DRIP                                                        R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: 24 April 2022                                   A. Wiethuechter
                                                           AX Enterprize
                                                               A. Gurtov
                                                    Linköping University
                                                         21 October 2021

                Secure UAS Network RID and C2 Transport


   This document provides the mechanisms for secure transport of
   Unmanned Aircraft System (UAS) Network Remote ID (N-RID) and Command-
   and-Control (C2) messaging.  Both HIP and DTLS based methods are

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   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Network Remote ID . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Network RID endpoints . . . . . . . . . . . . . . . . . .   4
       3.1.1.  N-RID from the UA . . . . . . . . . . . . . . . . . .   4
       3.1.2.  N-RID from the GCS  . . . . . . . . . . . . . . . . .   5
       3.1.3.  N-RID from the Operator . . . . . . . . . . . . . . .   5
     3.2.  UAS Identity  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Command and Control . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Securing MAVLink  . . . . . . . . . . . . . . . . . . . .   6
   5.  Secure Transports . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  HIPv2 for Secure Transport  . . . . . . . . . . . . . . .   6
     5.2.  DTLS for Secure Transport . . . . . . . . . . . . . . . .   7
     5.3.  Ciphers for Secure Transport  . . . . . . . . . . . . . .   7
     5.4.  HIP and DTLS contrasted and compared  . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document defines mechanisms to provide secure transport for
   Unmanned Aircraft System (UAS) ASTM Network Remote ID [F3411-19]
   (N-RID) and Command and Control (C2) messaging.

   A secure end-to-end transport for C2 is critical for UAS especially
   for Beyond Line of Sight (BLOS) operations.  It needs to provide data
   confidentiality, integrity, and authenticity (CIA).  Depending on the
   underlying network technology, this secure transport may need to
   manage IP address changes (IP mobility) for both the UA and GCS.

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   A secure end-to-end transport for N-RID (UAS to Network RID Service
   Provider (Net-RID SP)) also should provide full CIA.  It may seem
   that confidentiality is optional, as most of the information in N-RID
   is sent in the clear in Broadcast Remote ID (B-RID), but this is a
   potentially flawed analysis.  N-RID has evesdropping risks not in
   B-RID and may contain more sensitive information than B-RID.  The
   secure transport for N-RID should only need to manage IP address
   changes (IP mobility) for the UAS.

   Two options for secure transport are provided: HIPv2 [RFC7401] and
   DTLS 1.3 [DTLS-1.3-draft].  These options are generally defined and
   their applicability is compared and contrasted.  It is up to N-RID
   and C2 to select which is preferred for their situation.

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

   This document uses the terms defined in [drip-requirements].  The
   following new terms are used in the document:

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

      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.

3.  Network Remote ID

   The purpose/goal of Network Remote ID (N-RID) is to provide the UAS
   Traffic Management (UTM) UA situational awareness.  The data needed
   for this is already defined in [F3411-19], but a standard message
   format, protocol, and secure communications methodology are missing.
   This document will provide such an open standard.

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   The Broadcast Remote ID (B-RID) messages in [F3411-19] are sufficient
   to meet the needs of N-RID.  In particular, the Message Pack (Msg
   Type 0xF) is well suited, as this single message can send all the
   needed information.  Further, a UAS supporting B-RID will have
   minimal development to add N-RID support.

   This approach has the added advantage of being very compact,
   minimizing the N-RID communications cost.

3.1.  Network RID endpoints

   The FAA defines the Network Remote ID endpoints as a USS Network
   Service Provider (Net-RID SP) and the UAS.  Both of these are rather
   nebulous items and what they actually are will impact how
   communications flow between them.

   The Net-RID SP may be provided by the same entity serving as the UAS
   Service Provider (USS).  This simplifies a number of aspects of the
   N-RID communication flow.  An Operator is expected to register an
   operation with the USS.  If this is done via the GCS and the GCS is
   the source (directly acting as a gateway), this could set up the
   secure connection for N-RID.  The Net-RID SP is likely to be stable
   in the network, that is its IP address will not change during a
   mission.  This simplifies maintaining the N-RID communications.

   The UAS component in N-RID may be either the UA, GCS, or the
   Operator's Internet connected device (e.g. smartphone or tablet).  In
   all cases, mobility MUST be assumed.  That is the IP address of this
   end of the N-RID communication will change during an operation.  The
   N-RID mechanism MUST support this.  The UAS Identity for the secure
   connection may vary based on the UAS endpoint.

3.1.1.  N-RID from the UA

   Some UA will be equipped with direct Internet access.  These UA will
   also tend to have multiple radios for their Internet access (e.g.
   Cellular and WiFi).  Thus multi-homing with "make before break"
   behavior is needed.  This is on top of any IP address changes on any
   of the interfaces while in use.

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3.1.2.  N-RID from the GCS

   Many UA will lack direct Internet access, but their GCS may be so
   connected.  There are two sources for the GCS for the RID messages,
   both from the UA.  These are UA B-RID messages, or content from C2
   messages that the GCS converts to RID message format.  In either
   case, the GCS may be mobile with changing IP addresses.  The GCS may
   be in a fast moving ground device (e.g. delivery van), so it can have
   as mobility demanding connection needs as the UA.

