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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 176 has weird spacing: '... Public o---...' -- The document date (7 July 2021) is 1017 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: 8 January 2022 R. Moskowitz 6 HTT Consulting 7 A. Gurtov 8 Linköping University 9 7 July 2021 11 Drone Remote Identification Protocol (DRIP) Requirements 12 draft-ietf-drip-reqs-17 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). DRIP 21 will facilitate use of existing Internet resources to support RID and 22 to enable enhanced related services, and will enable online and 23 offline verification that RID information is trustworthy. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on 8 January 2022. 42 Copyright Notice 44 Copyright (c) 2021 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 49 license-info) in effect on the date of publication of this document. 50 Please review these documents carefully, as they describe your rights 51 and restrictions with respect to this document. Code Components 52 extracted from this document must include Simplified BSD License text 53 as described in Section 4.e of the Trust Legal Provisions and are 54 provided without warranty as described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Motivation and External Influences . . . . . . . . . . . 3 60 1.2. Concerns and Constraints . . . . . . . . . . . . . . . . 8 61 1.3. DRIP Scope . . . . . . . . . . . . . . . . . . . . . . . 10 62 1.4. Document Scope . . . . . . . . . . . . . . . . . . . . . 11 63 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 11 64 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 11 65 2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 11 66 3. UAS RID Problem Space . . . . . . . . . . . . . . . . . . . . 20 67 3.1. Network RID . . . . . . . . . . . . . . . . . . . . . . . 22 68 3.2. Broadcast RID . . . . . . . . . . . . . . . . . . . . . . 25 69 3.3. USS in UTM and RID . . . . . . . . . . . . . . . . . . . 28 70 3.4. DRIP Focus . . . . . . . . . . . . . . . . . . . . . . . 29 71 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 30 72 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 30 73 4.1.1. Normative Requirements . . . . . . . . . . . . . . . 30 74 4.1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 32 75 4.2. Identifier . . . . . . . . . . . . . . . . . . . . . . . 33 76 4.2.1. Normative Requirements . . . . . . . . . . . . . . . 33 77 4.2.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 34 78 4.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 35 79 4.3.1. Normative Requirements . . . . . . . . . . . . . . . 35 80 4.3.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 36 81 4.4. Registries . . . . . . . . . . . . . . . . . . . . . . . 36 82 4.4.1. Normative Requirements . . . . . . . . . . . . . . . 37 83 4.4.2. Rationale . . . . . . . . . . . . . . . . . . . . . . 37 84 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 85 6. Security Considerations . . . . . . . . . . . . . . . . . . . 38 86 7. Privacy and Transparency Considerations . . . . . . . . . . . 39 87 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 88 8.1. Normative References . . . . . . . . . . . . . . . . . . 40 89 8.2. Informative References . . . . . . . . . . . . . . . . . 40 90 Appendix A. Discussion and Limitations . . . . . . . . . . . . . 45 91 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 46 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 94 1. Introduction 96 For any unfamiliar or _a priori_ ambiguous terminology herein, see 97 Section 2. 99 1.1. Motivation and External Influences 101 Many considerations (especially safety and security) necessitate 102 Unmanned Aircraft Systems (UAS) Remote Identification and tracking 103 (RID). 105 Unmanned Aircraft (UA) may be fixed wing, rotary wing (e.g., 106 helicopter), hybrid, balloon, rocket, etc. Small fixed wing UA 107 typically have Short Take-Off and Landing (STOL) capability; rotary 108 wing and hybrid UA typically have Vertical Take-Off and Landing 109 (VTOL) capability. UA may be single- or multi-engine. The most 110 common today are multicopters: rotary wing, multi engine. The 111 explosion in UAS was enabled by hobbyist development, for 112 multicopters, of advanced flight stability algorithms, enabling even 113 inexperienced pilots to take off, fly to a location of interest, 114 hover, and return to the take-off location or land at a distance. 115 UAS can be remotely piloted by a human (e.g., with a joystick) or 116 programmed to proceed from Global Navigation Satellite System (GNSS) 117 waypoint to waypoint in a weak form of autonomy; stronger autonomy is 118 coming. 120 Small UA are "low observable" as they: 122 * typically have small radar cross sections; 124 * make noise quite noticeable at short ranges but difficult to 125 detect at distances they can quickly close (500 meters in under 13 126 seconds by the fastest consumer mass market drones available in 127 early 2021); 129 * typically fly at low altitudes (e.g., for those to which RID 130 applies in the US, under 400 feet Above Ground Level (AGL) as per 131 [Part107]); 133 * are highly maneuverable so can fly under trees and between 134 buildings. 136 UA can carry payloads including sensors, cyber and kinetic weapons, 137 or can be used themselves as weapons by flying them into targets. 138 They can be flown by clueless, careless, or criminal operators. Thus 139 the most basic function of UAS RID is "Identification Friend or Foe" 140 (IFF) to mitigate the significant threat they present. 142 Diverse other applications can be enabled or facilitated by RID. 143 Internet protocols typically start out with at least one entity 144 already knowing an identifier or locator of another; but an entity 145 (e.g., UAS or Observer device) encountering an _a priori_ unknown UA 146 in physical space has no identifier or logical space locator for that 147 UA, unless and until one is provided somehow. RID provides an 148 identifier, which, if well chosen, can facilitate use of a variety of 149 Internet family protocols and services to support arbitrary 150 applications, beyond the basic security functions of RID. For most 151 of these, some type of identifier is essential, e.g., Network Access 152 Identifier (NAI), Digital Object Identifier (DOI), Uniform Resource 153 Identifier (URI), domain name, or public key. DRIP motivations 154 include both the basic security and the broader application support 155 functions of RID. The general scenario is illustrated in Figure 1. 157 +-----+ +-----+ 158 | UA1 | | UA2 | 159 +-----+ +-----+ 161 +----------+ +----------+ 162 | General | | Public | 163 | Public | | Safety | 164 | Observer o------\ /------o Observer | 165 +----------+ | | +----------+ 166 | | 167 ************* 168 +----------+ * * +----------+ 169 | UA1 | * * | UA2 | 170 | Pilot/ o------* Internet *------o Pilot/ | 171 | Operator | * * | Operator | 172 +----------+ * * +----------+ 173 ************* 174 | | | 175 +----------+ | | | +----------+ 176 | Public o---/ | \---o Private | 177 | Registry | | | Registry | 178 +----------+ | +----------+ 179 +--o--+ 180 | DNS | 181 +-----+ 183 Figure 1: "General UAS RID Usage Scenario" 185 Figure 1 illustrates a typical case where there may be: multiple 186 Observers, some of them members of the general public, others 187 government officers with public safety/security responsibilities; 188 multiple UA in flight within observation range, each with its own 189 pilot/operator; at least one registry each for lookup of public and 190 (by authorized parties only) private information regarding the UAS 191 and their pilots/operators; and in the DRIP vision, DNS resolving 192 various identifiers and locators of the entities involved. 194 Note the absence of any links to/from the UA in the figure; this is 195 because UAS RID and other connectivity involving the UA varies. Some 196 connectivity paths do or do not exist depending upon the scenario. 197 Command and Control (C2) from the GCS to the UA via the Internet 198 (e.g., using LTE cellular) is expected to become much more common as 199 Beyond Visual Line Of Sight (BVLOS) operations increase; in such a 200 case, there is typically not also a direct wireless link between the 201 GCS and UA. Conversely, if C2 is running over a direct wireless 202 link, then typically the GCS has but the UA lacks Internet 203 connectivity. Further, paths that nominally exist, such as between 204 an Observer device and the Internet, may be severely intermittent. 205 These connectivity constraints are likely to have an impact, e.g., on 206 how reliably DRIP requirements can be satisfied. 208 An Observer of UA may need to classify them, as illustrated 209 notionally in Figure 2, for basic airspace Situational Awareness 210 (SA). An Observer who classifies a UAS: as Taskable, can ask it to 211 do something useful; as Low Concern, can reasonably assume it is not 212 malicious and would cooperate with requests to modify its flight 213 plans for safety concerns that arise; as High Concern or 214 Unidentified, can focus surveillance on it. 216 xxxxxxx 217 x x No +--------------+ 218 x ID? x+---->| Unidentified | 219 x x +--------------+ 220 xxxxxxx 221 + 222 | Yes 223 v 224 xxxxxxx 225 x x 226 .---------+x Type? x+----------. 227 | x x | 228 | xxxxxxx | 229 | + | 230 v v v 231 +--------------+ +--------------+ +--------------+ 232 | Taskable | | Low Concern | | High Concern | 233 +--------------+ +--------------+ +--------------+ 235 Figure 2: "Notional UAS Classification" 237 ASTM International, Technical Committee F38 (UAS), Subcommittee 238 F38.02 (Aircraft Operations), Work Item WK65041, developed the widely 239 cited Standard Specification for Remote ID and Tracking [F3411-19]: 240 the published standard is available for purchase from ASTM and as an 241 ASTM membership premium; early drafts are freely available as 242 [OpenDroneID] specifications. [F3411-19] is frequently referenced in 243 DRIP, where building upon its link layers and both enhancing support 244 for and expanding the scope of its applications are central foci. 246 In many applications, including UAS RID, identification and 247 identifiers are not ends in themselves; they exist to enable lookups 248 and provision of other services. 250 Using UAS RID to facilitate vehicular (V2X) communications and 251 applications such as Detect And Avoid (DAA), which would impose 252 tighter latency bounds than RID itself, is an obvious possibility, 253 explicitly contemplated in the United States (US) Federal Aviation 254 Administration (FAA) Remote Identification of Unmanned Aircraft rule 255 [FRUR]. However, usage of RID systems and information beyond mere 256 identification (primarily to hold operators accountable after the 257 fact), including DAA, have been declared out of scope in ASTM F38.02 258 WK65041, based on a distinction between RID as a security standard vs 259 DAA as a safety application. Aviation community Standards 260 Development Organizations (SDOs) generally set a higher bar for 261 safety than for security, especially with respect to reliability. 262 Each SDO has its own cultural set of connotations of safety vs 263 security; the denotative definitions of the International Civil 264 Aviation Organization (ICAO) are cited in Section 2. 266 [Opinion1] and [WG105] cite the Direct Remote Identification (DRI) 267 previously required and specified, explicitly stating that whereas 268 DRI is primarily for security purposes, the "Network Identification 269 Service" [Opinion1] (in the context of U-space [InitialView]) or 270 "Electronic Identification" [WG105] is primarily for safety purposes 271 (e.g., Air Traffic Management, especially hazards deconfliction) and 272 also is allowed to be used for other purposes such as support of 273 efficient operations. These emerging standards allow the security 274 and safety oriented systems to be separate or merged. In addition to 275 mandating both Broadcast and Network one-way to Observers, they will 276 use V2V to other UAS (also likely to and/or from some manned 277 aircraft). These reflect the broad scope of the European Union (EU) 278 U-space concept, as being developed in the Single European Sky ATM 279 Research (SESAR) Joint Undertaking, the U-space architectural 280 principles of which are outlined in [InitialView]. 