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'3') (Obsoleted by RFC 4966) == Outdated reference: A later version (-10) exists of draft-ietf-hip-base-00 == Outdated reference: A later version (-12) exists of draft-ietf-ipseckey-rr-10 == Outdated reference: A later version (-05) exists of draft-ietf-hip-mm-00 == Outdated reference: A later version (-03) exists of draft-ietf-mip6-ro-sec-00 == Outdated reference: A later version (-17) exists of draft-ietf-ipsec-ikev2-14 Summary: 6 errors (**), 0 flaws (~~), 8 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Moskowitz 3 Internet-Draft ICSAlabs, a Division of TruSecure 4 Expires: June 21, 2005 Corporation 5 P. Nikander 6 Ericsson Research Nomadic Lab 7 December 21, 2004 9 Host Identity Protocol Architecture 10 draft-ietf-hip-arch-01 12 Status of this Memo 14 This document is an Internet-Draft and is subject to all provisions 15 of section 3 of RFC 3667. By submitting this Internet-Draft, each 16 author represents that any applicable patent or other IPR claims of 17 which he or she is aware have been or will be disclosed, and any of 18 which he or she become aware will be disclosed, in accordance with 19 RFC 3668. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF), its areas, and its working groups. Note that 23 other groups may also distribute working documents as 24 Internet-Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 This Internet-Draft will expire on June 21, 2005. 39 Copyright Notice 41 Copyright (C) The Internet Society (2004). 43 Abstract 45 This memo describes a snapshot of the reasoning behind a proposed new 46 namespace, the Host Identity namespace, and a new protocol layer, the 47 Host Identity Protocol, between the internetworking and transport 48 layers. Herein are presented the basics of the current namespaces, 49 their strengths and weaknesses, and how a new namespace will add 50 completeness to them. The roles of this new namespace in the 51 protocols are defined. The memo describes the thinking of the 52 authors as of Fall 2003. The architecture may have evolved since. 53 This document represents one stable point in that evolution of 54 understanding. 56 Table of Contents 58 1. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3.1 Terms common to other documents . . . . . . . . . . . . . . 4 62 3.2 Terms specific to this and other HIP documents . . . . . . . 4 63 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 4.1 A desire for a namespace for computing platforms . . . . . . 7 65 5. Host Identity namespace . . . . . . . . . . . . . . . . . . 8 66 5.1 Host Identifiers . . . . . . . . . . . . . . . . . . . . . . 9 67 5.2 Storing Host Identifiers in DNS . . . . . . . . . . . . . . 9 68 5.3 Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . 10 69 5.4 Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 10 70 6. New stack architecture . . . . . . . . . . . . . . . . . . . 10 71 6.1 Transport associations and end-points . . . . . . . . . . . 11 72 7. End-host mobility and multi-homing . . . . . . . . . . . . . 12 73 7.1 Rendezvous mechanism . . . . . . . . . . . . . . . . . . . . 12 74 7.2 Protection against flooding attacks . . . . . . . . . . . . 13 75 8. HIP and IPsec . . . . . . . . . . . . . . . . . . . . . . . 13 76 9. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 14 77 9.1 HIP and TCP checksums . . . . . . . . . . . . . . . . . . . 15 78 10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 15 79 11. HIP policies . . . . . . . . . . . . . . . . . . . . . . . . 15 80 12. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . 16 81 12.1 HIP's answers to NSRG questions . . . . . . . . . . . . . . 17 82 13. Security considerations . . . . . . . . . . . . . . . . . . 19 83 13.1 HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . 20 84 13.2 Non-security considerations . . . . . . . . . . . . . . . . 21 85 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 21 86 15. Informative references . . . . . . . . . . . . . . . . . . . 22 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23 88 Intellectual Property and Copyright Statements . . . . . . . 24 90 1. Disclaimer 92 The purpose of this memo is to provide a stable reference point in 93 the development of the Host Identity Protocol architecture. This 94 memo describes the thinking of the authors as of Fall 2003; their 95 thinking may have evolved since then. Occasionally, this memo may be 96 confusing or self-contradicting. That is (partially) intentional, 97 and reflects the snapshot nature of this memo. 99 2. Introduction 101 The Internet has two important global namespaces: Internet Protocol 102 (IP) addresses and Domain Name Service (DNS) names. These two 103 namespaces have a set of features and abstractions that have powered 104 the Internet to what it is today. They also have a number of 105 weaknesses. Basically, since they are all we have, we try and do too 106 much with them. Semantic overloading and functionality extensions 107 have greatly complicated these namespaces. 109 The proposed Host Identity namespace fills an important gap between 110 the IP and DNS namespaces. The Host Identity namespace consists of 111 Host Identifiers (HI). A Host Identifier is cryptographic in its 112 nature; it is the public key of an asymmetric key-pair. Each host 113 will have at least one Host Identity, but it will typically have more 114 than one. Each Host Identity uniquely identifies a single host, 115 i.e., no two hosts have the same Host Identity. The Host Identity, 116 and the corresponding Host Identifier, can either be public (e.g. 117 published in the DNS), or unpublished. Client systems will tend to 118 have both public and unpublished Identities. 120 There is a subtle but important difference between Host Identities 121 and Host Identifiers. An Identity refers to the abstract entity that 122 is identified. An Identifier, on the other hand, refers to the 123 concrete bit pattern that is used in the identification process. 125 Although the Host Identifiers could be used in many authentication 126 systems, such as IKEv2 [11], the presented architecture introduces a 127 new protocol, called the Host Identity Protocol (HIP), and a 128 cryptographic exchange, called the HIP base exchange [6]; see also 129 Section 8. The new protocol provides for limited forms of trust 130 between systems. It enhances mobility, multi-homing and dynamic IP 131 renumbering [9], aids in protocol translation / transition [6], and 132 reduces certain types of denial-of-service (DoS) attacks [6]. 