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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 180 has weird spacing: '... Public o---...' -- The document date (14 June 2021) is 1045 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 4423 (Obsoleted by RFC 9063) -- Obsolete informational reference (is this intentional?): RFC 6347 (Obsoleted by RFC 9147) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DRIP S. Card, Ed. 3 Internet-Draft A. Wiethuechter 4 Intended status: Informational AX Enterprize 5 Expires: 16 December 2021 R. Moskowitz 6 HTT Consulting 7 A. Gurtov 8 Linköping University 9 14 June 2021 11 Drone Remote Identification Protocol (DRIP) Requirements 12 draft-ietf-drip-reqs-13 14 Abstract 16 This document defines terminology and requirements for Drone Remote 17 Identification Protocol (DRIP) Working Group solutions to support 18 Unmanned Aircraft System Remote Identification and tracking (UAS RID) 19 for security, safety, and other purposes (e.g., initiation of 20 identity based network sessions supporting UAS applications). 21 Complementing external technical standards as regulator-accepted 22 means of compliance with UAS RID regulations, DRIP will facilitate 23 use of existing Internet resources to support RID and to enable 24 enhanced related services, and will enable online and offline 25 verification that RID information is trustworthy. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on 16 December 2021. 44 Copyright Notice 46 Copyright (c) 2021 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 51 license-info) in effect on the date of publication of this document. 52 Please review these documents carefully, as they describe your rights 53 and restrictions with respect to this document. Code Components 54 extracted from this document must include Simplified BSD License text 55 as described in Section 4.e of the Trust Legal Provisions and are 56 provided without warranty as described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.1. Motivation and External Influences . . . . . . . . . . . 3 62 1.2. Concerns and Constraints . . . . . . . . . . . . . . . . 8 63 1.3. DRIP Scope . . . . . . . . . . . . . . . . . . . . . . . 10 64 1.4. Document Scope . . . . . . . . . . . . . . . . . . . . . 11 65 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 11 66 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 11 67 2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 12 68 3. UAS RID Problem Space . . . . . . . . . . . . . . . . . . . . 20 69 3.1. Network RID . . . . . . . . . . . . . . . . . . . . . . . 22 70 3.2. Broadcast RID . . . . . . . . . . . . . . . . . . . . . . 25 71 3.3. USS in UTM and RID . . . . . . . . . . . . . . . . . . . 29 72 3.4. DRIP Focus . . . . . . . . . . . . . . . . . . . . . . . 30 73 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 31 74 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 31 75 4.1.1. Normative Requirements . . . . . . . . . . . . . . . 31 76 4.1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 32 77 4.2. Identifier . . . . . . . . . . . . . . . . . . . . . . . 33 78 4.2.1. Normative Requirements . . . . . . . . . . . . . . . 33 79 4.2.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 34 80 4.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 35 81 4.3.1. Normative Requirements . . . . . . . . . . . . . . . 35 82 4.3.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 36 83 4.4. Registries . . . . . . . . . . . . . . . . . . . . . . . 37 84 4.4.1. Normative Requirements . . . . . . . . . . . . . . . 37 85 4.4.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 37 86 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 87 6. Security Considerations . . . . . . . . . . . . . . . . . . . 38 88 7. Privacy and Transparency Considerations . . . . . . . . . . . 39 89 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 90 8.1. Normative References . . . . . . . . . . . . . . . . . . 40 91 8.2. Informative References . . . . . . . . . . . . . . . . . 40 92 Appendix A. Discussion and Limitations . . . . . . . . . . . . . 44 93 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 46 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 96 1. Introduction 98 For any unfamiliar or _a priori_ ambiguous terminology herein, see 99 Section 2. 101 1.1. Motivation and External Influences 103 Many considerations (especially safety and security) necessitate 104 Unmanned Aircraft Systems (UAS) Remote Identification and tracking 105 (RID). 107 Unmanned Aircraft (UA) may be fixed wing, rotary wing (e.g., 108 helicopter), hybrid, balloon, rocket, etc. Small fixed wing UA 109 typically have Short Take-Off and Landing (STOL) capability; rotary 110 wing and hybrid UA typically have Vertical Take-Off and Landing 111 (VTOL) capability. UA may be single- or multi-engine. The most 112 common today are multicopters: rotary wing, multi engine. The 113 explosion in UAS was enabled by hobbyist development, for 114 multicopters, of advanced flight stability algorithms, enabling even 115 inexperienced pilots to take off, fly to a location of interest, 116 hover, and return to the take-off location or land at a distance. 117 UAS can be remotely piloted by a human (e.g., with a joystick) or 118 programmed to proceed from Global Navigation Satellite System (GNSS) 119 waypoint to waypoint in a weak form of autonomy; stronger autonomy is 120 coming. 122 Small UA are "low observable" as they: 124 * typically have small radar cross sections; 126 * make noise quite noticeable at short ranges but difficult to 127 detect at distances they can quickly close (500 meters in under 13 128 seconds by the fastest consumer mass market drones available in 129 early 2021); 131 * typically fly at low altitudes (e.g., for those to which RID 132 applies in the US, under 400 feet Above Ground Level (AGL) as per 133 [Part107]); 135 * are highly maneuverable so can fly under trees and between 136 buildings. 138 UA can carry payloads including sensors, cyber and kinetic weapons, 139 or can be used themselves as weapons by flying them into targets. 140 They can be flown by clueless, careless, or criminal operators. Thus 141 the most basic function of UAS RID is "Identification Friend or Foe" 142 (IFF) to mitigate the significant threat they present. 144 Diverse other applications can be enabled or facilitated by RID. 145 Internet protocols typically start out with at least one entity 146 already knowing an identifier or locator of another; but an entity 147 (e.g., UAS or Observer device) encountering an _a priori_ unknown UA 148 in physical space has no identifier or logical space locator for that 149 UA, unless and until one is provided somehow. RID provides an 150 identifier, which, if well chosen, can facilitate use of a variety of 151 Internet family protocols and services to support arbitrary 152 applications, beyond the basic security functions of RID. For most 153 of these, some type of identifier is essential, e.g., Network Access 154 Identifier (NAI), Digital Object Identifier (DOI), Uniform Resource 155 Identifier (URI), domain name, or public key. DRIP motivations 156 include both the basic security and the broader application support 157 functions of RID. 159 The general UAS RID usage scenario is illustrated in Figure 1. 161 +-----+ +-----+ 162 | UA1 | | UA2 | 163 +-----+ +-----+ 165 +----------+ +----------+ 166 | General | | Public | 167 | Public | | Safety | 168 | Observer o------\ /------o Observer | 169 +----------+ | | +----------+ 170 | | 171 ************* 172 +----------+ * * +----------+ 173 | UA1 | * * | UA2 | 174 | Pilot/ o------* Internet *------o Pilot/ | 175 | Operator | * * | Operator | 176 +----------+ * * +----------+ 177 ************* 178 | | | 179 +----------+ | | | +----------+ 180 | Public o---/ | \---o Private | 181 | Registry | | | Registry | 182 +----------+ | +----------+ 183 +--o--+ 184 | DNS | 185 +-----+ 187 Figure 1: "General UAS RID Usage Scenario" 189 Figure 1 illustrates a typical case where there may be: multiple 190 Observers, some of them members of the general public, others 191 government officers with public safety/security responsibilities; 192 multiple UA in flight within observation range, each with its own 193 pilot/operator; at least one registry each for lookup of public and 194 (by authorized parties only) private information regarding the UAS 195 and their pilots/operators; and in the DRIP vision, DNS resolving 196 various identifiers and locators of the entities involved. Note the 197 absence of any links to/from the UA in the figure; this is because 198 UAS RID and other connectivity involving the UA varies as described 199 below. 201 An Observer of UA may need to classify them, as illustrated 202 notionally in Figure 2, for basic airspace Situational Awareness 203 (SA). An Observer who classifies a UAS: as Taskable, can ask it to 204 do something useful; as Low Concern, can reasonably assume it is not 205 malicious and would cooperate with requests to modify its flight 206 plans for safety concerns that arise; as High Concern or 207 Unidentified, can focus surveillance on it. 209 xxxxxxx +--------------+ 210 x x No | | 211 x ID? x+---->| Unidentified | 212 x x | | 213 xxxxxxx +--------------+ 214 + 215 | Yes 216 v 217 xxxxxxx 218 x x 219 /---------+x Type? x+----------\ 220 | x x | 221 | xxxxxxx | 222 | + | 223 v v v 224 +--------------+ +--------------+ +--------------+ 225 | | | | | | 226 | Taskable | | Low Concern | | High Concern | 227 | | | | | | 228 +--------------+ +--------------+ +--------------+ 230 Figure 2: "Notional UAS Classification" 232 ASTM International, Technical Committee F38 (UAS), Subcommittee 233 F38.02 (Aircraft Operations), Work Item WK65041, developed the widely 234 cited Standard Specification for Remote ID and Tracking [F3411-19]: 235 the published standard is available for purchase from ASTM and as an 236 ASTM membership premium; early drafts are freely available as 237 [OpenDroneID] specifications. [F3411-19] is frequently referenced in 238 DRIP, where building upon its link layers and both enhancing support 239 for and expanding the scope of its applications are central foci. 241 In many applications, including UAS RID, identification and 242 identifiers are not ends in themselves; they exist to enable lookups 243 and provision of other services. 245 Using UAS RID to facilitate vehicular (V2X) communications and 246 applications such as Detect And Avoid (DAA), which would impose 247 tighter latency bounds than RID itself, is an obvious possibility, 248 explicitly contemplated in the United States (US) Federal Aviation 249 Administration (FAA) Remote Identification of Unmanned Aircraft rule 250 [FRUR]. However, applications of RID beyond RID itself, including 251 DAA, have been declared out of scope in ASTM F38.02 WK65041, based on 252 a distinction between RID as a security standard vs DAA as a safety 253 application. Each Standards Development Organization (SDO) has its 254 own cultural set of connotations of safety vs security; the 255 denotative definitions of the International Civil Aviation 256 Organization (ICAO) are cited in Section 2. 258 [Opinion1] and [WG105] cite the Direct Remote Identification (DRI) 259 previously required and specified, explicitly stating that whereas 260 DRI is primarily for security purposes, the "Network Identification 261 Service" [Opinion1] (in the context of U-space [InitialView]) or 262 "Electronic Identification" [WG105] is primarily for safety purposes 263 (e.g., Air Traffic Management, especially hazards deconfliction) and 264 also is allowed to be used for other purposes such as support of 265 efficient operations. These emerging standards allow the security 266 and safety oriented systems to be separate or merged. In addition to 267 mandating both Broadcast and Network one-way to Observers, they will 268 use V2V to other UAS (also likely to and/or from some manned 269 aircraft). These reflect the broad scope of the European Union (EU) 270 U-space concept, as being developed in the Single European Sky ATM 271 Research (SESAR) Joint Undertaking, the U-space architectural 272 principles of which are outlined in [InitialView]. 274 ASD-STAN is an Associated Body to CEN (European Committee for 275 Standardization) for Aerospace Standards. It is publishing an EU 276 standard "Aerospace series - Unmanned Aircraft Systems - Part 002: 277 Direct Remote Identification; English version prEN 4709-002:2020" for 278 which a current (early 2021) informal overview is freely available in 279 [ASDRI]. It will provide compliance to cover the identical DRI 280 requirements applicable to drones of classes C1 - [Delegated] Part 2, 281 C2 - [Delegated] Part 3, C3 - [Delegated] Part 4, C5 - [Amended] Part 282 16, and C6 - [Amended] Part 17. 