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Moskowitz 3 Internet-Draft HTT Consulting 4 Intended status: Standards Track S. Card 5 Expires: 18 February 2021 A. Wiethuechter 6 AX Enterprize 7 A. Gurtov 8 Linköping University 9 17 August 2020 11 UAS Remote ID 12 draft-moskowitz-drip-uas-rid-06 14 Abstract 16 This document describes the use of Hierarchical Host Identity Tags 17 (HHITs) as a self-asserting and thereby trustable Identifier for use 18 as the UAS Remote ID. HHITs include explicit hierarchy to provide 19 Registrar discovery for 3rd-party ID attestation. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on 18 February 2021. 38 Copyright Notice 40 Copyright (c) 2020 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 45 license-info) in effect on the date of publication of this document. 46 Please review these documents carefully, as they describe your rights 47 and restrictions with respect to this document. Code Components 48 extracted from this document must include Simplified BSD License text 49 as described in Section 4.e of the Trust Legal Provisions and are 50 provided without warranty as described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3 56 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3 57 2.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Hierarchical HITs as Remote ID . . . . . . . . . . . . . . . 5 60 3.1. Remote ID as one class of Hierarchical HITs . . . . . . . 5 61 3.2. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 5 62 3.3. Hierarchical HIT Registry . . . . . . . . . . . . . . . . 6 63 3.4. Remote ID Authentication using HHITs . . . . . . . . . . 6 64 4. UAS ID HHIT in DNS . . . . . . . . . . . . . . . . . . . . . 6 65 5. Other UTM uses of HHITs . . . . . . . . . . . . . . . . . . . 7 66 6. DRIP Requirements addressed . . . . . . . . . . . . . . . . . 7 67 7. ASTM Considerations . . . . . . . . . . . . . . . . . . . . . 7 68 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 69 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 70 9.1. Hierarchical HIT Trust . . . . . . . . . . . . . . . . . 9 71 9.2. Collision risks with Hierarchical HITs . . . . . . . . . 9 72 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 73 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 74 10.2. Informative References . . . . . . . . . . . . . . . . . 10 75 Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 12 76 Appendix B. The Hierarchical Host Identity Tag (HHIT) . . . . . 12 77 B.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 13 78 B.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 13 79 B.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 13 80 B.3.1. The Registered Assigning Authority (RAA) . . . . . . 13 81 B.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 14 82 Appendix C. ORCHIDs for Hierarchical HITs . . . . . . . . . . . 14 83 C.1. Adding additional information to the ORCHID . . . . . . . 15 84 C.2. ORCHID Decoding . . . . . . . . . . . . . . . . . . . . . 16 85 C.3. ORCHID Encoding . . . . . . . . . . . . . . . . . . . . . 16 86 Appendix D. Edward Digital Signature Algorithm for HITs . . . . 16 87 D.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . . . 17 88 D.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . . . 17 89 Appendix E. Calculating Collision Probabilities . . . . . . . . 18 90 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 93 1. Introduction 95 [drip-requirements] describes a UAS ID as a "unique (ID-4), non- 96 spoofable (ID-5), and identify a registry where the ID is listed (ID- 97 2)"; all within a 20 character Identifier (ID-1). 99 This document describes the use of Hierarchical HITs (HHITs) 100 (Appendix B) as self-asserting and thereby a trustable Identifier for 101 use as the UAS Remote ID. HHITs include explicit hierarchy to 102 provide Registrar discovery for 3rd-party ID attestation. 