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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Moskowitz, Ed. 3 Internet-Draft Verizon 4 Obsoletes: 4423 (if approved) M. Komu 5 Intended status: Informational Aalto 6 Expires: June 21, 2014 December 18, 2013 8 Host Identity Protocol Architecture 9 draft-ietf-hip-rfc4423-bis-07 11 Abstract 13 This memo describes a new namespace, the Host Identity namespace, and 14 a new protocol layer, the Host Identity Protocol, between the 15 internetworking and transport layers. Herein are presented the 16 basics of the current namespaces, their strengths and weaknesses, and 17 how a new namespace will add completeness to them. The roles of this 18 new namespace in the protocols are defined. 20 This document obsoletes RFC 4423 and addresses the concerns raised by 21 the IESG, particularly that of crypto agility. It incorporates 22 lessons learned from the implementations of RFC 5201 and goes further 23 to explain how HIP works as a secure signaling channel. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on June 21, 2014. 42 Copyright Notice 44 Copyright (c) 2013 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 This document may contain material from IETF Documents or IETF 58 Contributions published or made publicly available before November 59 10, 2008. The person(s) controlling the copyright in some of this 60 material may not have granted the IETF Trust the right to allow 61 modifications of such material outside the IETF Standards Process. 62 Without obtaining an adequate license from the person(s) controlling 63 the copyright in such materials, this document may not be modified 64 outside the IETF Standards Process, and derivative works of it may 65 not be created outside the IETF Standards Process, except to format 66 it for publication as an RFC or to translate it into languages other 67 than English. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . 4 72 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 73 2.1. Terms common to other documents . . . . . . . . . . . . . 5 74 2.2. Terms specific to this and other HIP documents . . . . . 5 75 3. Background . . . . . . . . . . . . . . . . . . . . . . . 7 76 3.1. A desire for a namespace for computing platforms . . . . 7 77 4. Host Identity namespace . . . . . . . . . . . . . . . . . 9 78 4.1. Host Identifiers . . . . . . . . . . . . . . . . . . . . 10 79 4.2. Host Identity Hash (HIH) . . . . . . . . . . . . . . . . 11 80 4.3. Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . 11 81 4.4. Local Scope Identifier (LSI) . . . . . . . . . . . . . . 11 82 4.5. Storing Host Identifiers in directories . . . . . . . . . 12 83 5. New stack architecture . . . . . . . . . . . . . . . . . 13 84 5.1. On the multiplicity of identities . . . . . . . . . . . . 14 85 6. Control plane . . . . . . . . . . . . . . . . . . . . . . 15 86 6.1. Base exchange . . . . . . . . . . . . . . . . . . . . . . 15 87 6.2. End-host mobility and multi-homing . . . . . . . . . . . 16 88 6.3. Rendezvous mechanism . . . . . . . . . . . . . . . . . . 16 89 6.4. Relay mechanism . . . . . . . . . . . . . . . . . . . . . 17 90 6.5. Termination of the control plane . . . . . . . . . . . . 17 91 7. Data plane . . . . . . . . . . . . . . . . . . . . . . . 17 92 8. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . 18 93 8.1. HIP and Upper-layer checksums . . . . . . . . . . . . . . 19 94 9. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 19 95 10. HIP policies . . . . . . . . . . . . . . . . . . . . . . 19 96 11. Design considerations . . . . . . . . . . . . . . . . . . 20 97 11.1. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . 20 98 11.2. Drawbacks of HIP . . . . . . . . . . . . . . . . . . . . 23 99 11.3. Deployment and adoption considerations . . . . . . . . . 24 100 11.3.1. Deployment analysis . . . . . . . . . . . . . . . . . . . 24 101 11.3.2. HIP in 802.15.4 networks . . . . . . . . . . . . . . . . 25 102 11.4. Answers to NSRG questions . . . . . . . . . . . . . . . . 26 103 12. Security considerations . . . . . . . . . . . . . . . . . 28 104 12.1. MiTM Attacks . . . . . . . . . . . . . . . . . . . . . . 28 105 12.2. Protection against flooding attacks . . . . . . . . . . . 29 106 12.3. HITs used in ACLs . . . . . . . . . . . . . . . . . . . . 30 107 12.4. Alternative HI considerations . . . . . . . . . . . . . . 31 108 13. IANA considerations . . . . . . . . . . . . . . . . . . . 32 109 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 32 110 15. Changes from RFC 4423 . . . . . . . . . . . . . . . . . . 32 111 16. References . . . . . . . . . . . . . . . . . . . . . . . 33 112 16.1. Normative References . . . . . . . . . . . . . . . . . . 33 113 16.2. Informative references . . . . . . . . . . . . . . . . . 34 114 Authors' Addresses . . . . . . . . . . . . . . . . . . . 40 116 1. Introduction 118 The Internet has two important global namespaces: Internet Protocol 119 (IP) addresses and Domain Name Service (DNS) names. These two 120 namespaces have a set of features and abstractions that have powered 121 the Internet to what it is today. They also have a number of 122 weaknesses. Basically, since they are all we have, we try and do too 123 much with them. Semantic overloading and functionality extensions 124 have greatly complicated these namespaces. 126 The proposed Host Identity namespace fills an important gap between 127 the IP and DNS namespaces. A Host Identity conceptually refers to a 128 computing platform, and there may be multiple such Host Identities 129 per computing platform (because the platform may wish to present a 130 different identity to different communicating peers). The Host 131 Identity namespace consists of Host Identifiers (HI). There is 132 exactly one Host Identifier for each Host Identity. While this text 133 later talks about non-cryptographic Host Identifiers, the 134 architecture focuses on the case in which Host Identifiers are 135 cryptographic in nature. Specifically, the Host Identifier is the 136 public key of an asymmetric key-pair. Each Host Identity uniquely 137 identifies a single host, i.e., no two hosts have the same Host 138 Identity. If two or more computing platforms have the same Host 139 Identifier, then they are instantiating a distributed host. The Host 140 Identifier can either be public (e.g. published in the DNS), or 141 unpublished. Client systems will tend to have both public and 142 unpublished Host Identifiers. 144 There is a subtle but important difference between Host Identities 145 and Host Identifiers. An Identity refers to the abstract entity that 146 is identified. An Identifier, on the other hand, refers to the 147 concrete bit pattern that is used in the identification process. 149 Although the Host Identifiers could be used in many authentication 150 systems, such as IKEv2 [RFC4306], the presented architecture 151 introduces a new protocol, called the Host Identity Protocol (HIP), 152 and a cryptographic exchange, called the HIP base exchange; see also 153 Section 7. HIP provides for limited forms of trust between systems, 154 enhance mobility, multi-homing and dynamic IP renumbering, aid in 155 protocol translation / transition, and reduce certain types of 156 denial-of-service (DoS) attacks. 158 When HIP is used, the actual payload traffic between two HIP hosts is 159 typically, but not necessarily, protected with ESP. The Host 160 Identities are used to create the needed ESP Security Associations 161 (SAs) and to authenticate the hosts. When ESP is used, the actual 162 payload IP packets do not differ in any way from standard ESP 163 protected IP packets. 165 Much has been learned about HIP [RFC6538] since [RFC4423] was 166 published. This document expands Host Identities beyond use to 167 enable IP connectivity and security to general interhost secure 168 signalling at any protocol layer. The signal may establish a 169 security association between the hosts, or simply pass information 170 within the channel. 172 2. Terminology 174 2.1. Terms common to other documents 176 +---------------+---------------------------------------------------+ 177 | Term | Explanation | 178 +---------------+---------------------------------------------------+ 179 | Public key | The public key of an asymmetric cryptographic key | 180 | | pair. Used as a publicly known identifier for | 181 | | cryptographic identity authentication. Public is | 182 | | a relative term here, ranging from known to peers | 183 | | only to known to the World. | 184 | | | 185 | Private key | The private or secret key of an asymmetric | 186 | | cryptographic key pair. Assumed to be known only | 187 | | to the party identified by the corresponding | 188 | | public key. Used by the identified party to | 189 | | authenticate its identity to other parties. | 190 | | | 191 | Public key | An asymmetric cryptographic key pair consisting | 192 | pair | of public and private keys. For example, | 193 | | Rivest-Shamir-Adelman (RSA), Digital Signature | 194 | | Algorithm (DSA) and Elliptic Curve DSA (ECDSA) | 195 | | key pairs are such key pairs. | 196 | | | 197 | End-point | A communicating entity. For historical reasons, | 198 | | the term 'computing platform' is used in this | 199 | | document as a (rough) synonym for end-point. | 200 +---------------+---------------------------------------------------+ 202 2.2. Terms specific to this and other HIP documents 204 It should be noted that many of the terms defined herein are 205 tautologous, self-referential or defined through circular reference 206 to other terms. This is due to the succinct nature of the 207 definitions. See the text elsewhere in this document and in RFC 5201 208 [I-D.ietf-hip-rfc5201-bis] for more elaborate explanations. 210 +---------------+---------------------------------------------------+ 211 | Term | Explanation | 212 +---------------+---------------------------------------------------+ 213 | Computing | An entity capable of communicating and computing, | 214 | platform | for example, a computer. See the definition of | 215 | | 'End-point', above. | 216 | | | 217 | HIP base | A cryptographic protocol; see also Section 7. | 218 | exchange | | 219 | | | 220 | HIP packet | An IP packet that carries a 'Host Identity | 221 | | Protocol' message. | 222 | | | 223 | Host Identity | An abstract concept assigned to a 'computing | 224 | | platform'. See 'Host Identifier', below. | 225 | | | 226 | Host Identity | A name space formed by all possible Host | 227 | namespace | Identifiers. | 228 | | | 229 | Host Identity | A protocol used to carry and authenticate Host | 230 | Protocol | Identifiers and other information. | 231 | | | 232 | Host Identity | The cryptographic hash used in creating the Host | 233 | Hash | Identity Tag from the Host Identity. | 234 | | | 235 | Host Identity | A 128-bit datum created by taking a cryptographic | 236 | Tag | hash over a Host Identifier plus bits to identify | 237 | | which hash used. | 238 | | | 239 | Host | A public key used as a name for a Host Identity. | 240 | Identifier | | 241 | | | 242 | Local Scope | A 32-bit datum denoting a Host Identity. | 243 | Identifier | | 244 | | | 245 | Public Host | A published or publicly known Host Identifier | 246 | Identifier | used as a public name for a Host Identity, and | 247 | and Identity | the corresponding Identity. | 248 | | | 249 | Unpublished | A Host Identifier that is not placed in any | 250 | Host | public directory, and the corresponding Host | 251 | Identifier | Identity. Unpublished Host Identities are | 252 | and Identity | typically short lived in nature, being often | 253 | | replaced and possibly used just once. | 254 | | | 255 | Rendezvous | A mechanism used to locate mobile hosts based on | 256 | Mechanism | their HIT. | 257 +---------------+---------------------------------------------------+ 259 3. Background 261 The Internet is built from three principal components: computing 262 platforms (end-points), packet transport (i.e., internetworking) 263 infrastructure, and services (applications). The Internet exists to 264 service two principal components: people and robotic services 265 (silicon-based people, if you will). All these components need to be 266 named in order to interact in a scalable manner. Here we concentrate 267 on naming computing platforms and packet transport elements. 