282 ASD-STAN is an Associated Body to CEN (European Committee for 283 Standardization) for Aerospace Standards. It is publishing an EU 284 standard "Aerospace series - Unmanned Aircraft Systems - Part 002: 286 Direct Remote Identification; English version prEN 4709-002:2020" for 287 which a current (early 2021) informal overview is freely available in 288 [ASDRI]. It will provide compliance to cover the identical DRI 289 requirements applicable to drones of classes C1 - [Delegated] Part 2, 290 C2 - [Delegated] Part 3, C3 - [Delegated] Part 4, C5 - [Amended] Part 291 16, and C6 - [Amended] Part 17. 293 The standard contemplated in [ASDRI] will provide UA capability to be 294 identified in real time during the whole duration of the flight, 295 without specific connectivity or ground infrastructure link, 296 utilizing existing mobile devices within broadcast range. It will 297 use Bluetooth 4, Bluetooth 5, Wi-Fi Neighbor Awareness Networking 298 (NAN, also known as Wi-Fi Aware, [WiFiNAN]) and/or IEEE 802.11 Beacon 299 modes. The EU standard emphasis was compatibility with [F3411-19], 300 although there are differences in mandatory and optional message 301 types and fields. 303 The [ASDRI] contemplated DRI system will broadcast locally: 305 1. the UAS operator registration number; 307 2. the [CTA2063A] compliant unique serial number of the UA; 309 3. a time stamp, the geographical position of the UA, and its height 310 AGL or above its take-off point; 312 4. the UA ground speed and route course measured clockwise from true 313 north; 315 5. the geographical position of the remote pilot, or if that is not 316 available, the geographical position of the UA take-off point; 317 and 319 6. for Classes C1, C2, C3, the UAS emergency status. 321 Under the [ASDRI] contemplated standard, data will be sent in plain 322 text and the UAS operator registration number will be represented as 323 a 16-byte string including the (European) state code. The 324 corresponding private ID part will contain 3 characters that are not 325 broadcast but used by authorities to access regional registration 326 databases for verification. 328 ASD-STAN also contemplates corresponding Network Remote 329 Identification (NRI) functionality. The ASD-STAN RID target is to 330 revise their current standard with additional functionality (e.g., 331 DRIP) to be published before 2022 [ASDRI]. 333 Security oriented UAS RID essentially has two goals: enable the 334 general public to obtain and record an opaque ID for any observed UA, 335 which they can then report to authorities; and enable authorities, 336 from such an ID, to look up information about the UAS and its 337 operator. Safety oriented UAS RID has stronger requirements. 339 Although dynamic establishment of secure communications between the 340 Observer and the UAS pilot seems to have been contemplated by the FAA 341 UAS ID and Tracking Aviation Rulemaking Committee (ARC) in their 342 [Recommendations], it is not addressed in any of the 343 subsequent regulations or international SDO technical specifications, 344 other than DRIP, known to the authors as of early 2021. 346 1.2. Concerns and Constraints 348 Disambiguation of multiple UA flying in close proximity may be very 349 challenging, even if each is reporting its identity, position, and 350 velocity as accurately as it can. 352 The origin of information in UAS RID and UAS Traffic Management (UTM) 353 generally is the UAS or its operator. Self-reports may be initiated 354 by the remote pilot at the console of the Ground Control Station 355 (GCS, the UAS subsystem used to remotely operate the UA), or 356 automatically by GCS software; in Broadcast RID, they typically would 357 be initiated automatically by a process on the UA. Data in the 358 reports may come from sensors available to the operator (e.g., radar 359 or cameras), the GCS (e.g., "dead reckoning" UA location, starting 360 from the takeoff location and estimating the displacements due to 361 subsequent piloting commands, wind, etc.), or the UA itself (e.g., an 362 on-board GNSS receiver); in Broadcast RID, all the data must be sent 363 proximately by, and most of the data comes ultimately from, the UA 364 itself. Whether information comes proximately from the operator, or 365 from automated systems configured by the operator, there are 366 possibilities not only of unintentional error in but also of 367 intentional falsification of this data. Mandating UAS RID, 368 specifying data elements required to be sent, monitoring compliance 369 and enforcing it (or penalizing non-compliance) are matters for Civil 370 Aviation Authorities (CAAs) et al; specifying message formats, etc. 371 to carry those data elements has been addressed by other SDOs; 372 offering technical means, as extensions to external standards, to 373 facilitate verifiable compliance and enforcement/monitoring, are 374 opportunities for DRIP. 376 Minimal specified information must be made available to the public. 377 Access to other data, e.g., UAS operator Personally Identifiable 378 Information (PII), must be limited to strongly authenticated 379 personnel, properly authorized in accordance with applicable policy. 380 The balance between privacy and transparency remains a subject for 381 public debate and regulatory action; DRIP can only offer tools to 382 expand the achievable trade space and enable trade-offs within that 383 space. [F3411-19], the basis for most current (2021) thinking about 384 and efforts to provide UAS RID, specifies only how to get the UAS ID 385 to the Observer: how the Observer can perform these lookups and how 386 the registries first can be populated with information are 387 unspecified therein. 389 The need for nearly universal deployment of UAS RID is pressing: 390 consider how negligible the value of an automobile license plate 391 system would be if only 90% of the cars displayed plates. This 392 implies the need to support use by Observers of already ubiquitous 393 mobile devices (typically smartphones and tablets). Anticipating CAA 394 requirements to support legacy devices, especially in light of 395 [Recommendations], [F3411-19] specifies that any UAS sending 396 Broadcast RID over Bluetooth must do so over Bluetooth 4, regardless 397 of whether it also does so over newer versions; as UAS sender devices 398 and Observer receiver devices are unpaired, this implies extremely 399 short "advertisement" (beacon) frames. 401 Wireless data links to or from UA are challenging. Flight is often 402 amidst structures and foliage at low altitudes over varied terrain. 403 UA are constrained in both total energy and instantaneous power by 404 their batteries. Small UA imply small antennas. Densely populated 405 volumes will suffer from link congestion: even if UA in an airspace 406 volume are few, other transmitters nearby on the ground, sharing the 407 same license free spectral band, may be many. Thus air to air and 408 air to ground links will generally be slow and unreliable. 410 UAS Cost, Size, Weight, and Power (CSWaP) constraints are severe. 411 CSWaP is a burden not only on the designers of new UAS for sale, but 412 also on owners of existing UAS that must be retrofit. Radio 413 Controlled (RC) aircraft modelers, "hams" who use licensed amateur 414 radio frequencies to control UAS, drone hobbyists, and others who 415 custom build UAS, all need means of participating in UAS RID, 416 sensitive to both generic CSWaP and application-specific 417 considerations. 419 To accommodate the most severely constrained cases, all these 420 conspire to motivate system design decisions that complicate the 421 protocol design problem. 423 Broadcast RID uses one-way local data links. UAS may have Internet 424 connectivity only intermittently, or not at all, during flight. 426 Internet-disconnected operation of Observer devices has been deemed 427 by ASTM F38.02 too infrequent to address. However, the preamble to 428 [FRUR] cites "remote and rural areas that do not have reliable 429 Internet access" as a major reason for requiring Broadcast rather 430 than Network RID, and states that "Personal wireless devices that are 431 capable of receiving 47 CFR part 15 frequencies, such as smart 432 phones, tablets, or other similar commercially available devices, 433 will be able to receive broadcast remote identification information 434 directly without reliance on an Internet connection". Internet- 435 disconnected operation presents challenges, e.g., for Observers 436 needing access to the [F3411-19] web based Broadcast Authentication 437 Verifier Service or needing to do external lookups. 439 As RID must often operate within these constraints, heavyweight 440 cryptographic security protocols or even simple cryptographic 441 handshakes are infeasible, yet trustworthiness of UAS RID information 442 is essential. Under [F3411-19], _even the most basic datum, the UAS 443 ID itself, can be merely an unsubstantiated claim_. 445 Observer devices being ubiquitous, thus popular targets for malware 446 or other compromise, cannot be generally trusted (although the user 447 of each device is compelled to trust that device, to some extent); a 448 "fair witness" functionality (inspired by [Stranger]) is desirable. 450 Despite work by regulators and SDOs, there are substantial gaps in 451 UAS standards generally and UAS RID specifically. [Roadmap] catalogs 452 UAS related standards, ongoing standardization activities and gaps 453 (as of 2020); Section 7.8 catalogs those related specifically to UAS 454 RID. DRIP will address the most fundamental of these gaps, as 455 foreshadowed above. 457 1.3. DRIP Scope 459 DRIP's initial charter is to make RID immediately actionable, in both 460 Internet and local-only connected scenarios (especially emergencies), 461 in severely constrained UAS environments, balancing legitimate (e.g., 462 public safety) authorities' Need To Know trustworthy information with 463 UAS operators' privacy. By "immediately actionable" is meant 464 information of sufficient precision, accuracy, timeliness, etc. for 465 an Observer to use it as the basis for immediate decisive action, 466 whether that be to trigger a defensive counter-UAS system, to attempt 467 to initiate communications with the UAS operator, to accept the 468 presence of the UAS in the airspace where/when observed as not 469 requiring further action, or whatever, with potentially severe 470 consequences of any action or inaction chosen based on that 471 information. For further explanation of the concept of immediate 472 actionability, see [ENISACSIRT]. 474 Note that UAS RID must achieve nearly universal adoption, but DRIP 475 can add value even if only selectively deployed. Authorities with 476 jurisdiction over more sensitive airspace volumes may set a higher 477 than generally mandated RID requirement for flight in such volumes. 478 Those with a greater need for high-confidence IFF can equip with 479 DRIP, enabling strong authentication of their own aircraft and allied 480 operators without regard for the weaker (if any) authentication of 481 others. 483 DRIP (originally Trustworthy Multipurpose Remote Identification, TM- 484 RID) potentially could be applied to verifiably identify other types 485 of registered things reported to be in specified physical locations, 486 and providing timely trustworthy identification data is also 487 prerequisite to identity-oriented networking, but the urgent 488 motivation and clear initial focus is UAS. Existing Internet 489 resources (protocol standards, services, infrastructure, and business 490 models) should be leveraged. 492 1.4. Document Scope 494 This document describes the problem space for UAS RID conforming to 495 proposed regulations and external technical standards, defines common 496 terminology, specifies numbered requirements for DRIP, identifies 497 some important considerations (IANA, security, privacy and 498 transparency), and discusses limitations. 500 A natural Internet-based approach to meet these requirements is 501 described in a companion architecture document [drip-architecture] 502 and elaborated in other DRIP documents. 