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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NETWORK WORKING GROUP N. Williams 3 Internet-Draft Sun 4 Intended status: Standards Track M. Richardson 5 Expires: October 3, 2007 SSW 6 April 2007 8 Better-Than-Nothing-Security: An Unauthenticated Mode of IPsec 9 draft-ietf-btns-core-03.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on October 3, 2007. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 This document specifies how to use the Internet Key Exchange (IKE) 43 protocols, such as IKEv1 and IKEv2, to setup "unauthenticated" 44 security associations (SAs) for use with the IPsec Encapsulating 45 Security Payload (ESP) and the IPsec Authentication Header (AH). No 46 IKE extensions are needed, but Peer Authorization Database (PAD) and 47 Security Policy Database (SPD) extensions are specified. 48 Unauthenticated IPsec is herein referred to by its popular acronym, 49 "BTNS" (Better Than Nothing Security). 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Conventions used in this document . . . . . . . . . . . . . 3 55 2. BTNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 57 3.1. Example #1: sgA . . . . . . . . . . . . . . . . . . . . . . 6 58 3.2. Example #2: Q . . . . . . . . . . . . . . . . . . . . . . . 8 59 3.3. Example #3: C . . . . . . . . . . . . . . . . . . . . . . . 9 60 3.4. Miscaellaneous examples . . . . . . . . . . . . . . . . . . 9 61 4. Security Considerations . . . . . . . . . . . . . . . . . . 10 62 4.1. Connection-Latching and Channel Binding . . . . . . . . . . 10 63 4.2. Leap-of-Faith (LoF) for BTNS . . . . . . . . . . . . . . . . 10 64 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12 65 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 66 6.1. Normative References . . . . . . . . . . . . . . . . . . . . 13 67 6.2. Informative References . . . . . . . . . . . . . . . . . . . 13 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14 69 Intellectual Property and Copyright Statements . . . . . . . 15 71 1. Introduction 73 Here we describe how to establish unauthenticated IPsec SAs using 74 IKEv1 [RFC2408] [RFC2409] or IKEv2 [RFC4306] and unauthenticated 75 public keys. No new on-the-wire protocol elements are added to IKE 76 or IKEv2. 78 The [RFC4301] processing model is assumed. 80 This document does not define an opportunistic BTNS mode of IPsec 81 whereby nodes may fallback on unprotected IP when their peers do not 82 support IKE or IKEv2, nor does it describe "leap-of-faith" modes, or 83 "connection latching." 85 See [I-D.ietf-btns-prob-and-applic] for the applicability and uses of 86 BTNS. 88 1.1. Conventions used in this document 90 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 91 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 92 document are to be interpreted as described in [RFC2119]. 94 2. BTNS 96 The IPsec processing model, IKE and IKEv2 are hereby modified as 97 follows: 99 o A new ID type is added, 'PUBLICKEY'; IDs of this type have public 100 keys as values. This ID type is not used on the wire. 102 o A BTNS-specific PAD entry. This entry is intended to be the last 103 entry in the PAD when BTNS is enabled. A peer that matches no 104 other PAD entries is to be "authenticated" by verifying that the 105 signature in its AUTH (or SIG) payload in the IKEv2 (or v1) 106 exchange with the public key from the peer's CERT payload. The 107 peer's ID MUST then be coerced to be of 'PUBLICKEY' type with the 108 peer's public key as its value. 110 o A new flag for SPD entries: 'BTNS_OK'. Traffic to/from peers that 111 match the BTNS PAD entry will only match SPD entries that have the 112 BTNS_OK flag set. The SPD may be searched by address or by ID (of 113 type PUBLICKEY, of course, for BTNS peers), as per the IPsec 114 processing model [RFC4301]; searching by ID in this case requires 115 creation of SPD entries that are bound to public key values (this 116 could be used to build "leap-of-faith" behaviour, for example). 118 Nodes MUST reject IKE_SA proposals from peers that match non-BTNS PAD 119 entries but fail to authenticate properly. 121 Nodes wishing to be treated as BTNS nodes by their peers SHOULD use 122 bare RSA key CERT payloads and MAY use certificates known not to have 123 been pre-shared with their peers or outside their trust anchors 124 (e.g., self-signed certificates). RSA keys for use in BTNS may be 125 generated at any time, but "connection latching" 126 [I-D.ietf-btns-connection-latching] requires that they remain 127 constant between IKE exchanges setting up SAs for latched 128 connections. 