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Wiethuechter 6 Expires: 4 September 2020 AX Enterprize 7 3 March 2020 9 Hierarchical HITs for HIPv2 10 draft-moskowitz-hip-hierarchical-hit-04 12 Abstract 14 This document describes using a hierarchical HIT to facilitate large 15 deployments of managed devices. Hierarchical HITs differ from HIPv2 16 flat HITs by only using 64 bits for mapping the Host Identity, 17 freeing 32 bits to bind in a hierarchy of Registering Entities that 18 provide services to the consumers of hierarchical HITs. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on 4 September 2020. 37 Copyright Notice 39 Copyright (c) 2020 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 44 license-info) in effect on the date of publication of this document. 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. Code Components 47 extracted from this document must include Simplified BSD License text 48 as described in Section 4.e of the Trust Legal Provisions and are 49 provided without warranty as described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 2 55 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3 56 2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Problem Space . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3.1. Meeting the future of Mobile Devices in a public space . 3 59 3.2. Semi-permanency of Identities . . . . . . . . . . . . . . 4 60 3.3. Managing a large flat address space . . . . . . . . . . . 4 61 3.4. Defense against fraudulent HITs . . . . . . . . . . . . . 4 62 4. The Hierarchical Host Identity Tag (HHIT) . . . . . . . . . . 4 63 4.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 5 64 4.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 5 65 4.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 5 66 4.3.1. The Registered Assigning Authority (RAA) . . . . . . 5 67 4.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 6 68 4.3.3. Example of the HID DNS . . . . . . . . . . . . . . . 6 69 4.3.4. HHIT DNS Retrieval . . . . . . . . . . . . . . . . . 6 70 4.3.5. Changes to ORCHIDv2 to support Hierarchical HITs . . 7 71 4.3.6. Collision risks with Hierarchical HITs . . . . . . . 7 72 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 74 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 75 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 77 8.2. Informative References . . . . . . . . . . . . . . . . . 8 78 Appendix A. Calculating Collision Probabilities . . . . . . . . 9 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 81 1. Introduction 83 This document expands on HIPv2 [RFC7401] to describe the structure of 84 a hierarchical HIT (HHIT). Some of the challenges for large scale 85 deployment addressed by HHITs are presented. The basics for the 86 hierarchical HIT registries are defined here. 88 Separate documents will further expand on the registry service and 89 how a device can advertise its availability and services provided. 91 2. Terms and Definitions 92 2.1. Requirements Terminology 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 96 "OPTIONAL" in this document are to be interpreted as described in BCP 97 14 [RFC2119] [RFC8174] when, and only when, they appear in all 98 capitals, as shown here. 100 2.2. Definitions 102 HDA (Hierarchical HIT Domain Authority): 103 The 14 bit field identifying the HIT Domain Authority under an 104 RAA. 106 HID (Hierarchy ID): 107 The 32 bit field providing the HIT Hierarchy ID. 109 RAA (Registered Assigning Authority): 110 The 18 bit field identifying the Hierarchical HIT Assigning 111 Authority. 113 RVS (Rendezvous Server): 114 The HIP Rendezvous Server for enabling mobility, as defined in 115 [RFC8004]. 117 3. Problem Space 119 3.1. Meeting the future of Mobile Devices in a public space 121 Public safety may impose a "right to know" what devices are in a 122 public space. Public space use may only be permitted to devices that 123 meet an exacting "who are you" query. This implies a device identity 124 that can be quickly validated by public safety personal and even the 125 general public in many situations. 127 Many proposals for mobile device identities are nothing more than a 128 string of bits. These may provide information about the device but 129 provide no assurance that the identity associated with a device 130 really belongs to a particular device; they are highly susceptible to 131 fraudulent use. Further they may impose a slow, complex method to 132 discover the device owner to those with appropriate authorization. 134 The Host Identity Tag (HIT) from the Host Identity Protocol (HIP) 135 provides a self-asserting Identity through a public key signing 136 operation using the Host Identity's (HI) private key. 138 Although the HIT provides a "trust me, I am me" claim, it does not 139 provide an assertion as to why the claim should be trusted and any 140 additional side information about the device. The later could be 141 distributed directly from the device in a secure manner, but again 142 there is no 3rd-party assertion of such a claim. 