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That text should be removed or replaced: By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) 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'N9' on line 474 looks like a reference -- Missing reference section? 'I2' on line 521 looks like a reference -- Missing reference section? 'I3' on line 551 looks like a reference Summary: 7 errors (**), 0 flaws (~~), 2 warnings (==), 20 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Gupta 3 Internet Draft Nokia 4 Document: draft-ietf-ospf-ospfv3-auth-06.txt N. Melam 5 Expires: June 2005 Nokia 6 December 2004 8 Authentication/Confidentiality for OSPFv3 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of RFC 3668. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 Abstract 35 This document describes means/mechanisms to provide 36 authentication/confidentiality to OSPFv3 using an IPv6 AH/ESP 37 Extension Header. 39 Copyright Notice 40 Copyright (C) The Internet Society. (2004) 42 Conventions used in this document 44 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 45 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 46 document are to be interpreted as described in RFC-2119 [N7]. 48 Table of Contents 50 1. Introduction...................................................2 51 2. Transport Mode vs Tunnel Mode..................................3 52 3. Authentication.................................................3 53 4. Confidentiality................................................3 54 5. Distinguishing OSPFv3 from OSPFv2..............................4 55 6. IPsec Requirements.............................................4 56 7. Key Management.................................................4 57 8. SA Granularity and Selectors...................................6 58 9. Virtual Links..................................................7 59 10. Rekeying......................................................8 60 10.1 Rekeying Procedure........................................8 61 10.2 KeyRolloverInterval.......................................9 62 10.3 Rekeying Interval.........................................9 63 11. IPsec rules...................................................9 64 12. Mandatory Encryption and Authentication Algorithms...........11 65 13. Entropy of manual keys.......................................11 66 14. Replay Protection............................................11 67 Security Considerations..........................................12 68 Normative References.............................................12 69 Informative References...........................................13 70 Acknowledgments..................................................13 71 Authors' Addresses...............................................14 73 1. Introduction 75 OSPF (Open Shortest Path First) Version 2 [N1] defines fields AuType 76 and Authentication in its protocol header in order to provide 77 security. In OSPF for IPv6 (OSPFv3) [N2], both of the authentication 78 fields were removed from OSPF headers. OSPFv3 relies on the IPv6 79 Authentication Header (AH) and IPv6 Encapsulating Security Payload 80 (ESP) to provide integrity, authentication and/or confidentiality. 82 This document describes how IPv6 AH/ESP extension headers can be used 83 to provide authentication/confidentiality to OSPFv3. 85 It is assumed that the reader is familiar with OSPFv3 [N2], AH [N5], 86 ESP [N4], the concept of security associations, tunnel and transport 87 mode of IPsec and the key management options available for AH and ESP 88 (manual keying [N3] and Internet Key Exchange (IKE)[I1]). 90 2. Transport Mode vs Tunnel Mode 92 Transport mode Security Association (SA) is the security association 93 between two hosts or routers/gateways when they are acting as hosts. 94 SA must be tunnel mode if either end of the security association is a 95 router/gateway. OSPFv3 packets are exchanged between the routers but 96 as the packets are destined to the routers, the routers act like 97 hosts in this case. So transport mode SA MUST be used in order to 98 provide required security to OSPFv3. 100 3. Authentication 102 Implementations conforming to this specification MUST support 103 Authentication for OSPFv3. 