134 When HIP is used, the actual payload traffic between two HIP hosts is 135 typically, but not necessarily, protected with IPsec. The Host 136 Identities are used to create the needed IPsec Security Associations 137 (SAs) and to authenticate the hosts. When IPsec is used, the actual 138 payload IP packets do not differ in any way from standard IPsec 139 protected IP packets. 141 3. Terminology 143 3.1 Terms common to other documents 145 +--------------+----------------------------------------------------+ 146 | Term | Explanation | 147 +--------------+----------------------------------------------------+ 148 | Public key | The public key of an asymmetric cryptographic key | 149 | | pair. Used as a publicly known identifier for | 150 | | cryptographic identity authentication. | 151 | | | 152 | Private key | The private or secret key of an asymmetric | 153 | | cryptographic key pair. Assumed to be known only | 154 | | to the party identified by the corresponding | 155 | | public key. Used by the identified party to | 156 | | authenticate its identity to other parties. | 157 | | | 158 | Public key | An asymmetric cryptographic key pair consisting of | 159 | pair | public and private keys. For example, | 160 | | Rivest-Shamir-Adelman (RSA) and Digital Signature | 161 | | Algorithm (DSA) key pairs are such key pairs. | 162 | | | 163 | End-point | A communicating entity. For historical reasons, | 164 | | the term 'computing platform' is used in this | 165 | | document as a (rough) synonym for end-point. | 166 +--------------+----------------------------------------------------+ 168 3.2 Terms specific to this and other HIP documents 170 It should be noted that many of the terms defined herein are 171 tautologous, self-referential or defined through circular reference 172 to other terms. This is due to the succinct nature of the 173 definitions. See the text elsewhere in this document for more 174 elaborate explanations. 176 +--------------+----------------------------------------------------+ 177 | Term | Explanation | 178 +--------------+----------------------------------------------------+ 179 | Computing | An entity capable of communicating and computing, | 180 | platform | for example, a computer. See the definition of | 181 | | 'End-point', above. | 182 | | | 183 | HIP base | A cryptographic protocol defined in [6]. See also | 184 | exchange | Section 8. | 185 | | | 186 | HIP packet | An IP packet that carries a 'Host Identity | 187 | | Protocol' message. | 188 | | | 189 | Host | An abstract concept assigned to a 'computing | 190 | Identity | platform'. See 'Host Identifier', below. | 191 | | | 192 | Host | A name space formed by all possible Host | 193 | Identity | Identifiers. | 194 | namespace | | 195 | | | 196 | Host | A protocol used to carry and authenticate Host | 197 | Identity | Identifiers and other information. | 198 | Protocol | | 199 | | | 200 | Host | A 128-bit datum created by taking a cryptographic | 201 | Identity Tag | hash over a Host Identifier. | 202 | | | 203 | Host | A public key used as a name for a Host Identity. | 204 | Identifier | | 205 | | | 206 | Local Scope | A 32-bit datum denoting a Host Identity. | 207 | Identifier | | 208 | | | 209 | Public Host | A published or publicly known Host Identfier used | 210 | Identifier | as a public name for a Host Identity, and the | 211 | and Identity | corresponding Identity. | 212 | | | 213 | Unpublished | A Host Identifier that is not placed in any public | 214 | Host | directory, and the corresponding Host Identity. | 215 | Identifier | Unpublished Host Identities are typically short | 216 | and Identity | lived in nature, being often replaced and possibly | 217 | | used just once. | 218 | | | 219 | Rendezvous | A mechanism used to locate mobile hosts based on | 220 | Mechanism | their HIT. | 221 +--------------+----------------------------------------------------+ 223 4. Background 225 The Internet is built from three principal components: computing 226 platforms (end-points), packet transport (i.e., internetworking) 227 infrastructure, and services (applications). The Internet exists to 228 service two principal components: people and robotic services 229 (silicon based people, if you will). All these components need to be 230 named in order to interact in a scalable manner. Here we concentrate 231 on naming computing platforms and packet transport elements. 233 There are two principal namespaces in use in the Internet for these 234 components: IP numbers, and Domain Names. Email, HTTP, and SIP 235 addresses are really only extensions of Domain Names. 237 IP numbers are a confounding of two namespaces, the names of a host's 238 networking interfaces and the names of the locations ('confounding' 239 is a term used in statistics to discuss metrics that are merged into 240 one with a gain in indexing, but a loss in informational value). The 241 names of locations should be understood as denoting routing direction 242 vectors, i.e., information that is used to deliver packets to their 243 destinations. 245 IP numbers name networking interfaces, and typically only when the 246 interface is connected to the network. Originally, IP numbers had 247 long-term significance. Today, the vast number of interfaces use 248 ephemeral and/or non-unique IP numbers. That is, every time an 249 interface is connected to the network, it is assigned an IP number. 251 In the current Internet, the transport layers are coupled to the IP 252 addresses. Neither can evolve separately from the other. IPng 253 deliberations were strongly shaped by the decision that a 254 corresponding TCPng would not be created. 256 Domain Names provide hierarchically assigned names for some computing 257 platforms and some services. Each hierarchy is delegated from the 258 level above; there is no anonymity in Domain Names. 260 Email, SIP and WWW addresses provide naming for humans, autonomous 261 applications, and documents. Email, SIP and WWW addresses are 262 extensions of Domain Names. 264 There are three critical deficiencies with the current namespaces. 265 Firstly, dynamic readdressing cannot be directly managed. Secondly, 266 anonymity is not provided in a consistent, trustable manner. 267 Finally, authentication for systems and datagrams is not provided. 268 All of these deficiencies arise because computing platforms are not 269 well named with the current namespaces. 271 4.1 A desire for a namespace for computing platforms 273 An independent namespace for computing platforms could be used in 274 end-to-end operations independent of the evolution of the 275 internetworking layer and across the many internetworking layers. 