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Secure UAS Network RID and C2 Transport

Document Type Active Internet-Draft (individual)
Authors Robert Moskowitz , Stuart W. Card , Adam Wiethuechter , Andrei Gurtov
Last updated 2024-03-16
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DRIP                                                        R. Moskowitz
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                                 S. Card
Expires: 17 September 2024                               A. Wiethuechter
                                                           AX Enterprize
                                                               A. Gurtov
                                                    Linköping University
                                                           16 March 2024

                Secure UAS Network RID and C2 Transport


   This document defines a transport mechanism between an Uncrewed
   Aircraft System (UAS) and its UAS Service Supplier (USS) for Network
   Remote ID (Net-RID) messages.  Either the Broadcast Remote ID (B-RID)
   messages, or alternatively, appropriate MAVLink Messages can be sent
   directly over UDP or via a more functional protocol using CoAP/CBOR
   for the Net-RID messaging.  This is secured via either HIP/ESP or
   DTLS.  HIP/ESP or DTLS secure messaging Command-and-Control (C2) for
   is also described.

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

   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 17 September 2024.

Copyright Notice

   Copyright (c) 2024 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 (
   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   4
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Network Remote ID . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Network RID Endpoints . . . . . . . . . . . . . . . . . .   6
       3.1.1.  Net-RID from the UA . . . . . . . . . . . . . . . . .   6
       3.1.2.  Net-RID from the GCS  . . . . . . . . . . . . . . . .   6
       3.1.3.  Net-RID from the Operator . . . . . . . . . . . . . .   7
     3.2.  Network RID Messaging . . . . . . . . . . . . . . . . . .   7
       3.2.1.  Secure Link Setup . . . . . . . . . . . . . . . . . .   7
       3.2.2.  Static Messages . . . . . . . . . . . . . . . . . . .   8
       3.2.3.  Vector/Location Message . . . . . . . . . . . . . . .   9
     3.3.  The Minimal, UDP, Net-RID Protocol  . . . . . . . . . . .   9
       3.3.1.  Compressing the MNet-RID message headers  . . . . . .  10
     3.4.  The MAVLink Net-RID Protocol  . . . . . . . . . . . . . .  11
       3.4.1.  Compressing the MavNet-RID message headers  . . . . .  12
     3.5.  CoAP Net-RID messages . . . . . . . . . . . . . . . . . .  12
   4.  Command and Control . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  Securing MAVLink  . . . . . . . . . . . . . . . . . . . .  13
       4.1.1.  Compressed ESP for MAVLink  . . . . . . . . . . . . .  13
     4.2.  Compressed UDP/DTLS for MAVLink . . . . . . . . . . . . .  14
   5.  Secure Transports . . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  HIP for Secure Transport  . . . . . . . . . . . . . . . .  14
     5.2.  DTLS for Secure Transport . . . . . . . . . . . . . . . .  15
     5.3.  Ciphers for Secure Transport  . . . . . . . . . . . . . .  15
     5.4.  HIP and DTLS contrasted and compared  . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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1.  Introduction

   This document defines two sets of messages for Uncrewed Aircraft
   System (UAS) Network Remote ID (Net-RID).  Minimal Net_RID (MNet-RID)
   is derived from the ASTM Remote ID [F3411-22a] broadcast messages and
   common data dictionary.  MAVLink Net_RID (MVNet-RID) is derived from
   the MAVLink protocol [MAVLINK].

   These messages are transported from the UAS to its UAS Service
   Supplier (USS) Network Service Provider (Net-RID SP) either directly
   over UDP or via CoAP/CBOR ([RFC7252]/[RFC8949]).

   Direct UDP and CoAP/CBOR were selected for their low communication
   "cost".  This may not be an issue if Net-RID originates from the
   Ground Control Station (GCS, Section 3.1.2), but it may be an
   important determinant when originating from the UA (Section 3.1.1).
   Particularly, very small messages may open Net-RID transmissions over
   a variety of constrained wireless technologies.

   This document also defines mechanisms to provide secure transport for
   these Net-RID messages and Command and Control (C2) messaging.

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

   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
   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.