104 HITs are statistically unique through the cryptographic hash feature 105 of second-preimage resistance. The cryptographically-bound addition 106 of the Hierarchy and thus HHIT Registries [hhit-registries] provide 107 complete, global HHIT uniqueness. This is in contrast to general IDs 108 (e.g. a UUID or device serial number) as the subject in an X.509 109 certificate. 111 In a multi-CA PKI, a subject can occur in multiple CAs, possibly 112 fraudulently. CAs within the PKI would need to implement an approach 113 to enforce assurance of uniqueness. 115 Hierarchical HITs are valid, though non-routable, IPv6 addresses. As 116 such, they fit in many ways within various IETF technologies. 118 2. Terms and Definitions 120 2.1. Requirements Terminology 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 124 "OPTIONAL" in this document are to be interpreted as described in BCP 125 14 [RFC2119] [RFC8174] when, and only when, they appear in all 126 capitals, as shown here. 128 2.2. Notation 130 | Signifies concatenation of information - e.g., X | Y is the 131 concatenation of X and Y. 133 2.3. Definitions 135 See [drip-requirements] for common DRIP terms. 137 cSHAKE (The customizable SHAKE function): 138 Extends the SHAKE scheme to allow users to customize their use of 139 the function. 141 HI 142 Host Identity. The public key portion of an asymmetric keypair 143 used in HIP. 145 HIP 146 Host Identity Protocol. The origin of HI, HIT, and HHIT, required 147 for DRIP. Optional full use of HIP enables additional DRIP 148 functionality. 150 HDA (Hierarchical HIT Domain Authority): 151 The 16 bit field identifying the HIT Domain Authority under an 152 RAA. 154 HHIT 155 Hierarchical Host Identity Tag. A HIT with extra hierarchical 156 information not found in a standard HIT. 158 HID (Hierarchy ID): 159 The 32 bit field providing the HIT Hierarchy ID. 161 HIT 162 Host Identity Tag. A 128 bit handle on the HI. HITs are valid 163 IPv6 addresses. 165 Keccak (KECCAK Message Authentication Code): 166 The family of all sponge functions with a KECCAK-f permutation as 167 the underlying function and multi-rate padding as the padding 168 rule. 170 RAA (Registered Assigning Authority): 171 The 16 bit field identifying the Hierarchical HIT Assigning 172 Authority. 174 RVS (Rendezvous Server): 175 The HIP Rendezvous Server for enabling mobility, as defined in 176 [RFC8004]. 178 SHAKE (Secure Hash Algorithm KECCAK): 179 A secure hash that allows for an arbitrary output length. 181 XOF (eXtendable-Output Function): 182 A function on bit strings (also called messages) in which the 183 output can be extended to any desired length. 185 3. Hierarchical HITs as Remote ID 187 Hierarchical HITs are a refinement on the Host Identity Tag (HIT) of 188 HIPv2 [RFC7401]. HHITs require a new ORCHID mechanism as described 189 in Appendix C. HHITs for UAS ID also use the new EdDSA/SHAKE128 HIT 190 suite defined in Appendix D (requirements GEN-2). This hierarchy, 191 cryptographically embedded within the HHIT, provides the information 192 for finding the UA's HHIT registry (ID-3). 194 The current ASTM [F3411-19] specifies three UAS ID types: 196 TYPE-1 A static, manufacturer assigned, hardware serial number per 197 ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers" 198 [CTA2063A]. 200 TYPE-2 A CAA assigned (presumably static) ID. 202 TYPE-3 A UTM system assigned UUID [RFC4122], which can but need not 203 be dynamic. 205 For HHITs to be used effectively as UAS IDs, F3411-19 SHOULD add UAS 206 ID type 4 as HHIT. 208 3.1. Remote ID as one class of Hierarchical HITs 210 UAS Remote ID may be one of a number of uses of HHITs. As such these 211 follow-on uses need to be considered in allocating the RAAs 212 Appendix B.3.1 or HHIT prefix assignments Section 8. 