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ART drip Internet-Draft This document defines an architecture for protocols and services to support Unmanned Aircraft System Remote Identification and tracking (UAS RID), plus RID-related communications, including required architectural building blocks and their interfaces.

This document describes a natural Internet and MAC-layer broadcast-based architecture for Unmanned Aircraft System Remote Identification and tracking (UAS RID), conforming to proposed regulations and external technical standards, satisfying the requirements listed in the companion requirements document . Many considerations (especially safety) dictate that UAS be remotely identifiable. Civil Aviation Authorities (CAAs) worldwide are mandating Unmanned Aircraft Systems (UAS) Remote Identification (RID). CAAs currently (2020) promulgate performance-based regulations that do not specify techniques, but rather cite industry consensus technical standards as acceptable means of compliance.

A RID is an application enabler for a UAS to be identified by a UTM/ USS or third parties entities such as law enforcement. Many safety and other considerations dictate that UAS be remotely identifiable. CAAs worldwide are mandating UAS RID. The European Union Aviation Safety Agency (EASA) has published and Regulations. The FAA has published a Notice of Proposed Rule Making . CAAs currently promulgate performance-based regulations that do not specify techniques, but rather cite industry consensus technical standards as acceptable means of compliance. ASTM ASTM International, Technical Committee F38 (UAS), Subcommittee F38.02 (Aircraft Operations), Work Item WK65041, developed the new ASTM Standard Specification for Remote ID and Tracking. ASTM defines one set of RID information and two means, MAC-layer broadcast and IP-layer network, of communicating it. If a UAS uses both communication methods, generally the same information must provided via both means. The is sighted by FAA in its RID as "one potential means of compliance" to a Remote ID rule. 3GPP 3GPP provides UA service in the LTE network since release 15 in published technical specification . Start from its release 16, it completed the UAS RID requirement study in and proposed use cases in the mobile network and the services that can be offered based on RID and ongoing release 17 specification works on enhanced UAS service requirement and provides the protocol and application architecture support which is applicable for both 4G and 5G network. ATIS's recent report proposes architecture approaches for the 3GPP network to support UAS and one of which is put RID in higher 3GPP protocol stack such as using ASTM remote ID .

Network RID defines a RID data dictionary and data flow: from a UAS via unspecified means to a Network Remote ID Service Provider (Net-RID SP); from the Net-RID SP to an integrated, or over the Internet to a separate, Network Remote ID Display Provider (Net- RID DP); from the Net-RID DP via the Internet to Network Remote ID clients in response to their queries (expected typically, but not specified exclusively, to be web based) specifying airspace volumes of interest. Network RID depends upon connectivity, in several segments, via the Internet, from the UAS to the Observer. The Network RID is illustrated in below.

Via the direct Radio Frequency (RF) link between the UA and GCS: Command and Control (C2) flows from the GCS to the UA; for all but the simplest hobby aircraft, position and status flow from the UA to the GCS. Via the Internet, through three distinct segments, Network RID information flows from the UAS (comprising the UA and its GCS) to the Observer.

Broadcast RID defines a set of RID messages and how the UA transmits them locally directly one-way, over Bluetooth or Wi-Fi. Broadcast RID should need Internet (or other Wide Area Network) connectivity only for UAS registry information lookup using the locally directly received UAS ID as a key. Broadcast RID should be functionally usable in situations with no Internet connectivity. The Broadcast RID is illustrated in below. Editor's note: Is there a need to add interconnections between B-RID and N-RID in the drawing

Editor's note: the following may more clarification: what Broadcast RID can do w/ & w/o Observer Internet connectivity How Broadcast RID transmits public info (obviating some registry lookups) how Network RID is “less constrained” than Broadcast RID

Editor's Note: Show how DRIP RID is an enabler of USS Interoperability

| USS-2 | +-------+ +-------+ ]]>

The requirements document also provides an extended introduction to the problem space, use cases, etc. Only a brief summary of that introduction will be restated here as context, with reference to the general architecture shown in below.

