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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 (25 June 2021) is 1033 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: 27 December 2021 R. Moskowitz 6 HTT Consulting 7 A. Gurtov 8 Linköping University 9 25 June 2021 11 Drone Remote Identification Protocol (DRIP) Requirements 12 draft-ietf-drip-reqs-14 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 27 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 . . . . . . . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . . . . . . 28 72 3.4. DRIP Focus . . . . . . . . . . . . . . . . . . . . . . . 29 73 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 30 74 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 30 75 4.1.1. Normative Requirements . . . . . . . . . . . . . . . 30 76 4.1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 32 77 4.2. Identifier . . . . . . . . . . . . . . . . . . . . . . . 33 78 4.2.1. Normative Requirements . . . . . . . . . . . . . . . 33 79 4.2.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 33 80 4.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 34 81 4.3.1. Normative Requirements . . . . . . . . . . . . . . . 34 82 4.3.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 35 83 4.4. Registries . . . . . . . . . . . . . . . . . . . . . . . 36 84 4.4.1. Normative Requirements . . . . . . . . . . . . . . . 36 85 4.4.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 37 86 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 87 6. Security Considerations . . . . . . . . . . . . . . . . . . . 37 88 7. Privacy and Transparency Considerations . . . . . . . . . . . 38 89 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 90 8.1. Normative References . . . . . . . . . . . . . . . . . . 39 91 8.2. Informative References . . . . . . . . . . . . . . . . . 40 92 Appendix A. Discussion and Limitations . . . . . . . . . . . . . 44 93 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 45 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45 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. The general scenario is illustrated in Figure 1. 159 *************** *************** 160 * UAS1 * * UAS2 * 161 * * * * 162 * +--------+ * DAA/V2V * +--------+ * 163 * | UA o--*----------------------------------------*--o UA | * 164 * +--o--o--+ * * +--o--o--+ * 165 * | | * +------+ Lookups +------+ * | | * 166 * | | * | GPOD o------. .------o PSOD | * | | * 167 * | | * +------+ | | +------+ * | | * 168 * | | * | | * | | * 169 * C2 | | * V2I ************ V2I * | | C2 * 170 * | '-----*--------------* *--------------*-----' | * 171 * | * * * * | * 172 * | o====NetRID====* *====NetRID====o | * 173 * +--o--+ * * Internet * * +--o--+ * 174 * | GCS o-----*--------------* *--------------*-----o GCS | * 175 * +-----+ * Registration * * Registration * +-----+ * 176 * * (and UTM) * * (and UTM) * * 177 *************** ************ *************** 178 | | | 179 +----------+ | | | +----------+ 180 | Public o---' | '---o Private | 181 | Registry | | | Registry | 182 +----------+ | +----------+ 183 +--o--+ 184 | DNS | 185 +-----+ 187 GPOD: General Public Observer Device (used only to fit this figure) 188 PSOD: Public Safety Observer Device (used only to fit this figure) 190 Figure 1: "General UAS RID Usage Scenario" 192 Figure 1 illustrates a typical case where there may be: multiple 193 Observers, some of them members of the general public, others 194 government officers with public safety/security responsibilities; 195 multiple UA in flight within observation range, each with its own 196 pilot/operator; at least one registry each for lookup of public and 197 (by authorized parties only) private information regarding the UAS 198 and their pilots/operators; and in the DRIP vision, DNS resolving 199 various identifiers and locators of the entities involved. Note that 200 Broadcast RID direct RF links are not shown, as they are indeed 201 broadcast, so reach anywhere within range; they do not connect 202 specific entity pairings, as edges do vertices in a graph. Further, 203 RID and other connectivity involving the UA varies, as described 204 subsequently herein under Figure 3. Not all the links shown in 205 Figure 1 above necessarily exist in all scenarios (e.g., UA support 206 for direct connectivity to the Internet is very rare as of 2021), and 207 even those links that exist sometimes in a given scenario are not 208 necessarily up at all times in that same scenario (e.g., remote 209 Observer connectivity to the Internet may be very intermittent). 211 An Observer of UA may need to classify them, as illustrated 212 notionally in Figure 2, for basic airspace Situational Awareness 213 (SA). An Observer who classifies a UAS: as Taskable, can ask it to 214 do something useful; as Low Concern, can reasonably assume it is not 215 malicious and would cooperate with requests to modify its flight 216 plans for safety concerns that arise; as High Concern or 217 Unidentified, can focus surveillance on it. 219 xxxxxxx 220 x x No +--------------+ 221 x ID? x+---->| Unidentified | 222 x x +--------------+ 223 xxxxxxx 224 + 225 | Yes 226 v 227 xxxxxxx 228 x x 229 .---------+x Type? x+----------. 230 | x x | 231 | xxxxxxx | 232 | + | 233 v v v 234 +--------------+ +--------------+ +--------------+ 235 | Taskable | | Low Concern | | High Concern | 236 +--------------+ +--------------+ +--------------+ 238 Figure 2: "Notional UAS Classification" 240 ASTM International, Technical Committee F38 (UAS), Subcommittee 241 F38.02 (Aircraft Operations), Work Item WK65041, developed the widely 242 cited Standard Specification for Remote ID and Tracking [F3411-19]: 243 the published standard is available for purchase from ASTM and as an 244 ASTM membership premium; early drafts are freely available as 245 [OpenDroneID] specifications. [F3411-19] is frequently referenced in 246 DRIP, where building upon its link layers and both enhancing support 247 for and expanding the scope of its applications are central foci. 249 In many applications, including UAS RID, identification and 250 identifiers are not ends in themselves; they exist to enable lookups 251 and provision of other services. 253 Using UAS RID to facilitate vehicular (V2X) communications and 254 applications such as Detect And Avoid (DAA), which would impose 255 tighter latency bounds than RID itself, is an obvious possibility, 256 explicitly contemplated in the United States (US) Federal Aviation 257 Administration (FAA) Remote Identification of Unmanned Aircraft rule 258 [FRUR]. However, usage of RID systems and information beyond mere 259 identification (primarily to hold operators accountable after the 260 fact), including DAA, have been declared out of scope in ASTM F38.02 261 WK65041, based on a distinction between RID as a security standard vs 262 DAA as a safety application. Aviation community Standards 263 Development Organizations (SDOs) generally set a higher bar for 264 safety than for security, especially with respect to reliability. 265 Each SDO has its own cultural set of connotations of safety vs 266 security; the denotative definitions of the International Civil 267 Aviation Organization (ICAO) are cited in Section 2. 269 [Opinion1] and [WG105] cite the Direct Remote Identification (DRI) 270 previously required and specified, explicitly stating that whereas 271 DRI is primarily for security purposes, the "Network Identification 272 Service" [Opinion1] (in the context of U-space [InitialView]) or 273 "Electronic Identification" [WG105] is primarily for safety purposes 274 (e.g., Air Traffic Management, especially hazards deconfliction) and 275 also is allowed to be used for other purposes such as support of 276 efficient operations. These emerging standards allow the security 277 and safety oriented systems to be separate or merged. In addition to 278 mandating both Broadcast and Network one-way to Observers, they will 279 use V2V to other UAS (also likely to and/or from some manned 280 aircraft). These reflect the broad scope of the European Union (EU) 281 U-space concept, as being developed in the Single European Sky ATM 282 Research (SESAR) Joint Undertaking, the U-space architectural 283 principles of which are outlined in [InitialView]. 285 ASD-STAN is an Associated Body to CEN (European Committee for 286 Standardization) for Aerospace Standards. It is publishing an EU 287 standard "Aerospace series - Unmanned Aircraft Systems - Part 002: 289 Direct Remote Identification; English version prEN 4709-002:2020" for 290 which a current (early 2021) informal overview is freely available in 291 [ASDRI]. It will provide compliance to cover the identical DRI 292 requirements applicable to drones of classes C1 - [Delegated] Part 2, 293 C2 - [Delegated] Part 3, C3 - [Delegated] Part 4, C5 - [Amended] Part 294 16, and C6 - [Amended] Part 17. 296 The standard contemplated in [ASDRI] will provide UA capability to be 297 identified in real time during the whole duration of the flight, 298 without specific connectivity or ground infrastructure link, 299 utilizing existing mobile devices within broadcast range. It will 300 use Bluetooth 4, Bluetooth 5, Wi-Fi Neighbor Awareness Networking 301 (NAN, also known as Wi-Fi Aware, [WiFiNAN]) and/or IEEE 802.11 Beacon 302 modes. The EU standard emphasis was compatibility with [F3411-19], 303 although there are differences in mandatory and optional message 304 types and fields. 306 The [ASDRI] contemplated DRI system will broadcast locally: 308 1. the UAS operator registration number; 310 2. the [CTA2063A] compliant unique serial number of the UA; 312 3. a time stamp, the geographical position of the UA, and its height 313 AGL or above its take-off point; 315 4. the UA ground speed and route course measured clockwise from true 316 north; 318 5. the geographical position of the remote pilot, or if that is not 319 available, the geographical position of the UA take-off point; 320 and 322 6. for Classes C1, C2, C3, the UAS emergency status. 324 Under the [ASDRI] contemplated standard, data will be sent in plain 325 text and the UAS operator registration number will be represented as 326 a 16-byte string including the (European) state code. The 327 corresponding private ID part will contain 3 characters that are not 328 broadcast but used by authorities to access regional registration 329 databases for verification. 331 ASD-STAN also contemplates corresponding Network Remote 332 Identification (NRI) functionality. The ASD-STAN RID target is to 333 revise their current standard with additional functionality (e.g., 334 DRIP) to be published before 2022 [ASDRI]. 336 Security oriented UAS RID essentially has two goals: enable the 337 general public to obtain and record an opaque ID for any observed UA, 338 which they can then report to authorities; enable authorities, from 339 such an ID, to look up information about the UAS and its operator. 340 Safety oriented UAS RID has stronger requirements. 342 Although dynamic establishment of secure communications between the 343 Observer and the UAS pilot seems to have been contemplated by the FAA 344 UAS ID and Tracking Aviation Rulemaking Committee (ARC) in their 345 [Recommendations], it is not addressed in any of the 346 subsequent regulations or international SDO technical specifications, 347 other than DRIP, known to the authors as of early 2021. 