214 3.2. Hierarchy in ORCHID Generation 216 ORCHIDS, as defined in [RFC7343], do not cryptographically bind the 217 IPv6 prefix nor the Orchid Generation Algorithm (OGA) ID (the HIT 218 Suite ID) to the hash of the HI. The justification then was attacks 219 against these fields are DoS attacks against protocols using them. 221 HHITs, as defined in Appendix C, cryptographically bind all content 222 in the ORCHID though the hashing function. Thus a recipient of a 223 HHIT that has the underlying HI can directly act on all content in 224 the HHIT. This is especially important to using the hierarchy to 225 find the HHIT Registry. 227 3.3. Hierarchical HIT Registry 229 HHITs are registered to Hierarchical HIT Domain Authorities (HDAs) as 230 described in [hhit-registries]. This registration process ensures 231 UAS ID global uniqueness (ID-4). It also provides the mechanism to 232 create UAS Public/Private data associated with the HHIT UAS ID (REG-1 233 and REG-2). 235 The 2 levels of hierarchy within the HHIT allows for CAAs to have 236 their own Registered Assigning Authority (RAA) for their National Air 237 Space (NAS). Within the RAA, the CAAs can delegate HDAs as needed. 238 There may be other RAAs allowed to operate within a given NAS; this 239 is a policy decision by the CAA. 241 3.4. Remote ID Authentication using HHITs 243 The EdDSA25519 Host Identity (HI) [Appendix D] underlying the HHIT is 244 used for the Message Wrapper, Sec 4.2 [drip-auth] (requirements GEN- 245 2). It and the HDA's HI/HHIT are used for the Auth Certificate, sec 246 5.1 [drip-auth] (requirements GEN-3). These messages also establish 247 that the UA owns the HHIT and that no other UA can assert ownership 248 of the HHIT (GEN-1). 250 The number of HDAs authorized to register UAs within an NAS 251 determines the size of the HDA credential cache a device processing 252 the Offline Authentication. This cache contains the HDA's HI/HHIT 253 and HDA meta-data; it could be very small. 255 4. UAS ID HHIT in DNS 257 There are 2 approaches for storing and retrieving the HHIT from DNS. 258 These are: 260 * As FQDNs in the .aero TLD. 262 * Reverse DNS lookups as IPv6 addresses per [RFC8005]. 264 The HHIT can be used to construct an FQDN that points to the USS that 265 has the Public/Private information for the UA (REG-1 and REG-2). For 266 example the USS for the HHIT could be found via the following. 267 Assume that the RAA is 100 and the HDA is 50. The PTR record is 268 constructed as: 270 100.50.hhit.uas.areo IN PTR foo.uss.areo. 272 The individual HHITs are potentially too numerous (e.g. 60 - 600M) 273 and dynamic to actually store in a signed, DNS zone. Rather the USS 274 would provide the HHIT detail response. 276 The HHIT reverse lookup can be a standard IPv6 reverse look up, or it 277 can leverage off the HHIT structure. Assume that the RAA is 10 and 278 the HDA is 20 and the HHIT is: 280 2001:14:28:14:a3ad:1952:ad0:a69e 282 An HHIT reverse lookup would be to is: 284 a69e.ad0.1952.a3ad14.28.14.2001.20.10.hhit.arpa. 286 5. Other UTM uses of HHITs 288 HHITs can be used extensively within the UTM architecture beyond UA 289 ID (and USS in UA ID registration and authentication). This includes 290 a GCS HHIT ID. It could use this if it is the source of Network 291 Remote ID for securing the transport and for secure C2 transport 292 [drip-secure-nrid-c2]. 294 Observers SHOULD have HHITs to facilitate UAS information retrieval 295 (e.g., for authorization to private UAS data). They could also use 296 their HHIT for establishing a HIP connection with the UA Pilot for 297 direct communications per authorization. Further, they can be used 298 by FINDER observers, [crowd-sourced-rid]. 300 6. DRIP Requirements addressed 302 This document provides solutions to GEN 1 - 3, ID 1 - 5, and REG 1 - 303 2. 305 7. ASTM Considerations 307 ASTM will need to make the following changes to the "UA ID" in the 308 Basic Message: 310 Type 4: 311 This document UA ID of Hierarchical HITs (see Section 3). 313 8. IANA Considerations 315 IANA will need to make the following changes to the "Host Identity 316 Protocol (HIP) Parameters" registries: 318 Host ID: 319 This document defines the new EdDSA Host ID (see Appendix D.1). 321 HIT Suite ID: 322 This document defines the new HIT Suite of EdDSA/cSHAKE (see 323 Appendix D.2). 