105 In order to provide authentication to OSPFv3, "ESP with NULL 106 encryption" MUST be supported and AH SHOULD be supported by the 107 implementation. 109 If "ESP with NULL encryption" in transport mode is used, it will 110 provide authentication to only OSPFv3 protocol headers but not to the 111 IPv6 header, extension headers and options. 113 If AH in transport mode is used, it will provide authentication to 114 OSPFv3 protocol headers, selected portions of IPv6 header, selected 115 portions of extension headers and selected options. 117 When OSPFv3 authentication is enabled, 119 O OSPFv3 packets that are not protected with AH or ESP MUST be 120 silently discarded. 122 O OSPFv3 packets that fail the authentication checks MUST be 123 silently discarded. 125 4. Confidentiality 127 Implementations conforming to this specification SHOULD support 128 confidentiality for OSPFv3. 130 If confidentiality is provided, "ESP with non-null encryption" MUST 131 be used. 133 When OSPFv3 confidentiality is enabled, 135 O OSPFv3 packets that are not protected with ESP MUST be silently 136 discarded. 138 O OSPFv3 packets that fail the confidentiality checks MUST be 139 silently discarded. 141 5. Distinguishing OSPFv3 from OSPFv2 143 The IP/IPv6 Protocol Type for OSPFv2 and OSPFv3 is same (89) and 144 OSPF distinguishes them based on the OSPF header version number. 145 However current IPsec standards do not allow using arbitrary protocol 146 specific header fields as the selectors. Therefore, in order to 147 distinguish OSPFv3 packets from the OSPFv2 packets, OSPF version 148 field in the OSPF header cannot be used. As OSPFv2 is only for IPv4 149 and OSPFv3 is only for IPv6, version field in IP header can be used 150 to distinguish OSPFv3 packets from OSPFv2 packets. 152 6. IPsec Requirements 154 In order to implement this specification, the following IPsec 155 capabilities are required. 157 Transport Mode 158 IPsec in transport mode MUST be supported. [N3] 160 Traffic Selectors 161 The implementation MUST be able to use interface index, source 162 address, destination address, protocol and direction for choosing 163 the right security action. 165 Manual key support 166 Manually configured keys MUST be able to secure the specified 167 traffic. [N3] 169 Encryption and Authentication Algorithms 170 AES-CBC and HMAC-SHA1 MUST be supported as the encryption and the 171 authentication algorithms respectively. [N6] 173 Dynamic IPsec rule configuration 174 Routing module SHOULD be able to configure, modify and delete 175 IPsec rules on the fly. This is needed mainly for securing 176 virtual links. 178 7. Key Management 180 OSPFv3 exchanges both multicast and unicast packets. While running 181 OSPFv3 over a broadcast interface, the authentication/confidentiality 182 required is "one to many". Since IKE is based on the Diffie-Hellman 183 key agreement protocol and works only for two communicating parties, 184 it is not possible to use IKE for providing the required "one to 185 many" authentication/confidentiality. Manual keying MUST be used for 186 this purpose. In manual keying SAs are statically installed on the 187 routers and these static SAs are used to authenticate/encrypt the 188 packets. 190 The following discussion explains that it is not scalable and 191 practically infeasible to use different security associations for 192 inbound and outbound traffic in order to provide the required "one to 193 many" security. Therefore, the implementations MUST use manually 194 configured keys with same SA for inbound and outbound traffic (as 195 shown in Figure 3). 197 A | 198 SAa ------------>| 199 SAb <------------| 200 | 201 B | 202 SAb ------------>| 203 SAa <------------| Figure: 1 204 | 205 C | 206 SAa/SAb ------------>| 207 SAa/SAb <------------| 208 | 209 Broadcast 210 Network 212 If we consider communication between A and B in Figure 1, everything 213 seems to be fine. A uses security association SAa for outbound 214 packets and B uses the same for inbound packets and vice versa. Now 215 if we include C in the group and C sends a packet out using SAa then 216 only A will be able to understand it or if C sends the packets out 217 using SAb then only B will be able to understand it. Since the 218 packets are multicast packets and