144 3.2. Semi-permanency of Identities 146 A device Identity has some degree of permanency. A device creates 147 its identity and registers it to some 3rd-party that will assert a 148 level of trust for that identity. A device may have multiple 149 identities to use in different contexts, and it may deprecate an 150 identity for any number of reasons. The asserting 3rd-party may 151 withdraw its assertion of an identity for any number of reasons. An 152 identity system needs to facilitate all of this. 154 3.3. Managing a large flat address space 156 For HITs to be successfully used by a large population of mobile 157 devices, they must support an Identity per device; potentially 10 158 billion Identities. Perhaps a Distributed Hash Table [RFC6537] can 159 scale this large. There is still the operational challenges in 160 establishing such a world-wide DHT implementation and how RVS 161 [RFC8004] works with such a large population. There is also the 162 challenge of how to turn this into a viable business. How can 163 different controlling jurisdictions operate in such an environment? 165 Even though the probability of collisions with 7B HITs (one HIT per 166 person) in a 96 bit flat address space is 3.9E-10, it is still real. 167 How are collisions managed? It is also possible that weak key 168 uniqueness, as has been shown in deployed TLS certificates 169 [WeakKeys], results in a much greater probability of collisions. 170 Thus resolution of collisions needs to be a feature in a global 171 namespace. 173 3.4. Defense against fraudulent HITs 175 How can a host protect against a fraudulent HIT? That is, a second 176 pre-image attack on the HI hash that produces the HIT. A strong 177 defense would require every HIT/HI registered and openly verifiable. 178 This would best be done as part of the R1 and I2 validation. Or any 179 other message that is signed by the HI private key. 181 4. The Hierarchical Host Identity Tag (HHIT) 183 The Hierarchical HIT (HHIT) is a small but important enhancement over 184 the flat HIT space. By adding two levels of hierarchical 185 administration control, the HHIT provides for device registration/ 186 ownership, thereby enhancing the trust framework for HITs. 188 HHITs represent the HI in only a 64 bit hash and uses the other 32 189 bits to create a hierarchical administration organization for HIT 190 domains. Hierarchical HITs are "Using cSHAKE in ORCHIDs" 191 [I-D.moskowitz-orchid-cshake]. The input values for the Encoding 192 rules are in Section 4.3.5. 194 A HHIT is built from the following fields: 196 * 28 bit IANA prefix 198 * 4 bit HIT Suite ID 200 * 32 bit Hierarchy ID (HID) 202 * 64 bit ORCHID hash 204 4.1. HHIT prefix 206 A unique 28 bit prefix for HHITs is recommended. It clearly 207 separates the flat-space HIT processing from HHIT processing per 208 Section 4 of "Using cSHAKE in ORCHIDs" [I-D.moskowitz-orchid-cshake]. 210 4.2. HHIT Suite IDs 212 The HIT Suite IDs specifies the HI and hash algorithms. Any HIT 213 Suite ID can be used for HHITs, provided that the prefix for HHITs is 214 different from flat space HITs. Without a unique prefix, 215 Section 4.1, additional HIT Suite IDs would be needed for HHITs. 216 This would risk exhausting the limited Suite ID space of only 15 IDs. 218 4.3. The Hierarchy ID (HID) 220 The Hierarchy ID (HID) provides the structure to organize HITs into 221 administrative domains. HIDs are further divided into 2 fields: 223 * 14 bit Registered Assigning Authority (RAA) 225 * 18 bit Hierarchical HIT Domain Authority (HDA) 227 4.3.1. The Registered Assigning Authority (RAA) 229 An RAA is a business or organization that manages a registry of HDAs. 230 For example, the Federal Aviation Authority (FAA) could be an RAA. 232 The RAA is a 14 bit field (16,384 RAAs) assigned by a numbers 233 management organization, perhaps ICANN's IANA service. An RAA must 234 provide a set of services to allocate HDAs to organizations. It must 235 have a public policy on what is necessary to obtain an HDA. The RAA 236 need not maintain any HIP related services. It must maintain a DNS 237 zone minimally for discovering HID RVS servers. 239 This DNS zone may be a PTR for its RAA. It may be a zone in a HHIT 240 specific DNS zone. Assume that the RAA is 100. The PTR record could 241 be constructed: 243 100.hhit.arpa IN PTR raa.bar.com. 245 4.3.2. The Hierarchical HIT Domain Authority (HDA) 247 An HDA may be an ISP or any third party that takes on the business to 248 provide RVS and other needed services for HIP enabled devices. 250 The HDA is an 18 bit field (262,144 HDAs per RAA) assigned by an RAA. 251 An HDA should maintain a set of RVS servers that its client HIP- 252 enabled customers use. How this is done and scales to the 253 potentially millions of customers is outside the scope of this 254 document. This service should be discoverable through the DNS zone 255 maintained by the HDA's RAA. 257 An RAA may assign a block of values to an individual organization. 258 This is completely up to the individual RAA's published policy for 259 delegation. 261 4.3.3. Example of the HID DNS 263 HID related services should be discoverable via DNS. For example the 264 RVS for a HID could be found via the following. Assume that the RAA 265 is 100 and the HDA is 50. The PTR record is constructed as: 267 50.100.hhit.arpa IN PTR rvs.foo.com. 269 The RAA is running its zone, 100.hhit.arpa under the hhit.arpa zone. 271 4.3.4. HHIT DNS Retrieval 273 The HDA SHOULD provide DNS retrieval per [RFC8005]. Assume that the 274 RAA is 10 and the HDA is 20 and the HHIT is: 276 2001:14:28:14:a3ad:1952:ad0:a69e 278 The HHIT FQDN is: 280 2001:14:28:14:a3ad:1952:ad0:a69e.20.10.hhit.arpa. 282 The NS record for the HDA zone is constructed as: 284 20.10.hhit.arpa IN NS registry.foo.com. 286 registry.foo.com returns a HIP RR with the HHIT and matching HI. The 287 HDA sets its policy on TTL for caching the HIP RR. Optionally, the 288 HDA may include RVS information. Including RVS in the HIP RR may 289 impact the TTL for the response. 