325 Because HHIT use of ORCHIDv2 format is not compatible with [RFC7343], 326 IANA is requested to allocated a new 28-bit prefix out of the IANA 327 IPv6 Special Purpose Address Block, namely 2001:0000::/23, as per 328 [RFC6890]. 330 9. Security Considerations 332 A 64 bit hash space presents a real risk of second pre-image attacks 333 Section 9.2. The HHIT Registry services effectively block attempts 334 to "take over" a HHIT. It does not stop a rogue attempting to 335 impersonate a known HHIT. This attack can be mitigated by the 336 receiver of the HHIT using DNS to find the HI for the HHIT. 338 Another mitigation of HHIT hijacking is if the HI owner supplies an 339 object containing the HHIT and signed by the HI private key of the 340 HDA. 342 The two risks with hierarchical HITs are the use of an invalid HID 343 and forced HIT collisions. The use of a DNS zone (e.g. 344 "hhit.arpa.") is a strong protection against invalid HIDs. Querying 345 an HDA's RVS for a HIT under the HDA protects against talking to 346 unregistered clients. The Registry service has direct protection 347 against forced or accidental HIT hash collisions. 349 Cryptographically Generated Addresses (CGAs) provide a unique 350 assurance of uniqueness. This is two-fold. The address (in this 351 case the UAS ID) is a hash of a public key and a Registry hierarchy 352 naming. Collision resistance (more important that it implied second- 353 preimage resistance) makes it statistically challenging to attacks. 354 A registration process as in HHIT Registries [hhit-registries] 355 provides a level of assured uniqueness unattainable without mirroring 356 this approach. 358 The second aspect of assured uniqueness is the digital signing 359 process of the HHIT by the HI private key and the further signing of 360 the HI public key by the Registry's key. This completes the 361 ownership process. The observer at this point does not know WHAT 362 owns the HHIT, but is assured, other than the risk of theft of the HI 363 private key, that this UAS ID is owned by something and is properly 364 registered. 366 9.1. Hierarchical HIT Trust 368 The HHIT UAS RID in the ASTM Basic Message (the actual Remote ID 369 message) does not provide any assertion of trust. The best that 370 might be done is 4 bytes truncated from a HI signing of the HHIT (the 371 UA ID field is 20 bytes and a HHIT is 16). It is in the ASTM 372 Authentication Messages as defined in [drip-auth] that provide all of 373 the actual ownership proofs. These claims include timestamps to 374 defend against replay attacks. But in themselves, they do not prove 375 which UA actually sent the message. They could have been sent by a 376 dog running down the street with a Broadcast Remote ID device 377 strapped to its back. 379 Proof of UA transmission comes when the Authentication Message 380 includes proofs for the Location/Vector Message and the observer can 381 see the UA or that information is validated by ground multilateration 382 [crowd-sourced-rid]. Only then does an observer gain full trust in 383 the HHIT Remote ID. 385 HHIT Remote IDs obtained via the Network Remote ID path provides a 386 different approach to trust. Here the UAS SHOULD be securely 387 communicating to the USS (see [drip-secure-nrid-c2]), thus asserting 388 HHIT RID trust. 390 9.2. Collision risks with Hierarchical HITs 392 The 64 bit hash size does have an increased risk of collisions over 393 the 96 bit hash size used for the other HIT Suites. There is a 0.01% 394 probability of a collision in a population of 66 million. The 395 probability goes up to 1% for a population of 663 million. See 396 Appendix E for the collision probability formula. 398 However, this risk of collision is within a single "Additional 399 Information" value. Some registration process should be used to 400 reject a collision, forcing the client to generate a new HI and thus 401 HIT and reapplying to the registration process. 