Editor's note: the archteture may need more clarification, and address the following: add network RID and broadcast RID in the picture (since those are the focus points) connectivity requirements among UA, GCS, SP, DP (if necessary) … DRIP will enable leveraging existing Internet resources (standard protocols, services, infrastructure and business models) to meet UAS RID and closely related needs. DRIP will specify how to apply IETF standards, complementing and other external standards, to satisfy UAS RID requirements. DRIP will update existing and develop new protocol standards as needed to accomplish the foregoing. This document will outline the UAS RID architecture into which DRIP must fit, and an architecture for DRIP itself. This includes presenting the gaps between the CAAs' Concepts of Operations and as it relates to use of Internet technologies and UA direct RF communications. Issues include, but are not limited to: Mechanisms to leverage Domain Name System (DNS: ) and Extensible Provisioning Protocol (EPP ) technology to provide for private () and public () Information Registry. Trustworthy Remote ID and trust in RID messages Privacy in RID messages (PII protection) Eiditor's Note: The following aspects are not covered in this draft, yet. We may consider add sections for each of them if necessary. UA -> Ground communications including Broadcast RID Broadcast RID 'harvesting' and secure forwarding into the UTM Secure UAS -> Net-RID SP communications Secure Observer -> Pilot communications

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

Editor's Note: to be updated. This document uses terms defined in . Editor's note: in order to make it self-contain, listing terms used in this draft should be okie, comments?

Editor's Note: to be updated. ADS-B:      Automatic Dependent Surveillance Broadcast DSS:        Discovery & Synchronization Service EdDSA:      Edwards-Curve Digital Signature Algorithm GCS:        Ground Control Station HHIT:       Hierarchical HIT Registries HIP:        Host Identity Protocol HIT:        Host Identity Tag RID:        Remote ID Net-RID SP: Network RID Service Provider Net-RID DP: Network RID Display Provider. PII:        Personally Identifiable Information RF:         Radio Frequency SDSP:       Supplemental Data Service Provider UA:         Unmanned Aircraft UAS:        Unmanned Aircraft System USS:        UAS Service Supplier UTM:        UAS Traffic Management

Editor's note: I think we should explain HHIT designs for UAS RID first and give readers a direct imporession what this draft is offering. This is one of Daniel's comment, we shall focus on solutions, without repeating too much of details from a sepecifc draft. This document describes the use of Hierarchical Host Identity Tags (HHITs) as self-asserting IPv6 addresses and thereby a trustable Identifier for use as the UAS Remote ID. HHITs self-attest to the included explicit hierarchy that provides Registrar discovery for 3rd-party ID attestation. HITs are statistically unique through the cryptographic hash feature of second-preimage resistance. The cryptographically-bound addition of the Hierarchy and a HHIT registration process (TBD; e.g. based on Extensible Provisioning Protocol, ) 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 certificate. other pointers: (mostly list how HHIT satisfy the reqs-) Why DRIP RID should/MUST/May be a HHIT? HHIT RID format, metadate, and other useful info HHIT RID registar workflow HHIT Users (operator/USS/NETRID-SP?) expand on different uses of & relationship between optional manufacturer-assigned HI & subsequent single-use HIs how security is guaranteed call X.509 PKI not “standard” but “classical”, describe it to justify why it won’t work here explain continuing role of some kind of CA even w/o X.509 PKI Editors' note: this is also one of the Michael's comment, we can address it here how DNS lookup may happen (Reverse DNS?) ….

Editor: This section descrips the DRIP RID ecosystem such as RID design philosophy, PII registration, Still not sure this is a good title since here mainly talks about regiter, maybe use this seciton focus on HHIT RID registration?? I also have suggestion to move the CS-RID to a seperated section Any DRIP solutions for UAS RID must fit into the UTM (or U-space) system. This implies interaction with entities including UA, GCS, USS, Net-RID SP, Net-RID DP, Observers, Operators, Pilots In Command, Remote Pilots, possibly SDSP, etc. The only additional entities introduced in this document are registries, required but not specified by the regulations and , and optionally CS-RID SDSP and Finder nodes. UAS registries hold both public and private UAS information. The public information is primarily pointers to the repositories of, and keys for looking up, the private information. Given these different uses, and to improve scalability, security and simplicity of administration, the public and private information can be stored in different registries, indeed different types of registry. Editor's note: what are differences & relationships among public & private registries, DP, SP, USS

The private information required for UAS RID is similar to that required for Internet domain name registration. Thus a DRIP RID solution can leverage existing Internet resources: registration protocols, infrastructure and business models, by fitting into an ID structure compatible with DNS names. This implies some sort of hierarchy, for scalability, and management of this hierarchy. It is expected that the private registry function will be provided by the same organizations that run USS, and likely integrated with USS.

