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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (17 May 2022) is 703 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'L' is mentioned on line 668, but not defined ** Downref: Normative reference to an Informational RFC: RFC 8032 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DRIP R. Moskowitz 3 Internet-Draft HTT Consulting 4 Updates: 7401, 7343 (if approved) S. Card 5 Intended status: Standards Track A. Wiethuechter 6 Expires: 18 November 2022 AX Enterprize, LLC 7 A. Gurtov 8 Linköping University 9 17 May 2022 11 DRIP Entity Tag (DET) for Unmanned Aircraft System Remote ID (UAS RID) 12 draft-ietf-drip-rid-28 14 Abstract 16 This document describes the use of Hierarchical Host Identity Tags 17 (HHITs) as self-asserting IPv6 addresses and thereby a trustable 18 identifier for use as the Unmanned Aircraft System Remote 19 Identification and tracking (UAS RID). 21 This document updates RFC7401 and RFC7343. 23 Within the context of RID, HHITs will be called DRIP Entity Tags 24 (DETs). HHITs self-attest to the included explicit hierarchy that 25 provides registry (via, e.g., DNS, EPP) discovery for 3rd-party 26 identifier attestation. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on 18 November 2022. 45 Copyright Notice 47 Copyright (c) 2022 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 52 license-info) in effect on the date of publication of this document. 53 Please review these documents carefully, as they describe your rights 54 and restrictions with respect to this document. Code Components 55 extracted from this document must include Revised BSD License text as 56 described in Section 4.e of the Trust Legal Provisions and are 57 provided without warranty as described in the Revised BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. HHIT Statistical Uniqueness different from UUID or X.509 63 Subject . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4 65 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4 66 2.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 4 67 2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4 68 3. The Hierarchical Host Identity Tag (HHIT) . . . . . . . . . . 6 69 3.1. HHIT Prefix for RID Purposes . . . . . . . . . . . . . . 7 70 3.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 7 71 3.2.1. HDA custom HIT Suite IDs . . . . . . . . . . . . . . 8 72 3.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 8 73 3.3.1. The Registered Assigning Authority (RAA) . . . . . . 8 74 3.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 9 75 3.4. Edward-Curve Digital Signature Algorithm for HHITs . . . 10 76 3.4.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . 10 77 3.4.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . 11 78 3.5. ORCHIDs for Hierarchical HITs . . . . . . . . . . . . . . 12 79 3.5.1. Adding Additional Information to the ORCHID . . . . . 12 80 3.5.2. ORCHID Encoding . . . . . . . . . . . . . . . . . . . 14 81 3.5.3. ORCHID Decoding . . . . . . . . . . . . . . . . . . . 15 82 3.5.4. Decoding ORCHIDs for HIPv2 . . . . . . . . . . . . . 15 83 4. Hierarchical HITs as DRIP Entity Tags . . . . . . . . . . . . 15 84 4.1. Nontransferablity of DETs . . . . . . . . . . . . . . . . 16 85 4.2. Encoding HHITs in CTA 2063-A Serial Numbers . . . . . . . 16 86 4.3. Remote ID DET as one Class of Hierarchical HITs . . . . . 17 87 4.4. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 18 88 4.5. DRIP Entity Tag (DET) Registry . . . . . . . . . . . . . 18 89 4.6. Remote ID Authentication using DETs . . . . . . . . . . . 18 90 5. DRIP Entity Tags (DETs) in DNS . . . . . . . . . . . . . . . 19 91 6. Other UAS Traffic Management (UTM) Uses of HHITs Beyond 92 DET . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 93 7. Summary of Addressed DRIP Requirements . . . . . . . . . . . 20 94 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 95 8.1. New Well-Known IPv6 prefix for DETs . . . . . . . . . . . 20 96 8.2. New IANA DRIP Registry . . . . . . . . . . . . . . . . . 21 97 8.3. IANA CGA Registry Update . . . . . . . . . . . . . . . . 22 98 8.4. IANA HIP Registry Updates . . . . . . . . . . . . . . . . 22 99 8.5. IANA IPSECKEY Registry Update . . . . . . . . . . . . . . 23 100 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 101 9.1. Post Quantum Computing out of scope . . . . . . . . . . . 25 102 9.2. DET Trust in ASTM messaging . . . . . . . . . . . . . . . 25 103 9.3. DET Revocation . . . . . . . . . . . . . . . . . . . . . 26 104 9.4. Privacy Considerations . . . . . . . . . . . . . . . . . 26 105 9.5. Collision Risks with DETs . . . . . . . . . . . . . . . . 27 106 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 107 10.1. Normative References . . . . . . . . . . . . . . . . . . 27 108 10.2. Informative References . . . . . . . . . . . . . . . . . 28 109 Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 31 110 Appendix B. The 14/14 HID split . . . . . . . . . . . . . . . . 32 111 Appendix C. Calculating Collision Probabilities . . . . . . . . 33 112 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34 113 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 115 1. Introduction 117 Drone Remote ID Protocol (DRIP) Requirements [RFC9153] describe an 118 Unmanned Aircraft System Remote ID (UAS ID) as unique (ID-4), non- 119 spoofable (ID-5), and identify a registry where the ID is listed (ID- 120 2); all within a 19-character identifier (ID-1). 122 This document describes (per Section 3 of [drip-architecture]) the 123 use of Hierarchical Host Identity Tags (HHITs) (Section 3) as self- 124 asserting IPv6 addresses and thereby a trustable identifier for use 125 as the UAS Remote ID. HHITs add explicit hierarchy to the 128-bit 126 HITs, enabling DNS HHIT queries (Host ID for authentication, e.g., 127 [drip-authentication]) and for Extensible Provisioning Protocol (EPP) 128 Registrar discovery [RFC9224] for 3rd-party identification 129 attestation (e.g., [drip-authentication]). 131 This addition of hierarchy to HITs is an extension to [RFC7401] and 132 requires an update to [RFC7343]. As this document also adds EdDSA 133 (Section 3.4) for Host Identities (HIs), a number of Host Identity 134 Protocol (HIP) parameters in [RFC7401] are updated, but these should 135 not be needed in a DRIP implementation that does not use HIP. 137 HHITs as used within the context of Unmanned Aircraft System (UAS) 138 are labeled as DRIP Entity Tags (DETs). Throughout this document 139 HHIT and DET will be used appropriately. HHIT will be used when 140 covering the technology, and DET for their context within UAS RID. 142 Hierarchical HITs provide self-attestation of the HHIT registry. A 143 HHIT can only be in a single registry within a registry system (e.g., 144 EPP and DNS). 146 Hierarchical HITs are valid, though non-routable, IPv6 addresses 147 [RFC8200]. As such, they fit in many ways within various IETF 148 technologies. 150 1.1. HHIT Statistical Uniqueness different from UUID or X.509 Subject 152 HHITs are statistically unique through the cryptographic hash feature 153 of second-preimage resistance. The cryptographically-bound addition 154 of the hierarchy and a HHIT registration process [drip-registries] 155 provide complete, global HHIT uniqueness. If the HHITs cannot be 156 looked up with services provided by the registrar identified via the 157 embedded hierarchical information or its registration validated by 158 registration attestations messages [drip-authentication], then the 159 HHIT is either fraudulent or revoked/expired. In-depth discussion of 160 these processes are out of scope for this document. 162 This contrasts with using general identifiers (e.g., a Universally 163 Unique IDentifiers (UUID) [RFC4122] or device serial numbers as the 164 subject in an X.509 [RFC5280] certificate. In either case, there can 165 be no unique proof of ownership/registration. 167 For example, in a multi-Certificate Authority (multi-CA) PKI 168 alternative to HHITs, a Remote ID as the Subject (Section 4.1.2.6 of 169 [RFC5280]) can occur in multiple CAs, possibly fraudulently. CAs 170 within the PKI would need to implement an approach to enforce 171 assurance of the uniqueness achieved with HHITs. 