403 10. References 405 10.1. Normative References 407 [F3411-19] ASTM International, "Standard Specification for Remote ID 408 and Tracking", February 2020, 409 . 411 [hhit-registries] 412 Moskowitz, R., Card, S., and A. Wiethuechter, 413 "Hierarchical HIT Registries", Work in Progress, Internet- 414 Draft, draft-moskowitz-hip-hhit-registries-02, 9 March 415 2020, . 418 [NIST.FIPS.202] 419 Dworkin, M., "SHA-3 Standard: Permutation-Based Hash and 420 Extendable-Output Functions", National Institute of 421 Standards and Technology report, 422 DOI 10.6028/nist.fips.202, July 2015, 423 . 425 [NIST.SP.800-185] 426 Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived 427 functions: cSHAKE, KMAC, TupleHash and ParallelHash", 428 National Institute of Standards and Technology report, 429 DOI 10.6028/nist.sp.800-185, December 2016, 430 . 432 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 433 Requirement Levels", BCP 14, RFC 2119, 434 DOI 10.17487/RFC2119, March 1997, 435 . 437 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 438 "Special-Purpose IP Address Registries", BCP 153, 439 RFC 6890, DOI 10.17487/RFC6890, April 2013, 440 . 442 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 443 Signature Algorithm (EdDSA)", RFC 8032, 444 DOI 10.17487/RFC8032, January 2017, 445 . 447 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 448 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 449 May 2017, . 451 10.2. Informative References 453 [corus] CORUS, "U-space Concept of Operations", September 2019, 454 . 456 [crowd-sourced-rid] 457 Moskowitz, R., Card, S., Wiethuechter, A., Zhao, S., and 458 H. Birkholz, "Crowd Sourced Remote ID", Work in Progress, 459 Internet-Draft, draft-moskowitz-drip-crowd-sourced-rid-04, 460 20 May 2020, . 463 [CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers", 464 September 2019. 466 [drip-auth] 467 Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP 468 Authentication Formats", Work in Progress, Internet-Draft, 469 draft-wiethuechter-drip-auth-03, 27 July 2020, 470 . 473 [drip-requirements] 474 Card, S., Wiethuechter, A., Moskowitz, R., and A. Gurtov, 475 "Drone Remote Identification Protocol (DRIP) 476 Requirements", Work in Progress, Internet-Draft, draft- 477 ietf-drip-reqs-03, 13 July 2020, 478 . 480 [drip-secure-nrid-c2] 481 Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, 482 "Secure UAS Network RID and C2 Transport", Work in 483 Progress, Internet-Draft, draft-moskowitz-drip-secure- 484 nrid-c2-00, 6 April 2020, . 487 [Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and 488 R. Van Keer, "The Keccak Function", 489 . 491 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 492 Unique IDentifier (UUID) URN Namespace", RFC 4122, 493 DOI 10.17487/RFC4122, July 2005, 494 . 496 [RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay 497 Routable Cryptographic Hash Identifiers Version 2 498 (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September 499 2014, . 501 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 502 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 503 RFC 7401, DOI 10.17487/RFC7401, April 2015, 504 . 506 [RFC8004] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 507 Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004, 508 October 2016, . 510 [RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name 511 System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005, 512 October 2016, . 514 Appendix A. EU U-Space RID Privacy Considerations 516 EU is defining a future of airspace management known as U-space 517 within the Single European Sky ATM Research (SESAR) undertaking. 518 Concept of Operation for EuRopean UTM Systems (CORUS) project 519 proposed low-level Concept of Operations [corus] for UAS in EU. It 520 introduces strong requirements for UAS privacy based on European GDPR 521 regulations. It suggests that UAs are identified with agnostic IDs, 522 with no information about UA type, the operators or flight 523 trajectory. Only authorized persons should be able to query the 524 details of the flight with a record of access. 