284 The standard contemplated in [ASDRI] will provide UA capability to be 285 identified in real time during the whole duration of the flight, 286 without specific connectivity or ground infrastructure link, 287 utilizing existing mobile devices within broadcast range. It will 288 use Bluetooth 4, Bluetooth 5, Wi-Fi Neighbor Awareness Networking 289 (NAN, also known as Wi-Fi Aware, [WiFiNAN]) and/or IEEE 802.11 Beacon 290 modes. The EU standard emphasis was compatibility with [F3411-19], 291 although there are differences in mandatory and optional message 292 types and fields. 294 The [ASDRI] contemplated DRI system will broadcast locally: 296 1. the UAS operator registration number; 298 2. the [CTA2063A] compliant unique serial number of the UA; 300 3. a time stamp, the geographical position of the UA, and its height 301 AGL or above its take-off point; 303 4. the UA ground speed and route course measured clockwise from true 304 north; 306 5. the geographical position of the remote pilot, or if that is not 307 available, the geographical position of the UA take-off point; 308 and 310 6. for Classes C1, C2, C3, the UAS emergency status. 312 Under the [ASDRI] contemplated standard, data will be sent in plain 313 text and the UAS operator registration number will be represented as 314 a 16-byte string including the (European) state code. The 315 corresponding private ID part will contain 3 characters that are not 316 broadcast but used by authorities to access regional registration 317 databases for verification. 319 ASD-STAN also contemplates corresponding Network Remote 320 Identification (NRI) functionality. The ASD-STAN RID target is to 321 revise their current standard with additional functionality (e.g., 322 DRIP) to be published before 2022 [ASDRI]. 324 Security oriented UAS RID essentially has two goals: enable the 325 general public to obtain and record an opaque ID for any observed UA, 326 which they can then report to authorities; enable authorities, from 327 such an ID, to look up information about the UAS and its operator. 328 Safety oriented UAS RID has stronger requirements. Aviation 329 community SDOs set a higher bar for safety than for security, 330 especially with respect to reliability. 332 Although dynamic establishment of secure communications between the 333 Observer and the UAS pilot seems to have been contemplated by the FAA 334 UAS ID and Tracking Aviation Rulemaking Committee (ARC) in their 335 [Recommendations], it is not addressed in any of the 336 subsequent regulations or international SDO technical specifications, 337 other than DRIP, known to the authors as of early 2021. 339 1.2. Concerns and Constraints 341 Disambiguation of multiple UA flying in close proximity may be very 342 challenging, even if each is reporting its identity, position, and 343 velocity as accurately as it can. 345 The origin of information in UAS RID and UAS Traffic Management (UTM) 346 generally is the UAS or its operator. Self-reports may be initiated 347 by the remote pilot at the console of the Ground Control Station 348 (GCS, the UAS subsystem used to remotely operate the UA), or 349 automatically by GCS software; in Broadcast RID, they typically would 350 be initiated automatically by a process on the UA. Data in the 351 reports may come from sensors available to the operator (e.g., radar 352 or cameras), the GCS (e.g., "dead reckoning" UA location, starting 353 from the takeoff location and estimating the displacements due to 354 subsequent piloting commands, wind, etc.), or the UA itself (e.g., an 355 on-board GNSS receiver); in Broadcast RID, all the data must be sent 356 proximately by, and most of the data comes ultimately from, the UA 357 itself. Whether information comes proximately from the operator, or 358 from automated systems configured by the operator, there are 359 possibilities not only of unintentional error in but also of 360 intentional falsification of this data. Mandating UAS RID, 361 specifying data elements required to be sent, monitoring compliance 362 and enforcing it (or penalizing non-compliance) are matters for Civil 363 Aviation Authorities (CAAs) et al; specifying message formats, etc. 364 to carry those data elements has been addressed by other SDOs; 365 offering technical means, as extensions to external standards, to 366 facilitate verifiable compliance and enforcement/monitoring, are 367 opportunities for DRIP. 369 Minimal specified information must be made available to the public. 370 Access to other data, e.g., UAS operator Personally Identifiable 371 Information (PII), must be limited to strongly authenticated 372 personnel, properly authorized in accordance with applicable policy. 373 The balance between privacy and transparency remains a subject for 374 public debate and regulatory action; DRIP can only offer tools to 375 expand the achievable trade space and enable trade-offs within that 376 space. [F3411-19], the basis for most current (2021) thinking about 377 and efforts to provide UAS RID, specifies only how to get the UAS ID 378 to the Observer: how the Observer can perform these lookups and how 379 the registries first can be populated with information are 380 unspecified therein. 382 The need for nearly universal deployment of UAS RID is pressing: 383 consider how negligible the value of an automobile license plate 384 system would be if only 90% of the cars displayed plates. This 385 implies the need to support use by Observers of already ubiquitous 386 mobile devices (typically smartphones and tablets). Anticipating CAA 387 requirements to support legacy devices, especially in light of 388 [Recommendations], [F3411-19] specifies that any UAS sending 389 Broadcast RID over Bluetooth must do so over Bluetooth 4, regardless 390 of whether it also does so over newer versions; as UAS sender devices 391 and Observer receiver devices are unpaired, this implies extremely 392 short "advertisement" (beacon) frames. 394 Wireless data links to or from UA are challenging. Flight is often 395 amidst structures and foliage at low altitudes over varied terrain. 396 UA are constrained in both total energy and instantaneous power by 397 their batteries. Small UA imply small antennas. Densely populated 398 volumes will suffer from link congestion: even if UA in an airspace 399 volume are few, other transmitters nearby on the ground, sharing the 400 same license free spectral band, may be many. Thus air to air and 401 air to ground links will generally be slow and unreliable. 403 UAS Cost, Size, Weight, and Power (CSWaP) constraints are severe. 404 CSWaP is a burden not only on the designers of new UAS for sale, but 405 also on owners of existing UAS that must be retrofit. Radio 406 Controlled (RC) aircraft modelers, "hams" who use licensed amateur 407 radio frequencies to control UAS, drone hobbyists, and others who 408 custom build UAS, all need means of participating in UAS RID, 409 sensitive to both generic CSWaP and application-specific 410 considerations. 412 To accommodate the most severely constrained cases, all these 413 conspire to motivate system design decisions that complicate the 414 protocol design problem. 416 Broadcast RID uses one-way local data links. UAS may have Internet 417 connectivity only intermittently, or not at all, during flight. 419 Internet-disconnected operation of Observer devices has been deemed 420 by ASTM F38.02 too infrequent to address. However, the preamble to 421 [FRUR] cites "remote and rural areas that do not have reliable 422 Internet access" as a major reason for requiring Broadcast rather 423 than Network RID, and states that "Personal wireless devices that are 424 capable of receiving 47 CFR part 15 frequencies, such as smart 425 phones, tablets, or other similar commercially available devices, 426 will be able to receive broadcast remote identification information 427 directly without reliance on an Internet connection". Internet- 428 disconnected operation presents challenges, e.g., for Observers 429 needing access to the [F3411-19] web based Broadcast Authentication 430 Verifier Service or external lookups. 432 As RID must often operate within these constraints, heavyweight 433 cryptographic security protocols or even simple cryptographic 434 handshakes are infeasible, yet trustworthiness of UAS RID information 435 is essential. Under [F3411-19], _even the most basic datum, the UAS 436 ID itself, can be merely an unsubstantiated claim_. 438 Observer devices being ubiquitous, thus popular targets for malware 439 or other compromise, cannot be generally trusted (although the user 440 of each device is compelled to trust that device, to some extent); a 441 "fair witness" functionality (inspired by [Stranger]) is desirable. 443 Despite work by regulators and SDOs, there are substantial gaps in 444 UAS standards generally and UAS RID specifically. [Roadmap] catalogs 445 UAS related standards, ongoing standardization activities and gaps 446 (as of 2020); Section 7.8 catalogs those related specifically to UAS 447 RID. DRIP will address the most fundamental of these gaps, as 448 foreshadowed above. 450 1.3. DRIP Scope 452 DRIP's initial charter is to make RID immediately actionable, in both 453 Internet and local-only connected scenarios (especially emergencies), 454 in severely constrained UAS environments, balancing legitimate (e.g., 455 public safety) authorities' Need To Know trustworthy information with 456 UAS operators' privacy. By "immediately actionable" is meant 457 information of sufficient precision, accuracy, timeliness, etc. for 458 an Observer to use it as the basis for immediate decisive action, 459 whether that be to trigger a defensive counter-UAS system, to attempt 460 to initiate communications with the UAS operator, to accept the 461 presence of the UAS in the airspace where/when observed as not 462 requiring further action, or whatever, with potentially severe 463 consequences of any action or inaction chosen based on that 464 information. For further explanation of the concept of immediate 465 actionability, see [ENISACSIRT]. 467 Note that UAS RID must achieve nearly universal adoption, but DRIP 468 can add value even if only selectively deployed. Authorities with 469 jurisdiction over more sensitive airspace volumes may set a higher 470 than generally mandated RID requirement for flight in such volumes. 471 Those with a greater need for high-confidence IFF can equip with 472 DRIP, enabling strong authentication of their own aircraft and allied 473 operators without regard for the weaker (if any) authentication of 474 others. 476 DRIP (originally Trustworthy Multipurpose Remote Identification, TM- 477 RID) potentially could be applied to verifiably identify other types 478 of registered things reported to be in specified physical locations, 479 and providing timely trustworthy identification data is also 480 prerequisite to identity-oriented networking, but the urgent 481 motivation and clear initial focus is UAS. Existing Internet 482 resources (protocol standards, services, infrastructure, and business 483 models) should be leveraged. 485 1.4. Document Scope 487 This document describes the problem space for UAS RID conforming to 488 proposed regulations and external technical standards, defines common 489 terminology, specifies numbered requirements for DRIP, identifies 490 some important considerations (IANA, security, privacy and 491 transparency), and discusses limitations. 493 A natural Internet-based approach to meet these requirements is 494 described in a companion architecture document [drip-architecture] 495 and elaborated in other DRIP documents. 497 2. Terms and Definitions 499 2.1. Requirements Terminology 501 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 502 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 503 "OPTIONAL" in this document are to be interpreted as described in BCP 504 14 [RFC2119] [RFC8174] when, and only when, they appear in all 505 capitals, as shown here. 507 2.2. Definitions 509 This section defines a non-comprehensive set of terms expected to be 510 used in DRIP documents. This list is meant to be the DRIP 511 terminology reference; as such, some of the terms listed below are 512 not used in this document. 514 [RFC4949] provides a glossary of Internet security terms that should 515 be used where applicable. 