504 2. Terms and Definitions 506 2.1. Requirements Terminology 508 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 509 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 510 "OPTIONAL" in this document are to be interpreted as described in BCP 511 14 [RFC2119] [RFC8174] when, and only when, they appear in all 512 capitals, as shown here. 514 2.2. Definitions 516 This section defines a non-comprehensive set of terms expected to be 517 used in DRIP documents. This list is meant to be the DRIP 518 terminology reference; as such, some of the terms listed below are 519 not used in this document. 521 [RFC4949] provides a glossary of Internet security terms that should 522 be used where applicable. 524 In the UAS community, the plural form of acronyms generally is the 525 same as the singular form, e.g., Unmanned Aircraft System (singular) 526 and Unmanned Aircraft Systems (plural) are both represented as UAS. 527 On this and other terminological issues, to encourage comprehension 528 necessary for adoption of DRIP by the intended user community, that 529 community's norms are respected herein, and definitions are quoted in 530 cases where they have been found in that community's documents. Most 531 of the listed terms are from that community (even if specific source 532 documents are not cited); any that are DRIP-specific or invented by 533 the authors of this document are marked "(DRIP)". 535 4-D 536 Four-dimensional. Latitude, Longitude, Altitude, Time. Used 537 especially to delineate an airspace volume in which an operation 538 is being or will be conducted. 540 AAA 541 Attestation, Authentication, Authorization, Access Control, 542 Accounting, Attribution, Audit, or any subset thereof (uses differ 543 by application, author, and context). (DRIP) 545 ABDAA 546 AirBorne DAA. Accomplished using systems onboard the aircraft 547 involved. Supports "self-separation" (remaining "well clear" of 548 other aircraft) and collision avoidance. 550 ADS-B 551 Automatic Dependent Surveillance - Broadcast. "ADS-B Out" 552 equipment obtains aircraft position from other on-board systems 553 (typically GNSS) and periodically broadcasts it to "ADS-B In" 554 equipped entities, including other aircraft, ground stations, and 555 satellite based monitoring systems. 557 AGL 558 Above Ground Level. Relative altitude, above the variously 559 defined local ground level, typically of a UA, measured in feet or 560 meters. Should be explicitly specified as either barometric 561 (pressure) or geodetic (GNSS) altitude. 563 ATC 564 Air Traffic Control. Explicit flight direction to pilots from 565 ground controllers. Contrast with ATM. 567 ATM 568 Air Traffic Management. A broader functional and geographic scope 569 and/or a higher layer of abstraction than ATC. "The dynamic, 570 integrated management of air traffic and airspace including air 571 traffic services, airspace management and air traffic flow 572 management - safely, economically and efficiently - through the 573 provision of facilities and seamless services in collaboration 574 with all parties and involving airborne and ground-based 575 functions" [ICAOATM]. 577 Authentication Message 578 [F3411-19] Message Type 2. Provides framing for authentication 579 data, only; the only message that can be extended in length by 580 segmenting it across more than one page. 582 Basic ID Message 583 [F3411-19] Message Type 0. Provides UA Type, UAS ID Type, and UAS 584 ID, only. 586 Broadcast Authentication Verifier Service 587 System component designed to handle any authentication of 588 Broadcast RID by offloading signature verification to a web 589 service [F3411-19]. 591 BVLOS 592 Beyond Visual Line Of Sight. See VLOS. 594 byte 595 Used here in its now-customary sense as a synonym for "octet", as 596 "byte" is used exclusively in definitions of data structures 597 specified in [F3411-19] 599 CAA 600 Civil Aviation Authority of a regulatory jurisdiction. Often so 601 named, but other examples include the United States Federal 602 Aviation Administration (FAA) and the Japan Civil Aviation Bureau. 604 CSWaP 605 Cost, Size, Weight, and Power. 607 C2 608 Command and Control. Previously mostly used in military contexts. 609 Properly refers to a function, exercisable over arbitrary 610 communications; but in the small UAS context, often refers to the 611 communications (typically RF data link) over which the GCS 612 controls the UA. 614 DAA 615 Detect And Avoid, formerly Sense And Avoid (SAA). A means of 616 keeping aircraft "well clear" of each other and obstacles for 617 safety. "The capability to see, sense or detect conflicting 618 traffic or other hazards and take the appropriate action to comply 619 with the applicable rules of flight" [ICAOUAS]. 621 DRI (not to be confused with DRIP) 622 Direct Remote Identification. EU regulatory requirement for "a 623 system that ensures the local broadcast of information about a UA 624 in operation, including the marking of the UA, so that this 625 information can be obtained without physical access to the UA". 626 [Delegated] that presumably can be satisfied with appropriately 627 configured [F3411-19] Broadcast RID. 629 DSS 630 Discovery and Synchronization Service. The UTM system overlay 631 network backbone. Most importantly, it enables one USS to learn 632 which other USS have UAS operating in a given 4-D airspace volume, 633 for strategic deconfliction of planned operations and Network RID 634 surveillance of active operations. [F3411-19] 636 EUROCAE 637 European Organisation for Civil Aviation Equipment. Aviation SDO, 638 originally European, now with broader membership. Cooperates 639 extensively with RTCA. 641 GBDAA 642 Ground Based DAA. Accomplished with the aid of ground based 643 functions. 645 GCS 646 Ground Control Station. The part of the UAS that the remote pilot 647 uses to exercise C2 over the UA, whether by remotely exercising UA 648 flight controls to fly the UA, by setting GNSS waypoints, or 649 otherwise directing its flight. 651 GNSS 652 Global Navigation Satellite System. Satellite based timing and/or 653 positioning with global coverage, often used to support 654 navigation. 656 GPS 657 Global Positioning System. A specific GNSS, but in the UAS 658 context, the term is typically misused in place of the more 659 generic term GNSS. 661 GRAIN 662 Global Resilient Aviation Interoperable Network. ICAO managed 663 IPv6 overlay internetwork based on IATF, dedicated to aviation 664 (but not just aircraft). Currently (2021) in design, 665 accommodating the proposed DRIP identifier. 667 IATF 668 International Aviation Trust Framework. ICAO effort to develop a 669 resilient and secure by design framework for networking in support 670 of all aspects of aviation. 672 ICAO 673 International Civil Aviation Organization. A United Nations 674 specialized agency that develops and harmonizes international 675 standards relating to aviation. 677 IFF 678 Identification Friend or Foe. Originally, and in its narrow sense 679 still, a self-identification broadcast in response to 680 interrogation via radar, to reduce friendly fire incidents, which 681 led to military and commercial transponder systems such as ADS-B. 682 In the broader sense used here, any process intended to 683 distinguish friendly from potentially hostile UA or other entities 684 encountered. 686 LAANC 687 Low Altitude Authorization and Notification Capability. Supports 688 ATC authorization requirements for UAS operations: remote pilots 689 can apply to receive a near real-time authorization for operations 690 under 400 feet in controlled airspace near airports. FAA 691 authorized partial stopgap in the US until UTM comes. 693 Location/Vector Message 694 [F3411-19] Message Type 1. Provides UA location, altitude, 695 heading, speed, and status. 697 LOS 698 Line Of Sight. An adjectival phrase describing any information 699 transfer that travels in a nearly straight line (e.g., 700 electromagnetic energy, whether in the visual light, RF, or other 701 frequency range) and is subject to blockage. A term to be avoided 702 due to ambiguity, in this context, between RF LOS and VLOS. 704 Message Pack 705 [F3411-19] Message Type 15. The framed concatenation, in message 706 type index order, of at most one message of each type of any 707 subset of the other types. Required to be sent in Wi-Fi NAN and 708 in Bluetooth 5 Extended Advertisements, if those media are used; 709 cannot be sent in Bluetooth 4. 711 MSL 712 Mean Sea Level. Shorthand for relative altitude, above the 713 variously defined mean sea level, typically of a UA (but in [FRUR] 714 also for a GCS), measured in feet or meters. Should be explicitly 715 specified as either barometric (pressure) or geodetic (e.g., as 716 indicated by GNSS, referenced to the WGS84 ellipsoid). 718 Net-RID DP 719 Network RID Display Provider. [F3411-19] logical entity that 720 aggregates data from Net-RID SPs as needed in response to user 721 queries regarding UAS operating within specified airspace volumes, 722 to enable display by a user application on a user device. 723 Potentially could provide not only information sent via UAS RID 724 but also information retrieved from UAS RID registries or 725 information beyond UAS RID. Under superseded [NPRM], not 726 recognized as a distinct entity, but a service provided by USS, 727 including Public Safety USS that may exist primarily for this 728 purpose rather than to manage any subscribed UAS. 730 Net-RID SP 731 Network RID Service Provider. [F3411-19] logical entity that 732 collects RID messages from UAS and responds to NetRID-DP queries 733 for information on UAS of which it is aware. Under superseded 734 [NPRM], the USS to which the UAS is subscribed ("Remote ID USS"). 736 Network Identification Service 737 EU regulatory requirement in [Opinion1] and [WG105] that 738 presumably can be satisfied with appropriately configured 739 [F3411-19] Network RID. 741 Observer 742 An entity (typically but not necessarily an individual human) who 743 has directly or indirectly observed a UA and wishes to know 744 something about it, starting with its ID. An Observer typically 745 is on the ground and local (within VLOS of an observed UA), but 746 could be remote (observing via Network RID or other surveillance), 747 operating another UA, aboard another aircraft, etc. (DRIP) 749 Operation 750 A flight, or series of flights of the same mission, by the same 751 UAS, separated by at most brief ground intervals. (Inferred from 752 UTM usage, no formal definition found) 754 Operator 755 "A person, organization or enterprise engaged in or offering to 756 engage in an aircraft operation" [ICAOUAS]. 758 Operator ID Message 759 [F3411-19] Message Type 5. Provides CAA issued Operator ID, only. 760 Operator ID is distinct from UAS ID. 762 page 763 Payload of a frame, containing a chunk of a message that has been 764 segmented, to allow transport of a message longer than can be 765 encapsulated in a single frame. [F3411-19] 767 PIC 768 Pilot In Command. "The pilot designated by the operator, or in 769 the case of general aviation, the owner, as being in command and 770 charged with the safe conduct of a flight" [ICAOUAS]. 772 PII 773 Personally Identifiable Information. In the UAS RID context, 774 typically of the UAS Operator, Pilot In Command (PIC), or Remote 775 Pilot, but possibly of an Observer or other party. This specific 776 term is used primarily in the US; other terms with essentially the 777 same meaning are more common in other jurisdictions (e.g., 778 "personal data" in the EU). Used herein generically to refer to 779 personal information, which the person might wish to keep private, 780 or may have a statutorily recognized right to keep private (e.g., 781 under the EU [GDPR]), potentially imposing (legally or ethically) 782 a confidentiality requirement on protocols/systems. 784 Remote Pilot 785 A pilot using a GCS to exercise proximate control of a UA. Either 786 the PIC or under the supervision of the PIC. "The person who 787 manipulates the flight controls of a remotely-piloted aircraft 788 during flight time" [ICAOUAS]. 790 RF 791 Radio Frequency. Adjective, e.g., "RF link", or noun. 793 RF LOS 794 RF Line Of Sight. Typically used in describing a direct radio 795 link between a GCS and the UA under its control, potentially 796 subject to blockage by foliage, structures, terrain, or other 797 vehicles, but less so than VLOS. 799 RTCA 800 Radio Technical Commission for Aeronautics. US aviation SDO. 801 Cooperates extensively with EUROCAE. 