276 This could support rapid readdressing of the internetworking layer 277 because of mobility, rehoming, or renumbering. 279 If the namespace for computing platforms is based on public-key 280 cryptography, it can also provide authentication services. If this 281 namespace is locally created without requiring registration, it can 282 provide anonymity. 284 Such a namespace (for computing platforms) and the names in it should 285 have the following characteristics: 287 o The namespace should be applied to the IP 'kernel'. The IP kernel 288 is the 'component' between applications and the packet transport 289 infrastructure. 291 o The namespace should fully decouple the internetworking layer from 292 the higher layers. The names should replace all occurrences of IP 293 addresses within applications (like in the Transport Control 294 Block, TCB). This may require changes to the current APIs. In 295 the long run, it is probable that some new APIs are needed. 297 o The introduction of the namespace should not mandate any 298 administrative infrastructure. Deployment must come from the 299 bottom up, in a pairwise deployment. 301 o The names should have a fixed length representation, for easy 302 inclusion in datagram headers and existing programming interfaces 303 (e.g the TCB). 305 o Using the namespace should be affordable when used in protocols. 306 This is primarily a packet size issue. There is also a 307 computational concern in affordability. 309 o The names must be statistically globally unique. 64 bits is 310 inadequate to make the probability of collisions sufficiently low 311 (1% chance of collision in a population of 640M); thus, 312 approximately 100 or more bits should be used. 314 o The names should have a localized abstraction so that it can be 315 used in existing protocols and APIs. 317 o It must be possible to create names locally. This can provide 318 anonymity at the cost of making resolvability very difficult. 320 * Sometimes the names may contain a delegation component. This 321 is the cost of resolvability. 323 o The namespace should provide authentication services. 325 o The names should be long lived, but replaceable at any time. This 326 impacts access control lists; short lifetimes will tend to result 327 in tedious list maintenance or require a namespace infrastructure 328 for central control of access lists. 330 In this document, a new namespace approaching these ideas is called 331 the Host Identity namespace. Using Host Identities requires its own 332 protocol layer, the Host Identity Protocol, between the 333 internetworking and transport layers. The names are based on 334 public-key cryptography to supply authentication services. Properly 335 designed, it can deliver all of the above stated requirements. 337 5. Host Identity namespace 339 A name in the Host Identity namespace, a Host Identifier (HI), 340 represents a statistically globally unique name for naming any system 341 with an IP stack. This identity is normally associated with, but not 342 limited to, an IP stack. A system can have multiple identities, some 343 'well known', some unpublished or 'anonymous'. A system may 344 self-assert its own identity, or may use a third-party authenticator 345 like DNSSEC [2], PGP, or X.509 to 'notarize' the identity assertion. 346 It is expected that the Host Identifiers will initially be 347 authenticated with DNSSEC and that all implementations will support 348 DNSSEC as a minimal baseline. 350 In theory, any name that can claim to be 'statistically globally 351 unique' may serve as a Host Identifier. However, in the authors' 352 opinion, a public key of a 'public key pair' makes the best Host 353 Identifier. As documented in the Host Identity Protocol 354 specification [6], a public-key-based HI can authenticate the HIP 355 packets and protect them for man-in-the-middle attacks. Since 356 authenticated datagrams are mandatory to provide much of HIP's 357 denial-of-service protection, the Diffie-Hellman exchange in HIP has 358 to be authenticated. Thus, only public-key HI and authenticated HIP 359 messages are supported in practice. In this document, the 360 non-cryptographic forms of HI and HIP are presented to complete the 361 theory of HI, but they should not be implemented as they could 362 produce worse denial-of-service attacks than the Internet has without 363 Host Identity. 365 5.1 Host Identifiers 367 Host Identity adds two main features to Internet protocols. The 368 first is a decoupling of the internetworking and transport layers; 369 see Section 6. This decoupling will allow for independent evolution 370 of the two layers. Additionally, it can provide end-to-end services 371 over multiple internetworking realms. The second feature is host 372 authentication. Because the Host Identifier is a public key, this 373 key can be used for authentication in security protocols like IPsec. 375 The only completely defined structure of the Host Identity is that of 376 a public/private key pair. In this case, the Host Identity is 377 referred to by its public component, the public key. Thus, the name 378 representing a Host Identity in the Host Identity namespace, i.e., 379 the Host Identifier, is the public key. In a way, the possession of 380 the private key defines the Identity itself. If the private key is 381 possessed by more than one node, the Identity can be considered to be 382 a distributed one. 384 Architecturally, any other Internet naming convention might form a 385 usable base for Host Identifiers. However, non-cryptographic names 386 should only be used in situations of high trust - low risk. That is 387 any place where host authentication is not needed (no risk of host 388 spoofing) and no use of IPsec. However, at least for interconnected 389 networks spanning several operational domains, the set of 390 environments where the risk of host spoofing allowed by 391 non-cryptographic Host Identifiers is acceptable is the null set. 392 Hence, the current HIP documents do not specify how to use any other 393 types of Host Identifiers but public keys. 395 The actual Host Identities are never directly used in any Internet 396 protocols. The corresponding Host Identifiers (public keys) may be 397 stored in various DNS or LDAP directories as identified elsewhere in 398 this document, and they are passed in the HIP base exchange. A Host 399 Identity Tag (HIT) is used in other protocols to represent the Host 400 Identity. Another representation of the Host Identities, the Local 401 Scope Identifier (LSI), can also be used in protocols and APIs. 403 5.2 Storing Host Identifiers in DNS 405 The public Host Identifiers should be stored in DNS; the unpublished 406 Host Identifiers should not be stored anywhere (besides the 407 communicating hosts themselves). The (public) HI is stored in a new 408 RR type, to be defined. This RR type is likely to be quite similar 409 to the IPSECKEY RR [7]. 