517 In the UAS community, the plural form of acronyms generally is the 518 same as the singular form, e.g., Unmanned Aircraft System (singular) 519 and Unmanned Aircraft Systems (plural) are both represented as UAS. 520 On this and other terminological issues, to encourage comprehension 521 necessary for adoption of DRIP by the intended user community, that 522 community's norms are respected herein, and definitions are quoted in 523 cases where they have been found in that community's documents. Most 524 of the listed terms are from that community (even if specific source 525 documents are not cited); any that are DRIP-specific or invented by 526 the authors of this document are marked "(DRIP)". 528 4-D 529 Four-dimensional. Latitude, Longitude, Altitude, Time. Used 530 especially to delineate an airspace volume in which an operation 531 is being or will be conducted. 533 AAA 534 Attestation, Authentication, Authorization, Access Control, 535 Accounting, Attribution, Audit, or any subset thereof (uses differ 536 by application, author, and context). (DRIP) 538 ABDAA 539 AirBorne DAA. Accomplished using systems onboard the aircraft 540 involved. Supports "self-separation" (remaining "well clear" of 541 other aircraft) and collision avoidance. 543 ADS-B 544 Automatic Dependent Surveillance - Broadcast. "ADS-B Out" 545 equipment obtains aircraft position from other on-board systems 546 (typically GNSS) and periodically broadcasts it to "ADS-B In" 547 equipped entities, including other aircraft, ground stations, and 548 satellite based monitoring systems. 550 AGL 551 Above Ground Level. Relative altitude, above the variously 552 defined local ground level, typically of a UA, measured in feet or 553 meters. Should be explicitly specified as either barometric 554 (pressure) or geodetic (GNSS) altitude. 556 ATC 557 Air Traffic Control. Explicit flight direction to pilots from 558 ground controllers. Contrast with ATM. 560 ATM 561 Air Traffic Management. A broader functional and geographic scope 562 and/or a higher layer of abstraction than ATC. "The dynamic, 563 integrated management of air traffic and airspace including air 564 traffic services, airspace management and air traffic flow 565 management - safely, economically and efficiently - through the 566 provision of facilities and seamless services in collaboration 567 with all parties and involving airborne and ground-based 568 functions" [ICAOATM]. 570 Authentication Message 571 [F3411-19] Message Type 2. Provides framing for authentication 572 data, only; the only message that can be extended in length by 573 segmenting it across more than one page. 575 Basic ID Message 576 [F3411-19] Message Type 0. Provides UA Type, UAS ID Type, and UAS 577 ID, only. 579 Broadcast Authentication Verifier Service 580 System component designed to handle any authentication of 581 Broadcast RID by offloading signature verification to a web 582 service [F3411-19]. 584 BVLOS 585 Beyond Visual Line Of Sight. See VLOS. 587 byte 588 Used here in its now-customary sense as a synonym for "octet", as 589 "byte" is used exclusively in definitions of data structures 590 specified in [F3411-19] 592 CAA 593 Civil Aviation Authority of a regulatory jurisdiction. Often so 594 named, but other examples include the United States Federal 595 Aviation Administration (FAA) and the Japan Civil Aviation Bureau. 597 CSWaP 598 Cost, Size, Weight, and Power. 600 C2 601 Command and Control. Previously mostly used in military contexts. 602 Properly refers to a function, exercisable over arbitrary 603 communications; but in the small UAS context, often refers to the 604 communications (typically RF data link) over which the GCS 605 controls the UA. 607 DAA 608 Detect And Avoid, formerly Sense And Avoid (SAA). A means of 609 keeping aircraft "well clear" of each other and obstacles for 610 safety. "The capability to see, sense or detect conflicting 611 traffic or other hazards and take the appropriate action to comply 612 with the applicable rules of flight" [ICAOUAS]. 614 DRI (not to be confused with DRIP) 615 Direct Remote Identification. EU regulatory requirement for "a 616 system that ensures the local broadcast of information about a UA 617 in operation, including the marking of the UA, so that this 618 information can be obtained without physical access to the UA". 619 [Delegated] that presumably can be satisfied with appropriately 620 configured [F3411-19] Broadcast RID. 622 DSS 623 Discovery and Synchronization Service. The UTM system overlay 624 network backbone. Most importantly, it enables one USS to learn 625 which other USS have UAS operating in a given 4-D airspace volume, 626 for strategic deconfliction of planned operations and Network RID 627 surveillance of active operations. [F3411-19] 629 EUROCAE 630 European Organisation for Civil Aviation Equipment. Aviation SDO, 631 originally European, now with broader membership. Cooperates 632 extensively with RTCA. 634 GBDAA 635 Ground Based DAA. Accomplished with the aid of ground based 636 functions. 638 GCS 639 Ground Control Station. The part of the UAS that the remote pilot 640 uses to exercise C2 over the UA, whether by remotely exercising UA 641 flight controls to fly the UA, by setting GNSS waypoints, or 642 otherwise directing its flight. 644 GNSS 645 Global Navigation Satellite System. Satellite based timing and/or 646 positioning with global coverage, often used to support 647 navigation. 649 GPS 650 Global Positioning System. A specific GNSS, but in the UAS 651 context, the term is typically misused in place of the more 652 generic term GNSS. 654 GRAIN 655 Global Resilient Aviation Interoperable Network. ICAO managed 656 IPv6 overlay internetwork based on IATF, dedicated to aviation 657 (but not just aircraft). Currently (2021) in design, 658 accommodating the proposed DRIP identifier. 660 IATF 661 International Aviation Trust Framework. ICAO effort to develop a 662 resilient and secure by design framework for networking in support 663 of all aspects of aviation. 665 ICAO 666 International Civil Aviation Organization. A United Nations 667 specialized agency that develops and harmonizes international 668 standards relating to aviation. 670 IFF 671 Identification Friend or Foe. Originally, and in its narrow sense 672 still, a self-identification broadcast in response to 673 interrogation via radar, to reduce friendly fire incidents, which 674 led to military and commercial transponder systems such as ADS-B. 675 In the broader sense used here, any process intended to 676 distinguish friendly from potentially hostile UA or other entities 677 encountered. 679 LAANC 680 Low Altitude Authorization and Notification Capability. Supports 681 ATC authorization requirements for UAS operations: remote pilots 682 can apply to receive a near real-time authorization for operations 683 under 400 feet in controlled airspace near airports. FAA 684 authorized partial stopgap in the US until UTM comes. 686 Location/Vector Message 687 [F3411-19] Message Type 1. Provides UA location, altitude, 688 heading, speed, and status. 690 LOS 691 Line Of Sight. An adjectival phrase describing any information 692 transfer that travels in a nearly straight line (e.g., 693 electromagnetic energy, whether in the visual light, RF, or other 694 frequency range) and is subject to blockage. A term to be avoided 695 due to ambiguity, in this context, between RF LOS and VLOS. 697 Message Pack 698 [F3411-19] Message Type 15. The framed concatenation, in message 699 type index order, of at most one message of each type of any 700 subset of the other types. Required to be sent in Wi-Fi NAN and 701 in Bluetooth 5 Extended Advertisements, if those media are used; 702 cannot be sent in Bluetooth 4. 704 MSL 705 Mean Sea Level. Shorthand for relative altitude, above the 706 variously defined mean sea level, typically of a UA (but in [FRUR] 707 also for a GCS), measured in feet or meters. Should be explicitly 708 specified as either barometric (pressure) or geodetic (e.g., as 709 indicated by GNSS, referenced to the WGS84 ellipsoid). 711 Net-RID DP 712 Network RID Display Provider. [F3411-19] logical entity that 713 aggregates data from Net-RID SPs as needed in response to user 714 queries regarding UAS operating within specified airspace volumes, 715 to enable display by a user application on a user device. 716 Potentially could provide not only information sent via UAS RID 717 but also information retrieved from UAS RID registries or 718 information beyond UAS RID. Under superseded [NPRM], not 719 recognized as a distinct entity, but a service provided by USS, 720 including Public Safety USS that may exist primarily for this 721 purpose rather than to manage any subscribed UAS. 723 Net-RID SP 724 Network RID Service Provider. [F3411-19] logical entity that 725 collects RID messages from UAS and responds to NetRID-DP queries 726 for information on UAS of which it is aware. Under superseded 727 [NPRM], the USS to which the UAS is subscribed ("Remote ID USS"). 729 Network Identification Service 730 EU regulatory requirement in [Opinion1] and [WG105] that 731 presumably can be satisfied with appropriately configured 732 [F3411-19] Network RID. 734 Observer 735 An entity (typically but not necessarily an individual human) who 736 has directly or indirectly observed a UA and wishes to know 737 something about it, starting with its ID. An Observer typically 738 is on the ground and local (within VLOS of an observed UA), but 739 could be remote (observing via Network RID or other surveillance), 740 operating another UA, aboard another aircraft, etc. (DRIP) 742 Operation 743 A flight, or series of flights of the same mission, by the same 744 UAS, separated by at most brief ground intervals. (Inferred from 745 UTM usage, no formal definition found) 747 Operator 748 "A person, organization or enterprise engaged in or offering to 749 engage in an aircraft operation" [ICAOUAS]. 751 Operator ID Message 752 [F3411-19] Message Type 5. Provides CAA issued Operator ID, only. 753 Operator ID is distinct from UAS ID. 755 page 756 Payload of a frame, containing a chunk of a message that has been 757 segmented, to allow transport of a message longer than can be 758 encapsulated in a single frame. [F3411-19] 760 PIC 761 Pilot In Command. "The pilot designated by the operator, or in 762 the case of general aviation, the owner, as being in command and 763 charged with the safe conduct of a flight" [ICAOUAS]. 765 PII 766 Personally Identifiable Information. In the UAS RID context, 767 typically of the UAS Operator, Pilot In Command (PIC), or Remote 768 Pilot, but possibly of an Observer or other party. This specific 769 term is used primarily in the US; other terms with essentially the 770 same meaning are more common in other jurisdictions (e.g., 771 "personal data" in the EU). Used herein generically to refer to 772 personal information, which the person might wish to keep private, 773 or may have a statutorily recognized right to keep private (e.g., 774 under the EU [GDPR]), potentially imposing (legally or ethically) 775 a confidentiality requirement on protocols/systems. 777 Remote Pilot 778 A pilot using a GCS to exercise proximate control of a UA. Either 779 the PIC or under the supervision of the PIC. "The person who 780 manipulates the flight controls of a remotely-piloted aircraft 781 during flight time" [ICAOUAS]. 783 RF 784 Radio Frequency. Adjective, e.g., "RF link", or noun. 786 RF LOS 787 RF Line Of Sight. Typically used in describing a direct radio 788 link between a GCS and the UA under its control, potentially 789 subject to blockage by foliage, structures, terrain, or other 790 vehicles, but less so than VLOS. 792 RTCA 793 Radio Technical Commission for Aeronautics. US aviation SDO. 794 Cooperates extensively with EUROCAE. 796 Safety 797 "The state in which risks associated with aviation activities, 798 related to, or in direct support of the operation of aircraft, are 799 reduced and controlled to an acceptable level." From Annex 19 of 800 the Chicago Convention, quoted in [ICAODEFS] 802 Security 803 "Safeguarding civil aviation against acts of unlawful 804 interference." From Annex 17 of the Chicago Convention, quoted in 805 [ICAODEFS] 807 Self-ID Message 808 [F3411-19] Message Type 3. Provides a 1 byte descriptor and 23 809 byte ASCII free text field, only. Expected to be used to provide 810 context on the operation, e.g., mission intent. 