803 Safety 804 "The state in which risks associated with aviation activities, 805 related to, or in direct support of the operation of aircraft, are 806 reduced and controlled to an acceptable level." From Annex 19 of 807 the Chicago Convention, quoted in [ICAODEFS] 809 Security 810 "Safeguarding civil aviation against acts of unlawful 811 interference." From Annex 17 of the Chicago Convention, quoted in 812 [ICAODEFS] 814 Self-ID Message 815 [F3411-19] Message Type 3. Provides a 1 byte descriptor and 23 816 byte ASCII free text field, only. Expected to be used to provide 817 context on the operation, e.g., mission intent. 819 SDO 820 Standards Development Organization. ASTM, IETF, et al. 822 SDSP 823 Supplemental Data Service Provider. An entity that participates 824 in the UTM system, but provides services beyond those specified as 825 basic UTM system functions (e.g., weather data). [FAACONOPS] 827 System Message 828 [F3411-19] Message Type 4. Provides general UAS information, 829 including remote pilot location, multiple UA group operational 830 area, etc. 832 U-space 833 EU concept and emerging framework for integration of UAS into all 834 classes of airspace, specifically including high density urban 835 areas, sharing airspace with manned aircraft [InitialView]. 837 UA 838 Unmanned Aircraft. In popular parlance, "drone". "An aircraft 839 which is intended to operate with no pilot on board" [ICAOUAS]. 841 UAS 842 Unmanned Aircraft System. Composed of UA, all required on-board 843 subsystems, payload, control station, other required off-board 844 subsystems, any required launch and recovery equipment, all 845 required crew members, and C2 links between UA and control station 846 [F3411-19]. 848 UAS ID 849 UAS identifier. Although called "UAS ID", it is actually unique 850 to the UA, neither to the operator (as some UAS registration 851 numbers have been and for exclusively recreational purposes are 852 continuing to be assigned), nor to the combination of GCS and UA 853 that comprise the UAS. _Maximum length of 20 bytes_ [F3411-19]. 855 UAS ID Type 856 UAS Identifier type index. 4 bits, see Section 3, Paragraph 6 for 857 currently defined values 0-3. [F3411-19] 859 UAS RID 860 UAS Remote Identification and tracking. System to enable 861 arbitrary Observers to identify UA during flight. 863 USS 864 UAS Service Supplier. "A USS is an entity that assists UAS 865 Operators with meeting UTM operational requirements that enable 866 safe and efficient use of airspace" and "... provide services to 867 support the UAS community, to connect Operators and other entities 868 to enable information flow across the USS Network, and to promote 869 shared situational awareness among UTM participants" [FAACONOPS]. 871 UTM 872 UAS Traffic Management. "A specific aspect of air traffic 873 management which manages UAS operations safely, economically and 874 efficiently through the provision of facilities and a seamless set 875 of services in collaboration with all parties and involving 876 airborne and ground-based functions" [ICAOUTM]. In the US, 877 according to the FAA, a "traffic management" ecosystem for 878 "uncontrolled" low altitude UAS operations, separate from, but 879 complementary to, the FAA's ATC system for "controlled" operations 880 of manned aircraft. 882 V2V 883 Vehicle-to-Vehicle. Originally communications between 884 automobiles, now extended to apply to communications between 885 vehicles generally. Often, together with Vehicle-to- 886 Infrastructure (V2I) etc., generalized to V2X. 888 VLOS 889 Visual Line Of Sight. Typically used in describing operation of a 890 UA by a "remote" pilot who can clearly directly (without video 891 cameras or any aids other than glasses or under some rules 892 binoculars) see the UA and its immediate flight environment. 893 Potentially subject to blockage by foliage, structures, terrain, 894 or other vehicles, more so than RF LOS. 896 3. UAS RID Problem Space 898 CAAs worldwide are mandating UAS RID. The European Union Aviation 899 Safety Agency (EASA) has published [Delegated] and [Implementing] 900 Regulations. The US FAA has published a "final" rule [FRUR] and has 901 described the key role that UAS RID plays in UAS Traffic Management 902 (UTM) in [FAACONOPS] (especially Section 2.6). CAAs currently (2021) 903 promulgate performance-based regulations that do not specify 904 techniques, but rather cite industry consensus technical standards as 905 acceptable means of compliance. 907 The most widely cited such industry consensus technical standard for 908 UAS RID is [F3411-19], which defines two means of UAS RID: 910 Network RID defines a set of information for UAS to make available 911 globally indirectly via the Internet, through servers that can be 912 queried by Observers. 914 Broadcast RID defines a set of messages for UA to transmit locally 915 directly one-way over Bluetooth or Wi-Fi (without IP or any other 916 protocols between the data link and application layers), to be 917 received in real time by local Observers. 919 UAS using both means must send the same UAS RID application layer 920 information via each [F3411-19]. The presentation may differ, as 921 Network RID defines a data dictionary, whereas Broadcast RID defines 922 message formats (which carry items from that same data dictionary). 923 The interval (or rate) at which it is sent may differ, as Network RID 924 can accommodate Observer queries asynchronous to UAS updates (which 925 generally need be sent only when information, such as location, 926 changes), whereas Broadcast RID depends upon Observers receiving UA 927 messages at the time they are transmitted. 929 Network RID depends upon Internet connectivity in several segments 930 from the UAS to each Observer. Broadcast RID should need Internet 931 (or other Wide Area Network) connectivity only to retrieve UAS 932 registry information using the directly locally received UAS 933 Identifier (UAS ID) as the primary unique key for database lookup. 934 Broadcast RID does not assume IP connectivity of UAS; messages are 935 encapsulated by the UA _without IP_, directly in link layer frames 936 (Bluetooth 4, Bluetooth 5, Wi-Fi NAN, IEEE 802.11 Beacon, or in the 937 future perhaps others). 939 [F3411-19] specifies three UAS ID Type values: 941 1 A static, manufacturer assigned, hardware serial number as defined 942 in ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers" 943 [CTA2063A]. 945 2 A CAA assigned (generally static) ID, like the registration number 946 of a manned aircraft. 948 3 A UTM system assigned UUID [RFC4122], which can but need not be 949 dynamic. 951 Per [Delegated], the EU allows only UAS ID Type 1. Under [FRUR], the 952 US allows types 1 and 3. [NPRM] proposed that a type 3 "Session ID" 953 would be "e.g., a randomly-generated alphanumeric code assigned by a 954 Remote ID UAS Service Supplier (USS) on a per-flight basis designed 955 to provide additional privacy to the operator", but given the 956 omission of Network RID from [FRUR], how this is to be assigned in 957 the US is still to be determined. 959 As yet apparently there are no CAA public proposals to use UAS ID 960 Type 2. In the preamble of [FRUR], the FAA argues that registration 961 numbers should not be sent in RID, insists that the capability of 962 looking up registration numbers from information contained in RID 963 should be restricted to FAA and other Government agencies, and 964 implies that Session ID would be linked to the registration number 965 only indirectly via the serial number in the registration database. 966 The possibility of cryptographically blinding registration numbers, 967 such that they can be revealed under specified circumstances, does 968 not appear to be mentioned in applicable regulations or external 969 technical standards. 971 Under [Delegated], the EU also requires an operator registration 972 number (an additional identifier distinct from the UAS ID) that can 973 be carried in an [F3411-19] optional Operator ID message. 975 [FRUR] allows RID requirements to be met by either the UA itself, 976 which is then designated a "standard remote identification unmanned 977 aircraft", or by an add-on "remote identification broadcast module". 978 Relative to a standard RID UA, the different requirements for a 979 module are that the latter: must transmit its own serial number 980 (neither the serial number of the UA to which it is attached, nor a 981 Session ID); must transmit takeoff location as a proxy for the 982 location of the pilot/GCS; need not transmit UA emergency status; and 983 is allowed to be used only for operations within VLOS of the remote 984 pilot. 986 Jurisdictions may relax or waive RID requirements for certain 987 operators and/or under certain conditions. For example, [FRUR] 988 allows operators with UAS not equipped for RID to conduct VLOS 989 operations at counter-intuitively named "FAA-recognized 990 identification areas" (FRIA); radio controlled model aircraft flying 991 clubs and other eligible organizations can apply to the FAA for such 992 recognition of their operating areas. 994 3.1. Network RID 996 +-------------+ ****************** 997 | UA | * Internet * 998 +--o-------o--+ * * 999 | | * * 1000 | | * * +------------+ 1001 | '--------*--(+)-----------*-----o | 1002 | * | * | | 1003 | .--------*--(+)-----------*-----o NET-Rid SP | 1004 | | * * | | 1005 | | * .------*-----o | 1006 | | * | * +------------+ 1007 | | * | * 1008 | | * | * +------------+ 1009 | | * '------*-----o | 1010 | | * * | NET-Rid DP | 1011 | | * .------*-----o | 1012 | | * | * +------------+ 1013 | | * | * 1014 | | * | * +------------+ 1015 +--o-------o--+ * '------*-----o Observer's | 1016 | GCS | * * | Device | 1017 +-------------+ ****************** +------------+ 1019 Figure 3: "Network RID Information Flow" 1021 Figure 3 illustrates Network RID information flows. Only two of the 1022 three typically wireless links shown involving the UAS (UA-GCS, UA- 1023 Internet, and GCS-Internet) need exist to support C2 and Network RID. 1024 All three may exist, at the same or different times, especially in 1025 BVLOS operations. There must be some information flow path (direct 1026 or indirect) between the GCS and the UA, for the former to exercise 1027 C2 over the latter. If this path is two-way (as increasingly it is, 1028 even for inexpensive small UAS), the UA will also send its status 1029 (and position, if suitably equipped, e.g., with GNSS) to the GCS. 1030 There also must be some path between at least one subsystem of the 1031 UAS (UA or GCS) and the Internet, for the former to send status and 1032 position updates to its USS (serving _inter alia_ as a Net-RID SP). 1034 Direct UA-Internet wireless links are expected to become more common, 1035 especially on larger UAS, but currently (2021) are rare. Instead, 1036 the RID data flow typically originates on the UA and passes through 1037 the GCS, or originates on the GCS. Network RID data makes three 1038 trips through the Internet (GCS-SP, SP-DP, DP-Observer, unless any of 1039 them are colocated), implying use of IP (and other middle layer 1040 protocols, e.g., TLS/TCP or DTLS/UDP) on those trips. IP is not 1041 necessarily used or supported on the UA-GCS link (if indeed that 1042 direct link exists, as it typically does now, but in BVLOS operations 1043 often will not). 1045 Network RID is publish-subscribe-query. In the UTM context: 1047 1. The UAS operator pushes an "operational intent" (the current term 1048 in UTM corresponding to a flight plan in manned aviation) to the 1049 USS (call it USS#1) that will serve that UAS (call it UAS#1) for 1050 that operation, primarily to enable deconfliction with other 1051 operations potentially impinging upon that operation's 4-D 1052 airspace volume (call it Volume#1). 1054 2. Assuming the operation is approved and commences, UAS#1 1055 periodically pushes location/status updates to USS#1, which 1056 serves _inter alia_ as the Network RID Service Provider (Net-RID 1057 SP) for that operation. 