269 There are two principal namespaces in use in the Internet for these 270 components: IP addresses, and Domain Names. Domain Names provide 271 hierarchically assigned names for some computing platforms and some 272 services. Each hierarchy is delegated from the level above; there is 273 no anonymity in Domain Names. Email, HTTP, and SIP addresses all 274 reference Domain Names. 276 The IP addressing namespace has been overloaded to name both 277 interfaces (at layer-3) and endpoints (for the endpoint-specific part 278 of layer-3, and for layer-4). In their role as interface names, IP 279 addresses are sometimes called "locators" and serve as an endpoint 280 within a routing topology. 282 IP addresses are numbers that name networking interfaces, and 283 typically only when the interface is connected to the network. 284 Originally, IP addresses had long-term significance. Today, the vast 285 number of interfaces use ephemeral and/or non-unique IP addresses. 286 That is, every time an interface is connected to the network, it is 287 assigned an IP address. 289 In the current Internet, the transport layers are coupled to the IP 290 addresses. Neither can evolve separately from the other. IPng 291 deliberations were strongly shaped by the decision that a 292 corresponding TCPng would not be created. 294 There are three critical deficiencies with the current namespaces. 295 Firstly, dynamic readdressing cannot be directly managed. Secondly, 296 confidentiality is not provided in a consistent, trustable manner. 297 Finally, authentication for systems and datagrams is not provided. 298 All of these deficiencies arise because computing platforms are not 299 well named with the current namespaces. 301 3.1. A desire for a namespace for computing platforms 303 An independent namespace for computing platforms could be used in 304 end-to-end operations independent of the evolution of the 305 internetworking layer and across the many internetworking layers. 306 This could support rapid readdressing of the internetworking layer 307 because of mobility, rehoming, or renumbering. 309 If the namespace for computing platforms is based on public-key 310 cryptography, it can also provide authentication services. If this 311 namespace is locally created without requiring registration, it can 312 provide anonymity. 314 Such a namespace (for computing platforms) and the names in it should 315 have the following characteristics: 317 o The namespace should be applied to the IP 'kernel' or stack. The 318 IP stack is the 'component' between applications and the packet 319 transport infrastructure. 321 o The namespace should fully decouple the internetworking layer from 322 the higher layers. The names should replace all occurrences of IP 323 addresses within applications (like in the Transport Control 324 Block, TCB). This replacement can be handled transparently for 325 legacy applications as the LSIs and HITs are compatible with IPv4 326 and IPv6 addresses [RFC5338]. However, HIP-aware applications 327 require some modifications from the developers, who may employ 328 networking API extensions for HIP [RFC6317]. 330 o The introduction of the namespace should not mandate any 331 administrative infrastructure. Deployment must come from the 332 bottom up, in a pairwise deployment. 334 o The names should have a fixed length representation, for easy 335 inclusion in datagram headers and existing programming interfaces 336 (e.g the TCB). 338 o Using the namespace should be affordable when used in protocols. 339 This is primarily a packet size issue. There is also a 340 computational concern in affordability. 342 o Name collisions should be avoided as much as possible. The 343 mathematics of the birthday paradox can be used to estimate the 344 chance of a collision in a given population and hash space. In 345 general, for a random hash space of size n bits, we would expect 346 to obtain a collision after approximately 1.2*sqrt(2**n) hashes 347 were obtained. For 64 bits, this number is roughly 4 billion. A 348 hash size of 64 bits may be too small to avoid collisions in a 349 large population; for example, there is a 1% chance of collision 350 in a population of 640M. For 100 bits (or more), we would not 351 expect a collision until approximately 2**50 (1 quadrillion) 352 hashes were generated. 354 o The names should have a localized abstraction so that it can be 355 used in existing protocols and APIs. 357 o It must be possible to create names locally. When such names are 358 not published, this can provide anonymity at the cost of making 359 resolvability very difficult. 361 o The namespace should provide authentication services. 363 o The names should be long lived, but replaceable at any time. This 364 impacts access control lists; short lifetimes will tend to result 365 in tedious list maintenance or require a namespace infrastructure 366 for central control of access lists. 368 In this document, a new namespace approaching these ideas is called 369 the Host Identity namespace. Using Host Identities requires its own 370 protocol layer, the Host Identity Protocol, between the 371 internetworking and transport layers. The names are based on public- 372 key cryptography to supply authentication services. Properly 373 designed, it can deliver all of the above stated requirements. 375 4. Host Identity namespace 377 A name in the Host Identity namespace, a Host Identifier (HI), 378 represents a statistically globally unique name for naming any system 379 with an IP stack. This identity is normally associated with, but not 380 limited to, an IP stack. A system can have multiple identities, some 381 'well known', some unpublished or 'anonymous'. A system may self- 382 assert its own identity, or may use a third-party authenticator like 383 DNSSEC [RFC2535], PGP, or X.509 to 'notarize' the identity assertion 384 to another namespace. It is expected that the Host Identifiers will 385 initially be authenticated with DNSSEC and that all implementations 386 will support DNSSEC as a minimal baseline. 388 In theory, any name that can claim to be 'statistically globally 389 unique' may serve as a Host Identifier. In the HIP architecture, the 390 public key of a private-public key pair has been chosen as the Host 391 Identifier because it can be self managed and it is computationally 392 difficult to forge. As specified in the Host Identity Protocol 393 [I-D.ietf-hip-rfc5201-bis] specification, a public-key-based HI can 394 authenticate the HIP packets and protect them for man-in-the-middle 395 attacks. Since authenticated datagrams are mandatory to provide much 396 of HIP's denial-of-service protection, the Diffie-Hellman exchange in 397 HIP BEX has to be authenticated. Thus, only public-key HI and 398 authenticated HIP messages are supported in practice. 400 In this document, the non-cryptographic forms of HI and HIP are 401 presented to complete the theory of HI, but they should not be 402 implemented as they could produce worse denial-of-service attacks 403 than the Internet has without Host Identity. There has been past 404 research in challenge puzzles to use non-cryptographic HI, for Radio 405 Frequency IDentification (RFID), in an HIP exchange tailored to the 406 workings of such challenges (as described further in [urien-rfid] and 407 [urien-rfid-draft]). 409 4.1. Host Identifiers 411 Host Identity adds two main features to Internet protocols. The 412 first is a decoupling of the internetworking and transport layers; 413 see Section 5. This decoupling will allow for independent evolution 414 of the two layers. Additionally, it can provide end-to-end services 415 over multiple internetworking realms. The second feature is host 416 authentication. Because the Host Identifier is a public key, this 417 key can be used for authentication in security protocols like ESP. 419 The only completely defined structure of the Host Identity is that of 420 a public/private key pair. In this case, the Host Identity is 421 referred to by its public component, the public key. Thus, the name 422 representing a Host Identity in the Host Identity namespace, i.e., 423 the Host Identifier, is the public key. In a way, the possession of 424 the private key defines the Identity itself. If the private key is 425 possessed by more than one node, the Identity can be considered to be 426 a distributed one. 428 Architecturally, any other Internet naming convention might form a 429 usable base for Host Identifiers. However, non-cryptographic names 430 should only be used in situations of high trust - low risk. That is 431 any place where host authentication is not needed (no risk of host 432 spoofing) and no use of ESP. However, at least for interconnected 433 networks spanning several operational domains, the set of 434 environments where the risk of host spoofing allowed by non- 435 cryptographic Host Identifiers is acceptable is the null set. Hence, 436 the current HIP documents do not specify how to use any other types 437 of Host Identifiers but public keys. For instance, Back-to-My-Mac 438 [RFC6281] from Apple comes pretty close to the functionality of HIP, 439 but unlike HIP, it is based on non-cryptographic identifiers. 441 The actual Host Identifiers are never directly used at the transport 442 or network layers. The corresponding Host Identifiers (public keys) 443 may be stored in various DNS or other directories as identified 444 elsewhere in this document, and they are passed in the HIP base 445 exchange. A Host Identity Tag (HIT) is used in other protocols to 446 represent the Host Identity. Another representation of the Host 447 Identities, the Local Scope Identifier (LSI), can also be used in 448 protocols and APIs. 450 4.2. Host Identity Hash (HIH) 452 The Host Identity Hash is the cryptographic hash algorithm used in 453 producing the HIT from the HI. It is also the hash used through out 454 the HIP protocol for consistency and simplicity. It is possible to 455 for the two hosts in the HIP exchange to use different hash 456 algorithms. 458 Multiple HIHs within HIP are needed to address the moving target of 459 creation and eventual compromise of cryptographic hashes. This 460 significantly complicates HIP and offers an attacker an additional 461 downgrade attack that is mitigated in the HIP protocol 462 [I-D.ietf-hip-rfc5201-bis]. 464 4.3. Host Identity Tag (HIT) 466 A Host Identity Tag is a 128-bit representation for a Host Identity. 