they are going to be processed by 219 both A and B, there is no SA for C to use so that A and B both can 220 understand it. 222 A | 223 SAa ------------>| 224 SAb <------------| 225 SAc <------------| 226 | 227 B | 229 SAb ------------>| 230 SAa <------------| Figure: 2 231 SAc <------------| 232 | 233 C | 234 SAc ------------>| 235 SAa <------------| 236 SAb <------------| 237 | 238 Broadcast 239 Network 241 The problem can be solved by configuring SAs for all the nodes on all 242 the nodes as shown in Figure 2. So A, B and C will use SAa, SAb and 243 SAc respectively for outbound traffic. Each node will lookup the SA 244 to be used based on the source (A will use SAb and SAc for packets 245 received from B and C respectively). This solution is not scalable 246 and practically infeasible because every node will need to be 247 configured with a large number of SAs and addition of a node in the 248 network will cause addition of another SA on all the nodes. 250 A | 251 SAs ------------>| 252 SAs <------------| 253 | 254 B | 255 SAs ------------>| 256 SAs <------------| Figure: 3 257 | 258 C | 259 SAs ------------>| 260 SAs <------------| 261 | 262 Broadcast 263 Network 265 The problem can also be solved by using the same SA for inbound and 266 outbound traffic as shown in Figure 3. 268 8. SA Granularity and Selectors 270 The user SHOULD be given a choice to share the same SA among multiple 271 interfaces or using unique SA per interface. 273 OSPFv3 supports running multiple instances over one interface using 274 the "Instance Id" field contained in the OSPFv3 header. As IPsec 275 does not support arbitrary fields in protocol header to be used as 276 the selectors, it is not possible to use different SAs for different 277 instances of OSPFv3 running over the same interface. Therefore, all 278 the instances of OSPFv3 running over the same interface will have to 279 use the same SA. In OSPFv3 RFC terminology, SAs are per-link and not 280 per-interface. 282 9. Virtual Links 284 Different SA than the SA of underlying interface MUST be provided for 285 virtual links. Packets sent out on virtual links use unicast non- 286 link local IPv6 addresses as the IPv6 source address and all the 287 other packets use multicast and unicast link local addresses. This 288 difference in the IPv6 source address is used in order to 289 differentiate the packets sent on interfaces and virtual links. 291 As the end point IP addresses of the virtual links are not known at 292 the time of configuration, the secure channel for these packets needs 293 to be set up dynamically. The end point IP addresses of virtual 294 links are learned during the routing table build up process. The 295 packet exchange over the virtual links starts only after the 296 discovery of end point IP addresses. In order to provide security to 297 these exchanges, the routing module should setup a secure IPsec 298 channel dynamically once it acquires the required information. 300 According to the OSPFv3 RFC [N2], the virtual neighbor's IP address 301 is set to the first prefix with the "LA-bit" set from the list of 302 prefixes in intra-area-prefix-LSAs originated by the virtual 303 neighbor. But when it comes to choosing the source address for the 304 packets that are sent over the virtual link, the RFC simply suggests 305 using one of the router's own site-local or global IPv6 addresses. 306 In order to install the required security rules for virtual links, 307 the source address also needs to be predictable. So the routers that 308 implement this specification MUST change the way the source and 309 destination addresses are chosen for the packets exchanged over 310 virtual links when the security is enabled on that virtual link. 312 The first IPv6 address with the "LA-bit" set in the list of prefixes 313 advertised in intra-area-prefix-LSAs in the transit area MUST be used 314 as the source address for packets exchanged over the virtual link. 315 When multiple intra-area-prefix-LSAs are originated they are 316 considered as being concatenated and are ordered by ascending Link 317 State ID. 319 The first IPv6 address with the "LA-bit" set in the list of prefixes 320 received in intra-area-prefix-LSAs from the virtual neighbor in the 321 transit area MUST be used as the destination address for packets 322 exchanged over the virtual link. When multiple intra-area-prefix- 323 LSAs are received they are considered as being concatenated and are 324 ordered by ascending Link State ID. 326 This makes both the source and destination addresses of the packets 327 exchanged over the virtual link, predictable on both the routers for 328 security purposes. 