526 Due to the high privacy requirements, a casual observer can only 527 query U-space if it is aware of a UA seen in a certain area. A 528 general observer can use a public U-space portal to query UA details 529 based on the UA transmitted "Remote identification" signal. Direct 530 remote identification (DRID) is based on a signal transmitted by the 531 UA directly. Network remote identification (NRID) is only possible 532 for UAs being tracked by U-Space and is based on the matching the 533 current UA position to one of the tracks. 535 The project lists "E-Identification" and "E-Registrations" services 536 as to be developed. These services can follow the privacy mechanism 537 proposed in this document. If an "agnostic ID" above refers to a 538 completely random identifier, it creates a problem with identity 539 resolution and detection of misuse. On the other hand, a classical 540 HIT has a flat structure which makes its resolution difficult. The 541 Hierarchical HITs provide a balanced solution by associating a 542 registry with the UA identifier. This is not likely to cause a major 543 conflict with U-space privacy requirements, as the registries are 544 typically few at a country level (e.g. civil personal, military, law 545 enforcement, or commercial). 547 Appendix B. The Hierarchical Host Identity Tag (HHIT) 549 The Hierarchical HIT (HHIT) is a small but important enhancement over 550 the flat HIT space. By adding two levels of hierarchical 551 administration control, the HHIT provides for device registration/ 552 ownership, thereby enhancing the trust framework for HITs. 554 HHITs represent the HI in only a 64 bit hash and uses the other 32 555 bits to create a hierarchical administration organization for HIT 556 domains. Hierarchical HITs are "Using cSHAKE in ORCHIDs" 557 (Appendix C). The input values for the Encoding rules are in 558 Appendix C.1. 560 A HHIT is built from the following fields: 562 * 28 bit IANA prefix 564 * 4 bit HIT Suite ID 566 * 32 bit Hierarchy ID (HID) 568 * 64 bit ORCHID hash 570 B.1. HHIT prefix 572 A unique 28 bit prefix for HHITs is recommended. It clearly 573 separates the flat-space HIT processing from HHIT processing per 574 "Using cSHAKE in ORCHIDs" (Appendix C). 576 B.2. HHIT Suite IDs 578 The HIT Suite IDs specifies the HI and hash algorithms. Any HIT 579 Suite ID can be used for HHITs, provided that the prefix for HHITs is 580 different from flat space HITs. Without a unique prefix, 581 Appendix B.1, additional HIT Suite IDs would be needed for HHITs. 582 This would risk exhausting the limited Suite ID space of only 15 IDs. 584 B.3. The Hierarchy ID (HID) 586 The Hierarchy ID (HID) provides the structure to organize HITs into 587 administrative domains. HIDs are further divided into 2 fields: 589 * 16 bit Registered Assigning Authority (RAA) 591 * 16 bit Hierarchical HIT Domain Authority (HDA) 593 B.3.1. The Registered Assigning Authority (RAA) 595 An RAA is a business or organization that manages a registry of HDAs. 596 For example, the Federal Aviation Authority (FAA) could be an RAA. 598 The RAA is a 16 bit field (65,536 RAAs) assigned by a numbers 599 management organization, perhaps ICANN's IANA service. An RAA must 600 provide a set of services to allocate HDAs to organizations. It must 601 have a public policy on what is necessary to obtain an HDA. The RAA 602 need not maintain any HIP related services. It must maintain a DNS 603 zone minimally for discovering HID RVS servers. 605 As HHITs may be used in many different domains, RAA should be 606 allocated in blocks with consideration on the likely size of a 607 particular usage. Alternatively, different Prefixes can be used to 608 separate different domains of use of HHTs. 610 This DNS zone may be a PTR for its RAA. It may be a zone in a HHIT 611 specific DNS zone. Assume that the RAA is 100. The PTR record could 612 be constructed: 614 100.hhit.arpa IN PTR raa.bar.com. 616 B.3.2. The Hierarchical HIT Domain Authority (HDA) 618 An HDA may be an ISP or any third party that takes on the business to 619 provide RVS and other needed services for HIP enabled devices. 