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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) ** Obsolete normative reference: RFC 4835 (Obsoleted by RFC 7321) -- Obsolete informational reference (is this intentional?): RFC 2401 (Obsoleted by RFC 4301) -- Obsolete informational reference (is this intentional?): RFC 4306 (Obsoleted by RFC 5996) -- Obsolete informational reference (is this intentional?): RFC 3547 (Obsoleted by RFC 6407) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PIM Working Group W. Atwood 3 Internet-Draft Concordia University/CSE 4 Updates: 4601 (if approved) S. Islam 5 Intended status: Standards Track INRS Energie, Materiaux et 6 Expires: August 30, 2009 Telecommunications 7 M. Siami 8 Concordia University/CIISE 9 February 26, 2009 11 Authentication and Confidentiality in PIM-SM Link-local Messages 12 draft-ietf-pim-sm-linklocal-07 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on August 30, 2009. 37 Copyright Notice 39 Copyright (c) 2009 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents in effect on the date of 44 publication of this document (http://trustee.ietf.org/license-info). 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. 48 Abstract 50 RFC 4601 mandates the use of IPsec to ensure authentication of the 51 link-local messages in the Protocol Independent Multicast - Sparse 52 Mode (PIM-SM) routing protocol. This document specifies mechanisms 53 to authenticate the PIM-SM link-local messages using the IP security 54 (IPsec) Encapsulating Security Payload (ESP) or (optionally) the 55 Authentication Header (AH). It specifies optional mechanisms to 56 provide confidentiality using the ESP. Manual keying is specified as 57 the mandatory and default group key management solution. To deal 58 with issues of scalability and security that exist with manual 59 keying, an optional support for automated group key management 60 mechanism is provided. However, the procedures for implementing 61 automated group key management are left to other documents. This 62 document updates RFC 4601. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 1.1. Goals and Non-goals . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 3. Transport Mode vs. Tunnel Mode . . . . . . . . . . . . . . . . 7 70 4. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 8 71 5. Confidentiality . . . . . . . . . . . . . . . . . . . . . . . 9 72 6. IPsec Requirements . . . . . . . . . . . . . . . . . . . . . . 10 73 7. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 12 74 7.1. Manual Key Management . . . . . . . . . . . . . . . . . . 12 75 7.2. Automated Key Management . . . . . . . . . . . . . . . . . 12 76 7.3. Communications Patterns . . . . . . . . . . . . . . . . . 13 77 7.4. Neighbor Relationships . . . . . . . . . . . . . . . . . . 15 78 8. Number of Security Associations . . . . . . . . . . . . . . . 16 79 9. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 80 9.1. Manual Rekeying Procedure . . . . . . . . . . . . . . . . 18 81 9.2. KeyRollover Interval . . . . . . . . . . . . . . . . . . . 18 82 9.3. Rekeying Interval . . . . . . . . . . . . . . . . . . . . 19 83 10. IPsec Protection Barrier and SPD/GSPD . . . . . . . . . . . . 20 84 10.1. Manual Keying . . . . . . . . . . . . . . . . . . . . . . 20 85 10.1.1. SAD Entries . . . . . . . . . . . . . . . . . . . . . 20 86 10.1.2. SPD Entries . . . . . . . . . . . . . . . . . . . . . 20 87 10.2. Automatic Keying . . . . . . . . . . . . . . . . . . . . . 20 88 10.2.1. SAD Entries . . . . . . . . . . . . . . . . . . . . . 20 89 10.2.2. GSPD Entries . . . . . . . . . . . . . . . . . . . . 20 90 10.2.3. PAD Entries . . . . . . . . . . . . . . . . . . . . . 21 91 11. Security Association Lookup . . . . . . . . . . . . . . . . . 22 92 12. Activating the Anti-replay Mechanism . . . . . . . . . . . . . 23 93 13. Implementing a Security Policy Database per Interface . . . . 24 94 14. Extended Sequence Number . . . . . . . . . . . . . . . . . . . 25 95 15. Security Considerations . . . . . . . . . . . . . . . . . . . 26 96 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 97 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 98 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 99 18.1. Normative References . . . . . . . . . . . . . . . . . . . 29 100 18.2. Informative References . . . . . . . . . . . . . . . . . . 29 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 103 1. Introduction 105 All the PIM-SM [RFC4601] control messages have IP protocol number 106 103. These messages are either unicast, or multicast with TTL = 1. 