   Two options for secure transport are provided: HIP [RFC7401] with ESP
   [RFC7402] and DTLS 1.3 [RFC9147].  These options are generally
   defined and their applicability is compared and contrasted.  It is up
   to Net-RID and C2 user to select which is preferred for their

   MOBIKE [RFC4555] is an alternative to HIP for ESP key establishment.
   It functions enough like HIP that it was left out, but implied, for
   document simplicity.  There may be some identity pieces needed to map
   HHITs and HIs to what MOBIKE uses.

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   To further reduce the communication cost, SCHC [RFC8724] is defined
   for both the direct UDP and CoAP layer [RFC8824].  For ESP
   "compression", ESP Implicit IV, [RFC8750] and Diet ESP [diet-esp] may
   be used together.  DTLS 1.3 [RFC9147] as defined in Section 5.2 is
   fully compressed.  DTLS for MNet-RID would only benefit from UDP
   compression.  CoAP Net-RID and C2 could benefit from specific
   application header compression.

   UDP SCHC compression is handled separately here from IP header as is
   currently defined by IP carrier (e.g.  LoRaWAN, [RFC9011]).  This is
   to allow for the endpoints to not need to know what constrained
   carrier is in-path and just design for worst case.

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 Section 2.2 of [RFC9153] for common DRIP terms.  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.

      A Minimal implementation of Network Remote ID, based on B-RID
      messages directly over UDP.

      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.

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3.  Network Remote ID

   In UAS Traffic Management (UTM), the purpose of Net-RID is to provide
   situational awareness of UA (in the form of flight tracking) in a
   user specified 4D volume.  The data needed for this is already
   defined in [F3411-22a], but a standard message format, protocol, and
   secure communications methodology are missing.  F3411, and other UTM
   based standards going through ASTM and other SDOs, provide JSON
   objects and some of the messages for passing information between
   various UTM entities (e.g., Net-RID SP to Net-RID SP and Net-RID SP
   to Net-RID DP) but does not specify how the data gets into UTM to
   begin with.  This document will provide such an open standard.

   A full-function CoAP-based Net-RID protocol is defined in
   Section 3.5.  This provides for either transport of the appropriate
   B-RID messages and/or the [F3411-22a] data elements encoded in CBOR.

   A minimal messaging approach (MNet-RID, Section 3.3), only using the
   Broadcast Remote ID (B-RID) messages in [F3411-22a], is sufficient to
   meet the needs of Net-RID.  These messages can be sent to the Net-RID
   SP when their contents change.  Further, a UAS supporting B-RID will
   have minimal development to add Net-RID support.

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

   Other messages may be needed in some Net-RID situations.  Thus a
   simple message multiplexer is provided for MNet-RID and CoAP is
   defined for a richer messaging environment.

   A MAVLink based messaging approach (MavNet-RID, Section 3.4) is also
   provided.  It differs from MNet-RID in message content, sending the
   appropriate MAVLink messages, but uses the same security options.  At
   this time, this approach is not complete; the minimal set of MAVLink
   messages need to be added.

   An example where MavNET-RID may be preferred is where the UAS
   endpoint is the GCS with the Internet access.  Through C2, it has all
   the MAVLink messages, and only needs forward appropriate MAVLink
   messages on to the Net-RID SP.  This is particular value when the UAS
   is operating in an area that does not require Broadcast RID but
   mandates Network RID.

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3.1.  Network RID Endpoints

   The US 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 USS.
   This simplifies a number of aspects of the Net-RID communication
   flow.  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 Net-RID communications.

   The UAS component in Net-RID may be either the UA, GCS, or the
   Operator's Internet connected device (e.g. smartphone or tablet that
   is not the GCS).  In all cases, mobility MUST be assumed.  That is
   the IP address of this end of the Net-RID communication may change
   during an operation (generally called a flight or mission).  The Net-
   RID mechanism MUST support this.  The UAS Identity for the secure
   connection may vary based on the UAS endpoint.

3.1.1.  Net-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.

   Multicast (GEN-10 in [RFC9153]) over multiple Internet connection
   technologies MAY be used improve QOS (GEN-7 in [RFC9153]) for Net-
   RID.  (Author's question: Does this really qualify as multicast?)

3.1.2.  Net-RID from the GCS

   Many UA will lack direct Internet access, but their GCS are
   connected.  As an Operator is expected to register an operation with
   its USS, this may be done via the Internet connected GCS.  The GCS
   could then be the source of the secure connection for Net-RID (acting
   as a gateway).