812 SDO 813 Standards Development Organization. ASTM, IETF, et al. 815 SDSP 816 Supplemental Data Service Provider. An entity that participates 817 in the UTM system, but provides services beyond those specified as 818 basic UTM system functions (e.g., weather data). [FAACONOPS] 820 System Message 821 [F3411-19] Message Type 4. Provides general UAS information, 822 including remote pilot location, multiple UA group operational 823 area, etc. 825 U-space 826 EU concept and emerging framework for integration of UAS into all 827 classes of airspace, specifically including high density urban 828 areas, sharing airspace with manned aircraft [InitialView]. 830 UA 831 Unmanned Aircraft. In popular parlance, "drone". "An aircraft 832 which is intended to operate with no pilot on board" [ICAOUAS]. 834 UAS 835 Unmanned Aircraft System. Composed of UA, all required on-board 836 subsystems, payload, control station, other required off-board 837 subsystems, any required launch and recovery equipment, all 838 required crew members, and C2 links between UA and control station 839 [F3411-19]. 841 UAS ID 842 UAS identifier. Although called "UAS ID", it is actually unique 843 to the UA, neither to the operator (as some UAS registration 844 numbers have been and for exclusively recreational purposes are 845 continuing to be assigned), nor to the combination of GCS and UA 846 that comprise the UAS. _Maximum length of 20 bytes_ [F3411-19]. 848 UAS ID Type 849 UAS Identifier type index. 4 bits, see Section 3, Paragraph 6 for 850 currently defined values 0-3. [F3411-19] 852 UAS RID 853 UAS Remote Identification and tracking. System to enable 854 arbitrary Observers to identify UA during flight. 856 USS 857 UAS Service Supplier. "A USS is an entity that assists UAS 858 Operators with meeting UTM operational requirements that enable 859 safe and efficient use of airspace" and "... provide services to 860 support the UAS community, to connect Operators and other entities 861 to enable information flow across the USS Network, and to promote 862 shared situational awareness among UTM participants" [FAACONOPS]. 864 UTM 865 UAS Traffic Management. "A specific aspect of air traffic 866 management which manages UAS operations safely, economically and 867 efficiently through the provision of facilities and a seamless set 868 of services in collaboration with all parties and involving 869 airborne and ground-based functions" [ICAOUTM]. In the US, 870 according to the FAA, a "traffic management" ecosystem for 871 "uncontrolled" low altitude UAS operations, separate from, but 872 complementary to, the FAA's ATC system for "controlled" operations 873 of manned aircraft. 875 V2V 876 Vehicle-to-Vehicle. Originally communications between 877 automobiles, now extended to apply to communications between 878 vehicles generally. Often, together with Vehicle-to- 879 Infrastructure (V2I) etc., generalized to V2X. 881 VLOS 882 Visual Line Of Sight. Typically used in describing operation of a 883 UA by a "remote" pilot who can clearly directly (without video 884 cameras or any aids other than glasses or under some rules 885 binoculars) see the UA and its immediate flight environment. 886 Potentially subject to blockage by foliage, structures, terrain, 887 or other vehicles, more so than RF LOS. 889 3. UAS RID Problem Space 891 CAAs worldwide are mandating UAS RID. The European Union Aviation 892 Safety Agency (EASA) has published [Delegated] and [Implementing] 893 Regulations. The US FAA has published a "final" rule [FRUR] and has 894 described the key role that UAS RID plays in UAS Traffic Management 895 (UTM) in [FAACONOPS] (especially Section 2.6). CAAs currently (2021) 896 promulgate performance-based regulations that do not specify 897 techniques, but rather cite industry consensus technical standards as 898 acceptable means of compliance. 900 The most widely cited such industry consensus technical standard for 901 UAS RID is [F3411-19], which defines two means of UAS RID: 903 Network RID defines a set of information for UAS to make available 904 globally indirectly via the Internet, through servers that can be 905 queried by Observers. 907 Broadcast RID defines a set of messages for UA to transmit locally 908 directly one-way over Bluetooth or Wi-Fi (without IP or any other 909 protocols between the data link and application layers), to be 910 received in real time by local Observers. 912 UAS using both means must send the same UAS RID application layer 913 information via each [F3411-19]. The presentation may differ, as 914 Network RID defines a data dictionary, whereas Broadcast RID defines 915 message formats (which carry items from that same data dictionary). 916 The interval (or rate) at which it is sent may differ, as Network RID 917 can accommodate Observer queries asynchronous to UAS updates (which 918 generally need be sent only when information, such as location, 919 changes), whereas Broadcast RID depends upon Observers receiving UA 920 messages at the time they are transmitted. 922 Network RID depends upon Internet connectivity in several segments 923 from the UAS to each Observer. Broadcast RID should need Internet 924 (or other Wide Area Network) connectivity only to retrieve UAS 925 registry information using the directly locally received UAS 926 Identifier (UAS ID) as the primary unique key for database lookup. 927 Broadcast RID does not assume IP connectivity of UAS; messages are 928 encapsulated by the UA _without IP_, directly in link layer frames 929 (Bluetooth 4, Bluetooth 5, Wi-Fi NAN, IEEE 802.11 Beacon, or in the 930 future perhaps others). 932 [F3411-19] specifies three UAS ID Type values: 934 1 A static, manufacturer assigned, hardware serial number as defined 935 in ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers" 936 [CTA2063A]. 938 2 A CAA assigned (generally static) ID, like the registration number 939 of a manned aircraft. 941 3 A UTM system assigned UUID [RFC4122], which can but need not be 942 dynamic. 944 Per [Delegated], the EU allows only UAS ID Type 1. Under [FRUR], the 945 US allows types 1 and 3. [NPRM] proposed that a type 3 "Session ID" 946 would be "e.g., a randomly-generated alphanumeric code assigned by a 947 Remote ID UAS Service Supplier (USS) on a per-flight basis designed 948 to provide additional privacy to the operator", but given the 949 omission of Network RID from [FRUR], how this is to be assigned in 950 the US is still to be determined. 952 As yet apparently there are no CAA public proposals to use UAS ID 953 Type 2. In the preamble of [FRUR], the FAA argues that registration 954 numbers should not be sent in RID, insists that the capability of 955 looking up registration numbers from information contained in RID 956 should be restricted to FAA and other Government agencies, and 957 implies that Session ID would be linked to the registration number 958 only indirectly via the serial number in the registration database. 959 The possibility of cryptographically blinding registration numbers, 960 such that they can be revealed under specified circumstances, does 961 not appear to be mentioned in applicable regulations or external 962 technical standards. 964 Under [Delegated], the EU also requires an operator registration 965 number (an additional identifier distinct from the UAS ID) that can 966 be carried in an [F3411-19] optional Operator ID message. 968 [FRUR] allows RID requirements to be met by either the UA itself, 969 which is then designated a "standard remote identification unmanned 970 aircraft", or by an add-on "remote identification broadcast module". 971 Relative to a standard RID UA, the different requirements for a 972 module are that the latter: must transmit its own serial number 973 (neither the serial number of the UA to which it is attached, nor a 974 Session ID); must transmit takeoff location as a proxy for the 975 location of the pilot/GCS; need not transmit UA emergency status; and 976 is allowed to be used only for operations within VLOS of the remote 977 pilot. 979 Jurisdictions may relax or waive RID requirements for certain 980 operators and/or under certain conditions. For example, [FRUR] 981 allows operators with UAS not equipped for RID to conduct VLOS 982 operations at counter-intuitively named "FAA-recognized 983 identification areas" (FRIA); radio controlled model aircraft flying 984 clubs and other eligible organizations can apply to the FAA for such 985 recognition of their operating areas. 987 3.1. Network RID 989 +-------------+ ****************** 990 | UA | * Internet * 991 +--o-------o--+ * * 992 | | * * 993 | | * * +------------+ 994 | \--------*--(+)-----------*-----o | 995 | * | * | | 996 | /--------*--(+)-----------*-----o NET-Rid SP | 997 | | * * | | 998 | | * /------*-----o | 999 | | * | * +------------+ 1000 | | * | * 1001 | | * | * +------------+ 1002 | | * \------*-----o | 1003 | | * * | NET-Rid DP | 1004 | | * /------*-----o | 1005 | | * | * +------------+ 1006 | | * | * 1007 | | * | * +------------+ 1008 +--o-------o--+ * \------*-----o Observer’s | 1009 | GCS | * * | Device | 1010 +-------------+ ****************** +------------+ 1012 Figure 3: "Network RID Information Flow" 1014 Figure 3 illustrates Network RID information flows. Only two of the 1015 three typically wireless links shown involving the UAS (UA-GCS, UA- 1016 Internet, and GCS-Internet) need exist. All three may exist, at the 1017 same or different times, especially in Beyond Visual Line Of Sight 1018 (BVLOS) operations. There must be some information flow path (direct 1019 or indirect) between the GCS and the UA, for the former to exercise 1020 C2 over the latter. If this path is two-way (as increasingly it is, 1021 even for inexpensive small UAS), the UA will also send its status 1022 (and position, if suitably equipped, e.g., with GNSS) to the GCS. 1023 There also must be some path between at least one subsystem of the 1024 UAS (UA or GCS) and the Internet, for the former to send status and 1025 position updates to its USS (serving _inter alia_ as a Net-RID SP). 1027 Direct UA-Internet wireless links are expected to become more common, 1028 especially on larger UAS, but currently (2021) are rare. Instead, 1029 the RID data flow typically originates on the UA and passes through 1030 the GCS, or originates on the GCS. Network RID data makes three 1031 trips through the Internet (GCS-SP, SP-DP, DP-Observer, unless any of 1032 them are colocated), implying use of IP (and other middle layer 1033 protocols, e.g., TLS/TCP or DTLS/UDP) on those trips. IP is not 1034 necessarily used or supported on the UA-GCS link (if indeed that 1035 direct link exists, as it typically does now, but in BVLOS operations 1036 often will not). 1038 Network RID is publish-subscribe-query. In the UTM context: 1040 1. The UAS operator pushes an "operational intent" (the current term 1041 in UTM corresponding to a flight plan in manned aviation) to the 1042 USS (call it USS#1) that will serve that UAS (call it UAS#1) for 1043 that operation, primarily to enable deconfliction with other 1044 operations potentially impinging upon that operation's 4-D 1045 airspace volume (call it Volume#1). 1047 2. Assuming the operation is approved and commences, UAS#1 1048 periodically pushes location/status updates to USS#1, which 1049 serves _inter alia_ as the Network RID Service Provider (Net-RID 1050 SP) for that operation. 1052 3. When users of any other USS (whether they be other UAS operators 1053 or Observers) develop an interest in any 4-D airspace volume 1054 (e.g., because they wish to submit an operational intent or 1055 because they have observed a UA), they query their own USS on the 1056 volumes in which they are interested. 1058 4. Their USS query, via the UTM Discovery and Synchronization 1059 Service (DSS), all other USS in the UTM system, and learn of any 1060 USS that have operations in those volumes (including any volumes 1061 intersecting them); thus those USS whose query volumes intersect 1062 Volume#1 (call them USS#2 through USS#n) learn that USS#1 has 1063 such operations. 1065 5. Interested parties can then subscribe to track updates on that 1066 operation of UAS#1, via their own USS, which serve as Network RID 1067 Display Providers (Net-RID DP) for that operation. 1069 6. USS#1 (as Net-RID SP) will then publish updates of UAS#1 status 1070 and position to all other subscribed USS in USS#2 through USS#n 1071 (as Net-RID DP). 1073 7. All Net-RID DP subscribed to that operation of UAS#1 will deliver 1074 its track information to their users who subscribed to that 1075 operation of UAS#1 (via means unspecified by [F3411-19] etc., but 1076 generally presumed to be web browser based). 