A DRIP UAS ID MUST be amenable to handling as an Internet domain name (at an arbitrary level in the hierarchy), MUST be registered in at least a pseudo-domain (e.g. .ip6.arpa for reverse lookup), and MAY be registered as a sub-domain (for forward lookup). A DRIP private information registry MUST support essential Internet domain name registry operations (e.g. add, delete, update, query) using interoperable open standard protocols. It SHOULD support the Extensible Provisioning Protocol (EPP) and the Registry Data Access Protocol (RDAP) with access controls. It MAY use XACML to specify those access controls. It MUST be listed in a DNS: that DNS MAY be private; but absent any compelling reasons for use of private DNS, SHOULD be the definitive public Internet DNS hierarchy. The DRIP private information registry in which a given UAS is registered MUST be findable, starting from the UAS ID, using the methods specified in . A DRIP private information registry MAY support WebFinger as specified in .

The public information required to be made available by UAS RID is transmitted as cleartext to local observers in Broadcast RID and is served to a client by a Net-RID DP in Network RID. Therefore, while IETF can offer e.g. as one way to implement Network RID, the only public information required to support essential DRIP functions for UAS RID is that required to look up Internet domain hosts, services, etc.

A DRIP public information registry MUST be a standard DNS server, in the definitive public Internet DNS hierarchy. It MUST support NS, MX, SRV, TXT, AAAA, PTR, CNAME and HIP RR (the last per ) types. If a DRIP public information registry lists, in a HIP RR, any HIP RVS servers for a given DRIP UAS ID, those RVS servers MUST restrict relay services per AAA policy; this may require extensions to .

Editor's Note: if CS-RID is optional, may be added in separately section stating optional features Maybe add the CS into architecture diagram ASTM anticipated that regulators would require both Broadcast RID and Network RID for large UAS, but allow RID requirements for small UAS to be satisfied with the operator's choice of either Broadcast RID or Network RID. The EASA initially specified Broadcast RID for UAS of essentially all UAS and is now considering Network RID also. The FAA NPRM requires both for Standard RID and specifies Network RID only for Limited RID. One obvious opportunity is to enhance the architecture with gateways from Broadcast RID to Network RID. This provides the best of both and gives regulators and operators flexibility. Such gateways could be pre-positioned (e.g. around airports and other sensitive areas) and/or crowdsourced (as nothing more than a smartphone with a suitable app is needed). As Broadcast RID media have limited range, gateways receiving messages claiming locations far from the gateway can alert authorities or a SDSP to the failed sanity check possibly indicating intent to deceive. Surveillance SDSPs can use messages with precise date/time/position stamps from the gateways to multilaterate UA location, independent of the locations claimed in the messages, which are entirely operator self-reported in UAS RID and UTM. Further, gateways with additional sensors (e.g. smartphones with cameras) can provide independent information on the UA type and size, confirming or refuting those claims made in the RID messages. CS-RID would be an option, beyond baseline DRIP functionality; if implemented, it adds two more entity types.

A CS-RID SDSP MUST appear (i.e. present the same interface) to a Net- RID SP as a Net-RID DP. A CS-RID SDSP MUST appear to a Net-RID DP as a Net-RID SP. A CS-RID SDSP MUST NOT present a standard GCS-facing interface as if it were a Net-RID SP. A CS-RID SDSP MUST NOT present a standard client-facing interface as if it were a Net-RID DP. A CS- RID SDSP MUST present a TBD interface to a CS-RID Finder; this interface SHOULD be based upon but readily distinguishable from that between a GCS and a Net-RID SP.

A CS-RID Finder MUST present a TBD interface to a CS-RID SDSP; this interface SHOULD be based upon but readily distinguishable from that between a GCS and a Net-RID SP. A CS-RID Finder must implement, integrate, or accept outputs from, a Broadcast RID receiver. A CS- RID Finder MUST NOT interface directly with a GCS, Net-RID SP, Net- RID DP or Network RID client.