291 4.3.5. Changes to ORCHIDv2 to support Hierarchical HITs 293 A new format for ORCHIDs to support Hierarchical HITs is defined in 294 "Using cSHAKE in ORCHIDs" [I-D.moskowitz-orchid-cshake]. For this 295 use the following values apply: 297 Prefix := HHIT Prefix 298 Note: per section 4.1, this should be different 299 than the Prefix for RFC 7401 300 OGA ID := 4-bit Orchid Generation Algorithm identifier 301 The HHIT Suite ID 302 Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40 303 Info (n) := 32 bit HID (Hierarchy ID) 304 Hash := Hash_function specified in OGA ID 305 If hash is not a variable length output hash, 306 then en Encode_m, similar to ORCHID Encode_96 307 is used 308 m := 64 310 4.3.6. Collision risks with Hierarchical HITs 312 The 64 bit hash size does have an increased risk of collisions over 313 the 96 bit hash size used for the other HIT Suites. There is a 0.01% 314 probability of a collision in a population of 66 million. The 315 probability goes up to 1% for a population of 663 million. See 316 Appendix A for the collision probability formula. 318 However, this risk of collision is within a single HDA. Further, all 319 HDAs are expected to provide a registration process for reverse 320 lookup validation. This registration process would reject a 321 collision, forcing the client to generate a new HI and thus 322 hierarchical HIT and reapplying to the registration process. 324 5. IANA Considerations 326 Because HHIT use of ORCHIDv2 format is not compatible with [RFC7343], 327 IANA is requested to allocated a new 28-bit prefix out of the IANA 328 IPv6 Special Purpose Address Block, namely 2001:0000::/23, as per 329 [RFC6890]. 331 6. Security Considerations 333 A 64 bit hash space presents a real risk of second pre-image attacks. 334 The HHIT Registry services effectively block attempts to "take over" 335 a HHIT. It does not stop a rogue attempting to impersonate a known 336 HHIT. This attack can be mitigated by the Responder using DNS to 337 find the HI for the HHIT or the RVS for the HHIT that then provides 338 the registered HI. 340 The two risks with hierarchical HITs are the use of an invalid HID 341 and forced HIT collisions. The use of the "hhit.arpa." DNS zone is 342 a strong protection against invalid HIDs. Querying an HDA's RVS for 343 a HIT under the HDA protects against talking to unregistered clients. 344 The Registry service has direct protection against forced or 345 accidental HIT hash collisions. 347 7. Acknowledgments 349 The initial versions of this document were developed with the 350 assistance of Xiaohu Xu and Bingyang Liu of Huawei. 352 Sue Hares contributed to the clarity in this document. 354 8. References 356 8.1. Normative References 358 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 359 Requirement Levels", BCP 14, RFC 2119, 360 DOI 10.17487/RFC2119, March 1997, 361 . 363 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 364 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 365 May 2017, . 367 8.2. Informative References 369 [I-D.moskowitz-orchid-cshake] 370 Moskowitz, R., Card, S., and A. Wiethuechter, "Using 371 cSHAKE in ORCHIDs", Work in Progress, Internet-Draft, 372 draft-moskowitz-orchid-cshake-00, 11 December 2019, 373 . 376 [RFC6537] Ahrenholz, J., "Host Identity Protocol Distributed Hash 377 Table Interface", RFC 6537, DOI 10.17487/RFC6537, February 378 2012, . 380 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 381 "Special-Purpose IP Address Registries", BCP 153, 382 RFC 6890, DOI 10.17487/RFC6890, April 2013, 383 . 385 [RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay 386 Routable Cryptographic Hash Identifiers Version 2 387 (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September 388 2014, . 390 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 391 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 392 RFC 7401, DOI 10.17487/RFC7401, April 2015, 393 . 395 [RFC8004] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 396 Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004, 397 October 2016, . 399 [RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name 400 System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005, 401 October 2016, . 403 [WeakKeys] Heninger, N.H., Durumeric, Z.D., Wustrow, E.W., and J.A.H. 404 Halderman, "Detection of Widespread Weak Keys in Network 405 Devices", August 2012, 406 . 408 Appendix A. Calculating Collision Probabilities 410 The accepted formula for calculating the probability of a collision 411 is: 413 p = 1 - e^{-k^2/(2n)} 415 P Collision Probability 416 n Total possible population 417 k Actual population 419 Authors' Addresses 421 Robert Moskowitz 422 HTT Consulting 423 Oak Park, MI 48237 424 United States of America 426 Email: rgm@labs.htt-consult.com 427 Stuart W. Card 428 AX Enterprize 429 4947 Commercial Drive 430 Yorkville, NY 13495 431 United States of America 433 Email: stu.card@axenterprize.com 435 Adam Wiethuechter 436 AX Enterprize 437 4947 Commercial Drive 438 Yorkville, NY 13495 439 United States of America 441 Email: adam.wiethuechter@axenterprize.com