173 2. Terms and Definitions 175 2.1. Requirements Terminology 177 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 178 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 179 "OPTIONAL" in this document are to be interpreted as described in BCP 180 14 [RFC2119] [RFC8174] when, and only when, they appear in all 181 capitals, as shown here. 183 2.2. Notations 185 | Signifies concatenation of information - e.g., X | Y is the 186 concatenation of X and Y. 188 2.3. Definitions 190 This document uses the terms defined in Section 2.2 of [RFC9153]. 191 The following new terms are used in the document: 193 cSHAKE (The customizable SHAKE function [NIST.SP.800-185]): 194 Extends the SHAKE [NIST.FIPS.202] scheme to allow users to 195 customize their use of the SHAKE function. 197 HDA (HHIT Domain Authority): 198 The 14-bit field that identifies the HHIT Domain Authority under a 199 Registered Assigning Authority (RAA). See Figure 1. 201 HHIT 202 Hierarchical Host Identity Tag. A HIT with extra hierarchical 203 information not found in a standard HIT [RFC7401]. 205 HI 206 Host Identity. The public key portion of an asymmetric key pair 207 as defined in [RFC9063]. 209 HID (Hierarchy ID): 210 The 28-bit field providing the HIT Hierarchy ID. See Figure 1. 212 HIP (Host Identity Protocol) 213 The origin [RFC7401] of HI, HIT, and HHIT. 215 HIT 216 Host Identity Tag. A 128-bit handle on the HI. HITs are valid 217 IPv6 addresses. 219 Keccak (KECCAK Message Authentication Code): 220 The family of all sponge functions with a KECCAK-f permutation as 221 the underlying function and multi-rate padding as the padding 222 rule. It refers in particular to all the functions referenced 223 from [NIST.FIPS.202] and [NIST.SP.800-185]. 225 KMAC (KECCAK Message Authentication Code [NIST.SP.800-185]): 226 A Pseudo Random Function (PRF) and keyed hash function based on 227 KECCAK. 229 RAA (Registered Assigning Authority): 230 The 14-bit field identifying the business or organization that 231 manages a registry of HDAs. See Figure 1. 233 RVS (Rendezvous Server): 234 A Rendezvous Server such as the HIP Rendezvous Server for enabling 235 mobility, as defined in [RFC8004]. 237 SHAKE (Secure Hash Algorithm KECCAK [NIST.FIPS.202]): 238 A secure hash that allows for an arbitrary output length. 240 XOF (eXtendable-Output Function [NIST.FIPS.202]): 241 A function on bit strings (also called messages) in which the 242 output can be extended to any desired length. 244 3. The Hierarchical Host Identity Tag (HHIT) 246 The Hierarchical HIT (HHIT) is a small but important enhancement over 247 the flat Host Identity Tag (HIT) space, constructed as an Overlay 248 Routable Cryptographic Hash IDentifier (ORCHID) [RFC7343]. By adding 249 two levels of hierarchical administration control, the HHIT provides 250 for device registration/ownership, thereby enhancing the trust 251 framework for HITs. 253 The 128-bit HHITs represent the HI in only a 64-bit hash, rather than 254 the 96 bits in HITs. 4 of these 32 freed up bits expand the Suite ID 255 to 8 bits, and the other 28 bits are used to create a hierarchical 256 administration organization for HIT domains. Hierarchical HIT 257 construction is defined in Section 3.5. The input values for the 258 Encoding rules are described in Section 3.5.1. 260 A HHIT is built from the following fields (Figure 1): 262 * p = an IPV6 prefix (max 28 bit) 264 * 28-bit Hierarchy ID (HID) which provides the structure to organize 265 HITs into administrative domains. HIDs are further divided into 266 two fields: 268 - 14-bit Registered Assigning Authority (RAA) (Section 3.3.1) 270 - 14-bit Hierarchical HIT Domain Authority (HDA) (Section 3.3.2) 272 * 8-bit HHIT Suite ID (HHSI) 274 * ORCHID hash (92 - prefix length, e.g., 64) See Section 3.5 for 275 more details. 277 14 bits| 14 bits 8 bits 278 +-------+-------+ +--------------+ 279 | RAA | HDA | |HHIT Suite ID | 280 +-------+-------+ +--------------+ 281 \ | ____/ ___________/ 282 \ \ _/ ___/ 283 \ \/ / 284 | p bits | 28 bits |8bits| o=92-p bits | 285 +--------------+------------+-----+------------------------+ 286 | IPV6 Prefix | HID |HHSI | ORCHID hash | 287 +--------------+------------+-----+------------------------+ 288 Figure 1: HHIT Format 290 The Context ID (generated with openssl rand) for the ORCHID hash is: 292 Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40 294 Context IDs are allocated out of the namespace introduced for 295 Cryptographically Generated Addresses (CGA) Type Tags [RFC3972]. 297 3.1. HHIT Prefix for RID Purposes 299 The IPv6 HHIT prefix MUST be distinct from that used in the flat- 300 space HIT as allocated in [RFC7343]. Without this distinct prefix, 301 the first 4 bits of the RAA would be interpreted as the HIT Suite ID 302 per HIPv2 [RFC7401]. 304 Initially, for DET use, one 28-bit prefix should be assigned out of 305 the IANA IPv6 Special Purpose Address Block ([RFC6890]). 307 HHIT Use Bits Value 308 DET 28 TBD6 (suggested value 2001:30::/28) 310 Other prefixes may be added in the future either for DET use or other 311 applications of HHITs. For a prefix to be added to the registry in 312 Section 8.2, its usage and HID allocation process have to be publicly 313 available. 315 3.2. HHIT Suite IDs 317 The HHIT Suite IDs specify the HI and hash algorithms. These are a 318 superset of the 4/8-bit HIT Suite ID as defined in Section 5.2.10 of 319 [RFC7401]. 321 The HHIT values of 1 - 15 map to the basic 4-bit HIT Suite IDs. HHIT 322 values of 17 - 31 map to the extended 8-bit HIT Suite IDs. HHIT 323 values unique to HHIT will start with value 32. 325 As HHIT introduces a new Suite ID, EdDSA/cSHAKE128, and since this is 326 of value to HIPv2, it will be allocated out of the 4-bit HIT space 327 and result in an update to HIT Suite IDs. Future HHIT Suite IDs may 328 be allocated similarly, or may come out of the additional space made 329 available by going to 8 bits. 331 The following HHIT Suite IDs are defined: 333 HHIT Suite Value 334 RESERVED 0 335 RSA,DSA/SHA-256 1 [RFC7401] 336 ECDSA/SHA-384 2 [RFC7401] 337 ECDSA_LOW/SHA-1 3 [RFC7401] 338 EdDSA/cSHAKE128 TBD3 (suggested value 5) (RECOMMENDED) 340 3.2.1. HDA custom HIT Suite IDs 342 Support for 8-bit HHIT Suite IDs allows for HDA custom HIT Suite IDs. 343 These will be assigned values greater than 15 as follows: 345 HHIT Suite Value 346 HDA Private Use 1 TBD4 (suggested value 254) 347 HDA Private Use 2 TBD5 (suggested value 255) 349 These custom HIT Suite IDs, for example, may be used for large-scale 350 experimenting with post quantum computing hashes or similar domain 351 specific needs. Note that currently there is no support for domain- 352 specific HI algorithms. 354 They should not be used to create a "de facto standardization". 355 Section 8.2 states that additional Suite IDs can be made through IETF 356 Review. 358 3.3. The Hierarchy ID (HID) 360 The Hierarchy ID (HID) provides the structure to organize HITs into 361 administrative domains. HIDs are further divided into two fields: 363 * 14-bit Registered Assigning Authority (RAA) 365 * 14-bit Hierarchical HIT Domain Authority (HDA) 367 The rationale for the 14/14 HID split is described in Appendix B. 369 The two levels of hierarchy allows for CAAs to have it least one RAA 370 for their National Air Space (NAS). Within its RAA(s), the CAAs can 371 delegate HDAs as needed. There may be other RAAs allowed to operate 372 within a given NAS; this is a policy decision of each CAA. 374 3.3.1. The Registered Assigning Authority (RAA) 376 An RAA is a business or organization that manages a registry of HDAs. 377 For example, the Federal Aviation Authority (FAA) or Japan Civil 378 Aviation Bureau (JCAB) could be an RAA. 380 The RAA is a 14-bit field (16,384 RAAs). The management of this 381 space is further elaborated in [drip-registries]. An RAA MUST 382 provide a set of services to allocate HDAs to organizations. It 383 SHOULD have a public policy on what is necessary to obtain an HDA. 384 The RAA need not maintain any HIP related services. It MUST maintain 385 a DNS zone minimally for discovering HIP RVS servers for the HID. 386 The zone delegation is also covered in [drip-registries]. 