130 To preserve standard IPsec access control semantics BTNS responders 131 MUST NOT allow BTNS peers to assert addresses which could be asserted 132 by non-BTNS peers. This can be achieved by processing the PAD in 133 order both, when peers authenticate and when BTNS peers negotiate 134 child SAs -- in the first case the PAD is searched for a matching PAD 135 entry as usual, and in the second it is searched to make sure that 136 BTNS peers' asserted child SA traffic selectors do not conflict with 137 non-BTNS PAD entries. Note that in general, if there are multiple 138 PAD entries with wildcard matching on peer ID then all but the last 139 one should constrain the traffic selectors for matching peers. 141 Note that nodes may unwittingly match peers' BTNS PAD entries and be 142 authenticated as BTNS nodes. This may be used in specifying the 143 "latching" of traffic flows to peer IDs 144 [I-D.ietf-btns-connection-latching]. 146 3. Usage Scenarios 148 In order to explain the above rules a number of scenarios will be 149 postulated. The goal here is to demonstrate that the above rules are 150 both sufficient and required. 152 To explain the scenarios a reference diagram describing a canonical 153 network will be used. It is as follows: 155 [Q] [R] 156 AS1 . . AS2 157 [A]----+----[SG-A].......+....+.......[SG-B]-------[B] 158 ...... \ 159 ..PI.. ----[btns-B] 160 ...... 161 [btns-C].....+....+.......[btns-D] 163 Figure 1: Reference Network Diagram 165 In this diagram, there are six end-nodes: A, B, C and D. Two of the 166 systems are security gateways: SG-A, SG-B, protecting networks on 167 which [A] and [B] reside. There is a node [Q] which is IPsec and 168 BTNS capable, and node [R] is a simple node, with no IPsec or BTNS 169 capability. Nodes [C] and [D] are BTNS capable. We will examine 170 interactions between the BTNS enabled nodes, and the IPsec enabled 171 nodes. 173 Nodes C and Q have a fixed addresses. Node D non-fixed addresses. 175 PI is the Public Internet ("The Wild"). 177 3.1. Example #1: sgA 179 The machine that we will care about will be [SG-A], a firewall device 180 of some kind which we wish to configure to respond to BTNS 181 connections from [C] 183 SG-A has the following "VPN" PAD and SPD entries: 185 Child SA 186 Rule Remote ID IDs allowed SPD Search by 187 ---- --------- ----------- ------------- 188 1 by-IP 189 2 by-IP 190 3 PUBLICKEY:any ANY by-IP 192 The last entry is the BTNS entry. 194 Figure 2: SG-A PAD table 196 Here is any address that is not part of A's network, and is not 197 claimed by any other entry. Note that sgA's PAD entry has one and 198 only one wildcard PAD entry: the BTNS catch-all PAD entry, so, as 199 described in Section 2. 201 and are from [RFC4301] section 202 4.4.3 204 Rule Local Remote Next Layer BTNS Action 205 addr addr Protocol ok 206 ---- ----- ------ ---------- ---- ----------------------- 207 1 A R ANY N/A BYPASS 208 2 A Q ANY no PROTECT(ESP,tunnel,AES, 209 SHA256) 210 3 A B-net ANY no PROTECT(ESP,tunnel,AES, 211 SHA256) 212 4 A ANY ANY yes PROTECT(ESP,transport, 213 integr+conf) 215 Figure 3: SG-A SPD table 217 The processing by sgA of various peers then is as follows: 219 o Q does not match PAD entry #1, but does match PAD entry #2; PAD 220 processing stops, then the SPD is searched by Q's ID to find entry 221 #2; CHILD SAs are then allowed that have sgA's and Q's addresses 222 as the end-point addresses. 224 o sgB matches PAD entry #1; PAD processing stops, then the SPD is 225 searched by sgB's ID to find SPD entry #3; CHILD SAs are then 226 allowed that have sgA's address and any addresses from B's network 227 as the end-point addresses. 229 o R does not initiate any IKE_SAs; its traffic to A is bypassed by 230 SPD entry #1. 232 o C does not match PAD entries #1 or #2, but does match entry #3, 233 the BTNS wildcard PAD entry; the SPD is searched by C's address 234 and SPD entry #4 is matched. CHILD SAs are then allowed that have 235 sgA's address and C's address as the end-point addresses provided 236 that C's address is neither Q's nor any of B's (see Section 2). 