621 The HDA is an 16 bit field (65,536 HDAs per RAA) assigned by an RAA. 622 An HDA should maintain a set of RVS servers that its client HIP- 623 enabled customers use. How this is done and scales to the 624 potentially millions of customers is outside the scope of this 625 document. This service should be discoverable through the DNS zone 626 maintained by the HDA's RAA. 628 An RAA may assign a block of values to an individual organization. 629 This is completely up to the individual RAA's published policy for 630 delegation. 632 Appendix C. ORCHIDs for Hierarchical HITs 634 This section adds the [Keccak] based cSHAKE XOF hash function from 635 NIST SP 800-185 [NIST.SP.800-185] to ORCHIDv2 [RFC7343]. cSHAKE is a 636 variable output length hash function. As such it does not use the 637 truncation operation that other hashes need. The invocation of 638 cSHAKE specifies the desired number of bits in the hash output. 640 This ORCHID construction includes the Prefix in the hash to protect 641 against Prefix subsitution attacks. It also provides for inclusion 642 of additional information, in particular the hierarchical bits of the 643 Hierarchical HIT, in the ORCHID generation. It should be viewed as 644 an addendum to ORCHIDv2 [RFC7343]. 646 cSHAKE is used, rather than SHAKE from NIST FIPS 202 [NIST.FIPS.202], 647 as cSHAKE has a parameter 'S' as a customization bit string. This 648 parameter will be used for including the ORCHID Context Identifier in 649 a standard fashion. 651 C.1. Adding additional information to the ORCHID 653 ORCHIDv2 [RFC7343] is currently defined as consisting of three 654 components: 656 ORCHID := Prefix | OGA ID | Encode_96( Hash ) 658 where: 660 Prefix : A constant 28-bit-long bitstring value 661 (IANA IPv6 assigned). 663 OGA ID : A 4-bit long identifier for the Hash_function 664 in use within the specific usage context. When 665 used for HIT generation this is the HIT Suite ID. 667 Encode_96( ) : An extraction function in which output is obtained 668 by extracting the middle 96-bit-long bitstring 669 from the argument bitstring. 671 This addendum will be constructed as follows: 673 ORCHID := Prefix | OGA ID | Info (n) | Hash (m) 675 where: 677 Prefix (p) : A (max 28-bit-long) bitstring value 678 (IANA IPv6 assigned). 680 OGA ID : A 4-bit long identifier for the Hash_function 681 in use within the specific usage context. When 682 used for HIT generation this is the HIT Suite ID. 684 Info (n) : n bits of information that define a use of the 685 ORCHID. n can be zero, that is no additional 686 information. 688 Hash (m) : An extraction function in which output is m bits. 690 p + n + m = 124 bits 691 With a 28 bit IPv6 Prefix, the 96 bits currently allocated to the 692 Encode_96 function can be divided in any manner between the 693 additional information and the hash output. Care must be taken in 694 determining the size of the hash portion, taking into account risks 695 like pre-image attacks. Thus 64 bits as used in Hierarchical HITs 696 may be as small as is acceptable. 698 C.2. ORCHID Decoding 700 With this addendum, the decoding of an ORCHID is determined by the 701 Prefix and OGA ID (HIT Suite ID). ORCHIDv2 [RFC7343] decoding is 702 selected when the Prefix is: 2001:20::/28. 704 For Heirarchical HITs, the decoding is determined by the presence of 705 the HHIT Prefix as specified in the HHIT document. 707 C.3. ORCHID Encoding 709 ORCHIDv2 has a number of inputs including a Context ID, some header 710 bits, the hash algorithm, and the input bitstream, normally just the 711 public key. The output is a 96 bit value. 