388 As DETs under an administrative control may be used in many different 389 domains (e.g., commercial, recreation, military), RAAs should be 390 allocated in blocks (e.g. 16-19) with consideration on the likely 391 size of a particular usage. Alternatively, different prefixes can be 392 used to separate different domains of use of HHITs. 394 The RAA DNS zone within the UAS DNS tree may be a PTR for its RAA. 395 It may be a zone in an HHIT specific DNS zone. Assume that the RAA 396 is decimal 100. The PTR record could be constructed as follows: 398 100.hhit.arpa IN PTR raa.example.com. 400 Note that if the zone hhit.arpa is ultimately used, some registrar 401 will need to manage this for all HHIT applications. Thus further 402 thought will be needed in the actual zone tree and registration 403 process [drip-registries]. 405 3.3.2. The Hierarchical HIT Domain Authority (HDA) 407 An HDA may be an Internet Service Provider (ISP), UAS Service 408 Supplier (USS), or any third party that takes on the business to 409 provide UAS services management, HIP RVSs or other needed services 410 such as those required for HHIT and/or HIP-enabled devices. 412 The HDA is a 14-bit field (16,384 HDAs per RAA) assigned by an RAA is 413 further elaborated in [drip-registries]. An HDA must maintain public 414 and private UAS registration information and should maintain a set of 415 RVS servers for UAS clients that may use HIP. How this is done and 416 scales to the potentially millions of customers are outside the scope 417 of this document, though covered in [drip-registries]. This service 418 should be discoverable through the DNS zone maintained by the HDA's 419 RAA. 421 An RAA may assign a block of values to an individual organization. 422 This is completely up to the individual RAA's published policy for 423 delegation. Such policy is out of scope. 425 3.4. Edward-Curve Digital Signature Algorithm for HHITs 427 The Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] is 428 specified here for use as HIs per HIPv2 [RFC7401]. 430 The intent in this document is to add EdDSA as a HI algorithm for 431 DETs, but doing so impacts the HIP parameters used in a HIP exchange. 432 The subsections of this section document the required updates of HIP 433 parameters. Other than the HIP DNS RR (Resource Record), these 434 should not be needed in a DRIP implementation that does not use HIP. 436 See Section 3.2 for use of the HIT Suite in the context of DRIP. 438 3.4.1. HOST_ID 440 The HOST_ID parameter specifies the public key algorithm, and for 441 elliptic curves, a name. The HOST_ID parameter is defined in 442 Section 5.2.9 of [RFC7401]. 444 Algorithm 445 profiles Values 447 EdDSA TBD1 (suggested value 13) [RFC8032] (RECOMMENDED) 449 3.4.1.1. HIP Parameter support for EdDSA 451 The addition of EdDSA as a HI algorithm requires a subfield in the 452 HIP HOST_ID parameter (Section 5.2.9 of [RFC7401]) as was done for 453 ECDSA when used in a HIP exchange. 455 For HIP hosts that implement EdDSA as the algorithm, the following 456 EdDSA curves are represented by the following fields: 458 0 1 2 3 459 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | EdDSA Curve | NULL / 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 / Public Key | 464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 466 EdDSA Curve Curve label 467 Public Key Represented in Octet-string format [RFC8032] 469 Figure 2 471 For hosts that implement EdDSA as a HIP algorithm the following EdDSA 472 curves are required: 474 Algorithm Curve Values 476 EdDSA RESERVED 0 477 EdDSA EdDSA25519 1 [RFC8032] (RECOMMENDED) 478 EdDSA EdDSA25519ph 2 [RFC8032] 479 EdDSA EdDSA448 3 [RFC8032] (RECOMMENDED) 480 EdDSA EdDSA448ph 4 [RFC8032] 482 3.4.1.2. HIP DNS RR support for EdDSA 484 The HIP DNS RR is defined in [RFC8005]. It uses the values defined 485 for the 'Algorithm Type' of the IPSECKEY RR [RFC4025] for its PK 486 Algorithm field. 488 The new EdDSA HI uses [RFC8080] for the IPSECKEY RR encoding: 490 Value Description 492 TBD2 (suggested value 4) 493 An EdDSA key is present, in the format defined in [RFC8080] 495 3.4.2. HIT_SUITE_LIST 497 The HIT_SUITE_LIST parameter contains a list of the supported HIT 498 suite IDs of the HIP Responder. Based on the HIT_SUITE_LIST, the HIP 499 Initiator can determine which source HIT Suite IDs are supported by 500 the Responder. The HIT_SUITE_LIST parameter is defined in 501 Section 5.2.10 of [RFC7401]. 503 The following HIT Suite ID is defined: 505 HIT Suite Value 506 EdDSA/cSHAKE128 TBD3 (suggested value 5) (RECOMMENDED) 508 Table 1 provides more detail on the above HIT Suite combination. 510 The output of cSHAKE128 is variable per the needs of a specific 511 ORCHID construction. It is at most 96 bits long and is directly used 512 in the ORCHID (without truncation). 514 +=======+===========+=========+===========+====================+ 515 | Index | Hash | HMAC | Signature | Description | 516 | | function | | algorithm | | 517 | | | | family | | 518 +=======+===========+=========+===========+====================+ 519 | 5 | cSHAKE128 | KMAC128 | EdDSA | EdDSA HI hashed | 520 | | | | | with cSHAKE128, | 521 | | | | | output is variable | 522 +-------+-----------+---------+-----------+--------------------+ 524 Table 1: HIT Suites 526 3.5. ORCHIDs for Hierarchical HITs 528 This section improves on ORCHIDv2 [RFC7343] with three enhancements: 530 * Optional "Info" field between the Prefix and OGA ID. 532 * Increased flexibility on the length of each component in the 533 ORCHID construction, provided the resulting ORCHID is 128 bits. 535 * Use of cSHAKE, NIST SP 800-185 [NIST.SP.800-185], for the hashing 536 function. 538 The Keccak [Keccak] based cSHAKE XOF hash function is a variable 539 output length hash function. As such it does not use the truncation 540 operation that other hashes need. The invocation of cSHAKE specifies 541 the desired number of bits in the hash output. Further, cSHAKE has a 542 parameter 'S' as a customization bit string. This parameter will be 543 used for including the ORCHID Context Identifier in a standard 544 fashion. 546 This ORCHID construction includes the fields in the ORCHID in the 547 hash to protect them against substitution attacks. It also provides 548 for inclusion of additional information, in particular the 549 hierarchical bits of the Hierarchical HIT, in the ORCHID generation. 550 This should be viewed as an update to ORCHIDv2 [RFC7343], as it can 551 produce ORCHIDv2 output. 553 3.5.1. Adding Additional Information to the ORCHID 555 ORCHIDv2 [RFC7343] is defined as consisting of three components: 557 ORCHID := Prefix | OGA ID | Encode_96( Hash ) 559 where: 561 Prefix : A constant 28-bit-long bitstring value 562 (IPV6 prefix) 564 OGA ID : A 4-bit long identifier for the Hash_function 565 in use within the specific usage context. When 566 used for HIT generation this is the HIT Suite ID. 568 Encode_96( ) : An extraction function in which output is obtained 569 by extracting the middle 96-bit-long bitstring 570 from the argument bitstring. 572 The new ORCHID function is as follows: 574 ORCHID := Prefix (p) | Info (n) | OGA ID (o) | Hash (m) 576 where: 578 Prefix (p) : An IPv6 prefix of length p (max 28-bit-long). 580 Info (n) : n bits of information that define a use of the 581 ORCHID. 'n' can be zero, that is no additional 582 information. 584 OGA ID (o) : A 4- or 8-bit long identifier for the Hash_function 585 in use within the specific usage context. When 586 used for HIT generation this is the HIT Suite ID. 587 When used for HHIT generation this is the 588 HHIT Suite ID. 590 Hash (m) : An extraction function in which output is 'm' bits. 592 p + n + o + m = 128 bits 594 The ORCHID length MUST be 128 bits. With a 28-bit IPv6 prefix, the 595 remaining 100 bits can be divided in any manner between the 596 additional information ("Info"), OGA ID, and the hash output. Care 597 must be considering the size of the hash portion, taking into account 598 risks like pre-image attacks. 