349 1.2. Concerns and Constraints 351 Disambiguation of multiple UA flying in close proximity may be very 352 challenging, even if each is reporting its identity, position, and 353 velocity as accurately as it can. 355 The origin of information in UAS RID and UAS Traffic Management (UTM) 356 generally is the UAS or its operator. Self-reports may be initiated 357 by the remote pilot at the console of the Ground Control Station 358 (GCS, the UAS subsystem used to remotely operate the UA), or 359 automatically by GCS software; in Broadcast RID, they typically would 360 be initiated automatically by a process on the UA. Data in the 361 reports may come from sensors available to the operator (e.g., radar 362 or cameras), the GCS (e.g., "dead reckoning" UA location, starting 363 from the takeoff location and estimating the displacements due to 364 subsequent piloting commands, wind, etc.), or the UA itself (e.g., an 365 on-board GNSS receiver); in Broadcast RID, all the data must be sent 366 proximately by, and most of the data comes ultimately from, the UA 367 itself. Whether information comes proximately from the operator, or 368 from automated systems configured by the operator, there are 369 possibilities not only of unintentional error in but also of 370 intentional falsification of this data. Mandating UAS RID, 371 specifying data elements required to be sent, monitoring compliance 372 and enforcing it (or penalizing non-compliance) are matters for Civil 373 Aviation Authorities (CAAs) et al; specifying message formats, etc. 374 to carry those data elements has been addressed by other SDOs; 375 offering technical means, as extensions to external standards, to 376 facilitate verifiable compliance and enforcement/monitoring, are 377 opportunities for DRIP. 379 Minimal specified information must be made available to the public. 380 Access to other data, e.g., UAS operator Personally Identifiable 381 Information (PII), must be limited to strongly authenticated 382 personnel, properly authorized in accordance with applicable policy. 383 The balance between privacy and transparency remains a subject for 384 public debate and regulatory action; DRIP can only offer tools to 385 expand the achievable trade space and enable trade-offs within that 386 space. [F3411-19], the basis for most current (2021) thinking about 387 and efforts to provide UAS RID, specifies only how to get the UAS ID 388 to the Observer: how the Observer can perform these lookups and how 389 the registries first can be populated with information are 390 unspecified therein. 392 The need for nearly universal deployment of UAS RID is pressing: 393 consider how negligible the value of an automobile license plate 394 system would be if only 90% of the cars displayed plates. This 395 implies the need to support use by Observers of already ubiquitous 396 mobile devices (typically smartphones and tablets). Anticipating CAA 397 requirements to support legacy devices, especially in light of 398 [Recommendations], [F3411-19] specifies that any UAS sending 399 Broadcast RID over Bluetooth must do so over Bluetooth 4, regardless 400 of whether it also does so over newer versions; as UAS sender devices 401 and Observer receiver devices are unpaired, this implies extremely 402 short "advertisement" (beacon) frames. 404 Wireless data links to or from UA are challenging. Flight is often 405 amidst structures and foliage at low altitudes over varied terrain. 406 UA are constrained in both total energy and instantaneous power by 407 their batteries. Small UA imply small antennas. Densely populated 408 volumes will suffer from link congestion: even if UA in an airspace 409 volume are few, other transmitters nearby on the ground, sharing the 410 same license free spectral band, may be many. Thus air to air and 411 air to ground links will generally be slow and unreliable. 413 UAS Cost, Size, Weight, and Power (CSWaP) constraints are severe. 414 CSWaP is a burden not only on the designers of new UAS for sale, but 415 also on owners of existing UAS that must be retrofit. Radio 416 Controlled (RC) aircraft modelers, "hams" who use licensed amateur 417 radio frequencies to control UAS, drone hobbyists, and others who 418 custom build UAS, all need means of participating in UAS RID, 419 sensitive to both generic CSWaP and application-specific 420 considerations. 422 To accommodate the most severely constrained cases, all these 423 conspire to motivate system design decisions that complicate the 424 protocol design problem. 426 Broadcast RID uses one-way local data links. UAS may have Internet 427 connectivity only intermittently, or not at all, during flight. 429 Internet-disconnected operation of Observer devices has been deemed 430 by ASTM F38.02 too infrequent to address. However, the preamble to 431 [FRUR] cites "remote and rural areas that do not have reliable 432 Internet access" as a major reason for requiring Broadcast rather 433 than Network RID, and states that "Personal wireless devices that are 434 capable of receiving 47 CFR part 15 frequencies, such as smart 435 phones, tablets, or other similar commercially available devices, 436 will be able to receive broadcast remote identification information 437 directly without reliance on an Internet connection". Internet- 438 disconnected operation presents challenges, e.g., for Observers 439 needing access to the [F3411-19] web based Broadcast Authentication 440 Verifier Service or external lookups. 442 As RID must often operate within these constraints, heavyweight 443 cryptographic security protocols or even simple cryptographic 444 handshakes are infeasible, yet trustworthiness of UAS RID information 445 is essential. Under [F3411-19], _even the most basic datum, the UAS 446 ID itself, can be merely an unsubstantiated claim_. 448 Observer devices being ubiquitous, thus popular targets for malware 449 or other compromise, cannot be generally trusted (although the user 450 of each device is compelled to trust that device, to some extent); a 451 "fair witness" functionality (inspired by [Stranger]) is desirable. 453 Despite work by regulators and SDOs, there are substantial gaps in 454 UAS standards generally and UAS RID specifically. [Roadmap] catalogs 455 UAS related standards, ongoing standardization activities and gaps 456 (as of 2020); Section 7.8 catalogs those related specifically to UAS 457 RID. DRIP will address the most fundamental of these gaps, as 458 foreshadowed above. 460 1.3. DRIP Scope 462 DRIP's initial charter is to make RID immediately actionable, in both 463 Internet and local-only connected scenarios (especially emergencies), 464 in severely constrained UAS environments, balancing legitimate (e.g., 465 public safety) authorities' Need To Know trustworthy information with 466 UAS operators' privacy. By "immediately actionable" is meant 467 information of sufficient precision, accuracy, timeliness, etc. for 468 an Observer to use it as the basis for immediate decisive action, 469 whether that be to trigger a defensive counter-UAS system, to attempt 470 to initiate communications with the UAS operator, to accept the 471 presence of the UAS in the airspace where/when observed as not 472 requiring further action, or whatever, with potentially severe 473 consequences of any action or inaction chosen based on that 474 information. For further explanation of the concept of immediate 475 actionability, see [ENISACSIRT]. 477 Note that UAS RID must achieve nearly universal adoption, but DRIP 478 can add value even if only selectively deployed. Authorities with 479 jurisdiction over more sensitive airspace volumes may set a higher 480 than generally mandated RID requirement for flight in such volumes. 481 Those with a greater need for high-confidence IFF can equip with 482 DRIP, enabling strong authentication of their own aircraft and allied 483 operators without regard for the weaker (if any) authentication of 484 others. 486 DRIP (originally Trustworthy Multipurpose Remote Identification, TM- 487 RID) potentially could be applied to verifiably identify other types 488 of registered things reported to be in specified physical locations, 489 and providing timely trustworthy identification data is also 490 prerequisite to identity-oriented networking, but the urgent 491 motivation and clear initial focus is UAS. Existing Internet 492 resources (protocol standards, services, infrastructure, and business 493 models) should be leveraged. 495 1.4. Document Scope 497 This document describes the problem space for UAS RID conforming to 498 proposed regulations and external technical standards, defines common 499 terminology, specifies numbered requirements for DRIP, identifies 500 some important considerations (IANA, security, privacy and 501 transparency), and discusses limitations. 503 A natural Internet-based approach to meet these requirements is 504 described in a companion architecture document [drip-architecture] 505 and elaborated in other DRIP documents. 507 2. Terms and Definitions 509 2.1. Requirements Terminology 511 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 512 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 513 "OPTIONAL" in this document are to be interpreted as described in BCP 514 14 [RFC2119] [RFC8174] when, and only when, they appear in all 515 capitals, as shown here. 517 2.2. Definitions 519 This section defines a non-comprehensive set of terms expected to be 520 used in DRIP documents. This list is meant to be the DRIP 521 terminology reference; as such, some of the terms listed below are 522 not used in this document. 524 [RFC4949] provides a glossary of Internet security terms that should 525 be used where applicable. 527 In the UAS community, the plural form of acronyms generally is the 528 same as the singular form, e.g., Unmanned Aircraft System (singular) 529 and Unmanned Aircraft Systems (plural) are both represented as UAS. 530 On this and other terminological issues, to encourage comprehension 531 necessary for adoption of DRIP by the intended user community, that 532 community's norms are respected herein, and definitions are quoted in 533 cases where they have been found in that community's documents. Most 534 of the listed terms are from that community (even if specific source 535 documents are not cited); any that are DRIP-specific or invented by 536 the authors of this document are marked "(DRIP)". 538 4-D 539 Four-dimensional. Latitude, Longitude, Altitude, Time. Used 540 especially to delineate an airspace volume in which an operation 541 is being or will be conducted. 543 AAA 544 Attestation, Authentication, Authorization, Access Control, 545 Accounting, Attribution, Audit, or any subset thereof (uses differ 546 by application, author, and context). (DRIP) 548 ABDAA 549 AirBorne DAA. Accomplished using systems onboard the aircraft 550 involved. Supports "self-separation" (remaining "well clear" of 551 other aircraft) and collision avoidance. 553 ADS-B 554 Automatic Dependent Surveillance - Broadcast. "ADS-B Out" 555 equipment obtains aircraft position from other on-board systems 556 (typically GNSS) and periodically broadcasts it to "ADS-B In" 557 equipped entities, including other aircraft, ground stations, and 558 satellite based monitoring systems. 560 AGL 561 Above Ground Level. Relative altitude, above the variously 562 defined local ground level, typically of a UA, measured in feet or 563 meters. Should be explicitly specified as either barometric 564 (pressure) or geodetic (GNSS) altitude. 566 ATC 567 Air Traffic Control. Explicit flight direction to pilots from 568 ground controllers. Contrast with ATM. 570 ATM 571 Air Traffic Management. A broader functional and geographic scope 572 and/or a higher layer of abstraction than ATC. "The dynamic, 573 integrated management of air traffic and airspace including air 574 traffic services, airspace management and air traffic flow 575 management - safely, economically and efficiently - through the 576 provision of facilities and seamless services in collaboration 577 with all parties and involving airborne and ground-based 578 functions" [ICAOATM]. 580 Authentication Message 581 [F3411-19] Message Type 2. Provides framing for authentication 582 data, only; the only message that can be extended in length by 583 segmenting it across more than one page. 585 Basic ID Message 586 [F3411-19] Message Type 0. Provides UA Type, UAS ID Type, and UAS 587 ID, only. 589 Broadcast Authentication Verifier Service 590 System component designed to handle any authentication of 591 Broadcast RID by offloading signature verification to a web 592 service [F3411-19]. 