411 Alternatively, or in addition to storing Host Identifiers in the DNS, 412 they may be stored in various kinds of Public Key Infrastructure 413 (PKI). Such a practice may allow them to be used for purposes other 414 than pure host identification. 416 5.3 Host Identity Tag (HIT) 418 A Host Identity Tag is a 128-bit representation for a Host Identity. 419 It is created by taking a cryptographic hash over the corresponding 420 Host Identifier. There are two advantages of using a hash over using 421 the Host Identifier in protocols. Firstly, its fixed length makes 422 for easier protocol coding and also better manages the packet size 423 cost of this technology. Secondly, it presents the identity in a 424 consistent format to the protocol independent of the cryptographic 425 algorithms used. 427 In the HIP packets, the HITs identify the sender and recipient of a 428 packet. Consequently, a HIT should be unique in the whole IP 429 universe as long as it is being used. In the extremely rare case of 430 a single HIT mapping to more than one Host Identity, the Host 431 Identifiers (public keys) will make the final difference. If there 432 is more than one public key for a given node, the HIT acts as a hint 433 for the correct public key to use. 435 5.4 Local Scope Identifier (LSI) 437 An LSI is a 32-bit localized representation for a Host Identity. The 438 purpose of an LSI is to facilitate using Host Identities in existing 439 protocols and APIs. LSI's advantage over HIT is its size; its 440 disadvantage is its local scope. The generation of LSIs is defined 441 in the Host Identity Protocol specification [6]. 443 Examples of how LSIs can be used include: as the address in an FTP 444 command and as the address in a socket call. Thus, LSIs act as a 445 bridge for Host Identities into IPv4-based protocols and APIs. 447 6. New stack architecture 449 One way to characterize Host Identity is to compare the proposed new 450 architecture with the current one. As discussed above, the IP 451 addresses can be seen to be a confounding of routing direction 452 vectors and interface names. Using the terminology from the IRTF 453 Name Space Research Group Report [8] and, e.g., the unpublished 454 Internet-Draft Endpoints and Endpoint Names [12] by Noel Chiappa, the 455 IP addresses currently embody the dual role of locators and end-point 456 identifiers. That is, each IP address names a topological location 457 in the Internet, thereby acting as a routing direction vector, or 458 locator. At the same time, the IP address names the physical network 459 interface currently located at the point-of-attachment, thereby 460 acting as a end-point name. 462 In the HIP architecture, the end-point names and locators are 463 separated from each other. IP addresses continue to act as locators. 464 The Host Identifiers take the role of end-point identifiers. It is 465 important to understand that the end-point names based on Host 466 Identities are slightly different from interface names; a Host 467 Identity can be simultaneously reachable through several interfaces. 469 The difference between the bindings of the logical entities are 470 illustrated in Figure 1. 472 Service ------ Socket Service ------ Socket 473 | | 474 | | 475 | | 476 | | 477 End-point | End-point --- Host Identity 478 \ | | 479 \ | | 480 \ | | 481 \ | | 482 Location --- IP address Location --- IP address 484 Figure 1 486 6.1 Transport associations and end-points 488 Architecturally, HIP provides for a different binding of 489 transport-layer protocols. That is, the transport-layer 490 associations, i.e., TCP connections and UDP associations, are no 491 longer bound to IP addresses but to Host Identities. 493 It is possible that a single physical computer hosts several logical 494 end-points. With HIP, each of these end-points would have a distinct 495 Host Identity. Furthermore, since the transport associations are 496 bound to Host Identities, HIP provides for process migration and 497 clustered servers. That is, if a Host Identity is moved from one 498 physical computer to another, it is also possible to simultaneously 499 move all the transport associations without breaking them. 500 Similarly, if it is possible to distribute the processing of a single 501 Host Identity over several physical computers, HIP provides for 502 cluster based services without any changes at the client end-point. 504 7. End-host mobility and multi-homing 506 HIP decouples the transport from the internetworking layer, and binds 507 the transport associations to the Host Identities (through actually 508 either the HIT or LSI). Consequently, HIP can provide for a degree 509 of internetworking mobility and multi-homing at a low infrastructure 510 cost. HIP mobility includes IP address changes (via any method) to 511 either party. Thus, a system is considered mobile if its IP address 512 can change dynamically for any reason like PPP, DHCP, IPv6 prefix 513 reassignments, or a NAT device remapping its translation. Likewise, 514 a system is considered multi-homed if it has more than one globally 515 routable IP address at the same time. HIP links IP addresses 516 together, when multiple IP addresses correspond to the same Host 517 Identity, and if one address becomes unusable, or a more preferred 518 address becomes available, existing transport associations can easily 519 be moved to another address. 521 When a node moves while communication is already on-going, address 522 changes are rather straightforward. The peer of the mobile node can 523 just accept a HIP or an integrity protected IPsec packet from any 524 address and ignore the source address. However, as discussed in 525 Section 7.2 below, a mobile node must send a HIP readdress packet to 526 inform the peer of the new address(es), and the peer must verify that 527 the mobile node is reachable through these addresses. This is 528 especially helpful for those situations where the peer node is 529 sending data periodically to the mobile node (that is re-starting a 530 connection after the initial connection). 