64 bits, as used in Hierarchical HITs 599 may be as small as is acceptable. The size of 'n' is determined as 600 what is left; in the case of the 8-bit OGA used for HHIT, this is 28 601 bits. 603 3.5.2. ORCHID Encoding 605 This update adds a different encoding process to that currently used 606 in ORCHIDv2. The input to the hash function explicitly includes all 607 the header content plus the Context ID. The header content consists 608 of the Prefix, the Additional Information ("Info"), and OGA ID (HIT 609 Suite ID). Secondly, the length of the resulting hash is set by sum 610 of the length of the ORCHID header fields. For example, a 28-bit 611 prefix with 28 bits for the HID and 8 bits for the OGA ID leaves 64 612 bits for the hash length. 614 To achieve the variable length output in a consistent manner, the 615 cSHAKE hash is used. For this purpose, cSHAKE128 is appropriate. 616 The cSHAKE function call for this update is: 618 cSHAKE128(Input, L, "", Context ID) 620 Input := Prefix | Additional Information | OGA ID | HOST_ID 621 L := Length in bits of hash portion of ORCHID 623 For full Suite ID support (those that use fixed length hashes like 624 SHA256), the following hashing can be used (Note: this does not 625 produce output Identical to ORCHIDv2 for a /28 prefix and Additional 626 Information of zero-length): 628 Hash[L](Context ID | Input) 630 Input := Prefix | Additional Information | OGA ID | HOST_ID 631 L := Length in bits of hash portion of ORCHID 633 Hash[L] := An extraction function in which output is obtained 634 by extracting the middle L-bit-long bitstring 635 from the argument bitstring. 637 Hierarchical HITs use the Context ID defined in Section 3. 639 3.5.2.1. Encoding ORCHIDs for HIPv2 641 This section discusses how to provide backwards compatibility for 642 ORCHIDv2 [RFC7343] as used in HIPv2 [RFC7401]. 644 For HIPv2, the Prefix is 2001:20::/28 (Section 6 of [RFC7343]). 645 'Info' is zero-length (i.e., not included), and OGA ID is 4-bit. 646 Thus, the HI Hash is 96-bit length. Further, the Prefix and OGA ID 647 are not included in the hash calculation. Thus, the following ORCHID 648 calculations for fixed output length hashes are used: 650 Hash[L](Context ID | Input) 652 Input := HOST_ID 653 L := 96 654 Context ID := 0xF0EF F02F BFF4 3D0F E793 0C3C 6E61 74EA 656 Hash[L] := An extraction function in which output is obtained 657 by extracting the middle L-bit-long bitstring 658 from the argument bitstring. 660 For variable output length hashes use: 662 Hash[L](Context ID | Input) 664 Input := HOST_ID 665 L := 96 666 Context ID := 0xF0EF F02F BFF4 3D0F E793 0C3C 6E61 74EA 668 Hash[L] := The L-bit output from the hash function 670 Then, the ORCHID is constructed as follows: 672 Prefix | OGA ID | Hash Output 674 3.5.3. ORCHID Decoding 676 With this update, the decoding of an ORCHID is determined by the 677 Prefix and OGA ID. ORCHIDv2 [RFC7343] decoding is selected when the 678 Prefix is: 2001:20::/28. 680 For Hierarchical HITs, the decoding is determined by the presence of 681 the HHIT Prefix as specified in Section 8.2. 683 3.5.4. Decoding ORCHIDs for HIPv2 685 This section is included to provide backwards compatibility for 686 ORCHIDv2 [RFC7343] as used for HIPv2 [RFC7401]. 688 HITs are identified by a Prefix of 2001:20::/28. The next 4 bits are 689 the OGA ID. The remaining 96 bits are the HI Hash. 691 4. Hierarchical HITs as DRIP Entity Tags 693 HHITs for UAS ID (called, DETs) use the new EdDSA/SHAKE128 HIT suite 694 defined in Section 3.4 (GEN-2 in [RFC9153]). This hierarchy, 695 cryptographically bound within the HHIT, provides the information for 696 finding the UA's HHIT registry (ID-3 in [RFC9153]). 698 The 2022 forthcoming updated release of ASTM Standard Specification 699 for Remote ID and Tracking [F3411] adds support for DETs. This is 700 within the UAS ID type 4, "Specific Session ID (SSI)". 702 Note to RFC Editor: This, and all references to F3411 need to be 703 updated to this new version which is in final ASTM editing. A new 704 link and replacement text will be provided when it is published. 706 The original UAS ID Types 1 - 3 allow for an UAS ID with a maximum 707 length of 20 bytes, this new SSI (Type 4) uses the first byte of the 708 ID for the SSI Type, thus restricting the UAS ID of this type to a 709 maximum of 19 bytes. The SSI Types initially assigned are: 711 ID 1 IETF - DRIP Drone Remote ID Protocol (DRIP) entity ID. 713 ID 2 3GPP - IEEE 1609.2-2016 HashedID8 715 4.1. Nontransferablity of DETs 717 A HI and its DET SHOULD NOT be transferable between UA or even 718 between replacement electronics (e.g., replacement of damaged 719 controller CPU) for a UA. The private key for the HI SHOULD be held 720 in a cryptographically secure component. 722 4.2. Encoding HHITs in CTA 2063-A Serial Numbers 724 In some cases, it is advantageous to encode HHITs as a CTA 2063-A 725 Serial Number [CTA2063A]. For example, the FAA Remote ID Rules 726 [FAA_RID] state that a Remote ID Module (i.e., not integrated with UA 727 controller) must only use "the serial number of the unmanned 728 aircraft"; CTA 2063-A meets this requirement. 730 Encoding an HHIT within the CTA 2063-A format is not simple. The CTA 731 2063-A format is defined as follows: 733 Serial Number := MFR Code | Length Code | MFR SN 735 where: 737 MFR Code : 4 character code assigned by ICAO 738 (International Civil Aviation Organization, 739 a UN Agency). 741 Length Code : 1 character Hex encoding of MFR SN length (1-F). 743 MFR SN : Alphanumeric code (0-9, A-Z except O and I). 744 Maximum length of 15 characters. 746 There is no place for the HID; there will need to be a mapping 747 service from Manufacturer Code to HID. The HHIT Suite ID and ORCHID 748 hash will take the full 15 characters (as described below) of the MFR 749 SN field. 751 A character in a CTA 2063-A Serial Number "shall include any 752 combination of digits and uppercase letters, except the letters O and 753 I, but may include all digits". This would allow for a Base34 754 encoding of the binary HHIT Suite ID and ORCHID hash in 15 755 characters. Although, programmatically, such a conversion is not 756 hard, other technologies (e.g., credit card payment systems) that 757 have used such odd base encoding have had performance challenges. 758 Thus, here a Base32 encoding will be used by also excluding the 759 letters Z and S (too similar to the digits 2 and 5). 761 The low-order 72 bits (HHIT Suite ID | ORCHID hash) of the HHIT SHALL 762 be left-padded with 3 bits of zeros. This 75-bit number will be 763 encoded into the 15-character MFR SN field using the digit/letters 764 above. The manufacturer MUST use a Length Code of F (15). 766 Using the sample DET from Section 5 that is for HDA=20 under RAA=10 767 and having the ICAO CTA MFR Code of 8653, the 20-character CTA 2063-A 768 Serial Number would be: 770 8653F02T7B8RA85D19LX 772 A mapping service (e.g., DNS) MUST provide a trusted (e.g., via 773 DNSSEC [RFC4034]) conversion of the 4-character Manufacturer Code to 774 high-order 58 bits (Prefix | HID) of the HHIT. Definition of this 775 mapping service is currently out of scope of this document. 777 It should be noted that this encoding would only be used in the Basic 778 ID Message (Section 2.2 of [RFC9153]). The DET is used in the 779 Authentication Messages (i.e., the messages that provide framing for 780 authentication data only). 782 4.3. Remote ID DET as one Class of Hierarchical HITs 784 UAS Remote ID DET may be one of a number of uses of HHITs. However, 785 it is out of the scope of the document to elaborate on other uses of 786 HHITs. As such these follow-on uses need to be considered in 787 allocating the RAAs (Section 3.3.1) or HHIT prefix assignments 788 (Section 8). 790 4.4. Hierarchy in ORCHID Generation 792 ORCHIDS, as defined in [RFC7343], do not cryptographically bind an 793 IPv6 prefix nor the ORCHID Generation Algorithm (OGA) ID (the HIT 794 Suite ID) to the hash of the HI. The rationale at the time of 795 developing ORCHID was attacks against these fields are Denial-of- 796 Service (DoS) attacks against protocols using ORCHIDs and thus up to 797 those protocols to address the issue. 