107 The source address used for unicast messages is a domain-wide 108 reachable address. For the multicast messages, a link-local address 109 of the interface on which the message is being sent is used as the 110 source address and a special multicast address, ALL_PIM_ROUTERS 111 (224.0.0.13 in IPv4 and ff02::d in IPv6) is used as the destination 112 address. These messages are called link-local messages. Hello, 113 Join/Prune and Assert messages are included in this category. A 114 forged link-local message may be sent to the ALL_PIM_ROUTERS 115 multicast address by an attacker. This type of message affects the 116 construction of the distribution tree [RFC4601]. The effects of 117 these forged messages are outlined in section 6.1 of [RFC4601]. Some 118 of the effects are very severe, whereas some are minor. 120 PIM-SM version 2 was originally specified in RFC 2117, and revised in 121 RFC 2362 and RFC 4601. RFC 4601 obsoletes RFC 2362, and corrects a 122 number of deficiencies. The Security Considerations section of RFC 123 4601 is based primarily on the Authentication Header (AH) 124 specification described in RFC 4302 [RFC4302]. 126 Securing the unicast messages can be achieved by the use of a normal 127 unicast IPsec Security Association between the two communicants. 129 This document focuses on the security issues for link-local messages. 130 It provides some guidelines to take advantage of the new permitted AH 131 functionality in RFC 4302 and the new permitted ESP functionality in 132 RFC 4303 [RFC4303], and to bring the PIM-SM specification into 133 alignment with the new AH and ESP specifications. In particular, in 134 accordance with RFC 4301, the use of ESP is made mandatory and AH is 135 specified as optional. This document specifies manual key management 136 as mandatory to implement, i.e., that all implementations MUST 137 support, and provides the necessary structure for an automated key 138 management protocol that the PIM routers may use. 140 1.1. Goals and Non-goals 142 The primary goal for link-local security is to provide data origin 143 authentication for each link-local message. A secondary goal is to 144 ensure that communication only happens between legitimate peers 145 (i.e., adjacent routers). An optional goal is to provide data 146 confidentiality for the link-local messages. 148 The first goal implies that each router has a unique identity. It is 149 possible (but not mandatory) that this identity will be based on the 150 unicast identity of the router. (The unicast identity could be, for 151 example, based on some individually-configured property of the 152 router, or be part of a region-wide public key infrastructure.) The 153 existence of this unique identity is assumed in this specification, 154 but procedures for establishing it are out-of-scope for this 155 document. 157 The second goal implies that there is some form of "adjacency matrix" 158 that controls the establishment of security associations among 159 adjacent multicast routers. For manual keying, this control will be 160 exercised by the Administrator of the router(s), through the setting 161 of initialization parameters. For automated keying, the existence of 162 this control will be reflected by the contents of the Peer 163 Authorization Database (PAD) and the Group Security Policy Database 164 (GSPD) in each router. Procedures for controling the adjacency and 165 building the asssociated PAD and GSPD are out-of-scope for this 166 document. 168 2. Terminology 170 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 171 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 172 document are to be interpreted as described in RFC 2119 [RFC2119]. 173 They indicate requirement levels for compliant PIM-SM 174 implementations. 176 3. Transport Mode vs. Tunnel Mode 178 As stated in Section 4.1 of RFC 4301 [RFC4301], a transport mode 179 Security Association (SA) is generally used between two hosts or 180 routers/gateways when they are acting as hosts. The SA must be a 181 tunnel mode SA if either end of the security association is acting as 182 a router/gateway. Two hosts MAY establish a tunnel mode SA between 183 themselves. PIM-SM link-local messages are exchanged between 184 routers. However, since the packets are locally delivered, the 185 routers assume the role of hosts in the context of the tunnel mode 186 SA. All implementations conforming to this specification MUST 187 support transport mode SA to provide required IPsec security to 188 PIM-SM link-local messages. They MAY also support tunnel mode SA to 189 provide required IPsec security to PIM-SM link-local messages. 191 4. Authentication 193 Implementations conforming to this specification MUST support 194 authentication for PIM-SM link-local messages. Implementations 195 conforming to this specification MUST support HMAC-SHA1. 