532 7.1 Rendezvous mechanism 534 Making a contact to a mobile node is slightly more involved. In 535 order to start the HIP exchange, the initiator node has to know how 536 to reach the mobile node. Although infrequently moving HIP nodes 537 could use Dynamic DNS [1] to update their reachability information in 538 the DNS, an alternative to using DNS in this fashion is to use a 539 piece of new static infrastructure to facilitate rendezvous between 540 HIP nodes. 542 The mobile node keeps the rendezvous infrastructure continuously 543 updated with its current IP address(es). The mobile nodes must trust 544 the rendezvous mechanism to properly maintain their HIT and IP 545 address mappings. 547 The rendezvous mechanism is also needed if both of the nodes happen 548 to change their address at the same time, either because they are 549 mobile and happen to move at the same time, because one of them is 550 off-line for a while, or because of some other reason. In such a 551 case, the HIP readdress packets will cross each other in the network 552 and never reach the peer node. 554 A separate document will specify the details of the HIP rendezvous 555 mechanism. 557 7.2 Protection against flooding attacks 559 Although the idea of informing about address changes by simply 560 sending packets with a new source address appears appealing, it is 561 not secure enough. That is, even if HIP does not rely on the source 562 address for anything (once the base exchange has been completed), it 563 appears to be necessary to check a mobile node's reachability at the 564 new address before actually sending any larger amounts of traffic to 565 the new address. 567 Blindly accepting new addresses would potentially lead to flooding 568 Denial-of-Service attacks against third parties [10]. In a 569 distributed flooding attack an attacker opens high volume HIP 570 connections with a large number of hosts (using unpublished HIs), and 571 then claims to all of these hosts that it has moved to a target 572 node's IP address. If the peer hosts were to simply accept the move, 573 the result would be a packet flood to the target node's address. To 574 close this attack, HIP includes an address check mechanism where the 575 reachability of a node is separately checked at each address before 576 using the address for larger amounts of traffic. 578 Whenever HIP is used between two hosts that fully trust each other, 579 the hosts may optionally decide to skip the address tests. However, 580 such performance optimization must be restricted to peers that are 581 known to be trustworthy and capable of protecting themselves from 582 malicious software. 584 8. HIP and IPsec 586 The preferred way of implementing HIP is to use IPsec to carry the 587 actual data traffic. As of today, the only completely defined method 588 is to use IPsec Encapsulated Security Payload (ESP) to carry the data 589 packets. In the future, other ways of transporting payload data may 590 be developed, including ones that do not use cryptographic 591 protection. 593 In practice, the HIP base exchange uses the cryptographic Host 594 Identifiers to set up a pair of ESP Security Associations (SAs) to 595 enable ESP in an end-to-end manner. This is implemented in a way 596 that can span addressing realms. 598 While it would be possible, at least in theory, to use some existing 599 cryptographic protocol, such as IKEv2 together with Host Identifiers, 600 to establish the needed SAs, HIP defines a new protocol. There are a 601 number of historical reasons for this, and there are also a few 602 architectural reasons. First, IKE (and IKEv2) were not designed with 603 middle boxes in mind. As adding a new naming layer allows one to 604 potentially add a new forwarding layer (see Section 9, below), it is 605 very important that the HIP protocols are friendly towards any middle 606 boxes. 608 Second, from a conceptual point of view, the IPsec Security Parameter 609 Index (SPI) in ESP provides a simple compression of the HITs. This 610 does require per-HIT-pair SAs (and SPIs), and a decrease of policy 611 granularity over other Key Management Protocols, such as IKE and 612 IKEv2. In particular, the current thinking is limited to a situation 613 where, conceptually, there is only one pair of SAs between any given 614 pair of HITs. In other words, from an architectural point of view, 615 HIP only supports host-to-host (or endpoint-to-endpoint) Security 616 Associations. If two hosts need more pairs of parallel SAs, they 617 should use separate HITs for that. However, future HIP extensions 618 may provide for more granularity and creation of several ESP SAs 619 between a pair of HITs. 621 Since HIP is designed for host usage, not for gateways or so called 622 Bump-in-the-Wire (BITW) implementations, only ESP transport mode is 623 supported. An ESP SA pair is indexed by the SPIs and the two HITs 624 (both HITs since a system can have more than one HIT). The SAs need 625 not to be bound to IP addresses; all internal control of the SA is by 626 the HITs. Thus, a host can easily change its address using Mobile 627 IP, DHCP, PPP, or IPv6 readdressing and still maintain the SAs. 628 Since the transports are bound to the SA (via an LSI or a HIT), any 629 active transport is also maintained. Thus, real-world conditions 630 like loss of a PPP connection and its re-establishment or a mobile 631 handover will not require a HIP negotiation or disruption of 632 transport services [14]. 634 Since HIP does not negotiate any SA lifetimes, all lifetimes are 635 local policy. The only lifetimes a HIP implementation must support 636 are sequence number rollover (for replay protection), and SA timeout 637 [6]. An SA times out if no packets are received using that SA. 638 Implementations may support lifetimes for the various ESP transforms. 640 9. HIP and NATs 642 Passing packets between different IP addressing realms requires 643 changing IP addresses in the packet header. This may happen, for 644 example, when a packet is passed between the public Internet and a 645 private address space, or between IPv4 and IPv6 networks. The 646 address translation is usually implemented as Network Address 647 Translation (NAT) [4] or NAT Protocol translation (NAT-PT) [3]. 649 In a network environment where identification is based on the IP 650 addresses, identifying the communicating nodes is difficult when NAT 651 is used. With HIP, the transport-layer end-points are bound to the 652 Host Identities. Thus, a connection between two hosts can traverse 653 many addressing realm boundaries. The IP addresses are used only for 654 routing purposes; they may be changed freely during packet traversal. 656 For a HIP-based flow, a HIP-aware NAT or NAT-PT system tracks the 657 mapping of HITs, and the corresponding IPsec SPIs, to an IP address. 