330 10. Rekeying 332 To maintain the security of a link, the authentication and encryption 333 key values SHOULD be changed from time to time. 335 10.1 Rekeying Procedure 337 The following three-step procedure SHOULD be provided to rekey the 338 routers on a link without dropping OSPFv3 protocol packets or 339 disrupting the adjacency. 341 (1) For every router on the link, create an additional inbound SA for 342 the interface being rekeyed using a new SPI and the new key. 344 (2) For every router on the link, replace the original outbound SA 345 with one using the new SPI and key values. The SA replacement 346 operation should be atomic with respect to sending OSPFv3 packets 347 on the link so that no OSPFv3 packets are sent without 348 authentication/encryption. 350 (3) For every router on the link, remove the original inbound SA. 352 Note that all the routers on the link must complete step 1 before any 353 begin step 2. Likewise, all the routers on the link must complete 354 step 2 before any begin step 3. 356 One way to control the progression from one step to the next is for 357 each router to have a configurable time constant KeyRolloverInterval. 358 After the router begins step 1 on a given link, it waits for this 359 interval and then moves to step 2. Likewise, after moving to step 2, 360 it waits for this interval and then moves to step 3. 362 In order to achieve smooth key transition, all the routers on a link 363 should use the same value for KeyRolloverInterval, and should 364 initiate the key rollover process within this time period. 366 At the end of this procedure, all the routers will have a single 367 inbound and outbound SA for OSPFv3 on the link with the new SPI and 368 key values. 370 10.2 KeyRolloverInterval 372 The configured value of KeyRolloverInterval should be long enough to 373 allow the administrator to change keys on all the involved routers. 374 As this value can vary significantly depending upon the 375 implementation and the deployment, it is left to the administrator to 376 choose the appropriate value. 378 10.3 Rekeying Interval 380 This section analyzes the security provided by the manual keying and 381 recommends that the encryption and authentication keys SHOULD be 382 changed at least every 90 days. 384 The weakest security provided by the security mechanisms discussed in 385 this specification is when NULL encryption is used with the HMAC-MD5 386 authentication. Any other algorithm combinations will at least be as 387 hard to break as the one mentioned above as shown by the following 388 examples: 390 O NULL Encryption and HMAC-SHA-1 Authentication will be more secure 391 as HMAC-SHA-1 is considered to be more secure than HMAC-MD5 393 O NON-NULL Encryption and NULL Authentication is not applicable as 394 this specification mandates the authentication when OSPFv3 security 395 is enabled 397 O DES Encryption and HMAC-MD5 Authentication will be more secure 398 because of the additional security provided by DES 400 O Other encryption algorithms like 3DES, AES will be more secure than 401 DES 403 RFC 3562 [I4] analyzes the rekeying requirements for the TCP MD5 404 signature option. The analysis provided in this RFC is also 405 applicable to OSPFv3 security specification as the analysis is 406 independent of data patterns. 408 11. IPsec rules 410 The following set of transport mode rules can be installed in a 411 typical IPsec implementation to provide the 412 authentication/confidentiality to OSPFv3 packets. 