197 In order to provide authentication to PIM-SM link-local messages, 198 implementations MUST support ESP [RFC4303] and MAY support AH 199 [RFC4302]. 201 If ESP in transport mode is used, it will only provide authentication 202 to PIM-SM protocol packets excluding the IP header, extension 203 headers, and options. 205 If AH in transport mode is used, it will provide authentication to 206 PIM-SM protocol packets, selected portions of the IP header, 207 extension headers and options. 209 When authentication for PIM-SM link-local messages is enabled, 211 o PIM-SM link-local packets that are not protected with AH or ESP 212 MUST be silently discarded. 214 o PIM-SM link-local packets that fail the authentication checks MUST 215 be silently discarded. 217 5. Confidentiality 219 Implementations conforming to this specification SHOULD support 220 confidentiality for PIM-SM. Implementations supporting 221 confidentiality MUST support AES-CBC with a 128-bit key. 223 If confidentiality is provided, ESP MUST be used. 225 When PIM-SM confidentiality is enabled, 227 o PIM-SM packets that are not protected with ESP MUST be silently 228 discarded. 230 o PIM-SM packets that fail the confidentiality checks MUST be 231 silently discarded. 233 Note that since authentication MUST be supported by a conforming 234 implementation, the combination of NON-NULL Encryption and NULL 235 Authentication is NOT permitted. 237 6. IPsec Requirements 239 In order to implement this specification, the following IPsec 240 capabilities are required. 242 Transport mode 243 IPsec in transport mode MUST be supported. 245 Multiple Security Policy Databases (SPDs) 246 The implementation MUST support multiple SPDs with an SPD 247 selection function that provides an ability to choose a specific 248 SPD based on interface. 250 Selectors 251 The implementation MUST be able to use source address, destination 252 address, protocol, and direction as selectors in the SPD. 254 Interface ID tagging 255 The implementation MUST be able to tag the inbound packets with 256 the ID of the interface (physical or virtual) via which it 257 arrived. 259 Manual key support 260 Manually configured keys MUST be able to secure the specified 261 traffic. 263 Encryption and authentication algorithms 264 Encryption and authentication algorithm requirements described in 265 RFC 4835 [RFC4835] apply when ESP and AH are used to protect 266 PIM-SM. Implementations MUST support ESP-NULL, and if providing 267 confidentiality MUST support the RFC4835 [RFC4835] required ESP 268 transforms providing confidentiality. However, in any case, 269 implementations MUST NOT allow the user to choose a stream cipher 270 or block mode cipher in counter mode for use with manual keys. 272 Encapsulation of ESP packet 273 IP encapsulation of ESP packets MUST be supported. For 274 simplicity, UDP encapsulation of ESP packets SHOULD NOT be used. 276 If the automatic keying features of this specification are 277 implemented, the following additional IPsec capabilities are 278 required: 280 Group Security Policy Database (GSPD) 281 The implementation MUST support the GSPD that is described in RFC 282 5374 [RFC5374]. 284 Multiple Group Security Policy Databases 285 The implementation MUST support multiple GSPDs with a GSPD 286 selection function that provides an ability to choose a specific 287 GSPD based on interface. 289 Selectors 290 The implementation MUST be able to use source address, destination 291 address, protocol and direction as selectors in the GSPD. 293 7. Key Management 295 All the implementations MUST support manual configuration of the 296 Security Associations (SAs) that will be used to authenticate PIM-SM 297 link-local messages. This does not preclude the use of a negotiation 298 protocol such as the Internet Key Exchange (IKE) [RFC4306] or Group 299 Secure Association Key Management Protocol (GSAKMP) [RFC4535] to 300 establish SAs. 302 7.1. Manual Key Management 304 To establish the SAs at PIM-SM routers, manual key configuration will 305 be feasible when the number of peers (directly connected routers) is 306 small. The Network Administrator will configure a router manually 307 during its boot up process. At that time, the authentication method 308 and the choice of keys SHOULD be configured. The Security 309 Association Database (SAD) entry will be created. The Network 310 Administrator will also configure the Security Policy Database of a 311 router to ensure the use of the associated SA while sending a link- 312 local message. 314 7.2. Automated Key Management 316 All the link-local messages of the PIM-SM protocol are sent to the 317 destination address, ALL_PIM_ROUTERS, which is a multicast address. 