658 The NAT system has to learn mappings both from HITs and from SPIs to 659 IP addresses. Many HITs (and SPIs) can map to a single IP address on 660 a NAT, simplifying connections on address poor NAT interfaces. The 661 NAT can gain much of its knowledge from the HIP packets themselves; 662 however, some NAT configuration may be necessary. 664 NAT systems cannot touch the datagrams within the IPsec envelope, 665 thus application-specific address translation must be done in the end 666 systems. HIP provides for 'Distributed NAT', and uses the HIT or the 667 LSI as a placeholder for embedded IP addresses. 669 9.1 HIP and TCP checksums 671 There is no way for a host to know if any of the IP addresses in an 672 IP header are the addresses used to calculate the TCP checksum. That 673 is, it is not feasible to calculate the TCP checksum using the actual 674 IP addresses in the pseudo header; the addresses received in the 675 incoming packet are not necessarily the same as they were on the 676 sending host. Furthermore, it is not possible to recompute the 677 upper-layer checksums in the NAT/NAT-PT system, since the traffic is 678 IPsec protected. Consequently, the TCP and UDP checksums are 679 calculated using the HITs in the place of the IP addresses in the 680 pseudo header. Furthermore, only the IPv6 pseudo header format is 681 used. This provides for IPv4 / IPv6 protocol translation. 683 10. Multicast 685 Back in the fall of 2003, there was little if any concrete thoughts 686 about how HIP might affect IP-layer or application-layer multicast. 688 11. HIP policies 690 There are a number of variables that will influence the HIP exchanges 691 that each host must support. All HIP implementations should support 692 at least 2 HIs, one to publish in DNS and an unpublished one for 693 anonymous usage. Although unpublished HIs will be rarely used as 694 responder HIs, they are likely be common for initiators. Support for 695 multiple HIs is recommended. 697 Many initiators would want to use a different HI for different 698 responders. The implementations should provide for a policy of 699 initiator HIT to responder HIT. This policy should also include 700 preferred transforms and local lifetimes. 702 Responders would need a similar policy, describing the hosts allowed 703 to participate in HIP exchanges, and the preferred transforms and 704 local lifetimes. 706 12. Benefits of HIP 708 In the beginning, the network layer protocol (i.e., IP) had the 709 following four "classic" invariants: 711 o Non-mutable: The address sent is the address received. 713 o Non-mobile: The address doesn't change during the course of an 714 "association". 716 o Reversible: A return header can always be formed by reversing the 717 source and destination addresses. 719 o Omniscient: Each host knows what address a partner host can use to 720 send packets to it. 722 Actually, the fourth can be inferred from 1 and 3, but it is worth 723 mentioning for reasons that will be obvious soon if not already. 725 In the current "post-classic" world, we are intentionally trying to 726 get rid of the second invariant (both for mobility and for 727 multi-homing), and we have been forced to give up the first and the 728 fourth. Realm Specific IP [5] is an attempt to reinstate the fourth 729 invariant without the first invariant. IPv6 is an attempt to 730 reinstate the first invariant. 732 Few systems on the Internet have DNS names that are meaningful. That 733 is, if they have a Fully Qualified Domain Name (FQDN), that name 734 typically belongs to a NAT device or a dial-up server, and does not 735 really identify the system itself but its current connectivity. 736 FQDNs (and their extensions as email names) are application-layer 737 names; more frequently naming services than a particular system. 738 This is why many systems on the Internet are not registered in the 739 DNS; they do not have services of interest to other Internet hosts. 741 DNS names are references to IP addresses. This only demonstrates the 742 interrelationship of the networking and application layers. DNS, as 743 the Internet's only deployed, distributed database is also the 744 repository of other namespaces, due in part to DNSSEC and application 745 specific key records. Although each namespace can be stretched (IP 746 with v6, DNS with KEY records), neither can adequately provide for 747 host authentication or act as a separation between internetworking 748 and transport layers. 750 The Host Identity (HI) namespace fills an important gap between the 751 IP and DNS namespaces. An interesting thing about the HI is that it 752 actually allows one to give up all but the 3rd network-layer 753 invariant. That is to say, as long as the source and destination 754 addresses in the network-layer protocol are reversible, then things 755 work ok because HIP takes care of host identification, and 756 reversibility allows one to get a packet back to one's partner host. 757 You do not care if the network-layer address changes in transit 758 (mutable) and you don't care what network-layer address the partner 759 is using (non-omniscient). 761 12.1 HIP's answers to NSRG questions 763 The IRTF Name Space Research Group has posed a number of evaluating 764 questions in their report [8]. In this section, we provide answers 765 to these questions. 767 1. How would a stack name improve the overall functionality of the 768 Internet? 770 HIP decouples the internetworking layer from the transport 771 layer, allowing each to evolve separately. The decoupling 772 makes end-host mobility and multi-homing easier, also across 773 IPv4 and IPv6 networks. HIs make network renumbering easier, 774 and they also make process migration and clustered servers 775 easier to implement. Furthermore, being cryptographic in 776 nature, they provide the basis for solving the security 777 problems related to end-host mobility and multi-homing. 779 2. What does a stack name look like? 781 A HI is a cryptographic public key. However, instead of using 782 the keys directly, most protocols use a fixed size hash of the 783 public key. 785 3. What is its lifetime? 787 HIP provides both stable and temporary Host Identifiers. 788 Stable HIs are typically long lived, with a lifetime of years 789 or more. The lifetime of temporary HIs depends on how long 790 the upper-layer connections and applications need them, and 791 can range from a few seconds to years. 793 4. Where does it live in the stack? 795 The HIs live between the transport and internetworking layers. 