594 BVLOS 595 Beyond Visual Line Of Sight. See VLOS. 597 byte 598 Used here in its now-customary sense as a synonym for "octet", as 599 "byte" is used exclusively in definitions of data structures 600 specified in [F3411-19] 602 CAA 603 Civil Aviation Authority of a regulatory jurisdiction. Often so 604 named, but other examples include the United States Federal 605 Aviation Administration (FAA) and the Japan Civil Aviation Bureau. 607 CSWaP 608 Cost, Size, Weight, and Power. 610 C2 611 Command and Control. Previously mostly used in military contexts. 612 Properly refers to a function, exercisable over arbitrary 613 communications; but in the small UAS context, often refers to the 614 communications (typically RF data link) over which the GCS 615 controls the UA. 617 DAA 618 Detect And Avoid, formerly Sense And Avoid (SAA). A means of 619 keeping aircraft "well clear" of each other and obstacles for 620 safety. "The capability to see, sense or detect conflicting 621 traffic or other hazards and take the appropriate action to comply 622 with the applicable rules of flight" [ICAOUAS]. 624 DRI (not to be confused with DRIP) 625 Direct Remote Identification. EU regulatory requirement for "a 626 system that ensures the local broadcast of information about a UA 627 in operation, including the marking of the UA, so that this 628 information can be obtained without physical access to the UA". 629 [Delegated] that presumably can be satisfied with appropriately 630 configured [F3411-19] Broadcast RID. 632 DSS 633 Discovery and Synchronization Service. The UTM system overlay 634 network backbone. Most importantly, it enables one USS to learn 635 which other USS have UAS operating in a given 4-D airspace volume, 636 for strategic deconfliction of planned operations and Network RID 637 surveillance of active operations. [F3411-19] 639 EUROCAE 640 European Organisation for Civil Aviation Equipment. Aviation SDO, 641 originally European, now with broader membership. Cooperates 642 extensively with RTCA. 644 GBDAA 645 Ground Based DAA. Accomplished with the aid of ground based 646 functions. 648 GCS 649 Ground Control Station. The part of the UAS that the remote pilot 650 uses to exercise C2 over the UA, whether by remotely exercising UA 651 flight controls to fly the UA, by setting GNSS waypoints, or 652 otherwise directing its flight. 654 GNSS 655 Global Navigation Satellite System. Satellite based timing and/or 656 positioning with global coverage, often used to support 657 navigation. 659 GPS 660 Global Positioning System. A specific GNSS, but in the UAS 661 context, the term is typically misused in place of the more 662 generic term GNSS. 664 GRAIN 665 Global Resilient Aviation Interoperable Network. ICAO managed 666 IPv6 overlay internetwork based on IATF, dedicated to aviation 667 (but not just aircraft). Currently (2021) in design, 668 accommodating the proposed DRIP identifier. 670 IATF 671 International Aviation Trust Framework. ICAO effort to develop a 672 resilient and secure by design framework for networking in support 673 of all aspects of aviation. 675 ICAO 676 International Civil Aviation Organization. A United Nations 677 specialized agency that develops and harmonizes international 678 standards relating to aviation. 680 IFF 681 Identification Friend or Foe. Originally, and in its narrow sense 682 still, a self-identification broadcast in response to 683 interrogation via radar, to reduce friendly fire incidents, which 684 led to military and commercial transponder systems such as ADS-B. 685 In the broader sense used here, any process intended to 686 distinguish friendly from potentially hostile UA or other entities 687 encountered. 689 LAANC 690 Low Altitude Authorization and Notification Capability. Supports 691 ATC authorization requirements for UAS operations: remote pilots 692 can apply to receive a near real-time authorization for operations 693 under 400 feet in controlled airspace near airports. FAA 694 authorized partial stopgap in the US until UTM comes. 696 Location/Vector Message 697 [F3411-19] Message Type 1. Provides UA location, altitude, 698 heading, speed, and status. 700 LOS 701 Line Of Sight. An adjectival phrase describing any information 702 transfer that travels in a nearly straight line (e.g., 703 electromagnetic energy, whether in the visual light, RF, or other 704 frequency range) and is subject to blockage. A term to be avoided 705 due to ambiguity, in this context, between RF LOS and VLOS. 707 Message Pack 708 [F3411-19] Message Type 15. The framed concatenation, in message 709 type index order, of at most one message of each type of any 710 subset of the other types. Required to be sent in Wi-Fi NAN and 711 in Bluetooth 5 Extended Advertisements, if those media are used; 712 cannot be sent in Bluetooth 4. 714 MSL 715 Mean Sea Level. Shorthand for relative altitude, above the 716 variously defined mean sea level, typically of a UA (but in [FRUR] 717 also for a GCS), measured in feet or meters. Should be explicitly 718 specified as either barometric (pressure) or geodetic (e.g., as 719 indicated by GNSS, referenced to the WGS84 ellipsoid). 721 Net-RID DP 722 Network RID Display Provider. [F3411-19] logical entity that 723 aggregates data from Net-RID SPs as needed in response to user 724 queries regarding UAS operating within specified airspace volumes, 725 to enable display by a user application on a user device. 726 Potentially could provide not only information sent via UAS RID 727 but also information retrieved from UAS RID registries or 728 information beyond UAS RID. Under superseded [NPRM], not 729 recognized as a distinct entity, but a service provided by USS, 730 including Public Safety USS that may exist primarily for this 731 purpose rather than to manage any subscribed UAS. 733 Net-RID SP 734 Network RID Service Provider. [F3411-19] logical entity that 735 collects RID messages from UAS and responds to NetRID-DP queries 736 for information on UAS of which it is aware. Under superseded 737 [NPRM], the USS to which the UAS is subscribed ("Remote ID USS"). 739 Network Identification Service 740 EU regulatory requirement in [Opinion1] and [WG105] that 741 presumably can be satisfied with appropriately configured 742 [F3411-19] Network RID. 744 Observer 745 An entity (typically but not necessarily an individual human) who 746 has directly or indirectly observed a UA and wishes to know 747 something about it, starting with its ID. An Observer typically 748 is on the ground and local (within VLOS of an observed UA), but 749 could be remote (observing via Network RID or other surveillance), 750 operating another UA, aboard another aircraft, etc. (DRIP) 752 Operation 753 A flight, or series of flights of the same mission, by the same 754 UAS, separated by at most brief ground intervals. (Inferred from 755 UTM usage, no formal definition found) 757 Operator 758 "A person, organization or enterprise engaged in or offering to 759 engage in an aircraft operation" [ICAOUAS]. 761 Operator ID Message 762 [F3411-19] Message Type 5. Provides CAA issued Operator ID, only. 763 Operator ID is distinct from UAS ID. 765 page 766 Payload of a frame, containing a chunk of a message that has been 767 segmented, to allow transport of a message longer than can be 768 encapsulated in a single frame. [F3411-19] 770 PIC 771 Pilot In Command. "The pilot designated by the operator, or in 772 the case of general aviation, the owner, as being in command and 773 charged with the safe conduct of a flight" [ICAOUAS]. 775 PII 776 Personally Identifiable Information. In the UAS RID context, 777 typically of the UAS Operator, Pilot In Command (PIC), or Remote 778 Pilot, but possibly of an Observer or other party. This specific 779 term is used primarily in the US; other terms with essentially the 780 same meaning are more common in other jurisdictions (e.g., 781 "personal data" in the EU). Used herein generically to refer to 782 personal information, which the person might wish to keep private, 783 or may have a statutorily recognized right to keep private (e.g., 784 under the EU [GDPR]), potentially imposing (legally or ethically) 785 a confidentiality requirement on protocols/systems. 787 Remote Pilot 788 A pilot using a GCS to exercise proximate control of a UA. Either 789 the PIC or under the supervision of the PIC. "The person who 790 manipulates the flight controls of a remotely-piloted aircraft 791 during flight time" [ICAOUAS]. 793 RF 794 Radio Frequency. Adjective, e.g., "RF link", or noun. 796 RF LOS 797 RF Line Of Sight. Typically used in describing a direct radio 798 link between a GCS and the UA under its control, potentially 799 subject to blockage by foliage, structures, terrain, or other 800 vehicles, but less so than VLOS. 802 RTCA 803 Radio Technical Commission for Aeronautics. US aviation SDO. 804 Cooperates extensively with EUROCAE. 806 Safety 807 "The state in which risks associated with aviation activities, 808 related to, or in direct support of the operation of aircraft, are 809 reduced and controlled to an acceptable level." From Annex 19 of 810 the Chicago Convention, quoted in [ICAODEFS] 812 Security 813 "Safeguarding civil aviation against acts of unlawful 814 interference." From Annex 17 of the Chicago Convention, quoted in 815 [ICAODEFS] 817 Self-ID Message 818 [F3411-19] Message Type 3. Provides a 1 byte descriptor and 23 819 byte ASCII free text field, only. Expected to be used to provide 820 context on the operation, e.g., mission intent. 822 SDO 823 Standards Development Organization. ASTM, IETF, et al. 825 SDSP 826 Supplemental Data Service Provider. An entity that participates 827 in the UTM system, but provides services beyond those specified as 828 basic UTM system functions (e.g., weather data). [FAACONOPS] 830 System Message 831 [F3411-19] Message Type 4. Provides general UAS information, 832 including remote pilot location, multiple UA group operational 833 area, etc. 835 U-space 836 EU concept and emerging framework for integration of UAS into all 837 classes of airspace, specifically including high density urban 838 areas, sharing airspace with manned aircraft [InitialView]. 840 UA 841 Unmanned Aircraft. In popular parlance, "drone". "An aircraft 842 which is intended to operate with no pilot on board" [ICAOUAS]. 844 UAS 845 Unmanned Aircraft System. Composed of UA, all required on-board 846 subsystems, payload, control station, other required off-board 847 subsystems, any required launch and recovery equipment, all 848 required crew members, and C2 links between UA and control station 849 [F3411-19]. 851 UAS ID 852 UAS identifier. Although called "UAS ID", it is actually unique 853 to the UA, neither to the operator (as some UAS registration 854 numbers have been and for exclusively recreational purposes are 855 continuing to be assigned), nor to the combination of GCS and UA 856 that comprise the UAS. _Maximum length of 20 bytes_ [F3411-19]. 858 UAS ID Type 859 UAS Identifier type index. 4 bits, see Section 3, Paragraph 6 for 860 currently defined values 0-3. [F3411-19] 862 UAS RID 863 UAS Remote Identification and tracking. System to enable 864 arbitrary Observers to identify UA during flight. 866 USS 867 UAS Service Supplier. "A USS is an entity that assists UAS 868 Operators with meeting UTM operational requirements that enable 869 safe and efficient use of airspace" and "... provide services to 870 support the UAS community, to connect Operators and other entities 871 to enable information flow across the USS Network, and to promote 872 shared situational awareness among UTM participants" [FAACONOPS]. 874 UTM 875 UAS Traffic Management. "A specific aspect of air traffic 876 management which manages UAS operations safely, economically and 877 efficiently through the provision of facilities and a seamless set 878 of services in collaboration with all parties and involving 879 airborne and ground-based functions" [ICAOUTM]. In the US, 880 according to the FAA, a "traffic management" ecosystem for 881 "uncontrolled" low altitude UAS operations, separate from, but 882 complementary to, the FAA's ATC system for "controlled" operations 883 of manned aircraft. 