318 By using the sender address in conjunction with the destination 319 address for Security Association lookup, link-local communication 320 turns into an SSM or "one to many" communication. Since IKE is based 321 on the Diffie-Hellman key agreement protocol and works only for two 322 communicating parties, it is not possible to use IKE for providing 323 the required "one to many" authentication. 325 The procedures for automated key management are not specified in this 326 document. 328 One option is to use Group Domain Of Interpretation (GDOI) [RFC3547], 329 which enables a group of users or devices to exchange encrypted data 330 using IPsec data encryption. GDOI has been developed to be used in 331 multicast applications, where the number of end users or devices may 332 be large and the end users or devices can dynamically join/leave a 333 multicast group. However, a PIM router is not expected to join/leave 334 very frequently, and the number of routers is small when compared to 335 the possible number of users of a multicast application. Moreover, 336 most of the PIM routers will be located inside the same 337 administrative domain and are considered as trusted parties. It is 338 possible that a subset of GDOI functionalities will be sufficient. 340 Another option is to use the Group Secure Association Key Management 341 Protocol (GSAKMP) [RFC4535]. 343 7.3. Communications Patterns 345 Before discussing the set of security associations that are required 346 to properly manage a multicast region that is under the control of a 347 single administration, it is necessary to understand the 348 communications patterns that will exist among the routers in this 349 region. From the perspective of a speaking router, the information 350 from that router is sent (multicast) to all of its neighbors. From 351 the perspective of a listening router, the information coming from 352 each of its neighbors is distinct from the information coming from 353 every other router to which it is directly connected. Thus an 354 administrative region contains many (small) distinct groups, all of 355 which happen to be using the same multicast destination address 356 (e.g., ALL_PIM_ROUTERS, see Section 11), and each of which is 357 centered on the associated speaking router. 359 Consider the example configuration as shown in Figure 1. 361 R2 R3 R4 R5 R6 362 | | | | | 363 | | | | | 364 --------- --------------- 365 | | 366 | | 367 \ / 368 R1 369 / \ 370 | | 371 | | 372 --------- -------------------- 373 | | | | | 374 | | | | | 375 R7 R8 R9 R10 R11 376 | | | | | 377 | 378 | 379 ------------- 380 | | | 381 | | | 382 R12 R13 R14 384 Figure 1: Set of router interconnections 386 In this configuration, router R1 has four interfaces, and is the 387 speaking router for a group whose listening routers are routers R2 388 through R11. Router R9 is the speaking router for a group whose 389 listening routers are routers R1, R8 and R10-R14. 391 From the perspective of R1 as a speaking router, if a Security 392 Association SA1 is assigned to protect outgoing packets from R1, then 393 it is necessary to distribute the key for this association to each of 394 the routers R2 through R11. Similarly, from the perspective of R9 as 395 a speaking router, if a Security Association is assigned to protect 396 the outgoing packets from R9, then it is necessary to distribute the 397 key for this association to each of the routers R1, R8, and R10 398 through R14. 400 From the perspective of R1 as a listening router, all packets 401 arriving from R2 through R11 need to be distinguished from each 402 other, to permit selecting the correct Security Association in the 403 SAD. (Packets from each of the peer routers (R2 through R11) 404 represent communication from a different speaker, with a separate 405 sequence number space, even though they are sent using the same 406 destination address.) For a multicast Security Association, RFC 4301 407 permits using the Source Address in the selection function. If the 408 source addresses used by routers R2 through R11 are globally unique, 409 then the source addresses of the peer routers are sufficient to 410 achieve the differentiation. If the sending routers use link-local 411 addresses, then these addresses are unique only on a per-interface 412 basis, and it is necessary to use the Interface ID tag as an 413 additional selector, i.e., either the selection function has to have 414 the Interface ID tag as one of its inputs, or separate SADs have to 415 be maintained for each interface. 