797 5. How is it used on the end points 799 The Host Identifiers may be used directly or indirectly (in 800 the form of HITs or LSIs) by applications when they access 801 network services. Additionally, the Host Identifiers, as 802 public keys, are used in the built in key agreement protocol, 803 called the HIP base exchange, to authenticate the hosts to 804 each other. 806 6. What administrative infrastructure is needed to support it? 808 In some environments, it is possible to use HIP 809 opportunistically, without any infrastructure. However, to 810 gain full benefit from HIP, the HIs must be stored in the DNS 811 or a PKI, and a new rendezvous mechanism is needed. Such a 812 new rendezvous mechanism may need new infrastructure to be 813 deployed. 815 7. If we add an additional layer would it make the address list in 816 SCTP unnecessary? 818 Yes 820 8. What additional security benefits would a new naming scheme 821 offer? 823 HIP reduces dependency on IP addresses, making the so called 824 address ownership [13] problems easier to solve. In practice, 825 HIP provides security for end-host mobility and multi-homing. 826 Furthermore, since HIP Host Identifiers are public keys, 827 standard public key certificate infrastructures can be applied 828 on the top of HIP. 830 9. What would the resolution mechanisms be, or what characteristics 831 of a resolution mechanisms would be required? 833 For most purposes, an approach where DNS names are resolved 834 simultaneously to HIs and IP addresses is sufficient. 835 However, if it becomes necessary to resolve HIs into IP 836 addresses or back to DNS names, a flat resolution 837 infrastructure is needed. Such an infrastructure could be 838 based on the ideas of Distributed Hash Tables, but would 839 require significant new development and deployment. 841 13. Security considerations 843 HIP takes advantage of the new Host Identity paradigm to provide 844 secure authentication of hosts and to provide a fast key exchange for 845 IPsec. HIP also attempts to limit the exposure of the host to 846 various denial-of-service (DoS) and man-in-the-middle (MitM) attacks. 847 In so doing, HIP itself is subject to its own DoS and MitM attacks 848 that potentially could be more damaging to a host's ability to 849 conduct business as usual. 851 Resource exhausting denial-of-service attacks take advantage of the 852 cost of setting up a state for a protocol on the responder compared 853 to the 'cheapness' on the initiator. HIP allows a responder to 854 increase the cost of the start of state on the initiator and makes an 855 effort to reduce the cost to the responder. This is done by having 856 the responder start the authenticated Diffie-Hellman exchange instead 857 of the initiator, making the HIP base exchange 4 packets long. There 858 are more details on this process in the Host Identity Protocol 859 specification [6]. 861 HIP optionally supports opportunistic negotiation. That is, if a 862 host receives a start of transport without a HIP negotiation, it can 863 attempt to force a HIP exchange before accepting the connection. 864 This has the potential for DoS attacks against both hosts. If the 865 method to force the start of HIP is expensive on either host, the 866 attacker need only spoof a TCP SYN. This would put both systems into 867 the expensive operations. HIP avoids this attack by having the 868 responder send a simple HIP packet that it can pre-build. Since this 869 packet is fixed and easily replayed, the initiator only reacts to it 870 if it has just started a connection to the responder. 872 Man-in-the-middle attacks are difficult to defend against, without 873 third-party authentication. A skillful MitM could easily handle all 874 parts of the HIP base exchange, but HIP indirectly provides the 875 following protection from a MitM attack. If the responder's HI is 876 retrieved from a signed DNS zone or secured by some other means, the 877 initiator can use this to authenticate the signed HIP packets. 878 Likewise, if the initiator's HI is in a secure DNS zone, the 879 responder can retrieve it and validate the signed HIP packets. 880 However, since an initiator may choose to use an unpublished HI, it 881 knowingly risks a MitM attack. The responder may choose not to 882 accept a HIP exchange with an initiator using an unknown HI. 884 In HIP, the Security Association for IPsec is indexed by the SPI; the 885 source address is always ignored, and the destination address may be 886 ignored as well. Therefore, HIP-enabled IPsec Encapsulated Security 887 Payload (ESP) is IP address independent. This might seem to make it 888 easier for an attacker, but ESP with replay protection is already as 889 well protected as possible, and the removal of the IP address as a 890 check should not increase the exposure of IPsec ESP to DoS attacks. 892 Since not all hosts will ever support HIP, ICMPv4 'Destination 893 Unreachable, Protocol Unreachable' and ICMPv6 'Parameter Problem, 894 Unrecognized Next Header' messages are to be expected and present a 895 DoS attack. Against an initiator, the attack would look like the 896 responder does not support HIP, but shortly after receiving the ICMP 897 message, the initiator would receive a valid HIP packet. Thus, to 898 protect against this attack, an initiator should not react to an ICMP 899 message until a reasonable time has passed, allowing it to get the 900 real responder's HIP packet. A similar attack against the responder 901 is more involved. 903 Another MitM attack is simulating a responder's administrative 904 rejection of a HIP initiation. This is a simple ICMP 'Destination 905 Unreachable, Administratively Prohibited' message. A HIP packet is 906 not used because it would either have to have unique content, and 907 thus difficult to generate, resulting in yet another DoS attack, or 908 just as spoofable as the ICMP message. Like in the previous case, 909 the defense against this attack is for the initiator to wait a 910 reasonable time period to get a valid HIP packet. If one does not 911 come, then the initiator has to assume that the ICMP message is 912 valid. Since this is the only point in the HIP base exchange where 913 this ICMP message is appropriate, it can be ignored at any other 914 point in the exchange. 