1078 Network RID has several connectivity scenarios: 1080 _Persistently Internet connected UA_ can consistently directly 1081 source RID information; this requires wireless coverage throughout 1082 the intended operational airspace volume, plus a buffer (e.g., 1083 winds may drive the UA out of the volume). 1085 _Intermittently Internet connected UA_, can usually directly 1086 source RID information, but when offline (e.g., due to signal 1087 blockage by a large structure being inspected using the UAS), need 1088 the GCS to proxy source RID information. 1090 _Indirectly connected UA_ lack the ability to send IP packets that 1091 will be forwarded into and across the Internet, but instead have 1092 some other form of communications to another node that can relay 1093 or proxy RID information to the Internet; typically this node 1094 would be the GCS (which to perform its function must know where 1095 the UA is, although C2 link outages do occur). 1097 _Non-connected UA_ have no means of sourcing RID information, in 1098 which case the GCS or some other interface available to the 1099 operator must source it. In the extreme case, this could be the 1100 pilot or other agent of the operator using a web browser/ 1101 application to designate, to a USS or other UTM entity, a time- 1102 bounded airspace volume in which an operation will be conducted. 1103 This is referred to as a "non-equipped network participant" 1104 engaging in "area operations". This may impede disambiguation of 1105 ID if multiple UAS operate in the same or overlapping 4-D volumes. 1106 In most airspace volumes, most classes of UA will not be permitted 1107 to fly if non-connected. 1109 In most cases in the near term (2021), the Network RID first hop data 1110 link is likely to be cellular, which can also support BVLOS C2 over 1111 existing large coverage areas, or Wi-Fi, which can also support 1112 Broadcast RID. However, provided the data link can support at least 1113 UDP/IP and ideally also TCP/IP, its type is generally immaterial to 1114 higher layer protocols. The UAS, as the ultimate source of Network 1115 RID information, feeds a Net-RID SP (typically the USS to which the 1116 UAS operator subscribes), which proxies for the UAS and other data 1117 sources. An Observer or other ultimate consumer of Network RID 1118 information obtains it from a Net-RID DP (also typically a USS), 1119 which aggregates information from multiple Net-RID SPs to offer 1120 airspace Situational Awareness (SA) coverage of a volume of interest. 1121 Network RID Service and Display providers are expected to be 1122 implemented as servers in well-connected infrastructure, 1123 communicating with each other via the Internet, and accessible by 1124 Observers via means such as web Application Programming Interfaces 1125 (APIs) and browsers. 1127 Network RID is the less constrained of the defined UAS RID means. 1128 [F3411-19] specifies only Net-RID SP to Net-RID DP information 1129 exchanges. It is presumed that IETF efforts supporting the more 1130 constrained Broadcast RID (see next section) can be generalized for 1131 Network RID and potentially also for UAS to USS or other UTM 1132 communications. 1134 3.2. Broadcast RID 1135 +-------------------+ 1136 | Unmanned Aircraft | 1137 +---------o---------+ 1138 | 1139 | 1140 | 1141 | app messages directly over one-way RF data link 1142 | 1143 | 1144 | 1145 +------------------o-------------------+ 1146 | Observer's device (e.g., smartphone) | 1147 +--------------------------------------+ 1149 Figure 4: "Broadcast RID Information Flow" 1151 Figure 4 illustrates Broadcast RID information flow. Note the 1152 absence of the Internet from the figure. This is because Broadcast 1153 RID is one-way direct transmission of application layer messages over 1154 a RF data link (without IP) from the UA to local Observer devices. 1155 Internet connectivity is involved only in what the Observer chooses 1156 to do with the information received, such as verify signatures using 1157 a web-based Broadcast Authentication Verifier Service and look up 1158 information in registries using the UAS ID as the primary unique key. 1160 Broadcast RID is conceptually similar to Automatic Dependent 1161 Surveillance - Broadcast (ADS-B). However, for various technical and 1162 other reasons, regulators including the EASA have not indicated 1163 intent to allow, and FAA has explicitly prohibited, use of ADS-B for 1164 UAS RID. 1166 [F3411-19] specifies four Broadcast RID data links: Bluetooth 4.x, 1167 Bluetooth 5.x with Extended Advertisements and Long Range Coded PHY 1168 (S=8), Wi-Fi NAN at 2.4 GHz, and Wi-Fi NAN at 5 GHz. A UA must 1169 broadcast (using advertisement mechanisms where no other option 1170 supports broadcast) on at least one of these. If sending on 1171 Bluetooth 5.x, it is also required concurrently to do so on 4.x 1172 (referred to in [F3411-19] as Bluetooth Legacy); current (2021) 1173 discussions in ASTM F38.02 on revising the standard, motivated by 1174 European standards drafts, suggest that both Bluetooth versions will 1175 be required. If broadcasting Wi-Fi NAN at 5 GHz, it is also required 1176 concurrently to do so at 2.4 GHz; current discussions in F38.02 1177 include relaxing this. Wi-Fi Beacons are also under consideration. 1178 Future revisions of [F3411-19] may allow other data links. 1180 The selection of the Broadcast media was driven by research into what 1181 is commonly available on 'ground' units (smartphones and tablets) and 1182 what was found as prevalent or 'affordable' in UA. Further, there 1183 must be an API for the Observer's receiving application to have 1184 access to these messages. As yet only Bluetooth 4.x support is 1185 readily available, thus the current focus is on working within the 31 1186 byte payload limit of the Bluetooth 4.x "Broadcast Frame" transmitted 1187 as an "advertisement" on beacon channels. After overheads, this 1188 limits the RID message to 25 bytes and UAS ID string to a maximum 1189 length of 20 bytes. 1191 Length constraints also preclude a single Bluetooth 4.x frame 1192 carrying not only the UAS ID but also position, velocity, and other 1193 information that should be bound to the UAS ID, much less strong 1194 authentication data. Messages that cannot be encapsulated in a 1195 single frame (thus far, only the Authentication Message) must be 1196 segmented into message "pages" (in the terminology of [F3411-19]). 1197 Message pages must somehow be correlated as belonging to the same 1198 message. Messages carrying position, velocity and other data must 1199 somehow be correlated with the Basic ID message that carries the UAS 1200 ID. This correlation is expected to be done on the basis of MAC 1201 address: this may be complicated by MAC address randomization; not 1202 all the common devices expected to be used by Observers have APIs 1203 that make sender MAC addresses available to user space receiver 1204 applications; and MAC addresses are easily spoofed. Data elements 1205 are not so detached on other media (see Message Pack in the paragraph 1206 after next). 1208 [F3411-19] Broadcast RID specifies several message types. The 4 bit 1209 message type field in the header can index up to 16 types. Only 7 1210 are currently defined. Only 2 are mandatory. All others are 1211 optional, unless required by a jurisdictional authority, e.g., a CAA. 1212 To satisfy both EASA and FAA rules, all types are needed, except 1213 Self-ID and Authentication, as the data elements required by the 1214 rules are scattered across several message types (along with some 1215 data elements not required by the rules). 1217 The Message Pack (type 0xF) is not actually a message, but the framed 1218 concatenation of at most one message of each type of any subset of 1219 the other types, in type index order. Some of the messages that it 1220 can encapsulate are mandatory, others optional. The Message Pack 1221 itself is mandatory on data links that can encapsulate it in a single 1222 frame (Bluetooth 5.x and Wi-Fi). 1224 +-----------------------+-----------------+-----------+-----------+ 1225 | Index | Name | Req | Notes | 1226 +-----------------------+-----------------+-----------+-----------+ 1227 | 0x0 | Basic ID | Mandatory | - | 1228 +-----------------------+-----------------+-----------+-----------+ 1229 | 0x1 | Location/Vector | Mandatory | - | 1230 +-----------------------+-----------------+-----------+-----------+ 1231 | 0x2 | Authentication | Optional | paged | 1232 +-----------------------+-----------------+-----------+-----------+ 1233 | 0x3 | Self-ID | Optional | free text | 1234 +-----------------------+-----------------+-----------+-----------+ 1235 | 0x4 | System | Optional | - | 1236 +-----------------------+-----------------+-----------+-----------+ 1237 | 0x5 | Operator | Optional | - | 1238 +-----------------------+-----------------+-----------+-----------+ 1239 | 0xF | Message Pack | - | BT5 and | 1240 | | | | Wi-Fi | 1241 +-----------------------+-----------------+-----------+-----------+ 1242 | See Section 5.4.5 and | - | - | - | 1243 | Table 3 of [F3411-19] | | | | 1244 +-----------------------+-----------------+-----------+-----------+ 1246 Table 1: F3411-19 Message Types 1248 [F3411-19] Broadcast RID specifies very few quantitative performance 1249 requirements: static information must be transmitted at least once 1250 per 3 seconds; dynamic information (the Location/Vector message) must 1251 be transmitted at least once per second and be no older than one 1252 second when sent. [FRUR] requires all information be sent at least 1253 once per second. 1255 [F3411-19] Broadcast RID transmits all information as cleartext 1256 (ASCII or binary), so static IDs enable trivial correlation of 1257 patterns of use, unacceptable in many applications, e.g., package 1258 delivery routes of competitors. 1260 Any UA can assert any ID using the [F3411-19] required Basic ID 1261 message, which lacks any provisions for verification. The Position/ 1262 Vector message likewise lacks provisions for verification, and does 1263 not contain the ID, so must be correlated somehow with a Basic ID 1264 message: the developers of [F3411-19] have suggested using the MAC 1265 addresses on the Broadcast RID data link, but these may be randomized 1266 by the operating system stack to avoid the adversarial correlation 1267 problems of static identifiers. 1269 The [F3411-19] optional Authentication Message specifies framing for 1270 authentication data, but does not specify any authentication method, 1271 and the maximum length of the specified framing is too short for 1272 conventional digital signatures and far too short for conventional 1273 certificates (e.g., X.509). Fetching certificates via the Internet 1274 is not always possible (e.g., Observers working in remote areas, such 1275 as national forests), so devising a scheme whereby certificates can 1276 be transported over Broadcast RID is necessary. The one-way nature 1277 of Broadcast RID precludes challenge-response security protocols 1278 (e.g., Observers sending nonces to UA, to be returned in signed 1279 messages). Without DRIP extensions to [F3411-19], an Observer would 1280 be seriously challenged to validate the asserted UAS ID or any other 1281 information about the UAS or its operator looked up therefrom. 