885 V2V 886 Vehicle-to-Vehicle. Originally communications between 887 automobiles, now extended to apply to communications between 888 vehicles generally. Often, together with Vehicle-to- 889 Infrastructure (V2I) etc., generalized to V2X. 891 VLOS 892 Visual Line Of Sight. Typically used in describing operation of a 893 UA by a "remote" pilot who can clearly directly (without video 894 cameras or any aids other than glasses or under some rules 895 binoculars) see the UA and its immediate flight environment. 896 Potentially subject to blockage by foliage, structures, terrain, 897 or other vehicles, more so than RF LOS. 899 3. UAS RID Problem Space 901 CAAs worldwide are mandating UAS RID. The European Union Aviation 902 Safety Agency (EASA) has published [Delegated] and [Implementing] 903 Regulations. The US FAA has published a "final" rule [FRUR] and has 904 described the key role that UAS RID plays in UAS Traffic Management 905 (UTM) in [FAACONOPS] (especially Section 2.6). CAAs currently (2021) 906 promulgate performance-based regulations that do not specify 907 techniques, but rather cite industry consensus technical standards as 908 acceptable means of compliance. 910 The most widely cited such industry consensus technical standard for 911 UAS RID is [F3411-19], which defines two means of UAS RID: 913 Network RID defines a set of information for UAS to make available 914 globally indirectly via the Internet, through servers that can be 915 queried by Observers. 917 Broadcast RID defines a set of messages for UA to transmit locally 918 directly one-way over Bluetooth or Wi-Fi (without IP or any other 919 protocols between the data link and application layers), to be 920 received in real time by local Observers. 922 UAS using both means must send the same UAS RID application layer 923 information via each [F3411-19]. The presentation may differ, as 924 Network RID defines a data dictionary, whereas Broadcast RID defines 925 message formats (which carry items from that same data dictionary). 926 The interval (or rate) at which it is sent may differ, as Network RID 927 can accommodate Observer queries asynchronous to UAS updates (which 928 generally need be sent only when information, such as location, 929 changes), whereas Broadcast RID depends upon Observers receiving UA 930 messages at the time they are transmitted. 932 Network RID depends upon Internet connectivity in several segments 933 from the UAS to each Observer. Broadcast RID should need Internet 934 (or other Wide Area Network) connectivity only to retrieve UAS 935 registry information using the directly locally received UAS 936 Identifier (UAS ID) as the primary unique key for database lookup. 937 Broadcast RID does not assume IP connectivity of UAS; messages are 938 encapsulated by the UA _without IP_, directly in link layer frames 939 (Bluetooth 4, Bluetooth 5, Wi-Fi NAN, IEEE 802.11 Beacon, or in the 940 future perhaps others). 942 [F3411-19] specifies three UAS ID Type values: 944 1 A static, manufacturer assigned, hardware serial number as defined 945 in ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers" 946 [CTA2063A]. 948 2 A CAA assigned (generally static) ID, like the registration number 949 of a manned aircraft. 951 3 A UTM system assigned UUID [RFC4122], which can but need not be 952 dynamic. 954 Per [Delegated], the EU allows only UAS ID Type 1. Under [FRUR], the 955 US allows types 1 and 3. [NPRM] proposed that a type 3 "Session ID" 956 would be "e.g., a randomly-generated alphanumeric code assigned by a 957 Remote ID UAS Service Supplier (USS) on a per-flight basis designed 958 to provide additional privacy to the operator", but given the 959 omission of Network RID from [FRUR], how this is to be assigned in 960 the US is still to be determined. 962 As yet apparently there are no CAA public proposals to use UAS ID 963 Type 2. In the preamble of [FRUR], the FAA argues that registration 964 numbers should not be sent in RID, insists that the capability of 965 looking up registration numbers from information contained in RID 966 should be restricted to FAA and other Government agencies, and 967 implies that Session ID would be linked to the registration number 968 only indirectly via the serial number in the registration database. 969 The possibility of cryptographically blinding registration numbers, 970 such that they can be revealed under specified circumstances, does 971 not appear to be mentioned in applicable regulations or external 972 technical standards. 974 Under [Delegated], the EU also requires an operator registration 975 number (an additional identifier distinct from the UAS ID) that can 976 be carried in an [F3411-19] optional Operator ID message. 978 [FRUR] allows RID requirements to be met by either the UA itself, 979 which is then designated a "standard remote identification unmanned 980 aircraft", or by an add-on "remote identification broadcast module". 981 Relative to a standard RID UA, the different requirements for a 982 module are that the latter: must transmit its own serial number 983 (neither the serial number of the UA to which it is attached, nor a 984 Session ID); must transmit takeoff location as a proxy for the 985 location of the pilot/GCS; need not transmit UA emergency status; and 986 is allowed to be used only for operations within VLOS of the remote 987 pilot. 989 Jurisdictions may relax or waive RID requirements for certain 990 operators and/or under certain conditions. For example, [FRUR] 991 allows operators with UAS not equipped for RID to conduct VLOS 992 operations at counter-intuitively named "FAA-recognized 993 identification areas" (FRIA); radio controlled model aircraft flying 994 clubs and other eligible organizations can apply to the FAA for such 995 recognition of their operating areas. 997 3.1. Network RID 999 +-------------+ ****************** 1000 | UA | * Internet * 1001 +--o-------o--+ * * 1002 | | * * 1003 | | * * +------------+ 1004 | '--------*--(+)-----------*-----o | 1005 | * | * | | 1006 | .--------*--(+)-----------*-----o NET-Rid SP | 1007 | | * * | | 1008 | | * .------*-----o | 1009 | | * | * +------------+ 1010 | | * | * 1011 | | * | * +------------+ 1012 | | * '------*-----o | 1013 | | * * | NET-Rid DP | 1014 | | * .------*-----o | 1015 | | * | * +------------+ 1016 | | * | * 1017 | | * | * +------------+ 1018 +--o-------o--+ * '------*-----o Observer's | 1019 | GCS | * * | Device | 1020 +-------------+ ****************** +------------+ 1022 Figure 3: "Network RID Information Flow" 1024 Figure 3 illustrates Network RID information flows. Only two of the 1025 three typically wireless links shown involving the UAS (UA-GCS, UA- 1026 Internet, and GCS-Internet) need exist. All three may exist, at the 1027 same or different times, especially in Beyond Visual Line Of Sight 1028 (BVLOS) operations. There must be some information flow path (direct 1029 or indirect) between the GCS and the UA, for the former to exercise 1030 C2 over the latter. If this path is two-way (as increasingly it is, 1031 even for inexpensive small UAS), the UA will also send its status 1032 (and position, if suitably equipped, e.g., with GNSS) to the GCS. 1033 There also must be some path between at least one subsystem of the 1034 UAS (UA or GCS) and the Internet, for the former to send status and 1035 position updates to its USS (serving _inter alia_ as a Net-RID SP). 1037 Direct UA-Internet wireless links are expected to become more common, 1038 especially on larger UAS, but currently (2021) are rare. Instead, 1039 the RID data flow typically originates on the UA and passes through 1040 the GCS, or originates on the GCS. Network RID data makes three 1041 trips through the Internet (GCS-SP, SP-DP, DP-Observer, unless any of 1042 them are colocated), implying use of IP (and other middle layer 1043 protocols, e.g., TLS/TCP or DTLS/UDP) on those trips. IP is not 1044 necessarily used or supported on the UA-GCS link (if indeed that 1045 direct link exists, as it typically does now, but in BVLOS operations 1046 often will not). 1048 Network RID is publish-subscribe-query. In the UTM context: 1050 1. The UAS operator pushes an "operational intent" (the current term 1051 in UTM corresponding to a flight plan in manned aviation) to the 1052 USS (call it USS#1) that will serve that UAS (call it UAS#1) for 1053 that operation, primarily to enable deconfliction with other 1054 operations potentially impinging upon that operation's 4-D 1055 airspace volume (call it Volume#1). 1057 2. Assuming the operation is approved and commences, UAS#1 1058 periodically pushes location/status updates to USS#1, which 1059 serves _inter alia_ as the Network RID Service Provider (Net-RID 1060 SP) for that operation. 1062 3. When users of any other USS (whether they be other UAS operators 1063 or Observers) develop an interest in any 4-D airspace volume 1064 (e.g., because they wish to submit an operational intent or 1065 because they have observed a UA), they query their own USS on the 1066 volumes in which they are interested. 1068 4. Their USS query, via the UTM Discovery and Synchronization 1069 Service (DSS), all other USS in the UTM system, and learn of any 1070 USS that have operations in those volumes (including any volumes 1071 intersecting them); thus those USS whose query volumes intersect 1072 Volume#1 (call them USS#2 through USS#n) learn that USS#1 has 1073 such operations. 1075 5. Interested parties can then subscribe to track updates on that 1076 operation of UAS#1, via their own USS, which serve as Network RID 1077 Display Providers (Net-RID DP) for that operation. 1079 6. USS#1 (as Net-RID SP) will then publish updates of UAS#1 status 1080 and position to all other subscribed USS in USS#2 through USS#n 1081 (as Net-RID DP). 1083 7. All Net-RID DP subscribed to that operation of UAS#1 will deliver 1084 its track information to their users who subscribed to that 1085 operation of UAS#1 (via means unspecified by [F3411-19] etc., but 1086 generally presumed to be web browser based). 1088 Network RID has several connectivity scenarios: 1090 _Persistently Internet connected UA_ can consistently directly 1091 source RID information; this requires wireless coverage throughout 1092 the intended operational airspace volume, plus a buffer (e.g., 1093 winds may drive the UA out of the volume). 1095 _Intermittently Internet connected UA_, can usually directly 1096 source RID information, but when offline (e.g., due to signal 1097 blockage by a large structure being inspected using the UAS), need 1098 the GCS to proxy source RID information. 1100 _Indirectly connected UA_ lack the ability to send IP packets that 1101 will be forwarded into and across the Internet, but instead have 1102 some other form of communications to another node that can relay 1103 or proxy RID information to the Internet; typically this node 1104 would be the GCS (which to perform its function must know where 1105 the UA is, although C2 link outages do occur). 1107 _Non-connected UA_ have no means of sourcing RID information, in 1108 which case the GCS or some other interface available to the 1109 operator must source it. In the extreme case, this could be the 1110 pilot or other agent of the operator using a web browser/ 1111 application to designate, to a USS or other UTM entity, a time- 1112 bounded airspace volume in which an operation will be conducted. 1113 This is referred to as a "non-equipped network participant" 1114 engaging in "area operations". This may impede disambiguation of 1115 ID if multiple UAS operate in the same or overlapping 4-D volumes. 1116 In most airspace volumes, most classes of UA will not be permitted 1117 to fly if non-connected. 