A DRIP UA ID needs to be "Trustworthy". This means that within the framework of the RID messages, an observer can establish that the RID used does uniquely belong to the UA. That the only way for any other UA to assert this RID would be to steal something from within the UA. The RID is self-generated by the UAS (either UA or GCS) and registered with the USS. Within the limitations of Broadcast RID, this is extremely challenging as: An RID can at most be 20 characters The ASTM Basic RID message (the message containing the RID) is 25 characters; only 3 characters are currently unused The ASTM Authentication message, with some changes from can carry 224 bytes of payload. Standard approaches like X.509 and PKI will not fit these constraints, even using the new EdDSA algorithm. An example of a technology that will fit within these limitations is an enhancement of the Host Identity Tag (HIT) of HIPv2 introducing hierarchy as defined in HHIT ; using Hierarchical HITs for UAS RID is outlined in HHIT based UAS RID . As PKI with X.509 is being used in other systems with which UAS RID must interoperate (e.g. the UTM Discovery and Synchronization Service and the UTM InterUSS protocol) mappings between the more flexible but larger X.509 certificates and the HHIT based structures must be devised. By using the EdDSA HHIT suite, self-assertions of the RID can be done in as little as 84 bytes. Third-party assertions can be done in 200 bytes. An observer would need Internet access to validate a self- assertion claim. A third-party assertion can be validated via a small credential cache in a disconnected environment. This third- party assertion is possible when the third-party also uses HHITs for its identity and the UA has the public key for that HHIT.

A DRIP UAS ID MUST be a HHIT. It SHOULD be self-generated by the UAS (either UA or GCS) and MUST be registered with the Private Information Registry identified in its hierarchy fields. Each UAS ID HHIT MUST NOT be used more than once, with one exception as follows. Each UA MAY be assigned, by its manufacturer, a single HI and derived HHIT encoded as a hardware serial number per . Such a static HHIT SHOULD be used only to bind one-time use UAS IDs (other HHITs) to the unique UA. Depending upon implementation, this may leave a HI private key in the possession of the manufacturer (see Security Considerations). Each UA equipped for Broadcast RID MUST be provisioned not only with its HHIT but also with the HI public key from which the HHIT was derived and the corresponding private key, to enable message signature. Each UAS equipped for Network RID MUST be provisioned likewise; the private key SHOULD reside only in the ultimate source of Network RID messages (i.e. on the UA itself if the GCS is merely relaying rather than sourcing Network RID messages). Each observer device MUST be provisioned with public keys of the UAS RID root registries and MAY be provisioned with public keys or certificates for subordinate registries. Operators and Private Information Registries MUST possess and other UTM entities MAY possess UAS ID style HHITs. When present, such HHITs SHOULD be used with HIP to strongly mutually authenticate and optionally encrypt communications.

Each Operator MUST generate a Host Identity of the Operator (HIo) and derived Hierarchical HIT of the Operator (HHITo), register them with a Private Information Registry along with whatever Operator data (inc. PII) is required by the cognizant CAA and the registry, and obtain a Certificate from the Registry on the Operator (Cro) signed with the Host Identity of the Registry private key (HIr(priv)) proving such registration. To add an UA, an Operator MUST generate a Host Identity of the Aircraft (HIa) and derived Hierarchical HIT of the Aircraft (HHITa), create a Certificate from the Operator on the Aircraft (Coa) signed with the Host Identity of the Operator private key (HIo(priv)) to associate the UA with its Operator, register them with a Private Information Registry along with whatever UAS data is required by the cognizant CAA and the registry, obtain a Certificate from the Registry on the Operator and Aircraft ("Croa") signed with the HIr(priv) proving such registration, and obtain a Certificate from the Registry on the Aircraft (Cra) signed with HIr(priv) proving UA registration in that specific registry while preserving Operator privacy. The operator then MUST provision the UA with HIa, HIa(priv), HHITa and Cra. UA engaging in Broadcast RID MUST use HIa(priv) to sign Auth Messages and MUST periodically broadcast Cra. UAS engaging in Network RID MUST use HIa(priv) to sign Auth Messages. Observers MUST use HIa from received Cra to verify received Broadcast RID Auth messages. Observers without Internet connectivity MAY use Cra to identify the trust class of the UAS based on known registry vetting. Observers with Internet connectivity MAY use HHITa to perform lookups in the Public Information Registry and MAY then query the Private Information Registry, which MUST enforce AAA policy on Operator PII and other sensitive information.