1283 3.3. USS in UTM and RID 1285 UAS RID and UTM are complementary; Network RID is a UTM service. The 1286 backbone of the UTM system is comprised of multiple USS: one or 1287 several per jurisdiction; some limited to a single jurisdiction, 1288 others spanning multiple jurisdictions. USS also serve as the 1289 principal or perhaps the sole interface for operators and UAS into 1290 the UTM environment. Each operator subscribes to at least one USS. 1291 Each UAS is registered by its operator in at least one USS. Each 1292 operational intent is submitted to one USS; if approved, that UAS and 1293 operator can commence that operation. During the operation, status 1294 and location of that UAS must be reported to that USS, which in turn 1295 provides information as needed about that operator, UAS, and 1296 operation into the UTM system and to Observers via Network RID. 1298 USS provide services not limited to Network RID; indeed, the primary 1299 USS function is deconfliction of airspace usage by different UAS and 1300 other (e.g., manned aircraft, rocket launch) operations. Most 1301 deconfliction involving a given operation is hoped to be completed 1302 prior to commencing that operation, and is called "strategic 1303 deconfliction". If that fails, "tactical deconfliction" comes into 1304 play; ABDAA may not involve USS, but GBDAA likely will. Dynamic 1305 constraints, formerly called UAS Volume Restrictions (UVR), can be 1306 necessitated by local emergencies, extreme weather, etc., specified 1307 by authorities on the ground, and propagated in UTM. 1309 No role for USS in Broadcast RID is currently specified by regulators 1310 or [F3411-19]. However, USS are likely to serve as registries (or 1311 perhaps registrars) for UAS (and perhaps operators); if so, USS will 1312 have a role in all forms of RID. Supplemental Data Service Providers 1313 (SDSP) are also likely to find roles, not only in UTM as such but 1314 also in enhancing UAS RID and related services. Whether USS, SDSP, 1315 etc. are involved or not, RID services, narrowly defined, provide 1316 regulator specified identification information; more broadly defined, 1317 RID services may leverage identification to facilitate related 1318 services or functions, likely beginning with V2X. 1320 3.4. DRIP Focus 1322 In addition to the gaps described above, there is a fundamental gap 1323 in almost all current or proposed regulations and technical standards 1324 for UAS RID. As noted above, ID is not an end in itself, but a 1325 means. Protocols specified in [F3411-19] etc. provide limited 1326 information potentially enabling, and no technical means for, an 1327 Observer to communicate with the pilot, e.g., to request further 1328 information on the UAS operation or exit from an airspace volume in 1329 an emergency. The System Message provides the location of the pilot/ 1330 GCS, so an Observer could physically go to the asserted location to 1331 look for the remote pilot; this is at best slow and may not be 1332 feasible. What if the pilot is on the opposite rim of a canyon, or 1333 there are multiple UAS operators to contact, whose GCS all lie in 1334 different directions from the Observer? An Observer with Internet 1335 connectivity and access privileges could look up operator PII in a 1336 registry, then call a phone number in hopes someone who can 1337 immediately influence the UAS operation will answer promptly during 1338 that operation; this is at best unreliable and may not be prudent. 1339 Should pilots be encouraged to answer phone calls while flying? 1340 Internet technologies can do much better than this. 1342 Thus complementing [F3411-19] with protocols enabling strong 1343 authentication, preserving operator privacy while enabling immediate 1344 use of information by authorized parties, is critical to achieve 1345 widespread adoption of a RID system supporting safe and secure 1346 operation of UAS. 1348 DRIP will focus on making information obtained via UAS RID 1349 immediately usable: 1351 1. by making it trustworthy (despite the severe constraints of 1352 Broadcast RID); 1354 2. by enabling verification that a UAS is registered for RID, and if 1355 so, in which registry (for classification of trusted operators on 1356 the basis of known registry vetting, even by Observers lacking 1357 Internet connectivity at observation time); 1359 3. by facilitating independent reports of UA aeronautical data 1360 (location, velocity, etc.) to confirm or refute the operator 1361 self-reports upon which UAS RID and UTM tracking are based; 1363 4. by enabling instant establishment, by authorized parties, of 1364 secure communications with the remote pilot. 1366 The foregoing considerations, beyond those addressed by baseline UAS 1367 RID standards such as [F3411-19], imply the following requirements 1368 for DRIP. 1370 4. Requirements 1372 The following requirements apply to DRIP as a set of related 1373 protocols, various subsets of which, in conjunction with other IETF 1374 and external technical standards, may suffice to comply with the 1375 regulations in any given jurisdiction or meet any given user need. 1376 It is not intended that each and every DRIP protocol alone satisfy 1377 each and every requirement. 1379 4.1. General 1381 4.1.1. Normative Requirements 1383 GEN-1 Provable Ownership: DRIP MUST enable verification that the 1384 UAS ID asserted in the Basic ID message is that of the actual 1385 current sender of the message (i.e., the message is not a 1386 replay attack or other spoof, authenticating, e.g., by 1387 verifying an asymmetric cryptographic signature using a 1388 sender provided public key from which the asserted ID can be 1389 at least partially derived), even on an Observer device 1390 lacking Internet connectivity at the time of observation. 1392 GEN-2 Provable Binding: DRIP MUST enable binding all other 1393 [F3411-19] messages from the same actual current sender to 1394 the UAS ID asserted in the Basic ID message. 1396 GEN-3 Provable Registration: DRIP MUST enable verification that the 1397 UAS ID is in a registry and identification of which one, even 1398 on an Observer device lacking Internet connectivity at the 1399 time of observation; with UAS ID Type 3, the same sender may 1400 have multiple IDs, potentially in different registries, but 1401 each ID must clearly indicate in which registry it can be 1402 found. 1404 GEN-4 Readability: DRIP MUST enable information (regulation 1405 required elements, whether sent via UAS RID or looked up in 1406 registries) to be read and utilized by both humans and 1407 software. 1409 GEN-5 Gateway: DRIP MUST enable Broadcast RID to Network RID 1410 application layer gateways to stamp messages with precise 1411 date/time received and receiver location, then relay them to 1412 a network service (e.g., SDSP or distributed ledger). 1414 GEN-6 Finger: DRIP MUST enable dynamically establishing, with AAA, 1415 per policy, strongly mutually authenticated, end-to-end 1416 strongly encrypted communications with the UAS RID sender and 1417 entities looked up from the UAS ID, including at least the 1418 remote pilot and USS. 1420 GEN-7 QoS: DRIP MUST enable policy based specification of 1421 performance and reliability parameters. 1423 GEN-8 Mobility: DRIP MUST support physical and logical mobility of 1424 UA, GCS and Observers. DRIP SHOULD support mobility of 1425 essentially all participating nodes (UA, GCS, Observers, Net- 1426 RID SP, Net-RID DP, Private Registry, SDSP, and potentially 1427 others as RID and UTM evolve). 1429 GEN-9 Multihoming: DRIP MUST support multihoming of UA and GCS, for 1430 make-before-break smooth handoff and resiliency against path/ 1431 link failure. DRIP SHOULD support multihoming of essentially 1432 all participating nodes. 1434 GEN-10 Multicast: DRIP SHOULD support multicast for efficient and 1435 flexible publish-subscribe notifications, e.g., of UAS 1436 reporting positions in designated airspace volumes. 1438 GEN-11 Management: DRIP SHOULD support monitoring of the health and 1439 coverage of Broadcast and Network RID services. 1441 4.1.2. Rationale 1443 Requirements imposed either by regulation or [F3411-19] are not 1444 reiterated here, but drive many of the numbered requirements listed 1445 here. The [FRUR] regulatory QoS requirement currently would be 1446 satisfied by ensuring information refresh rates of at least 1 Hertz, 1447 with latencies no greater than 1 second, at least 80% of the time, 1448 but these numbers may vary between jurisdictions and over time. So 1449 instead the DRIP QoS requirement is that performance, reliability, 1450 etc. parameters be user policy specifiable, which does not imply 1451 satisfiable in all cases, but (especially together with the 1452 management requirement) implies that when specifications are not met, 1453 appropriate parties are notified. 1455 The "provable ownership" requirement addresses the possibility that 1456 the actual sender is not the claimed sender (i.e., is a spoofer). 1457 The "provable binding" requirement addresses the MAC address 1458 correlation problem of [F3411-19] noted above. The "provable 1459 registration" requirement may impose burdens not only on the UAS 1460 sender and the Observer's receiver, but also on the registry; yet it 1461 cannot depend upon the Observer being able to contact the registry at 1462 the time of observing the UA. The "readability" requirement pertains 1463 to the structure and format of information at endpoints rather than 1464 its encoding in transit, so may involve machine assisted format 1465 conversions, e.g., from binary encodings, and/or decryption (see 1466 Section 4.3). 1468 The "gateway" requirement is in pursuit of three objectives: (1) mark 1469 up a RID message with where and when it was actually received, which 1470 may agree or disagree with the self-report in the set of messages; 1471 (2) defend against replay attacks; and (3) support optional SDSP 1472 services such as multilateration, to complement UAS position self- 1473 reports with independent measurements. This is the only instance in 1474 which DRIP transports [F3411-19] messages; most of DRIP pertains to 1475 the authentication of such messages and identifiers carried in them. 1477 The "QoS" requirement is only that performance and reliability 1478 parameters can be _specified_ by policy, not that any such 1479 specifications must be guaranteed to be met; any failure to meet such 1480 would be reported under the "management" requirement. Examples of 1481 such parameters are the maximum time interval at which messages 1482 carrying required data elements may be transmitted, the maximum 1483 tolerable rate of loss of such messages, and the maximum tolerable 1484 latency between a dynamic data element (e.g., GNSS position of UA) 1485 being provided to the DRIP sender and that element being delivered by 1486 the DRIP receiver to an application. 1488 The "mobility" requirement refers to rapid geographic mobility of 1489 nodes, changes of their points of attachment to networks, and changes 1490 to their IP addresses; it is not limited to micro-mobility within a 1491 small geographic area or single Internet access provider. 1493 4.2. Identifier 1495 4.2.1. Normative Requirements 1497 ID-1 Length: The DRIP entity identifier MUST NOT be longer than 20 1498 bytes, to fit in the UAS ID field of the Basic ID message of 1499 [F3411-19]. 1501 ID-2 Registry ID: The DRIP identifier MUST be sufficient to identify 1502 a registry in which the entity identified therewith is listed. 1504 ID-3 Entity ID: The DRIP identifier MUST be sufficient to enable 1505 lookups of other data associated with the entity identified 1506 therewith in that registry. 1508 ID-4 Uniqueness: The DRIP identifier MUST be unique within the 1509 applicable global identifier space from when it is first 1510 registered therein until it is explicitly de-registered 1511 therefrom (due to, e.g., expiration after a specified lifetime, 1512 revocation by the registry, or surrender by the operator). 1514 ID-5 Non-spoofability: The DRIP identifier MUST NOT be spoofable 1515 within the context of a minimal Remote ID broadcast message set 1516 (to be specified within DRIP to be sufficient collectively to 1517 prove sender ownership of the claimed identifier). 1519 ID-6 Unlinkability: The DRIP identifier MUST NOT facilitate 1520 adversarial correlation over multiple operations. If this is 1521 accomplished by limiting each identifier to a single use or 1522 brief period of usage, the DRIP identifier MUST support well- 1523 defined, scalable, timely registration methods. 1525 4.2.2. Rationale 1527 The DRIP identifier can refer to various entities. In the primary 1528 initial use case, the entity to be identified is the UA. Entities to 1529 be identified in other likely use cases include but are not limited 1530 to the operator, USS, and Observer. In all cases, the entity 1531 identified must own (have the exclusive capability to use, such that 1532 receivers can verify its ownership of) the identifier. 1534 The DRIP identifier can be used at various layers. In Broadcast RID, 1535 it would be used by the application running directly over the data 1536 link. In Network RID, it would be used by the application running 1537 over HTTPS (and possibly other protocols). In RID initiated V2X 1538 applications such as DAA and C2, it could be used between the network 1539 and transport layers, e.g., with the Host Identity Protocol (HIP, 1540 [RFC4423], [RFC7401], etc.), or between the transport and application 1541 layers, e.g., with Datagram Transport Layer Security (DTLS, 1542 [RFC6347]). 