1119 In most cases in the near term (2021), the Network RID first hop data 1120 link is likely to be cellular, which can also support BVLOS C2 over 1121 existing large coverage areas, or Wi-Fi, which can also support 1122 Broadcast RID. However, provided the data link can support at least 1123 UDP/IP and ideally also TCP/IP, its type is generally immaterial to 1124 higher layer protocols. The UAS, as the ultimate source of Network 1125 RID information, feeds a Net-RID SP (typically the USS to which the 1126 UAS operator subscribes), which proxies for the UAS and other data 1127 sources. An Observer or other ultimate consumer of Network RID 1128 information obtains it from a Net-RID DP (also typically a USS), 1129 which aggregates information from multiple Net-RID SPs to offer 1130 airspace Situational Awareness (SA) coverage of a volume of interest. 1132 Network RID Service and Display providers are expected to be 1133 implemented as servers in well-connected infrastructure, 1134 communicating with each other via the Internet, and accessible by 1135 Observers via means such as web Application Programming Interfaces 1136 (APIs) and browsers. 1138 Network RID is the less constrained of the defined UAS RID means. 1139 [F3411-19] specifies only Net-RID SP to Net-RID DP information 1140 exchanges. It is presumed that IETF efforts supporting the more 1141 constrained Broadcast RID (see next section) can be generalized for 1142 Network RID and potentially also for UAS to USS or other UTM 1143 communications. 1145 3.2. Broadcast RID 1147 +-------------------+ 1148 | Unmanned Aircraft | 1149 +---------o---------+ 1150 | 1151 | 1152 | 1153 | app messages directly over one-way RF data link 1154 | 1155 | 1156 v 1157 +------------------o-------------------+ 1158 | Observer's device (e.g., smartphone) | 1159 +--------------------------------------+ 1161 Figure 4: "Broadcast RID Information Flow" 1163 Figure 4 illustrates Broadcast RID information flow. Note the 1164 absence of the Internet from the figure. This is because Broadcast 1165 RID is one-way direct transmission of application layer messages over 1166 a RF data link (without IP) from the UA to local Observer devices. 1167 Internet connectivity is involved only in what the Observer chooses 1168 to do with the information received, such as verify signatures using 1169 a web-based Broadcast Authentication Verifier Service and look up 1170 information in registries using the UAS ID as the primary unique key. 1172 Broadcast RID is conceptually similar to Automatic Dependent 1173 Surveillance - Broadcast (ADS-B). However, for various technical and 1174 other reasons, regulators including the EASA have not indicated 1175 intent to allow, and FAA has explicitly prohibited, use of ADS-B for 1176 UAS RID. 1178 [F3411-19] specifies four Broadcast RID data links: Bluetooth 4.x, 1179 Bluetooth 5.x with Extended Advertisements and Long Range Coded PHY 1180 (S=8), Wi-Fi NAN at 2.4 GHz, and Wi-Fi NAN at 5 GHz. A UA must 1181 broadcast (using advertisement mechanisms where no other option 1182 supports broadcast) on at least one of these. If sending on 1183 Bluetooth 5.x, it is also required concurrently to do so on 4.x 1184 (referred to in [F3411-19] as Bluetooth Legacy); current (2021) 1185 discussions in ASTM F38.02 on revising the standard, motivated by 1186 European standards drafts, suggest that both Bluetooth versions will 1187 be required. If broadcasting Wi-Fi NAN at 5 GHz, it is also required 1188 concurrently to do so at 2.4 GHz; current discussions in F38.02 1189 include relaxing this. Wi-Fi Beacons are also under consideration. 1190 Future revisions of [F3411-19] may allow other data links. 1192 The selection of the Broadcast media was driven by research into what 1193 is commonly available on 'ground' units (smartphones and tablets) and 1194 what was found as prevalent or 'affordable' in UA. Further, there 1195 must be an API for the Observer's receiving application to have 1196 access to these messages. As yet only Bluetooth 4.x support is 1197 readily available, thus the current focus is on working within the 31 1198 byte payload limit of the Bluetooth 4.x "Broadcast Frame" transmitted 1199 as an "advertisement" on beacon channels. After overheads, this 1200 limits the RID message to 25 bytes and UAS ID string to a maximum 1201 length of 20 bytes. 1203 Length constraints also preclude a single Bluetooth 4.x frame 1204 carrying not only the UAS ID but also position, velocity, and other 1205 information that should be bound to the UAS ID, much less strong 1206 authentication data. Messages that cannot be encapsulated in a 1207 single frame (thus far, only the Authentication Message) must be 1208 segmented into message "pages" (in the terminology of [F3411-19]). 1209 Message pages must somehow be correlated as belonging to the same 1210 message. Messages carrying position, velocity and other data must 1211 somehow be correlated with the Basic ID message that carries the UAS 1212 ID. This correlation is expected to be done on the basis of MAC 1213 address: this may be complicated by MAC address randomization; not 1214 all the common devices expected to be used by Observers have APIs 1215 that make sender MAC addresses available to user space receiver 1216 applications; and MAC addresses are easily spoofed. Data elements 1217 are not so detached on other media (see Message Pack in the paragraph 1218 after next). 1220 [F3411-19] Broadcast RID specifies several message types. The 4 bit 1221 message type field in the header can index up to 16 types. Only 7 1222 are currently defined. Only 2 are mandatory. All others are 1223 optional, unless required by a jurisdictional authority, e.g., a CAA. 1224 To satisfy both EASA and FAA rules, all types are needed, except 1225 Self-ID and Authentication, as the data elements required by the 1226 rules are scattered across several message types (along with some 1227 data elements not required by the rules). 1229 The Message Pack (type 0xF) is not actually a message, but the framed 1230 concatenation of at most one message of each type of any subset of 1231 the other types, in type index order. Some of the messages that it 1232 can encapsulate are mandatory, others optional. The Message Pack 1233 itself is mandatory on data links that can encapsulate it in a single 1234 frame (Bluetooth 5.x and Wi-Fi). 1236 +-----------------------+-----------------+-----------+-----------+ 1237 | Index | Name | Req | Notes | 1238 +-----------------------+-----------------+-----------+-----------+ 1239 | 0x0 | Basic ID | Mandatory | - | 1240 +-----------------------+-----------------+-----------+-----------+ 1241 | 0x1 | Location/Vector | Mandatory | - | 1242 +-----------------------+-----------------+-----------+-----------+ 1243 | 0x2 | Authentication | Optional | paged | 1244 +-----------------------+-----------------+-----------+-----------+ 1245 | 0x3 | Self-ID | Optional | free text | 1246 +-----------------------+-----------------+-----------+-----------+ 1247 | 0x4 | System | Optional | - | 1248 +-----------------------+-----------------+-----------+-----------+ 1249 | 0x5 | Operator | Optional | - | 1250 +-----------------------+-----------------+-----------+-----------+ 1251 | 0xF | Message Pack | - | BT5 and | 1252 | | | | Wi-Fi | 1253 +-----------------------+-----------------+-----------+-----------+ 1254 | See Section 5.4.5 and | - | - | - | 1255 | Table 3 of [F3411-19] | | | | 1256 +-----------------------+-----------------+-----------+-----------+ 1258 Table 1: F3411-19 Message Types 1260 [F3411-19] Broadcast RID specifies very few quantitative performance 1261 requirements: static information must be transmitted at least once 1262 per 3 seconds; dynamic information (the Location/Vector message) must 1263 be transmitted at least once per second and be no older than one 1264 second when sent. [FRUR] requires all information be sent at least 1265 once per second. 1267 [F3411-19] Broadcast RID transmits all information as cleartext 1268 (ASCII or binary), so static IDs enable trivial correlation of 1269 patterns of use, unacceptable in many applications, e.g., package 1270 delivery routes of competitors. 1272 Any UA can assert any ID using the [F3411-19] required Basic ID 1273 message, which lacks any provisions for verification. The Position/ 1274 Vector message likewise lacks provisions for verification, and does 1275 not contain the ID, so must be correlated somehow with a Basic ID 1276 message: the developers of [F3411-19] have suggested using the MAC 1277 addresses on the Broadcast RID data link, but these may be randomized 1278 by the operating system stack to avoid the adversarial correlation 1279 problems of static identifiers. 1281 The [F3411-19] optional Authentication Message specifies framing for 1282 authentication data, but does not specify any authentication method, 1283 and the maximum length of the specified framing is too short for 1284 conventional digital signatures and far too short for conventional 1285 certificates (e.g., X.509). Fetching certificates via the Internet 1286 is not always possible (e.g., Observers working in remote areas, such 1287 as national forests), so devising a scheme whereby certificates can 1288 be transported over Broadcast RID is necessary. The one-way nature 1289 of Broadcast RID precludes challenge-response security protocols 1290 (e.g., Observers sending nonces to UA, to be returned in signed 1291 messages). Without DRIP extensions to [F3411-19], an Observer would 1292 be seriously challenged to validate the asserted UAS ID or any other 1293 information about the UAS or its operator looked up therefrom. 1295 3.3. USS in UTM and RID 1297 UAS RID and UTM are complementary; Network RID is a UTM service. The 1298 backbone of the UTM system is comprised of multiple USS: one or 1299 several per jurisdiction; some limited to a single jurisdiction, 1300 others spanning multiple jurisdictions. USS also serve as the 1301 principal or perhaps the sole interface for operators and UAS into 1302 the UTM environment. Each operator subscribes to at least one USS. 1303 Each UAS is registered by its operator in at least one USS. Each 1304 operational intent is submitted to one USS; if approved, that UAS and 1305 operator can commence that operation. During the operation, status 1306 and location of that UAS must be reported to that USS, which in turn 1307 provides information as needed about that operator, UAS, and 1308 operation into the UTM system and to Observers via Network RID. 1310 USS provide services not limited to Network RID; indeed, the primary 1311 USS function is deconfliction of airspace usage by different UAS and 1312 other (e.g., manned aircraft, rocket launch) operations. Most 1313 deconfliction involving a given operation is hoped to be completed 1314 prior to commencing that operation, and is called "strategic 1315 deconfliction". If that fails, "tactical deconfliction" comes into 1316 play; ABDAA may not involve USS, but GBDAA likely will. Dynamic 1317 constraints, formerly called UAS Volume Restrictions (UVR), can be 1318 necessitated by local emergencies, extreme weather, etc., specified 1319 by authorities on the ground, and propagated in UTM. 1321 No role for USS in Broadcast RID is currently specified by regulators 1322 or [F3411-19]. However, USS are likely to serve as registries (or 1323 perhaps registrars) for UAS (and perhaps operators); if so, USS will 1324 have a role in all forms of RID. Supplemental Data Service Providers 1325 (SDSP) are also likely to find roles, not only in UTM as such but 1326 also in enhancing UAS RID and related services. Whether USS, SDSP, 1327 etc. are involved or not, RID services, narrowly defined, provide 1328 regulator specified identification information; more broadly defined, 1329 RID services may leverage identification to facilitate related 1330 services or functions, likely beginning with V2X. 1332 3.4. DRIP Focus 1334 In addition to the gaps described above, there is a fundamental gap 1335 in almost all current or proposed regulations and technical standards 1336 for UAS RID. As noted above, ID is not an end in itself, but a 1337 means. Protocols specified in [F3411-19] etc. provide limited 1338 information potentially enabling, and no technical means for, an 1339 Observer to communicate with the pilot, e.g., to request further 1340 information on the UAS operation or exit from an airspace volume in 1341 an emergency. The System Message provides the location of the pilot/ 1342 GCS, so an Observer could physically go to the asserted location to 1343 look for the remote pilot; this is at best slow and may not be 1344 feasible. What if the pilot is on the opposite rim of a canyon, or 1345 there are multiple UAS operators to contact, whose GCS all lie in 1346 different directions from the Observer? An Observer with Internet 1347 connectivity and access privileges could look up operator PII in a 1348 registry, then call a phone number in hopes someone who can 1349 immediately influence the UAS operation will answer promptly during 1350 that operation; this is at best unreliable and may not be prudent. 