467 It is created from an HIH and other information, like an IPv6 prefix 468 and a hash identifier. There are two advantages of using the HIT 469 over using the Host Identifier in protocols. Firstly, its fixed 470 length makes for easier protocol coding and also better manages the 471 packet size cost of this technology. Secondly, it presents the 472 identity in a consistent format to the protocol independent of the 473 cryptographic algorithms used. 475 In essence, the HIT is a hash over the public key. As such, two 476 algorithms affect the generation of a HIT: the public-key algorithm 477 of the HI and the used HIH. The two algorithms are encoded in the 478 bit presentation of the HIT. As the two communicating parties may 479 support different algorithms, [I-D.ietf-hip-rfc5201-bis] defines the 480 minimum set for interoperability. For further interoperability, the 481 responder may store its keys in DNS records, and thus the initiator 482 may have to couple destination HITs with appropriate source HIts 483 according to matching HIH. 485 In the HIP packets, the HITs identify the sender and recipient of a 486 packet. Consequently, a HIT should be unique in the whole IP 487 universe as long as it is being used. In the extremely rare case of 488 a single HIT mapping to more than one Host Identity, the Host 489 Identifiers (public keys) will make the final difference. If there 490 is more than one public key for a given node, the HIT acts as a hint 491 for the correct public key to use. 493 4.4. Local Scope Identifier (LSI) 495 An LSI is a 32-bit localized representation for a Host Identity. The 496 purpose of an LSI is to facilitate using Host Identities in existing 497 APIs for IPv4-based applications. Besides facilitating HIP-based 498 connectivity for legacy IPv4 applications, the LSIs are beneficial in 499 two other scenarios [RFC6538]. 501 In the first scenario, two IPv4-only applications are residing on two 502 separate hosts connected by IPv6-only network. With HIP-based 503 connectivity, the two applications are able to communicate despite of 504 the mismatch in the protocol families of the applications and the 505 underlying network. The reason is that the HIP layer translates the 506 LSIs originating from the upper layers into routable IPv6 locators 507 before delivering the packets on the wire. 509 The second scenario is the same as the first one, but with the 510 difference that one of the applications supports only IPv6. Now two 511 obstacles hinder the communication between the application: the 512 addressing families of the two applications differ, and the 513 application residing at the IPv4-only side is again unable to 514 communicate because of the mismatch between addressing families of 515 the application (IPv4) and network (IPv6). With HIP-based 516 connectivity for applications, this scenario works; the HIP layer can 517 choose whether to translate the locator of an incoming packet into an 518 LSI or HIT. 520 Effectively, LSIs improve IPv6 interoperability at the network layer 521 as described in the first scenario and at the application layer as 522 depicted in the second example. The interoperability mechanism 523 should not be used to avoid transition to IPv6; the authors firmly 524 believe in IPv6 adoption and encourage developers to port existing 525 IPv4-only applications to use IPv6. However, some proprietary, 526 closed-source, IPv4-only applications may never see the daylight of 527 IPv6, and the LSI mechanism is suitable for extending the lifetime of 528 such applications even in IPv6-only networks. 530 The main disadvantage of an LSI is its local scope. Applications may 531 violate layering principles and pass LSIs to each other in 532 application-layer protocols. As the LSIs are valid only in the 533 context of the local host, they may represent an entirely different 534 host when passed to another host. However, it should be emphasized 535 here that the LSI concept is effectively a host-based NAT and does 536 not introduce any more issues than the prevalent middlebox based NATs 537 for IPv4. In other words, the applications violating layering 538 principles are already broken by the NAT boxes that are ubiquitously 539 deployed. 541 4.5. Storing Host Identifiers in directories 543 The public Host Identifiers should be stored in DNS; the unpublished 544 Host Identifiers should not be stored anywhere (besides the 545 communicating hosts themselves). The (public) HI along with the 546 supported HIHs are stored in a new RR type. This RR type is defined 547 in HIP DNS Extension [I-D.ietf-hip-rfc5205-bis]. 549 Alternatively, or in addition to storing Host Identifiers in the DNS, 550 they may be stored in various other directories. For instance, 551 Light-weight Directory Access Protocol (LDAP) or in a Public Key 552 Infrastructure (PKI) [I-D.ietf-hip-rfc6253-bis]. Alternatively, 553 Distributed Hash Tables (DHTs) [RFC6537] have successfully been 554 utilized [RFC6538]. Such a practice may allow them to be used for 555 purposes other than pure host identification. 557 Some types of application may cache and use Host Identifiers 558 directly, while others may indirectly discover them through symbolic 559 host name (such as FQDN) look up from a directory. Even though Host 560 Identities can have a substantially longer lifetime associate with 561 them than routable IP addresses, directories may be a better approach 562 to manage the lifespan of Host Identities. For example, a LDAP or 563 DHT can be used for locally published identities whereas DNS can be 564 more suitable for public advertisement. 566 5. New stack architecture 568 One way to characterize Host Identity is to compare the proposed new 569 architecture with the current one. As discussed above, the IP 570 addresses can be seen to be a confounding of routing direction 571 vectors and interface names. Using the terminology from the IRTF 572 Name Space Research Group Report [nsrg-report] and, e.g., the 573 unpublished Internet-Draft Endpoints and Endpoint Names 574 [chiappa-endpoints], the IP addresses currently embody the dual role 575 of locators and end-point identifiers. That is, each IP address 576 names a topological location in the Internet, thereby acting as a 577 routing direction vector, or locator. At the same time, the IP 578 address names the physical network interface currently located at the 579 point-of-attachment, thereby acting as a end-point name. 581 In the HIP architecture, the end-point names and locators are 582 separated from each other. IP addresses continue to act as locators. 583 The Host Identifiers take the role of end-point identifiers. It is 584 important to understand that the end-point names based on Host 585 Identities are slightly different from interface names; a Host 586 Identity can be simultaneously reachable through several interfaces. 588 The difference between the bindings of the logical entities are 589 illustrated in Figure 1. Left side illustrates the current TCP/IP 590 architecture and right side the HIP-based architecture. 592 Transport ---- Socket Transport ------ Socket 593 association | association | 594 | | 595 | | 596 | | 597 End-point | End-point --- Host Identity 598 \ | | 599 \ | | 600 \ | | 601 \ | | 602 Location --- IP address Location --- IP address 604 Figure 1 606 Architecturally, HIP provides for a different binding of transport- 607 layer protocols. That is, the transport-layer associations, i.e., 608 TCP connections and UDP associations, are no longer bound to IP 609 addresses but rather to Host Identities. In practice, the Host 610 Identities are exposed as LSIs and HITs for legacy applications and 611 the transport layer to facilitate backward compatibility with 612 existing networking APIs and stacks. 614 5.1. On the multiplicity of identities 616 A host may have multiple identities both at the client and server 617 side. This raises some additional concerns that are addressed in 618 this section. 620 For security reasons, it may be a bad idea to duplicate the same Host 621 Identity on multiple hosts because the compromise of a single host 622 taints the identities of the other hosts. Management of machines 623 with identical Host Identities may also present other challenges and, 624 therefore, it is advisable to have a unique identity for each host. 626 Instead of duplicating identities, HIP opportunistic mode can be 627 employed, where the initiator leaves out the identifier of the 628 responder when initiating the key exchange and learns it upon the 629 completion of the exchange. The tradeoffs are related to lowered 630 security guarantees, but a benefit of the approach is to avoid 631 publishing of Host Identifiers in any directories [komu-leap]. The 632 approach could also be used for load balancing purposes at the HIP 633 layer because the identity of the responder can be decided 634 dynamically during the key exchange. Thus, the approach has the 635 potential to be used as a HIP-layer "anycast", either directly 636 between two hosts or indirectly through the rendezvous service 637 [komu-diss]. 639 At the client side, a host may have multiple Host Identities, for 640 instance, for privacy purposes. Another reason can be that the 641 person utilizing the host employs different identities for different 642 administrative domains as an extra security measure. If a HIP-aware 643 middlebox, such as a HIP-based firewall, is on the path between the 644 client and server, the user or the underlying system should carefully 645 choose the correct identity to avoid the firewall to unnecessarily 646 drop HIP-base connectivity [komu-diss]. 648 Similarly, a server may have multiple Host Identities. For instance, 649 a single web server may serve multiple different administrative 650 domains. Typically, the distinction is accomplished based on the DNS 651 name, but also the Host Identity could be used for this purpose. 652 However, a more compelling reason to employ multiple identities are 653 HIP-aware firewalls that are unable see the HTTP traffic inside the 654 encrypted IPsec tunnel. In such a case, each service could be 655 configured with a separate identity, thus allowing the firewall to 656 segregate the different services of the single web server from each 657 other [lindqvist-enterprise]. 659 6. Control plane 661 HIP decouples control and data plane from each other. Two end-hosts 662 initialize the control plane using a key exchange procedure called 663 the base exchange. The procedure can be assisted by new 664 infrastructural intermediaries called rendezvous or relay servers. 665 In the event of IP address changes, the end-hosts sustain control 666 plane connectivity with mobility and multihoming extensions. 667 Eventually, the end-hosts terminate the control plane and remove the 668 associated state. 670 6.1. Base exchange 672 The base exchange is a key exchange procedure that authenticates the 673 initiator and responder to each other using their public keys. 674 Typically, the initiator is the client-side host and the responder is 675 the server-side host. The roles are used by the state machine of a 676 HIP implementation, but discarded upon successful completion. 