799 HHITs, as defined in Section 3.5, cryptographically bind all content 800 in the ORCHID through the hashing function. A recipient of a DET 801 that has the underlying HI can directly trust and act on all content 802 in the HHIT. This provides a strong, self-attestation for using the 803 hierarchy to find the DET Registry based on the HID (Section 4.5). 805 4.5. DRIP Entity Tag (DET) Registry 807 DETs are registered to HDAs. A registration process, 808 [drip-registries], ensures DET global uniqueness (ID-4 in [RFC9153]). 809 It also provides the mechanism to create UAS public/private data that 810 are associated with the DET (REG-1 and REG-2 in [RFC9153]). 812 4.6. Remote ID Authentication using DETs 814 The EdDSA25519 HI (Section 3.4) underlying the DET can be used in an 815 84-byte self-proof attestation (timestamp, HHIT, and signature of 816 these) to provide proof of Remote ID ownership (GEN-1 in [RFC9153]). 817 In practice, the Wrapper and Manifest authentication formats 818 (Sections 6.3.3 and 6.3.4 of [drip-authentication]) implicitly 819 provide this self-attestation. A lookup service like DNS can provide 820 the HI and registration proof (GEN-3 in [RFC9153]). 822 Similarly, for Observers without Internet access, a 200-byte offline 823 self-attestation could provide the same Remote ID ownership proof. 824 This attestation would contain the HDA's signing of the UA's HHIT, 825 itself signed by the UA's HI. Only a small cache that contains the 826 HDA's HI/HHIT and HDA meta-data is needed by the Observer. However, 827 such an object would just fit in the ASTM Authentication Message 828 (Section 2.2 of [RFC9153]) with no room for growth. In practice, 829 [drip-authentication] provides this offline self-attestation in two 830 authentication messages: the HDA's certification of the UA's HHIT 831 registration in a Link authentication message whose hash is sent in a 832 Manifest authentication message. 834 Hashes of any previously sent ASTM messages can be placed in a 835 Manifest authentication message (GEN-2 in [RFC9153]). When a 836 Location/Vector Message (i.e., a message that provides UA location, 837 altitude, heading, speed, and status) hash along with the hash of the 838 HDA's UA HHIT attestation are sent in a Manifest authentication 839 message and the Observer can visually see a UA at the claimed 840 location, the Observer has a very strong proof of the UA's Remote ID. 842 All this behavior and how to mix these authentication messages into 843 the flow of UA operation messages are detailed in 844 [drip-authentication]. 846 5. DRIP Entity Tags (DETs) in DNS 848 There are two approaches for storing and retrieving DETs using DNS. 849 The following are examples of how this may be done. This will serve 850 as guidance to the actual deployment of DETs in DNS. However, this 851 document does not intend to provide a recommendation. Further DNS- 852 related considerations are covered in [drip-registries]. 854 * As FQDNs, for example, ".icao.int.". 856 * Reverse DNS lookups as IPv6 addresses per [RFC8005]. 858 A DET can be used to construct an FQDN that points to the USS that 859 has the public/private information for the UA (REG-1 and REG-2 in 860 [RFC9153]). For example, the USS for the HHIT could be found via the 861 following: assume the RAA is decimal 100 and the HDA is decimal 50. 862 The PTR record is constructed as follows: 864 100.50.det.uas.icao.int IN PTR foo.uss.icao.int. 866 The individual DETs may be potentially too numerous (e.g., 60 - 600M) 867 and dynamic (e.g., new DETs every minute for some HDAs) to store in a 868 signed, DNS zone. The HDA SHOULD provide DNS service for its zone 869 and provide the HHIT detail response. 871 The DET reverse lookup can be a standard IPv6 reverse look up, or it 872 can leverage off the HHIT structure. Using the allocated prefix for 873 HHITs TBD6 [suggested value 2001:30::/28] (See Section 3.1), the RAA 874 is 10 and the HDA is 20, the DET is: 876 2001:30:280:1405:a3ad:1952:ad0:a69e 878 A DET reverse lookup could be to: 880 a69e.ad0.1952.a3ad.1405.280.30.2001.20.10.det.arpa. 882 or: 884 a3ad1952ad0a69e.5.20.10.30.2001.det.remoteid.icao.int. 886 A 'standard' ip6.arpa RR has the advantage of only one Registry 887 service supported. 889 $ORIGIN 5.0.4.1.0.8.2.0.0.3.0.0.1.0.0.2.ip6.arpa. 890 e.9.6.a.0.d.a.0.2.5.9.1.d.a.3.a IN PTR 891 a3ad1952ad0a69e.20.10.det.rid.icao.int. 893 This DNS entry for the DET can also provide a revocation service. 894 For example, instead of returning the HI RR it may return some record 895 showing that the HI (and thus DET) has been revoked. Guidance on 896 revocation service will be provided in [drip-registries]. 898 6. Other UAS Traffic Management (UTM) Uses of HHITs Beyond DET 900 HHITs will be used within the UTM architecture beyond DET (and USS in 901 UA ID registration and authentication), for example, as a Ground 902 Control Station (GCS) HHIT ID. Some GCS will use its HHIT for 903 securing its Network Remote ID (to USS HHIT) and Command and Control 904 (C2, Section 2.2.2 of [RFC9153]) transports. 906 Observers may have their own HHITs to facilitate UAS information 907 retrieval (e.g., for authorization to private UAS data). They could 908 also use their HHIT for establishing a HIP connection with the UA 909 Pilot for direct communications per authorization. Details about 910 such issues are out of the scope of this document). 912 7. Summary of Addressed DRIP Requirements 914 This document provides the details to solutions for GEN 1 - 3, ID 1 - 915 5, and REG 1 - 2 requirements that are described in [RFC9153]. 917 8. IANA Considerations 919 8.1. New Well-Known IPv6 prefix for DETs 921 Since the DET format is not compatible with [RFC7343], IANA is 922 requested to allocate a new prefix following this template for the 923 IPv6 Special-Purpose Address Registry. 925 Address Block: 926 IANA is requested to allocate a new 28-bit prefix out of the IANA 927 IPv6 Special Purpose Address Block, namely 2001::/23, as per 928 [RFC6890] (TBD6, suggested: 2001:30::/28). 930 Name: 931 This block should be named "DRIP Entity Tags (DETs) Prefix". 933 RFC: 934 This document. 936 Allocation Date: 937 Date this document published. 939 Termination Date: 940 Forever. 942 Source: 943 False. 945 Destination: 946 False. 948 Forwardable: 949 False. 951 Globally Reachable: 952 False. 954 Reserved-by-Protocol: 955 False. 957 8.2. New IANA DRIP Registry 959 This document requests IANA to create a new registry titled "Drone 960 Remote ID Protocol" registry. The following two subregistries should 961 be created under that registry. 963 Hierarchical HIT (HHIT) Prefixes: 964 Initially, for DET use, one 28-bit prefix should be assigned out 965 of the IANA IPv6 Special Purpose Address Block, namely 2001::/23, 966 as per [RFC6890]. Future additions to this subregistry are to be 967 made through Expert Review (Section 4.5 of [RFC8126]). Entries 968 with network-specific prefixes may be present in the registry. 970 HHIT Use Bits Value 971 DET 28 TBD6 (suggested value 2001:30::/28) 973 Hierarchical HIT (HHIT) Suite ID: 974 This 8-bit valued subregistry is a superset of the 4/8-bit "HIT 975 Suite ID" subregistry of the "Host Identity Protocol (HIP) 976 Parameters" registry in [IANA-HIP]. Future additions to this 977 subregistry are to be made through IETF Review (Section 4.8 of 978 [RFC8126]). The following HHIT Suite IDs are defined: 980 HHIT Suite Value 981 RESERVED 0 982 RSA,DSA/SHA-256 1 [RFC7401] 983 ECDSA/SHA-384 2 [RFC7401] 984 ECDSA_LOW/SHA-1 3 [RFC7401] 985 EdDSA/cSHAKE128 TBD3 (suggested value 5) (RECOMMENDED) 986 HDA Private Use 1 TBD4 (suggested value 254) 987 HDA Private Use 2 TBD5 (suggested value 255) 989 The HHIT Suite ID values 1 - 31 are reserved for IDs that MUST be 990 replicated as HIT Suite IDs (Section 8.4) as is TBD3 here. Higher 991 values (32 - 255) are for those Suite IDs that need not or cannot 992 be accommodated as a HIT Suite ID. 994 8.3. IANA CGA Registry Update 996 This document requests that this document be added to the reference 997 field for the "CGA Extension Type Tags" registry [IANA-CGA], where 998 IANA registers the following Context ID: 1000 Context ID: 1001 The Context ID (Section 3) shares the namespace introduced for CGA 1002 Type Tags. Defining new Context IDs follow the rules in Section 8 1003 of [RFC3972]: 1005 Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40 1007 8.4. IANA HIP Registry Updates 1009 This document requests IANA to make the following changes to the IANA 1010 "Host Identity Protocol (HIP) Parameters" [IANA-HIP] registry: 1012 Host ID: 1013 This document defines the new EdDSA Host ID with value TBD1 1014 (suggested: 13) (Section 3.4.1) in the "HI Algorithm" subregistry 1015 of the "Host Identity Protocol (HIP) Parameters" registry. 