Editor's ntoe: move this to a subsction of Operator Privacy? Broadcast RID messages may contain PII. This may be information about the UA such as its destination or Operator information such as GCS location. There is no absolute "right" in hiding PII, as there will be times (e.g., disasters) and places (buffer zones around airports and sensitive facilities) where policy may mandate all information be sent as cleartext. Otherwise, the modern general position (consistent with, e.g., the EU General Data Protection Regulation) is to hide PII unless otherwise instructed. While some have argued that a system like that of automobile registration plates should suffice for UAS, others have argued persuasively that each generation of new identifiers should take advantage of advancing technology to protect privacy, to the extent compatible with the transparency needed to protect safety. A viable architecture for PII protection would be symmetric encryption of the PII using a key known to the UAS and a USS service. An authorized Observer may send the encrypted PII along with the Remote ID (to their UAS display service) to get the plaintext. The authorized Observer may send the Remote ID (to their UAS display service) and receive the key to directly decrypt all PII content from the UA. PII is protected unless the UAS is informed otherwise. This may come from operational instructions to even permit flying in a space/time. It may be special instructions at the start or during an operation. PII protection should not be used if the UAS loses connectivity to the USS. The USS always has the option to abort the operation if PII protection is disallowed. An authorized observer may instruct a UAS via the USS that conditions have changed mandating no PII protection or land the UA.

Editor's note: placeholder

DRIP is all about safety and security, so content pertaining to such is not limited to this section. The security provided by asymmetric cryptographic techniques depends upon protection of the private keys. A manufacturer that embeds a private key in an UA may have retained a copy. A manufacturer whose UA are configured by a closed source application on the GCS which communicates over the Internet with the factory may be sending a copy of a UA or GCS self-generated key back to the factory. Keys may be extracted from a GCS or UA; the RID sender of a small harmless UA (or the entire UA) could be carried by a larger dangerous UA as a "false flag." Compromise of a registry private key could do widespread harm. Key revocation procedures are as yet to be determined. These risks are in addition to those involving Operator key management practices.

The work of the FAA's UAS Identification and Tracking (UAS ID) Aviation Rulemaking Committee (ARC) is the foundation of later ASTM and proposed IETF DRIP WG efforts. The work of ASTM F38.02 in balancing the interests of diverse stakeholders is essential to the necessary rapid and widespread deployment of UAS RID. IETF volunteers who have contributed to this draft include Amelia Andersdotter and Mohamed Boucadair.