1544 Registry ID (which registry the entity is in) and Entity ID (which 1545 entity it is, within that registry) are requirements on a single DRIP 1546 entity identifier, not separate (types of) ID. In the most common 1547 use case, the entity will be the UA, and the DRIP identifier will be 1548 the UAS ID; however, other entities may also benefit from having DRIP 1549 identifiers, so the entity type is not prescribed here. 1551 Whether a UAS ID is generated by the operator, GCS, UA, USS, 1552 registry, or some collaboration thereamong, is unspecified; however, 1553 there must be agreement on the UAS ID among these entities. 1554 Management of DRIP identifiers is the primary function of their 1555 registration hierarchies, from the root (presumably IANA), through 1556 sector-specific and regional authorities (presumably ICAO and CAAs), 1557 to the identified entities themselves. 1559 While "uniqueness" might be considered an implicit requirement for 1560 any identifier, here the point of the explicit requirement is not 1561 just that it should be unique, but also where and when it should be 1562 unique: global scope within a specified space, from registration to 1563 deregistration. 1565 While "non-spoofability" imposes requirements for and on a DRIP 1566 authentication protocol, it also imposes requirements on the 1567 properties of the identifier itself. An example of how the nature of 1568 the identifier can support non-spoofability is embedding a hash of 1569 both the registry ID and a public key of the entity in the entity 1570 identifier, thus making it self-authenticating any time the entity's 1571 corresponding private key is used to sign a message. 1573 While "unlinkability" is a privacy desideratum (see next section), it 1574 imposes requirements on the DRIP identifier itself, as distinct from 1575 other currently permitted choices for the UAS ID (including primarily 1576 the static serial number of the UA or RID module). 1578 4.3. Privacy 1580 4.3.1. Normative Requirements 1582 PRIV-1 Confidential Handling: DRIP MUST enable confidential handling 1583 of private information (i.e., any and all information 1584 designated by neither cognizant authority nor the information 1585 owner as public, e.g., personal data). 1587 PRIV-2 Encrypted Transport: DRIP MUST enable selective strong 1588 encryption of private data in motion in such a manner that 1589 only authorized actors can recover it. If transport is via 1590 IP, then encryption MUST be end-to-end, at or above the IP 1591 layer. DRIP MUST NOT encrypt safety critical data to be 1592 transmitted over Broadcast RID in any situation where it is 1593 unlikely that local Observers authorized to access the 1594 plaintext will be able to decrypt it or obtain it from a 1595 service able to decrypt it. DRIP MUST NOT encrypt data when/ 1596 where doing so would conflict with applicable regulations or 1597 CAA policies/procedures, i.e., DRIP MUST support configurable 1598 disabling of encryption. 1600 PRIV-3 Encrypted Storage: DRIP SHOULD facilitate selective strong 1601 encryption of private data at rest in such a manner that only 1602 authorized actors can recover it. 1604 PRIV-4 Public/Private Designation: DRIP SHOULD facilitate 1605 designation, by cognizant authorities and information owners, 1606 of which information is public and which is private. By 1607 default, all information required to be transmitted via 1608 Broadcast RID, even when actually sent via Network RID or 1609 stored in registries, is assumed to be public; all other 1610 information held in registries for lookup using the UAS ID is 1611 assumed to be private. 1613 PRIV-5 Pseudonymous Rendezvous: DRIP MAY enable mutual discovery of 1614 and communications among participating UAS operators whose UA 1615 are in 4-D proximity, using the UAS ID without revealing 1616 pilot/operator identity or physical location. 1618 4.3.2. Rationale 1620 Most data to be sent via Broadcast RID or Network RID is public, thus 1621 the "encrypted transport" requirement for private data is selective, 1622 e.g., for the entire payload of the Operator ID Message, but only the 1623 pilot/GCS location fields of the System Message. 1625 In some jurisdictions, the configurable enabling and disabling of 1626 encryption may need to be outside the control of the operator. 1627 [FRUR] mandates manufacturers design RID equipment with some degree 1628 of tamper resistance; the preamble and other FAA commentary suggest 1629 this is to reduce the likelihood that an operator, intentionally or 1630 unintentionally, might alter the values of the required data elements 1631 or disable their transmission in the required manner (e.g., as 1632 cleartext). 1634 How information is stored on end systems is out of scope for DRIP. 1635 Encouraging privacy best practices, including end system storage 1636 encryption, by facilitating it with protocol design reflecting such 1637 considerations, is in scope. Similar logic applies to methods for 1638 designating information as public or private. 1640 The privacy requirements above are for DRIP, neither for [F3411-19] 1641 (which requires obfuscation of location to any Network RID subscriber 1642 engaging in wide area surveillance, limits data retention periods, 1643 etc., in the interests of privacy), nor for UAS RID in any specific 1644 jurisdiction (which may have its own regulatory requirements). The 1645 requirements above are also in a sense parameterized: who are the 1646 "authorized actors", how are they designated, how are they 1647 authenticated, etc.? 1649 4.4. Registries 1651 4.4.1. Normative Requirements 1653 REG-1 Public Lookup: DRIP MUST enable lookup, from the UAS ID, of 1654 information designated by cognizant authority as public, and 1655 MUST NOT restrict access to this information based on identity 1656 or role of the party submitting the query. 1658 REG-2 Private Lookup: DRIP MUST enable lookup of private information 1659 (i.e., any and all information in a registry, associated with 1660 the UAS ID, that is designated by neither cognizant authority 1661 nor the information owner as public), and MUST, according to 1662 applicable policy, enforce AAA, including restriction of 1663 access to this information based on identity or role of the 1664 party submitting the query. 1666 REG-3 Provisioning: DRIP MUST enable provisioning registries with 1667 static information on the UAS and its operator, dynamic 1668 information on its current operation within the U-space/UTM 1669 (including means by which the USS under which the UAS is 1670 operating may be contacted for further, typically even more 1671 dynamic, information), and Internet direct contact information 1672 for services related to the foregoing. 1674 REG-4 AAA Policy: DRIP AAA MUST be specifiable by policies; the 1675 definitive copies of those policies must be accessible in 1676 registries; administration of those policies and all DRIP 1677 registries must be protected by AAA. 1679 4.4.2. Rationale 1681 Registries are fundamental to RID. Only very limited information can 1682 be Broadcast, but extended information is sometimes needed. The most 1683 essential element of information sent is the UAS ID itself, the 1684 unique key for lookup of extended information in registries. Beyond 1685 designating the UAS ID as that unique key, the registry information 1686 model is not specified herein, in part because regulatory 1687 requirements for different registries (UAS operators and their UA, 1688 each narrowly for UAS RID and broadly for U-space/UTM) and business 1689 models for meeting those requirements are in flux. While it is 1690 expected that registry functions will be integrated with USS, who 1691 will provide them is not yet determined in most, and is expected to 1692 vary between, jurisdictions. However this evolves, the essential 1693 registry functions, starting with management of identifiers, are 1694 expected to remain the same, so are specified herein. 1696 While most data to be sent via Broadcast or Network RID is public, 1697 much of the extended information in registries will be private. Thus 1698 AAA for registries is essential, not just to ensure that access is 1699 granted only to strongly authenticated, duly authorized parties, but 1700 also to support subsequent attribution of any leaks, audit of who 1701 accessed information when and for what purpose, etc. As specific AAA 1702 requirements will vary by jurisdictional regulation, provider 1703 philosophy, customer demand, etc., they are left to specification in 1704 policies, which should be human readable to facilitate analysis and 1705 discussion, and machine readable to enable automated enforcement, 1706 using a language amenable to both, e.g., XACML. 1708 5. IANA Considerations 1710 This document does not make any IANA request. 1712 6. Security Considerations 1714 DRIP is all about safety and security, so content pertaining to such 1715 is not limited to this section. This document does not define any 1716 protocols, so security considerations of such are speculative. 1717 Potential vulnerabilities of DRIP solutions to these requirements 1718 include but are not limited to: 1720 * Sybil attacks 1722 * confusion created by many spoofed unsigned messages 1724 * processing overload induced by attempting to verify many spoofed 1725 signed messages (where verification will fail but still consume 1726 cycles) 1728 * malicious or malfunctioning registries 1730 * interception by on-path attacker of (i.e., Man In The Middle 1731 attacks on) registration messages 1733 * UA impersonation through private key extraction, improper key 1734 sharing, or carriage of a small (presumably harmless) UA, i.e., as 1735 a "false flag", by a larger (malicious) UA 1737 It may be inferred from the general requirements (Section 4.1) for 1738 provable ownership, provable binding, and provable registration, 1739 together with the identifier requirements (Section 4.2), that DRIP 1740 must provide: 1742 * message integrity 1743 * non-repudiation 1745 * defense against replay attacks 1747 * defense against spoofing 1749 One approach to so doing involves verifiably binding the DRIP 1750 identifier to a public key. Providing these security features, 1751 whether via this approach or another, is likely to be especially 1752 challenging for Observers without Internet connectivity at the time 1753 of observation. For example, checking the signature of a registry on 1754 a public key certificate received via Broadcast RID in a remote area 1755 presumably would require that the registry's public key had been 1756 previously installed on the Observer's device, yet there may be many 1757 registries and the Observer's device may be storage constrained, and 1758 new registries may come on-line subsequent to installation of DRIP 1759 software on the Observer's device. Thus there may be caveats on the 1760 extent to which requirements can be satisfied in such cases, yet 1761 strenuous effort should be made to satisfy them, as such cases, e.g., 1762 firefighting in a national forest, are important. 1764 7. Privacy and Transparency Considerations 1766 Privacy and transparency are important for legal reasons including 1767 regulatory consistency. [EU2018] states "harmonised and 1768 interoperable national registration systems... should comply with the 1769 applicable Union and national law on privacy and processing of 1770 personal data, and the information stored in those registration 1771 systems should be easily accessible." 1773 Privacy and transparency (where essential to security or safety) are 1774 also ethical and moral imperatives. Even in cases where old 1775 practices (e.g., automobile registration plates) could be imitated, 1776 when new applications involving PII (such as UAS RID) are addressed 1777 and newer technologies could enable improving privacy, such 1778 opportunities should not be squandered. Thus it is recommended that 1779 all DRIP work give due regard to [RFC6973] and more broadly 1780 [RFC8280]. 1782 However, privacy and transparency are often conflicting goals, 1783 demanding careful attention to their balance. 1785 DRIP information falls into two classes: that which, to achieve the 1786 purpose, must be published openly as cleartext, for the benefit of 1787 any Observer (e.g., the basic UAS ID itself); and that which must be 1788 protected (e.g., PII of pilots) but made available to properly 1789 authorized parties (e.g., public safety personnel who urgently need 1790 to contact pilots in emergencies). 