1017 Algorithm 1018 profiles Values 1020 EdDSA TBD1 (suggested value 13) [RFC8032] (RECOMMENDED) 1022 EdDSA Curve Label: 1023 This document specifies a new algorithm-specific subregistry named 1024 "EdDSA Curve Label". The values for this subregistry are defined 1025 in Section 3.4.1.1. Future additions to this subregistry are to 1026 be made through IETF Review (Section 4.8 of [RFC8126]). 1028 Algorithm Curve Values 1030 EdDSA RESERVED 0 1031 EdDSA EdDSA25519 1 [RFC8032] (RECOMMENDED) 1032 EdDSA EdDSA25519ph 2 [RFC8032] 1033 EdDSA EdDSA448 3 [RFC8032] (RECOMMENDED) 1034 EdDSA EdDSA448ph 4 [RFC8032] 1035 5-65535 Unassigned 1037 HIT Suite ID: 1038 This document defines the new HIT Suite of EdDSA/cSHAKE with value 1039 TBD3 (suggested: 5) (Section 3.4.2) in the "HIT Suite ID" 1040 subregistry of the "Host Identity Protocol (HIP) Parameters" 1041 registry. 1043 HIT Suite Value 1044 EdDSA/cSHAKE128 TBD3 (suggested value 5) (RECOMMENDED) 1046 The HIT Suite ID 4-bit values 1 - 15 and 8-bit values 0x00 - 0x0F 1047 MUST be replicated as HHIT Suite IDs (Section 8.2) as is TBD3 1048 here. 1050 8.5. IANA IPSECKEY Registry Update 1052 This document requests IANA to make the following change to the 1053 "IPSECKEY Resource Record Parameters" [IANA-IPSECKEY] registry: 1055 IPSECKEY: 1056 This document defines the new IPSECKEY value TBD2 (suggested: 4) 1057 (Section 3.4.1.2) in the "Algorithm Type Field" subregistry of the 1058 "IPSECKEY Resource Record Parameters" registry. 1060 Value Description 1062 TBD2 (suggested value 4) 1063 An EdDSA key is present, in the format defined in [RFC8080] 1065 9. Security Considerations 1067 The 64-bit hash in HHITs presents a real risk of second pre-image 1068 cryptographic hash attack Section 9.5. There are no known (to the 1069 authors) studies of hash size to cryptographic hash attacks. A 1070 Python script is available to randomly generate 1M HHITs that did not 1071 produce a hash collision which is a simpler attack than a first or 1072 second pre-image attack. 1074 However, with today's computing power, producing 2^64 EdDSA keypairs 1075 and then generating the corresponding HHIT is economically feasible. 1076 Consider that a *single* bitcoin mining ASIC can do on the order of 1077 2^46 sha256 hashes a second or about 2^62 hashes in a single day. 1078 The point being, 2^64 is not prohibitive, especially as this can be 1079 done in parallel. 1081 Now it should be noted that the 2^64 attempts is for stealing a 1082 specific HHIT. Consider a scenario of a street photography company 1083 with 1,024 UAs (each with its own HHIT); you'd be happy stealing any 1084 one of them. Then rather than needing to satisfy a 64-bit condition 1085 on the cSHAKE128 output, you need only satisfy what is equivalent to 1086 a 54-bit condition (since there are 2^10 more opportunities for 1087 success). 1089 Thus, although the probability of a collision or pre-image attack is 1090 low in a collection of 1,024 HHITs out of a total population of 2^64, 1091 per Section 9.5, it is computationally and economically feasible. 1092 Therefore, the HHIT registration and HHIT/HI registration validation 1093 is strongly recommended. 1095 The DET Registry services effectively block attempts to "take over" 1096 or "hijack" a DET. It does not stop a rogue attempting to 1097 impersonate a known DET. This attack can be mitigated by the 1098 receiver of messages containing DETs using DNS to find the HI for the 1099 DET. As such, use of DNSSEC by the DET registries is recommended to 1100 provide trust in HI retrieval. 1102 Another mitigation of HHIT hijacking is if the HI owner (UA) supplies 1103 an object containing the HHIT and signed by the HI private key of the 1104 HDA such as detailed in [drip-authentication]. 1106 The two risks with hierarchical HITs are the use of an invalid HID 1107 and forced HIT collisions. The use of a DNS zone (e.g., "det.arpa.") 1108 is a strong protection against invalid HIDs. Querying an HDA's RVS 1109 for a HIT under the HDA protects against talking to unregistered 1110 clients. The Registry service [drip-registries], through its HHIT 1111 uniqueness enforcement, provides against forced or accidental HHIT 1112 hash collisions. 1114 Cryptographically Generated Addresses (CGAs) provide an assurance of 1115 uniqueness. This is two-fold. The address (in this case the UAS ID) 1116 is a hash of a public key and a Registry hierarchy naming. Collision 1117 resistance (more important that it implied second-preimage 1118 resistance) makes it statistically challenging to attacks. A 1119 registration process [drip-registries] within the HDA provides a 1120 level of assured uniqueness unattainable without mirroring this 1121 approach. 1123 The second aspect of assured uniqueness is the digital signing 1124 (attestation) process of the DET by the HI private key and the 1125 further signing (attestation) of the HI public key by the Registry's 1126 key. This completes the ownership process. The observer at this 1127 point does not know what owns the DET, but is assured, other than the 1128 risk of theft of the HI private key, that this UAS ID is owned by 1129 something and is properly registered. 1131 9.1. Post Quantum Computing out of scope 1133 As stated in Section 8.1 of [drip-architecture], there has been no 1134 effort, at this time, to address post quantum computing cryptography. 1135 UAs and Broadcast Remote ID communications are so constrained that 1136 current post quantum computing cryptography is not applicable. Plus 1137 since a UA may use a unique DET for each operation, the attack window 1138 could be limited to the duration of the operation. 1140 HHITs contain the ID for the cryptographic suite used in its 1141 creation, a future post quantum computing safe algorithm that fits 1142 the Remote ID constraints may readily be added. 1144 9.2. DET Trust in ASTM messaging 1146 The DET in the ASTM Basic ID Message (Msg Type 0x0, the actual Remote 1147 ID message) does not provide any assertion of trust. The best that 1148 might be done within this Basic ID Message is 4 bytes truncated from 1149 a HI signing of the HHIT (the UA ID field is 20 bytes and a HHIT is 1150 16). This is not trustable; that is, too open to a hash attack. 1151 Minimally, it takes 84 bytes (Section 4.6) to prove ownership of a 1152 DET with a full EdDSA signature. Thus, no attempt has been made to 1153 add DET trust directly within the very small Basic ID Message. 1155 The ASTM Authentication Message (Msg Type 0x2) as shown in 1156 Section 4.6 can provide practical actual ownership proofs. These 1157 attestations include timestamps to defend against replay attacks. 1158 But in themselves, they do not prove which UA sent the message. They 1159 could have been sent by a dog running down the street with a 1160 Broadcast Remote ID module strapped to its back. 1162 Proof of UA transmission comes when the Authentication Message 1163 includes proofs for the ASTM Location/Vector Message (Msg Type 0x1) 1164 and the observer can see the UA or that information is validated by 1165 ground multilateration. Only then does an observer gain full trust 1166 in the DET of the UA. 1168 DETs obtained via the Network RID path provides a different approach 1169 to trust. Here the UAS SHOULD be securely communicating to the USS, 1170 thus asserting DET trust. 1172 9.3. DET Revocation 1174 The DNS entry for the DET can also provide a revocation service. For 1175 example, instead of returning the HI RR it may return some record 1176 showing that the HI (and thus DET) has been revoked. Guidance on 1177 revocation service will be provided in [drip-registries]. 