414 Outbound Rules for interface running OSPFv3 security: 416 No. source destination protocol action 417 1 fe80::/10 any OSPF apply 418 Outbound Rules for virtual links running OSPFv3 security: 420 No. source destination protocol action 421 2 src/128 dst/128 OSPF apply 423 Inbound Rules for interface running OSPFv3 security: 425 No. source destination protocol action 426 3 fe80::/10 any ESP/OSPF or AH/OSPF apply 427 4 fe80::/10 any OSPF drop 429 Inbound Rules for virtual links running OSPFv3 security: 431 No. source destination protocol action 432 5 src/128 dst/128 ESP/OSPF or AH/OSPF apply 433 6 src/128 dst/128 OSPF drop 435 For outbound rules, action "apply" means encrypting/calculating ICV 436 and adding ESP or AH header. For inbound rules, action "apply" means 437 decrypting/authenticating the packets and stripping ESP or AH header. 439 Rules 4 and 6 are to drop the insecure OSPFv3 packets without ESP/AH 440 headers. 442 ESP/OSPF or AH/OSPF in rules 3 and 5 mean that it is an OSPF packet 443 secured with ESP or AH. 445 Rules 1, 3 and 4 are meant to secure the unicast and multicast OSPF 446 packets that are not being exchanged over the virtual links. These 447 rules MUST be installed only in the security policy database (SPD) of 448 the interface running OSPFv3 security. 450 Rules 2, 5 and 6 are meant to secure the packets being exchanged over 451 virtual links. These rules are dynamically installed after learning 452 the end point IP addresses of a virtual link. These rules MUST be 453 installed on at least the interfaces that are connected to the 454 transit area for the virtual link. These rules MAY alternatively be 455 installed on all the interfaces. If these rules are not installed on 456 all the interfaces, clear text or malicious OSPFv3 packets with same 457 source and destination addresses as virtual link end point addresses 458 will be delivered to OSPFv3. Though OSPFv3 drops these packets 459 because they were not received on the right interface, OSPFv3 460 receives some clear text or malicious packets even when the security 461 is on. Installing these rules on all the interfaces insures that 462 OSPFv3 does not receive these clear text or malicious packets when 463 security is turned on. On the other hand installing these rules on 464 all the interfaces increases the processing overhead on the 465 interfaces where there is no IPsec processing otherwise. The 466 decision of installing these rules on all the interfaces or on just 467 the interfaces that are connected to the transit area is a private 468 decision and doesn't affect the interoperability in any way. So this 469 decision is left to the implementers. 471 12. Mandatory Encryption and Authentication Algorithms 473 The implementation MUST allow the user to choose AES-CBC [N8] as the 474 encryption algorithm and HMAC-SHA1-96 [N9] as the authentication 475 algorithm for securing OSPFv3 packets. 477 The implementation MUST NOT allow the user to choose stream ciphers 478 as the encryption algorithm for securing OSPFv3 packets as the stream 479 ciphers are not suitable for manual keys. 481 13. Entropy of manual keys 482 The implementations MUST allow the administrator to configure the 483 cryptographic and authentication keys in hexadecimal format instead 484 of restricting it a subset of ASCII characters (letters, numbers 485 etc). Otherwise the entropy of the keys reduces significantly as 486 discussed in [I2]. 488 14. Replay Protection 490 As it is not possible as per the current standards to provide 491 complete replay protection while using manual keying, the proposed 492 solution will not provide protection against replay attacks. This 493 section analyzes the protection built in OSPF protocol to guard 494 itself against replay attacks. 496 OSPF protocol has the following types of packets: 498 Hello: OSPF does not have any protection against replayed hello 499 messages thus OSPF will be vulnerable to the attacks performed by 500 replaying hello messages even after enabling security. 502 Database Description: These packets are exchanged while building the 503 adjacencies to describe the OSPF database. There are no known 504 threats of replaying these type of packets. 506 Link State Request, Link State Acknowledgment and Link State Updates: 507 Fields LS age, LS Sequence Number and LS checksum in LSA header are 508 kept intact in OSPFv3. Though these fields do not provide the 509 complete protection, they certainly help against replay attacks of 510 Link State packets. 512 Detailed analysis of various vulnerabilities of the routing protocols 513 is discussed in [I3]. 