This document defines terminology and requirements for Drone Remote Identification Protocol (DRIP) Working Group protocols to support Unmanned Aircraft System Remote Identification and tracking (UAS RID) for security, safety and other purposes. Complementing external technical standards as regulator-accepted means of compliance with UAS RID regulations, DRIP will: facilitate use of existing Internet resources to support UAS RID and to enable enhanced related services; enable online and offline verification that UAS RID information is trustworthy. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. ATIS ASTM ANSI European Union Aviation Safety Agency (EASA) European Union Aviation Safety Agency (EASA) United States Federal Aviation Administration (FAA) United States Federal Aviation Administration (FAA) 3GPP 3GPP European Organization for the Safety of Air Navigation (EUROCONTROL) This specification defines a Uniform Resource Name namespace for UUIDs (Universally Unique IDentifier), also known as GUIDs (Globally Unique IDentifier). A UUID is 128 bits long, and can guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System and later in the Open Software Foundation\'s (OSF) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms.This specification is derived from the DCE specification with the kind permission of the OSF (now known as The Open Group). Information from earlier versions of the DCE specification have been incorporated into this document. [STANDARDS-TRACK] Location-based services (such as navigation applications, emergency services, and management of equipment in the field) need geographic location information about Internet hosts, their users, and other related entities. These applications need to securely gather and transfer location information for location services, and at the same time protect the privacy of the individuals involved. This document describes an architecture for privacy-preserving location-based services in the Internet, focusing on authorization, security, and privacy requirements for the data formats and protocols used by these services. This memo documents an Internet Best Current Practice. This specification defines the WebFinger protocol, which can be used to discover information about people or other entities on the Internet using standard HTTP methods. WebFinger discovers information for a URI that might not be usable as a locator otherwise, such as account or email URIs. This document specifies the details of the Host Identity Protocol (HIP). HIP allows consenting hosts to securely establish and maintain shared IP-layer state, allowing separation of the identifier and locator roles of IP addresses, thereby enabling continuity of communications across IP address changes. HIP is based on a Diffie-Hellman key exchange, using public key identifiers from a new Host Identity namespace for mutual peer authentication. The protocol is designed to be resistant to denial-of-service (DoS) and man-in-the-middle (MitM) attacks. When used together with another suitable security protocol, such as the Encapsulating Security Payload (ESP), it provides integrity protection and optional encryption for upper-layer protocols, such as TCP and UDP.This document obsoletes RFC 5201 and addresses the concerns raised by the IESG, particularly that of crypto agility. It also incorporates lessons learned from the implementations of RFC 5201. This document specifies a method to find which Registration Data Access Protocol (RDAP) server is authoritative to answer queries for a requested scope, such as domain names, IP addresses, or Autonomous System numbers. This document defines a rendezvous extension for the Host Identity Protocol (HIP). The rendezvous extension extends HIP and the HIP Registration Extension for initiating communication between HIP nodes via HIP rendezvous servers. Rendezvous servers improve reachability and operation when HIP nodes are multihomed or mobile. This document obsoletes RFC 5204. This document specifies a resource record (RR) for the Domain Name System (DNS) and how to use it with the Host Identity Protocol (HIP). This RR allows a HIP node to store in the DNS its Host Identity (HI), the public component of the node public-private key pair; its Host Identity Tag (HIT), a truncated hash of its public key (PK); and the domain names of its rendezvous servers (RVSs). This document obsoletes RFC 5205. This document describes an Extensible Provisioning Protocol (EPP) mapping for the provisioning and management of Internet domain names stored in a shared central repository. Specified in XML, the mapping defines EPP command syntax and semantics as applied to domain names. This document obsoletes RFC 4931. [STANDARDS-TRACK] This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This document describes an application-layer client-server protocol for the provisioning and management of objects stored in a shared central repository. Specified in XML, the protocol defines generic object management operations and an extensible framework that maps protocol operations to objects. This document includes a protocol specification, an object mapping template, and an XML media type registration. This document obsoletes RFC 4930. [STANDARDS-TRACK] This document describes using the ASTM Broadcast Remote ID (B-RID) specification in a "crowd sourced" smart phone environment to provide much of the FAA mandated Network Remote ID (N-RID) functionality. This crowd sourced B-RID data will use multilateration to add a level of reliability in the location data on the Unmanned Aircraft (UA). The crowd sourced environment will also provide a monitoring coverage map to authorized observers. This document describes how to include trust into the ASTM Remote ID specification defined in ASTM 3411-19 under a Broadcast Remote ID (RID) scenario. It defines a few different message schemes (based on the Authentication Message) that can be used to assure past messages sent by a UA and also act as an assurance for UA trustworthiness in the absence of Internet connectivity at the receiving node. This document describes the Identity Claims or Certificates for use in various Drone Remote ID Protocols (DRIP) and the wider Unmanned Traffic Management (UTM) system. This document provides the mechanisms for secure transport of UAS Network-RemoteID and Command-and-Control messaging. Both HIP and DTLS based methods are described. This document describes the use of Hierarchical Host Identity Tags (HHITs) as self-asserting IPv6 addresses and thereby a trustable Identifier for use as the UAS Remote ID. HHITs self-attest to the included explicit hierarchy that provides Registrar discovery for 3rd-party ID attestation. This document describes using the registration protocol and registries to support hierarchical HITs (HHITs). New and existing HIP parameters are used to communicate Registry Policies and data about the HHIT device and the Registries. Further Registries are expected to provide RVS services for registered HHIT devices. This document describes using a hierarchical HIT to facilitate large deployments of managed devices. Hierarchical HITs differ from HIPv2 flat HITs by only using 64 bits for mapping the Host Identity, freeing 32 bits to bind in a hierarchy of Registering Entities that provide services to the consumers of hierarchical HITs. This document provides an overview of the architecture of the L-band Digital Aeronautical Communications System (LDACS), which provides a secure, scalable and spectrum efficient terrestrial data link for civil aviation. LDACS is a scheduled, reliable multi-application cellular broadband system with support for IPv6. LDACS shall provide a data link for IP network-based aircraft guidance. High reliability and availability for IP connectivity over LDACS are therefore essential. This document provides new cryptographic algorithms to be used with HIP. The Edwards Elliptic Curve and the Keccak sponge functions are the main focus. The HIP parameters and processing instructions impacted by these algorithms are defined. This document specifies how to use the cSHAKE hash for ORCHID generation and allows for varying sized hashes in the ORCHID along with additional information within the ORCHID. It is an addendum to ORCHIDv2 [RFC7343].