1351 Should pilots be encouraged to answer phone calls while flying? 1352 Internet technologies can do much better than this. 1354 Thus complementing [F3411-19] with protocols enabling strong 1355 authentication, preserving operator privacy while enabling immediate 1356 use of information by authorized parties, is critical to achieve 1357 widespread adoption of a RID system supporting safe and secure 1358 operation of UAS. 1360 DRIP will focus on making information obtained via UAS RID 1361 immediately usable: 1363 1. by making it trustworthy (despite the severe constraints of 1364 Broadcast RID); 1366 2. by enabling verification that a UAS is registered for RID, and if 1367 so, in which registry (for classification of trusted operators on 1368 the basis of known registry vetting, even by Observers lacking 1369 Internet connectivity at observation time); 1371 3. by facilitating independent reports of UA aeronautical data 1372 (location, velocity, etc.) to confirm or refute the operator 1373 self-reports upon which UAS RID and UTM tracking are based; 1375 4. by enabling instant establishment, by authorized parties, of 1376 secure communications with the remote pilot. 1378 The foregoing considerations, beyond those addressed by baseline UAS 1379 RID standards such as [F3411-19], imply the following requirements 1380 for DRIP. 1382 4. Requirements 1384 The following requirements apply to DRIP as a set of related 1385 protocols, various subsets of which, in conjunction with other IETF 1386 and external technical standards, may suffice to comply with the 1387 regulations in any given jurisdiction or meet any given user need. 1388 It is not intended that each and every DRIP protocol alone satisfy 1389 each and every requirement. 1391 4.1. General 1393 4.1.1. Normative Requirements 1395 GEN-1 Provable Ownership: DRIP MUST enable verification that the 1396 UAS ID asserted in the Basic ID message is that of the actual 1397 current sender of the message (i.e., the message is not a 1398 replay attack or other spoof, authenticating, e.g., by 1399 verifying an asymmetric cryptographic signature using a 1400 sender provided public key from which the asserted ID can be 1401 at least partially derived), even on an Observer device 1402 lacking Internet connectivity at the time of observation. 1404 GEN-2 Provable Binding: DRIP MUST enable binding all other 1405 [F3411-19] messages from the same actual current sender to 1406 the UAS ID asserted in the Basic ID message. 1408 GEN-3 Provable Registration: DRIP MUST enable verification that the 1409 UAS ID is in a registry and identification of that registry, 1410 even on an Observer device lacking Internet connectivity at 1411 the time of observation; with UAS ID Type 3, the same sender 1412 may have multiple IDs, potentially in different registries, 1413 but each ID must clearly indicate in which registry it can be 1414 found. 1416 GEN-4 Readability: DRIP MUST enable information (regulation 1417 required elements, whether sent via UAS RID or looked up in 1418 registries) to be read and utilized by both humans and 1419 software. 1421 GEN-5 Gateway: DRIP MUST enable Broadcast RID to Network RID 1422 application layer gateways to stamp messages with precise 1423 date/time received and receiver location, then relay them to 1424 a network service (e.g., SDSP or distributed ledger). 1426 GEN-6 Contact: DRIP MUST enable dynamically establishing, with AAA, 1427 per policy, strongly mutually authenticated, end-to-end 1428 strongly encrypted communications with the UAS RID sender and 1429 entities looked up from the UAS ID, including at least the 1430 pilot (remote pilot or Pilot In Command), the USS (if any) 1431 under which the operation is being conducted, and registries 1432 in which data on the UA and pilot are held. 1434 GEN-7 QoS: DRIP MUST enable policy based specification of 1435 performance and reliability parameters. 1437 GEN-8 Mobility: DRIP MUST support physical and logical mobility of 1438 UA, GCS and Observers. DRIP SHOULD support mobility of 1439 essentially all participating nodes (UA, GCS, Observers, Net- 1440 RID SP, Net-RID DP, Private Registry, SDSP, and potentially 1441 others as RID and UTM evolve). 1443 GEN-9 Multihoming: DRIP MUST support multihoming of UA and GCS, for 1444 make-before-break smooth handoff and resiliency against path/ 1445 link failure. DRIP SHOULD support multihoming of essentially 1446 all participating nodes. 1448 GEN-10 Multicast: DRIP SHOULD support multicast for efficient and 1449 flexible publish-subscribe notifications, e.g., of UAS 1450 reporting positions in designated airspace volumes. 1452 GEN-11 Management: DRIP SHOULD support monitoring of the health and 1453 coverage of Broadcast and Network RID services. 1455 4.1.2. Rationale 1457 Requirements imposed either by regulation or [F3411-19] are not 1458 reiterated here, but drive many of the numbered requirements listed 1459 here. The [FRUR] regulatory QoS requirement currently would be 1460 satisfied by ensuring information refresh rates of at least 1 Hertz, 1461 with latencies no greater than 1 second, at least 80% of the time, 1462 but these numbers may vary between jurisdictions and over time. So 1463 instead the DRIP QoS requirement is that performance, reliability, 1464 etc. parameters be user policy specifiable, which does not imply 1465 satisfiable in all cases, but (especially together with the 1466 management requirement) implies that when specifications are not met, 1467 appropriate parties are notified. 1469 The "provable ownership" requirement addresses the possibility that 1470 the actual sender is not the claimed sender (i.e., is a spoofer). 1471 The "provable binding" requirement addresses the MAC address 1472 correlation problem of [F3411-19] noted above. The "provable 1473 registration" requirement may impose burdens not only on the UAS 1474 sender and the Observer's receiver, but also on the registry; yet it 1475 cannot depend upon the Observer being able to contact the registry at 1476 the time of observing the UA. The "readability" requirement pertains 1477 to the structure and format of information at endpoints rather than 1478 its encoding in transit, so may involve machine assisted format 1479 conversions, e.g., from binary encodings, and/or decryption (see 1480 Section 4.3). 1482 The "gateway" requirement is in pursuit of three objectives: (1) mark 1483 up a RID message with where and when it was actually received, which 1484 may agree or disagree with the self-report in the set of messages; 1485 (2) defend against replay attacks; and (3) support optional SDSP 1486 services such as multilateration, to complement UAS position self- 1487 reports with independent measurements. This is the only instance in 1488 which DRIP transports [F3411-19] messages; most of DRIP pertains to 1489 the authentication of such messages and identifiers carried in them. 1491 The "QoS" requirement is only that performance and reliability 1492 parameters can be _specified_ by policy, not that any such 1493 specifications must be guaranteed to be met; any failure to meet such 1494 would be reported under the "management" requirement. Examples of 1495 such parameters are the maximum time interval at which messages 1496 carrying required data elements may be transmitted, the maximum 1497 tolerable rate of loss of such messages, and the maximum tolerable 1498 latency between a dynamic data element (e.g., GNSS position of UA) 1499 being provided to the DRIP sender and that element being delivered by 1500 the DRIP receiver to an application. 1502 The "mobility" requirement refers to rapid geographic mobility of 1503 nodes, changes of their points of attachment to networks, and changes 1504 to their IP addresses; it is not limited to micro-mobility within a 1505 small geographic area or single Internet access provider. 1507 4.2. Identifier 1509 4.2.1. Normative Requirements 1511 ID-1 Length: The DRIP entity identifier MUST NOT be longer than 20 1512 bytes, to fit in the UAS ID field of the Basic ID message of 1513 [F3411-19]. 1515 ID-2 Registry ID: The DRIP identifier MUST be sufficient to identify 1516 a registry in which the entity identified therewith is listed. 1518 ID-3 Entity ID: The DRIP identifier MUST be sufficient to enable 1519 lookups of other data associated with the entity identified 1520 therewith in that registry. 1522 ID-4 Uniqueness: The DRIP identifier MUST be unique within the 1523 applicable global identifier space from when it is first 1524 registered therein until it is explicitly de-registered 1525 therefrom (due to, e.g., expiration after a specified lifetime, 1526 revocation by the registry, or surrender by the operator). 1528 ID-5 Non-spoofability: The DRIP identifier MUST NOT be spoofable 1529 within the context of a minimal Remote ID broadcast message set 1530 (to be specified within DRIP to be sufficient collectively to 1531 prove sender ownership of the claimed identifier). 1533 ID-6 Unlinkability: The DRIP identifier MUST NOT facilitate 1534 adversarial correlation over multiple operations. If this is 1535 accomplished by limiting each identifier to a single use or 1536 brief period of usage, the DRIP identifier MUST support well- 1537 defined, scalable, timely registration methods. 1539 4.2.2. Rationale 1541 The DRIP identifier can refer to various entities. In the primary 1542 initial use case, the entity to be identified is the UA. Entities to 1543 be identified in other likely use cases include but are not limited 1544 to the operator, USS, and Observer. In all cases, the entity 1545 identified must own (have the exclusive capability to use, such that 1546 receivers can verify its ownership of) the identifier. 1548 The DRIP identifier can be used at various layers. In Broadcast RID, 1549 it would be used by the application running directly over the data 1550 link. In Network RID, it would be used by the application running 1551 over HTTPS (and possibly other protocols). In RID initiated V2X 1552 applications such as DAA and C2, it could be used between the network 1553 and transport layers, e.g., with the Host Identity Protocol (HIP, 1554 [RFC4423], [RFC7401], etc.), or between the transport and application 1555 layers, e.g., with Datagram Transport Layer Security (DTLS, 1556 [RFC6347]). 1558 Registry ID (which registry the entity is in) and Entity ID (which 1559 entity it is, within that registry) are requirements on a single DRIP 1560 entity identifier, not separate (types of) ID. In the most common 1561 use case, the entity will be the UA, and the DRIP identifier will be 1562 the UAS ID; however, other entities may also benefit from having DRIP 1563 identifiers, so the entity type is not prescribed here. 1565 Whether a UAS ID is generated by the operator, GCS, UA, USS, 1566 registry, or some collaboration thereamong, is unspecified; however, 1567 there must be agreement on the UAS ID among these entities. 1568 Management of DRIP identifiers is the primary function of their 1569 registration hierarchies, from the root (presumably IANA), through 1570 sector-specific and regional authorities (presumably ICAO and CAAs), 1571 to the identified entities themselves. 1573 While "uniqueness" might be considered an implicit requirement for 1574 any identifier, here the point of the explicit requirement is not 1575 just that it should be unique, but also where and when it should be 1576 unique: global scope within a specified space, from registration to 1577 deregistration. 