417 If the assumption of connectivity to the key server can be made 418 (which is true in the PIM-SM case), then the Group Controller/Key 419 Server (GC/KS) that is used for the management of the keys can be 420 centrally located (and duplicated for reliability). If this 421 assumption cannot be made (i.e., in the case of adjacencies for a 422 unicast router), then some form of "local" key server must be 423 available for each group. Given that the listening routers are never 424 more than one hop away from the speaking router, the speaking router 425 is the obvious place to locate the "local" key server. As such, this 426 may be a useful approach even in the PIM-SM case. This approach has 427 the additional advantage that there is no need to duplicate the local 428 key server for reliability, since if the key server is down, it is 429 very likely that the speaking router is also down. 431 7.4. Neighbor Relationships 433 Each distinct group consists of one speaker, and the set of directly 434 connected listeners. If the decision is made to maintain one 435 Security Association per speaker (see Section 8), then the key server 436 will need to be aware of the adjacencies of each speaker. Procedures 437 for managing and distributing these adjacencies are out-of-scope for 438 this document. 440 8. Number of Security Associations 442 The number of Security Associations to be maintained by a PIM router 443 depends on the required security level and available key management. 444 This SHOULD be decided by the Network Administrator. Two different 445 ways are shown in Figure 2 and 3. It is assumed that A, B and C are 446 three PIM routers, where B and C are directly connected with A, and 447 there is no direct link between B and C. 449 | 450 B | 451 SAb ------------>| 452 SAa <------------| 453 | 454 A | 455 SAb <------------| 456 ---->| 457 / 458 SAa ------- 459 \ 460 ---->| 461 SAc <------------| 462 | 463 C | 464 SAc ------------>| 465 SAa <------------| 466 | 467 Directly connected network 469 Figure 2: Activate unique Security Association for each peer 471 The first method, shown in Figure 2, is OPTIONAL to implement. In 472 this method, each node will use a unique SA for its outbound traffic. 473 A, B, and C will use SAa, SAb, and SAc, respectively for sending any 474 traffic. Each node will include the source address when searching 475 the SAD for a match. A will use SAb and SAc for packets received 476 from B and C, respectively. The number of SAs to be activated and 477 maintained by a PIM router will be equal to the number of directly 478 connected routers, plus one for sending its own traffic. Also, the 479 addition of a PIM router in the network will require the addition of 480 another SA on every directly connected PIM router. This solution 481 will be scalable and practically feasible with an automated key 482 management protocol. However, it MAY be used with manual key 483 management, if the number of directly connected routers is small. 485 B | 486 SAo ------------>| 487 SAi <------------| 488 | 489 A | 490 SAi <------------| 491 ---->| 492 / 493 SAo ------- 494 \ 495 ---->| 496 SAi <------------| 497 | 498 C | 499 SAo ------------>| 500 SAi <------------| 501 | 502 Directly connected network 504 Figure 3: Activate two Security Associations 506 The second method, shown in Figure 3, MUST be supported by every 507 implementation. In this simple method, all the nodes will use two 508 SAs, one for sending (SAo) and the other for receiving (SAi) traffic. 509 Thus, the number of SAs is always two and will not be affected by 510 addition of a PIM router. Although two different SAs are used in 511 this method, the SA parameters (keys, Security Parameter Index (SPI), 512 etc.) for the two SAs are identical, i.e., the same information is 513 shared among all the routers in an administrative region. This 514 document RECOMMENDS the above method for manual key configuration. 515 However, it MAY also be used with automated key configuration. 517 9. Rekeying 519 To maintain the security of a link, the authentication and encryption 520 key values SHOULD be changed periodically, to limit the risk of 521 undetected key disclosure. Keys should also be changed when there is 522 a change of trusted personnel. 524 9.1. Manual Rekeying Procedure 526 The following three-step procedure SHOULD be provided to rekey the 527 routers on a link without dropping PIM-SM protocol packets or 528 disrupting the adjacency. 530 1. For every router on the link, create an additional inbound SA for 531 the interface being rekeyed using a new SPI and the new key. 533 2. For every router on the link, replace the original outbound SA 534 with one using the new SPI and key values. The SA replacement 535 operation should be atomic with respect to sending PIM-SM packets 536 on the link, so that no PIM-SM packets are sent without 537 authentication/encryption 539 3. For every router on the link, remove the original inbound SA. 541 Note that all routers on the link must complete step 1 before any 542 begin step 2. Likewise, all the routers on the link must complete 543 step 2 before any begin step 3. 