1059 3. When users of any other USS (whether they be other UAS operators 1060 or Observers) develop an interest in any 4-D airspace volume 1061 (e.g., because they wish to submit an operational intent or 1062 because they have observed a UA), they query their own USS on the 1063 volumes in which they are interested. 1065 4. Their USS query, via the UTM Discovery and Synchronization 1066 Service (DSS), all other USS in the UTM system, and learn of any 1067 USS that have operations in those volumes (including any volumes 1068 intersecting them); thus those USS whose query volumes intersect 1069 Volume#1 (call them USS#2 through USS#n) learn that USS#1 has 1070 such operations. 1072 5. Interested parties can then subscribe to track updates on that 1073 operation of UAS#1, via their own USS, which serve as Network RID 1074 Display Providers (Net-RID DP) for that operation. 1076 6. USS#1 (as Net-RID SP) will then publish updates of UAS#1 status 1077 and position to all other subscribed USS in USS#2 through USS#n 1078 (as Net-RID DP). 1080 7. All Net-RID DP subscribed to that operation of UAS#1 will deliver 1081 its track information to their users who subscribed to that 1082 operation of UAS#1 (via means unspecified by [F3411-19] etc., but 1083 generally presumed to be web browser based). 1085 Network RID has several connectivity scenarios: 1087 _Persistently Internet connected UA_ can consistently directly 1088 source RID information; this requires wireless coverage throughout 1089 the intended operational airspace volume, plus a buffer (e.g., 1090 winds may drive the UA out of the volume). 1092 _Intermittently Internet connected UA_, can usually directly 1093 source RID information, but when offline (e.g., due to signal 1094 blockage by a large structure being inspected using the UAS), need 1095 the GCS to proxy source RID information. 1097 _Indirectly connected UA_ lack the ability to send IP packets that 1098 will be forwarded into and across the Internet, but instead have 1099 some other form of communications to another node that can relay 1100 or proxy RID information to the Internet; typically this node 1101 would be the GCS (which to perform its function must know where 1102 the UA is, although C2 link outages do occur). 1104 _Non-connected UA_ have no means of sourcing RID information, in 1105 which case the GCS or some other interface available to the 1106 operator must source it. In the extreme case, this could be the 1107 pilot or other agent of the operator using a web browser/ 1108 application to designate, to a USS or other UTM entity, a time- 1109 bounded airspace volume in which an operation will be conducted. 1110 This is referred to as a "non-equipped network participant" 1111 engaging in "area operations". This may impede disambiguation of 1112 ID if multiple UAS operate in the same or overlapping 4-D volumes. 1113 In most airspace volumes, most classes of UA will not be permitted 1114 to fly if non-connected. 1116 In most cases in the near term (2021), the Network RID first hop data 1117 link is likely to be cellular, which can also support BVLOS C2 over 1118 existing large coverage areas, or Wi-Fi, which can also support 1119 Broadcast RID. However, provided the data link can support at least 1120 UDP/IP and ideally also TCP/IP, its type is generally immaterial to 1121 higher layer protocols. The UAS, as the ultimate source of Network 1122 RID information, feeds a Net-RID SP (typically the USS to which the 1123 UAS operator subscribes), which proxies for the UAS and other data 1124 sources. An Observer or other ultimate consumer of Network RID 1125 information obtains it from a Net-RID DP (also typically a USS), 1126 which aggregates information from multiple Net-RID SPs to offer 1127 airspace Situational Awareness (SA) coverage of a volume of interest. 1129 Network RID Service and Display providers are expected to be 1130 implemented as servers in well-connected infrastructure, 1131 communicating with each other via the Internet, and accessible by 1132 Observers via means such as web Application Programming Interfaces 1133 (APIs) and browsers. 1135 Network RID is the less constrained of the defined UAS RID means. 1136 [F3411-19] specifies only Net-RID SP to Net-RID DP information 1137 exchanges. It is presumed that IETF efforts supporting the more 1138 constrained Broadcast RID (see next section) can be generalized for 1139 Network RID and potentially also for UAS to USS or other UTM 1140 communications. 1142 3.2. Broadcast RID 1144 +-------------------+ 1145 | Unmanned Aircraft | 1146 +---------o---------+ 1147 | 1148 | 1149 | 1150 | app messages directly over one-way RF data link 1151 | 1152 | 1153 v 1154 +------------------o-------------------+ 1155 | Observer's device (e.g., smartphone) | 1156 +--------------------------------------+ 1158 Figure 4: "Broadcast RID Information Flow" 1160 Figure 4 illustrates Broadcast RID information flow. Note the 1161 absence of the Internet from the figure. This is because Broadcast 1162 RID is one-way direct transmission of application layer messages over 1163 a RF data link (without IP) from the UA to local Observer devices. 1164 Internet connectivity is involved only in what the Observer chooses 1165 to do with the information received, such as verify signatures using 1166 a web-based Broadcast Authentication Verifier Service and look up 1167 information in registries using the UAS ID as the primary unique key. 1169 Broadcast RID is conceptually similar to Automatic Dependent 1170 Surveillance - Broadcast (ADS-B). However, for various technical and 1171 other reasons, regulators including the EASA have not indicated 1172 intent to allow, and FAA has explicitly prohibited, use of ADS-B for 1173 UAS RID. 1175 [F3411-19] specifies four Broadcast RID data links: Bluetooth 4.x, 1176 Bluetooth 5.x with Extended Advertisements and Long Range Coded PHY 1177 (S=8), Wi-Fi NAN at 2.4 GHz, and Wi-Fi NAN at 5 GHz. A UA must 1178 broadcast (using advertisement mechanisms where no other option 1179 supports broadcast) on at least one of these. If sending on 1180 Bluetooth 5.x, it is also required concurrently to do so on 4.x 1181 (referred to in [F3411-19] as Bluetooth Legacy); current (2021) 1182 discussions in ASTM F38.02 on revising the standard, motivated by 1183 European standards drafts, suggest that both Bluetooth versions will 1184 be required. If broadcasting Wi-Fi NAN at 5 GHz, it is also required 1185 concurrently to do so at 2.4 GHz; current discussions in F38.02 1186 include relaxing this. Wi-Fi Beacons are also under consideration. 1187 Future revisions of [F3411-19] may allow other data links. 1189 The selection of the Broadcast media was driven by research into what 1190 is commonly available on 'ground' units (smartphones and tablets) and 1191 what was found as prevalent or 'affordable' in UA. Further, there 1192 must be an API for the Observer's receiving application to have 1193 access to these messages. As yet only Bluetooth 4.x support is 1194 readily available, thus the current focus is on working within the 31 1195 byte payload limit of the Bluetooth 4.x "Broadcast Frame" transmitted 1196 as an "advertisement" on beacon channels. After overheads, this 1197 limits the RID message to 25 bytes and UAS ID string to a maximum 1198 length of 20 bytes. 1200 Length constraints also preclude a single Bluetooth 4.x frame 1201 carrying not only the UAS ID but also position, velocity, and other 1202 information that should be bound to the UAS ID, much less strong 1203 authentication data. Messages that cannot be encapsulated in a 1204 single frame (thus far, only the Authentication Message) must be 1205 segmented into message "pages" (in the terminology of [F3411-19]). 1206 Message pages must somehow be correlated as belonging to the same 1207 message. Messages carrying position, velocity and other data must 1208 somehow be correlated with the Basic ID message that carries the UAS 1209 ID. This correlation is expected to be done on the basis of MAC 1210 address: this may be complicated by MAC address randomization; not 1211 all the common devices expected to be used by Observers have APIs 1212 that make sender MAC addresses available to user space receiver 1213 applications; and MAC addresses are easily spoofed. Data elements 1214 are not so detached on other media (see Message Pack in the paragraph 1215 after next). 1217 [F3411-19] Broadcast RID specifies several message types. The 4 bit 1218 message type field in the header can index up to 16 types. Only 7 1219 are currently defined. Only 2 are mandatory. All others are 1220 optional, unless required by a jurisdictional authority, e.g., a CAA. 1221 To satisfy both EASA and FAA rules, all types are needed, except 1222 Self-ID and Authentication, as the data elements required by the 1223 rules are scattered across several message types (along with some 1224 data elements not required by the rules). 1226 The Message Pack (type 0xF) is not actually a message, but the framed 1227 concatenation of at most one message of each type of any subset of 1228 the other types, in type index order. Some of the messages that it 1229 can encapsulate are mandatory, others optional. The Message Pack 1230 itself is mandatory on data links that can encapsulate it in a single 1231 frame (Bluetooth 5.x and Wi-Fi). 1233 +-----------------------+-----------------+-----------+-----------+ 1234 | Index | Name | Req | Notes | 1235 +-----------------------+-----------------+-----------+-----------+ 1236 | 0x0 | Basic ID | Mandatory | - | 1237 +-----------------------+-----------------+-----------+-----------+ 1238 | 0x1 | Location/Vector | Mandatory | - | 1239 +-----------------------+-----------------+-----------+-----------+ 1240 | 0x2 | Authentication | Optional | paged | 1241 +-----------------------+-----------------+-----------+-----------+ 1242 | 0x3 | Self-ID | Optional | free text | 1243 +-----------------------+-----------------+-----------+-----------+ 1244 | 0x4 | System | Optional | - | 1245 +-----------------------+-----------------+-----------+-----------+ 1246 | 0x5 | Operator | Optional | - | 1247 +-----------------------+-----------------+-----------+-----------+ 1248 | 0xF | Message Pack | - | BT5 and | 1249 | | | | Wi-Fi | 1250 +-----------------------+-----------------+-----------+-----------+ 1251 | See Section 5.4.5 and | - | - | - | 1252 | Table 3 of [F3411-19] | | | | 1253 +-----------------------+-----------------+-----------+-----------+ 1255 Table 1: F3411-19 Message Types 1257 [F3411-19] Broadcast RID specifies very few quantitative performance 1258 requirements: static information must be transmitted at least once 1259 per 3 seconds; dynamic information (the Location/Vector message) must 1260 be transmitted at least once per second and be no older than one 1261 second when sent. [FRUR] requires all information be sent at least 1262 once per second. 1264 [F3411-19] Broadcast RID transmits all information as cleartext 1265 (ASCII or binary), so static IDs enable trivial correlation of 1266 patterns of use, unacceptable in many applications, e.g., package 1267 delivery routes of competitors. 1269 Any UA can assert any ID using the [F3411-19] required Basic ID 1270 message, which lacks any provisions for verification. The Position/ 1271 Vector message likewise lacks provisions for verification, and does 1272 not contain the ID, so must be correlated somehow with a Basic ID 1273 message: the developers of [F3411-19] have suggested using the MAC 1274 addresses on the Broadcast RID data link, but these may be randomized 1275 by the operating system stack to avoid the adversarial correlation 1276 problems of static identifiers. 1278 The [F3411-19] optional Authentication Message specifies framing for 1279 authentication data, but does not specify any authentication method, 1280 and the maximum length of the specified framing is too short for 1281 conventional digital signatures and far too short for conventional 1282 certificates (e.g., X.509). Fetching certificates via the Internet 1283 is not always possible (e.g., Observers working in remote areas, such 1284 as national forests), so devising a scheme whereby certificates can 1285 be transported over Broadcast RID is necessary. The one-way nature 1286 of Broadcast RID precludes challenge-response security protocols 1287 (e.g., Observers sending nonces to UA, to be returned in signed 1288 messages). Without DRIP extensions to [F3411-19], an Observer would 1289 be seriously challenged to validate the asserted UAS ID or any other 1290 information about the UAS or its operator looked up therefrom. 