   There are two sources of the RID messages for the GCS, both from the
   UA.  These are UA B-RID messages, or content from C2 messages that
   the GCS converts to RID message format (or sends as MAVLink
   messages).  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.

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   In a constrained wireless environment for the UA that is not
   functioning autonomously (i.e., at least C2 traffic to the GCS), this
   approach may be the most economical.  It only uses the wireless to
   send the UA status once, to the GCS, that then provides the Net-RID

3.1.3.  Net-RID from the Operator

   Many UAS will have no Internet connectivity, but the UA is sending
   B-RID messages and the Operator, when within RF range, can receive
   these B-RID messages on an Internet Connected device that can act as
   the proxy for these messages, turning them into Net-RID messages.

3.2.  Network RID Messaging

   Net-RID messaging is tied to a UA operation.  This consists of an
   initial secure link setup, followed by a set of mostly static
   information related to the operation.  During the operation,
   continuous location information is sent by the UA with any needed
   updates to the mostly static operation information.

   The Net-RID SP SHOULD send regular "heartbeats" to the UAS.  If the
   UAS does not receive these heartbeats for some policy set time, the
   UA MUST take the policy set response to loss of Net-RID SP
   connectivity.  For example, this could be a mandated immediate
   landing.  There may be other messages from the Net-RID SP to the UAS
   (e.g., call the USS operator at this number NOW!).  The UAS MUST
   follow acknowledge policy for these messages.

   If the Net-RID SP stops receiving messages from the UAS
   (Section 3.2.3), it should notify the UTM of a non-communicating UA
   while still in operation.

3.2.1.  Secure Link Setup

   The secure link setup MUST be done before the operation begins, thus
   it can use a high capacity connection like WiFi.  It MAY use the ASTM
   [F3411-22a] UAS ID for this setup, including other data elements
   provided in the B-RID Basic ID (Msg Type 0x0) Message.  If the Basic
   ID information is NOT included via the secure setup (including the
   Net-RID SP querying the USS for this information), it MUST be sent as
   part of the Static Messages (Section 3.2.2)  UAS Identity

   The UAS MAY use its UAS ID if it is a HHIT (DET per [RFC9374]).  It
   may use some other Identity, based on the Net-RID SP policy.

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   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.  HIP for ESP Secure Link

   HIP [RFC7401] for ESP Secure Link is a natural choice for a DET UAS
   ID.  For this, the Net-RID SP would also need a HHIT, possibly
   following the process in [drip-registries].  DTLS Secure Link

   There are two approaches for DTLS [RFC9147] secure link.

   The DET's HI may be encoded in PKIX SubjectPublicKeyInfo format, and
   then follow [RFC7250].  Note that SubjectPublicKeyInfo only contains
   a DET's HI.  The parties in the DTLS setup will have to have a unique
   mapping of HI to DET (i.e. the HID value).

   Alternatively, DANCE [dane-clients] may be used with a DET's DNS
   lookup to retrieve a TLSA RR [RFC6698] with the DET's HI encoded in
   PKIX SubjectPublicKeyInfo format (per [RFC7250]).  This has the added
   advantage of the full DET is sent in the DTLS exchange as part of the

   The Net-RID SP DTLS credential may follow DANE [RFC6698] or any other
   DTLS server credential method.

3.2.2.  Static Messages

   For simplicity, a class of UAS information is called here "Static",
   though in practice any of it can change during the operation, but
   will change infrequently.  This information is the contents of the
   B-RID Self-ID (Msg Type 0x3), Operator ID (Msg Type 0x5), and System
   Messages (Msg Type 0x4).  This information can simply be sent in the
   same format as the B-RID messages.  Alternatively the individual data
   elements may be send as separate CBOR objects.

   The Basic ID (Msg Type 0x0) Message may be included as a static
   message if this information was not used for the secure setup.  There
   may be more than one Basic ID Message needed if as in the case where
   the Japan Civil Aviation Bureau (JCAB) has mandated that the Civil
   Aviation Authority (CAA) assigned ID (UA ID type 2) and Serial Number
   (UA ID type 1) be broadcasted.

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   The information in the System Message is most likely to change during
   an operation.  Notably the Operator Location data elements are
   subject to change if the GCS is physically moving (e.g.  hand-held
   and the operator is walking or driving in a car).  The whole System
   Message may be sent, or only the changing data elements as CBOR

   These static message elements may be sent before the operation
   begins, thus their transmission can use a high capacity connection
   like WiFi.  Once the operation is underway, any updates will have to
   traverse the operational link which may be very constrained and this
   will impact data element formatting.