545 One way to control the progression from one step to another is for 546 each router to have a configurable time constant KeyRolloverInterval. 547 After the router begins step 1 on a given link, it waits for this 548 interval and then moves to step 2. Likewise, after moving to step 2, 549 it waits for this interval and then moves to step 3. 551 In order to achieve smooth key transition, all routers on a link 552 should use the same value for KeyRolloverInterval and should initiate 553 the key rollover process within this time period. 555 At the end of this time period, all the routers on the link will have 556 a single inbound and outbound SA for PIM-SM with the new SPI and key 557 values. 559 9.2. KeyRollover Interval 561 The configured value of KeyRolloverInterval should be long enough to 562 allow the administrator to change keys on all the PIM-SM routers. As 563 this value can vary significantly depending on the implementation and 564 the deployment, it is left to the administrator to choose an 565 appropriate value. 567 9.3. Rekeying Interval 569 In keeping with the goal of reducing key exposure, the encryption and 570 authentication keys SHOULD be changed at least every 90 days. 572 10. IPsec Protection Barrier and SPD/GSPD 574 10.1. Manual Keying 576 10.1.1. SAD Entries 578 The Administrator must configure the necessary Security Associations. 579 Each SA entry has the Source Address of an authorized peer, and a 580 Destination Address of ALL_PIM_ROUTERS. Unique SPI values for the 581 manually configured SAs MUST be assigned by the Administrator, to 582 ensure that the SPI does not conflict with existing SPI values in the 583 SAD. 585 10.1.2. SPD Entries 587 The Administrator must configure the necessary SPD entries. The SPD 588 entry must ensure that any outbound IP traffic packet traversing the 589 IPsec boundary, with PIM as its next layer protocol, and sent to the 590 Destination Address of ALL_PIM_ROUTERS, is protected by ESP or AH. 591 Note that this characterization includes all the link-local messages 592 (Hello, Join/Prune, Bootstrap, Assert). 594 10.2. Automatic Keying 596 When automatic keying is used, the SA creation is done dynamically 597 using a group key management protocol. The GSPD and PAD tables are 598 configured by the Administrator. The PAD table provides the link 599 between the IPsec subsystem and the group key management protocol. 600 For automatic keying, the implementation MUST support the multicast 601 extensions described in [RFC5374]. 603 10.2.1. SAD Entries 605 All PIM routers participate in an authentication scheme that 606 identifies permitted neighbors and achieves peer authentication 607 during SA negotiation, leading to child SAs being established and 608 saved in the SAD. 610 10.2.2. GSPD Entries 612 The Administrator must configure the necessary GSPD entries for "send 613 only" directionality. This rule MUST trigger the group key 614 management protocol for a registration exchange. This exchange will 615 set up the outbound SAD entry that encrypts the multicast PIM control 616 message. Considering that this rule is "sender only", no inbound SA 617 is created in the reverse direction. 619 In addition, the registration exchange will trigger the installation 620 of the GSPD entries corresponding to each legitimate peer router, 621 with direction "receive only". Procedures for achieving the 622 registration exchange are out-of-scope for this document. 624 A router SHOULD NOT dynamically detect new neighbors as the result of 625 receiving an unauthenticated PIM-SM link-local message or an IPsec 626 packet that fails an SAD lookup. An automated key management 627 protocol SHOULD provide a means of notifying a router of new, 628 legitimate neighbors. 630 10.2.3. PAD Entries 632 The PAD will be configured with information to permit identification 633 of legitimate group members and senders (i.e., to control the 634 adjacency). Procedures for doing this are out-of-scope for this 635 document. 637 11. Security Association Lookup 639 For an SA that carries unicast traffic, three parameters (SPI, 640 destination address and security protocol type (AH or ESP)) are used 641 in the Security Association lookup process for inbound packets. The 642 SPI is sufficient to specify an SA. However, an implementation may 643 use the SPI in conjunction with the IPsec protocol type (AH or ESP) 644 for the SA lookup process. According to RFC 4301 [RFC4301], for 645 multicast SAs, in conjunction with the SPI, the destination address 646 or the destination address plus the sender address may also be used 647 in the SA lookup. This applies to both ESP and AH. The security 648 protocol field is not employed for a multicast SA lookup. 