchical HITs are valid, though non-routable, IPv6 addresses.  As
   such, they fit in many ways within various IETF technologies.

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

   See [drip-requirements] for common DRIP terms.

      Host Identity.  The public key portion of an asymmetric keypair
      used in HIP.

      Host Identity Protocol.  The origin of HI, HIT, and HHIT, required
      for DRIP.  Optional full use of HIP enables additional DRIP

      Hierarchical Host Identity Tag.  A HIT with extra hierarchical
      information not found in a standard HIT.

      Host Identity Tag.  A 128 bit handle on the HI.  HITs are valid
      IPv6 addresses.

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3.  Hierarchical HITs as Remote ID

   Hierarchical HITs are a refinement on the Host Identity Tag (HIT) of
   HIPv2 [RFC7401].  HHITs require a new ORCHID mechanism as described
   in [new-orchid].  HHITs for UAS ID also use the new EdDSA/SHAKE128
   HIT suite defined in [new-hip-crypto] (requirements GEN-2).  This
   hierarchy, cryptographically embedded within the HHIT, provides the
   information for finding the UA's HHIT registry (ID-3).

   The current ASTM [F3411-19] supports three types of UAS IDs, namely
   the [CTA2063A] serial number, CAA registration ID, and UTM-provided
   UUID session ID.  For HHITs to be used effectively as UAS IDs,
   F3411-19 SHOULD add HHIT as the fourth UAS ID type.

3.1.  Hierarchy in ORCHID Generation

   ORCHIDS, as defined in [RFC7343], do not cryptographically bind the
   IPv6 prefix nor the Orchid Generation Algorithm (OGA) ID to the hash
   of the HI.  The justification then was attacks against these fields
   are DoS attacks against protocols using them.

   HHITs, as defined in [new-orchid], cryptographically bind all content
   in the ORCHID though the hashing function.  Thus a recipient of a
   HHIT that has the underlying HI can directly act on all content in
   the HHIT.  This is especially important to using the hierarchy to
   find the HHIT Registry.

3.2.  Hierarchical HIT Registry

   HHITs are registered to Hierarchical HIT Domain Authorities (HDAs) as
   described in [hhit-registries].  This registration process ensures
   UAS ID global uniqueness (ID-4).  It also provides the mechanism to
   create UAS Public/Private data associated with the HHIT UAS ID (REG-1
   and REG-2).

   The 2 levels of hierarchy within the HHIT allows for CAAs to have
   their own Registered Assigning Authority (RAA) for their National Air
   Space (NAS).  Within the RAA, the CAAs can delegate HDAs as needed.
   There may be other RAAs allowed to operate within a given NAS; this
   is a policy decision by the CAA.

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3.3.  Remote ID Authentication using HHITs

   The EdDSA25519 Host Identity (HI) underlying the HHIT is used for the
   Message Wrapper, Sec 4.2 [drip-auth] (requirements GEN-2).  It and
   the HDA's HI/HHIT are used for the Auth Certificate, sec 5.1
   [drip-auth] (requirements GEN-3).  These messages also establish that
   the UA owns the HHIT and that no other UA can assert ownership of the
   HHIT (GEN-1).

   The number of HDAs authorized to register UAs within an NAS
   determines the size of the HDA credential cache a device processing
   the Offline Authentication.  This cache contains the HDA's HI/HHIT
   and HDA meta-data; it could be very small.


   There are 2 approaches for storing and retrieving the HHIT from DNS.
   These are:

   *  As FQDNs in the .aero TLD.

   *  Reverse DNS lookups as IPv6 addresses per [RFC8005].

   The HHIT can be used to construct an FQDN that points to the USS that
   has the Public/Private information for the UA (REG-1 and REG-2).  For
   example the USS for the HHIT could be found via the following.
   Assume that the RAA is 100 and the HDA is 50.  The PTR record is
   constructed as:

       100.50.hhit.uas.areo   IN PTR      foo.uss.areo.

   The individual HHITs are potentially too numerous (e.g. 63M) and
   dynamic to actually store in a signed, DNS zone.  Rather the USS
   would provide the HHIT detail response.

   The HHIT reverse lookup can be a standard IPv6 reverse look up, or it
   can leverage off the HHIT structure.  Assume that the RAA is 10 and
   the HDA is 20 and the HHIT is:


   An HHIT reverse lookup would be to is:


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5.  Other UTM uses of HHITs

   HHITs can be used extensively within the UTM architecture beyond UA
   ID (and USS in UA ID registration and authentication).  This includes
   a GCS HHIT ID.  It could use this if it is the source of Network
   Remote ID for securing the transport and for secure C2 transport

   Observers SHOULD have HHITs to facilitate UAS information retrieval
   (e.g., for authorization to private UAS data).  They could also use
   their HHIT for establishing a HIP connection with the UA Pilot for
   direct communications per authorization.  Further, they can be used
   by FINDER observers, [crowd-sourced-rid].

6.  DRIP Requirements addressed

   This document provides solutions to GEN 1 - 3, ID 1 - 5, and REG 1 -

7.  ASTM Considerations

   ASTM will need to make the following changes to the "UA ID" in the
   Basic Message:

   Type 4:
      This document UA ID of Hierarchical HITs (see Section 3).

8.  IANA Considerations


9.  Security Considerations

   The security considerations with Hierarchical HITs, most notably the
   short hash of the HI, are discussed in [hierarchical-hit].  The
   binding of the hierarchy to the hash of the HI is covered in

   Cryptographically Generated Addresses (CGAs) provide a unique
   assurance of uniqueness.  This is two-fold.  The address (in this
   case the UAS ID) is a hash of a public key and a Registry hierarchy
   naming.  Collision resistance (more important that it implied second-
   preimage resistance) makes it statistically challenging to attacks.
   A registration process as in HHIT Registries [hhit-registries]
   provides a level of assured uniqueness unattainable without mirroring
   this approach.