The National Aeronautics and Space Administration (NASA) and FAAs' effort of integrating UAS's operation into the national airspace system (NAS) leads to the development of the concept of UTM and the ecosystem around it. The UTM concept was initially presented in 2013. The eventual development and implementation are conducted by the UTM research transition team which is the joint workforce by FAA and NASA. World efforts took place afterward. The Single European Sky ATM Research (SESAR) started the CORUS project to research its UTM counterpart concept, namely . This effort is led by the European Organization for the Safety of Air Navigation (Eurocontrol). Both NASA and SESAR have published the UTM concept of operations to guide the development of their future air traffic management (ATM) system and make sure safe and efficient integrations of manned and unmanned aircraft into the national airspace. The UTM composes of UAS operation infrastructure, procedures and local regulation compliance policies to guarantee UAS's safe integration and operation. The main functionality of a UTM includes, but is not limited to, providing means of communication between UAS operators and service providers and a platform to facilitate communication among UAS service providers.

A USS plays an important role to fulfill the key performance indicators (KPIs) that a UTM has to offer. Such Entity acts as a proxy between UAS operators and UTM service providers. It provides services like real-time UAS traffic monitor and planning, aeronautical data archiving, airspace and violation control, interacting with other third-party control entities, etc. A USS can coexist with other USS(s) to build a large service coverage map which can load-balance, relay and share UAS traffic information. The FAA works with UAS industry shareholders and promotes the Low Altitude Authorization and Notification Capability program which is the first implementation to realize UTM's functionality. The LAANC program can automate the UAS's fly plan application and approval process for airspace authorization in real-time by checking against multiple aeronautical databases such as airspace classification and fly rules associated with it, FAA UAS facility map, special use airspace, Notice to airman (NOTAM) and Temporary flight rule (TFR).

This section illustrates a couple of use case scenarios where UAS participation in UTM has significant safety improvement. For a UAS participating in UTM and takeoff or land in a controlled airspace (e.g., Class Bravo, Charlie, Delta and Echo in United States), the USS where UAS is currently communicating with is responsible for UAS's registration, authenticating the UAS's fly plan by checking against designated UAS fly map database, obtaining the air traffic control (ATC) authorization and monitor the UAS fly path in order to maintain safe boundary and follow the pre-authorized route. For a UAS participating in UTM and take off or land in an uncontrolled airspace (ex. Class Golf in the United States), pre-fly authorization must be obtained from a USS when operating beyond-visual-of-sight (BVLOS) operation. The USS either accepts or rejects received intended fly plan from the UAS. Accepted UAS operation may share its current fly data such as GPS position and altitude to USS. The USS may keep the UAS operation status near real-time and may keep it as a record for overall airspace air traffic monitor.

The ADS-B is the de facto technology used in manned aviation for sharing locaiton infomraiton, which is a ground and satellite based system designed in the early 2000s. Broadcast RID is conceptually similar to ADS-B. However, for numerous technical and regulatory reasons, ADS-B itself is not suitable for low-flying small UA. Technical reasons include: needing RF-LOS to large, expensive (hence scarce) ground stations; needing both a satellite receiver and 1090 MHz transceiver onboard CSWaP constrained UA; the limited bandwidth of both uplink and downlink, which are adequate for the current manned aviation traffic volume, but would likely be saturated by large numbers of UAS, endangering manned aviation; etc. Understanding these technical shortcomings, regulators world-wide have ruled out use of ADS-B for the small UAS for which UAS RID and DRIP are intended.