1792 How properly authorized parties are authorized, authenticated, etc. 1793 are questions that extend beyond the scope of DRIP, but DRIP may be 1794 able to provide support for such processes. Classification of 1795 information as public or private must be made explicit and reflected 1796 with markings, design, etc. Classifying the information will be 1797 addressed primarily in external standards; herein it will be regarded 1798 as a matter for CAA, registry, and operator policies, for which 1799 enforcement mechanisms will be defined within the scope of DRIP WG 1800 and offered. Details of the protection mechanisms will be provided 1801 in other DRIP documents. Mitigation of adversarial correlation will 1802 also be addressed. 1804 8. References 1806 8.1. Normative References 1808 [F3411-19] ASTM International, "Standard Specification for Remote ID 1809 and Tracking", February 2020, 1810 . 1812 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1813 Requirement Levels", BCP 14, RFC 2119, 1814 DOI 10.17487/RFC2119, March 1997, 1815 . 1817 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1818 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1819 May 2017, . 1821 8.2. Informative References 1823 [Amended] European Union Aviation Safety Agency (EASA), "Commission 1824 Delegated Regulation (EU) 2020/1058 of 27 April 2020 1825 amending Delegated Regulation (EU) 2019/945", April 2020, 1826 . 1829 [ASDRI] ASD-STAN, "Introduction to the European UAS Digital Remote 1830 ID Technical Standard", January 2021, . 1834 [CPDLC] Gurtov, A., Polishchuk, T., and M. Wernberg, "Controller- 1835 Pilot Data Link Communication Security", MDPI 1836 Sensors 18(5), 1636, 2018, 1837 . 1839 [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers", 1840 September 2019, . 1843 [Delegated] 1844 European Union Aviation Safety Agency (EASA), "Commission 1845 Delegated Regulation (EU) 2019/945 of 12 March 2019 on 1846 unmanned aircraft systems and on third-country operators 1847 of unmanned aircraft systems", March 2019, 1848 . 1850 [drip-architecture] 1851 Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S., 1852 and A. Gurtov, "Drone Remote Identification Protocol 1853 (DRIP) Architecture", Work in Progress, Internet-Draft, 1854 draft-ietf-drip-arch-11, 23 February 2021, 1855 . 1857 [ENISACSIRT] 1858 European Union Agency for Cybersecurity (ENISA), 1859 "Actionable information for Security Incident Response", 1860 November 2014, . 1864 [EU2018] European Parliament and Council, "2015/0277 (COD) PE-CONS 1865 2/18", February 2018, 1866 . 1869 [FAACONOPS] 1870 FAA Office of NextGen, "UTM Concept of Operations v2.0", 1871 March 2020, . 1874 [FR24] Flightradar24 AB, "Flightradar24 Live Air Traffic", May 1875 2021, . 1877 [FRUR] Federal Aviation Administration, "Remote Identification of 1878 Unmanned Aircraft", January 2021, 1879 . 1883 [GDPR] European Parliament and Council, "General Data Protection 1884 Regulation", April 2016, 1885 . 1887 [I-D.maeurer-raw-ldacs] 1888 Maeurer, N., Graeupl, T., and C. Schmitt, "L-band Digital 1889 Aeronautical Communications System (LDACS)", Work in 1890 Progress, Internet-Draft, draft-maeurer-raw-ldacs-06, 2 1891 October 2020, 1892 . 1894 [ICAOATM] International Civil Aviation Organization, "Doc 4444: 1895 Procedures for Air Navigation Services: Air Traffic 1896 Management", November 2016, . 1900 [ICAODEFS] International Civil Aviation Organization, "Defined terms 1901 from the Annexes to the Chicago Convention and ICAO 1902 guidance material", July 2017, 1903 . 1906 [ICAOUAS] International Civil Aviation Organization, "Circular 328: 1907 Unmanned Aircraft Systems", February 2011, 1908 . 1911 [ICAOUTM] International Civil Aviation Organization, "Unmanned 1912 Aircraft Systems Traffic Management (UTM) - A Common 1913 Framework with Core Principles for Global Harmonization, 1914 Edition 3", October 2020, 1915 . 1918 [Implementing] 1919 European Union Aviation Safety Agency (EASA), "Commission 1920 Implementing Regulation (EU) 2019/947 of 24 May 2019 on 1921 the rules and procedures for the operation of unmanned 1922 aircraft", May 2019, 1923 . 1925 [InitialView] 1926 SESAR Joint Undertaking, "Initial view on Principles for 1927 the U-space architecture", July 2019, 1928 . 1932 [NPRM] United States Federal Aviation Administration (FAA), 1933 "Notice of Proposed Rule Making on Remote Identification 1934 of Unmanned Aircraft Systems", December 2019, 1935 . 1939 [OpenDroneID] 1940 Intel Corp., "Open Drone ID", March 2019, 1941 . 1943 [OpenSky] OpenSky Network non-profit association, "The OpenSky 1944 Network", May 2021, 1945 . 1947 [Opinion1] European Union Aviation Safety Agency (EASA), "Opinion No 1948 01/2020: High-level regulatory framework for the U-space", 1949 March 2020, . 1952 [Part107] United States Federal Aviation Administration, "Code of 1953 Federal Regulations Part 107", June 2016, 1954 . 1956 [Recommendations] 1957 FAA UAS Identification and Tracking Aviation Rulemaking 1958 Committee, "UAS ID and Tracking ARC Recommendations Final 1959 Report", September 2017, . 1963 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 1964 Unique IDentifier (UUID) URN Namespace", RFC 4122, 1965 DOI 10.17487/RFC4122, July 2005, 1966 . 1968 [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol 1969 (HIP) Architecture", RFC 4423, DOI 10.17487/RFC4423, May 1970 2006, . 1972 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 1973 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 1974 . 1976 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1977 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1978 January 2012, . 1980 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1981 Morris, J., Hansen, M., and R. Smith, "Privacy 1982 Considerations for Internet Protocols", RFC 6973, 1983 DOI 10.17487/RFC6973, July 2013, 1984 . 1986 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 1987 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 1988 RFC 7401, DOI 10.17487/RFC7401, April 2015, 1989 . 1991 [RFC8280] ten Oever, N. and C. Cath, "Research into Human Rights 1992 Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280, 1993 October 2017, . 1995 [Roadmap] American National Standards Institute (ANSI) Unmanned 1996 Aircraft Systems Standardization Collaborative (UASSC), 1997 "Standardization Roadmap for Unmanned Aircraft Systems 1998 draft v2.0", April 2020, . 2002 [Stranger] Heinlein, R.A., "Stranger in a Strange Land", June 1961. 2004 [WG105] EUROCAE, "WG-105 draft ED-282 Minimum Operational 2005 Performance Standards (MOPS) for Unmanned Aircraft System 2006 (UAS) Electronic Identification", June 2020. 2008 [WiFiNAN] Wi-Fi Alliance, "Wi-Fi Aware™ Specification Version 3.2", 2009 October 2020, . 2012 Appendix A. Discussion and Limitations 2014 This document is largely based on the process of one SDO, ASTM. 2015 Therefore, it is tailored to specific needs and data formats of this 2016 standard. Other organizations, for example in EU, do not necessary 2017 follow the same architecture. 2019 The need for drone ID and operator privacy is an open discussion 2020 topic. For instance, in the ground vehicular domain each car carries 2021 a publicly visible plate number. In some countries, for nominal cost 2022 or even for free, anyone can resolve the identity and contact 2023 information of the owner. Civil commercial aviation and maritime 2024 industries also have a tradition of broadcasting plane or ship ID, 2025 coordinates, and even flight plans in plain text. Community networks 2026 such as OpenSky [OpenSky] and Flightradar24 [FR24] use this open 2027 information through ADS-B to deploy public services of flight 2028 tracking. Many researchers also use these data to perform 2029 optimization of routes and airport operations. Such ID information 2030 should be integrity protected, but not necessarily confidential. 2032 In civil aviation, aircraft identity is broadcast by a device known 2033 as transponder. It transmits a four octal digit squawk code, which 2034 is assigned by a traffic controller to an airplane after approving a 2035 flight plan. There are several reserved codes such as 7600 which 2036 indicate radio communication failure. The codes are unique in each 2037 traffic area and can be re-assigned when entering another control 2038 area. The code is transmitted in plain text by the transponder and 2039 also used for collision avoidance by a system known as Traffic alert 2040 and Collision Avoidance System (TCAS). The system could be used for 2041 UAS as well initially, but the code space is quite limited and likely 2042 to be exhausted soon. The number of UAS far exceeds the number of 2043 civil airplanes in operation. 2045 The ADS-B system is utilized in civil aviation for each "ADS-B Out" 2046 equipped airplane to broadcast its ID, coordinates, and altitude for 2047 other airplanes and ground control stations. If this system is 2048 adopted for drone IDs, it has additional benefit with backward 2049 compatibility with civil aviation infrastructure; then, pilots and 2050 dispatchers will be able to see UA on their control screens and take 2051 those into account. If not, a gateway translation system between the 2052 proposed drone ID and civil aviation system should be implemented. 2053 Again, system saturation due to large numbers of UAS is a concern. 2055 The Mode S transponders used in all TCAS and most ADS-B Out 2056 installations are assigned an ICAO 24 bit "address" (arguably really 2057 an identifier rather than a locator) that is associated with the 2058 aircraft as part of its registration. In the US alone, well over 2059 2^20 UAS are already flying; thus, a 24 bit space likely would be 2060 rapidly exhausted if used for UAS (other than large UAS flying in 2061 controlled airspace, especially internationally, under rules other 2062 than those governing small UAS at low altitudes). 2064 Wi-Fi and Bluetooth are two wireless technologies currently 2065 recommended by ASTM specifications due to their widespread use and 2066 broadcast nature. However, those have limited range (max 100s of 2067 meters) and may not reliably deliver UAS ID at high altitude or 2068 distance. Therefore, a study should be made of alternative 2069 technologies from the telecom domain (WiMAX / IEEE 802.16, 5G) or 2070 sensor networks (Sigfox, LoRa). Such transmission technologies can 2071 impose additional restrictions on packet sizes and frequency of 2072 transmissions, but could provide better energy efficiency and range. 2074 In civil aviation, Controller-Pilot Data Link Communications (CPDLC) 2075 is used to transmit command and control between the pilots and ATC. 2076 It could be considered for UAS as well due to long range and proven 2077 use despite its lack of security [CPDLC]. 2079 L-band Digital Aeronautical Communications System (LDACS) is being 2080 standardized by ICAO and IETF for use in future civil aviation 2081 [I-D.maeurer-raw-ldacs]. It provides secure communication, 2082 positioning, and control for aircraft using a dedicated radio band. 2083 It should be analyzed as a potential provider for UAS RID as well. 2084 This will bring the benefit of a global integrated system creating a 2085 global airspace use awareness. 2087 Acknowledgments 2089 The work of the FAA's UAS Identification and Tracking (UAS ID) 2090 Aviation Rulemaking Committee (ARC) is the foundation of later ASTM 2091 [F3411-19] and IETF DRIP efforts. The work of Gabriel Cox, Intel 2092 Corp., and their Open Drone ID collaborators opened UAS RID to a 2093 wider community. The work of ASTM F38.02 in balancing the interests 2094 of diverse stakeholders is essential to the necessary rapid and 2095 widespread deployment of UAS RID. IETF volunteers who have 2096 extensively reviewed or otherwise contributed to this document 2097 include Amelia Andersdotter, Carsten Bormann, Mohamed Boucadair, 2098 Toerless Eckert, Susan Hares, Mika Jarvenpaa, Daniel Migault, 2099 Alexandre Petrescu, Saulo Da Silva and Shuai Zhao. Thanks to Linda 2100 Dunbar for the Secdir review and Nagendra Nainar for the Opsdir 2101 review. 2103 Authors' Addresses 2105 Stuart W. Card (editor) 2106 AX Enterprize 2107 4947 Commercial Drive 2108 Yorkville, NY 13495 2109 United States of America 2111 Email: stu.card@axenterprize.com 2113 Adam Wiethuechter 2114 AX Enterprize 2115 4947 Commercial Drive 2116 Yorkville, NY 13495 2117 United States of America 2119 Email: adam.wiethuechter@axenterprize.com 2120 Robert Moskowitz 2121 HTT Consulting 2122 Oak Park, MI 48237 2123 United States of America 2125 Email: rgm@labs.htt-consult.com 2127 Andrei Gurtov 2128 Linköping University 2129 IDA 2130 SE-58183 Linköping 2131 Sweden 2133 Email: gurtov@acm.org