1292 3.3. USS in UTM and RID 1294 UAS RID and UTM are complementary; Network RID is a UTM service. The 1295 backbone of the UTM system is comprised of multiple USS: one or 1296 several per jurisdiction; some limited to a single jurisdiction, 1297 others spanning multiple jurisdictions. USS also serve as the 1298 principal or perhaps the sole interface for operators and UAS into 1299 the UTM environment. Each operator subscribes to at least one USS. 1300 Each UAS is registered by its operator in at least one USS. Each 1301 operational intent is submitted to one USS; if approved, that UAS and 1302 operator can commence that operation. During the operation, status 1303 and location of that UAS must be reported to that USS, which in turn 1304 provides information as needed about that operator, UAS, and 1305 operation into the UTM system and to Observers via Network RID. 1307 USS provide services not limited to Network RID; indeed, the primary 1308 USS function is deconfliction of airspace usage by different UAS and 1309 other (e.g., manned aircraft, rocket launch) operations. Most 1310 deconfliction involving a given operation is hoped to be completed 1311 prior to commencing that operation, and is called "strategic 1312 deconfliction". If that fails, "tactical deconfliction" comes into 1313 play; ABDAA may not involve USS, but GBDAA likely will. Dynamic 1314 constraints, formerly called UAS Volume Restrictions (UVR), can be 1315 necessitated by local emergencies, extreme weather, etc., specified 1316 by authorities on the ground, and propagated in UTM. 1318 No role for USS in Broadcast RID is currently specified by regulators 1319 or [F3411-19]. However, USS are likely to serve as registries (or 1320 perhaps registrars) for UAS (and perhaps operators); if so, USS will 1321 have a role in all forms of RID. Supplemental Data Service Providers 1322 (SDSP) are also likely to find roles, not only in UTM as such but 1323 also in enhancing UAS RID and related services. Whether USS, SDSP, 1324 etc. are involved or not, RID services, narrowly defined, provide 1325 regulator specified identification information; more broadly defined, 1326 RID services may leverage identification to facilitate related 1327 services or functions, likely beginning with V2X. 1329 3.4. DRIP Focus 1331 In addition to the gaps described above, there is a fundamental gap 1332 in almost all current or proposed regulations and technical standards 1333 for UAS RID. As noted above, ID is not an end in itself, but a 1334 means. Protocols specified in [F3411-19] etc. provide limited 1335 information potentially enabling, and no technical means for, an 1336 Observer to communicate with the pilot, e.g., to request further 1337 information on the UAS operation or exit from an airspace volume in 1338 an emergency. The System Message provides the location of the pilot/ 1339 GCS, so an Observer could physically go to the asserted location to 1340 look for the remote pilot; this is at best slow and may not be 1341 feasible. What if the pilot is on the opposite rim of a canyon, or 1342 there are multiple UAS operators to contact, whose GCS all lie in 1343 different directions from the Observer? An Observer with Internet 1344 connectivity and access privileges could look up operator PII in a 1345 registry, then call a phone number in hopes someone who can 1346 immediately influence the UAS operation will answer promptly during 1347 that operation; this is at best unreliable and may not be prudent. 1348 Should pilots be encouraged to answer phone calls while flying? 1349 Internet technologies can do much better than this. 1351 Thus complementing [F3411-19] with protocols enabling strong 1352 authentication, preserving operator privacy while enabling immediate 1353 use of information by authorized parties, is critical to achieve 1354 widespread adoption of a RID system supporting safe and secure 1355 operation of UAS. Just as [F3411-19] is expected to be approved by 1356 regulators as a basic means of compliance with UAS RID regulations, 1357 DRIP is expected likewise to be approved to address further issues, 1358 starting with the creation and registration of Session IDs. 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 the cryptographic binding 1405 of all other [F3411-19] messages from the same actual current 1406 sender to the UAS ID asserted in the Basic ID message. 1408 GEN-3 Provable Registration: DRIP MUST enable cryptographically 1409 secure verification that the UAS ID is in a registry and 1410 identification of that registry, even on an Observer device 1411 lacking Internet connectivity at the time of observation; 1412 with UAS ID Type 3, the same sender may have multiple IDs, 1413 potentially in different registries, but each ID must clearly 1414 indicate in which registry it can be 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 "contact" requirement allows any party that learns a UAS ID (that 1492 is a DRIP entity identifier rather than another UAS ID Type) to 1493 request establishment of a communications session with the 1494 corresponding UAS RID sender and certain entities associated with 1495 that UAS, but AAA and policy restrictions, _inter alia_ on resolving 1496 the identifier to any locators (typically IP addresses), should 1497 prevent unauthorized parties from distracting or harassing pilots. 1498 Thus some but not all Observers of UA, receivers of Broadcast RID, 1499 clients of Network RID, and other parties can become successfully 1500 initiating endpoints for these sessions. 1502 The "QoS" requirement is only that performance and reliability 1503 parameters can be _specified_ by policy, not that any such 1504 specifications must be guaranteed to be met; any failure to meet such 1505 would be reported under the "management" requirement. Examples of 1506 such parameters are the maximum time interval at which messages 1507 carrying required data elements may be transmitted, the maximum 1508 tolerable rate of loss of such messages, and the maximum tolerable 1509 latency between a dynamic data element (e.g., GNSS position of UA) 1510 being provided to the DRIP sender and that element being delivered by 1511 the DRIP receiver to an application. 1513 The "mobility" requirement refers to rapid geographic mobility of 1514 nodes, changes of their points of attachment to networks, and changes 1515 to their IP addresses; it is not limited to micro-mobility within a 1516 small geographic area or single Internet access provider. 1518 4.2. Identifier 1520 4.2.1. Normative Requirements 1522 ID-1 Length: The DRIP entity identifier MUST NOT be longer than 20 1523 bytes, to fit in the UAS ID field of the Basic ID message of 1524 [F3411-19]. 1526 ID-2 Registry ID: The DRIP identifier MUST be sufficient to identify 1527 a registry in which the entity identified therewith is listed. 1529 ID-3 Entity ID: The DRIP identifier MUST be sufficient to enable 1530 lookups of other data associated with the entity identified 1531 therewith in that registry. 1533 ID-4 Uniqueness: The DRIP identifier MUST be unique within the 1534 applicable global identifier space from when it is first 1535 registered therein until it is explicitly de-registered 1536 therefrom (due to, e.g., expiration after a specified lifetime, 1537 revocation by the registry, or surrender by the operator). 1539 ID-5 Non-spoofability: The DRIP identifier MUST NOT be spoofable 1540 within the context of a minimal Remote ID broadcast message set 1541 (to be specified within DRIP to be sufficient collectively to 1542 prove sender ownership of the claimed identifier). 1544 ID-6 Unlinkability: The DRIP identifier MUST NOT facilitate 1545 adversarial correlation over multiple operations. If this is 1546 accomplished by limiting each identifier to a single use or 1547 brief period of usage, the DRIP identifier MUST support well- 1548 defined, scalable, timely registration methods. 1550 4.2.2. Rationale 1552 The DRIP identifier can refer to various entities. In the primary 1553 initial use case, the entity to be identified is the UA. Entities to 1554 be identified in other likely use cases include but are not limited 1555 to the operator, USS, and Observer. In all cases, the entity 1556 identified must own (have the exclusive capability to use, such that 1557 receivers can verify its ownership of) the identifier. 1559 The DRIP identifier can be used at various layers. In Broadcast RID, 1560 it would be used by the application running directly over the data 1561 link. In Network RID, it would be used by the application running 1562 over HTTPS (not required by DRIP but generally used by Network RID 1563 implementations) and possibly other protocols. In RID initiated V2X 1564 applications such as DAA and C2, it could be used between the network 1565 and transport layers, e.g., with the Host Identity Protocol (HIP, 1566 [RFC4423], [RFC7401], etc.), or between the transport and application 1567 layers, e.g., with Datagram Transport Layer Security (DTLS, 1568 [RFC6347]). 1570 Registry ID (which registry the entity is in) and Entity ID (which 1571 entity it is, within that registry) are requirements on a single DRIP 1572 entity identifier, not separate (types of) ID. In the most common 1573 use case, the entity will be the UA, and the DRIP identifier will be 1574 the UAS ID; however, other entities may also benefit from having DRIP 1575 identifiers, so the entity type is not prescribed here. 1577 Whether a UAS ID is generated by the operator, GCS, UA, USS, 1578 registry, or some collaboration thereamong, is unspecified; however, 1579 there must be agreement on the UAS ID among these entities. 1580 Management of DRIP identifiers is the primary function of their 1581 registration hierarchies, from the root (presumably IANA), through 1582 sector-specific and regional authorities (presumably ICAO and CAAs), 1583 to the identified entities themselves. 1585 While "uniqueness" might be considered an implicit requirement for 1586 any identifier, here the point of the explicit requirement is not 1587 just that it should be unique, but also where and when it should be 1588 unique: global scope within a specified space, from registration to 1589 deregistration. 1591 While "non-spoofability" imposes requirements for and on a DRIP 1592 authentication protocol, it also imposes requirements on the 1593 properties of the identifier itself. An example of how the nature of 1594 the identifier can support non-spoofability is embedding a hash of 1595 both the registry ID and a public key of the entity in the entity 1596 identifier, thus making it self-authenticating any time the entity's 1597 corresponding private key is used to sign a message. 1599 While "unlinkability" is a privacy desideratum (see next section), it 1600 imposes requirements on the DRIP identifier itself, as distinct from 1601 other currently permitted choices for the UAS ID (including primarily 1602 the static serial number of the UA or RID module). 1604 4.3. Privacy 1606 4.3.1. Normative Requirements 1608 PRIV-1 Confidential Handling: DRIP MUST enable confidential handling 1609 of private information (i.e., any and all information 1610 designated by neither cognizant authority nor the information 1611 owner as public, e.g., personal data). 1613 PRIV-2 Encrypted Transport: DRIP MUST enable selective strong 1614 encryption of private data in motion in such a manner that 1615 only authorized actors can recover it. If transport is via 1616 IP, then encryption MUST be end-to-end, at or above the IP 1617 layer. DRIP MUST NOT encrypt safety critical data to be 1618 transmitted over Broadcast RID in any situation where it is 1619 unlikely that local Observers authorized to access the 1620 plaintext will be able to decrypt it or obtain it from a 1621 service able to decrypt it. DRIP MUST NOT encrypt data when/ 1622 where doing so would conflict with applicable regulations or 1623 CAA policies/procedures, i.e., DRIP MUST support configurable 1624 disabling of encryption. 