1579 While "non-spoofability" imposes requirements for and on a DRIP 1580 authentication protocol, it also imposes requirements on the 1581 properties of the identifier itself. An example of how the nature of 1582 the identifier can support non-spoofability is embedding a hash of 1583 both the registry ID and a public key of the entity in the entity 1584 identifier, thus making it self-authenticating any time the entity's 1585 corresponding private key is used to sign a message. 1587 While "unlinkability" is a privacy desideratum (see next section), it 1588 imposes requirements on the DRIP identifier itself, as distinct from 1589 other currently permitted choices for the UAS ID (including primarily 1590 the static serial number of the UA or RID module). 1592 4.3. Privacy 1594 4.3.1. Normative Requirements 1595 PRIV-1 Confidential Handling: DRIP MUST enable confidential handling 1596 of private information (i.e., any and all information 1597 designated by neither cognizant authority nor the information 1598 owner as public, e.g., personal data). 1600 PRIV-2 Encrypted Transport: DRIP MUST enable selective strong 1601 encryption of private data in motion in such a manner that 1602 only authorized actors can recover it. If transport is via 1603 IP, then encryption MUST be end-to-end, at or above the IP 1604 layer. DRIP MUST NOT encrypt safety critical data to be 1605 transmitted over Broadcast RID in any situation where it is 1606 unlikely that local Observers authorized to access the 1607 plaintext will be able to decrypt it or obtain it from a 1608 service able to decrypt it. DRIP MUST NOT encrypt data when/ 1609 where doing so would conflict with applicable regulations or 1610 CAA policies/procedures, i.e., DRIP MUST support configurable 1611 disabling of encryption. 1613 PRIV-3 Encrypted Storage: DRIP SHOULD facilitate selective strong 1614 encryption of private data at rest in such a manner that only 1615 authorized actors can recover it. 1617 PRIV-4 Public/Private Designation: DRIP SHOULD facilitate 1618 designation, by cognizant authorities and information owners, 1619 of which information is public and which is private. By 1620 default, all information required to be transmitted via 1621 Broadcast RID, even when actually sent via Network RID or 1622 stored in registries, is assumed to be public; all other 1623 information held in registries for lookup using the UAS ID is 1624 assumed to be private. 1626 PRIV-5 Pseudonymous Rendezvous: DRIP MAY enable mutual discovery of 1627 and communications among participating UAS operators whose UA 1628 are in 4-D proximity, using the UAS ID without revealing 1629 pilot/operator identity or physical location. 1631 4.3.2. Rationale 1633 Most data to be sent via Broadcast RID or Network RID is public, thus 1634 the "encrypted transport" requirement for private data is selective, 1635 e.g., for the entire payload of the Operator ID Message, but only the 1636 pilot/GCS location fields of the System Message. 1638 In some jurisdictions, the configurable enabling and disabling of 1639 encryption may need to be outside the control of the operator. 1640 [FRUR] mandates manufacturers design RID equipment with some degree 1641 of tamper resistance; the preamble and other FAA commentary suggest 1642 this is to reduce the likelihood that an operator, intentionally or 1643 unintentionally, might alter the values of the required data elements 1644 or disable their transmission in the required manner (e.g., as 1645 cleartext). 1647 How information is stored on end systems is out of scope for DRIP. 1648 Encouraging privacy best practices, including end system storage 1649 encryption, by facilitating it with protocol design reflecting such 1650 considerations, is in scope. Similar logic applies to methods for 1651 designating information as public or private. 1653 The privacy requirements above are for DRIP, neither for [F3411-19] 1654 (which requires obfuscation of location to any Network RID subscriber 1655 engaging in wide area surveillance, limits data retention periods, 1656 etc., in the interests of privacy), nor for UAS RID in any specific 1657 jurisdiction (which may have its own regulatory requirements). The 1658 requirements above are also in a sense parameterized: who are the 1659 "authorized actors", how are they designated, how are they 1660 authenticated, etc.? 1662 4.4. Registries 1664 4.4.1. Normative Requirements 1666 REG-1 Public Lookup: DRIP MUST enable lookup, from the UAS ID, of 1667 information designated by cognizant authority as public, and 1668 MUST NOT restrict access to this information based on identity 1669 or role of the party submitting the query. 1671 REG-2 Private Lookup: DRIP MUST enable lookup of private information 1672 (i.e., any and all information in a registry, associated with 1673 the UAS ID, that is designated by neither cognizant authority 1674 nor the information owner as public), and MUST, according to 1675 applicable policy, enforce AAA, including restriction of 1676 access to this information based on identity or role of the 1677 party submitting the query. 1679 REG-3 Provisioning: DRIP MUST enable provisioning registries with 1680 static information on the UAS and its operator, dynamic 1681 information on its current operation within the U-space/UTM 1682 (including means by which the USS under which the UAS is 1683 operating may be contacted for further, typically even more 1684 dynamic, information), and Internet direct contact information 1685 for services related to the foregoing. 1687 REG-4 AAA Policy: DRIP AAA MUST be specifiable by policies; the 1688 definitive copies of those policies must be accessible in 1689 registries; administration of those policies and all DRIP 1690 registries must be protected by AAA. 1692 4.4.2. Rationale 1694 Registries are fundamental to RID. Only very limited information can 1695 be Broadcast, but extended information is sometimes needed. The most 1696 essential element of information sent is the UAS ID itself, the 1697 unique key for lookup of extended information in registries. Beyond 1698 designating the UAS ID as that unique key, the registry information 1699 model is not specified herein, in part because regulatory 1700 requirements for different registries (UAS operators and their UA, 1701 each narrowly for UAS RID and broadly for U-space/UTM) and business 1702 models for meeting those requirements are in flux. While it is 1703 expected that registry functions will be integrated with USS, who 1704 will provide them is not yet determined in most, and is expected to 1705 vary between, jurisdictions. However this evolves, the essential 1706 registry functions, starting with management of identifiers, are 1707 expected to remain the same, so are specified herein. 1709 While most data to be sent via Broadcast or Network RID is public, 1710 much of the extended information in registries will be private. Thus 1711 AAA for registries is essential, not just to ensure that access is 1712 granted only to strongly authenticated, duly authorized parties, but 1713 also to support subsequent attribution of any leaks, audit of who 1714 accessed information when and for what purpose, etc. As specific AAA 1715 requirements will vary by jurisdictional regulation, provider 1716 philosophy, customer demand, etc., they are left to specification in 1717 policies, which should be human readable to facilitate analysis and 1718 discussion, and machine readable to enable automated enforcement, 1719 using a language amenable to both, e.g., XACML. 1721 5. IANA Considerations 1723 This document does not make any IANA request. 1725 6. Security Considerations 1727 DRIP is all about safety and security, so content pertaining to such 1728 is not limited to this section. This document does not define any 1729 protocols, so security considerations of such are speculative. 1730 Potential vulnerabilities of DRIP solutions to these requirements 1731 include but are not limited to: 1733 * Sybil attacks 1735 * confusion created by many spoofed unsigned messages 1737 * processing overload induced by attempting to verify many spoofed 1738 signed messages (where verification will fail but still consume 1739 cycles) 1741 * malicious or malfunctioning registries 1743 * interception by on-path attacker of (i.e., Man In The Middle 1744 attacks on) registration messages 1746 * UA impersonation through private key extraction, improper key 1747 sharing, or carriage of a small (presumably harmless) UA, i.e., as 1748 a "false flag", by a larger (malicious) UA 1750 It may be inferred from the general requirements (Section 4.1) for 1751 provable ownership, provable binding, and provable registration, 1752 together with the identifier requirements (Section 4.2), that DRIP 1753 must provide: 1755 * message integrity 1757 * non-repudiation 1759 * defense against replay attacks 1761 * defense against spoofing 1763 One approach to so doing involves verifiably binding the DRIP 1764 identifier to a public key. Providing these security features, 1765 whether via this approach or another, is likely to be especially 1766 challenging for Observers without Internet connectivity at the time 1767 of observation. For example, checking the signature of a registry on 1768 a public key certificate received via Broadcast RID in a remote area 1769 presumably would require that the registry's public key had been 1770 previously installed on the Observer's device, yet there may be many 1771 registries and the Observer's device may be storage constrained, and 1772 new registries may come on-line subsequent to installation of DRIP 1773 software on the Observer's device. Thus there may be caveats on the 1774 extent to which requirements can be satisfied in such cases, yet 1775 strenuous effort should be made to satisfy them, as such cases, e.g., 1776 firefighting in a national forest, are important. 1778 7. Privacy and Transparency Considerations 1780 Privacy and transparency are important for legal reasons including 1781 regulatory consistency. [EU2018] states "harmonised and 1782 interoperable national registration systems... should comply with the 1783 applicable Union and national law on privacy and processing of 1784 personal data, and the information stored in those registration 1785 systems should be easily accessible." 1786 Privacy and transparency (where essential to security or safety) are 1787 also ethical and moral imperatives. Even in cases where old 1788 practices (e.g., automobile registration plates) could be imitated, 1789 when new applications involving PII (such as UAS RID) are addressed 1790 and newer technologies could enable improving privacy, such 1791 opportunities should not be squandered. Thus it is recommended that 1792 all DRIP work give due regard to [RFC6973] and more broadly 1793 [RFC8280]. 1795 However, privacy and transparency are often conflicting goals, 1796 demanding careful attention to their balance. 1798 DRIP information falls into two classes: that which, to achieve the 1799 purpose, must be published openly as cleartext, for the benefit of 1800 any Observer (e.g., the basic UAS ID itself); and that which must be 1801 protected (e.g., PII of pilots) but made available to properly 1802 authorized parties (e.g., public safety personnel who urgently need 1803 to contact pilots in emergencies). 1805 How properly authorized parties are authorized, authenticated, etc. 1806 are questions that extend beyond the scope of DRIP, but DRIP may be 1807 able to provide support for such processes. Classification of 1808 information as public or private must be made explicit and reflected 1809 with markings, design, etc. Classifying the information will be 1810 addressed primarily in external standards; herein it will be regarded 1811 as a matter for CAA, registry, and operator policies, for which 1812 enforcement mechanisms will be defined within the scope of DRIP WG 1813 and offered. Details of the protection mechanisms will be provided 1814 in other DRIP documents. Mitigation of adversarial correlation will 1815 also be addressed. 