1179 9.4. Privacy Considerations 1181 There is no expectation of privacy for DETs; it is not part of the 1182 privacy normative requirements listed in, Section 4.3.1, of 1183 [RFC9153]. DETs are broadcast in the clear over the open air via 1184 Bluetooth and Wi-Fi. They will be collected and collated with other 1185 public information about the UAS. This will include DET registration 1186 information and location and times of operations for a DET. A DET 1187 can be for the life of a UA if there is no concern about DET/UA 1188 activity harvesting. 1190 Further, the MAC address of the wireless interface used for Remote ID 1191 broadcasts are a target for UA operation aggregation that may not be 1192 mitigated through MAC address randomization. For Bluetooth 4 Remote 1193 ID messaging, the MAC address is used by observers to link the Basic 1194 ID Message that contains the RID with other Remote ID messages, thus 1195 must be constant for a UA operation. This message linkage use of MAC 1196 addresses may not be needed with the Bluetooth 5 or Wi-Fi PHYs. 1197 These PHYs provide for a larger message payload and can use the 1198 Message Pack (Msg Type 0xF) and the Authentication Message to 1199 transmit the RID with other Remote ID messages. However, it is not 1200 mandatory to send the RID in a Message Pack or Authentication 1201 Message, so allowance for using the MAC address for UA message 1202 linking must be maintained. That is, the MAC address should be 1203 stable for at least a UA operation. 1205 Finally, it is not adequate to simply change the DET and MAC for a UA 1206 per operation to defeat historically tracking a UA's activity. 1208 Any changes to the UA MAC may have impacts to C2 setup and use. A 1209 constant GCS MAC may well defeat any privacy gains in UA MAC and RID 1210 changes. UA/GCS binding is complicated with changing MAC addresses; 1211 historically UAS design assumed these to be "forever" and made setup 1212 a one-time process. Additionally, if IP is used for C2, a changing 1213 MAC may mean a changing IP address to further impact the UAS 1214 bindings. Finally, an encryption wrapper's identifier (such as ESP 1215 [RFC4303] SPI) would need to change per operation to insure operation 1216 tracking separation. 1218 Creating and maintaining UAS operational privacy is a multifaceted 1219 problem. Many communication pieces need to be considered to truly 1220 create a separation between UA operations. Simply changing the DET 1221 only starts the changes that need to be implemented. 1223 These privacy realities may present challenges for the EU U-space 1224 (Appendix A) program. 1226 9.5. Collision Risks with DETs 1228 The 64-bit hash size does have an increased risk of collisions over 1229 the 96-bit hash size used for the other HIT Suites. There is a 0.01% 1230 probability of a collision in a population of 66 million. The 1231 probability goes up to 1% for a population of 663 million. See 1232 Appendix C for the collision probability formula. 1234 However, this risk of collision is within a single "Additional 1235 Information" value, i.e., a RAA/HDA domain. The UAS/USS registration 1236 process should include registering the DET and MUST reject a 1237 collision, forcing the UAS to generate a new HI and thus HHIT and 1238 reapplying to the DET registration process. 1240 Thus an adversary trying to generate a collision and 'steal' the DET 1241 would run afoul of this registration process and associated 1242 validation process mentioned in Section 1.1. 1244 10. References 1246 10.1. Normative References 1248 [NIST.FIPS.202] 1249 Dworkin, M., "SHA-3 Standard: Permutation-Based Hash and 1250 Extendable-Output Functions", National Institute of 1251 Standards and Technology report, 1252 DOI 10.6028/nist.fips.202, July 2015, 1253 . 1255 [NIST.SP.800-185] 1256 Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived 1257 functions: cSHAKE, KMAC, TupleHash and ParallelHash", 1258 National Institute of Standards and Technology report, 1259 DOI 10.6028/nist.sp.800-185, December 2016, 1260 . 1262 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1263 Requirement Levels", BCP 14, RFC 2119, 1264 DOI 10.17487/RFC2119, March 1997, 1265 . 1267 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 1268 "Special-Purpose IP Address Registries", BCP 153, 1269 RFC 6890, DOI 10.17487/RFC6890, April 2013, 1270 . 1272 [RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay 1273 Routable Cryptographic Hash Identifiers Version 2 1274 (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September 1275 2014, . 1277 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 1278 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 1279 RFC 7401, DOI 10.17487/RFC7401, April 2015, 1280 . 1282 [RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name 1283 System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005, 1284 October 2016, . 1286 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 1287 Signature Algorithm (EdDSA)", RFC 8032, 1288 DOI 10.17487/RFC8032, January 2017, 1289 . 1291 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1292 Writing an IANA Considerations Section in RFCs", BCP 26, 1293 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1294 . 1296 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1297 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1298 May 2017, . 1300 10.2. Informative References 1302 [cfrg-comment] 1303 "A CFRG review of draft-ietf-drip-rid", September 2021, 1304 . 1307 [corus] CORUS, "U-space Concept of Operations", September 2019, 1308 . 1310 [CTA2063A] ANSI/CTA, "Small Unmanned Aerial Systems Serial Numbers", 1311 September 2019, . 1314 [drip-architecture] 1315 Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S., 1316 and A. Gurtov, "Drone Remote Identification Protocol 1317 (DRIP) Architecture", Work in Progress, Internet-Draft, 1318 draft-ietf-drip-arch-22, 21 March 2022, 1319 . 1322 [drip-authentication] 1323 Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP Entity 1324 Tag Authentication Formats & Protocols for Broadcast 1325 Remote ID", Work in Progress, Internet-Draft, draft-ietf- 1326 drip-auth-10, 11 May 2022, 1327 . 1330 [drip-registries] 1331 Wiethuechter, A., Card, S., Moskowitz, R., and J. Reid, 1332 "DRIP Entity Tag Registration & Lookup", Work in Progress, 1333 Internet-Draft, draft-ietf-drip-registries-03, 11 May 1334 2022, . 1337 [F3411] ASTM International, "Standard Specification for Remote ID 1338 and Tracking", 1339 . 1341 [FAA_RID] United States Federal Aviation Administration (FAA), 1342 "Remote Identification of Unmanned Aircraft", 2021, 1343 . 1346 [IANA-CGA] IANA, "Cryptographically Generated Addresses (CGA) Message 1347 Type Name Space", . 1350 [IANA-HIP] IANA, "Host Identity Protocol (HIP) Parameters", 1351 . 1354 [IANA-IPSECKEY] 1355 IANA, "IPSECKEY Resource Record Parameters", 1356 . 1359 [Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and 1360 R. Van Keer, "The Keccak Function", 1361 . 1363 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1364 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1365 . 1367 [RFC4025] Richardson, M., "A Method for Storing IPsec Keying 1368 Material in DNS", RFC 4025, DOI 10.17487/RFC4025, March 1369 2005, . 1371 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1372 Rose, "Resource Records for the DNS Security Extensions", 1373 RFC 4034, DOI 10.17487/RFC4034, March 2005, 1374 . 1376 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 1377 Unique IDentifier (UUID) URN Namespace", RFC 4122, 1378 DOI 10.17487/RFC4122, July 2005, 1379 . 1381 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 1382 RFC 4303, DOI 10.17487/RFC4303, December 2005, 1383 . 1385 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 1386 Housley, R., and W. Polk, "Internet X.509 Public Key 1387 Infrastructure Certificate and Certificate Revocation List 1388 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 1389 . 1391 [RFC8004] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1392 Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004, 1393 October 2016, . 