238 o Rogue BTNS nodes attempting to assert Q's or B's addresses will 239 either match the PAD entries for Q or B and fail to authenticate 240 as Q or B, in which case they are rejected, or they will match PAD 241 entry #3 but will not be allowed to create CHILD SAs with Q's or 242 B's addresses as traffic selectors. 244 o Rogue BTNS nodes attempting to assert C's address are allowed. 245 Protection for C requires additional bindings of C's specific BTNS 246 ID (that is, its public key) to its traffic flows through 247 connection-latching and channel binding, or leap-of-faith, none of 248 which are described here. 250 3.2. Example #2: Q 252 Q is either a BITS or native IPsec implementation; if it is a native 253 implementation it may have IPsec-aware applications, specifically 254 NFSv4 (TCP port 2049). 256 In any case, Q wants to communicate with A generally, and with BTNS 257 peers for NFSv4 only. It's PAD and SPD are configured as follows: 259 Child SA 260 Rule Remote ID IDs allowed SPD Search by 261 ---- --------- ----------- ------------- 262 1 by-IP 263 2 PUBLICKEY:any ANY by-IP 265 The last entry is the BTNS entry. 267 Figure 4: Q PAD table 269 Rule Local Remote Next Layer BTNS Action 270 addr addr Protocol ok 271 ---- ----- ------ ---------- ---- ----------------------- 272 1 Q A ANY no PROTECT(ESP,tunnel,AES, 273 SHA256) 274 2 Q ANY ANY yes PROTECT(ESP,transport, 275 and integr+conf) 276 port 277 2049 279 Figure 5: SG-A SPD table 281 The same analysis shown above in Section 3.1 applies here with 282 respect to sgA, C and rogue peers, except that C is allowed only 283 access to the NFSv4 service on Q. Additionally sgB is treated as a 284 BTNS peer as it is not known to Q, and therefore any host behind sgB 285 can access the NFSv4 service on Q (and, because Q has no formal 286 relationship with sgB, rogues can impersonate B). 288 3.3. Example #3: C 290 C only supports BTNS and wants to use BTNS to protect NFSv4 traffic. 291 It's PAD and SPD are configured as follows: 293 Child SA 294 Rule Remote ID IDs allowed SPD Search by 295 ---- --------- ----------- ------------- 296 1 PUBLICKEY:any ANY by-IP 298 The last entry is the BTNS entry. 300 Figure 6: Q PAD table 302 Rule Local Remote Next Layer BTNS Action 303 addr addr Protocol ok 304 ---- ----- ------ ---------- ---- ----------------------- 305 1 C ANY ANY yes PROTECT(ESP,transport, 306 and integr+conf) 307 port 308 2049 310 2 C ANY ANY N/A BYPASS 312 Figure 7: SG-A SPD table 314 3.4. Miscaellaneous examples 316 If sgA were not BTNS-capable then it would not have PAD and SPD 317 entries #3 and #4, respectively. Then C would be rejected as usual 318 under the standard IPsec model [RFC4301]. 320 Similarly, if Q were not BTNS-capable then it would not have PAD and 321 SPD entries #2. Then C would be rejected as usual under the standard 322 IPsec model [RFC4301]. 324 4. Security Considerations 326 Unauthenticated security association negotiation is subject to MITM 327 attacks and should be used with care. Where security infrastructures 328 are lacking this may indeed be better than nothing. 330 Use with applications that bind authentication at higher network 331 layers to secure channels at lower layers may provide one secure way 332 to use unauthenticated IPsec, but this is not specified herein. 334 Use of multiple wildcard PAD entries can be problematic. Where it is 335 important that addresses and node identities be tightly bound it is 336 important that such PAD entries limit the addresses that matching 337 peers can assert for their CHILD SAs to non-overlapping address 338 spaces. In practice this may be difficult to configure; if it is not 339 feasible to configure systems in this way then either BTNS should not 340 be used or BTNS PAD entries should constrain matching peers only to 341 using services for which authentication is not normally necessary or 342 where IPsec-aware/connection-latching applications are used. 344 4.1. Connection-Latching and Channel Binding 346 BTNS is subject to MITM attacks. One way to protect against MITM 347 attacks subsequent to initial communications is to use "connection 348 latching" [I-D.ietf-btns-connection-latching], whereby ULPs cooperate 349 with IPsec in native IPsec implementations to bind individual packet 350 flows to sequences of SAs whose end-point IDs (public keys, in the 351 case of BTNS end-points) and other characteristics (e.g., quality of 352 protection) must all be the same. 354 MITMs can be detected by using application-layer authentication 355 frameworks and/or mechanisms, such as the GSS-API [RFC2743], with 356 channel binding [I-D.williams-on-channel-binding], where the channels 357 to be bound to application-layer authentication are latched 358 connections and where the channel bindings data strongly identify the 359 end-points of the latched connection (e.g., the public keys of the 360 end-points). 