   The Net-RID SP MUST acknowledge these messages.  The UAS MUST receive
   these ACKs.  If no ACK is received, the UAS MUST resend the
   message(s).  This send/ACK sequence continues either until ACK is
   received, or some policy number of tries.  If this fails, the UAS
   MUST act that the Net-RID SP connection is lost and MUST take the
   policy set response to loss of Net-RID SP connectivity.  If the
   information changes during this cycle, the latest information MUST
   always be sent.

3.2.3.  Vector/Location Message

   Many CAAs mandate that the UA Vector/Location information be updated
   at least once per second.  Without careful message design, this
   messaging volume would overwhelm many wireless technologies.  Thus to
   enable the widest deployment choices, a highly compressed format is

   The B-RID Vector/Location Message (Msg Type 0x1) is the simplest
   small object (24 bytes) for sending this information as a single CBOR
   object or via MNet-RID.  It may be possible to send only those data
   elements that changed in the last time interval.  This may result in
   smaller individual transmissions, but should not be used if the
   resulting message is larger than the Vector/Location Message.

3.3.  The Minimal, UDP, Net-RID Protocol

   The Minimal Network Remote ID protocol is a simple UDP messaging
   consisting of a 1-byte message type field and a message field of
   maximum 25-bytes length.

   The Message Type Field is defined as follows:

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        Value        Type

        0            RESERVED
        1            B-RID Message     [F3411]
        2            Net-RID SP ACK
        3            Net-RID SP Heartbeat

   The B-RID Message is 25 bytes:

        Bytes        Description

        1            B-RID Message Type/version
        24           B-RID Message

   The Net-RID SP ACK is 5 bytes:

        Bytes        Description

        4            Timestamp
        1            B-RID Message Type/version from message ACKed

        Should a 12byte hash of message be included as in Manifest?

   The Net-RID SP Heartbeat is 4 bytes:

        Bytes        Description

        4            Timestamp

3.3.1.  Compressing the MNet-RID message headers

   The security envelope (ESP of DTLS) and UDP headers may be compressed
   to further minimize the communication cost of MNet-RID.  Compressing ESP/UDP headers

   A normal ESP/AES-GCM-12/UDP wrapper for the NMet-RID messages is
   10+28+8=46 bytes.  By applying the SCHC compression via [diet-esp]
   and using [RFC8750] Implicit Cipher IVs, this is reduced to 4+12+0=16

   AES-CCM-12 has a smaller, but valuable, size reduction on
   compression, as CCM's IV is only 8 bytes compared to GCM's 16-byte
   IV.  Thus uncompressed, the wrapper is 10+20+8=38 bytes.  Compressed
   it is 4+12+0=16 bytes.  Or "over the wire", compressed CCM offers no
   improvements to GCM and its 2-pass process will tend to result in a
   poorer performance compared to GCM, even on these small messages.
   Thus GCM is the recommended mode-of-operation for AES.

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   Note that [RFC8750] does not provide implicit IV use for AES-GCM-12.
   At the time of writing the use case for the smaller ICV was not
   apparent.  Here, the smaller hash is not a lower risk given the
   limited traffic within a single operation.  If not provided
   elsewhere, this document will request ENCR_AES_GCM_12_IIV for IKE and
   both AES_GCM_12 and AES_GCM_12_IIV for HIP.

   [diet-esp] may be completely statically configured, or may have HIP
   or IKE negotiated values.  This will be determined by Net-RID SP

   TBD: diet-esp context and rules.  Compressing UDP/DTLS message headers

   DTLS 1.3 [RFC9147] is designed for minimal header overhead.
   Section 5.2 defines the DTLS header fields to use for minimal header
   size.  The only practical compression gain with SCHC would be the UDP
   header, it could be compressed to zero bytes, but would require

   The DTLS header defined in Section 5.2 with a 1-byte Sequence and no
   Length is 4 bytes.  Only AES-GCM-16 is defined for DTLS, but has an
   implicit IV for 16 bytes length.  This along with the 8-byte UDP
   header is 28 bytes total.  Using SCHC for UDP header compression to
   zero bytes (and an implicit SCHC rule) would require adding the DTLS
   2-byte Length field.  This results in a further 6 byte header size
   reduction.  The resulting 22 bytes is similar to that in ESP
   compression above.  However the complexity of SCHC for only UDP
   compression may not be of value in some implementations.