713 This addendum adds a different encoding process to that currently 714 used. The input to the hash function explicitly includes all the 715 fixed header content plus the Context ID. The fixed header content 716 consists of the Prefix, OGA ID (HIT Suite ID), and the Additional 717 Information. Secondly, the length of the resulting hash is set by 718 the rules set by the Prefix/OGA ID. In the case of Hierarchical 719 HITs, this is 64 bits. 721 To achieve the variable length output in a consistent manner, the 722 cSHAKE hash is used. For this purpose, cSHAKE128 is appropriate. 723 The the cSHAKE function call for this addendum is: 725 cSHAKE128(Input, L, "", Context ID) 727 Input := Prefix | OGA ID | Additional Information | HOST_ID 728 L := Length in bits of hash portion of ORCHID 730 Hierarchical HIT uses the same context as all other HIPv2 HIT Suites 731 as they are clearly separated by the distinct HIT Suite ID. 733 Appendix D. Edward Digital Signature Algorithm for HITs 735 Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] are 736 specified here for use as Host Identities (HIs). 738 D.1. HOST_ID 740 The HOST_ID parameter specifies the public key algorithm, and for 741 elliptic curves, a name. The HOST_ID parameter is defined in 742 Section 5.2.19 of [RFC7401]. 744 Algorithm 745 profiles Values 747 EdDSA 13 [RFC8032] (RECOMMENDED) 749 For hosts that implement EdDSA as the algorithm, the following ECC 750 curves are available: 752 Algorithm Curve Values 754 EdDSA RESERVED 0 755 EdDSA EdDSA25519 1 [RFC8032] 756 EdDSA EdDSA25519ph 2 [RFC8032] 757 EdDSA EdDSA448 3 [RFC8032] 758 EdDSA EdDSA448ph 4 [RFC8032] 760 D.2. HIT_SUITE_LIST 762 The HIT_SUITE_LIST parameter contains a list of the supported HIT 763 suite IDs of the Responder. Based on the HIT_SUITE_LIST, the 764 Initiator can determine which source HIT Suite IDs are supported by 765 the Responder. The HIT_SUITE_LIST parameter is defined in 766 Section 5.2.10 of [RFC7401]. 768 The following HIT Suite ID is defined, and the relationship between 769 the four-bit ID value used in the OGA ID field and the eight-bit 770 encoding within the HIT_SUITE_LIST ID field is clarified: 772 HIT Suite Four-bit ID Eight-bit encoding 773 RESERVED 0 0x00 774 EdDSA/cSHAKE128 5 0x50 (RECOMMENDED) 776 The following table provides more detail on the above HIT Suite 777 combinations. The input for each generation algorithm is the 778 encoding of the HI as defined in this Appendix. The output is 96 779 bits long and is directly used in the ORCHID. 781 +=======+===========+=========+===========+===================+ 782 | Index | Hash | HMAC | Signature | Description | 783 | | function | | algorithm | | 784 | | | | family | | 785 +=======+===========+=========+===========+===================+ 786 | 5 | cSHAKE128 | KMAC128 | EdDSA | EdDSA HI hashed | 787 | | | | | with cSHAKE128, | 788 | | | | | output is 96 bits | 789 +-------+-----------+---------+-----------+-------------------+ 791 Table 1: HIT Suites 793 Appendix E. Calculating Collision Probabilities 795 The accepted formula for calculating the probability of a collision 796 is: 798 p = 1 - e^{-k^2/(2n)} 800 P Collision Probability 801 n Total possible population 802 k Actual population 804 Acknowledgments 806 Dr. Gurtov is an adviser on Cybersecurity to the Swedish Civil 807 Aviation Administration. 809 Quynh Dang of NIST gave considerable guidance on using Keccak and the 810 NIST supporting documents. Joan Deamen of the Keccak team was 811 especially helpful in many aspects of using Keccak. 813 Authors' Addresses 815 Robert Moskowitz 816 HTT Consulting 817 Oak Park, MI 48237 818 United States of America 820 Email: rgm@labs.htt-consult.com 821 Stuart W. Card 822 AX Enterprize 823 4947 Commercial Drive 824 Yorkville, NY 13495 825 United States of America 827 Email: stu.card@axenterprize.com 829 Adam Wiethuechter 830 AX Enterprize 831 4947 Commercial Drive 832 Yorkville, NY 13495 833 United States of America 835 Email: adam.wiethuechter@axenterprize.com 837 Andrei Gurtov 838 Linköping University 839 IDA 840 SE-58183 Linköping 841 Sweden 843 Email: gurtov@acm.org