1626 PRIV-3 Encrypted Storage: DRIP SHOULD facilitate selective strong 1627 encryption of private data at rest in such a manner that only 1628 authorized actors can recover it. 1630 PRIV-4 Public/Private Designation: DRIP SHOULD facilitate 1631 designation, by cognizant authorities and information owners, 1632 of which information is public and which is private. By 1633 default, all information required to be transmitted via 1634 Broadcast RID, even when actually sent via Network RID or 1635 stored in registries, is assumed to be public; all other 1636 information held in registries for lookup using the UAS ID is 1637 assumed to be private. 1639 PRIV-5 Pseudonymous Rendezvous: DRIP MAY enable mutual discovery of 1640 and communications among participating UAS operators whose UA 1641 are in 4-D proximity, using the UAS ID without revealing 1642 pilot/operator identity or physical location. 1644 4.3.2. Rationale 1646 Most data to be sent via Broadcast RID or Network RID is public, thus 1647 the "encrypted transport" requirement for private data is selective, 1648 e.g., for the entire payload of the Operator ID Message, but only the 1649 pilot/GCS location fields of the System Message. Safety critical 1650 data includes at least the UA location. Other data also may be 1651 deemed safety critical, e.g., in some jurisdictions the pilot/GCS 1652 location is implied to be safety critical. 1654 UAS have several potential means of assessing the likelihood that 1655 local Observers authorized to access the plaintext will be able to 1656 decrypt it or obtain it from a service able to decrypt it. If the 1657 UAS is not participating in UTM, an Observer would have no means of 1658 obtaining a decryption key or decryption services from a cognizant 1659 USS. If the UAS is participating in UTM, but has lost connectivity 1660 with its USS, then an Observer within visual LOS of the UA is also 1661 unlikely to be able to communicate with that USS (whether due to the 1662 USS being offline or the UAS and Observer being in an area with poor 1663 Internet connectivity). Either of these conditions (UTM non- 1664 participation or USS unreachability) would be known to the UAS. 1666 In some jurisdictions, the configurable enabling and disabling of 1667 encryption may need to be outside the control of the operator. 1668 [FRUR] mandates manufacturers design RID equipment with some degree 1669 of tamper resistance; the preamble and other FAA commentary suggest 1670 this is to reduce the likelihood that an operator, intentionally or 1671 unintentionally, might alter the values of the required data elements 1672 or disable their transmission in the required manner (e.g., as 1673 cleartext). 1675 How information is stored on end systems is out of scope for DRIP. 1676 Encouraging privacy best practices, including end system storage 1677 encryption, by facilitating it with protocol design reflecting such 1678 considerations, is in scope. Similar logic applies to methods for 1679 designating information as public or private. 1681 The privacy requirements above are for DRIP, neither for [F3411-19] 1682 (which requires obfuscation of location to any Network RID subscriber 1683 engaging in wide area surveillance, limits data retention periods, 1684 etc., in the interests of privacy), nor for UAS RID in any specific 1685 jurisdiction (which may have its own regulatory requirements). The 1686 requirements above are also in a sense parameterized: who are the 1687 "authorized actors", how are they designated, how are they 1688 authenticated, etc.? 1690 4.4. Registries 1691 4.4.1. Normative Requirements 1693 REG-1 Public Lookup: DRIP MUST enable lookup, from the UAS ID, of 1694 information designated by cognizant authority as public, and 1695 MUST NOT restrict access to this information based on identity 1696 or role of the party submitting the query. 1698 REG-2 Private Lookup: DRIP MUST enable lookup of private information 1699 (i.e., any and all information in a registry, associated with 1700 the UAS ID, that is designated by neither cognizant authority 1701 nor the information owner as public), and MUST, according to 1702 applicable policy, enforce AAA, including restriction of 1703 access to this information based on identity or role of the 1704 party submitting the query. 1706 REG-3 Provisioning: DRIP MUST enable provisioning registries with 1707 static information on the UAS and its operator, dynamic 1708 information on its current operation within the U-space/UTM 1709 (including means by which the USS under which the UAS is 1710 operating may be contacted for further, typically even more 1711 dynamic, information), and Internet direct contact information 1712 for services related to the foregoing. 1714 REG-4 AAA Policy: DRIP AAA MUST be specifiable by policies; the 1715 definitive copies of those policies must be accessible in 1716 registries; administration of those policies and all DRIP 1717 registries must be protected by AAA. 1719 4.4.2. Rationale 1721 Registries are fundamental to RID. Only very limited information can 1722 be Broadcast, but extended information is sometimes needed. The most 1723 essential element of information sent is the UAS ID itself, the 1724 unique key for lookup of extended information in registries. Beyond 1725 designating the UAS ID as that unique key, the registry information 1726 model is not specified herein, in part because regulatory 1727 requirements for different registries (UAS operators and their UA, 1728 each narrowly for UAS RID and broadly for U-space/UTM) and business 1729 models for meeting those requirements are in flux. While it is 1730 expected that registry functions will be integrated with USS, who 1731 will provide them is not yet determined in most, and is expected to 1732 vary between, jurisdictions. However this evolves, the essential 1733 registry functions, starting with management of identifiers, are 1734 expected to remain the same, so are specified herein. 1736 While most data to be sent via Broadcast or Network RID is public, 1737 much of the extended information in registries will be private. Thus 1738 AAA for registries is essential, not just to ensure that access is 1739 granted only to strongly authenticated, duly authorized parties, but 1740 also to support subsequent attribution of any leaks, audit of who 1741 accessed information when and for what purpose, etc. As specific AAA 1742 requirements will vary by jurisdictional regulation, provider 1743 philosophy, customer demand, etc., they are left to specification in 1744 policies, which should be human readable to facilitate analysis and 1745 discussion, and machine readable to enable automated enforcement, 1746 using a language amenable to both, e.g., XACML. 1748 The intent of the negative and positive access control requirements 1749 on registries is to ensure that no member of the public would be 1750 hindered from accessing public information, while only duly 1751 authorized parties would be enabled to access private information. 1752 Mitigation of Denial of Service attacks and refusal to allow database 1753 mass scraping would be based on those behaviors, not on identity or 1754 role of the party submitting the query _per se_, but querant identity 1755 information might be gathered (by security systems protecting DRIP 1756 implementations) on such misbehavior. 1758 By "Internet direct contact information" is meant a locator (e.g., IP 1759 address), or identifier (e.g., FQDN) that can be resolved to a 1760 locator, which would enable initiation of an end-to-end communication 1761 session using a well known protocol (e.g., SIP). 1763 5. IANA Considerations 1765 This document does not make any IANA request. 1767 6. Security Considerations 1769 DRIP is all about safety and security, so content pertaining to such 1770 is not limited to this section. This document does not define any 1771 protocols, so security considerations of such are speculative. 1772 Potential vulnerabilities of DRIP solutions to these requirements 1773 include but are not limited to: 1775 * Sybil attacks 1777 * confusion created by many spoofed unsigned messages 1779 * processing overload induced by attempting to verify many spoofed 1780 signed messages (where verification will fail but still consume 1781 cycles) 1783 * malicious or malfunctioning registries 1785 * interception by on-path attacker of (i.e., Man In The Middle 1786 attacks on) registration messages 1788 * UA impersonation through private key extraction, improper key 1789 sharing, or carriage of a small (presumably harmless) UA, i.e., as 1790 a "false flag", by a larger (malicious) UA 1792 It may be inferred from the general requirements (Section 4.1) for 1793 provable ownership, provable binding, and provable registration, 1794 together with the identifier requirements (Section 4.2), that DRIP 1795 must provide: 1797 * message integrity 1799 * non-repudiation 1801 * defense against replay attacks 1803 * defense against spoofing 1805 One approach to so doing involves verifiably binding the DRIP 1806 identifier to a public key. Providing these security features, 1807 whether via this approach or another, is likely to be especially 1808 challenging for Observers without Internet connectivity at the time 1809 of observation. For example, checking the signature of a registry on 1810 a public key certificate received via Broadcast RID in a remote area 1811 presumably would require that the registry's public key had been 1812 previously installed on the Observer's device, yet there may be many 1813 registries and the Observer's device may be storage constrained, and 1814 new registries may come on-line subsequent to installation of DRIP 1815 software on the Observer's device. See also Figure 1 and the 1816 associated explanatory text, especially the second paragraph after 1817 the figure. Thus there may be caveats on the extent to which 1818 requirements can be satisfied in such cases, yet strenuous effort 1819 should be made to satisfy them, as such cases, e.g., firefighting in 1820 a national forest, are important. 1822 7. Privacy and Transparency Considerations 1824 Privacy and transparency are important for legal reasons including 1825 regulatory consistency. [EU2018] states "harmonised and 1826 interoperable national registration systems... should comply with the 1827 applicable Union and national law on privacy and processing of 1828 personal data, and the information stored in those registration 1829 systems should be easily accessible." 1831 Privacy and transparency (where essential to security or safety) are 1832 also ethical and moral imperatives. Even in cases where old 1833 practices (e.g., automobile registration plates) could be imitated, 1834 when new applications involving PII (such as UAS RID) are addressed 1835 and newer technologies could enable improving privacy, such 1836 opportunities should not be squandered. Thus it is recommended that 1837 all DRIP work give due regard to [RFC6973] and more broadly 1838 [RFC8280]. 1840 However, privacy and transparency are often conflicting goals, 1841 demanding careful attention to their balance. 1843 DRIP information falls into two classes: that which, to achieve the 1844 purpose, must be published openly as cleartext, for the benefit of 1845 any Observer (e.g., the basic UAS ID itself); and that which must be 1846 protected (e.g., PII of pilots) but made available to properly 1847 authorized parties (e.g., public safety personnel who urgently need 1848 to contact pilots in emergencies). 1850 How properly authorized parties are authorized, authenticated, etc. 1851 are questions that extend beyond the scope of DRIP, but DRIP may be 1852 able to provide support for such processes. Classification of 1853 information as public or private must be made explicit and reflected 1854 with markings, design, etc. Classifying the information will be 1855 addressed primarily in external standards; herein it will be regarded 1856 as a matter for CAA, registry, and operator policies, for which 1857 enforcement mechanisms will be defined within the scope of DRIP WG 1858 and offered. Details of the protection mechanisms will be provided 1859 in other DRIP documents. Mitigation of adversarial correlation will 1860 also be addressed. 