678 The exchange consists of four messages during which the hosts also 679 create symmetric keys to protect the control plane with Hash-based 680 message authentication codes (HMACs). The keys can be also used to 681 protect the data plane, and IPsec ESP [I-D.ietf-hip-rfc5202-bis] is 682 typically used as the data-plane protocol, albeit HIP can also 683 accommodate others. Both the control and data plane are terminated 684 using a closing procedure consisting of two messages. 686 In addition, the base exchange also includes a computational puzzle 687 [I-D.ietf-hip-rfc5201-bis] that the initiator must solve. The 688 responder chooses the difficulty of the puzzle which permits the 689 responder to delay new incoming initiators according to local 690 policies, for instance, when the responder is under heavy load. The 691 puzzle can offer some resiliency against DoS attacks because the 692 design of the puzzle mechanism allows the responder to remain 693 stateless until the very end of the base exchange [aura-dos]. HIP 694 puzzles have also been studied under steady-state DDoS attacks 695 [beal-dos], on multiple adversary models with varying puzzle 696 difficulties [tritilanunt-dos] and with ephemeral Host Identities 697 [komu-mitigation]. 699 6.2. End-host mobility and multi-homing 701 HIP decouples the transport from the internetworking layer, and binds 702 the transport associations to the Host Identities (actually through 703 either the HIT or LSI). After the initial key exchange, the HIP 704 layer maintains transport-layer connectivity and data flows using its 705 mobility [I-D.ietf-hip-rfc5206-bis] and multihoming 706 [I-D.ietf-hip-multihoming] extensions. Consequently, HIP can provide 707 for a degree of internetworking mobility and multi-homing at a low 708 infrastructure cost. HIP mobility includes IP address changes (via 709 any method) to either party. Thus, a system is considered mobile if 710 its IP address can change dynamically for any reason like PPP, DHCP, 711 IPv6 prefix reassignments, or a NAT device remapping its translation. 712 Likewise, a system is considered multi-homed if it has more than one 713 globally routable IP address at the same time. HIP links IP 714 addresses together, when multiple IP addresses correspond to the same 715 Host Identity. If one address becomes unusable, or a more preferred 716 address becomes available, existing transport associations can easily 717 be moved to another address. 719 When a node moves while communication is already on-going, address 720 changes are rather straightforward. The peer of the mobile node can 721 just accept a HIP or an integrity protected ESP packet from any 722 address and ignore the source address. However, as discussed in 723 Section 12.2 below, a mobile node must send a HIP UPDATE packet to 724 inform the peer of the new address(es), and the peer must verify that 725 the mobile node is reachable through these addresses. This is 726 especially helpful for those situations where the peer node is 727 sending data periodically to the mobile node (that is, re-starting a 728 connection after the initial connection). 730 6.3. Rendezvous mechanism 732 Establishing a contact to a mobile, moving node is slightly more 733 involved. In order to start the HIP exchange, the initiator node has 734 to know how to reach the mobile node. For instance, the mobile node 735 can employ Dynamic DNS [RFC2136] to update its reachability 736 information in the DNS. To avoid the dependency to DNS, HIP provides 737 its own HIP-specific alternative: the HIP rendezvous mechanism as 738 defined in HIP Rendezvous specifications [I-D.ietf-hip-rfc5204-bis]. 740 Using the HIP rendezvous extensions, the mobile node keeps the 741 rendezvous infrastructure continuously updated with its current IP 742 address(es). The mobile nodes trusts the rendezvous mechanism in 743 order to properly maintain their HIT and IP address mappings. 745 The rendezvous mechanism is especially useful in scenarios where both 746 of the nodes are expected to change their address at the same time. 747 In such a case, the HIP UPDATE packets will cross each other in the 748 network and never reach the peer node. 750 6.4. Relay mechanism 752 The HIP relay mechanism [I-D.ietf-hip-native-nat-traversal] is an 753 alternative to the HIP rendezvous mechanism. The HIP relay mechanism 754 is more suitable for IPv4 networks with NATs because a HIP relay can 755 forward all control and data plane communications in order to 756 guarantee successful NAT traversal. 758 6.5. Termination of the control plane 760 The control plane between two hosts is terminated using a secure two 761 message exchange as specified in base exchange specification 762 [I-D.ietf-hip-rfc5201-bis]. The related state (i.e. host 763 associations) should be removed upon successful termination. 765 7. Data plane 767 The encapsulation format for the data plane used for carrying the 768 application-layer traffic can be dynamically negotiated during the 769 key exchange. For instance, HICCUPS extensions [RFC6078] define one 770 way to transport application-layer datagrams directly over the HIP 771 control plane, protected by asymmetric key cryptography. Also, S-RTP 772 has been considered as the data encapsulation protocol [hip-srtp]. 773 However, the most widely implemented method is the Encapsulated 774 Security Payload (ESP) [I-D.ietf-hip-rfc5202-bis] that is protected 775 by symmetric keys derived during the key exchange. ESP Security 776 Associations (SAs) offer both confidentiality and integrity 777 protection, of which the former can be disabled during the key 778 exchange. In the future, other ways of transporting application- 779 layer data may be defined. 781 The ESP SAs are established and terminated between the initiator and 782 the responder hosts. Usually, the hosts create at least two SAs, one 783 in each direction (initiator-to-responder SA and responder-to- 784 initiator SA). If the IP addresses of either host changes, the HIP 785 mobility extensions can be used to re-negotiate the corresponding 786 SAs. 788 On the wire, the difference in the use of identifiers between the HIP 789 control and data plane is that the HITs are included in all control 790 packets, but not in the data plane when ESP is employed. Instead, 791 the ESP employs SPI numbers that act as compressed HITs. Any HIP- 792 aware middlebox (for instance, a HIP-aware firewall) interested in 793 the ESP based data plane should keep track between the control and 794 data plane identifiers in order to associate them with each other. 796 Since HIP does not negotiate any SA lifetimes, all lifetimes are 797 subject to local policy. The only lifetimes a HIP implementation 798 must support are sequence number rollover (for replay protection), 799 and SA timeout. An SA times out if no packets are received using 800 that SA. Implementations may support lifetimes for the various ESP 801 transforms and other data-plane protocols. 803 8. HIP and NATs 805 Passing packets between different IP addressing realms requires 806 changing IP addresses in the packet header. This may occur, for 807 example, when a packet is passed between the public Internet and a 808 private address space, or between IPv4 and IPv6 networks. The 809 address translation is usually implemented as Network Address 810 Translation (NAT) [RFC3022] or NAT Protocol translation (NAT-PT) 811 [RFC2766]. 813 In a network environment where identification is based on the IP 814 addresses, identifying the communicating nodes is difficult when NATs 815 are employed because private address spaces are overlapping. In 816 other words, two hosts cannot distinguished from each other solely 817 based on their IP address. With HIP, the transport-layer end-points 818 (i.e. applications) are bound to unique Host Identities rather than 819 overlapping private addresses. This allows two end-points to 820 distinguish one other even when they are located in different private 821 address realms. Thus, the IP addresses are used only for routing 822 purposes and can be changed freely by NATs when a packet between two 823 HIP capable hosts traverses through multiple private address realms. 825 NAT traversal extensions for HIP [I-D.ietf-hip-native-nat-traversal] 826 can be used to realize the actual end-to-end connectivity through NAT 827 devices. To support basic backward compatibility with legacy NATs, 828 the extensions encapsulate both HIP control and data plane in UDP. 829 The extensions define mechanisms for forwarding the two planes 830 through an intermediary host called HIP relay and procedures to 831 establish direct end-to-end connectivity by penetrating NATs. 832 Besides this "native" NAT traversal mode for HIP, other NAT traversal 833 mechanisms have been successfully utilized, such as Teredo 834 [varjonen-split]. 836 Besides legacy NATs, a HIP-aware NAT has been designed and 837 implemented [ylitalo-spinat]. For a HIP-based flow, a HIP-aware NAT 838 or NAT-PT system tracks the mapping of HITs, and the corresponding 839 ESP SPIs, to an IP address. The NAT system has to learn mappings 840 both from HITs and from SPIs to IP addresses. Many HITs (and SPIs) 841 can map to a single IP address on a NAT, simplifying connections on 842 address poor NAT interfaces. The NAT can gain much of its knowledge 843 from the HIP packets themselves; however, some NAT configuration may 844 be necessary. 846 8.1. HIP and Upper-layer checksums 848 There is no way for a host to know if any of the IP addresses in an 849 IP header are the addresses used to calculate the TCP checksum. That 850 is, it is not feasible to calculate the TCP checksum using the actual 851 IP addresses in the pseudo header; the addresses received in the 852 incoming packet are not necessarily the same as they were on the 853 sending host. Furthermore, it is not possible to recompute the 854 upper-layer checksums in the NAT/NAT-PT system, since the traffic is 855 ESP protected. Consequently, the TCP and UDP checksums are 856 calculated using the HITs in the place of the IP addresses in the 857 pseudo header. Furthermore, only the IPv6 pseudo header format is 858 used. This provides for IPv4 / IPv6 protocol translation. 860 9. Multicast 862 A number of studies intestigating HIP-based multicast have been 863 published (including [shields-hip], [xueyong-hip], [xueyong-hip], 864 [amir-hip], [kovacshazi-host] and [xueyong-secure]). Particularly, 865 so called bloom filters, that allow compressing of multiple labels 866 into small datastructures, may be a promising way forward 867 [sarela-bloom]. However, the different schemes have not been adopted 868 by HIP working group (nor the HIP research group in IRTF), so the 869 details are not further elaborated here. 871 10. HIP policies 873 There are a number of variables that influence the HIP exchange that 874 each host must support. All HIP implementations should support at 875 least 2 HIs, one to publish in DNS or similar directory service and 876 an unpublished one for anonymous usage. Although unpublished HIs 877 will be rarely used as responder HIs, they are likely to be common 878 for initiators. Support for multiple HIs is recommended. This 879 provides new challenges for systems or users to decide which type of 880 HI to expose when they start a new session. 882 Opportunistic mode (where the initiator starts a HIP exchange without 883 prior knowledge of the responder's HI) presents a security tradeoff. 884 At the expense of being subject to MITM attacks, the opportunistic 885 mode allows the initiator to learn the identity of the responder 886 during communication rather than from an external directory. 