1817 8. References 1819 8.1. Normative References 1821 [F3411-19] ASTM International, "Standard Specification for Remote ID 1822 and Tracking", February 2020, 1823 . 1825 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1826 Requirement Levels", BCP 14, RFC 2119, 1827 DOI 10.17487/RFC2119, March 1997, 1828 . 1830 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1831 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1832 May 2017, . 1834 8.2. Informative References 1836 [Amended] European Union Aviation Safety Agency (EASA), "Commission 1837 Delegated Regulation (EU) 2020/1058 of 27 April 2020 1838 amending Delegated Regulation (EU) 2019/945", April 2020, 1839 . 1842 [ASDRI] ASD-STAN, "Introduction to the European UAS Digital Remote 1843 ID Technical Standard", January 2021, . 1847 [CPDLC] Gurtov, A., Polishchuk, T., and M. Wernberg, "Controller- 1848 Pilot Data Link Communication Security", MDPI 1849 Sensors 18(5), 1636, 2018, 1850 . 1852 [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers", 1853 September 2019, . 1856 [Delegated] 1857 European Union Aviation Safety Agency (EASA), "Commission 1858 Delegated Regulation (EU) 2019/945 of 12 March 2019 on 1859 unmanned aircraft systems and on third-country operators 1860 of unmanned aircraft systems", March 2019, 1861 . 1863 [drip-architecture] 1864 Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S., 1865 and A. Gurtov, "Drone Remote Identification Protocol 1866 (DRIP) Architecture", Work in Progress, Internet-Draft, 1867 draft-ietf-drip-arch-11, 23 February 2021, 1868 . 1870 [ENISACSIRT] 1871 European Union Agency for Cybersecurity (ENISA), 1872 "Actionable information for Security Incident Response", 1873 November 2014, . 1877 [EU2018] European Parliament and Council, "2015/0277 (COD) PE-CONS 1878 2/18", February 2018, 1879 . 1882 [FAACONOPS] 1883 FAA Office of NextGen, "UTM Concept of Operations v2.0", 1884 March 2020, . 1887 [FR24] Flightradar24 AB, "Flightradar24 Live Air Traffic", May 1888 2021, . 1890 [FRUR] Federal Aviation Administration, "Remote Identification of 1891 Unmanned Aircraft", January 2021, 1892 . 1896 [GDPR] European Parliament and Council, "General Data Protection 1897 Regulation", April 2016, 1898 . 1900 [I-D.maeurer-raw-ldacs] 1901 Maeurer, N., Graeupl, T., and C. Schmitt, "L-band Digital 1902 Aeronautical Communications System (LDACS)", Work in 1903 Progress, Internet-Draft, draft-maeurer-raw-ldacs-06, 2 1904 October 2020, 1905 . 1907 [ICAOATM] International Civil Aviation Organization, "Doc 4444: 1908 Procedures for Air Navigation Services: Air Traffic 1909 Management", November 2016, . 1913 [ICAODEFS] International Civil Aviation Organization, "Defined terms 1914 from the Annexes to the Chicago Convention and ICAO 1915 guidance material", July 2017, 1916 . 1919 [ICAOUAS] International Civil Aviation Organization, "Circular 328: 1920 Unmanned Aircraft Systems", February 2011, 1921 . 1924 [ICAOUTM] International Civil Aviation Organization, "Unmanned 1925 Aircraft Systems Traffic Management (UTM) - A Common 1926 Framework with Core Principles for Global Harmonization, 1927 Edition 3", October 2020, 1928 . 1931 [Implementing] 1932 European Union Aviation Safety Agency (EASA), "Commission 1933 Implementing Regulation (EU) 2019/947 of 24 May 2019 on 1934 the rules and procedures for the operation of unmanned 1935 aircraft", May 2019, 1936 . 1938 [InitialView] 1939 SESAR Joint Undertaking, "Initial view on Principles for 1940 the U-space architecture", July 2019, 1941 . 1945 [NPRM] United States Federal Aviation Administration (FAA), 1946 "Notice of Proposed Rule Making on Remote Identification 1947 of Unmanned Aircraft Systems", December 2019, 1948 . 1952 [OpenDroneID] 1953 Intel Corp., "Open Drone ID", March 2019, 1954 . 1956 [OpenSky] OpenSky Network non-profit association, "The OpenSky 1957 Network", May 2021, 1958 . 1960 [Opinion1] European Union Aviation Safety Agency (EASA), "Opinion No 1961 01/2020: High-level regulatory framework for the U-space", 1962 March 2020, . 1965 [Part107] United States Federal Aviation Administration, "Code of 1966 Federal Regulations Part 107", June 2016, 1967 . 1969 [Recommendations] 1970 FAA UAS Identification and Tracking Aviation Rulemaking 1971 Committee, "UAS ID and Tracking ARC Recommendations Final 1972 Report", September 2017, . 1976 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 1977 Unique IDentifier (UUID) URN Namespace", RFC 4122, 1978 DOI 10.17487/RFC4122, July 2005, 1979 . 1981 [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol 1982 (HIP) Architecture", RFC 4423, DOI 10.17487/RFC4423, May 1983 2006, . 1985 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 1986 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 1987 . 1989 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1990 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1991 January 2012, . 1993 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1994 Morris, J., Hansen, M., and R. Smith, "Privacy 1995 Considerations for Internet Protocols", RFC 6973, 1996 DOI 10.17487/RFC6973, July 2013, 1997 . 1999 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 2000 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 2001 RFC 7401, DOI 10.17487/RFC7401, April 2015, 2002 . 2004 [RFC8280] ten Oever, N. and C. Cath, "Research into Human Rights 2005 Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280, 2006 October 2017, . 2008 [Roadmap] American National Standards Institute (ANSI) Unmanned 2009 Aircraft Systems Standardization Collaborative (UASSC), 2010 "Standardization Roadmap for Unmanned Aircraft Systems 2011 draft v2.0", April 2020, . 2015 [Stranger] Heinlein, R.A., "Stranger in a Strange Land", June 1961. 2017 [WG105] EUROCAE, "WG-105 draft ED-282 Minimum Operational 2018 Performance Standards (MOPS) for Unmanned Aircraft System 2019 (UAS) Electronic Identification", June 2020. 2021 [WiFiNAN] Wi-Fi Alliance, "Wi-Fi Aware™ Specification Version 3.2", 2022 October 2020, . 2025 Appendix A. Discussion and Limitations 2027 This document is largely based on the process of one SDO, ASTM. 2028 Therefore, it is tailored to specific needs and data formats of this 2029 standard. Other organizations, for example in EU, do not necessary 2030 follow the same architecture. 2032 The need for drone ID and operator privacy is an open discussion 2033 topic. For instance, in the ground vehicular domain each car carries 2034 a publicly visible plate number. In some countries, for nominal cost 2035 or even for free, anyone can resolve the identity and contact 2036 information of the owner. Civil commercial aviation and maritime 2037 industries also have a tradition of broadcasting plane or ship ID, 2038 coordinates, and even flight plans in plain text. Community networks 2039 such as OpenSky [OpenSky] and Flightradar24 [FR24] use this open 2040 information through ADS-B to deploy public services of flight 2041 tracking. Many researchers also use these data to perform 2042 optimization of routes and airport operations. Such ID information 2043 should be integrity protected, but not necessarily confidential. 2045 In civil aviation, aircraft identity is broadcast by a device known 2046 as transponder. It transmits a four octal digit squawk code, which 2047 is assigned by a traffic controller to an airplane after approving a 2048 flight plan. There are several reserved codes such as 7600 which 2049 indicate radio communication failure. The codes are unique in each 2050 traffic area and can be re-assigned when entering another control 2051 area. The code is transmitted in plain text by the transponder and 2052 also used for collision avoidance by a system known as Traffic alert 2053 and Collision Avoidance System (TCAS). The system could be used for 2054 UAS as well initially, but the code space is quite limited and likely 2055 to be exhausted soon. The number of UAS far exceeds the number of 2056 civil airplanes in operation. 2058 The ADS-B system is utilized in civil aviation for each "ADS-B Out" 2059 equipped airplane to broadcast its ID, coordinates, and altitude for 2060 other airplanes and ground control stations. If this system is 2061 adopted for drone IDs, it has additional benefit with backward 2062 compatibility with civil aviation infrastructure; then, pilots and 2063 dispatchers will be able to see UA on their control screens and take 2064 those into account. If not, a gateway translation system between the 2065 proposed drone ID and civil aviation system should be implemented. 2066 Again, system saturation due to large numbers of UAS is a concern. 2068 The Mode S transponders used in all TCAS and most ADS-B Out 2069 installations are assigned an ICAO 24 bit "address" (arguably really 2070 an identifier rather than a locator) that is associated with the 2071 aircraft as part of its registration. In the US alone, well over 2072 2^20 UAS are already flying; thus, a 24 bit space likely would be 2073 rapidly exhausted if used for UAS (other than large UAS flying in 2074 controlled airspace, especially internationally, under rules other 2075 than those governing small UAS at low altitudes). 2077 Wi-Fi and Bluetooth are two wireless technologies currently 2078 recommended by ASTM specifications due to their widespread use and 2079 broadcast nature. However, those have limited range (max 100s of 2080 meters) and may not reliably deliver UAS ID at high altitude or 2081 distance. Therefore, a study should be made of alternative 2082 technologies from the telecom domain (WiMAX / IEEE 802.16, 5G) or 2083 sensor networks (Sigfox, LoRa). Such transmission technologies can 2084 impose additional restrictions on packet sizes and frequency of 2085 transmissions, but could provide better energy efficiency and range. 2087 In civil aviation, Controller-Pilot Data Link Communications (CPDLC) 2088 is used to transmit command and control between the pilots and ATC. 2089 It could be considered for UAS as well due to long range and proven 2090 use despite its lack of security [CPDLC]. 2092 L-band Digital Aeronautical Communications System (LDACS) is being 2093 standardized by ICAO and IETF for use in future civil aviation 2094 [I-D.maeurer-raw-ldacs]. It provides secure communication, 2095 positioning, and control for aircraft using a dedicated radio band. 2096 It should be analyzed as a potential provider for UAS RID as well. 2097 This will bring the benefit of a global integrated system creating a 2098 global airspace use awareness. 2100 Acknowledgments 2102 The work of the FAA's UAS Identification and Tracking (UAS ID) 2103 Aviation Rulemaking Committee (ARC) is the foundation of later ASTM 2104 [F3411-19] and IETF DRIP efforts. The work of Gabriel Cox, Intel 2105 Corp., and their Open Drone ID collaborators opened UAS RID to a 2106 wider community. The work of ASTM F38.02 in balancing the interests 2107 of diverse stakeholders is essential to the necessary rapid and 2108 widespread deployment of UAS RID. IETF volunteers who have 2109 extensively reviewed or otherwise contributed to this document 2110 include Amelia Andersdotter, Carsten Bormann, Mohamed Boucadair, 2111 Toerless Eckert, Susan Hares, Mika Jarvenpaa, Daniel Migault, 2112 Alexandre Petrescu, Saulo Da Silva and Shuai Zhao. Thanks to Linda 2113 Dunbar for the Secdir review and Nagendra Nainar for the Opsdir 2114 review. 2116 Authors' Addresses 2118 Stuart W. Card (editor) 2119 AX Enterprize 2120 4947 Commercial Drive 2121 Yorkville, NY 13495 2122 United States of America 2124 Email: stu.card@axenterprize.com 2126 Adam Wiethuechter 2127 AX Enterprize 2128 4947 Commercial Drive 2129 Yorkville, NY 13495 2130 United States of America 2132 Email: adam.wiethuechter@axenterprize.com 2134 Robert Moskowitz 2135 HTT Consulting 2136 Oak Park, MI 48237 2137 United States of America 2139 Email: rgm@labs.htt-consult.com 2141 Andrei Gurtov 2142 Linköping University 2143 IDA 2144 SE-58183 Linköping 2145 Sweden 2147 Email: gurtov@acm.org