1862 8. References 1864 8.1. Normative References 1866 [F3411-19] ASTM International, "Standard Specification for Remote ID 1867 and Tracking", February 2020, 1868 . 1870 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1871 Requirement Levels", BCP 14, RFC 2119, 1872 DOI 10.17487/RFC2119, March 1997, 1873 . 1875 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1876 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1877 May 2017, . 1879 8.2. Informative References 1881 [Amended] European Union Aviation Safety Agency (EASA), "Commission 1882 Delegated Regulation (EU) 2020/1058 of 27 April 2020 1883 amending Delegated Regulation (EU) 2019/945", April 2020, 1884 . 1887 [ASDRI] ASD-STAN, "Introduction to the European UAS Digital Remote 1888 ID Technical Standard", January 2021, . 1892 [CPDLC] Gurtov, A., Polishchuk, T., and M. Wernberg, "Controller- 1893 Pilot Data Link Communication Security", MDPI 1894 Sensors 18(5), 1636, 2018, 1895 . 1897 [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers", 1898 September 2019, . 1901 [Delegated] 1902 European Union Aviation Safety Agency (EASA), "Commission 1903 Delegated Regulation (EU) 2019/945 of 12 March 2019 on 1904 unmanned aircraft systems and on third-country operators 1905 of unmanned aircraft systems", March 2019, 1906 . 1908 [drip-architecture] 1909 Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S., 1910 and A. Gurtov, "Drone Remote Identification Protocol 1911 (DRIP) Architecture", Work in Progress, Internet-Draft, 1912 draft-ietf-drip-arch-11, 23 February 2021, 1913 . 1916 [ENISACSIRT] 1917 European Union Agency for Cybersecurity (ENISA), 1918 "Actionable information for Security Incident Response", 1919 November 2014, . 1923 [EU2018] European Parliament and Council, "2015/0277 (COD) PE-CONS 1924 2/18", February 2018, 1925 . 1928 [FAACONOPS] 1929 FAA Office of NextGen, "UTM Concept of Operations v2.0", 1930 March 2020, . 1933 [FR24] Flightradar24 AB, "Flightradar24 Live Air Traffic", May 1934 2021, . 1936 [FRUR] Federal Aviation Administration, "Remote Identification of 1937 Unmanned Aircraft", January 2021, 1938 . 1942 [GDPR] European Parliament and Council, "General Data Protection 1943 Regulation", April 2016, 1944 . 1946 [I-D.maeurer-raw-ldacs] 1947 Maeurer, N., Graeupl, T., and C. Schmitt, "L-band Digital 1948 Aeronautical Communications System (LDACS)", Work in 1949 Progress, Internet-Draft, draft-maeurer-raw-ldacs-06, 2 1950 October 2020, . 1953 [ICAOATM] International Civil Aviation Organization, "Doc 4444: 1954 Procedures for Air Navigation Services: Air Traffic 1955 Management", November 2016, . 1959 [ICAODEFS] International Civil Aviation Organization, "Defined terms 1960 from the Annexes to the Chicago Convention and ICAO 1961 guidance material", July 2017, 1962 . 1965 [ICAOUAS] International Civil Aviation Organization, "Circular 328: 1966 Unmanned Aircraft Systems", February 2011, 1967 . 1970 [ICAOUTM] International Civil Aviation Organization, "Unmanned 1971 Aircraft Systems Traffic Management (UTM) - A Common 1972 Framework with Core Principles for Global Harmonization, 1973 Edition 3", October 2020, 1974 . 1977 [Implementing] 1978 European Union Aviation Safety Agency (EASA), "Commission 1979 Implementing Regulation (EU) 2019/947 of 24 May 2019 on 1980 the rules and procedures for the operation of unmanned 1981 aircraft", May 2019, 1982 . 1984 [InitialView] 1985 SESAR Joint Undertaking, "Initial view on Principles for 1986 the U-space architecture", July 2019, 1987 . 1991 [NPRM] United States Federal Aviation Administration (FAA), 1992 "Notice of Proposed Rule Making on Remote Identification 1993 of Unmanned Aircraft Systems", December 2019, 1994 . 1998 [OpenDroneID] 1999 Intel Corp., "Open Drone ID", March 2019, 2000 . 2002 [OpenSky] OpenSky Network non-profit association, "The OpenSky 2003 Network", May 2021, 2004 . 2006 [Opinion1] European Union Aviation Safety Agency (EASA), "Opinion No 2007 01/2020: High-level regulatory framework for the U-space", 2008 March 2020, . 2011 [Part107] United States Federal Aviation Administration, "Code of 2012 Federal Regulations Part 107", June 2016, 2013 . 2015 [Recommendations] 2016 FAA UAS Identification and Tracking Aviation Rulemaking 2017 Committee, "UAS ID and Tracking ARC Recommendations Final 2018 Report", September 2017, . 2022 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 2023 Unique IDentifier (UUID) URN Namespace", RFC 4122, 2024 DOI 10.17487/RFC4122, July 2005, 2025 . 2027 [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol 2028 (HIP) Architecture", RFC 4423, DOI 10.17487/RFC4423, May 2029 2006, . 2031 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 2032 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 2033 . 2035 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2036 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2037 January 2012, . 2039 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 2040 Morris, J., Hansen, M., and R. Smith, "Privacy 2041 Considerations for Internet Protocols", RFC 6973, 2042 DOI 10.17487/RFC6973, July 2013, 2043 . 2045 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 2046 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 2047 RFC 7401, DOI 10.17487/RFC7401, April 2015, 2048 . 2050 [RFC8280] ten Oever, N. and C. Cath, "Research into Human Rights 2051 Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280, 2052 October 2017, . 2054 [Roadmap] American National Standards Institute (ANSI) Unmanned 2055 Aircraft Systems Standardization Collaborative (UASSC), 2056 "Standardization Roadmap for Unmanned Aircraft Systems 2057 draft v2.0", April 2020, . 2061 [Stranger] Heinlein, R.A., "Stranger in a Strange Land", June 1961. 2063 [WG105] EUROCAE, "WG-105 draft ED-282 Minimum Operational 2064 Performance Standards (MOPS) for Unmanned Aircraft System 2065 (UAS) Electronic Identification", June 2020. 2067 [WiFiNAN] Wi-Fi Alliance, "Wi-Fi Aware™ Specification Version 3.2", 2068 October 2020, . 2071 Appendix A. Discussion and Limitations 2073 This document is largely based on the process of one SDO, ASTM. 2074 Therefore, it is tailored to specific needs and data formats of this 2075 standard. Other organizations, for example in EU, do not necessarily 2076 follow the same architecture. 2078 The need for drone ID and operator privacy is an open discussion 2079 topic. For instance, in the ground vehicular domain each car carries 2080 a publicly visible plate number. In some countries, for nominal cost 2081 or even for free, anyone can resolve the identity and contact 2082 information of the owner. Civil commercial aviation and maritime 2083 industries also have a tradition of broadcasting plane or ship ID, 2084 coordinates, and even flight plans in plain text. Community networks 2085 such as OpenSky [OpenSky] and Flightradar24 [FR24] use this open 2086 information through ADS-B to deploy public services of flight 2087 tracking. Many researchers also use these data to perform 2088 optimization of routes and airport operations. Such ID information 2089 should be integrity protected, but not necessarily confidential. 2091 In civil aviation, aircraft identity is broadcast by a device known 2092 as transponder. It transmits a four octal digit squawk code, which 2093 is assigned by a traffic controller to an airplane after approving a 2094 flight plan. There are several reserved codes such as 7600 which 2095 indicate radio communication failure. The codes are unique in each 2096 traffic area and can be re-assigned when entering another control 2097 area. The code is transmitted in plain text by the transponder and 2098 also used for collision avoidance by a system known as Traffic alert 2099 and Collision Avoidance System (TCAS). The system could be used for 2100 UAS as well initially, but the code space is quite limited and likely 2101 to be exhausted soon. The number of UAS far exceeds the number of 2102 civil airplanes in operation. 2104 The ADS-B system is utilized in civil aviation for each "ADS-B Out" 2105 equipped airplane to broadcast its ID, coordinates, and altitude for 2106 other airplanes and ground control stations. If this system is 2107 adopted for drone IDs, it has additional benefit with backward 2108 compatibility with civil aviation infrastructure; then, pilots and 2109 dispatchers will be able to see UA on their control screens and take 2110 those into account. If not, a gateway translation system between the 2111 proposed drone ID and civil aviation system should be implemented. 2112 Again, system saturation due to large numbers of UAS is a concern. 2114 The Mode S transponders used in all TCAS and most ADS-B Out 2115 installations are assigned an ICAO 24 bit "address" (arguably really 2116 an identifier rather than a locator) that is associated with the 2117 aircraft as part of its registration. In the US alone, well over 2118 2^20 UAS are already flying; thus, a 24 bit space likely would be 2119 rapidly exhausted if used for UAS (other than large UAS flying in 2120 controlled airspace, especially internationally, under rules other 2121 than those governing small UAS at low altitudes). 2123 Wi-Fi and Bluetooth are two wireless technologies currently 2124 recommended by ASTM specifications due to their widespread use and 2125 broadcast nature. However, those have limited range (max 100s of 2126 meters) and may not reliably deliver UAS ID at high altitude or 2127 distance. Therefore, a study should be made of alternative 2128 technologies from the telecom domain (WiMAX / IEEE 802.16, 5G) or 2129 sensor networks (Sigfox, LoRa). Such transmission technologies can 2130 impose additional restrictions on packet sizes and frequency of 2131 transmissions, but could provide better energy efficiency and range. 2133 In civil aviation, Controller-Pilot Data Link Communications (CPDLC) 2134 is used to transmit command and control between the pilots and ATC. 2135 It could be considered for UAS as well due to long range and proven 2136 use despite its lack of security [CPDLC]. 2138 L-band Digital Aeronautical Communications System (LDACS) is being 2139 standardized by ICAO and IETF for use in future civil aviation 2140 [I-D.maeurer-raw-ldacs]. It provides secure communication, 2141 positioning, and control for aircraft using a dedicated radio band. 2142 It should be analyzed as a potential provider for UAS RID as well. 2143 This will bring the benefit of a global integrated system creating a 2144 global airspace use awareness. 2146 Acknowledgments 2148 The work of the FAA's UAS Identification and Tracking (UAS ID) 2149 Aviation Rulemaking Committee (ARC) is the foundation of later ASTM 2150 [F3411-19] and IETF DRIP efforts. The work of Gabriel Cox, Intel 2151 Corp., and their Open Drone ID collaborators opened UAS RID to a 2152 wider community. The work of ASTM F38.02 in balancing the interests 2153 of diverse stakeholders is essential to the necessary rapid and 2154 widespread deployment of UAS RID. IETF volunteers who have 2155 extensively reviewed or otherwise contributed to this document 2156 include Amelia Andersdotter, Carsten Bormann, Toerless Eckert, Susan 2157 Hares, Mika Jarvenpaa, Alexandre Petrescu, Saulo Da Silva and Shuai 2158 Zhao. Thanks to Linda Dunbar for the Secdir review, Nagendra Nainar 2159 for the Opsdir review and Suresh Krishnan for the Gen-ART review. 2160 Thanks to IESG members Roman Danyliw, Erik Kline, Murray Kucherawy 2161 and Robert Wilton for helpful and positive comments. Thanks to 2162 chairs Daniel Migault and Mohamed Boucadair for direction of our team 2163 of authors and editor, some of whom are newcomers to writing IETF 2164 documents. Thanks especially to Internet Area Director Eric Vyncke 2165 for guidance and support. 2167 Authors' Addresses 2169 Stuart W. Card (editor) 2170 AX Enterprize 2171 4947 Commercial Drive 2172 Yorkville, NY 13495 2173 United States of America 2175 Email: stu.card@axenterprize.com 2177 Adam Wiethuechter 2178 AX Enterprize 2179 4947 Commercial Drive 2180 Yorkville, NY 13495 2181 United States of America 2183 Email: adam.wiethuechter@axenterprize.com 2185 Robert Moskowitz 2186 HTT Consulting 2187 Oak Park, MI 48237 2188 United States of America 2190 Email: rgm@labs.htt-consult.com 2192 Andrei Gurtov 2193 Linköping University 2194 IDA 2195 SE-58183 Linköping 2196 Sweden 2198 Email: gurtov@acm.org