1395 [RFC8080] Sury, O. and R. Edmonds, "Edwards-Curve Digital Security 1396 Algorithm (EdDSA) for DNSSEC", RFC 8080, 1397 DOI 10.17487/RFC8080, February 2017, 1398 . 1400 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1401 (IPv6) Specification", STD 86, RFC 8200, 1402 DOI 10.17487/RFC8200, July 2017, 1403 . 1405 [RFC9063] Moskowitz, R., Ed. and M. Komu, "Host Identity Protocol 1406 Architecture", RFC 9063, DOI 10.17487/RFC9063, July 2021, 1407 . 1409 [RFC9153] Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A. 1410 Gurtov, "Drone Remote Identification Protocol (DRIP) 1411 Requirements and Terminology", RFC 9153, 1412 DOI 10.17487/RFC9153, February 2022, 1413 . 1415 [RFC9224] Blanchet, M., "Finding the Authoritative Registration Data 1416 Access Protocol (RDAP) Service", STD 95, RFC 9224, 1417 DOI 10.17487/RFC9224, March 2022, 1418 . 1420 Appendix A. EU U-Space RID Privacy Considerations 1422 The EU is defining a future of airspace management known as U-space 1423 within the Single European Sky ATM Research (SESAR) undertaking. 1424 Concept of Operation for EuRopean UTM Systems (CORUS) project 1425 proposed low-level Concept of Operations [corus] for UAS in the EU. 1426 It introduces strong requirements for UAS privacy based on European 1427 GDPR regulations. It suggests that UAs are identified with agnostic 1428 IDs, with no information about UA type, the operators or flight 1429 trajectory. Only authorized persons should be able to query the 1430 details of the flight with a record of access. 1432 Due to the high privacy requirements, a casual observer can only 1433 query U-space if it is aware of a UA seen in a certain area. A 1434 general observer can use a public U-space portal to query UA details 1435 based on the UA transmitted "Remote identification" signal. Direct 1436 remote identification (DRID) is based on a signal transmitted by the 1437 UA directly. Network remote identification (NRID) is only possible 1438 for UAs being tracked by U-Space and is based on the matching the 1439 current UA position to one of the tracks. 1441 This is potentially a contrary expectation as that presented in 1442 Section 9.4. U-space will have to deal with this reality within the 1443 GDPR regulations. Still, DETs as defined here present a large step 1444 in the right direction for agnostic IDs. 1446 The project lists "E-Identification" and "E-Registrations" services 1447 as to be developed. These services can use DETs and follow the 1448 privacy considerations outlined in this document for DETs. 1450 If an "agnostic ID" above refers to a completely random identifier, 1451 it creates a problem with identity resolution and detection of 1452 misuse. On the other hand, a classical HIT has a flat structure 1453 which makes its resolution difficult. The DET (Hierarchical HIT) 1454 provides a balanced solution by associating a registry with the UA 1455 identifier. This is not likely to cause a major conflict with 1456 U-space privacy requirements, as the registries are typically few at 1457 a country level (e.g., civil personal, military, law enforcement, or 1458 commercial). 1460 Appendix B. The 14/14 HID split 1462 The following explains the logic behind selecting to divide the 28 1463 bits of the HID into 2 14-bit components. 1465 At this writing ICAO has 273 member "States", each may want to 1466 control RID assignment within its National Air Space (NAS). Some 1467 members may want separate RAAs to use for Civil, general Government, 1468 and Military use. They may also want allowances for competing Civil 1469 RAA operations. It is reasonable to plan for 8 RAAs per ICAO member 1470 (plus regional aviation organizations like in the European Union). 1471 Thus at a start a 4,096 RAA space is advised. 1473 There will be requests by commercial entities for their own, RAA 1474 allotments. Examples could include international organizations that 1475 will be using UAS and international delivery service associations. 1476 These may be smaller than the RAA space needed by ICAO member States 1477 and could be met with a 2,048 space allotment, but as will be seen, 1478 might as well be 4,096 as well. 1480 This may well cover currently understood RAA entities. There will be 1481 future new applications, branching off into new areas. So yet 1482 another space allocation should be set aside. If this is equal to 1483 all that has been reserved, we should allow for 16,384 (2^14) RAAs. 1485 The HDA allocation follows a different logic from that of RAAs. Per 1486 Appendix C, an HDA should be able to easily assign 63M RIDs and even 1487 manage 663M with a "first come, first assigned" registration process. 1488 For most HDAs this is more than enough, and a single HDA assignment 1489 within their RAA will suffice. Most RAAs will only delegate to a 1490 couple HDAs for their operational needs. But there are major 1491 exceptions that point to some RAAs needing large numbers of HDA 1492 assignments. 1494 Delivery service operators like Amazon (est. 30K delivery vans) and 1495 UPS (est. 500K delivery vans) may choose, for anti-tracking reasons, 1496 to use unique RIDs per day or even per operation. 30K delivery UA 1497 could need 11M upwards to 44M RIDs. Anti-tracking would be hard to 1498 provide if the HID were the same for a delivery service fleet, so 1499 such a company may turn to an HDA that provides this service to 1500 multiple companies so that who's UA is who's is not evident in the 1501 HID. A USS providing this service could well use multiple HDA 1502 assignments per year, depending on strategy. 1504 Perhaps a single RAA providing HDAs for delivery service (or similar 1505 behaving) UAS could 'get by' with a 2048 HDA space (11-bits). So the 1506 HDA space could well be served with only 12 bits allocated out of the 1507 28-bit HID space. But as this is speculation, and it will take years 1508 of deployment experience, a 14-bit HDA space has been selected. 1510 There may also be 'small' ICAO member States that opt for a single 1511 RAA and allocate their HDAs for all UA that are permitted in their 1512 NAS. The HDA space is large enough that some to use part for 1513 government needs as stated above and for small commercial needs. Or 1514 the State may use a separate, consecutive RAA for commercial users. 1515 Thus it would be 'easy' to recognize State-approved UA by HID high- 1516 order bits. 1518 Appendix C. Calculating Collision Probabilities 1520 The accepted formula for calculating the probability of a collision 1521 is: 1523 p = 1 - e^{-k^2/(2n)} 1525 P Collision Probability 1526 n Total possible population 1527 k Actual population 1529 The following table provides the approximate population size for a 1530 collision for a given total population. 1532 Deployed Population 1533 Total With Collision Risk of 1534 Population .01% 1% 1536 2^96 4T 42T 1537 2^72 1B 10B 1538 2^68 250M 2.5B 1539 2^64 66M 663M 1540 2^60 16M 160M 1542 Acknowledgments 1544 Dr. Gurtov is an adviser on Cybersecurity to the Swedish Civil 1545 Aviation Administration. 1547 Quynh Dang of NIST gave considerable guidance on using Keccak and the 1548 NIST supporting documents. Joan Deamen of the Keccak team was 1549 especially helpful in many aspects of using Keccak. Nicholas 1550 Gajcowski [cfrg-comment] provided a concise hash pre-image security 1551 assessment via the CFRG list. 1553 Many thanks to Michael Richardson and Brian Haberman for the iotdir 1554 review, Magnus Nystrom for the secdir review, Elwyn Davies for genart 1555 review and DRIP co-chair and draft shepherd, Mohamed Boucadair for 1556 his extensive comments and help on document clarity. 1558 Authors' Addresses 1560 Robert Moskowitz 1561 HTT Consulting 1562 Oak Park, MI 48237 1563 United States of America 1564 Email: rgm@labs.htt-consult.com 1566 Stuart W. Card 1567 AX Enterprize, LLC 1568 4947 Commercial Drive 1569 Yorkville, NY 13495 1570 United States of America 1571 Email: stu.card@axenterprize.com 1573 Adam Wiethuechter 1574 AX Enterprize, LLC 1575 4947 Commercial Drive 1576 Yorkville, NY 13495 1577 United States of America 1578 Email: adam.wiethuechter@axenterprize.com 1580 Andrei Gurtov 1581 Linköping University 1582 IDA 1583 SE-58183 Linköping 1584 Sweden 1585 Email: gurtov@acm.org