362 4.2. Leap-of-Faith (LoF) for BTNS 364 "Leap of faith" is the term generally used for the habit of accepting 365 that a given key identifies a peer that one wanted to talk to without 366 strong evidence for that proposition. Specifically this is a common 367 mode of operation for Secure Shell [RFC4251] clients where, when a 368 server is encountered for the first time the client may ask the user 369 whether to accept the server's public key as its identity and, if so, 370 records the server's name (as given by the user) and public key in a 371 database. 373 Leap of Faith can work in a similar way for BTNS nodes, but it is 374 currently still being designed and specified by the IETF BTNS WG. 376 5. IANA Considerations 378 This document has no IANA considerations, neither seeking to create 379 new registrations nor new registries. (The new ID type is not used 380 on the wire, therefore it need not be assigned a number from the IANA 381 IKEv2 Identification Payload ID Types registry.) 383 6. References 385 6.1. Normative References 387 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 388 Requirement Levels", BCP 14, RFC 2119, March 1997. 390 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 391 Internet Protocol", RFC 4301, December 2005. 393 6.2. Informative References 395 [I-D.ietf-btns-connection-latching] 396 Williams, N., "IPsec Channels: Connection Latching", 397 draft-ietf-btns-connection-latching-00 (work in progress), 398 February 2006. 400 [I-D.ietf-btns-prob-and-applic] 401 Touch, J., "Problem and Applicability Statement for Better 402 Than Nothing Security (BTNS)", 403 draft-ietf-btns-prob-and-applic-05 (work in progress), 404 February 2007. 406 [I-D.williams-on-channel-binding] 407 Williams, N., "On the Use of Channel Bindings to Secure 408 Channels", draft-williams-on-channel-binding-00 (work in 409 progress), August 2006. 411 [RFC2408] Maughan, D., Schneider, M., and M. Schertler, "Internet 412 Security Association and Key Management Protocol 413 (ISAKMP)", RFC 2408, November 1998. 415 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 416 (IKE)", RFC 2409, November 1998. 418 [RFC2743] Linn, J., "Generic Security Service Application Program 419 Interface Version 2, Update 1", RFC 2743, January 2000. 421 [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) 422 Protocol Architecture", RFC 4251, January 2006. 424 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 425 RFC 4306, December 2005. 427 Authors' Addresses 429 Nicolas Williams 430 Sun Microsystems 431 5300 Riata Trace Ct 432 Austin, TX 78727 433 US 435 Email: Nicolas.Williams@sun.com 437 Michael C. Richardson 438 Sandelman Software Works 439 470 Dawson Avenue 440 Ottawa, ON K1Z 5V7 441 CA 443 Email: mcr@sandelman.ottawa.on.ca 444 URI: http://www.sandelman.ottawa.on.ca/ 446 Full Copyright Statement 448 Copyright (C) The IETF Trust (2007). 450 This document is subject to the rights, licenses and restrictions 451 contained in BCP 78, and except as set forth therein, the authors 452 retain all their rights. 454 This document and the information contained herein are provided on an 455 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 456 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 457 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 458 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 459 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 460 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 462 Intellectual Property 464 The IETF takes no position regarding the validity or scope of any 465 Intellectual Property Rights or other rights that might be claimed to 466 pertain to the implementation or use of the technology described in 467 this document or the extent to which any license under such rights 468 might or might not be available; nor does it represent that it has 469 made any independent effort to identify any such rights. 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