515 Security Considerations 517 This memo discusses the use of IPsec AH and ESP headers in order to 518 provide security to OSPFv3 for IPv6. Hence security permeates 519 throughout this document. 521 OSPF Security Vulnerabilities Analysis [I2] identifies OSPF 522 vulnerabilities in two scenarios - One with no authentication or 523 simple password authentication and the other with cryptographic 524 authentication. The solution described in this specification 525 provides security against all the vulnerabilities identified for 526 scenario with cryptographic authentication with the following 527 exceptions: 529 Limitations of manual key: 530 This specification mandates the usage of manual keys. The following 531 are the known limitations of the usage of manual keys. 533 O As the sequence numbers can not be negotiated, replay protection 534 can not be provided. This leaves OSPF insecure against all the 535 attacks that can be performed by replaying OSPF packets. 537 O Manual keys are usually long lived (changing them very often is 538 a tedious task). This gives an attacker enough time to discover 539 the keys. 541 O As the administrator is manually configuring the keys, there is 542 a chance that the configured keys are weak (there are known weak 543 keys for DES/3DES at least). 545 Impersonating Attacks: 546 The usage of the same key on all the routers on the same link for 547 securing OSPF leaves it insecure against impersonating attacks if one 548 of the routers is compromised, malfunctioning or misconfigured. 550 Detailed analysis of various vulnerabilities of the routing protocols 551 is discussed in [I3]. 553 Normative References 555 N1. Moy, J., "OSPF version 2", RFC 2328, April 1998. 557 N2. Coltun, R., Ferguson, D. and J. Moy, "OSPF for IPv6", RFC 2740, 558 December 1999. 560 N3. Kent, S. and K. Seo, "Security Architecture for the Internet 561 Protocol", RFC XXXX, date [Note to RFC-Editor: Replace XXXX with 562 the number of the RFC 2401 replacement]. 564 N4. Kent, S., "IP Encapsulating Security Payload (ESP)", RFC XXXY, 565 date [Note to RFC-Editor: Replace XXXY with the number of the RFC 566 2406 replacement]. 568 N5. Kent, S., "IP Authentication Header (AH)", RFC XXXZ, date [Note to 569 RFC-Editor: Replace XXXZ with the number of the RFC 2402 570 replacement]. 572 N6. Eastlake, D., "Cryptographic Algorithm Implementation Requirements 573 For ESP And AH", RFC XXYY, date [Note to RFC-Editor: Replace XXYY 574 with the number of the RFC that the draft draft-ietf-ipsec-esp-ah- 575 algorithms-02.txt gets]. 577 N7. Bradner, S., "Key words for use in RFCs to Indicate Requirement 578 Level", BCP 14, RFC 2119, March 1997. 580 N8. Frankel, S., Glenn, R. and S. Kelly, "The AES-CBC Cipher Algorithm 581 and Its Use with IPsec", RFC 3602, September 2003. 583 N9. Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within ESP and 584 AH", RFC 2404, November 1998. 586 Informative References 588 I1. Kaufman, C., "The Internet Key Exchange (IKEv2) Protocol", RFC 589 XXZZ, date [Note to RFC-Editor: Replace XXZZ with the number of the 590 RFC 2409 replacement]. 592 I2. Jones, E. and O. Moigne, "OSPF Security Vulnerabilities Analysis", 593 draft-ietf-rpsec-ospf-vuln-01.txt, work in progress. 595 I3. Barbir, A., Murphy, S. and Y. Yang, "Generic Threats to Routing 596 Protocols", draft-ietf-rpsec-routing-threats-07.txt, work in 597 progress. 599 I4. Leech, M., "Key Management Considerations for the TCP MD5 600 Signature Option", RFC 3562, July 2003. 602 Acknowledgments 604 Authors would like to extend sincere thanks to Marc Solsona, Janne 605 Peltonen, John Cruz, Dhaval Shah, Abhay Roy and Paul Wells for 606 providing useful information and critiques in order to write this 607 memo. 609 We would also like to thank IPsec and OSPF WG people to provide 610 valuable review comments. 612 Authors' Addresses 614 Mukesh Gupta 615 Nokia 616 313 Fairchild Drive 617 Mountain View, CA 94043 618 Phone: 650-625-2264 619 Email: Mukesh.Gupta@nokia.com 621 Nagavenkata Suresh Melam 622 Nokia 623 313 Fairchild Drive 624 Mountain View, CA 94043 625 Phone: 650-625-2949 626 Email: Nagavenkata.Melam@nokia.com 628 Full copyright statement 630 Copyright (C) The Internet Society (2004). 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