   TBD: udp context and rules.

3.4.  The MAVLink Net-RID Protocol

   The MAVLink Network Remote ID protocol is also a simple UDP messaging
   consisting of a 1-byte message type field as in MNet-RID, the 3-byte
   MAVLink Msg ID, 1-byte LEN, and a message field of maximum 255-bytes

   The MAVLink Message Type Field is defined as follows:

        Value        Type

        0            RESERVED
        1            MAVLink Message
        2            Net-RID SP ACK
        3            Net-RID SP Heartbeat

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   It is initially identical to that in MNet-RID, but may deviate over
   time, thus separately defined.

   The MAVLink Message format is:

        Bytes        Description

        3            MAVLink ID
        1            MAVLink message length
        0-255        MAVLink Message

   The MAVLink message length is included as this value may be needed to
   successfully process some MAVLink messages.

   The Net-RID SP ACK and Net-RID SP Heartbeat are the same as defined
   in MNet-RID.

3.4.1.  Compressing the MavNet-RID message headers

   The security envelope (ESP of DTLS) and UDP headers may be compressed
   to further minimize the communication cost of MavNet-RID.  This is
   the same as in MNet-RID with the added potential rule to compress the
   MAVLink message length, as it can be computed from the header length.

3.5.  CoAP Net-RID messages

   The CoAP based Net-RID protocol is intended for a richer conversation
   between the UAS and USS.  The USS, through the Net-RID SP, may
   compare actual UA progress against the filed flight plan and against
   other UA actual traffic.  The USS may then send to the UAS
   recommended changes to the flight plan to de-conflict traffic or
   advise the UAS to avoid hazards (1st responder event, avoid space).
   The UAS may then negotiate changes to the plan, and act on them, as

   This sort of advanced UAS behavior is envisioned as part of total UTM
   activities.  Discussions now ongoing in UTM will provide the data
   models and transactional UAS/USS interactions, that will drive UAS
   communications past the MNet-RID defined in Section 3.3 toward this
   more functional CoAP Net-RID protocol.

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4.  Command and Control

   The Command and Control (C2) connection is between the UA and GCS.
   This is often 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

   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 that uses UDP
   port 14550 for transport over IP.  Message authenticity was added in
   MAVLink 2 in the form of a SHA-256 (secret | message) left-truncated
   to 6 byte.  This does not follow HMAC [RFC2104] security
   recommendations, nor provides confidentiality.

   The MAVLink authentication only provides 24-bit collision resistance
   but is not susceptible to a hash length attack.  By following the
   security approach here, UAS C2 is superior to that currently provided
   within MAVLink.  It provides 48-bit collision resistance and full

4.1.1.  Compressed ESP for MAVLink

   The approach in Section can be used to fully secure MAVLink
   and include the UDP header for IP transport.  Further, MAVLink itself
   can be compressed.

   MAVLink messages contain a 1-byte Seq number and 2-byte CRC.  Both of
   these can be generated from SCHC rules.  These 3 bytes along with the
   13-byte MAVLink signature provides the 16 bytes so that the over-the-
   wire cost is the same.

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   This secure MAVLink format may be sent directly over a local wireless
   link.  The UDP port processing adds little cost.  Sending this over
   IP provides the needed confidentiality at 8 bytes less than
   unencrypted messages.

   TBD: MAVLink SCHC context and rules.  These will be part of the
   MAVLink ESP setup.

4.2.  Compressed UDP/DTLS for MAVLink

   At this time, DTLS is NOT recommended for C2 security, as it is
   challenged with server mobility.  It may be added at a later time.

   DTLS may be viable when there is no possibility for an IP address
   change for the GCS during an operation.  An example of this is where
   the GCS is an Operations Center like might be used in a package
   delivery business.

5.  Secure Transports

   Secure UDP-based protocols are preferred for both Network Remote ID
   (Net-RID) and C2.  Both HIPv2 and DTLS can be used.  It will be shown
   below that HIPv2 is better suited in most cases.