887 Opportunistic mode can be used for registration to HIP-based services 888 [I-D.ietf-hip-rfc5203-bis] (i.e. utilized by HIP for its own internal 889 purposes) or by the application layer [komu-leap]. For security 890 reasons, especially the latter requires some involvement from the 891 user to accept the identity of the responder in a similar vain as SSH 892 prompts the user when connecting to a server for the first time 893 [pham-leap]. In practice, this can be realized in end-host based 894 firewalls in the case of legacy applications [karvonen-usable] or 895 with native APIs for HIP APIs [RFC6317] in the case of HIP-aware 896 applications. 898 Many initiators would want to use a different HI for different 899 responders. The implementations should provide for a policy of 900 initiator HIT to responder HIT. This policy should also include 901 preferred transforms and local lifetimes. 903 Responders would need a similar policy, describing the hosts allowed 904 to participate in HIP exchanges, and the preferred transforms and 905 local lifetimes. 907 11. Design considerations 909 11.1. Benefits of HIP 911 In the beginning, the network layer protocol (i.e., IP) had the 912 following four "classic" invariants: 914 1. Non-mutable: The address sent is the address received. 916 2. Non-mobile: The address doesn't change during the course of an 917 "association". 919 3. Reversible: A return header can always be formed by reversing the 920 source and destination addresses. 922 4. Omniscient: Each host knows what address a partner host can use 923 to send packets to it. 925 Actually, the fourth can be inferred from 1 and 3, but it is worth 926 mentioning explicitly for reasons that will be obvious soon if not 927 already. 929 In the current "post-classic" world, we are intentionally trying to 930 get rid of the second invariant (both for mobility and for multi- 931 homing), and we have been forced to give up the first and the fourth. 932 Realm Specific IP [RFC3102] is an attempt to reinstate the fourth 933 invariant without the first invariant. IPv6 is an attempt to 934 reinstate the first invariant. 936 Few client-side systems on the Internet have DNS names that are 937 meaningful. That is, if they have a Fully Qualified Domain Name 938 (FQDN), that name typically belongs to a NAT device or a dial-up 939 server, and does not really identify the system itself but its 940 current connectivity. FQDNs (and their extensions as email names) 941 are application-layer names; more frequently naming services than 942 particular systems. This is why many systems on the Internet are not 943 registered in the DNS; they do not have services of interest to other 944 Internet hosts. 946 DNS names are references to IP addresses. This only demonstrates the 947 interrelationship of the networking and application layers. DNS, as 948 the Internet's only deployed and distributed database, is also the 949 repository of other namespaces, due in part to DNSSEC and application 950 specific key records. Although each namespace can be stretched (IP 951 with v6, DNS with KEY records), neither can adequately provide for 952 host authentication or act as a separation between internetworking 953 and transport layers. 955 The Host Identity (HI) namespace fills an important gap between the 956 IP and DNS namespaces. An interesting thing about the HI is that it 957 actually allows a host to give up all but the 3rd network-layer 958 invariant. That is to say, as long as the source and destination 959 addresses in the network-layer protocol are reversible, HIP takes 960 care of host identification, and reversibility allows a local host to 961 receive a packet back from a remote host. The address changes 962 occurring during NAT transit (non-mutable) or host movement (non- 963 omniscient or non-mobile) can be managed by the HIP layer. 965 With the exception High-Performance Computing applications, the 966 Sockets API is the most common way to develop network applications. 967 Applications use the Sockets API either directly or indirectly 968 through some libraries or frameworks. However, the Sockets API is 969 based on the assumption of static IP addresses, and DNS with its 970 lifetime values was invented at later stages during the evolution of 971 the Internet. Hence, the Sockets API does not deal with the lifetime 972 of addresses [RFC6250]. As majority of the end-user equipment is 973 mobile today, their addresses are effectively ephemeral, but the 974 Sockets API still gives a fallacious illusion of persistent IP 975 addresses to the unwary developer. HIP can be used to solidify this 976 illusion because HIP provides persistent surrogate addresses to the 977 application layer in the form of LSIs and HITs. 979 The persistent identifiers as provided by HIP are useful in multiple 980 scenarios (see, e.g., [ylitalo-diss] or [komu-diss], for a more 981 elaborate discussion): 983 o When a mobile host moves physically between two different WLAN 984 networks and obtains a new address, an application using the 985 identifiers remains isolated regardless of the topology changes 986 while the underlying HIP layer re-establishes connectivity (i.e. a 987 horizontal handoff). 989 o Similarly, the application utilizing the identifiers remains again 990 unaware of the topological changes when the underlying host 991 equipped with WLAN and cellular network interfaces switches 992 between the two different access technologies (i.e. a vertical 993 handoff). 995 o Even when hosts are located in private address realms, 996 applications can uniquely distinguish different hosts from each 997 other based on their identifiers. In other words, it can be 998 stated that HIP improves Internet transparency for the application 999 layer [komu-diss]. 1001 o Site renumbering events for services can occur due to corporate 1002 mergers or acquisitions, or by changes in Internet Service 1003 Provider. They can involve changing the entire network prefix of 1004 an organization, which is problematic due to hard-coded addresses 1005 in service configuration files or cached IP addresses at the 1006 client side [RFC5887]. Considering such human errors, a site 1007 employing location-independent identifiers as promoted by HIP may 1008 experience less problems while renumbering their network. 1010 o More agile IPv6 interoperability as discussed in Section 4.4. 1011 IPv6-based applications can communicate using HITs with IPv4-based 1012 applications that are using LSIs. An addition, the underlying 1013 network type (IPv4 or IPv6) becomes independent of the addressing 1014 family of the application. 1016 o HITs (or LSIs) can be used in IP-based access control lists as a 1017 more secure replacement for IPv6 addresses. Besides security, HIT 1018 based access control has two other benefits. First, the use of 1019 HITs halves the size of access control lists because separate 1020 rules for IPv4 are not needed [komu-diss]. Second, HIT-based 1021 configuration rules in HIP-aware middleboxes remain static and 1022 independent of topology changes, thus simplifying administrative 1023 efforts particularly for mobile environments. For instance, the 1024 benefits of HIT based access control have been harnessed in the 1025 case of HIP-aware firewalls, but can be utilized directly at the 1026 end-hosts as well [RFC6538]. 1028 While some of these benefits could be and have been redundantly 1029 implemented by individual applications, providing such generic 1030 functionality at the lower layers is useful because it reduces 1031 software development effort and networking software bugs (as the 1032 layer is tested with multiple applications). It also allows the 1033 developer to focus on building the application itself rather than 1034 delving into the intricacies of mobile networking, thus facilitating 1035 separation of concerns. 1037 HIP could also be realized by combining a number of different 1038 protocols, but the complexity of the resulting software may become 1039 substantially larger, and the interaction between multiple possibly 1040 layered protocols may have adverse effects on latency and throughput. 1041 It is also worth noting that virtually nothing prevents realizing the 1042 HIP architecture, for instance, as an application-layer library, 1043 which has been actually implemented in the past [xin-hip-lib]. 1044 However, the tradeoff in moving the HIP layer to the application 1045 layer is that legacy applications may not be supported. 1047 11.2. Drawbacks of HIP 1049 In computer science, many problems can be solved with an extra layer 1050 of indirection. However, the indirection always involves some costs 1051 as there is no such a thing as "free lunch". In the case of HIP, the 1052 main costs could be stated as follows: 1054 o In general, a new layer and a new namespace always involve some 1055 initial effort in terms of implementation, deployment and 1056 maintenance. Some education of developers and administrators may 1057 also be needed. However, the HIP community at the IETF has spent 1058 years in experimenting, exploring, testing, documenting and 1059 implementing HIP to ease the adoption costs. 1061 o HIP decouples identifier and locator roles of IP addresses. 1062 Consequently, a mapping mechanism is needed to associate them 1063 together. A failure to map a HIT to its corresponding locator may 1064 result in failed connectivity because a HIT is "flat" by its 1065 nature and cannot be looked up from the hierarchically organized 1066 DNS. HITs are flat by design due to a security tradeoff. The 1067 more bits are allocated for the hash in the HIT, the less likely 1068 there will be (malicious) collisions. 1070 o From performance viewpoint, HIP control and data plane processing 1071 introduces some overhead in terms of throughput and latency as 1072 elaborated below. 1074 The key exchange introduces some extra latency (two round trips) in 1075 the initial transport layer connection establishment between two 1076 hosts. With TCP, additional delay occurs if the underlying network 1077 stack implementation drops the triggering SYN packet during the key 1078 exchange. The same cost may also occur during HIP handoff 1079 procedures. However, subsequent TCP sessions using the same HIP 1080 association will not bear this cost (within the key lifetime). Both 1081 the key exchange and handoff penalties can be minimized by caching 1082 TCP packets. The latter case can further be optimized with TCP user 1083 timeout extensions [RFC5482] as described in further detail by 1084 Schuetz et al [scultz-intermittent]. 1086 The most CPU-intensive operations involve the use of the asymmetric 1087 keys and Diffie-Hellman key derivation at the control plane, but this 1088 occurs only during the key exchange, its maintenance (handoffs, 1089 refreshing of key material) and tear down procedures of HIP 1090 associations. The data plane is typically implemented with ESP 1091 because it has a smaller overhead due to symmetric key encryption. 1092 Naturally, even ESP involves some overhead in terms of latency 1093 (processing costs) and throughput (tunneling) (see e.g. 1094 [ylitalo-diss] for a performance evaluation). 1096 11.3. Deployment and adoption considerations 1098 This section describes some deployment and adoption considerations 1099 related to HIP from a technical perspective. 