650 Given that, from the prospective of a receiving router, each peer 651 router is an independent sender and given that the destination 652 address will be the same for all senders, the receiving router MUST 653 use SPI plus destination address plus sender address when performing 654 the SA lookup. In effect, link-local communication is an SSM 655 communication that happens to use an ASM address (which is shared 656 among all the routers). 658 Given that it is always possible to distinguish a connection using 659 IPsec from a connection not using IPsec, it is recommended that the 660 address ALL_PIM_ROUTERS be used, to maintain consistency with present 661 practice. 663 Given that the sender address of an incoming packet may be only 664 locally unique (because of the use of link-local addresses), it is 665 necessary for a receiver to use the interface ID tag to determine the 666 associated SA for that sender. Therefore, this document mandates 667 that the interface ID tag, the SPI and the sender address MUST be 668 used in the SA lookup process. 670 12. Activating the Anti-replay Mechanism 672 Although link-level messages on a link constitute a multiple-sender, 673 multiple-receiver group, the use of the interface ID tag and sender 674 address for SA lookup essentially resolves the communication into a 675 separate SA for each sender/destination pair, even for the case where 676 only two SAs (with identical SA parameters) are used for the entire 677 administrative region. Therefore, the statement in the AH RFC 678 (section 2.5 of [RFC4302]) that "for a multi-sender SA, the anti- 679 replay features are not available" becomes irrelevant to the PIM-SM 680 link-local message exchange. 682 To activate the anti-replay mechanism in a unicast communication, the 683 receiver uses the sliding window protocol and it maintains a sequence 684 number for this protocol. This sequence number starts from zero. 685 Each time the sender sends a new packet, it increments this number by 686 one. In a multi-sender multicast group communication, a single 687 sequence number for the entire group would not be enough. 689 The whole scenario is different for PIM link-local messages. These 690 messages are sent to local links with TTL = 1. A link-local message 691 never propagates through one router to another. The use of the 692 sender address and the interface ID tag for SA lookup converts the 693 relationship from a multiple-sender group to multiple single-sender 694 associations. This specification RECOMMENDS activation of the anti- 695 replay mechanism only if the SAs are assigned using an automated key 696 management procedure. If manual key management is used, the anti- 697 replay SHOULD NOT be activated. 699 If an existing router has to restart, in accordance with RFC 4303 700 [RFC4303], the sequence number counter at the sender MUST be 701 correctly maintained across local reboots, etc., until the key is 702 replaced. 704 13. Implementing a Security Policy Database per Interface 706 RFC 4601 suggests that it may be desirable to implement a separate 707 Security Policy Database (SPD) for each router interface. The use of 708 link-local addresses in certain circumstances implies that 709 differentiation of ambiguous speaker addresses requires the use of 710 the interface ID tag in the SA lookup. One way to do this is through 711 the use of multiple SPDs. Alternatively, the interface ID tag may be 712 a specific component of the selector algorithm. This is in 713 conformance with RFC 4301, which explicitly removes the requirement 714 for separate SPDs that was present in RFC 2401 [RFC2401]. 716 14. Extended Sequence Number 718 In the [RFC4302], there is a provision for a 64-bit Extended Sequence 719 Number (ESN) as the counter of the sliding window used in the anti- 720 replay protocol. Both the sender and the receiver maintain a 64-bit 721 counter for the sequence number, although only the lower order 32 722 bits are sent in the transmission. In other words, it will not 723 affect the present header format of AH. If ESN is used, a sender 724 router can send 2^64 -1 packets without any intervention. This 725 number is very large, and from a PIM router's point of view, a PIM 726 router can never exceed this number in its lifetime. This makes it 727 reasonable to permit manual configuration