3.1.3.  N-RID from the Operator

   Many UAS will have no Internet connectivity, but the UA is sending
   B-RID messages and the Operator has an Internet Connected device that
   is receiving these B-RID messages.  The Operator's device can act as
   the proxy for these messages, turning them into N-RID messages.

3.2.  UAS Identity

   The UA MAY use its RID if it is a HHIT [drip-uas-rid].  It may use
   some other Identity, based on the Net-RID SP policy.

   The GCS or Operator smart device may have a copy of the UA
   credentials and use them in the connection to the Net-RID SP.  In
   this case, they are indistinguishable from the UA as seen from the
   Net-RID SP.  Alternatively, they may use their own credentials with
   the Net-RID SP which would need some internal mechanism to tie that
   to the UA.

4.  Command and Control

   The Command and Control (C2) connection is between the UA and GCS.
   This is often this over a direct link radio.  Some times,
   particularly for BLOS, it is via Internet connections.  In either
   case C2 SHOULD be secure from eavesdropping and tampering.  For
   design and implementation consistency it is best to treat the direct
   link as a local link Internet connection and use constrained
   networking compression standards.

   Both the UA and GCS need to be treated as fully mobile in the IP
   networking sense.  Either one can have its IP address change and both
   could change at the same time (the double jump problem).  It is
   preferable to use a peer-to-peer (P2P) secure technology like HIPv2

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   Finally UA may also tend to have multiple radios for their C2
   communications.  Thus multi-homing with "make before break" behavior
   is needed.  This is on top of any IP address changes on any of the
   interfaces while in use.

4.1.  Securing MAVLink

   MAVLink [MAVLINK] is a commonly used protocol for C2.  Message
   authenticity was added in MAVLink 2 in the form of a SHA-256 (secret
   + message hash) left-truncated to 6 byte.  This does not follow HMAC
   [RFC2104] security recommendations, nor provides confidentiality.

   By following the security approach here, UAS C2 is superior to that
   currently provided within MAVlink.

5.  Secure Transports

   The raw N-RID and C2 messages will be wrapped in UDP.  These UDP
   packets will either be transported in ESP for the HIPv2 approach or
   DTLS application messages for DTLS.  In both cases header compression
   technologies SHOULD be used and negotiated based on policy.

   For IPv6 over both WiFi and Bluetooth (or any other radio link),
   Robust Header Compression (ROHC) [RFC5795] and/or Generic Header
   Compression (6LoWAN-HGC) [RFC7400] can significantly reduce the per
   packet transmission cost of IPv6.  For Bluetooth, there is also IPv6
   over Bluetooth LE [RFC7668] for more guidance.

   Local link (direct radio) C2 security is possible with the link's MAC
   layer security.  Both WiFi and Bluetooth link security can provide
   appropriate security, but this would not provide trustworthy multi-
   homed security.

5.1.  HIPv2 for Secure Transport

   HIP has already been used for C2 mobility, managing the ongoing
   connectivity over WiFi at start of an operation, switching to LTE
   once out of WiFi range, and returning to WiFi connectivity at the end
   of the operation.  This functionality is especially important for
   BLOS.  HHITs are already defined for RID, and need only be added to
   the GCS via a GCS Registration as part of the UAS to USS registration
   to be usedfor C2 HIP.

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   When the UA is the UAS endpoint for N-RID, and particularly when HIP
   is used for C2, HIP for N-RID simplifies protocol use on the UA.  The
   Net-RID SP endpoint may already support HIP if it is also the HHIT
   Registrar.  If the UA lacks any IP ability and the RID HHIT
   registration was done via the GCS or Operator device, then they may
   also be set for using HIP for N-RID.

   Further, double jump and multi-homing support is mandatory for C2
   mobility.  This is inherent in the HIP design.  The HIP address
   update can be improved with [hip-fast-mobility].

5.2.  DTLS for Secure Transport

   DTLS is a good fit for N-RID for any of the possible UAS endpoints.
   There are challenges in using it for C2.  To use DTLS for C2, the GCS
   will need to be the DTLS server.  How does it 'push' commands to the
   UA?  How does it reestablish DTLS security if state is lost?  And
   finally, how is the double jump scenario handled?

   All the above DTLS for C2 probably have solutions.  None of them are
   inherent in the DTLS design.

5.3.  Ciphers for Secure Transport

   The cipher choice for either HIP or DTLS depends, in large measure,
   on the UAS endpoint.  If the endpoint is computationally constrained,
   the cipher computations become important.  If any of the links are
   constrained or expensive, then the over-the-wire cost needs to be
   minimized.  AES-CCM and AES-GCM are the preferred, modern, AEAD

   For ESP with HIP [RFC7402], an additional 4 - 8 bytes can be trimmed
   by using the Implicit IV for ESP option [RFC8750].

   NIST is working on selecting a new lightweight cipher that may be the
   best choice for use on a UA.  The Keccak Xoodyak cipher in
   [new-crypto] is a good "Green Cipher".