1101 11.3.1. Deployment analysis 1103 HIP has commercially been utilized at Boeing airplane factory for 1104 their internal purposes [paine-hip]. It has been included in a 1105 security product called Tofino to support layer-two Virtual Private 1106 Networks [henderson-vpls] to facilitate, e.g, supervisory control and 1107 data acquisition (SCADA) security. However, HIP has not been a "wild 1108 success" [RFC5218] in the Internet as argued by Levae et al 1109 [leva-barriers]. Here, we briefly highlight some of their findings 1110 based on interviews with 19 experts from the industry and academia. 1112 From a marketing perspective, the demand for HIP has been low and 1113 substitute technologies have been favored. Another identified reason 1114 has been that some technical misconceptions related to the early 1115 stages of HIP specifications still persist. Two identified 1116 misconceptions are that HIP does not support NAT traversal, and that 1117 HIP must be implemented in the OS kernel. Both of these claims are 1118 untrue; HIP does have NAT traversal extensions 1119 [I-D.ietf-hip-native-nat-traversal], and kernel modifications can be 1120 avoided with modern operating systems by diverting packets for 1121 userspace processing. 1123 The analysis by Levae et al clarifies infrastructural requirements 1124 for HIP. In a minimal set up, a client and server machine have to 1125 run HIP software. However, to avoid manual configurations, usually 1126 DNS records for HIP are set up. For instance, the popular DNS server 1127 software Bind9 does not require any changes to accomodate DNS records 1128 for HIP because they can be supported in binary format in its 1129 configuration files [RFC6538]. HIP rendezvous servers and firewalls 1130 are optional. No changes are required to network address points, 1131 NATs, edge routers or core networks. HIP may require holes in legacy 1132 firewalls. 1134 The analysis also clarifies the requirements for the host components 1135 that consist of three parts. First, a HIP control plane component is 1136 required, typically implemented as a userspace daemon. Second, a 1137 data plane component is needed. Most HIP implementations utilize the 1138 so called BEET mode of ESP that has been available since Linux kernel 1139 2.6.27, but is included also as a userspace component in a few of the 1140 implementations. Third, HIP systems usually provide a DNS proxy for 1141 the local host that translates HIP DNS records to LSIs and HITs, and 1142 communicates the corresponding locators to HIP userspace daemon. 1143 While the third component is not strictly speaking mandatory, it is 1144 very useful for avoiding manual configurations. The three components 1145 are further described in the HIP experiment report [RFC6538]. 1147 Based on the interviews, Levae et al suggest further directions to 1148 facilitate HIP deployment. Transitioning the HIP specifications to 1149 the standards track may help, but other measures could be taken. As 1150 a more radical measure, the authors suggest to implement HIP as a 1151 purely application-layer library [xin-hip-lib] or other kind of 1152 middleware. On the other hand, more conservative measures include 1153 focusing on private deployments controlled by a single stakeholder. 1154 As a more concrete example of such a scenario, HIP could be used by a 1155 single service provider to facilitate secure connectivity between its 1156 servers [komu-cloud]. 1158 11.3.2. HIP in 802.15.4 networks 1160 The IEEE 802 standards have been defining MAC layered security. Many 1161 of these standards use EAP [RFC3748] as a Key Management System (KMS) 1162 transport, but some like IEEE 802.15.4 [IEEE.802-15-4.2011] leave the 1163 KMS and its transport as "Out of Scope". 1165 HIP is well suited as a KMS in these environments: 1167 o HIP is independent of IP addressing and can be directly 1168 transported over any network protocol. 1170 o Master Keys in 802 protocols are commonly pair-based with group 1171 keys transported from the group controller using pair-wise keys. 1173 o AdHoc 802 networks can be better served by a peer-to-peer KMS than 1174 the EAP client/server model. 1176 o Some devices are very memory constrained and a common KMS for both 1177 MAC and IP security represents a considerable code savings. 1179 11.4. Answers to NSRG questions 1181 The IRTF Name Space Research Group has posed a number of evaluating 1182 questions in their report [nsrg-report]. In this section, we provide 1183 answers to these questions. 1185 1. How would a stack name improve the overall functionality of the 1186 Internet? 1188 HIP decouples the internetworking layer from the transport 1189 layer, allowing each to evolve separately. The decoupling 1190 makes end-host mobility and multi-homing easier, also across 1191 IPv4 and IPv6 networks. HIs make network renumbering easier, 1192 and they also make process migration and clustered servers 1193 easier to implement. Furthermore, being cryptographic in 1194 nature, they provide the basis for solving the security 1195 problems related to end-host mobility and multi-homing. 1197 2. What does a stack name look like? 1199 A HI is a cryptographic public key. However, instead of using 1200 the keys directly, most protocols use a fixed size hash of the 1201 public key. 1203 3. What is its lifetime? 1205 HIP provides both stable and temporary Host Identifiers. 1206 Stable HIs are typically long lived, with a lifetime of years 1207 or more. The lifetime of temporary HIs depends on how long 1208 the upper-layer connections and applications need them, and 1209 can range from a few seconds to years. 1211 4. Where does it live in the stack? 1213 The HIs live between the transport and internetworking layers. 1215 5. How is it used on the end points? 1217 The Host Identifiers may be used directly or indirectly (in 1218 the form of HITs or LSIs) by applications when they access 1219 network services. Additionally, the Host Identifiers, as 1220 public keys, are used in the built in key agreement protocol, 1221 called the HIP base exchange, to authenticate the hosts to 1222 each other. 1224 6. What administrative infrastructure is needed to support it? 1226 In some environments, it is possible to use HIP 1227 opportunistically, without any infrastructure. However, to 1228 gain full benefit from HIP, the HIs must be stored in the DNS 1229 or a PKI, and a new rendezvous mechanism is needed 1230 [I-D.ietf-hip-rfc5205-bis]. 1232 7. If we add an additional layer would it make the address list in 1233 SCTP unnecessary? 1235 Yes 1237 8. What additional security benefits would a new naming scheme 1238 offer? 1240 HIP reduces dependency on IP addresses, making the so called 1241 address ownership [Nik2001] problems easier to solve. In 1242 practice, HIP provides security for end-host mobility and 1243 multi-homing. Furthermore, since HIP Host Identifiers are 1244 public keys, standard public key certificate infrastructures 1245 can be applied on the top of HIP. 1247 9. What would the resolution mechanisms be, or what characteristics 1248 of a resolution mechanisms would be required? 1250 For most purposes, an approach where DNS names are resolved 1251 simultaneously to HIs and IP addresses is sufficient. 1252 However, if it becomes necessary to resolve HIs into IP 1253 addresses or back to DNS names, a flat resolution 1254 infrastructure is needed. Such an infrastructure could be 1255 based on the ideas of Distributed Hash Tables, but would 1256 require significant new development and deployment. 1258 12. Security considerations 1260 This section includes discussion on some issues and solutions related 1261 to security in the HIP architecture. 1263 12.1. MiTM Attacks 1265 HIP takes advantage of the new Host Identity paradigm to provide 1266 secure authentication of hosts and to provide a fast key exchange for 1267 ESP. HIP also attempts to limit the exposure of the host to various 1268 denial-of-service (DoS) and man-in-the-middle (MitM) attacks. In so 1269 doing, HIP itself is subject to its own DoS and MitM attacks that 1270 potentially could be more damaging to a host's ability to conduct 1271 business as usual. 1273 Resource exhausting denial-of-service attacks take advantage of the 1274 cost of setting up a state for a protocol on the responder compared 1275 to the 'cheapness' on the initiator. HIP allows a responder to 1276 increase the cost of the start of state on the initiator and makes an 1277 effort to reduce the cost to the responder. This is done by having 1278 the responder start the authenticated Diffie-Hellman exchange instead 1279 of the initiator, making the HIP base exchange 4 packets long. The 1280 first packet sent by the responder can be prebuilt to further 1281 mitigate the costs. This packet also includes a computational puzzle 1282 that can optionally be used to further delay the initiator, for 1283 instance, when the responder is overloaded. The details are 1284 explained in the base exchange specification 1285 [I-D.ietf-hip-rfc5201-bis]. 1287 Man-in-the-middle (MitM) attacks are difficult to defend against, 1288 without third-party authentication. A skillful MitM could easily 1289 handle all parts of the HIP base exchange, but HIP indirectly 1290 provides the following protection from a MitM attack. If the 1291 responder's HI is retrieved from a signed DNS zone or securely 1292 obtained by some other means, the initiator can use this to 1293 authenticate the signed HIP packets. Likewise, if the initiator's HI 1294 is in a secure DNS zone, the responder can retrieve it and validate 1295 the signed HIP packets. However, since an initiator may choose to 1296 use an unpublished HI, it knowingly risks a MitM attack. The 1297 responder may choose not to accept a HIP exchange with an initiator 1298 using an unknown HI. 1300 Other types of MitM attacks against HIP can be mounted using ICMP 1301 messages that can be used to signal about problems. As a overall 1302 guideline, the ICMP messages should be considered as unreliable 1303 "hints" and should be acted upon only after timeouts. The exact 1304 attack scenarios and countermeasures are described in full detail the 1305 base exchange specification [I-D.ietf-hip-rfc5201-bis]. 1307 The need to support multiple hashes for generating the HIT from the 1308 HI affords the MitM to mount a potentially powerful downgrade attack 1309 due to the a-priori need of the HIT in the HIP base exchange. The 1310 base exchange has been augmented to deal with such an attack by 1311 restarting on detecting the attack. At worst this would only lead to 1312 a situation in which the base exchange would never finish (or would 1313 be aborted after some retries). As a drawback, this leads to an 1314 6-way base exchange which may seem bad at first. However, since this 1315 only occurs in an attack scenario and since the attack can be handled 1316 (so it is not interesting to mount anymore), we assume the subsequent 1317 messages do not represent a security threat. Since the MitM cannot 1318 be successful with a downgrade attack, these sorts of attacks will 1319 only occur as 'nuisance' attacks. So, the base exchange would still 1320 be usually just four packets even though implementations must be 1321 prepared to protect themselves against the downgrade attack. 