   For IPv6 and CoAP over both WiFi and Bluetooth (or any other radio
   link), SCHC [RFC8724] is defined to significantly reduce the per
   packet transmission cost.  SCHC is used both within the secure
   envelope and before the secure envelope as shown in Section 5.2.10 of
   [schc-architecture].  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.  SCHC SHOULD still be used as above.  Both WiFi and
   Bluetooth link security can provide appropriate security, but this
   would not provide trustworthy multi-homed security.

5.1.  HIP 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 Net-RID (Section 3.1.1), and
   particularly when HIP is used for C2, HIP for Net-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 Net-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 Net-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.

   DTLS implementations SHOULD use a CID of 2 bytes.  This is to support
   mobility and simplify SCHC rule handling.  The Sequence Number size
   is a deployment choice.  For MNet-RID rate of one Vector/Location
   update per second, a 1-byte value would result in a rollover in 4
   minutes.  This should not poise an operational challenge.  The length
   field is recommended when SCHC is used as it can provided an
   authenticated length to use to regenerate the UDP header length field
   and any application length field like that in MAVLink.

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
   ciphers.  Section shows that proper compression can provide
   the more efficient GCM at no over-the-wire cost.  Thus AES-GCM is the
   recommended AES mode-of-operation.

   NIST has selected a new lightweight cipher, ASCON, that may be the
   best choice for use on a UA.  Work will be needed to develop full
   support for Ascon in both ESP and DTLS.

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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.

   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

   TBD: May need ESP ciphers defined.

   TBD: Add MNet-RID Message Type Field to DRIP registry.

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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 Net-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.  Net-RID and C2 do not present new challenges, rather
   new opportunities to provide communications security using well
   researched technologies.

8.  Acknowledgments

   Stuart Card and Adam Wiethuechter provided 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,

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,

9.2.  Informative References

              Huque, S. and V. Dukhovni, "TLS Client Authentication via
              DANE TLSA records", Work in Progress, Internet-Draft,

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              draft-ietf-dance-client-auth-05, 13 January 2024,

   [diet-esp] Migault, D., Guggemos, T., Bormann, C., and D. Schinazi,
              "ESP Header Compression Profile", Work in Progress,
              Internet-Draft, draft-mglt-ipsecme-diet-esp-10, 29 June
              2023, <

              Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
              Identity Management Architecture", Work in Progress,
              Internet-Draft, draft-ietf-drip-registries-14, 4 December
              2023, <

              ASTM International, "Standard Specification for Remote ID
              and Tracking - F3411−22a", July 2022,

              Moskowitz, R., Card, S. W., and A. Wiethuechter, "Fast HIP
              Host Mobility", Work in Progress, Internet-Draft, draft-
              moskowitz-hip-fast-mobility-07, 7 December 2023,

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

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

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <>.

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   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              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,

   [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,

   [RFC8004]  Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
              Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004,
              October 2016, <>.

   [RFC8724]  Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zuniga, "SCHC: Generic Framework for Static Context Header
              Compression and Fragmentation", RFC 8724,
              DOI 10.17487/RFC8724, April 2020,

   [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,

   [RFC8824]  Minaburo, A., Toutain, L., and R. Andreasen, "Static
              Context Header Compression (SCHC) for the Constrained
              Application Protocol (CoAP)", RFC 8824,
              DOI 10.17487/RFC8824, June 2021,

   [RFC9011]  Gimenez, O., Ed. and I. Petrov, Ed., "Static Context
              Header Compression and Fragmentation (SCHC) over LoRaWAN",
              RFC 9011, DOI 10.17487/RFC9011, April 2021,

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   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,

   [RFC9153]  Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A.
              Gurtov, "Drone Remote Identification Protocol (DRIP)
              Requirements and Terminology", RFC 9153,
              DOI 10.17487/RFC9153, February 2022,

   [RFC9374]  Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
              "DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
              ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,

              Pelov, A., Thubert, P., and A. Minaburo, "Static Context
              Header Compression (SCHC) Architecture", Work in Progress,
              Internet-Draft, draft-ietf-schc-architecture-01, 6 October
              2023, <

              Moskowitz, R., Card, S. W., Wiethuechter, A., and P.
              Thubert, "Protocol Numbers for SCHC", Work in Progress,
              Internet-Draft, draft-ietf-intarea-schc-protocol-numbers-
              01, 12 October 2023,

   [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

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

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

   Andrei Gurtov
   Linköping University
   SE-58183 Linköping

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