916 13.1 HITs used in ACLs 918 It is expected that HITs will be used in ACLs. Future firewalls can 919 use HITs to control egress and ingress to networks, with an assurance 920 level difficult to achieve today. As discussed above in Section 8, 921 once a HIP session has been established, the SPI value in an IPsec 922 packet may be used as an index, indicating the HITs. In practice, 923 firewalls can inspect HIP packets to learn of the bindings between 924 HITs, SPI values, and IP addresses. They can even explicitly control 925 IPsec usage, dynamically opening IPsec ESP only for specific SPI 926 values and IP addresses. The signatures in HIP packets allow a 927 capable firewall to ensure that the HIP exchange is indeed happening 928 between two known hosts. This may increase firewall security. 930 There has been considerable bad experience with distributed ACLs that 931 contain public key related material, for example, with SSH. If the 932 owner of a key needs to revoke it for any reason, the task of finding 933 all locations where the key is held in an ACL may be impossible. If 934 the reason for the revocation is due to private key theft, this could 935 be a serious issue. 937 A host can keep track of all of its partners that might use its HIT 938 in an ACL by logging all remote HITs. It should only be necessary to 939 log responder hosts. With this information, the host can notify the 940 various hosts about the change to the HIT. There has been no attempt 941 to develop a secure method to issue the HIT revocation notice. 943 HIP-aware NATs, however, are transparent to the HIP aware systems by 944 design. Thus, the host may find it difficult to notify any NAT that 945 is using a HIT in an ACL. Since most systems will know of the NATs 946 for their network, there should be a process by which they can notify 947 these NATs of the change of the HIT. This is mandatory for systems 948 that function as responders behind a NAT. In a similar vein, if a 949 host is notified of a change in a HIT of an initiator, it should 950 notify its NAT of the change. In this manner, NATs will get updated 951 with the HIT change. 953 13.2 Non-security considerations 955 The definition of the Host Identifier states that the HI need not be 956 a public key. It implies that the HI could be any value; for example 957 a FQDN. This document does not describe how to support such a 958 non-cryptographic HI. A non-cryptographic HI would still offer the 959 services of the HIT or LSI for NAT traversal. It would be possible 960 to carry HITs in HIP packets that had neither privacy nor 961 authentication. Since such a mode would offer so little additional 962 functionality for so much addition to the IP kernel, it has not been 963 defined. Given how little public key cryptography HIP requires, HIP 964 should only be implemented using public key Host Identities. 966 If it is desirable to use HIP in a low security situation where 967 public key computations are considered expensive, HIP can be used 968 with very short Diffie-Hellman and Host Identity keys. Such use 969 makes the participating hosts vulnerable to MitM and connection 970 hijacking attacks. However, it does not cause flooding dangers, 971 since the address check mechanism relies on the routing system and 972 not on cryptographic strength. 974 14. Acknowledgments 976 For the people historically involved in the early stages of HIP, see 977 the Acknowledgements section in the Host Identity Protocol 978 specification [6]. 980 During the later stages of this document, when the editing baton was 981 transfered to Pekka Nikander, the comments from the early 982 implementors and others, including Jari Arkko, Tom Henderson, Petri 983 Jokela, Miika Komu, Mika Kousa, Andrew McGregor, Jan Melen, Tim 984 Shepard, Jukka Ylitalo, and Jorma Wall, were invaluable. Finally, 985 Lars Eggert, Spencer Dawkins and Dave Crocker provided valuable input 986 during the final stages of publication, most of which was 987 incorporated but some of which the authors decided to ignore in order 988 to get this document published in the first place. 990 15 Informative references 992 [1] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic 993 Updates in the Domain Name System (DNS UPDATE)", RFC 2136, 994 April 1997. 996 [2] Eastlake, D., "Domain Name System Security Extensions", RFC 997 2535, March 1999. 999 [3] Tsirtsis, G. and P. Srisuresh, "Network Address Translation - 1000 Protocol Translation (NAT-PT)", RFC 2766, February 2000. 1002 [4] Srisuresh, P. and K. Egevang, "Traditional IP Network Address 1003 Translator (Traditional NAT)", RFC 3022, January 2001. 1005 [5] Borella, M., Lo, J., Grabelsky, D. and G. Montenegro, "Realm 1006 Specific IP: Framework", RFC 3102, October 2001. 1008 [6] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-00 1009 (work in progress), June 2004. 1011 [7] Richardson, M., "A method for storing IPsec keying material in 1012 DNS", draft-ietf-ipseckey-rr-10 (work in progress), April 2004. 1014 [8] Lear, E. and R. Droms, "What's In A Name:Thoughts from the 1015 NSRG", draft-irtf-nsrg-report-10 (work in progress), September 1016 2003. 1018 [9] Nikander, P., "End-Host Mobility and Multi-Homing with Host 1019 Identity Protocol", draft-ietf-hip-mm-00 (work in progress), 1020 October 2004. 1022 [10] Nikander, P., "Mobile IP version 6 Route Optimization Security 1023 Design Background", draft-ietf-mip6-ro-sec-00 (work in 1024 progress), April 2004. 1026 [11] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1027 draft-ietf-ipsec-ikev2-14 (work in progress), June 2004. 1029 [12] Chiappa, J., "Endpoints and Endpoint Names: A Proposed 1030 Enhancement to the Internet Architecture", URL 1031 http://users.exis.net/~jnc/tech/endpoints.txt, 1999. 1033 [13] Nikander, P., "Denial-of-Service, Address Ownership, and Early 1034 Authentication in the IPv6 World", in Proceesings of Security 1035 Protocols, 9th International Workshop, Cambridge, UK, April 1036 25-27 2001, LNCS 2467, pp. 12-26, Springer, 2002. 1038 [14] Bellovin, S., "EIDs, IPsec, and HostNAT", in Proceesings of 1039 41th IETF, Los Angeles, CA, March 1998. 1041 Authors' Addresses 1043 Robert Moskowitz 1044 ICSAlabs, a Division of TruSecure Corporation 1045 1000 Bent Creek Blvd, Suite 200 1046 Mechanicsburg, PA 1047 USA 1049 EMail: rgm@icsalabs.com 1051 Pekka Nikander 1052 Ericsson Research Nomadic Lab 1053 JORVAS FIN-02420 1054 FINLAND 1056 Phone: +358 9 299 1 1057 EMail: pekka.nikander@nomadiclab.com 1059 Intellectual Property Statement 1061 The IETF takes no position regarding the validity or scope of any 1062 Intellectual Property Rights or other rights that might be claimed to 1063 pertain to the implementation or use of the technology described in 1064 this document or the extent to which any license under such rights 1065 might or might not be available; nor does it represent that it has 1066 made any independent effort to identify any such rights. 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