1323 In HIP, the Security Association for ESP is indexed by the SPI; the 1324 source address is always ignored, and the destination address may be 1325 ignored as well. Therefore, HIP-enabled Encapsulated Security 1326 Payload (ESP) is IP address independent. This might seem to make 1327 attacking easier, but ESP with replay protection is already as well 1328 protected as possible, and the removal of the IP address as a check 1329 should not increase the exposure of ESP to DoS attacks. 1331 12.2. Protection against flooding attacks 1333 Although the idea of informing about address changes by simply 1334 sending packets with a new source address appears appealing, it is 1335 not secure enough. That is, even if HIP does not rely on the source 1336 address for anything (once the base exchange has been completed), it 1337 appears to be necessary to check a mobile node's reachability at the 1338 new address before actually sending any larger amounts of traffic to 1339 the new address. 1341 Blindly accepting new addresses would potentially lead to flooding 1342 Denial-of-Service attacks against third parties [RFC4225]. In a 1343 distributed flooding attack an attacker opens high volume HIP 1344 connections with a large number of hosts (using unpublished HIs), and 1345 then claims to all of these hosts that it has moved to a target 1346 node's IP address. If the peer hosts were to simply accept the move, 1347 the result would be a packet flood to the target node's address. To 1348 prevent this type of attack, HIP mobility extensions include a return 1349 routability check procedure where the reachability of a node is 1350 separately checked at each address before using the address for 1351 larger amounts of traffic. 1353 A credit-based authorization approach Host Mobility with the Host 1354 Identity Protocol [I-D.ietf-hip-rfc5206-bis] can be used between 1355 hosts for sending data prior to completing the address tests. 1356 Otherwise, if HIP is used between two hosts that fully trust each 1357 other, the hosts may optionally decide to skip the address tests. 1358 However, such performance optimization must be restricted to peers 1359 that are known to be trustworthy and capable of protecting themselves 1360 from malicious software. 1362 12.3. HITs used in ACLs 1364 At end-hosts, HITs can be used in IP-based access control lists at 1365 the application and network layers. At middleboxes, HIP-aware 1366 firewalls [lindqvist-enterprise] can use HITs or public keys to 1367 control both ingress and egress access to networks or individual 1368 hosts, even in the presence of mobile devices because the HITs and 1369 public keys are topologically independent. As discussed earlier in 1370 Section 7, once a HIP session has been established, the SPI value in 1371 an ESP packet may be used as an index, indicating the HITs. In 1372 practice, firewalls can inspect HIP packets to learn of the bindings 1373 between HITs, SPI values, and IP addresses. They can even explicitly 1374 control ESP usage, dynamically opening ESP only for specific SPI 1375 values and IP addresses. The signatures in HIP packets allow a 1376 capable firewall to ensure that the HIP exchange is indeed occurring 1377 between two known hosts. This may increase firewall security. 1379 A potential drawback of HITs in ACLs is their 'flatness' means they 1380 cannot be aggregated, and this could potentially result in larger 1381 table searches in HIP-aware firewalls. A way to optimize this could 1382 be to utilize bloom filters for grouping of HITs [sarela-bloom]. 1383 However, it should be noted that it is also easier to exclude 1384 individual, misbehaving hosts out when the firewall rules concern 1385 individual HITs rather than groups. 1387 There has been considerable bad experience with distributed ACLs that 1388 contain public key related material, for example, with SSH. If the 1389 owner of a key needs to revoke it for any reason, the task of finding 1390 all locations where the key is held in an ACL may be impossible. If 1391 the reason for the revocation is due to private key theft, this could 1392 be a serious issue. 1394 A host can keep track of all of its partners that might use its HIT 1395 in an ACL by logging all remote HITs. It should only be necessary to 1396 log responder hosts. With this information, the host can notify the 1397 various hosts about the change to the HIT. There has been attempts 1398 to develop a secure method to issue the HIT revocation notice 1399 [zhang-revocation]. 1401 Some of the HIP-aware middleboxes, such as firewalls 1402 [lindqvist-enterprise] or NATs [ylitalo-spinat], may observe the on- 1403 path traffic passively. Such middleboxes are transparent by their 1404 nature and may not get a notification when a host moves to a 1405 different network. Thus, such middleboxes should maintain soft state 1406 and timeout when the control and data plane between two HIP end-hosts 1407 has been idle too long. Correspondingly, the two end-hosts may send 1408 periodically keepalives, such as UPDATE packets or ICMP messages 1409 inside the ESP tunnel, to sustain state at the on-path middleboxes. 1411 One general limitation related to end-to-end encryption is that 1412 middleboxes may not be able to participate to the protection of 1413 malign data flows. While the issue may affect also other protocols, 1414 Heer at al [heer-end-host] have analyzed the problem in the context 1415 of HIP. More specifically, when ESP is used as the data-plane 1416 protocol for HIP, the association between the control and data plane 1417 is weak and can be exploited under certain assumptions. In the 1418 scenario, the attacker has already gained access to the target 1419 network protected by a HIP-aware firewall, but wants to circumvent 1420 the HIP-based firewall. To achieve this, the attacker passively 1421 observes a base exchange between two HIP hosts and later replays it. 1422 This way, the attacker manages to penetrate the firewall and can use 1423 a fake ESP tunnel to transport its own data. This is possible 1424 because the firewall cannot distinguish when the ESP tunnel is valid. 1425 As a solution, HIP-aware middleboxes may participate to the control 1426 plane interaction by adding random nonce parameters to the control 1427 traffic, which the the end-hosts have to sign to guarantee the 1428 freshness of the control traffic [heer-midauth]. As an alternative, 1429 extensions for transporting data plane directly over the control 1430 plane can be used [RFC6078]. 1432 12.4. Alternative HI considerations 1434 The definition of the Host Identifier states that the HI need not be 1435 a public key. It implies that the HI could be any value; for example 1436 a FQDN. This document does not describe how to support such a non- 1437 cryptographic HI, but examples of such protocol variants do exist 1438 ([urien-rfid], [urien-rfid-draft]). A non-cryptographic HI would 1439 still offer the services of the HIT or LSI for NAT traversal. It 1440 would be possible to carry HITs in HIP packets that had neither 1441 privacy nor authentication. Such schemes may be employed for 1442 resource constrained devices, such as small sensors operating on 1443 battery power, but are not further analyzed here. 1445 If it is desirable to use HIP in a low security situation where 1446 public key computations are considered expensive, HIP can be used 1447 with very short Diffie-Hellman and Host Identity keys. Such use 1448 makes the participating hosts vulnerable to MitM and connection 1449 hijacking attacks. However, it does not cause flooding dangers, 1450 since the address check mechanism relies on the routing system and 1451 not on cryptographic strength. 1453 13. IANA considerations 1455 This document has no actions for IANA. 1457 14. Acknowledgments 1459 For the people historically involved in the early stages of HIP, see 1460 the Acknowledgments section in the Host Identity Protocol 1461 specification. 1463 During the later stages of this document, when the editing baton was 1464 transferred to Pekka Nikander, the comments from the early 1465 implementers and others, including Jari Arkko, Tom Henderson, Petri 1466 Jokela, Miika Komu, Mika Kousa, Andrew McGregor, Jan Melen, Tim 1467 Shepard, Jukka Ylitalo, Sasu Tarkoma, and Jorma Wall, were 1468 invaluable. Also, the comments from Lars Eggert, Spencer Dawkins and 1469 Dave Crocker were also useful. 1471 The authors want to express their special thanks to Tom Henderson, 1472 who took the burden of editing the document in response to IESG 1473 comments at the time when both of the authors were busy doing other 1474 things. Without his perseverance original document might have never 1475 made it as RFC4423. 1477 This main effort to update and move HIP forward within the IETF 1478 process owes its impetuous to a number of HIP development teams. The 1479 authors are grateful for Boeing, Helsinki Institute for Information 1480 Technology (HIIT), NomadicLab of Ericsson, and the three 1481 universities: RWTH Aachen, Aalto and University of Helsinki, for 1482 their efforts. Without their collective efforts HIP would have 1483 withered as on the IETF vine as a nice concept. 1485 Thanks also for Suvi Koskinen for her help with proofreading and with 1486 the reference jungle. 1488 15. Changes from RFC 4423 1490 In a nutshell, the changes from RFC 4424 [RFC4423] are mostly 1491 editorial, including clarifications on topics described in a 1492 difficult way and omitting some of the non-architectural 1493 (implementation) details that are already described in other 1494 documents. A number of missing references to the literature were 1495 also added. New topics include the drawbacks of HIP, discussion on 1496 802.15.4 and MAC security, deployment considerations and description 1497 of the base exchange. 1499 16. References 1501 16.1. Normative References 1503 [I-D.ietf-hip-multihoming] 1504 Henderson, T., Vogt, C., and J. Arkko, "Host Multihoming 1505 with the Host Identity Protocol", 1506 draft-ietf-hip-multihoming-03 (work in progress), 1507 July 2013. 1509 [I-D.ietf-hip-native-nat-traversal] 1510 Keranen, A. and J. Melen, "Native NAT Traversal Mode for 1511 the Host Identity Protocol", 1512 draft-ietf-hip-native-nat-traversal-05 (work in progress), 1513 June 2013. 1515 [I-D.ietf-hip-rfc5201-bis] 1516 Moskowitz, R., Heer, T., Jokela, P., and T. Henderson, 1517 "Host Identity Protocol Version 2 (HIPv2)", 1518 draft-ietf-hip-rfc5201-bis-14 (work in progress), 1519 October 2013. 1521 [I-D.ietf-hip-rfc5202-bis] 1522 Jokela, P., Moskowitz, R., and J. Melen, "Using the 1523 Encapsulating Security Payload (ESP) Transport Format with 1524 the Host Identity Protocol (HIP)", 1525 draft-ietf-hip-rfc5202-bis-05 (work in progress), 1526 November 2013. 1528 [I-D.ietf-hip-rfc5203-bis] 1529 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1530 Registration Extension", draft-ietf-hip-rfc5203-bis-02 1531 (work in progress), September 2012. 1533 [I-D.ietf-hip-rfc5204-bis] 1534 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1535 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-02 (work 1536 in progress), September 2012. 1538 [I-D.ietf-hip-rfc5205-bis] 1539 Laganier, J., "Host Identity Protocol (HIP) Domain Name 1540 System (DNS) Extension", draft-ietf-hip-rfc5205-bis-02 1541 (work in progress), September 2012. 