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   The second aspect of assured uniqueness is the digital signing
   process of the HHIT by the HI private key and the further signing of
   the HI public key by the Registry's key.  This completes the
   ownership process.  The observer at this point does not know WHAT
   owns the HHIT, but is assured, other than the risk of theft of the HI
   private key, that this UAS ID is owned by something and is properly

9.1.  Hierarchical HIT Trust

   The HHIT UAS RID in the ASTM Basic Message (the actual Remote ID
   message) does not provide any assertion of trust.  The best that
   might be done is 4 bytes truncated from a HI signing of the HHIT (the
   UA ID field is 20 bytes and a HHIT is 16).  It is in the ASTM
   Authentication Messages as defined in [drip-auth] that provide all of
   the actual ownership proofs.  These claims include timestamps to
   defend against replay attacks.  But in themselves, they do not prove
   which UA actually sent the message.  They could have been sent by a
   dog running down the street with a Broadcast Remote ID device
   strapped to its back.

   Proof of UA transmission comes when the Authentication Message
   includes proofs for the Location/Vector Message and the observer can
   see the UA or that information is validated by ground multilateration
   [crowd-sourced-rid].  Only then does an observer gain full trust in
   the HHIT Remote ID.

   HHIT Remote IDs obtained via the Network Remote ID path provides a
   different approach to trust.  Here the UAS SHOULD be securely
   communicating to the USS (see [drip-secure-nrid-c2]), thus asserting
   HHIT RID trust.

10.  Normative References

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

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

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              Draft, draft-moskowitz-hip-hierarchical-hit-05, 13 May
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-

              Moskowitz, R., Card, S., and A. Wiethuechter, "New
              Cryptographic Algorithms for HIP", Work in Progress,
              Internet-Draft, draft-moskowitz-hip-new-crypto-05, 26 July
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-

   [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>.

11.  Informative References

   [corus]    CORUS, "U-space Concept of Operations", September 2019,

              Moskowitz, R., Card, S., Wiethuechter, A., Zhao, S., and
              H. Birkholz, "Crowd Sourced Remote ID", Work in Progress,
              Internet-Draft, draft-moskowitz-drip-crowd-sourced-rid-04,
              20 May 2020, <https://tools.ietf.org/html/draft-moskowitz-

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

              Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP
              Authentication Formats", Work in Progress, Internet-Draft,
              draft-wiethuechter-drip-auth-03, 27 July 2020,

              Card, S., Wiethuechter, A., and R. Moskowitz, "Drone
              Remote Identification Protocol (DRIP) Requirements", Work
              in Progress, Internet-Draft, draft-card-drip-reqs-02, 20
              April 2020,

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              Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
              "Secure UAS Network RID and C2 Transport", Work in
              Progress, Internet-Draft, draft-moskowitz-drip-secure-
              nrid-c2-00, 6 April 2020, <https://tools.ietf.org/html/

              Moskowitz, R., Card, S., and A. Wiethuechter, "Using
              cSHAKE in ORCHIDs", Work in Progress, Internet-Draft,
              draft-moskowitz-orchid-cshake-01, 21 May 2020,

   [RFC7343]  Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
              Routable Cryptographic Hash Identifiers Version 2
              (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
              2014, <https://www.rfc-editor.org/info/rfc7343>.

   [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,

   [RFC8005]  Laganier, J., "Host Identity Protocol (HIP) Domain Name
              System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005,
              October 2016, <https://www.rfc-editor.org/info/rfc8005>.

Appendix A.  EU U-Space RID Privacy Considerations

   EU is defining a future of airspace management known as U-space
   within the Single European Sky ATM Research (SESAR) undertaking.
   Concept of Operation for EuRopean UTM Systems (CORUS) project
   proposed low-level Concept of Operations [corus] for UAS in EU.  It
   introduces strong requirements for UAS privacy based on European GDPR
   regulations.  It suggests that UAs are identified with agnostic IDs,
   with no information about UA type, the operators or flight
   trajectory.  Only authorized persons should be able to query the
   details of the flight with a record of access.

   Due to the high privacy requirements, a casual observer can only
   query U-space if it is aware of a UA seen in a certain area.  A
   general observer can use a public U-space portal to query UA details
   based on the UA transmitted "Remote identification" signal.  Direct
   remote identification (DRID) is based on a signal transmitted by the
   UA directly.  Network remote identification (NRID) is only possible
   for UAs being tracked by U-Space and is based on the matching the
   current UA position to one of the tracks.

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   The project lists "E-Identification" and "E-Registrations" services
   as to be developed.  These services can follow the privacy mechanism
   proposed in this document.  If an "agnostic ID" above refers to a
   completely random identifier, it creates a problem with identity
   resolution and detection of misuse.  On the other hand, a classical
   HIT has a flat structure which makes its resolution difficult.  The
   Hierarchical HITs provide a balanced solution by associating a
   registry with the UA identifier.  This is not likely to cause a major
   conflict with U-space privacy requirements, as the registries are
   typically few at a country level (e.g. civil personal, military, law
   enforcement, or commercial).


   Dr. Gurtov is an adviser on Cybersecurity to the Swedish Civil
   Aviation Administration.

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
   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

   Andrei Gurtov
   Linköping University

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   SE-58183 Linköping

   Email: gurtov@acm.org

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