for a small number of PIM 728 routers, since the sequence number will never roll over. For this 729 reason, when manual configuration is used, ESN SHOULD be deployed as 730 the sequence number for the sliding window protocol. In addition, 731 when an ESN is used with a manually-keyed SA, it MUST be saved over a 732 reboot, along with an indication of which sequence numbers have been 733 used. 735 15. Security Considerations 737 The whole document considers the security issues of PIM link-local 738 messages and proposes a mechanism to protect them. 740 Limitations of manual keys: 742 The following are some of the known limitations of the usage of 743 manual keys. 745 o If replay protection cannot be provided, the PIM routers will not 746 be secured against all the attacks that can be performed by 747 replaying PIM packets. 749 o Manual keys are usually long lived (changing them often is a 750 tedious task). This gives an attacker enough time to discover the 751 keys. 753 o As the administrator is manually configuring the keys, there is a 754 chance that the configured keys are weak (there are known weak 755 keys for DES/3DES at least). 757 Impersonation attacks: 759 The usage of the same key on all the PIM routers connected to a link 760 leaves them all insecure against impersonation attacks if any one of 761 the PIM routers is compromised, malfunctioning, or misconfigured. 763 Detailed analysis of various vulnerabilities of routing protocols is 764 provided in RFC 4593 [RFC4593]. For further discussion of PIM-SM and 765 multicast security the reader is referred to RFC 5294 [RFC5294], RFC 766 4609 [RFC4609] and the Security Considerations section of RFC 4601 767 [RFC4601]. 769 16. IANA Considerations 771 This document has no actions for IANA. 773 17. Acknowledgements 775 The structure and text of this document draw heavily from RFC 4552 776 [RFC4552]. The authors of this document thank M. Gupta and N. Melam 777 for permisison to do this. 779 The quality of this document was substiantially improved after SECDIR 780 pre-review by Brian Weis. 782 18. References 784 18.1. Normative References 786 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 787 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 788 Protocol Specification (Revised)", RFC 4601, August 2006. 790 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 791 December 2005. 793 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 794 Requirement Levels", BCP 14, RFC 2119, March 1997. 796 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 797 Internet Protocol", RFC 4301, December 2005. 799 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 800 RFC 4303, December 2005. 802 [RFC4835] Manral, V., "Cryptographic Algorithm Implementation 803 Requirements for Encapsulating Security Payload (ESP) and 804 Authentication Header (AH)", RFC 4835, April 2007. 806 [RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast 807 Extensions to the Security Architecture for the Internet 808 Protocol", RFC 5374, November 2008. 810 18.2. Informative References 812 [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the 813 Internet Protocol", RFC 2401, November 1998. 815 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 816 RFC 4306, December 2005. 818 [RFC4535] Harney, H., Meth, U., Colegrove, A., and G. Gross, 819 "GSAKMP: Group Secure Association Key Management 820 Protocol", RFC 4535, June 2006. 822 [RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The 823 Group Domain of Interpretation", RFC 3547, July 2003. 825 [RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to 826 Routing Protocols", RFC 4593, October 2006. 828 [RFC5294] Savola, P. and J. Lingard, "Host Threats to Protocol 829 Independent Multicast (PIM)", RFC 5294, August 2008. 831 [RFC4609] Savola, P., Lehtonen, R., and D. Meyer, "Protocol 832 Independent Multicast - Sparse Mode (PIM-SM) Multicast 833 Routing Security Issues and Enhancements", RFC 4609, 834 October 2006. 836 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 837 for OSPFv3", RFC 4552, June 2006. 839 Authors' Addresses 841 J. William Atwood 842 Concordia University/CSE 843 1455 de Maisonneuve Blvd, West 844 Montreal, QC H3G 1M8 845 Canada 847 Phone: +1(514)848-2424 ext3046 848 Email: bill@cse.concordia.ca 849 URI: http://users.encs.concordia.ca/~bill 851 Salekul Islam 852 INRS Energie, Materiaux et Telecommunications 853 800, de La Gauchetiere, suite 800 854 Montreal, QC H5A 1K6 855 Canada 857 Email: Salekul.Islam@emt.inrs.ca 858 URI: http://users.encs.concordia.ca/~salek_is 860 Maziar Siami 861 Concordia University/CIISE 862 1455 de Maisonneuve Blvd, West 863 Montreal, QC H3G 1M8 864 Canada 866 Email: m_siamis@ciise.concordia.ca