1543 [I-D.ietf-hip-rfc5206-bis] 1544 Henderson, T., Vogt, C., and J. Arkko, "Host Mobility with 1545 the Host Identity Protocol", draft-ietf-hip-rfc5206-bis-06 1546 (work in progress), July 2013. 1548 [I-D.ietf-hip-rfc6253-bis] 1549 Heer, T. and S. Varjonen, "Host Identity Protocol 1550 Certificates", draft-ietf-hip-rfc6253-bis-01 (work in 1551 progress), October 2013. 1553 [RFC5482] Eggert, L. and F. Gont, "TCP User Timeout Option", 1554 RFC 5482, March 2009. 1556 16.2. Informative references 1558 [IEEE.802-15-4.2011] 1559 "Information technology - Telecommunications and 1560 information exchange between systems - Local and 1561 metropolitan area networks - Specific requirements - Part 1562 15.4: Wireless Medium Access Control (MAC) and Physical 1563 Layer (PHY) Specifications for Low-Rate Wireless Personal 1564 Area Networks (WPANs)", IEEE Standard 802.15.4, 1565 September 2011, . 1568 [Nik2001] Nikander, P., "Denial-of-Service, Address Ownership, and 1569 Early Authentication in the IPv6 World", in Proceesings 1570 of Security Protocols, 9th International Workshop, 1571 Cambridge, UK, April 25-27 2001, LNCS 2467, pp. 12-26, 1572 Springer, 2002. 1574 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 1575 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 1576 RFC 2136, April 1997. 1578 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 1579 RFC 2535, March 1999. 1581 [RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address 1582 Translation - Protocol Translation (NAT-PT)", RFC 2766, 1583 February 2000. 1585 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 1586 Address Translator (Traditional NAT)", RFC 3022, 1587 January 2001. 1589 [RFC3102] Borella, M., Lo, J., Grabelsky, D., and G. Montenegro, 1590 "Realm Specific IP: Framework", RFC 3102, October 2001. 1592 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 1593 Levkowetz, "Extensible Authentication Protocol (EAP)", 1594 RFC 3748, June 2004. 1596 [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 1597 Nordmark, "Mobile IP Version 6 Route Optimization Security 1598 Design Background", RFC 4225, December 2005. 1600 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1601 RFC 4306, December 2005. 1603 [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol 1604 (HIP) Architecture", RFC 4423, May 2006. 1606 [RFC5218] Thaler, D. and B. Aboba, "What Makes For a Successful 1607 Protocol?", RFC 5218, July 2008. 1609 [RFC5338] Henderson, T., Nikander, P., and M. Komu, "Using the Host 1610 Identity Protocol with Legacy Applications", RFC 5338, 1611 September 2008. 1613 [RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering 1614 Still Needs Work", RFC 5887, May 2010. 1616 [RFC6078] Camarillo, G. and J. Melen, "Host Identity Protocol (HIP) 1617 Immediate Carriage and Conveyance of Upper-Layer Protocol 1618 Signaling (HICCUPS)", RFC 6078, January 2011. 1620 [RFC6250] Thaler, D., "Evolution of the IP Model", RFC 6250, 1621 May 2011. 1623 [RFC6281] Cheshire, S., Zhu, Z., Wakikawa, R., and L. Zhang, 1624 "Understanding Apple's Back to My Mac (BTMM) Service", 1625 RFC 6281, June 2011. 1627 [RFC6317] Komu, M. and T. Henderson, "Basic Socket Interface 1628 Extensions for the Host Identity Protocol (HIP)", 1629 RFC 6317, July 2011. 1631 [RFC6537] Ahrenholz, J., "Host Identity Protocol Distributed Hash 1632 Table Interface", RFC 6537, February 2012. 1634 [RFC6538] Henderson, T. and A. Gurtov, "The Host Identity Protocol 1635 (HIP) Experiment Report", RFC 6538, March 2012. 1637 [amir-hip] 1638 Amir, K., Forsgren, H., Grahn, K., Karvi, T., and G. 1639 Pulkkis, "Security and Trust of Public Key Cryptography 1640 for HIP and HIP Multicast", International Journal of 1641 Dependable and Trustworthy Information Systems (IJDTIS), 1642 2(3), 17-35, DOI: 10.4018/jdtis.2011070102, 2013. 1644 [aura-dos] 1645 Aura, T., Nikander, P., and J. Leiwo, "DOS-resistant 1646 Authentication with Client Puzzles", 8th International 1647 Workshop on Security Protocols, pages 170-177. Springer, , 1648 April 2001. 1650 [beal-dos] 1651 Beal, J. and T. Shephard, "Deamplification of DoS Attacks 1652 via Puzzles", , October 2004. 1654 [chiappa-endpoints] 1655 Chiappa, J., "Endpoints and Endpoint Names: A Proposed 1656 Enhancement to the Internet Architecture", 1657 URL http://www.chiappa.net/~jnc/tech/endpoints.txt, 1999. 1659 [heer-end-host] 1660 Heer, T., Hummen, R., Komu, M., Goetz, S., and K. Wehre, 1661 "End-host Authentication and Authorization for Middleboxes 1662 based on a Cryptographic Namespace", ICC2009 Communication 1663 and Information Systems Security Symposium, , 2009. 1665 [heer-midauth] 1666 Heer, T. and M. Komu, "End-Host Authentication for HIP 1667 Middleboxes", Working draft draft-heer-hip-middle-auth-02, 1668 September 2009. 1670 [henderson-vpls] 1671 Henderson, T. and D. Mattes, "", Working 1672 draft draft-henderson-hip-vpls-06, June 2013. 1674 [hip-srtp] 1675 Tschofenig, H., Muenz, F., and M. Shanmugam, "Using SRTP 1676 transport format with HIP", Working 1677 draft draft-tschofenig-hiprg-hip-srtp-01, October 2005. 1679 [karvonen-usable] 1680 Karvonen, K., Komu, M., and A. Gurtov, "Usable Security 1681 Management with Host Identity Protocol", 7th ACS/IEEE 1682 International Conference on Computer Systems and 1683 Applications, (AICCSA-2009), 2009. 1685 [komu-cloud] 1686 Komu, M., Sethi, M., Mallavarapu, R., Oirola, H., Khan, 1687 R., and S. Tarkoma, "Secure Networking for Virtual 1688 Machines in the Cloud", International Workshop on Power 1689 and QoS Aware Computing (PQoSCom2012), IEEE, ISBN: 978-1- 1690 4244-8567-3, September 2012. 1692 [komu-diss] 1693 Komu, M., "A Consolidated Namespace for Network 1694 Applications, Developers, Administrators and Users", 1695 Dissertation, Aalto University, Espoo, Finland ISBN: 978- 1696 952-60-4904-5 (printed), ISBN: 978-952-60-4905-2 1697 (electronic). , December 2012. 1699 [komu-leap] 1700 Komu, M. and J. Lindqvist, "Leap-of-Faith Security is 1701 Enough for IP Mobility", 6th Annual IEEE Consumer 1702 Communications and Networking Conference IEEE CCNC 2009, 1703 Las Vegas, Nevada, , January 2009. 1705 [komu-mitigation] 1706 Komu, M., Tarkoma, S., and A. Lukyanenko, "Mitigation of 1707 Unsolicited Traffic Across Domains with Host Identities 1708 and Puzzles", 15th Nordic Conference on Secure IT Systems 1709 (NordSec 2010), Springer Lecture Notes in Computer 1710 Science, Volume 7127, pp. 33-48, ISBN: 978-3-642-27936-2, 1711 October 2010. 1713 [kovacshazi-host] 1714 Kovacshazi, Z. and R. Vida, "Host Identity Specific 1715 Multicast", International conference on Networking and 1716 Services (ICNS'06), IEEE Computer Society, Los Alamitos, 1717 CA, USA, http://doi.ieeecomputersociety.org/10.1109/ 1718 ICNS.2007.66, 2007. 1720 [leva-barriers] 1721 Levae, A., Komu, M., and S. Luukkainen, "Adoption Barriers 1722 of Network-layer Protocols: the Case of Host Identity 1723 Protocol", The International Journal of Computer and 1724 Telecommunications Networking, ISSN: 1389-1286, 1725 March 2013. 1727 [lindqvist-enterprise] 1728 Lindqvist, J., Vehmersalo, E., Manner, J., and M. Komu, 1729 "Enterprise Network Packet Filtering for Mobile 1730 Cryptographic Identities", International Journal of 1731 Handheld Computing Research, 1 (1), 79-94, , January- 1732 March 2010. 1734 [nsrg-report] 1735 Lear, E. and R. Droms, "What's In A Name:Thoughts from the 1736 NSRG", draft-irtf-nsrg-report-10 (work in progress), 1737 September 2003. 1739 [paine-hip] 1740 Paine, R., "Beyond HIP: The End to Hacking As We Know It", 1741 BookSurge Publishing, ISBN: 1439256047, 9781439256046, 1742 2009. 1744 [pham-leap] 1745 Pham, V. and T. Aura, "Security Analysis of Leap-of-Faith 1746 Protocols", Seventh ICST International Conference on 1747 Security and Privacy for Communication Networks, , 1748 September 2011. 1750 [sarela-bloom] 1751 Saerelae, M., Esteve Rothenberg, C., Zahemszky, A., 1752 Nikander, P., and J. Ott, "BloomCasting: Security in Bloom 1753 filter based multicast", , Lecture Notes in Computer 1754 Science 2012, , pages 1-16, Springer Berlin Heidelberg, 1755 2012. 1757 [scultz-intermittent] 1758 Schuetz, S., Eggert, L., Schmid, S., and M. Brunner, 1759 "Protocol enhancements for intermittently connected 1760 hosts", SIGCOMM Comput. Commun. Rev., 35(3):5-18, , 1761 July 2005. 1763 [shields-hip] 1764 Shields, C. and J. Garcia-Luna-Aceves, "The HIP protocol 1765 for hierarchical multicast routing", Proceedings of the 1766 seventeenth annual ACM symposium on Principles of 1767 distributed computing, pages 257-266. ACM, New York, NY, 1768 USA, ISBN: 0-89791-977-7, DOI: 10.1145/277697.277744, 1769 1998. 1771 [tritilanunt-dos] 1772 Tritilanunt, S., Boyd, C., Foo, E., and J. Nieto, 1773 "Examining the DoS Resistance of HIP", OTM Workshops (1), 1774 volume 4277 of Lecture Notes in Computer Science, pages 1775 616-625,Springer , 2006. 1777 [urien-rfid] 1778 Urien, P., Chabanne, H., Bouet, M., de Cunha, D., Guyot, 1779 V., Pujolle, G., Paradinas, P., Gressier, E., and J. 1780 Susini, "HIP-based RFID Networking Architecture", IFIP 1781 International Conference on Wireless and Optical 1782 Communications Networks, DOI: 10.1109/WOCN.2007.4284140, 1783 July 2007. 1785 [urien-rfid-draft] 1786 Urien, P., Lee, G., and G. Pujolle, "HIP support for 1787 RFIDs", IRTF Working draft draft-irtf-hiprg-rfid-07, 1788 April 2013. 1790 [varjonen-split] 1791 Varjonen, S., Komu, M., and A. Gurtov, "Secure and 1792 Efficient IPv4/IPv6 Handovers Using Host-Based Identifier- 1793 Location Split", Journal of Communications Software and 1794 Systems, 6(1), 2010, ISSN: 18456421, 2010. 1796 [xin-hip-lib] 1797 Xin, G., "Host Identity Protocol Version 2.5", Master's 1798 Thesis, Aalto University, Espoo, Finland, , June 2012. 1800 [xueyong-hip] 1801 Xueyong, Z., Zhiguo, D., and W. Xinling, "A Multicast 1802 Routing Algorithm Applied to HIP-Multicast Model", 1803 Proceedings of the 2011 International Conference on 1804 Network Computing and Information Security - Volume 01 1805 (NCIS '11), Vol. 1. IEEE Computer Society, Washington, DC, 1806 USA, pages 169-174, DOI: 10.1109/NCIS.2011.42, 2011. 1808 [xueyong-secure] 1809 Xueyong, Z. and J. Atwood, "A Secure Multicast Model for 1810 Peer-to-Peer and Access Networks Using the Host Identity 1811 Protocol", Consumer Communications and Networking 1812 Conference. CCNC 2007. 4th IEEE, pages 1098,1102, DOI: 1813 10.1109/CCNC.2007.221, January 2007. 1815 [ylitalo-diss] 1816 Ylitalo, J., "Secure Mobility at Multiple Granularity 1817 Levels over Heterogeneous Datacom Networks", Dissertation, 1818 Helsinki University of Technology, Espoo, Finland ISBN 1819 978-951-22-9531-9, 2008. 1821 [ylitalo-spinat] 1822 Ylitalo, J., Salmela, P., and H. Tschofenig, "SPINAT: 1823 Integrating IPsec into overlay routing", Proceedings of 1824 the First International Conference on Security and Privacy 1825 for Emerging Areas in Communication Networks (SecureComm 1826 2005). Athens, Greece. IEEE Computer Society, pages 315- 1827 326, ISBN: 0-7695-2369-2, September 2005. 1829 [zhang-revocation] 1830 Zhang, D., Kuptsov, D., and S. Shen, "Host Identifier 1831 Revocation in HIP", IRTF Working 1832 draft draft-irtf-hiprg-revocation-05, Mar 2012. 1834 Authors' Addresses 1836 Robert Moskowitz (editor) 1837 Verizon 1838 1000 Bent Creek Blvd, Suite 200 1839 Mechanicsburg, PA 1840 USA 1842 Email: robert.moskowitz@verizon.com 1844 Miika Komu 1845 Aalto University 1846 Konemiehentie 2 1847 Espoo 1848 Finland 1850 Email: miika.komu@aalto.fi