5.4.  HIP and DTLS contrasted and compared

   This document specifies the use of DTLS 1.3 for its 0-RTT mobility
   feature and improved (over 1.2) handshake.  DTLS 1.3 is still an IETF
   draft, so there is little data available to properly contrast it with
   HIPv2.  This section will be based on the current DTLS 1.2.  The
   basic client-server model is unchanged.

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   The use of DTLS vs HIPv2 (both over UDP, HIP in IPsec ESP BEET mode)
   has pros and cons.  DTLS is currently at version 1.2 and based on TLS
   1.2.  It is a more common protocol than HIP, with many different
   implementations available for various platforms and languages.

   DTLS implements a client-server model, where the client initiates the
   communication.  In HIP, two parties are equal and either can be an
   Initiator or Responder of the Base Exchange.  HIP provides separation
   between key management (base exchange) and secure transport (for
   example IPsec ESP BEET) while both parts are tightly coupled in DTLS.

   DTLS 1.2 still has quite chatty connection establishment taking 3-5
   RTTs and 15 packets.  HIP connection establishment requires 4 packets
   (I1,R1,I2,R2) over 2 RTTs.  This is beneficial for constrained
   environments of UAs.  HIPv2 supports cryptoagility with possibility
   to negotiate cryptography mechanisms during the Base Exchange.

   Both DTLS and HIP support mobility with a change of IP address.
   However, in DTLS only client mobility is well supported, while in HIP
   either party can be mobile.  The double-jump problem (simultaneous
   mobility) is supported in HIP with a help of Rendezvous Server (RVS)
   [RFC8004].  HIP can implement secure mobility with IP source address
   validation in 2 RTTs, and in 1 RTT with fast mobility extension.

   One study comparing DTLS and IPsec-ESP performance concluded that
   DTLS is recommended for memory-constrained applications while IPSec-
   ESP for battery power-constrained [Vignesh].

6.  IANA Considerations


7.  Security Considerations

   Designing secure transports is challenging.  Where possible, existing
   technologies SHOULD be used.  Both ESP and DTLS have stood "the test
   of time" against many attack scenarios.  Their use here for N-RID and
   C2 do not represent new uses, but rather variants on existing

   The same can be said for both key establishment, using HIPv2 and
   DTLS, and the actual cipher choice for per packet encryption and
   authentication.  N-RID and C2 do not present new challenges, rather
   new opportunities to provide communications security using well
   researched technologies.

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8.  Acknowledgments

   Stuart Card and Adam Wiethuechter provivded information on their use
   of HIP for C2 at the Syracuse NY UAS test corridor.  This, in large
   measure, was the impetus to develop this document.

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,

   [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>.

9.2.  Informative References

              Card, S. W., Wiethuechter, A., Moskowitz, R., and A.
              Gurtov, "Drone Remote Identification Protocol (DRIP)
              Requirements", Work in Progress, Internet-Draft, draft-
              ietf-drip-reqs-18, 8 September 2021,

              Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
              Gurtov, "DRIP Entity Tag (DET) for Unmanned Aircraft
              System Remote Identification (UAS RID)", Work in Progress,
              Internet-Draft, draft-ietf-drip-rid-11, 20 October 2021,

              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
              dtls13-43, 30 April 2021,

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

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              Moskowitz, R., Card, S. W., and A. Wiethuechter, "Fast HIP
              Host Mobility", Work in Progress, Internet-Draft, draft-
              moskowitz-hip-fast-mobility-03, 3 April 2020,

   [MAVLINK]  "Micro Air Vehicle Communication Protocol", 2021,

              Moskowitz, R., Card, S. W., and A. Wiethuechter, "New
              Cryptographic Algorithms for HIP", Work in Progress,
              Internet-Draft, draft-moskowitz-hip-new-crypto-10, 2
              August 2021, <https://datatracker.ietf.org/doc/html/draft-

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,

   [RFC5795]  Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795,
              DOI 10.17487/RFC5795, March 2010,

   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [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,

   [RFC7402]  Jokela, P., Moskowitz, R., and J. Melen, "Using the
              Encapsulating Security Payload (ESP) Transport Format with
              the Host Identity Protocol (HIP)", RFC 7402,
              DOI 10.17487/RFC7402, April 2015,

   [RFC7668]  Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
              Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,

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   [RFC8004]  Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
              Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004,
              October 2016, <https://www.rfc-editor.org/info/rfc8004>.

   [RFC8750]  Migault, D., Guggemos, T., and Y. Nir, "Implicit
              Initialization Vector (IV) for Counter-Based Ciphers in
              Encapsulating Security Payload (ESP)", RFC 8750,
              DOI 10.17487/RFC8750, March 2020,

   [Vignesh]  Vignesh, K., "Performance analysis of end-to-end DTLS and
              IPsec-based communication in IoT environments", Thesis
              no. MSEE-2017: 42, 2017, <http://www.diva-

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

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   Andrei Gurtov
   Linköping University
   SE-58183 Linköping

   Email: gurtov@acm.org

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